Dissertations / Theses on the topic 'Vacancy Engineering'
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1
Cui, Shanying. "Near-surface Nitrogen Vacancy Centers in Diamond." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13064815.
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The nitrogen-vacancy (NV) center is a point defect in diamond and has been championed as a promising solid-state "artificial atom." NV center properties such as its bright luminescence, room-temperature optical readout of spin states, and long spin decoherence lifetime make it an excellent system for applications in quantum information processing, high sensitivity magnetometry, and biotagging. In all applications, near-surface NVs are desirable. However, it has been found that the favorable properties of the NV center are significantly diminished as the NV center nears the surface.
This dissertation presents efforts in understanding the effect of the surface on the luminescence of NV centers less than a wavelength of light from the surface. We use plasma assisted etching to, independently, change the surface termination and bring the NV closer to the surface. We find that treating the surface with CF4 plasma results in a deposited polymerous fluorocarbon which helps stabilize nearby NVs. We propose using a downstream etcher to bring NVs closer to the surface, while minimizing damage and maintaining NV luminescence. Finally, we enhance emission of these near-surface NVs by coupling them into a hybrid diamond plasmonic cavity. The fabricated devices result in a measured Q of 170, higher than other previously fabricated diamond plasmonic devices.Engineering and Applied Sciences
2
Smith, Andy. "The formation of ultra-shallow p-type junctions using vacancy engineering." Thesis, University of Surrey, 2006. http://epubs.surrey.ac.uk/843072/.
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For the last 40 years a natural demand for faster, more complex, and therefore, more functional electronic systems, has been the fundamental driving force behind the miniaturisation of the complementary metal oxide semiconductor transistor. The formation of highly conducting, ultra-shallow, p-type junctions is a key component for the source/drain contact and extension regions of the p-channel metal oxide semiconductor transistor. However, the requirements are becoming increasingly more difficult to achieve as technology advances. In fact, new ways of achieving device improvements are being considered. One method currently being implemented within industry is a switch from bulk silicon substrates to silicon on insulator (SOI). Therefore, it is important for any new techniques to be SOI compatible. The most commonly used p-type dopant, boron, suffers from process related phenomena which hinders the creation of such shallow junctions. During annealing interstitial defects remaining from the implantation process impede the junction formation through a defect-dopant interaction, which reduces the electrical activation and enhances the junction depth - the exact opposite to what is required! This thesis studies a technique which generates an excess of vacancy defects (a vacancy is essentially a missing silicon atom). The vacancies counteract the effect via an interstitial-vacancy recombination mechanism, thus reducing their detrimental effect on the subsequent boron implant. A detailed investigation into the optimisation of such a technique has been achieved through Monte Carlo simulations and experimental studies on diffusion, electrical activation and lattice damage in bulk silicon and SOI. It has been shown that it is possible to optimise the boron and vacancy generating implants to achieve a near "diffusionless" process, producing a junction depth of around 17nm, with an extremely high level of electrical activation (~5x1020cm-3) at low annealing temperatures. Furthermore, the junction is extremely thermally stable (600-900°C) giving rise to a large process window for ease of integration. Overall, this optimised technique rivals competing processes with a much lower equipment cost and "footprint" making it potentially a highly viable alternative to the current preferred methodology within industry.
3
Teale, Carson (Carson Arthur). "Magnetometry with ensembles of nitrogen vacancy centers in bulk diamond." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/103852.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-57).
This thesis summarizes experiments conducted to develop a high sensitivity vector magnetometer using nitrogen vacancy (NV) centers in a bulk diamond sample. This project began by analyzing the sensitivity of a single NV orientation using a continuous wave electron spin resonance approach. A protocol for determining the diamond's orientation was developed to map vector magnetic field readings in the diamond reference frame to the lab frame. Preliminary vector field measurements and differential vector measurements were performed. Although these showed promising results, significant instrument and ambient magnetic noise limited the achievable sensitivity. A new frequency locking measurement technique was developed to allow for simultaneous measurements between two separate sensors for future differential experiments. This technique provides a host of other benefits including much improved dynamic range and steady-state immunity to fluctuations in linewidth and contrast.
by Carson Teale.
S.M.
4
Alsid, Scott T. "Optimizing chemical-vapor-deposition diamond for nitrogen-vacancy center ensemble magnetometry." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112367.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 119-125).
The nitrogen-vacancy (NV) center in diamond has emerged as a promising platform for high-sensitivity, vector magnetic field detection and high spatial resolution magnetic-field imaging due to its unique combination of optical and spin properties. NV diamond magnetometry has enabled a wide array of applications from the noninvasive measurement of a single neuron action potential to the mapping [mu]T-fields in [mu]m-size meteorite grains. To further improve the magnetic sensitivity of an ensemble NV magnetometer, the growth and processing of the host diamond must be taken into account. This thesis presents a systematic study of the effects of diamond processing on bulk chemical-vapor-deposition diamond. In particular, NV charge-state composition and spin decoherence times are measured for diamonds irradiated with 1 MeV electrons at doses of 1x1015-5x1019 e-/cm2 and thermally annealed at temperatures of 850°C and 1250°C. The study provides an optimal range for diamond processing and shows the quenching of the NV center at high irradiation dosage from the creation of additional vacancy-related defects.
by Scott T. Alsid.
S.M.
5
Eisenach, Erik Roger. "Tunable and broadband loop gap resonator for nitrogen vacancy centers in diamond." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118052.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-68).
Nitrogen vacancy centers in diamond have emerged as a solid-state analog to atomic systems with applications ranging from room temperature quantum computing to quantum sensing and metrology. To date, with notably few exceptions, all NV applications rely on coherent manipulation of spin states via resonant microwave driving. In this thesis the loop gap resonator (LGR) is presented as a mechanism for the delivery of resonantly enhanced and uniform microwave fields to large volume samples of nitrogen vacancy (NV) centers in diamond. Specifically, an S-band tunable LGR and its constituent excitation circuitry are designed and fabricated to enable directionally uniform, strong, homogeneous, and broadband microwave (MW) driving of an NV ensemble over an area larger than 32 mm2 . The LGR design, based on the anode block of a cavity magnetron, demonstrates an average field amplitude of 5 gauss at 42 dBm of input power, and achieves a peak-to-peak field uniformity of 89.5% over an area of 32 mm2 and 97% over an area of 11 mm2 . The broad bandwidth of the LGR is capable of addressing all resonances of an NV ensemble for bias magnetic Fields up to 14 gauss. Furthermore, with cavity ring-down-times in the single nanoseconds, the resonator is compatible with the pulsed MW techniques necessary for a wide range of NV-diamond applications.
by Erik Roger Eisenach.
S.M.
6
Bandyopadhyay, Saumil. "Frequency down-conversion for quantum networking with nitrogen-vacancy centers in diamond." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119544.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 49-54).
Quantum frequency conversion (QFC) devices are critical to building long-distance quantum networks, which would connect quantum memories located at distant nodes through optical channels for efficient entanglement distribution. The nitrogen-vacancy (NV) center in diamond is an attractive candidate for these memories because of its long coherence time and the ability to optically write to and read out information from its spin. However, the NV-center fluoresces in the visible range, which experiences strong losses (8 dB/km) in optical fiber and has limited the current distance record for entanglement between two NVs to 1.3 km. Using difference frequency generation, we demonstrate a free-space quantum frequency conversion system that could be used to convert photons emitted by the NV to 1080 nm. This thesis reports the building and characterization of the system, which demonstrates exceptionally high signal-to-noise ratio (SNR). While not as optimal as conversion to the telecom C-band, losses at 1080 nm are significantly lower (<2 dB/km), and along with the system's high SNR, should enable much longer distance entanglement experiments than previously achieved.
by Saumil Bandyopadhyay.
M. Eng.
7
Holmström, Alexander. "Counting Cars and Determining the Vacancy of a Parking Lotusing Neural Networks." Thesis, Umeå universitet, Institutionen för datavetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-149689.
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A lot of time, energy and money is being wasted when people are trying tond a parking lot. These elements could be reduced if the driver is provided vacancy information of a parking lot beforehand. In this thesis Google's Object Detection API is implemented and two pre-trained models are being used on the PKLot dataset to detect and count the number of cars in a parking lot. The models are based on a Region-based Convolutional Neural Network (R-CNN) which is explained in more detail. The models are compared with each other and its result presented. The result is presented with three factors in focus, the number of predictions made by the models, the number of cars a model missed to predict and how many objects that were wrongfully predicted. This was then tested on a Raspberry PI with the purpose to avoid using a remote computer for the image processing and prevent potential laws regarding camera surveillance. Finally, we determine if this functionality can actually be delivered using state-of-the-art technology.
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Lopez, Nicolas A. "All-optical method of nanoscale magnetometry for ensembles of nitrogen-vacancy defects in diamond." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/103712.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-65).
The Nitrogen-Vacancy (NV) defect in diamond has shown considerable promise in the field of small scale magnetometry due to its high localization and retention of favorable optical properties at ambient conditions. Current methods of magnetometry with the NV center achieve high sensitivity to fields aligned with the defect axis; however, with most present methods transverse fields are not directly measurable. The all-optical method of NV magnetometry provides a means to detect transverse fields by monitoring changes in the overall fluorescence profile. In this work the all-optical method is extended to ensembles of non-interacting NV centers. By establishing an external bias field aligned with the (1, 1, 1) axis, the magnitude of an unknown transverse field can be unambiguously identified through the measurement of the signal curvature. The angular orientation can be determined up to a two-fold degeneracy by observing the change in signal curvature produced when the bias field is shifted off-axis. The magnetometry method explored in this thesis thus provides good sensitivity to transverse fields, while reducing to a minimum the experimental apparatus required to operate the magnetometer.
by Nicolas A. Lopez.
S.B.
9
Oliveira, Felipe de [Verfasser], and Jörg [Akademischer Betreuer] Wrachtrup. "Forefront engineering of nitrogen-vacancy centers in diamond for quantum technologies / Felipe de Oliveira ; Betreuer: Jörg Wrachtrup." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1147381496/34.
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Sakakibara, Reyu. "Electrochemical modulation of fluorescence of nitrogen vacancy centers in nanodiamonds for voltage sensing applications." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97766.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 105-112).
The nitrogen vacancy (NV) color center in diamond has been used to sense environmental variables such as temperature and electric and magnetic fields. Most sensing protocols depend on the optically detectable magnetic resonance of the negatively charged NV- spin state. As such, fluctuations in the NV charge state present a challenge for NV- spin-based sensing. This thesis discusses the electrochemical modulation of NV charge state and fluorescence as the basis for an alternative sensing scheme. An externally applied electrochemical potential shifts the occupation probabilities of the NV in each charge state, which manifest as changes in NV fluorescence intensity and emission spectra. In this thesis, the voltage dependence of fluorescence in high pressure high temperature nanodiamonds is demonstrated in an electrochemical cell. Following this, the mechanisms for NV response to externally applied electrical bias are investigated in other electrochemical cell morphologies, capacitors, and interdigitated electrode arrays. Finally, a design of an optical microscope setup for future studies of NV sensing in nanodiamond is outlined.
by Reyu Sakakibara.
S.M.
11
Chen, Edward H. (Edward Hong). "Coherent control of nitrogen-vacancy centers in diamond nanostructures for quantum sensing and networking." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107324.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 99-123).
The exceptional optical and spin properties of the negatively charged nitrogen-vacancy (NV-) center in diamond have led to numerous applications ranging from super-resolution imaging to the exploration of previously untested new phenomena using quantum entanglement for information processing and sensing. The solid-state environment of the diamond allows us to engineer nanostructures, which are promising for enhancing the optical and spin properties of the NV-. To help develop a component needed for a diamond-based quantum network, we recently achieved coherent electron spin control of long-lived NV-s in diamond nanostructures using a transferrable hard-mask for both etching and ion implantation. We also developed a super-resolution imaging technique for characterizing such systems, and we furthermore demonstrate high-sensitivity electrometry using a large number of NV-s. However, it remains an open area of investigation whether certain nano-fabrication processes for patterning nanostructures into diamond cause irrecoverable damage or introduce atomic impurities to the crystal that would lead to a significant degradation of the NV- properties. Another remaining challenge is to produce fault-tolerant multi-qubit registers within nanostructures for improved robustness and scalability for use in compact quantum sensors or quantum networks. By building on the results in this thesis, it may be possible to design nanostructures for enhancing initialization, control and read-out fidelities of defect-based solid-state quantum technologies.
by Edward H. Chen.
Ph. D.
12
Anubhav, Sinha Anubhav M. Eng Massachusetts Institute of Technology. "Development of a platform for sensing cellular electrical activity using nitrogen vacancy centers in nanodiamonds." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/106445.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 69-77).
The nitrogen vacancy center (NV) in diamond hosts unique optical properties that allows it to be used for sensing magnetic fields, electric fields, and temperature. In addition, the photostability of the NV center and the biocompatibility of diamond suggests the utility of the NV center for biosensing. The dependence of the charge state of the NV center on the local electrochemical environment suggests that the NV center could be used as an optical sensor for electrophysiology. In this thesis, a platform to evaluate the utility of the NV center for voltage sensing is established. First, an electrophysiology setup is built and characterized on HEK293 cells. The setup adds functionality to a home built microscope so that cells can be electrically controlled while simultaneously observing the fluorescence. Second, the staining of neurons with hydrogen-terminated nanodiamonds (NDs) with NV centers is improved. Together, the improved staining of neurons with nanodiamonds along with using the electrophysiology setup to observe modulation forms a platform for future study of the NV center as a voltage sensor.
by Anubhav Sinha.
M. Eng.
13
Foy, Christopher Ph D. (Christopher C. ). Massachusetts Institute of Technology. "Wide-field magnetic field imaging with nitrogen vacancy centers in nanodiamonds at high frame-rates." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103750.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 83-88).
The nitrogen vacancy center (NV) is a promising single spin system in diamond with optical polarization, readout and optically detected magnetic resonances (ODMR). The NV has been shown to be a sensitive magnetometer at room temperature. In particular, owing to their small size, NV centers in nanocrystals (nanodiamonds) offer magnetic field imaging with high spatial resolution. Competitive magnetic field imaging methods such as magnetic force microscopy (MFM) or superconducting quantum interference devices (SQUID) either image serially, and are thus slow, or are limited in their use for biological systems. Nanodiamonds in contrast have the advantage that they can be attached to biological tissues in vivo and can be imaged in parallel at high speeds. Unfortunately, nanodiamonds tend to aggregate due to Coulomb interactions of their surface species. This aggregation results in a inhomogeneous broadening of the NV's ODMR with applied magnetic field. This broadening makes imaging magnetic fields non-trivial. In this work, we present a model to understand aggregated nanodiamonds. Despite NVs with defined crystallographic orientations demonstrating vectorial resolution of magnetic fields, this model predicts that aggregated nanodiamonds should be treated as absolute magnetometers. Further, a sparse sampling protocol is implemented that enables time resolved magnetometry and is used to image the magnetic field of a current carrying wire at greater than 33 Hz speeds with magnetic field sensitivities better than ... over a 10 [mu]m x 10 [mu]m field of view.
by Christopher Foy.
S.M.
14
Abraham, Isaac P. "Logistic Function based Nonlinear Modeling and Circuit Analysis of the Bipolar Vacancy Migration Memristor." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1587033379577733.
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Goswami, Kamal Nayan. "Ab initio study of the effect of solute atoms on vacancy diffusion in Ni-based superalloys." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8509/.
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Single crystal Ni-based superalloys are used in the highest temperature components in jet turbine engines owing to their excellent properties under creep conditions. These alloys owe their properties greatly to their chemical composition, and in particular the addition of slow diffusing elements like Re delays the creep deformation significantly. Vacancy diffusion has been suggested to be the rate-controlling process for creep deformation at high temperatures, and elements like Re are expected to interact with the vacancies in slowing them down. This has been investigated in the present work using ab initio calculations. Specifically, dilute as well as non-dilute binary alloys of Re, W and Ta in Ni were considered to study the effect of chemical composition on the rate of vacancy diffusion. Analytical formulations were used to describe the diffusion equations, however their applicability was restricted to the dilute regime. For the calculation of diffusion coefficients particularly in the non-dilute regime, kinetic Monte Carlo simulations were performed. The energies and the diffusion barriers were described using the cluster expansion method. Results suggested appreciable modifications of the vacancy diffusion coefficients, suggesting that the beneficial role of slow-diffusing elements in Ni-based superalloys could be partly explained by their effect on vacancy diffusion.
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Amponsah, Sylvester. "Optical Characterization of Nitrogen-vacancy Centers andResonance Analysis of CVD Grown Diamond MEMS Devices." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1528479091207253.
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Kasper, Christian Andreas [Verfasser], Vladimir [Gutachter] Dyakonov, Björn [Gutachter] Trauzettel, and Volker [Gutachter] Behr. "Engineering of Highly Coherent Silicon Vacancy Defects in Silicon Carbide / Christian Andreas Kasper ; Gutachter: Vladimir Dyakonov, Björn Trauzettel, Volker Behr." Würzburg : Universität Würzburg, 2021. http://d-nb.info/1233968130/34.
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Maiti, Debtanu. "Defect Laden Metal Oxides and Oxynitrides for Sustainable Low Temperature Carbon Dioxide Conversion to Fuel Feedstocks." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7694.
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The current energy and environmental scenario in the world demands acute attention on sustainable repurposing of waste CO2 to high value hydrocarbons that not only addresses the CO2 mitigation problem, but also provides pathways for a closed loop synthetic carbon cycle. Difference in the scales of global CO2 emissions (about 40 Gtpa, 2017) and the carbon capture and sequestration (CCS) facilities (estimated cumulative 40 Mtpa, 2018) provokes active research on this topic. Solar thermochemical (STC) and visible light photocatalysis are two of the most promising routes that have garnered attention for this purpose. While STC has the advantages of high CO2 conversion rates, it operates at high temperatures (more than 1000 °C) limiting its industrial implementation. Photocatalysis, on the contrary, is plagued by the poor quantum efficiency and conversion rates, although its exhibits the benefits of low temperature operation. Thus, any significant progress towards low temperature STC and visible light photocatalytic CO2 reduction is a giant leap towards a greener and sustainable energy solution. This dissertation is an effort towards improving both the STC and photocatalytic CO2 reduction.
Reverse water gas shift - chemical looping (RWGS-CL) is a modified STC approach that has the potential for low temperature CO2 conversion. RWGS-CL process uses mixed metal oxides like perovskite oxides (ABO3) for the conversion to CO, a potential feedstock for subsequent hydrocarbon production. Generation of oxygen vacancy defects on these perovskite oxides is a key step of RWGS-CL and thus, oxygen vacancy formation energy has been found to be a key descriptor for this process. Using density functional theory based calculations, this intrinsic material property has been used towards rational design of better catalysts. Highest rate of CO2 conversion at the low temperatures of 450 °C was demonstrated by earth abundant perovskite oxide via RWGS-CL. This low temperature and stable CO2 conversion process enables thermal integration with subsequent Fischer Tropsch processes for the hydrogenation of CO to hydrocarbons. Parallel to the developments on materials discovery, another crucial parameter that deserves attention is the surface termination effects of the perovskite oxides. Hence, the site specificity of the bulk and surface oxygen vacancies have been probed in detail towards elucidating the CO2 conversion performance over these materials. In the view of recent progress on the growth of selective crystal facets and terminations, this study opens new avenues for enhanced CO2 conversion performance not only through bulk composition variation, but also via exposing desired crystal facets.
Type-II semiconductor heterojunctions (staggered type) are promising candidates for efficient photocatalytic reactions, not only because of their capabilities of electronic density of states tuning, but also their ability to segregate the excited electrons and holes into different materials thereby restricting exciton recombination. Metal oxynitride heterojunctions have recently demonstrated promising activity on visible light water splitting. Elucidating the structure-function relationships for these materials can pave the way towards designing better CO2 conversion photocatalysts. This dissertation focuses on unravelling the roles of material composition, anion vacancy defects and lattice strain towards modulating the electronic density of states of lateral and vertical heterojunctions of (ZnO)X(AlN)1-X and (ZnO)X(GaN)1-X. The heterojunctions consist of periodic potential wells that allows for restricting interlayer charge transport. Increased ZnO concentration was explicitly shown to decrease the band gap due to N 2p and Zn-3d repulsion. Biaxial and vertical compressive strain effected increased band gap while tensile strain reduced the same. Oxygen vacancies was found to have different effect on the electronic state of the materials. When present in charged state (+2), it promotes mid gap state formation, while in neutral state it revealed increased electronic densities near the valence band and conduction band edges. These fundamental site specific material property tuning insights are essential for designing better photocatalysts for future.
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Dalponte, Mateus. "Redistribuição e ativação de dopantes em Si com excesso de vacâncias." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2008. http://hdl.handle.net/10183/15397.
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A redistribuição e ativação elétrica dos dopantes tipo n (As e Sb) e tipo p (Ga e In) em Si com excesso de vacâncias foram analisadas. As vacâncias foram geradas por implantação iônica de altas doses de oxigênio ou nitrogênio em alta temperatura, de acordo com procedimentos já estudados. Em seguida foram implantados os dopantes com dose de 5x1014 cm-2 a 20 keV na região rica em vacâncias. Dopagens idênticas foram realizadas em amostras de Si sem vacâncias e em SIMOX. Em seguida foram feitos recozimentos a 1000ºC por 10 s ou 15 min. Os perfis atômicos dos dopantes foram medidos com Medium Energy Ion Scattering e os perfis dos dopantes ativados, com Hall diferencial. A redistribuição e as propriedades elétricas de cada um dos dopantes no Si sem vacâncias foram bastante similares às observadas no SIMOX, porém várias diferenças foram observadas em relação às amostras com excesso de vacâncias. As vacâncias reduziram a ativação elétrica do As e do Sb, mas proporcionaram maior estabilidade da ativação após recozimentos longos. A redistribuição destes dopantes foi infuenciada pelo íon usado na geração das vacâncias, ou seja, nitrogênio ou oxigênio. O oxigênio proporcionou maior dose retida de As e o nitrogênio, maior dose retida de Sb. Já para o Ga e o In, as vacâncias tiveram papel fundamental na sua redistribuição, diminuindo a difusão para fora das amostras e garantindo maior dose retida. A ativação elétrica do Ga e especialmente a do In foram baixas, onde observamos forte influência do íon pré-implantado, principalmente o oxigênio.The redistribution and electrical activation of n type (As and Sb) and p type (Ga and In) dopants in Si with excess vacancy concentration were analyzed. The vacancies were formed by high dose ion implantation of oxygen or nitrogen at high temperature, following previously studied procedures. Dopants were implanted to a dose of 5x1014 cm-2 at 20 keV in the vacancy rich regions of the samples. Identical doping implantations were performed in bulk Si and SIMOX. Samples were then submitted to thermal annealing at 1000ºC for 10 s or 15 min. The dopants atomic profiles were obtained by Medium Energy Ion Scattering and the active dopant profiles, by differential Hall measurements. The redistribution and the electrical properties of each dopant in bulk Si were similar to those observed in SIMOX, but several differences were observed in the vacancy-rich samples. Vacancies reduced the electrical activation of As and Sb, although the activation was maintained stable after long annealing times. The redistribution of these dopants was, otherwise, dominated by the ion used in the vacancy generation, i.e., nitrogen or oxygen. The presence of oxygen resulted in larger As retained dose, while the presence of nitrogen, in larger Sb retained dose. Regarding the p type dopants, Ga and In, the vacancies played an important role in their redistribution, reducing their out-diffusion and allowing larger retained doses. Ga and especially In electrical activation was low, where strong influence of the pre-implanted ions was observed, especially oxygen.
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Hillman, Sara, and Beatrice Niklasson. "Konvertering av kontorsfastigheter till äldreboenden : Fastighetsägarens perspektiv." Thesis, KTH, Fastigheter och byggande, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-230935.
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Det finns flera sätt för en fastighetsägare att minska vakanser. Ett sätt är att konvertera fastigheten, eller delar av den, till ett annat ändamål som passar dagens efterfrågan. Lokalanpassningar har gjorts i alla tider med anledning av att det kan vara dyrare att riva och bygga nytt. En konvertering kan vara bra ur flera olika perspektiv. Ur ett hållbarhetsperspektiv kan det leda till ökade sociala-, ekonomiska- och miljömässiga värden. Under 1970-talet byggdes många kommersiella fastigheter runt om i världen. Historiskt sett har den kommersiella fastighetsbranschen varit cyklisk. Nederländerna var ett land som under 1990-talet led av höga vakanser, framförallt på kontorsfastigheter. Under slutet av decenniet skapades verktyget Conversion Meter som ett hjälpmedel för att bedöma potentialen att konvertera kontorsfastigheter till bostäder. Idag finns tecken på att kontorsfastigheter inte möter hyresgästernas krav. Effektiva och flexibla kontorsfastigheter i centrala lägen är, ur hyresgästernas perspektiv, en attraktiv arbetsplats. Föråldrade kontorsfastigheter i perifera lägen har en lägre efterfrågan och riskerar i framtiden att få en ännu högre vakansnivå. Samtidigt finns en stark efterfrågan på bostäder för äldre runt om i landet. Sverige står inför utmaningen att tillhandahålla särskilda bostäder för den åldrande befolkningen. En konvertering av föråldrade kontorslokaler i perifera lägen till denna typ av bostäder kan på många sätt ses som en möjlighet. Några av anledningarna är att fastighetens lokalisering är mindre avgörande, möjlighet att teckna längre hyresavtal till en generellt sett högre hyresnivå än för kontorslokaler samt möjlighet till statliga subventioner. Studien har undersökt möjligheten att utveckla Conversion Meter för att ta fram ett verktyg som kan vara tillämpbart vid en konvertering av kontorsfastigheter till särskilt boende för äldre på den svenska marknaden. Tre fallstudier har genomförts med den modifierade versionen av Conversion Meter. Studien visar att det går att modifiera Conversion Meter. Det modifierade verktyget har i studien kompletterats med en kassaflödesanalys samt med ett tillägg i checklistan för riskbedömning. Studien har visat att verktyget huvudsakligen modifierats utifrån målgruppens preferenser samt svenska byggnadstekniska- och juridiska aspekter. Fallstudierna visar, med hjälp av kassaflödesanalys, att det är lönsamt att konvertera kontorsfastigheterna till särskilt boende för äldre. Störst lönsamheten visar fastigheten i Upplands Väsby. Beräkningarnas utfall påverkas av kalkylräntan, vakansnivån och skillnader i hyresnivå före och efter konverteringen. Potentiella invändningar mot studien kan vara att vissa parametrar i Conversion Meter inte är tillräckligt precisa samt att verktyget måste kontinuerligt uppdateras efter förändringar i gällande regelverk.There are several ways for a property owner to reduce vacancies. One way is to convert the property to another purpose. Adaption of properties has always been done due to the fact that it may be more expensive to demolish and rebuild. Conversions of vacant office properties into other uses are desirable from a sustainability perspective because it may lead to an increase in social-, economic-, and environmental values. During the 1970s many commercial properties were built around the world. Historically, the commercial real estate industry has been cyclical. Netherlands was one of the countries that suffer due to high vacancies during the real estate crisis in the 1990s, especially in office buildings. By the end of the decade, Conversion Meter was created as a tool to assess the potential of converting office properties into housing. Today there are signs that office properties do not meet the tenant’s requirements. Efficient and flexible office properties in central locations are attractive as a workplace. While outdated office properties in less popular locations have a lower demand and hence might have a risk of high vacancy rates. At the same time there is a high demand on housing for the elderly. Sweden faces the challenge of providing care homes for the aging population. A conversion of obsolete office spaces in peripheral locations into care homes can be seen as an opportunity. There are several reasons why property owners would be interested in this market. This includes the location being less sensitive to location aspects, having the possibility to establish long leases, and the ability to receive government grants during conversion as well as generally higher rental levels as compared to office spaces. The main aim of this study is to investigate whether it is possible to develop a modified version of Conversion Meter to measure the potential for converting office properties into housing for elderly in Sweden. Three case studies have been conducted by creating and using a modified version of Conversion Meter with cash flow analysis for office properties in Lidingö, Sollentuna, and Upplands Väsby municipalities. The study shows that it is possible to modify Conversion Meter to measure the potential for converting office properties into care homes. In the study, Conversion Meter has been modified to a Swedish context and a cash flow analysis has been added. Additionally, political risks have been added to the tool. The main differences between the models are the target group's preferences, legal and building law, addition of cash flow analysis, and addition of political risks. By using cash flow analysis, the case studies show that it is profitable to convert office buildings into care homes. The greatest profitability observed is in the property in Upplands Väsby. The outcome of the calculations depends on the level of interest rates, vacancy rates, and differences in rental levels before and after the conversion. Potential biases to the study include parameters in the modified Conversion Meter are not precise and the tool must undergo continuous updates after changes.
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Yousefian, Pedram. "Pore Formation in Aluminum Castings: Theoretical Calculations and the Extrinsic Effect of Entrained Surface Oxide Films." UNF Digital Commons, 2017. https://digitalcommons.unf.edu/etd/761.
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Aluminum alloy castings are being integrated increasingly into automotive and aerospace assemblies due to their extraordinary properties, especially high strength-to-density ratio. To produce high quality castings, it is necessary to understand the mechanisms of the formation of defects, specifically pores and inclusion, in aluminum. There have been numerous studies on pore formation during solidification which lead to hot tearing and/or reduction in mechanical properties. However, a comprehensive study that correlates pore formation theory with in situ observations and modeling assumptions from the literature as well as experimental observations in not available. The present study is motivated to fill this gap.
An in-depth discussion of pore formation is presented in this study by first reinterpreting in situ observations reported in the literature as well as assumptions commonly made to model pore formation in aluminum castings. The physics of pore formation is reviewed through theoretical fracture pressure calculations based on classical nucleation theory (i) for homogeneous and heterogeneous nucleation, and (ii) with and without dissolved gas, i.e., hydrogen. Based on the fracture pressure for aluminum, critical pore size and corresponding probability of vacancies clustering to form the critical-size pore have been calculated by using thermodynamic data reported in the literature. Calculations show that it is impossible for a pore to nucleate either homogeneously or heterogeneously in aluminum, even with dissolved hydrogen. The formation of pores in aluminum castings can only be explained by inflation of entrained surface oxide films entrained during prior damage to liquid aluminum (bifilms) under reduced pressure and/or with dissolved gas, which involves only growth, avoiding any nucleation problem. This mechanism is consistent with reinterpretations of in situ observations as well as assumptions made in the literature to model pore formation.
To determine whether damage to liquid aluminum by entrainment of surface oxides can be observed and measured, Reduced Pressure Tests (RPT) have been conducted by using high quality, continuously cast A356.0 aluminum alloys ingots. Analyses of RPT samples via micro-computer tomography (μ-CT) scanning have demonstrated that number of pores and volume fraction of pore in aluminum casting increased by raising the pouring height (i.e., velocity of the liquid). Moreover, pore size distributions were observed to be lognormal, consistent with the literature.
Cross-sections of RPT samples have been investigated via scanning electron microscopy. In all cases, the presence of oxygen was detected inside, around and between the pores. The existence of oxide films inside all pores indicates that oxide films act as initiation sites for pores and hydrogen only assist to growth of pores. For the first time, the pore formation is reconciled with physical metallurgy principles, supported by observations of oxide films in aluminum castings. Results clearly indicate that pores are extrinsic defects and can be eliminated by careful design of the entire melting and casting process.
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Green, Robert David. "Carbon Dioxide Reduction on Gadolinia-Doped Ceria Cathodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1232574534.
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Lhuillier, Pierre-Emile. "Etude du comportement de l'hélium et des défauts lacunaires dans le tungstène." Phd thesis, Université d'Orléans, 2010. http://tel.archives-ouvertes.fr/tel-00587482.
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Dans les réacteurs à fusion, le tungstène subira des contraintes sévères dont, l'irradiation neutronique induisant la création de défauts ponctuels, et l'implantation d'hélium. La compréhension du comportement synergique des défauts lacunaires et de l'hélium est cruciale pour modéliser le comportement des composants en tungstène des futurs réacteurs à fusion thermonucléaire.Cette étude utilise la spectroscopie d'annihilation des positons (PAS) pour déterminer la nature et l'évolution en température des défauts d'implantation et l'analyse par réaction nucléaire (NRA)couplée ponctuellement à la microscopie électronique pour suivre le comportement de l'hélium.Les défauts générés dépendent des paramètres d'implantation (nature des ions, énergie, fluence). Par implantation d'3He à 800 keV, des monolacunes ont été créées et sont mobiles entre 473 et 623 K.L'augmentation de la concentration initiale en monolacunes décale le seuil de migration vers les basses températures. Des implantations à fort dpa (Fe 10 MeV) génèrent des amas lacunaires. Les impuretés jouent un rôle prépondérant sur le comportement en température des défauts.Le comportement de l'hélium a été étudié sous trois conditions d'implantation différentes. Les implantations à basse énergie (0,32 keV) montrent la création de complexes hélium-lacune par mutation. Les implantations à 60 keV mettent en évidence la compétition entre la migration, à basse fluence et le piégeage de l'hélium, à haute fluence. Finalement, des implantations à haute énergie(500 keV) renseignent sur l'influence de la microstructure sur la distribution des bulles d'hélium.
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Sidibe, Moussa. "Etude du comportement du tungstène sous irradiation : applications aux réacteurs de fusion." Phd thesis, Université d'Orléans, 2014. http://tel.archives-ouvertes.fr/tel-01068634.
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La fusion thermonucléaire est envisagée comme nouvelle source énergétique pratiquement inépuisable. Le projet ITER " International Thermonuclear Experimental Reactor " doit démontrer la faisabilité scientifique et la maitrise de la fusion thermonucléaire. Le tungstène (W) a été choisi pour recouvrir le " divertor ", un composant essentiel du réacteur ITER. Il sera soumis à des conditions extrêmes de fonctionnement : au bombardement neutronique, à d'intenses flux de chaleur et de particules (hélium, hydrogène). Ces conditions induiront dans le W des défauts et introduiront de l'hélium et de l'hydrogène, qui pourront conduire à des modifications de sa microstructure et de ses propriétés physiques, chimiques et mécaniques. L'objectif de ce travail est d'étudier, à l'échelle atomique, l'évolution de la microstructure du tungstène sous irradiation. Afin de simuler les atomes de recul générés par les irradiations aux neutrons, des échantillons de W ont été irradiés avec des ions lourds et/ou implantés avec de l'hélium. La nature des défauts a été étudiée à l'aide de la Spectroscopie d'Annihilation de Positons (PAS). Les résultats montrent que les irradiations aux ions lourds conduisent à la formation de monolacunes et de clusters lacunaires dont la taille et la concentration augmente avec la fluence. Des irradiations ou des recuits effectués à une température supérieure à 450 K conduisent à l'agglomération des défauts lacunaires essentiellement par migration des monolacunes. Pour des recuits à très hautes températures (1773 K), les observations MET montrent la présence de cavités nanométriques (∼10 nm). Les implantations avec les ions 4He 60 keV induisent dans le W une distribution de défauts complexes de type nHe-mv, ainsi qu'une faible concentration de monolacunes v. Une majorité de complexes He-v est formée pour la faible fluence et la fraction des défauts complexes (nHe-mv) augmente quand la fluence augmente. La nature et la distribution des défauts évolue en fonction de la température de recuit et dépend du ratio [He]/[v]. Le premier stade de recuit des défauts lacunaires (∼ 450 K) est masqué par la présence de l'hélium dans les défauts lacunaires. Pour un ratio [He]/[v] supérieur à 1, un stade d'agglomération des défauts est clairement observé à partir de 1623 K. Pour des conditions d'introduction de défauts et d'hélium proches de celles attendus dans les réacteurs de fusion (He/dpa allant de 0.03 à 8 appm He/dpa), la signature positon après irradiation est similaire à celle mesurée dans des échantillons seulement endommagés dans des conditions équivalentes mais sans introduire de l'hélium. Pour des rapports He/dpa allant de 0.3 à 8 appm He/dpa, les recuits révèlent des différences de distribution en taille et en concentration des défauts lacunaires. La présence d'hélium dans les amas lacunaires modifie les caractéristiques d'annihilation des positons et favorise la stabilisation des amas lacunaires.
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Guttman, Jeremy. "Polymer-based Tunnel Diodes Fabricated using Ultra-thin, ALD Deposited, Interfacial Films." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469125487.
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Dalkic, Yurdaer, and Hadi Deknache. "A Self-policing Smart Parking Solution." Thesis, Malmö universitet, Fakulteten för teknik och samhälle (TS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-20898.
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With the exponential growth of vehicles on our streets, the need for finding an unoccupied parking spot today could most of the time be problematic, but even more in the coming future. Smart parking solutions have proved to be a helpful approach to facilitate the localization of unoccupied parking spots. In many smart parking solutions, sensors are used to determine the vacancy of a parking spot. The use of sensors can provide a highly accurate solution in terms of determining the status of parking lots. However, this is not ideal from a scalability point of view, since the need for installing and maintaining each of the sensors is not considered cost-effective. In the latest years vision based solutions have been considered more when building a smart parking solution, since cameras can easily be installed and used on a large parking area. Furthermore, the use of cameras can be developed to provide a more advanced solution for checking in at a parking spot and also for providing the information about whether a vehicle is placed unlawfully. In our thesis, we developed a dynamic vision-based smart parking prototype with the aim to detect vacant parking spots and illegally parked vehicles.
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Kasper, Christian Andreas. "Engineering of Highly Coherent Silicon Vacancy Defects in Silicon Carbide." Doctoral thesis, 2021. https://doi.org/10.25972/OPUS-23779.
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In this work the creation of silicon vacancy spin defects in silicon carbide with predictable properties is demonstrated. Neutron and electron irradiation was used to create silicon vacancy ensembles and proton beam writing to create isolated vacancies at a desired position. The coherence properties of the created silicon vacancies as a function of the emitter density were investigated and a power-law function established. Sample annealing was implemented to increase the coherence properties of existing silicon vacancies. Further, spectral hole burning was used to implement absolute dc-magnetometryIn dieser Arbeit wird die Erzeugung von Silizium Fehlstellen in Siliziumkarbid mit vorhersagbaren Eigenschaften nachgewiesen. Neutronen- und Elektronenbestrahlung wurden zur Erzeugung von Ensembles von Silizium Fehlstellen verwendet, während isolierte Fehlstellen an einer gewünschten Position mit Hilfe eines Protonenstrahls erzeugt wurden. Die Kohärenz der erzeugten Silizium Fehlstellen wurde in Abhängigkeit der Emitterdichte untersucht und eine Gesetzmäßigkeit hierfür eingeführt. Um die Kohärenz der Silizium Fehlstellen zu erhöhen, wurden Annealing Experimente durchgeführt. Des Weiteren wurde spektrales Holeburning verwendet, um absolute DC-Magnetometrie nachzuweisen
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HSIEH, TSU-HSIU, and 謝祖修. "High Sensitivity NO gas sensor using SnO2 nanofiber by oxygen vacancy engineering." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/43bha3.
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Zang, Donghui. "Statistical mechanics and kinetics of hydrogen vacancy interaction of metals." Thesis, 1999. http://hdl.handle.net/1911/19456.
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Several important aspects of hydrogen vacancy interaction are discussed with a physical model as well as numerical methods for the model presented. A statistical mechanical model was first introduced to calculate the solubility and diffusivity of H in Ni based upon the concept of H-atoms possessing translational mobility over path lengths of several lattice parameters. It has been shown to be compatible with the solubility behavior but not compatible with the Arrhenius behavior of H-diffusivity above 300K. Statistical mechanical calculations were carried out to determine the vacancy concentration in Ni crystals containing dissolved hydrogen, the surface situation was discussed in particular using modified energy level spectra taken from effective medium calculations. The results showed that the presence of H-atoms results in an enhancement of the vacancy concentrations, and the effect is even more obvious for surface.
Finite Difference Method (FDM) were employed to treat the "upquenching" process, ie vacancy formation due to rapid hydrogenation. A nickel crystal was studied and it was shown that the atomic fraction of vacancies was substantially increased by the presence of a tensile stress fields and that the relative magnitude of the effect decreases with increasing temperature. Finally using Ni as example again, the hydrogen diffusion under high fugacity conditions was computed considering the H-H and H-lattice interaction. Results show much greater H-concentration are produced than the previously estimated.
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Fung, Brian. "Stress engineering in impurity free vacancy disordering for III-V compound semiconductors: Theory and application." 2007. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=452839&T=F.
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Bhattacharjee, Shubhadeep. "Materials, Processes and Device Design for High Performance, Sub-thermionic MoS2 FETs." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/4268.
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The shrinking of the field-effect transistor (FET), commonly termed CMOS scaling, has revolutionised the semiconductor industry and impacted most aspects of human life. However, this decades-long successful trend of scaling the FET is now facing serious fundamental and technological challenges resulting in diminishing economic returns. The first challenge is that, as device dimensions shrink, electric fields in close proximity start to interfere with each other and disrupt the transistor’s operations. This phenomenon is called the short channel effect (SCE). Second, concurrent (quadratic) reduction in power consumption, an important aspect of scaling, is not possible because of the inability to reduce supply voltage below 1 V. This is primarily because the fundamental nature of charge transport governed by Boltzmann’s statistics restricts the sub-threshold swing (SS, abruptness between OFF to ON transitions) of FETs to the thermionic limit of 60 mV/dec at room temperature. Hence, as we cram in more transistors into the same footprint, energy dissipation and heat management have become fundamental bottlenecks. Clearly, the road ahead needs breakthroughs in new materials and device design.
In this thesis, we attempt to tackle both these challenges (SCE and power consumption) by developing high performance, sub-thermionic (SS<60 mV/dec) transistors on 2D semiconductors. Excellent electrostatics inherent to 2D semiconductors make them promising candidates for mitigating SCE, with recent demonstrations of sub-10 nm channel length molybdenum disulphide (MoS2) FETs. However, the development of sub-thermionic transistors on 2D semiconductors has been stymied by inefficient contacts, doping and dielectric integration, which motivates the initial portion of this work. First, we demonstrate how a facile sulfur-based solution can be employed to engineer surface states between MoS2/metal contacts, resulting in substantial reduction in Schottky barrier height. This enables record performance due to a ~6x/10x (Ni/Pd) reduction in contact resistance, along with complete mitigation in contact variability. In addition, through an empirical model we can predict the intrinsic limit of contact resistance in multilayer TMDs. Second, we develop an air-stable, area-selective, CMOS-compatible counterdoping strategy through vacancy engineering, enabling p-FETs and in-plane p/n junction photodioides. Third, we lay a two-part focus on dielectrics. In the first part, we examine the interplay of different scattering mechanisms in 2D charge transport and demonstrate ‘ideal’ nitride dielectric environments for large performance gains (field-effect mobility ~ 73 cm2V-1s-1). In the second part, we
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break the paradigm of atomic layer deposition and employ functionalisation-free e-beam evaporated top gate high-κ HfO2 to achieve near-perfect SS~60 mV/dec operation. Finally, leveraging on the insights from the previous sections, we demonstrate, for the first time, sub-thermionic transport through tunable Schottky contacts in dual gated MoS2 FETs. Two device configurations, the GT3FET and DVATFET, are expounded. The GT3FET has the flexibility to operate either in the sub-thermionic tunnel regime, yielding steep SS<60 mV/dec OR thermionic high mobility regime. Combining the best of both tunnelling and thermionic regimes in the same operation cycle, the DVATFET, the closest to an ‘ideal transistor’, registers SS~29 mV/dec (3 dec) AND high mobility (100 cm2V-1s-1). This work is envisioned to pave a new path in the development of sub-thermionic, high performance FETs operating in the sub-0.5 V ‘green computing’ regime.MeiTY Visvesvariaya PhD Fellowship