Dissertations / Theses on the topic 'Nanoelectronic device'

This project is to develope a new method of characterization for Silicon-nano-wire (SiNW) FET and SET devices by using KPFM technology to derive the information of local surface potential change on the channel of SiNW devices. The surface potential is related to many important parameters on material's surface, e.g. fixed surface charge, doping profile variation, distribution of charge carriers under applied bias, and individual dopant atoms near the surface. Those parameters are strongly related to the characteristics of SiNW devices. The KPFM equipment is designed to extract the contact potential difference (CPD) between tip and sample. The change of CPD is related to the Fermi energy level in materials. Therefore any factors which induce Fermi energy level change inside material are detectable. The significantly improved lateral resolution (sub-nanometer) gives us confidence for the measurement of local surface potential variation. Much of the time has been dedicated for the KPFM equipment calibration and optimization. By the end of PhD project the surface potential characterisation of three different types of the silicon-nano-wire (SiNW) devices (uniformly doped SiNW, n-pn SiNW Field-Effect-Transistor (FET), and n-p-n-p-n SiNW Single-Electron-Transistor (SET)) has been achieved. By using surface potential information the surface traped charge and change in local resistivity in SiNW is successfully estimated and the result is confirmed well agreed with the characterisation of other conventional method. This characterisation result also suggest the accuracy of local surface potential measurement. In-situ potential mapping and proling of n-p-n FET channel under device operation has been successfully performed. By comparing the data with simulation and electrical characterisation of the same device, correspondence between the line-shape of the surface potential and electrical field profiles and device parameters has been clarified for the first time. An attempt has been made to observe the surface potential of the channel of SET devices which have shown clear Coulomb oscillation at low temperature (5K). The formation of a conductive channel in 330-nm-wide SiNW channel by the side gate modulation is successfully observed. Four main achievements can be claimed at the end of this project. First, the metallurgic p-n junction in thin (50nm) SOI has been first time ever detected by Ex curve extraction from measured potential profile and the Ex curve was used to study the charge transport in the n-p-n structure under different biasing condition. Secondary, the novel single side gate doping modulated single electron transistors was fabricated and shown Coulomb oscillations which was consistent with theoretical predictions. Furthermore, the operation of FET/SET was investigated by scanned high resolution surface potential profile which revealed the status of p-n junction under biasing. In the end, this study discovered a new method to investigate nano-electronic devices by KPFM scan and more information such as change in build-in voltage at low temperature, and charge in charge state of island can be extracted if the high vacuum and low temperature is applied.

La simulazione dei moderni dispositivi elettronici è una grande sfida per la comunità ingegneristica. L'enorme progresso nei processi di fabbricazione ha permesso una riduzione della dimensione dei dispositivi talmente spinta che fenomeni tipici della scala di lunghezza nanometrica giocano un ruolo cruciale. Inoltre stiamo assistendo a un grande sforzo teso ad esplorare soluzioni tecnologiche alternatice ai tradizionali dispositivi a semiconduttore. Questo sforzo è rivolto verso la frontiera dell'elettronica molecolare, dei polimeri semiconduttori, delle strutture autoassemblanti, dei materiali quasi-unidimensionali e bidimensionali. In uno scenario simile è cruciale sviluppare strumenti di simulazione modulari, capaci di connettere modelli fisici differenti su scale geometriche differenti. Gli effetti quantistici giocano un ruolo fondamentale ed è necessario includere modelli che li descrivano, evitando però la tipica esplosione di complessità nell'implementazione di suddetti modelli. Per realizzare ciò è necessario andare verso un approccio multiscala, approccio già utilizzato con successo in meccanica statica. Lo scopo di questo lavoro è includere descrizioni e modelli atomistici in TiberCAD, un codice TCAD per la simulazione di dispositivi optoelettronici che può vantare eccellenti strumenti per interfacciare diversi modelli fisici in un ambiente multifisica/multiscala. I modelli atomistici inclusi sono utili al calcolo delle deformazioni elastiche, della geometria della struttura e degli stati elettronici. Infine, viene presentata anche una tecnica inedita per una descrizione quantistica efficiente del trasporto di carica. Questo lavoro vuole contrubuire a rendere TiberCAD uno strumento di riferimento per la simulazione di dispositivi optoelettronici su nanoscala.
The simulation of novel optoelectronic devices is a great challenge for the engineering community. The enoromous progress in device fabrication technology allowed such a massive downscaling that geometrical feature in the nanoscale play a crucial role. Furthermore we have a great effort in exploring alternative solutions respect to more traditional semiconductor devices. It involves molecular electronic, semiconductive polymers, self-assembled structures, quasi-one dimensional and two dimensional materials. In such scenario it's crucial to develop modular simulation tools able to connect different physical models on different length scales. Quantum effect play an important role and we need to take them into account, avoiding anyway an explosion of the computational complexity. Thus it's needed to go in the direction of a multiscale approach, which is already applied with success in mechanical science. The goal of this work is to include atomistic description and atomistic models in TiberCAD, a Technology CAD code for simulation of optoelectronic devices which can rely on excellent instruments for interfacing different models in a multyphisics/multiscale environment. Atomistic models for the calculation of strain, structure geometry and electronic states have been included. A novel technique for describing quantum transport with an efficient algorithm is also presented. These work wants to push TiberCAD to be a reference tool for calculation of complex optoeletronic devices at the nanoscale.

A fast and efficient hierarchical optimization engine was developed to benchmark and optimize various emerging device and interconnect technologies and system-level innovations at the early design stage. As the semiconductor industry approaches sub-20nm technology nodes, both devices and interconnects are facing severe physical challenges. Many novel device and interconnect concepts and system integration techniques are proposed in the past decade to reinforce or even replace the conventional Si CMOS technology and Cu interconnects. To efficiently benchmark and optimize these emerging technologies, a validated system-level design methodology is developed based on the compact models from all hierarchies, starting from the bottom material-level, to the device- and interconnect-level, and to the top system-level models. Multiple design parameters across all hierarchies are co-optimized simultaneously to maximize the overall chip throughput instead of just the intrinsic delay or energy dissipation of the device or interconnect itself. This optimization is performed under various constraints such as the power dissipation, maximum temperature, die size area, power delivery noise, and yield. For the device benchmarking, novel graphen PN junction devices and InAs nanowire FETs are investigated for both high-performance and low-power applications. For the interconnect benchmarking, a novel local interconnect structure and hybrid Al-Cu interconnect architecture are proposed, and emerging multi-layer graphene interconnects are also investigated, and compared with the conventional Cu interconnects. For the system-level analyses, the benefits of the systems implemented with 3D integration and heterogeneous integration are analyzed. In addition, the impact of the power delivery noise and process variation for both devices and interconnects are quantified on the overall chip throughput.

Bismuth (Bi) is a unique electronic material with small effective mass (∼0.001me) and long carrier mean free path (100 nm at 300K). It is particularly suitable for studying nano scale related phenomena such as size effect and energy level spacing. In this thesis work, bismuth based nanoelectronic devices were studied. Devices were fabricated using a combination of electron beam (e-beam) writing and thermal evaporation techniques. Dimensions of the fabricated devices were in the order of 100 rim. All structures were optimized for individual electrical characterization. Three types of devices were studied: Bi nanowires, Bi nanowires with dual side-gate structures and Bi nanodot structures. In the study of Bi nanowires, metal-to-semiconductor transition phenomenon and size effect were observed. The conduction behavior of Bi nanowires changed from metallic to semiconductor when the device's critical dimension was reduced to below 50 nm. It is a solid experimental evidence of the quantum confinement-induced bandgap theory. Additionally, it has been found in the present work that resistivity of individual Bi nanowire increased as linewidth decreased indicating size effect occurred in the Bi nanowires. Dual side-gate structures were formed adjacent to the Bi nanowires in an attempt to modulate the current. Measurements showed a 7% of current modulation. The small current modulation suggested the high carrier density in the nanowire which has prevented the full depletion of free carriers. 100 nm-diameter Bi nanodot structures were fabricated utilizing proximity effect of e-beam writing. Precise control of electron doses and process conditions led to the successful fabrication of sub-nanometer tunneling junctions to the nanodots. Significant non-linear current-voltage (I-V) characteristic was observed at low temperatures. The step like I-V characteristic was a strong indication of energy level spacing in the zero-dimensional nanodot structure. The successful observation of energy level spacing in a relatively large nanodot is due to the small effective mass of bismuth material which leads to a measurable energy level spacing.

This thesis introduces novel multiple-gate vacuum nanoelectronic devices, presenting details of their theoretical and experimental characterization, and of the methods that have been established for their fabrication. These devices, based upon the nanotriode of Driskill-Smith et al, have multiple-gates placed within an anode-cathode vacuum gap of only a few hundred nanometres, permitting a wide range of potential-energy landscapes to be created in front of its tungsten-nanopillar field-emitting cathode. The current transport in such devices is suggested to be influenced by quantum interference of the electron wave function in the anode-cathode gap, and this work seeks to control this effect. The device fabrication and electrical characterisation focuses on a pentode device, which has an integrated anode and tungsten-nanopillar cathode structure and three gate-electrodes with aperture-diameters of less than 100 nm; the fabrication can readily be adapted to devices with fewer gates. A calculation of the transmission probability for electrons through the entire pentode anode-cathode gap shows resonances at certain gate-voltage arrangements, strengthening the possibility of observing quantum interference effects in these devices. A study of the tungsten nanopillar formation-process gives new information upon their geometry and formation. The details of the process required to form nanopillars in the pentode chamber are suggested to differ from those required on large area samples. Thus, the observed pentode device characteristics are best explained by dielectric leakage mechanisms, which were also evident in the nanotriode work. However, the reliable range of field emission observation, in two-terminal devices where field emission was observed, has been increased in comparison to the nanotriode by using a tungsten pedestal cathode structure. In response to the pentode characteristics, an alternative cathode structure was fabricated, based upon carbon contaminated scanning electron microscope deposited tips.

As the miniaturization of devices begins to reveal the atomic nature of materials, where chemical bonding and quantum effects are important, one must resort to a parameter-free theory for predictions. This thesis theoretically investigates the quantum transport properties of nanoelectronic devices using atomistic first principles. Our theoretical formalism employs density functional theory (DFT) in combination with Keldysh nonequilibrium Green's functions (NEGF). Self-consistently solving the DFT Hamiltonian with the NEGF charge density provides a way to simulate nonequilibrium systems without phenomenological parameters. This state-of-the-art technique was used to study three problems related to the field of nanoelectronics. First, we investigated the role of metallic contacts (Cu, Ni and Co) on the transport characteristics of graphene devices. With Cu, the graphene is simply electron-doped (Fermi level shift of −0.7 eV) which creates a unique signature in the conduction profile allowing one to extract the doping level. With Ni and Co, spin-dependent band gaps are formed in graphene's linear dispersion bands, thus leading to the prediction of high spin injection efficiencies reaching 60% and 80%, respectively. Second, we studied how controlled doping distributions in nano-scale Si transistors could suppress OFF-state leakage currents. By assuming the dopants (B and P) are confined in 1.1 nm regions in the channel, we discovered large conductance variations (Gmax/Gmin ~ 10^5) as a function of the doping location. The largest fluctuations arise when the dopants are in the vicinity of the electrodes. Our results indicate that if the dopants are located away from the leads, a distance equal to 20% of the channel length, the tunneling current can be suppressed by a factor of 2 when compared to the case of uniform doping. Thus, controlled doping engineering is found to suppress device-to-device variations and lower the undesirable leakage current. Finally, we incorporated a dephasing model into our ab initio transport formalism, which was used to study the effect of phase-breaking scattering in three different systems. Our calculations revealed the complex role of dephasing, where conduction increased or decreased depending on the system under consideration. We demon- strated that the backscattering component of this dephasing scheme also allows one to retrieve Ohm's law.
Comme la miniaturisation des dispositifs commence à révéler la nature atomique des matériaux, où les liaisons chimiques et les effets quantiques sont importants, nous devons recourir à une théorie sans paramètre pour obtenir des prédictions. Cette thèse étudie les propriétés de transport quantique des dispositifs nanoélectroniques en utilisant des méthodes ab initio atomiques. Notre formalisme théorique combine la théorie de la fonctionnelle de la densité (DFT) avec les fonctions de Green hors-équilibres (NEGF). Résoudre l'Hamiltonien DFT de manière auto-consistante avec la densité de charge NEGF permet de simuler des systèmes hors-équilibres sans utiliser des paramètres. Cette technique sophistiquée a été utilisée pour étudier trois problèmes liés au domaine de la nanoélectronique. Premièrement, nous avons étudié le rôle des contacts métalliques (Cu, Ni et Co) sur les caractéristiques de transport des dispositifs à base de graphène. Dans le cas du Cu, le graphène est simplement dopé en électrons (décalage du niveau de Fermi = −0.7 eV) ce qui crée une signature unique dans le profil de conduction permettant d'extraire le niveau de dopage. Avec Ni et Co, la formation de bandes interdites dépendantes du spin détruit la dispersion linéaire des états du graphène ce qui permet d'atteindre une efficacité d'injection de spin de 60% et 80%, respectivement. Deuxièmement, nous avons étudié comment des distributions de dopage contrôlées dans les nano-transistors en Si pourraient supprimer les courants de fuite à l'état OFF. En supposant que les dopants (B et P) sont confinés dans des régions de 1.1 nm dans le canal, nous avons découvert de grandes variations de conductances (Gmax/Gmin ~ 10^5) en fonction de l'emplacement du dopage. Les plus grandes fluctuations surviennent lorsque les dopants sont à proximité des électrodes. Nos résultats indiquent que si les dopants sont éloignés des électrodes, d'une distance égale à 20% de la longueur du canal, le courant tunnel peut être supprimé par un facteur de 2 par rapport au dopage uniforme. Ainsi, l'ingénierie du dopage pourrait réduire les variations d'un dispositif à un autre et diminuer le courant de fuite. Dernièrement, nous avons intégré un modèle de déphasage dans notre théorie de transport ab initio qui a été utilisé pour étudier l'effet des collisions dans trois systèmes différents. Nos calculs ont révélé le rôle complexe du déphasage; parfois la conduction augmente ou diminue selon le système. Nous avons démontré que la rétrodiffusion, présent dans ce modèle, permet de récupérer la loi d'Ohm.

Primary goal of this thesis work is to develop and implement microscopic modeling strategies able to describe semiconductor-based nanomaterials and nanodevices, overcoming both the intrinsic limits of the semiclassical transport theory and the huge computational costs of non Markovian approaches. The progressive reduction of modern optoelectronic devices space-scales, triggered by the evolution on semiconductor heterostructures at the nanoscale, together with the decrease of the typical time-scales involved, pushes device miniaturization toward limits where the application of the traditional Boltzmann transport theory becomes questionable, and a comparison with more rigorous quantum transport approaches is imperative. In spite of the quantum-mechanical nature of electron and photon dynamics in the core region of typical solid-state nanodevices, the overall behavior of such quantum systems is often governed by a highly non-trivial interplay between phase coherence and dissipation/dephasing. To this aim, the crucial step is to adopt a quantum mechanical description of the carrier subsystem; this can be performed at different levels, ranging from phenomenological dissipation/decoherence models to quantum-kinetic treatments. However, due to their high computational cost, non-Markovian Green’ s-function as well as density-matrix approaches like quantum Monte Carlo techniques or quantum-kinetics are currently unsuitable for the design and optimization of new-generation nanodevices. On the other end, the Wigner-function technique is a widely used approach which, in principle, is well suited to describe an interplay between coherence and dissipation: in fact it can be regarded both as a phase space formulation of the electronic density matrix and a quantum equivalent of the classical distribution function. The evolution of this quasi-distribution function is governed by the Wigner-equation, which is usually solved by applying local spatial boundary conditions. However, such a scheme has recently shown some intrinsic limits. In this thesis work we analyze both the reasons for these unphysical features –pointing out the needing of different and purely quantum approaches– and the limits in which they should not appear, thus justifying why these problems had not been encountered in numerous quantum-transport simulations based on this procedure. For these reasons here we present a novel single-particle simulation strategy able to describe the interplay between coherence and dissipation/dephasing. In the presence of one- as well as two-body scattering mechanisms, we apply the mean-field approximation to the many-body Lindblad-type (hence, positive-definite) scattering superoperators provided by a recently proposed Markov approach, and we derive a closed equation of motion for the electronic single-particle density matrix. Although the resulting scattering superoperator turns out to be, at finite or high carrier densities, nonlinear and non-Lindblad, we prove that it is able to guarantee the positivity of the evolution (in striking contrast with conventional Markov approaches) independently of the scattering mechanisms, an essential prerequisite of any reliable kinetic treatment of semiconductor quantum devices; furthermore, it may be extended to the cases of quantum systems with open spatial boundaries (in this regard, it provides a formal derivation of a recently proposed Lindblad-like device-reservoir scattering superoperator). The proposed theoretical scheme is able, one the one hand, to recover the space-dependent Boltzmann equation and, on the other, to point out the regimes where a relevant role may be played by scattering-nonlocality effects, e.g. scattering-induced variations of the spatial charge-density which may not be provided by semiclassical treatments. Supplementing our analytical investigation with a number of simulated experiments in homogeneous as well as inhomogeneous GaN-based systems, we provide a rigorous treatment of scattering nonlocality in semiconductor nanostructures: in particular, we show how the scattering-nonlocality effects (i) are particularly significant in the presence of a carrier localization on the nanometric space scale, (ii) cause a speedup of the diffusion and (iii) in superlattice structures induce, with respect to scattering-free evolutions, a suppression of coherent oscillations between adjacent wells. These genuine quantum effects may be predicted also by other simplified treatments of the dissipation/decoherence like, e.g., the Relaxation Time Approximation: the latter however turns out to be, contrary to the proposed microscopic theoretical scheme, totally nonlocal, e.g. it is unable to recover the local character of the Boltzmann collision term in the semiclassical limit and it leads, especially for the case of quasielastic dissipation processes, to a significant overestimation of the diffusion speedup.

Questa tesi analizza la possibile implementazione di due tipologie di dispositivi elettronici con funzionalità innovative: dispositivi per la computazione quantistica e transistors a film sottile. Negli ultimi decenni l’industria dei semiconduttori ha portato alla realizzazione di circuiti integrati con milioni di transistors e performance sempre migliori a costi contenuti. Tuttavia, questo processo di miniaturizzazione è giunto a un punto tale che i dispositivi elettronici sono ora composti da pochissimi atomi e ridurne ulteriormente le dimensioni sta diventando sempre più difficile. L’International Technology Roadmap of Semiconductors (ITRS) suggerisce due vie alternative per migliorare le caratteristiche dei dispositivi a partire dalla Front-End-Of-Line. La prima si avvale di nuovi dispositivi sulla base di architetture innovative o dell’utilizzo di diverse variabili di stato (Emerging Research Devices), mentre la seconda punta all’utilizzo di nuovi materiali (Emerging Research Materials). Questa tesi esamina due possibili candidati in questa ottica: i dispositivi per la computazione quantistica su architettura Complementary Metal-Oxide-Semiconductor (CMOS) e i transistors a film sottile basati su un semiconduttore bidimensionale come il MoS2. Da un lato, l’integrazione della computazione quantistica su Si sfrutterebbe il background tecnologico dell’industria dei semiconduttori per implementare su larga scala un nuovo protocollo di computazione dotato di un potenziale enorme e ancora inesplorato. D’altra parte il di-solfuro di molibdeno (MoS2) è intrinsecamente scalabile, in quanto può essere esfoliato fino allo spessore di un singolo strato atomico. Per questo motivo potrebbe essere un semiconduttore ideale per dispositivi elettronici ultrascalati, così come per applicazioni nella sensoristica, nell’optoelettronica e nell’elettronica flessibile. Questo lavoro mostra l’attività svolta al Laboratorio MDM-IMM-CNR nell’ambito del corso di dottorato in Nanostrutture e Nanotecnologie all’Università di Milano Bicocca. Lo sviluppo e l’utilizzo di processi di fabbricazione della nanoelettronica, in particolare la litografia a fascio elettronico (EBL), sono stati parte integrante dell’attività sperimentale dedicata alla realizzazione di dispositivi CMOS-compatibili per la computazione quantistica e per l’integrazione di film sottili di MoS2 in strutture Metal-Oxide-Semiconductor Field-Effect-Transistor (MOS FET). I necessari passi di processo sono stati adeguatamente calibrati e ottimizzati in modo da ottenere dispositivi quantistici basati su Quantum Dots (QD) con dimensioni caratteristiche inferiori a 50 nm. Tali dispositivi sono stati sviluppati con tecnologia Silicon-On-Insulator (SOI), mantenendo così la compatibilità con lo standard della tecnologia CMOS. Dispositivi a singolo donore e con QD di silicio sono stati poi caratterizzati elettricamente a temperature criogeniche (fino a 300 mK). Impulsando i potenziali di gate in modo controllato, è stato possibile studiare fenomeni di tunneling di singoli elettroni su un donore in alti campi magnetici (8T). In modo analogo è stato dimostrato il controllo dello stato di carica di QDs di Si. In particolare, si è osservato l’insorgere di rumore telegrafico associato al movimento di un singolo elettrone tra due QDs. Infine è stato condotto uno studio di fattibilità per l’integrazione su larga scala di un’architettura di computazione quantistica (il cosiddetto hybrid spin qubit) basata su doppi QDs di Si. Sul secondo fronte sono stati realizzati dei MOS FETs a film sottile basati su frammenti di MoS2, ottenuti per esfoliazione meccanica e contattati elettricamente tramite litografia EBL. Tali transistors sono poi stati caratterizzati elettricamente, con particolare attenzione alle proprietà di trasporto di carica e alla spettroscopia delle trappole all’interfaccia con l’ossido.
This work of thesis explores two emerging research device concepts as possible platforms for novel integrated circuits with unconventional functionalities. Nowadays integrated circuits with advanced performances are available at affordable costs, thanks to the progressive miniaturization of electronic components in the last decades. However, bare geometrical scaling is no more a practical way to improve the device performances and alternative strategies must be considered to achieve an equivalent scaling of the functionalities. The introduction of conceptually new devices and paradigms of information processing (Emerging Research Devices) or new materials with unconventional properties (Emerging Research Materials) are viable approaches, as indicated by the International Technology Roadmap of Semiconductors (ITRS), to enhance the functionalities of integrated circuits at the Front-End-Of-Line. The two options investigated to this respect are silicon devices for quantum computation based on a classical Complementary Metal-Oxide-Semiconductor (CMOS) platform and standard Metal-Oxide-Semiconductor Field-Effect-Transistors (MOSFETs) based on MoS2 thin film. In particular, the integration of Quantum Information Processing (QIP) in Si would take advantage of Si-based technology to introduce a completely new paradigm of information processing that has the potential to outperform classical computers in some computational tasks, like prime number factoring and the search in a big database. MoS2, conversely, can be exfoliated up to the single layer thickness. Such intrinsic and extreme scalability makes this material suitable for end-of-roadmap ultrascaled electronic devices as well as for other applications in the fields of sensors, optoelectronics and flexible electronics. This work reports on the experimental activity carried out at Laboratory MDM-IMM-CNR in the framework of the PhD school on Nanostructures and Nanotechnology at Università di Milano Bicocca. Electron Beam Lithography (EBL) and mainstream clean-room processing techniques have been intensively utilized to fabricate CMOS devices for QIP on the one hand and to integrate mechanically exfoliated MoS2 flakes in a conventional FET structure on the other hand. After a careful calibration and optimization of the process parameters, several different Quantum Dot (QD) configurations were designed and fully realized, achieving critical dimensions under 50 nm. Such device architectures were developed on a Silicon-On-Insulator (SOI) platform, in order to eventually access a straightforward integration into the CMOS mainstream technology. Si-QDs and donor-based devices have been then tested by electrical characterization techniques at cryogenic temperatures down to 300 mK. In detail, single electron tunneling events on a donor atom have been controlled by pulsed-gate techniques in high magnetic fields up to 8T, providing a preliminary characterization for the initialization procedure of donor qubits. The control of the charge states of Si-QDs have been also demonstrated by means of stability diagrams as well as the analysis of random telegraph noise arising from single electron tunneling between two QDs. Finally, a feasibility study for the large scale integration of quantum information processing was done based on a double QD hybrid qubit architecture. On the other side, MoS2 thin film transistors have been made by mechanical exfoliation of crystalline MoS2 and electrodes definition by EBL. Electrical characterization was performed on such devices, with a particular focus on the electrical transport in a FET device and on the spectroscopy of interface traps, that turns out to be a limiting factor for the logic operation.

Cooling physical experiments to low temperatures removes thermal excitations to reveal quantum mechanical phenomena. The progression of nanotechnologies provides new and exciting research opportunities to probe nature at ever smaller length scales. The coupling of nanotechnologies and low temperature techniques has potential for scientific discoveries as well as real world applications. This work demonstrates techniques to further extend physical experimental research into the millikelvin-nanoscale domain. The challenge of thermometry becomes an increasingly complex problem as the temperature of a physical system lowers. We describe the development and methods for a specially modified Coulomb blockade thermometer to achieve electron thermometry below 4mK overcoming the challenge of electron thermalisation for on-chip devices. Mechanically vibrating devices can directly probe bulk and surface fluid properties. We developed practical measurement techniques and analysis methods to demonstrate the use of nanomechanical resonators, which for the first time were used to probe both the normal and the superfluid phases of helium-4. The doubly clamped beams had a cross section of 100nm by 100nm and were tested in length variants between 15um to 50um, The flexural resonance between 1MHz and 10MHz in response to the helium temperature dependent properties showed an encouraging agreement with established theories, providing experimental verification on a new smaller length scale. The smallest beams achieved a mass sensitivity in liquid of 10ag. We also created and analysed a new method of sampling peak-like functions that is applicable to many physical systems to provide around 20% improvements over the existing methods under certain situations. This was verified in ultra low temperature applications as a drop-in addition to accompany existing techniques.

Semiconductor nanowire materials and devices provide unique opportunities in the frontier between nanoelectronics and biology. The bottom-up paradigm enables flexible synthesis and patterning of nanoscale building blocks with novel structures and properties, and nano-to-micro fabrication methods allow the advantages of functional nanowire elements to interface with biological systems in new ways. In this thesis, I will focus on the development of bottom-up nanoscience platforms, which includes rational synthesis and assembly of semiconductor nanowires with new capabilities, as well as design and fabrication of the first free-standing three-dimensional (3D) nanoprobes, with special focus on applications in intracellular recording and stimulation. I will first introduce kinked p-n junction nanowires as a new and powerful family of high spatial resolution biological and chemical sensors with proof-of-concept applications. Next, I will discuss a variety of functional kinked nanowires with synthetically controlled properties and the potential of achieving more detailed and less invasive cellular studies. Furthermore, I will present a general shape-controlled deterministic nanowire assembly method to produce large-scale arrays of devices with well-defined geometry and position. Then, I will present the design of a general method to fabricate these nanowire structures into free-standing 3D probes. I will show that free-standing nanowire bioprobes can be manipulated to target specific cells and record stable intracellular action potentials. I will demonstrate simultaneous measurements from the same cell using both kinked nanowire and patch-clamp probes. Moreover, I will discuss two strategies of multiplexed recording using free-standing probes. Finally, I will report localized stimulation on single cells enabled by the unique properties of p-n kinked nanowires. I will show with simulation and electrical characterization that in reverse bias, localized electric field generated around the nanoscale p-n junction should exceed the threshold for opening voltage-gated sodium channels. Moreover, I will present measurements of localized cell stimulation using p-n nanowire free-standing probes. Together with the capability of stable intracellular recording, these results complete the two-way communication between semiconductor nanowire electronics and biological systems at a natural nanoscale, which can open up new directions in the fields ranging from cellular electrophysiology, brain activity mapping to brain-machine interface.
Chemistry and Chemical Biology

The environment interacts with the electron and leads to electron relaxation pro cesses. To measure the relaxation rate the system is disturbed from equilibrium. T₁ time characterizes the time for the system to restore equilibrium.

Understanding and controlling the spin-relaxation mechanism is crucial for real izing a spin-qubit based quantum computer. The spin-lattice relaxation time (T₁) is one of the two important timescales of a qubit, and in addition, it can provide valu able information about the qubit and its interaction with the device environment. Here, we investigate the T₁ time of electronic spins bound to donors in silicon in a scanning tunneling microscopy (STM) fabricated device. A tight-binding treatment of the electron-phonon problem is being developed. Together with Fermi’s Golden rule the T₁ time of the system can be obtained with atomic level details. This method is extended to treat the multi-electron system, where the electron-electron interaction is captured by atomistic con?guration interaction method. We also show that under applied gate bias, an unconventional spin-orbit coupling the external electric ?eld and magnetic ?eld dominates over Rashba spin-orbit for donors in Si. Various spin relaxation mechanisms are investigated, considering both the valley repopulation and single valley e?ects. We ?nd that T₁ is strongly dependent on the directions of the external magnetic and electric ?elds relative to the crystalline directions. We show good agreements between this theory and recent experimental measurements.

Modelling of phosphorus donor-based silicon (Si:P) qubit devices and mesoscopic single-electron devices is presented in this thesis. This theoretical analysis is motivated by the use of Si:P devices for scalable quantum computing. Modelling of Si:P single-electron devices (SEDs) using readily available simulation tools is presented. The mesoscopic properties of single and double island devices with source-drain leads is investigated through ion implantation simulation (using Crystal-TRIM), 3D capacitance extraction (FastCap) and single-electron circuit simulation (SIMON). Results from modelling two generations of single and double island Si:P devices are given, which are shown to accurately capture their charging behaviour. The trends extracted are used to forecast limits to the reduction in size of this Si:P architecture. Theoretical analysis of P2+:Si charge qubits is then presented. Calculations show large ranges for the SET measurement signal, Δq, and geometric ratio factor, α, are possible given the 'top-down' fabrication procedure. The charge qubit energy levels are calculated using the atomistic simulator NEMO 3-D coupled to TCAD calculations of the electrostatic potential distribution, further demonstrating the precise control required over the position of the donors. Theory has also been developed to simulate the microwave spectroscopy of P2+:Si charge qubits in a decohering environment using Floquet theory. This theory uses TCAD finite-volume modelling to incorporate realistic fields from actual device gate geometries. The theory is applied to a specific P2+:Si charge qubit device design to study the effects of fabrication variations on the measurement signal. The signal is shown to be a sensitive function of donor position. Design and analysis of two different spin qubit architectures concludes this thesis. The first uses a high-barrier Schottky contact, SET and an implanted P donor to create a double-well suitable for implementation as a qubit. The second architecture is a MOS device that combines an electron reservoir and SET into a single structure, formed from a locally depleted accumulation layer. The design parameters of both architectures are explored through capacitance modelling, TCAD simulation, tunnel barrier transmission and NEMO 3-D calculations. The results presented strengthen the viability of each architecture, and show a large Δq (> 0.1e) can be expected.

Dans la lignée des progrès technologiques récents en électronique, ces dernières décennies ont vu l’émergence d’une variété de systèmes permettant l’interface bioélectronique, allant de la mesure de l’activité électrique émise par l’ensemble du cerveau jusqu’à la mesure du signal émis par un neurone unique. Bien que des interfaces électroniques avec les neurones ont montré leur utilité pour des applications cliniques et sont communément utilisés par les neurosciences fondamentales, leurs performances sont encore très limitées, notamment en raison de l’incompatibilité relative entre les systèmes à l’état solide et le vivant. Dans ce travail de thèse, nous avons étudié des techniques et des matériaux nouveaux permettant une approche alternative et qui pourraient améliorer le suivi de l’activité de réseaux de neurones cultivés in situ et à terme la performance des neuroprothèses in vivo. Dans ce travail, des réseaux de nanofils de silicium et des microélectrodes en diamant sont élaborés pour respectivement améliorer la résolution spatiale et la stabilité des électrodes dans un environnement biologique. Un point important de cette thèse est également l’évaluation des performances de transistors à effet de champ en graphène pour la bio électronique. En raison des performances remarquables et combinées sur les aspects électrique, mécanique et chimique du graphène, ce matériau apparaît comme un candidat très prometteur pour la réalisation d’une électronique permettant une interface stable et sensible avec un réseau de neurones. Nous montrons dans ce travail l’affinité exceptionnelle des neurones avec une surface de graphène brut et la réalisation d’une électronique de détection rapide et sensible à base de transistor en graphène
In line with the technological progress of last decades a variety of adapted bioelectrical interfaces was developed to record electrical activity from the nervous system reaching from whole brain activity to single neuron signaling. Although neural interfaces have reached clinical utility and are commonly used in fundamental neuroscience, their performance is still limited. In this work we investigated alternative materials and techniques, which could improve the monitoring of neuronal activity of cultured networks, and the long-term performance of prospective neuroprosthetics. While silicon nanowire transistor arrays and diamond based microelectrodes are proposed for improving the spatial resolution and the electrode stability in biological environment respectively, the main focus of this thesis is set on the evaluation of graphene based field effect transistor arrays for bioelectronics. Due to its outstanding electrical, mechanical and chemical properties graphene appears as a promising candidate for the realization of chemically stable flexible electronics required for long-term neural interfacing. Here we demonstrate the outstanding neural affinity of pristine graphene and the realization of highly sensitive fast graphene transistors for neural interfaces

The work describes the features of simulation of the ultrahigh-frequency electromagnetic interaction, which forms an internal solenoid status of monolithic integrated circuits. As an example, is the study of matching devices, which are made in the form of the band-pass lines. The proposed method of modeling, to determine the dependence of the finite frequency and temporal characteristics of the cascading schemes amplifiers. Thus, the proposed method of modeling physical processes appear not only domestic but also external display spatially distributed nano-and micro-strip technology structures. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35357

Molecules due to their very small sizes, possess discrete energy levels and electrons can transmit from one side of the molecule to the other with high probability if their energy coincides with molecular energy levels. In the weak coupling limit such on-resonance electron transport is described by the simple Lorentzian-shaped Breit-Wigner formula. On the other hand, electrons with energy different than the molecular energy levels have to tunnel through the energy gap between two molecular energy levels (off resonance transmission). Consequently the electron transmission probability is much smaller than on resonance regime. Interesting phenomena including quantum interference could be observed in this regime at room temperature. In this thesis, I discuss both regimes though, my main aim is to introduce a new theory called ”mid- gap theory” to predict the conductance ratio between different connectivities driven by quantum interference (QI) in the tunneling regime. Both theory and experiment have focused primarily on elucidating the conditions for the appearance of constructive or destructive interference. In the simplest case, where electrons are injected at the Fermi energy EF of the electrodes, constructive QI arises when EF coincides with a delocalized energy level En of the molecule. Similarly a simple form of destructive QI occurs when EF coincides with the energy Eb of a bound state located on a pendant moiety. Unless energy levels are tuned by electrostatic, electrochemical or mechanical gating, molecules located within a junction rarely exhibit these types of QI, because EF is usually located in the HOMO-LUMO (H-L) gap. Furthermore few analytic formulas are available, which means that pre-screening of molecules often requires expensive numerical simulations. For this reason, discussions have often focused on conditions for destructive or constructive QI when EF is located at the centre of the H-L gap. In this thesis, based on a simple description of connectivity, I demonstrate that the conductance ratio between two different connectivities of a core molecule could be predicted simply by using the ratio between two magic numbers of the core molecule. This will be discussed in the chapters 4-6. This simple theory not only predicts conductance ratios, but it could be used also to propose new strategies for molecular electronic design and applications such as single molecule switches and thermoelectricity. In this thesis after an introduction to nano and molecular electronics, I discuss general ideas about nanoscale transport and the methods which could be applied to model nano and molecular scale devices. In chapter 3, on resonance transport is discussed. For a wide variety of molecules, the conductance G decays with length L as Aexp(−βL) and it is widely accepted that the attenuation coefficient β is determined by position of the Fermi energy of the electrodes relative to the energy gap of the molecular bridge, whereas the terminal anchor groups which bind the molecule to the electrodes contribute to A. In contrast with this expectation, in chapter 3, I demonstrate that gateway orbitals located on the anchor groups can significantly decrease the value of β, thereby creating a new design strategy for realizing low-conductance molecular wires. In chapters 4-6, I introduce mid-gap theory and drive a mid-gap ratio rule (MRR) which is an exact formula for conductance ratios of tight-binding representations of molecules in the weak coupling limit, when the Fermi energy is located at the centre of the HOMO-LUMO (H-L) gap. It does not depend on the size of the H-L gap and is independent of asymmetries in the contacts. I also show how conductance ratios change, when one of the carbon atoms within the parent polycyclic aromatic hydrocarbons (PAH) core is replaced by a heteroatom to yield a daughter molecule. I show that this heteroatom substitution could be used to enhance the conductance in a PAH molecule by several orders of magnitude. A good agreement between this new simple theory and experiment shows that, the MRR provides a useful tool to predict the conductances of PAH molecules prior to synthesis. Therefore it could be used to design molecules with desirable properties or to propose new molecular devices.

In this thesis various subjects at the crossroads of quantummechanics and device physics are treated, spanning from afundamental study on quantum measurements to fabricationtechniques of controlling gates for nanoelectroniccomponents.

Electron waveguide components, i.e. electronic componentswith a size such that the wave nature of the electron dominatesthe device characteristics, are treated both experimentally andtheoretically. On the experimental side, evidence of partialballistic transport at room-temperature has been found anddevices controlled by in-plane Pt/GaAs gates have beenfabricated exhibiting an order of magnitude improvedgate-efficiency as compared to an earlier gate-technology. Onthe theoretical side, a novel numerical method forself-consistent simulations of electron waveguide devices hasbeen developed. The method is unique as it incorporates anenergy resolved charge density calculation allowing for e.g.calculations of electron waveguide devices to which a finitebias is applied. The method has then been used in discussionson the influence of space-charge on gate-control of electronwaveguide Y-branch switches.

Electron waveguides were also used in a proposal for a novelscheme of carrierinjection in low-dimensional semiconductorlasers, a scheme which altogether by- passes the problem ofslow carrier relaxation in suchstructures. By studying aquantum mechanical two-level system serving as a model forelectroabsorption modulators, the ultimate limits of possiblemodulation rates of such modulators have been assessed andfound to largely be determined by the adiabatic response of thesystem. The possibility of using a microwave field to controlRabi oscillations in two-level systems such that a large numberof states can be engineered has also been explored.

A more fundamental study on quantum mechanical measurementshas been done, in which the transition from a classical to aquantum "interaction free" measurement was studied, making aconnection with quantum non-demolition measurements.

L’objectif principal de ce travail est d’appliquer des méthodes exactes (matrice de transfert) ou semi-exactes (en utilisant des simulations Monte Carlo avec l’algorithme de l’échantillonnage entropique) à l’étude du comportement des matériaux moléculaires. Nous avons utilisé le modèle type-Ising en tenant compte des interactions à courte et à longue portée afin de simuler la réponse à des effets extérieurs dans des composés à transition de spin de taille macroscopique ainsi que des tailles nanométriques. Grâce à leur bistabilité ces composés à transition de spin sont potentiellement utilisables dans la fabrication de nouveaux dispositifs (capteurs de températures et/ou de pression, stockage de l’information). Notre travail contient deux parties. La première partie, les trois premiers chapitres, est consacrée à l’état de l’art des matériaux à transition de spin (SCO) et à la description de modèles et méthodes proposés pour expliquer le phénomène de transition de spin. La deuxième partie, les 4 derniers chapitres, concerne nos études théoriques sur l’effet de la taille, la forme et l’effet des molécules en surface dans le domaine des matériaux à transition de spin. Cette thèse, dans le domaine de la Sciences des matériaux, traite à travers tous ces chapitres de deux axes. Dans un premier axe nous avons modélisé et simulé le comportement de plusieurs matériaux SCO existant en utilisant le modèle type Ising afin de comprendre le mécanisme de transition de spin. Nous avons également analysé les effets des différents facteurs extérieurs, notamment l’effet des molécules en surface, dans les composés à transition de spin avec différents types de configurations : 1D, 2D et 3D. Ayant trouvé un bon accord entre les résultats numériques et les données expérimentales, nous avons étudié de nouveaux comportements thermiques de ces matériaux à transition spin obtenus expérimentalement : transition incomplète et transition à plusieurs étapes
The main purpose of this thesis is to develop exact methods (i. E. Matrix transfer) or semi-exact methods (using Monte Carlo technique with entropic sampling algorithm) to study the behaviour of molecular materials. Using an Ising like model that takes into account both short-range and long-range interactions in Spin Crossover (SCO materials) the response resulting from the spin state switching phenomenon (from bulk materials down to nanoscale size) was simulated. SCO materials have potential applications in the fabrication of novel devices (i. E. Storing information, sensing, and display). This work contains two main parts divided in seven chapters. The first part, the first three chapters, is devoted to some overview of SCO materials and to the description of several models and methods proposed to explain the Spin Transition (ST) phenomenon while the second part, the last four chapters, is focused on some theoretical studies on size and shape effects as well as the molecules at the surface effect in the SCO area which is a new subject. This thesis, in the field of Computing Materials Science, treats two axes. In the first axe we have modeled and simulated the behaviour of several existing materials using an Ising like model in order to understand the ST mechanism and the effects of different external factors in different SCO compounds in 1D, 2D or 3D structures. From the good agreement between the numerical and the experimental data in the first part, we have studied in the second part different architectures and we have predicted some novel SCO behaviours, obtained recently experimentally, as incomplete or multi-step transition

L'intérêt porté au domaine Terahertz (THz) ayant beau être en pleine expansion depuis les années 1990, un gros effort de recherche doit encore être effectué pour tirer la quintessence des applications actuelles ou potentielles que représente cette gamme du spectre électromagnétique dans des domaines aussi variés que la spectroscopie, la cosmologie, l'imagerie médicale, la sécurité ou les télécommunications. En effet les sources, les détecteurs mais également les outils qui permettent d'amplifier ou de moduler un signal – dispositifs très présents dans les régions voisines du spectre électromagnétique que sont l'infrarouge et les micro-ondes - sont encore particulièrement limités par des facteurs tels que la compacité, la température de fonctionnement, l'intégrabilité mais également la puissance, la sensibilité ou encore le coût.Cette thèse porte sur l'étude expérimentale de divers composants en nitrure de gallium (GaN) contenant un puits quantique avec pour objectif de déterminer leurs capacités d'émission, d'amplification ou de détection d'une radiation THz.Pour ce faire, trois différents dispositifs expérimentaux ont été utilisés, améliorés ou même créés dans le but de pouvoir faire varier des paramètres tels que la polarisation électrique, leur température de fonctionnement, les fréquences THz sondées et bien sûr les différentes géométries des échantillons.De plus amples détails sur le monde des THz, sur les dispositifs électroniques GaN utilisés ainsi que sur les montages expérimentaux mis en places sont développés dans ce manuscrit de thèse. Les principaux résultats expérimentaux obtenus montrent :- une émission vers 3 THz avec une fréquence accordable en fonction du champ électrique appliqué au puits quantique GaN,- un coefficient de transmission variable en fonction de la tension appliquée aux contacts en doigts interdigités de différentes structures GaN,- la détection hétérodyne de radiations avec une fréquence RF de 0,3 THz et IF pouvant monter jusqu'à 40 GHz. De plus, chaque type de résultats expérimentaux a été expliqué théoriquement à l'aide de modèles analytiques développés en collaboration avec des équipes internationales au cours de ces trois dernières années
Even if the interest upon the Terahertz (THz) domain is increasing since the 1990s, a strong research effort still needs to be done to get the most of the current and potential applications that this area of the electromagnetic spectrum has to offer in the various domains of spectroscopy, cosmology, medical imaging, security and telecommunications. Indeed, sources, detectors and even the tools that permits to amplify or modulate a signal – these devices are well developed in the neighboring regions of infrared and microwaves – are still particularly limited by characteristics like compactness, operating temperature, integrability but also power, sensitivity or cost.This thesis focuses on the experimental study of different gallium nitride (GaN) devices containing a quantum well. The main objective was to determine their capacities in emission, amplification or detection of a THz radiation.To do so, three different experimental setups where used, improved or even created in order to be able to change parameters like the electric bias, their working temperature, the probed THz frequencies and of course the different geometries of the samples.More details about the THz domain, the studied GaN electronic devices and the used experimental setups are developed in this PhD thesis.The main obtained experimental results show:- an emission of radiation near 3 THz with a tunable frequency versus electric field applied to the GaN quantum well,- a transmission coefficient variable as a function of the voltage applied to the contacts of different GaN interdigitated fingers structures,- heterodyne detection of radiation with a RF frequency of 0.3 THz and an IF that can reach up 40 GHz.In addition, each type of experimental results has been investigated theoretically using analytical models developed in collaboration with international teams during the past three years

The push for electronic devices on smaller and smaller scales has driven research in the direction of transition metal dichalcogenides (TMD) as new ultra-thin semiconducting materials. These ‘two-dimensional' (2D) materials are typically on the order of a few nanometers in thickness with a minimum all the way down to monolayer. These materials have several layer-dependent properties such as a transition to direct band gap at single-layer. In addition, their lack of dangling bonding and remarkable response to electric fields makes them promising candidates for future electronic devices. For the purposes of this work, two 2D TMDs were studied, MoS2 and MoTe2. This dissertation comprises of three sections, which report on exploration of charge lifetimes, investigation environmental stability at elevated temperatures in air, and establishing feasibility of UV laser annealing for large area processing of 2D TMDs, providing a necessary knowledge needed for practical use of these 2D TMDs in optoelectronic and electronic devices. (1) A study investigating the layer-dependence on the lifetime of photo-generated electrons in exfoliated 2D MoTe2 was performed. The photo-generated lifetimes of excited electrons were found to be strongly surface dependent, implying recombination events are dominated by Shockley-Read-Hall effects (SRH). Given this, the measured lifetime was shown to increase with the thickness of exfoliated MoTe¬2; in agreement with SRH recombination. Lifetimes were also measured with an applied potential bias and demonstrated to exhibit a unique voltage dependence. Shockley-Read-Hall recombination effects, driven by surface states were attributed to this result. The applied electric field was also shown to control the surface recombination velocity, which lead to an unexpected rise and fall of measured lifetimes as the potential bias was increased from 0 to 0.5 volts. (2) An investigation into the environmental stability of exfoliated 2D MoTe2 was conducted using a passivation layer of amorphous boron nitride as a capping layer for back-gated MoTe2 field effect transistor (FET) devices. A systematic approach was taken to understand the effects of heat treatment in air on the performance of FET devices. Atmospheric oxygen was shown to negatively affect uncoated MoTe2 devices while BN-covered FETs showed remarkable chemical and electronic characteristic stability. Uncapped MoTe2 FET devices, which were heated in air for one minute, showed a polarity switch from n- to p-type at 150 °C, while BN-MoTe2 devices switched only after 200 °C of heat treatment. Time-dependent experiments at 100 °C showed that uncapped MoTe2 samples exhibited the polarity switch after 15 min of heat treatment while the BN-capped device maintained its n-type conductivity. X-ray photoelectron spectroscopy (XPS) analysis suggests that oxygen incorporation into MoTe2 was the primary doping mechanism for the polarity switch. (3) The feasibility of UV laser annealing as a post-process technique to sinter 2D crystal structures from sputtered amorphous MoS2 was explored. Highly crystalline materials are sought after for their use in electron and opto-electronic devices. Sputtered MoS2 has the advantage of potential for large area deposition and high scalability, however, it requires high temperatures (>350 °C) for their crystalline growth. Which creates difficulty for devices grown on polymer substrates. Low-temperature and room temperature deposition results in amorphous films which is detrimental for electric devices. A one-step lase annealing procedure was developed to provide amorphous to crystalline conversion of nanometer thin MoS2 films. Samples were annealed using an unfocused laser beam from a KrF (248 nm) excimer source. The power density was found to be 1.04 mJ/mm2. Raman analysis of laser annealed MoS2 was shown to exhibit a significant improvement of the 2D MoS2 crystallinity compared to as-deposited films on both SiO2/Si, as well as polydimethylsiloxane (PDMS) substrates. Annealed samples showed improvement of their conductivity on an order of magnitude. A top-gated FET device was fabricated on flexible PDMS substrates using Al2O3 as a gate oxide. Measured field effect mobility of annealed samples showed significant improvement over as-deposited devices.

Due to its truly two dimensional (2D) character and its particular lattice, single layer graphene (SLG) possesses exceptional properties: it is semimetallic, transparent, strong yet flexible ... Complementary features such as the insulating character of hexagonal boron nitride (h-BN) and semiconducting properties of transition metal dichalcogenides (TMDs) enable the whole spectrum of electronic devices to be built with combinations of these 2D materials. Due to this and the ease of exfoliation with a sticky tape, a vast amount of research was sparked. The mechanical exfoliation method, however, is only suitable for novel or proof-of-concept devices. The trend nowadays in electronics is towards transparent, lightweight, flexible, embedded smart devices and sensors in everyday objects such as windows and mirrors, garments, windshields, car seats, parachutes...These demands are already met inherently by these new materials, thus the challenges remaining are within their synthesis, deposition and processing, where more scalable ways of production and device fabrication need to be developed. This thesis explores innovative approaches using established techniques that aim to bridge the gap between proof-of-concept devices and real applications of 2D materials in future commercial level technologies. Methods to create graphene and engineer its properties are employed with a special focus on scalability and adaptability towards the industry. These graphene materials have been processed using pioneering schemes to create different optoelectronic devices and sensors. The techniques employed here for synthesis, transfer and deposition, device processing and characterization of graphene and derivatives, are suitable for their use in large manufacturing and mass-production. Depending on the application envisaged, different materials are used and optimize in order to balance good performance, cost-effectiveness and suitability/scalability of the process for the specific target the device was designed for.

The tri-gate FET has been hailed as the biggest breakthrough in transistor technology in the last 20 years. The increase in device performance (faster switching, less delay, improved short channel effects, etc.) coupled with the reduction in device size, would allow for huge gains in the electronics industry. This thesis aims to not only investigate the validity of these claims, but also how random dopant fluctuation (RDF) affects the tri-gates performance and how to curb these issues. In order to achieve this, an atomistic 3-D device simulation program was utilized in order to capture the many quantum mechanical effects that devices of this size experience and compare the results against a similar planar device. We see the tri-gate FET does indeed perform extremely well compared to its planar counterpart, but both devices experience a great deal of fluctuations due to the random dopants in the device. In order to limit the RDF effects a variety of methods were implemented including increasing doping concentrations in the channel, source, and drain regions, varying the source/drain junction depths, and varying the source/drain contact workfunction. The results showed that increasing doping concentrations in order to reduce the amount of space the dopants had to diffuse did not reduce the randomness experienced by the devices, but rather the randomness increased. The dopant fluctuation was insensitive to the varying of the workfunction, but was found to decrease with an increase in junction depth in the source/drain regions. With randomness in the tri-gate reduced, the overall performance should increase when used in ICs, where consistency in device characteristics is essential.

The increasing interest in Si-based nanostructures for quantum information purposes is motivated by the advantages offered by the physical properties of the material and by the maturity of the industrial CMOS technology which ensures a real chance of scalability. In such wide framework this thesis has investigated coherence-related effects of single electrons confined in silicon impurity or quantum dot in presence of oscillating electric fields. High frequency excitations in the MHz – GHz range on the one hand are demonstrated to be detrimental for coherent electron transfers; on the other hand they represent a tool for non-invasive and scalable charge detection through reflectometry. The research activity has also concerned the development and assembly of a new setup for broadband manipulation and current sensing of nanoscaled MOSFETs at cryogenic temperatures. Quantum transport measurements at 4 K in a single-gate FET evidence a hitherto unobserved selection rule on valley quantum numbers of the electrons. Here the 6-fold valley degeneracy typical of bulk Si is lifted by the confinement and electric field: the source-drain conduction is mediated by the energy levels of a single P atom that selects the valley state of the electron under tunneling. Analogously to Coulomb blockade for charges and Pauli blockade for spins, this valley blockade determines the transport suppression by the orthogonality of valley-orbital degrees in the reservoirs and at the impurity site. The conservation of the electron valley index is further confirmed by the observation of spin-valley Kondo transitions at the neutral charge state of the atom. The quantum transport is then driven out of equilibrium by an external field at several GHz frequencies and powers. The spin coherent fluctuations sustaining the Kondo effect are quenched by strong ac fields because of the spin-flips induced by electron-photon couplings. By contrast, the electron valley parity is not altered and the valley blockade phenomenology is fully preserved at several powers. Interestingly, very small excitations of ~ 100 MHz are exploitable to measure physical mechanisms of transport at the nanoscale through phase sensitive detection by radio frequency reflectometry. By means of a new dual-port reflectometric apparatus several aspects of the ultra-low temperature transport of a nanodevice are investigated. The multiplexing scheme exploiting the double-gate geometry of the sample allows clearer and more complete measurement of the charge stability diagrams than standardly used one-port setups. The dispersive detection of spin-dependent transitions makes gate-based reflectometry a promising yet barely explored technique combining high sensitivity and large bandwidth. Transport data are critically compared with reflectometry. Finally, the development and characterization at 4 K of a cryogenic modular setup for electrical measurements in multigate devices is reported. Degradation of ns voltage signals for electrical manipulation is minimized and custom cryogenic electronics allows low-noise current sensing. The versatile approach adopted for such platform can be replicated in more complicate systems like cryostats.

El treball presentat en aquesta tesi es dedica a la comprensió de desafiaments pràctics i conceptuals en la simulació de propietats dinàmiques més enllà de l’aproximació quasi-estàtica en dispositius quàntics d’estat sòlid en escenaris on és necessari un tractament mecànic quàntic complet. Els resultats d’aquesta tesi són particularment rellevants per al càlcul de les fluctuacions del corrent elèctric en el règim de THz, per a l’avaluació dels temps de túnel que defineixen la freqüència de tall dels dispositius operats a alta freqüència, o per a l’avaluació del treball termodinàmic per a la realització de motors tèrmics quàntics. Les propietats dinàmiques esmentades impliquen mesures en diversos temps i, per tant, són sensibles a la “”retracció”” quàntica de la mesura. En el context de la mecànica quàntica ortodoxa, la definició d’aquestes propietats dinàmiques no es pot desvincular de l’especificació de l’aparell de mesura. És a dir, definir propietats dinàmiques intrínseques o independents dels aparells de mesura és incompatible amb els postulats de la mecànica quàntica ortodoxa. Per tot plegat, un enginyer de dispositius com jo, que treballa en problemes pràctics relacionats amb els dispositius d’estat sòlid actuals i futurs, es veu obligat a aprofundir en els fonaments de la mecànica quàntica. En aquest sentit, mostraré que les dificultats associades a la comprensió de propietats dinàmiques de sistemes quàntics es poden resoldre mirant més enllà de la mecànica quàntica ortodoxa. En particular, he explorat la interpretació modal de la mecànica quàntica, que és una teoria quàntica matemàticament precisa que reprodueix tots els fenòmens de la mecànica quàntica. Mostraré que les propietats intrínseques es poden definir fàcilment en aquest nou context (no ortodox). Demostraré també que les propietats intrínseques es poden identificar amb la mesura de “weak values” i, per tant, que es poden mesurar. Centrat en una teoria modal particular, viz., la mecànica de Bohm, es discutirà i s’aplicarà un simulador de transport d’electrons per abordar qüestions tant metodològiques com pràctiques relacionades amb la simulació del transport quàntic d’electrons. L’ontologia de la mecànica de Bohmian permet descriure de manera natural sistemes quàntics oberts monitoritzats contínuament amb una descripció precisa dels estats condicionals per als règims markovians i no markovians. Això ajuda a proporcionar un enfocament alternatiu a la matriu densitat en la descripció de sistemes quàntics oberts, que escala exponencialment amb el nombre de graus de llibertat. Tantmateix, l’estratègia d’estats condicionals Bohmians, que ha conduït al desenvolupament del simulador de transport d’electrons BITLLES, es demostrarà en el càlcul dels temps de permanència dels electrons en una barrera de grafè de dos terminals. Es demostrarà que les trajectòries de Bohmian són molt adequades per proporcionar una descripció inequívoca dels temps de trànsit (túnel) i la seva relació amb les freqüències de tall en dispositius electrònics pràctics. Finalment, es discutirà un protocol que incorpora mesures similars als “collective measurements” per eludir la incertesa de mesura en dispositius electrònics de computació clàssica i quàntica.
El trabajo presentado en esta tesis está dedicado a la comprensión de desafíos prácticos y conceptuales en la simulación de propiedades dinámicas más allá de la aproximación cuasiestática en dispositivos cuánticos de estado sólido en escenarios donde es necesario un tratamiento mecánico cuántico completo. Los resultados de esta tesis son particularmente relevantes para el cálculo de las fluctuaciones de la corriente eléctrica en el régimen THz, la evaluación de los tiempos de tunelización que definen la frecuencia de corte de los dispositivos operados por alta frecuencia, o la evaluación del trabajo termodinámico para realizar motores térmicos cuánticos. Las propiedades dinámicas mencionadas anteriormente implican medidas en múltiples tiempos y, por lo tanto, son sensibles a la ""retroacción "" cuántica de la medida. En el contexto de la mecánica cuántica ortodoxa, la definición de estas propiedades dinámicas no puede separarse de la especificación del aparato de medida. Es decir, definir propiedades dinámicas intrínsecas o independientes del aparato de medida es incompatible con los postulados de la mecánica cuántica ortodoxa. Con todo, un ingeniero de dispositivos como yo, que trabaja en problemas prácticos relacionados con los dispositivos de estado sólido presentes y futuros, se ve obligado a profundizar en los fundamentos de la mecánica cuántica. En este sentido, mostraré que las dificultades asociadas a la comprensión de las propiedades dinámicas se pueden resolver mirando más allá de la mecánica cuántica ortodoxa. En particular, he explorado la interpretación modal de la mecánica cuántica, que es una teoría cuántica matemáticamente precisa que reproduce todos los fenómenos de la mecánica cuántica. Mostraré que las propiedades intrínsecas pueden definirse fácilmente en este nuevo contexto (no ortodoxo). Es importante destacar que demostraré también que las propiedades intrínsecas pueden identificarse con la medida de ""weak values"" y que, por lo tanto, ¡pueden medirse! Enfocado en una teoría modal particular, a saber la mecánica de Bohm, se discutirá y aplicará un simulador de transporte de electrones para abordar cuestiones metodológicas y prácticas relacionadas con la simulación del transporte cuántico de electrones. La ontología de la mecánica bohmiana permite describir de manera natural sistemas cuánticos abiertos monitoreados continuamente con una descripción precisa de los estados condicionales para los regímenes Markoviano y no-Markoviano. Esto ayuda a proporcionar un enfoque alternativo al de la matriz de densidad en la descripción de sistemas cuánticos abiertos, que escala exponencialmente con el número de grados de libertad. Por lo tanto, se mostrará que la estrategia de estado condicionales de Bohm, que ha llevado al desarrollo de un simulador de transporte de electrones BITLLES, permite, por ejemplo, calcular los tiempos de permanencia de los electrones en una barrera de grafeno de dos terminales. Se demostrará también que las trayectorias bohmianas son muy apropiadas para proporcionar una descripción inequívoca de los tiempos de tránsito (de tunel) y su relación con las frecuencias de corte en dispositivos electrónicos. Finalmente, se discutirá un protocolo que incorpora mediciones de tipo colectivo para evadir la incertidumbre de medición actual en los dispositivos electrónicos de computación clásica y cuántica.
The work presented in this thesis is dedicated to the understanding of practical and conceptual challenges in simulating dynamical properties beyond the quasi-static approximation, in solid-state quantum devices in scenarios where a full quantum mechanical treatment is necessary. The results of this thesis are particularly relevant for the computation of the fluctuations of the electric current in the THz regime which aids in determining the correlations, the evaluation of tunnelling times that define the cut-off frequency of high-frequency operated devices, or the assessment of thermodynamic work to realize quantum thermal engines.The above mentioned dynamical properties involve multi-time measurements and hence are sensitive to quantum backaction. In the context of Orthodox quantum mechanics, the definition of these dynamical properties cannot be detached from the specification of the measurement apparatus. That is, defining apparatus-independent or intrinsic dynamical properties of quantum systems is incompatible with the postulates of Orthodox quantum mechanics. All in all, a device engineer like me, working on practical problems related with the present and future solid-state devices, is forced to delve into the foundations of quantum mechanics if I really want to properly understand the high-frequency performance of solid-state devices. In this regard, I will show that the difficulties associated to the understanding of dynamical properties can be solved by looking beyond Orthodox quantum mechanics. In particular, I have explored the modal interpretation of quantum mechanics, which is a mathematically precise quantum theory that reproduces all quantum mechanical phenomena. I will show that intrinsic properties can be easily defined in this new (non-orthodox) context. Importantly, I will prove that intrinsic properties can be identified with weak values and hence that they can be measured! Focused on a particular modal theory, viz., Bohmian mechanics, an electron transport simulator will be discussed and applied to address both methodological and practical issues related to the simulation of quantum electron transport. The ontology of Bohmian mechanics naturally enables describing continuously monitored open quantum systems with a precise description of the conditional states for Markovian and non-Markovian regimes. This helps to provide an alternate to density matrix approach in the description of open quantum systems, which scales poorly computationally with the number of degrees of freedom. Thus the Bohmian conditional state strategy, which has led to the development of an electron transport simulator, BITLLES will be shown to compute the dwell times for electrons in a two-terminal graphene barrier. It will be demonstrated that Bohmian trajectories are very appropriate to provide an unambiguous description of transit (tunnelling) times and its relation to the cut-off frequencies in practical electron devices. Finally, a protocol incorporating collective-like measurements to evade the current measurement uncertainty in the classical and quantum computing electron devices will be discussed.

This dissertation research is focused on first principles studies of graphene and single organic molecules for nanoelectronics applications. These nanosized objects attracted considerable interest from the scientific community due to their promise to serve as building blocks of nanoelectronic devices with low power consumption, high stability, rich functionality, scalability, and unique potentials for device integration. Both graphene electronics and molecular electronics pursue the same goal by using two different approaches: top-down approach for graphene devices scaling to smaller and smaller dimensions, and bottom-up approach for single molecule devices. One of the goals of this PhD research is to apply first-principles density functional theory (DFT) to study graphene/metal and molecule/metal contacts at atomic level. In addition, the DFT-based approach allowed us to predict the electronic characteristics of single molecular devices. The ideal and defective graphene/metal interfaces in weak and strong coupling regimes were systematically studied to aid experimentalists in understanding graphene growth. In addition, a theory of resonant charge transport in molecular tunnel junctions has been developed. The first part of this dissertation is devoted to the study of atomic, electronic, electric, and thermal properties of molecular tunnel junctions. After describing the model and justifying the approximations that have been made, the theory of resonant charge transport is introduced to explain the nature of current rectification within a chemically asymmetric molecule. The interaction of the tunneling charges (electrons and holes) with the electron density of the metal electrodes, which in classical physics is described using the notion of an image potential, are taken into account at the quantum-mechanical level within the tight binding formalism. The amount of energy released onto a molecule by tunneling electrons and holes in the form of thermal vibration excitations is related to the reorganization energy of the molecule, which is also responsible for an effective broadening of molecular levels. It was also predicted that due to the asymmetry of electron and hole resonant energy levels with respect to the Fermi energy of the electrodes, the Joule heating released from the metallic electrodes is also non-symmetric and can be used for the experimental determination of the type of charge carriers contributing to the molecular conductance. In the second part of the dissertation research ideal and defective graphene/metal interfaces are studied in weak and strong interface coupling regimes. The theoretical predictions suggest that the interface coupling may be controlled by depositing an extra metallic layer on top of the graphene. DFT calculations were performed to evaluate the stability of a surface nickel carbide, and to study graphene/carbide phase coexistence at initial stages of graphene growth on Ni(111) substrate at low growth temperatures. Point defects in graphene were also investigated by DFT, which showed that the defect formation energy is reduced due to interfacial interactions with the substrate, the effect being more pronounced in chemisorbed graphene on Ni(111) substrate than in physisorbed graphene on Cu(111) substrate. Our findings are correlated with recent experiments that demonstrated the local etching of transfered graphene by metal substrate imperfections. Both graphene and molecular electronics components of the PhD dissertation research were conducted in close collaboration with several experimental groups at the University of South Florida, Brookhaven National Laboratory, University of Chicago, and Arizona State University.

Microfluidics miniaturizes many benchtop processes and provides advantages of low cost, reduced reagent usage, process integration, and faster analyses. Microfluidic devices have been fabricated from a wide variety of materials and methods for many applications. This dissertation describes four such examples, each employing different features and fabrication methods or materials in order to achieve their respective goals. In the first example of microfluidic applications in this dissertation, thermoplastics are hot embossed to form t-shaped channels for microchip electrophoresis. These devices are used to separate six preterm birth (PTB) biomarkers and establish a limit of detection for each. The next chapter describes 3D printed devices with reversed-phase monoliths for solid-phase extraction and on-chip fluorescent labeling of PTB biomarkers. I demonstrate the optimization of the monolith and selective retention of nine PTB biomarkers, the first microchip study to perform an analysis on this entire panel. The third project describes the iterative design and fabrication of glass/polydimethylsiloxane (PDMS) devices with gold and nickel electrodes for the self-assembly of DNA nanotubes for site-selective placement of nanowires. Simple flow channels and “patch electrode” devices were successfully used, and DNA seeding was achieved on gold electrodes. Finally, a 3D printed device for cancer drug screening was developed as a replacement for one previously fabricated in PDMS. Devices of increasing complexity were fabricated, and those tested found to give good control over fluid flow for multiple inlets and valves. Although the applications and methods of these projects are varied, the work in this dissertation demonstrates the potential of microfluidics in several fields, particularly for diagnostics, therapeutics, and nanoelectronics. Furthermore, it demonstrates the importance of applying appropriate tools to each problem to gain specific advantages. Each of the described devices has the potential for increased complexity and integration, which further emphasizes the advantages of miniaturized analyses and the potential for microfluidics for analytical testing in years to come.

The objective of this research is to present a set of powerful simulation, design, and characterization tools suitable for studying novel nanophotonic devices. The simulation tools include a three-dimensional finite-difference time-domain code adapted for parallel computing that allows for a wide range of simulation conditions and material properties to be studied, as well as a semi-analytical Green's function-based complex mode technique for studying loss in photonic crystal waveguides. The design tools consist of multifunctional photonic crystal-based template that has been simulated with nonlinear effects and measured experimentally, and planar slab waveguide structure that provides highly efficient second harmonic generation is a chip-scale device suitable for photonic integrated circuit applications. The characterization tool is composed of a phase-sensitive measurement system using a lock-in amplifier and high-precision optical stages, suitable for probing the optical characteristics of nanoscale devices. The high signal-to-noise ratio and phase shift data provided by the lock-in amplifier allow for accurate transmission measurements as well as a phase spectrum that contains information about the propagation behavior of the device beyond what is provided by the amplitude spectrum alone.

Dielectrics are insulating materials used in many different electronic devices (e.g. capacitors, transistors, barristors), and play an important role in all of them. In fact, the dielectric is probably the most critical element in most devices, as it is exposed to electrical fields that can degrade its performance. In this PhD thesis I have investigated the use of monolayer and multilayer hexagonal boron nitride (h-BN) as dielectric for electronic devices, as it is a 2D material with a band gap of ~5.9 eV. My work has mainly focused on the synthesis of the h-BN using chemical vapor deposition, the study of its intrinsic morphological and electrical properties at the nanoscale, and its performance as dielectric in different electronic devices, such as capacitors and memristors. We observe that monolayer and multilayer h-BN can be growth by CVD on Pt, Cu and Fe substrates. The main parameters affecting the growth of the h-BN are: i) a proper temperature determines the decomposition of the precursor. Lower temperatures will produce remaining particles and more defects in BN layer. ii) The flow rate of precursor/H2 influences the density of seeds. Excessive precursor will give rise to the formation of h-BN multilayer islands. iii) High vacuum and low pressure help to remove impurities in the tube furnace (e.g. oxygen, carbon), and therefore it produces better quality h-BN, i.e. uniform thickness with less defects. h-BN sheets grown on polycrystalline Pt substrates show different thicknesses depending on the crystallographic orientation at the surface of each Pt grain. This produces an undesired fluctuation on the leakage current from one Pt grain to another. However, the leakage current across the h-BN on the same Pt grain is very uniform, much more than that observed across amorphous HfO2 and TiO2 thin films. This phenomenon doesn't take place when growing the h-BN on Cu or Fe substrates. For example, the leakage current across h-BN grown on Cu substrates display small current variability among different Cu grains. The dielectric breakdown behavior in multilayer h-BN shows surface extrusion, similar to what happens in SiO2, HfO2 and Al2O3. However, monolayer h-BN keeps unaltered its structure even for harder breakdown events. The reason may be the extremely high thermal conductivity of monolayer h-BN. Multilayer h-BN shows random telegraph noise signals when applying constant voltage stresses, both at the device level and at the nanoscale. This strongly indicates the trapping and de-trapping of charges during the stress. This observation has been confirmed by the detection of charges at the dielectric breakdown location. The breakdown spot shows a singular ring-like structure that contains fixed negative charges, mobile negative charges, and positive fixed charges. The synthesis of h-BN on polycrystalline Fe substrates required longer cooling down times than when using Pt and Cu substrates. The reason is that the growth of h-BN on Fe substrates mainly takes place by surface precipitation mechanism, while on Pt and Cu substrates the mechanism is by surface-mediated reaction. Memristors with Ag/h-BN/Fe structure show both threshold resistive switching when the set is induced by applying positive voltage to the Ag electrode, and bipolar resistive switching when the set/reset processes are induced by applying negative/positive voltage to the Ag electrode. The reason should be that in threshold mode the filament is formed by Ag+ ions that penetrate in the h-BN stack, while in bipolar mode Fe+ ions penetrate in the h-BN stack. Ag+ ions show higher diffusivity than Fe+ ions and produce volatile switching.
Los dieléctricos son materiales aislantes utilizados en muchos dispositivos electrónicos (por ejemplo condensadores, transistores, baristores), en los que juegan un papel muy importante. En realidad, el dieléctrico es probablemente la parte más crítica en la gran mayoría de dispositivos electrónicos, ya que casi siempre está expuesto a campos eléctricos que pueden degradar sus prestaciones. El dióxido de silicio (SiO2) ha sido el material aislante tradicionalmente utilizado en la industria; sin embargo la miniaturización de los dispositivos requirió una reducción del grosor de los dieléctricos SiO2, lo que provocó un incremento dramático de la corriente de fugas y el fallo del dispositivo entero. Actualmente los dispositivos electrónicos más avanzados utilizan materiales aislantes con una constante dieléctrica alta (por ejemplo HfO2, Al2O3 y TiO2), y así no es necesario reducir tanto su grosor, lo que mantiene una baja corriente de fugas. Sin embargo, estos materiales muestran muchos problemas intrínsecos, y también una mala interacción con materiales adyacentes. Por lo tanto, la carrera para encontrar un material dieléctrico ideal para dispositivos electrónicos sigue abierta. En este contexto, los materiales bidimensionales se han convertido en una seria opción, no sólo por sus excelentes propiedades, sino también gracias al desarrollo de nuevos métodos de síntesis escalables. En esta tesis doctoral he investigado el uso de nitruro de boro hexagonal (h-BN), monocapa y multicapa, como material dieléctrico en dispositivos electrónicos, ya su banda de energías prohibidas es de ~5.9 eV. Mi trabajo se ha focalizado en la síntesis de h-BN mediante el método chemical vapor deposition, el estudio de sus propiedades morfológicas y eléctricas a escala nanométrica, y sus prestaciones como dieléctrico en diferentes dispositivos (condensadores y memristores). Nuestros experimentos indican que h-BN es un material dieléctrico muy fiable, y que es apto para su uso en dispositivos. Sus prestaciones dependen de diferentes parámetros, como el sustrato en el que ha sido crecido, su grosor, y los materiales usados como electrodos adyacentes. Además, h-BN muestra propiedades adicionales nunca observadas en dieléctricos tradicionales, como modulación de la resistividad volátil, lo que podría extender su uso a nuevas aplicaciones.

Розроблення сенсорних пристроїв на вітчизняному та світовому ринках є прогресивним напрямом в подальшому розвитку наноелектроніки. На основі поверхневих хвиль розроблена велика кількість сенсорів з високими показниками точності, що дозволяють вимірювати вагу, тиск, прискорення та ін. До переваг даних пристроїв можна віднести те, що вони створюються на основі елементів інтегральної електроніки, оптики та різноманітних мікроелектронних технологій і при цьому забезпечують контроль декількох фізичних величин. Проте актуальними залишаються питання пошуку нових матеріалів для підкладки та топології її виготовлення.

Le graphène possède un gaz bidimensionnel de porteurs de charge stable et exposé à l'environnement sans aucune protection. Par conséquent, ses performances électriques sont extrêmement sensibles aux conditions environnementales, notamment aux impuretés chargées et aux corrugations imposées par le substrat sous-jacent. Ces éléments ont une contribution majeure dans la dégradation des propriétés de transport électronique du matériau.L'objectif de cette thèse est d'explorer par diverses techniques des méthodes pour atténuer ces effets par optimisation de son environnement direct.La première méthode consiste à reporter le graphènesur une couche neutre d'un cristal de nitrure de bore hexagonal (BN). Diverses techniques de fabrication d'empilement de Graphène sur BN sont présentées, notamment la croissance directe de graphène sur un cristal de BN exfolié sur un substrat catalytique qui aboutit à la formation d'empilements de structure bien contrôlée. Les échantillons sont mesurés à très basse température. Les effets de localisation faible mesurés par magnéto-transport montrent une amélioration nette des performances notamment de la longueur de cohérence et de la mobilité électronique par rapport à un échantillon de référence constitué du même ruban de graphène déposé sur substrat conventionnel de silicium oxydé.La deuxième technique consiste à isoler le graphène de son support par surgravure de la silice et suspension du graphène sous la forme d'une membrane autosupportée et tenue par ses extrémités. Après avoir introduit des techniques de fabrication spécifiques, les mesures de transport et le couplage à des modes de vibration mécanique sont étudiés température variable. Ces données permettent notamment une mesure du coefficient d'expansion thermique du graphène
Charge carriers in graphene form stable two-dimensional gases which are fully exposed to the environment. As a consequence, the electrical performance of graphene is strongly affected by surface charged impurities as well as topographic perturbations inherited from the underlying substrate.This thesis addresses several methods to circumvent that issue.The first method consists in embedding graphene in an optimized environment by depositing graphene onto some neutral and crystalline material. Novel 2D insulating materials such as hexagonal boron nitride buffer layer (BN) appears as ideal substrates to get rid of detrimental effect of interfacial charges and corrugation. Several fabrication schemes of Graphene/BN stacks are shown including some direct in-situ growth of graphene on BN crystal using an innovative proximity-driven chemical vapour growth based on BN exfoliation on copper. In order to explore the effects of the improved substrate on the transport properties of graphene, we have performed low temperature magneto-transport studies on these stacks. We present a direct comparison of weak localization signals with those acquired on a graphene/silica reference device. A clear increase of the coherence length is shown on Graphene/BN stacks together with improved electronic mobility and charge neutrality.Removing the substrate and suspending graphene is another approach for optimization of the graphene environment which forms the second topic covered in this thesis. After introducing an improved recipe for preserving the quality of graphene throughout an elaborate fabrication process, we probe the room- and low-temperature performance of the nano-electro-mechanical devices based on doubly clamped suspended graphene ribbons. The obtained data are used for characterizing the thermal expansion of CVD graphene

We present the development of a novel, UHV-compatible device fabrication strategy for the realisation of nano- and atomic-scale devices in silicon by harnessing the atomic-resolution capability of a scanning tunnelling microscope (STM). We develop etched registration markers in the silicon substrate in combination with a custom-designed STM/ molecular beam epitaxy system (MBE) to solve one of the key problems in STM device fabrication ??? connecting devices, fabricated in UHV, to the outside world. Using hydrogen-based STM lithography in combination with phosphine, as a dopant source, and silicon MBE, we then go on to fabricate several planar Si:P devices on one chip, including control devices that demonstrate the efficiency of each stage of the fabrication process. We demonstrate that we can perform four terminal magnetoconductance measurements at cryogenic temperatures after ex-situ alignment of metal contacts to the buried device. Using this process, we demonstrate the lateral confinement of P dopants in a delta-doped plane to a line of width 90nm; and observe the cross-over from 2D to 1D magnetotransport. These measurements enable us to extract the wire width which is in excellent agreement with STM images of the patterned wire. We then create STM-patterned Si:P wires with widths from 90nm to 8nm that show ohmic conduction and low resistivities of 1 to 20 micro Ohm-cm respectively ??? some of the highest conductivity wires reported in silicon. We study the dominant scattering mechanisms in the wires and find that temperature-dependent magnetoconductance can be described by a combination of both 1D weak localisation and 1D electron-electron interaction theories with a potential crossover to strong localisation at lower temperatures. We present results from STM-patterned tunnel junctions with gap sizes of 50nm and 17nm exhibiting clean, non-linear characteristics. We also present preliminary conductance results from a 70nm long and 90nm wide dot between source-drain leads which show evidence of Coulomb blockade behaviour. The thesis demonstrates the viability of using STM lithography to make devices in silicon down to atomic-scale dimensions. In particular, we show the enormous potential of this technology to directly correlate images of the doped regions with ex-situ electrical device characteristics.

La miniaturisation croissante des transistors MOS a rendu les mémoires RAM de plus en plus sensibles aux particules alpha émises par les éléments radioactifs naturellement présents dans les matériaux utilisés dans la fabrication de ces mémoires. En effet, au niveau du sol, le taux d'erreurs logiques déclenchées par ces particules est comparable à celui déclenché par les neutrons issus du rayonnement cosmique. L'objectif principal de ce travail de thèse est la mise au point de méthodes d'évaluation de ce taux et permettre par la suite de proposer des solutions technologiques. Ainsi, dans le cadre d'une approche théorique, nous avons développé des modèles permettant d'évaluer le taux des erreurs logiques déclenchées par les chaines de l'uranium et du thorium dans un état d'équilibre séculaire mais aussi de déséquilibre. Ceci passe par une identification des radioéléments critiques, c'est-à-dire ceux qui sont capables d'augmenter l'émissivité (et ainsi le taux d'erreurs d'aléas logiques) à des niveaux inacceptables pendant la durée de vie du composant. La prise en compte de l'état de déséquilibre des chaines de désintégration radioactive dans ce volet théorique permet une approche réaliste de la contamination. Nous avons également proposé une méthode expérimentale pour analyser l'évolution de l'état radioactif dans les matériaux utilisés dans la fabrication des mémoires. Dans cette approche expérimentale, nous avons combiné trois techniques de mesure complémentaires: la spectroscopie alpha, la spectroscopie gamma et l'ICPMS
The increasing miniaturisation of MOS transistors has made RAM memories more and more sensitive to alpha particles emitted by radioactive elements naturally present in the materials used for memory fabrication. Indeed, at ground level, the soft error rate triggered by these particles is comparable to that triggered by neutrons from cosmic rays. The main purpose of this work aims to develop methods to evaluate this rate allowing thereafter suggesting technologies mitigations. Thus, in the context of a theoretical approach, we have developed models to estimate soft errors rate triggered by uranium and thorium chains in secular equilibrium but also disequilibrium state. This requires identification of critical radionuclides those are able to increase the emissivity (and thus the soft error rate) to unacceptable levels during device lifetime. Taking into account disequilibrium state of decay chains in theoretical study provides a realistic approach to the contamination. We have also proposed an experimental method to analyze the radioactive state evolution in materials used for memory fabrication. In this experimental approach, we have combined three complementary measurement techniques: alpha spectroscopy, gamma spectroscopy and ICPMS

Zinc oxide (ZnO) is perhaps one of the most widely studied material in the last two decades. It has received so much of attention because of its incredible potential for wide ranging applications. ZnO is a wide band gap semiconductor (Eg = 3.37 eV at 300 K) with a rather large excitonic binding energy (~60 meV). This combination of properties makes it an ideal choice for several optoelectronic devices that can easily work at room temperature. ZnO is a truly multifunctional material possessing several desirable electrical, optical, optoelectronic, and piezoelectric properties. In addition, it is highly amenable to production of various kinds of nanostructures such as nanorods, nanotubes, nanoribbons, nanoneedles, etc., which makes it even more desirable for nanoscale devices. Examples of ZnO based nanodevices could include photodiodes, photodetectors, nano-lasers, field-emission devices and memristors. In order to make such devices, one could need device quality nanostructures that must be reproducible and cost effective. Naturally, one has to look for a synthesis process that has great controls and is relatively inexpensive. The study provided here shows that among the various methods available for ZnO synthesis, the microwave-assisted chemical synthesis offers outstanding advantages in terms of rapid growth of nanostructures, economical use of energy and excellent controls of process parameters. In order to produce device quality ZnO nanostructures using microwave-assisted synthesis, one has to study the effect of various process parameters and optimise them for the desired growth. Therefore, in the current study, first, a systematic study was undertaken to synthesize ZnO nanostructures both in a aqueous and non-aqueous medium and their characterization was carried out in order to understand the effect of microwave power, time of irradiation, pressure, solvent and salt concentration, etc. The goal was to develop synthesis protocols for various kinds of nanostructures that could guarantee reproducibility, good yield, and device quality structures. This study has led to successful growth of ZnO nanostructures on various substrates, vertically aligned ZnO nanorods and templated arrays of desired structures, all with outstanding properties of the structures as confirmed by XRD, MicroRaman, photoluminescence, cathodoluminescence, FESEM, TEM, PFM studies and pole figure analysis. Piezoelectric force microscopy (PFM) and physical property measurement system (PPMS, Quantum Design), have been used to study the multifunctional properties of ZnO nanostructures. The PFM is a powerful technique to measure the local piezoelectric coefficient of nanostructures and nanoscale thin films. PFM works on the converse piezoelectric effect in which electric potential is applied and mechanical strain is measured using a cantilever deflection. The PFM (Brucker’s AFM dimension Scan Assist) was used to characterize individual ZnO nanorods. Extensive studies were carried out with PFM measurements and it was observed that the nanorods consistently showed high piezoelectric coupling coefficients (d33~50-154 pm/V). It was also found that the variation in d33 depended on morphology and size of nanostructure. The multifunctional properties were observed in small ZnO nanocrystals (NCs). Such high values of piezoelectric coupling coefficients open the door for novel ZnO based nanoscale sensors and actuators. The synthesized ZnO nanostructures were further optimized and characterized keeping in view three device applications namely Field emission, Memristors and Gas Sensors. The fabrication and characterization of these three devices with ZnO nanostructure was carried out using electron beam lithography and direct laser writing micromachining. Device fabrication using lithography involved several steps such as substrate cleaning, photoresist spin coating, pre-baking, post-baking, pattern writing, developing, sputtering/deposition of material for lift-off, ZnO growth, and overlay lithography. For field emission devices, high quality, well aligned, c-axis oriented ZnO nano-needles were grown on sputter coated Ti/Pt (20nm/100nm) on SiO2/Si substrate by rapid microwave-assisted method in aqueous medium. The diameter of the tip was found to be 1~2 nm and the length of the rod was approximately 3~5μm. For a particular batch the tip size, morphology, and lengths were found to be the same and highly repeatable. Pole figure analysis revealed that nanorods were highly oriented towards <002> direction. Field-emission measurements using the ZnO nanoneedles arrays as cathode showed very low turn-on electric field of 0.9 V/μm and a very high field enhancement factor ~ 20200. Such a high emission current density, low turn-on electric field, and high field enhancement factor are attributed to the high aspect ratio, narrow tip size, high quality and single crystallinity of the nanoneedles. The high emission current density, high stability, low threshold electric field (0.95 V/μm) and low turn-on field make the ZnO nanoneedle arrays one of the ideal candidates for field-emission displays and field emission sensors. In the suitability of ZnO nanostructures for memristor application it was found that the single crystalline ZnO nanorods were not suitable as they did not show memristive behaviour but the ZnO nanorods with native defects exhibited considerable memristive behaviour. Therefore the microwave-assisted grown ZnO nanorods with defects were used to fabricate memristive devices. Single and multiple ZnO nanorods based memristors were fabricated using electron beam lithography. These devices were characterized electrically by measuring the hysteresis in the I/V characteristics. A high degree of repeatability has been established in terms of growth, device fabrication, and measurements. The switching in single nanorod based devices was found to have “ON-to- OFF” resistance ratio of approximately 104 and current switching ratio (ION/IOFF) of 106. Gas sensing based on electrical resistance change depends on absorption and desorption rate of gases on the analyte which is governed by surface properties, morphologies and activation energy. Therefore, various morphologies of nanostructure were grown for gas sensing application. Through experimentation, the emphasis shifted to c-axis oriented ZnO nanostructures on SiO2 substrate for gas sensing. The c-axis orientation of ZnO nanostructures was preferred mainly due to its huge surface area. The measurements showed that the c-axis oriented ZnO nanorods were excellent hydrogen sensors, able to detect H2 as low concentration as 2 ppm, even when the sensing temperature is as low as 200 ˚C. However, oxygen sensing was achieved at a higher temperature (300 ˚C). Thus, the study undertaken in this thesis presents a microwave based rapid and economical method for synthesizing high quality, device grade ZnO nanostructures, their extensive characterization that shows the multifunctional properties of these structures, and there examples of varied device applications of the synthesized nanostructures as field emitters, memristors, and gas sensors.

This thesis introduces functional nanomaterials including superatoms and carbon nanotubes (CNTs) for new layered solids and molecular devices. Chapters 1-3 present how we incorporate superatoms into two-dimensional (2D) materials. Chapter 1 describes a new and simple approach to dope transition metal dichalcogenides (TMDCs) using the superatom Co6Se8(PEt3)6 as the electron dopant. Doping is an effective method to modulate the electrical properties of materials, and we demonstrate an electron-rich cluster can be used as a tunable and controllable surface dopant for semiconducting TMDCs via charge transfer. As a demonstration of the concept, we make a p-n junction by patterning on specific areas of TMDC films. Chapter 2 and Chapter 3 introduce new 2D materials by molecular design of superatoms. Traditional atomic van der Waals materials such as graphene, hexagonal boron-nitride, and TMDCs have received widespread attention due to the wealth of unusual physical and chemical behaviors that arise when charges, spins, and vibrations are confined to a plane. Though not as widespread as their atomic counterparts, molecule-based layered solids offer significant benefits; their structural flexibility will enable the development of materials with tunable properties. Chapter 2 describes a layered van der Waals solid self-assembled from a structure-directing building block and C60 fullerene. The resulting crystalline solid contains a corrugated monolayer of neutral fullerenes and can be mechanically exfoliated. Chapter 3 describes a new method to functionalize electroactive superatoms with groups that can direct their assembly into covalent and non-covalent multi-dimensional frameworks. We synthesized Co6Se8[PEt2(4-C6H4COOH)]6 and found that it forms two types of crystalline assemblies with Zn(NO3)2, one is a three-dimensional solid and the other consists of stacked layers of two-dimensional sheets. The dimensionality is controlled by subtle changes in reaction conditions. CNT-based field-effect transistor (FETs), in which a single molecule spans an oxidatively cut gap in the CNT, provide a versatile, ground-state platform with well-defined electrical contacts. For statistical studies of a variety of small molecule bridges, Chapter 4 presents a novel fabrication method to produce hundreds of FETs on one single carbon nanotube. A large number of devices allows us to study the stability and uniformity of CNT FET properties. Moreover, the new platform also enables a quantitative analysis of molecular devices. In particular, we used CNT FETs for studying DNA-mediated charge transport. DNA conductance was measured by connecting DNA molecules of varying lengths to lithographically cut CNT FETs.

碩士
國立成功大學
物理學系碩博士班
100
In this thesis, a transient quantum transport theory incorporated with initial correlations is developed to study the transport dynamic in nanoelectronic system. It extends the quantum transport theory based on the Feynman-Vernon influence functional approach and the Keldysh nonequilibirum Green function technique to an arbitrary initial state. The nanoelectronic devices concerned in this thesis consist of the central island coupled to the source and the drain. The time-convolutionless exact master equation which incorporates with the correlations is also derived, where the back-reactions between the island and the reservoirs are fully taken into account. By using the quantum dot system coupled to two leads as an example, the transport dynamics incorporated with initial correlations is discussed. Moreover, The fluctuating current-current correlations and the noise spectrum are obtained to understand the intrinsic characteristic and structure of the nanoelectronic devices. At last, the transient quantum transport is applied to study the time-dependent transport phenomena such as the photon-assisted transport and single-electron pumpings and turnstile operations in nanoelectronic devices.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.
Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7560. Adviser: John Tucker. Includes bibliographical references (leaves 118-128) Available on microfilm from Pro Quest Information and Learning.

As optical interconnects make their paces to replace traditional electrical interconnects, implementing low cost optical components and hybrid optic-electronic systems are of great interest. In the research work described in this dissertation, we are making our efforts to develop several practical optical components using novel printing technologies including imprinting, ink-jet printing and a combination of both. Imprinting process using low cost electroplating mold is investigated and applied to the waveguide molding process, and it greatly reduces the surface roughness and thus the optical propagation loss. The imprinting process can be applied to photonic components from multi-mode waveguides with 50[mu]m critical dimension down to photonic crystal structures with 500nm hole diameter. Compared to traditional lithography process, imprinting process is featured by its great repeatability and high yield to define patterns on existing layers. Furthermore we still need an approach to deposit layers and that is the reason we integrate the ink-jet printing technology, another low-cost, low material consumption, environmental friendly process. Ink-jet printing process is capable of depositing a wide range of materials, including conductive layer, dielectric layer or other functional layers with defined patterns. Together with molding technology, we demonstrate three applications: proximity coupler, thermo-optic (TO) switch and electro-optic (EO) polymer modulator. The proximity coupler uses imprinted 50[mu]m waveguide with embedded mirrors and ink-jet printed micro-lenses to improve the board-to-board optical interconnects quality. The TO switch and EO modulator both utilize imprinting technology to define a core pattern in the cladding layer. Ink-jet printing is used to deposit the core layer for TO switch and the electrode layers for EO modulator. The fabricated TO switch operates at 1 kHz with less than 0.5ms switching time and the EO modulator shows V[pi][middle dot]L=5.68V[middle dot]cm. To the best of our knowledge, these are the first demonstrations of functional optical switches and modulators using printing method. To further enable the high rate fabrication of ink-jet printed photonic and electronic devices with multiple layers on flexible substrate, we develop a roll-to-roll ink-jet printing system, from hardware integration to software implementation. Machine vision aided real time automatic registration is achieved when printing multiple layers.
text

Graphene's superlative electrical and mechanical properties, combined with its compatibility with existing planar silicon-based technology, make it an attractive platform for novel nanoelectronic devices. The development of two such devices is reported—a nonvolatile memory element exploiting the nanoscale graphene edge and a field-effect transistor using graphene for both the conducting channel and, in oxidized form, the gate dielectric. These experiments were enabled by custom software written to fully utilize both instrument-based and computer-based data acquisition hardware and provide a simple measurement automation system.

Graphene break junctions were studied and found to exhibit switching behavior in response to an electric field. This switching allows the devices to act as nonvolatile memory elements which have demonstrated thousands of writing cycles and long retention times. A model for device operation is proposed based on the formation and breaking of carbon-atom chains that bridge the junctions. Information storage was demonstrated using the concept of rank coding, in which information is stored in the relative conductance of multiple graphene switches in a memory cell.

The high mobility and two dimensional nature of graphene make it an attractive material for field-effect transistors. Another ultrathin layered material—graphene's insulating analogue, graphite oxide—was studied as an alternative to bulk gate dielectric materials such as Al₂O₃ or HfO₂. Transistors were fabricated comprising single or bilayer graphene channels, graphite oxide gate insulators, and metal top-gates. Electron transport measurements reveal minimal leakage through the graphite oxide at room temperature. Its breakdown electric field was found to be comparable to SiO₂, typically 1–3 × 10⁸ V/m, while its dielectric constant is slightly higher, κ ≈ 4.3.

As nanoelectronics experiments and their associated instrumentation continue to grow in complexity the need for powerful data acquisition software has only increased. This role has traditionally been filled by semiconductor parameter analyzers or desktop computers running LabVIEW. Mezurit 2 represents a hybrid approach, providing basic virtual instruments which can be controlled in concert through a comprehensive scripting interface. Each virtual instrument's model of operation is described and an architectural overview is provided.

Single-walled carbon nanotubes (SWNTs), with their superior combination of electrical and mechanical properties, have drawn attention from many researchers for potential applications in electronics. Many SWNT-based electronic device prototypes have been developed including transistors, interconnects and flexible electronics. In this thesis, a fabrication method for patterned SWNT networks and devices based on colloidal lithography is presented. Patterned SWNT networks are for the first time formed via solution deposition on a heterogeneous surface. This method demonstrates a simple and straight-forward way to fabricate SWNT networks in a controllable manner. Colloidal sphere monolayers were obtained by drop-casting from solution onto clean substrates. The colloidal monolayer was utilized as a mask for the fabrication of patterned SWNT networks. SWNT networks were shown to be patterned either by depositing SWNT solutions on top of a colloidal monolayer or by depositing a mixed SWNT-colloidal sphere aqueous suspension on the substrates. Colloidal monolayers were examined by optical microscopy and it was found that the monolayer quality can be affected by the concentration of colloids in solution. Polystyrene colloidal solution with concentration of 0.02 wt% ~ 0.04 wt % was found optimal for maximum coverage of colloidal monolayers on SiO2 substrates. After removing the colloidal spheres, the topology of the patterned SWNT networks was characterized by atomic force microscopy and scanning electron v microscopy. Two-dimensional ordered arrays of SWNT rings and SWNTs interconnecting the SWNT rings were observed in the resulting network structure. The height of the rings was about 4-10 nm and the diameter was about 400 nm. In some samples, mesh-like patterned SWNT networks are also observed. It is hypothesized that the capillary forces induced by Van der Waals interaction at liquid/air/solid interfaces play an important role during the formation of the patterned SWNT networks. Raman spectroscopy was also employed to identify the chirality and diameter of the SWNTs in the networks. Both metallic and semiconducting SWNTs were found in the networks and the diameter of the SWNTs was about 1 to 2 nm. The electrical properties of SWNT networks, including random SWNT networks, partially patterned SWNT networks and fully patterned SWNT networks were characterized by a probe station and a Keithley 4200 semiconductor measurement system. The random SWNT networks had two-terminal resistance varying between several MΩ to several hundred MΩ. Field effect behavior was observed in some devices with relatively high resistance and nonlinear I-V curves. Those devices had on/off ratio of less than 100. There was significant leakage current in the ―off‖ state likely due to metallic tube pathways in the networks. The partially patterned SWNT networks had resistance that varied from 20 KΩ to 10 MΩ, but did not display field effect behavior in our studies. The resistance of the patterned SWNT networks was about 10 MΩ - 100 MΩ. The electrical characteristics of the patterned SWNT networks as thin film transistors were investigated, and the on/off ratio of the devices varied from 3 to 105. The upper limit of mobility in the devices was about ~ 0.71 – 5 cm2/V·s. The subthreshold slope of patterned SWNT network FETs can be as low as 210 meV/dec.
Graduate
0544

In the field of spintronics there is a strong need for an efficient spin-polarizing device. To that end, two basic devices are proposed: a series of Aharonov-Bohm (AB) rings linked in series with intermediate quantum dots (IQD) and the quantum dot spin polarizer (QDSP). In each case the system is built of quantum dots (QD), each of which can be Zeeman split with a tunable external magnetic field. Spin neutral input and output leads are also attached to each system. The Tight Binding Approximation (TBA) is used to model each system. Mathematica is used to solve the systems generated by TBA, so that the transmission or reflection of a system can be evaluated. We find that a series of AB rings provides for wide, energetically separated, spin polarized conduction bands. The QDSP provides physical separation of spin polarized electrons, making a spin polarized base current possible.
Methods of analysis -- The Aharonov-Bohm ring -- The quantum dot spin-polarizer.
Department of Physics and Astronomy

Thesis (M. Sc.)--University of Alberta, 2009.
Title from pdf file main screen (viewed on Sept 22, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science, Department of Electrical and Computer Engineering, University of Alberta." Includes bibliographical references.