Dissertations / Theses on the topic 'Novel Nano-structures'

In this work, the use of theoretical tools of molecular modeling for tailoring 1D novel nanomaterials is demonstrated. There are four selected nano-structures as examples, each tailored for a specic demand of nano-technology that is yet to be fullled. For the purpose of modeling/calculating the electronic and structural properties, various methods of dening the interatomic interaction, such as empirical potential energy functions, semi-empirical methods and density functional theory, are used. Each of these methods have a dierent level of approximations leading to limitations in their use. Furthermore, each method needs to be calibrated carefully in order to obtain physically meaningful results. Examples being novel nano-structures, there does not exist any experimental observations directly studying the material at hand. Thus, in order to obtain a parameter set that best describes the system, a series of pre-existing structures that are physically and/or chemically related are used. Among the methods employed, the density functional theory (DFT) is certainly the most popular one, due to its accuracy and more importantly the framework it provides for perturbative extensions otherwise nearly impossible to calculate in Hartree-Fock level.

Patterning, the utilisation and manipulation of geometric properties, is important both for the rational design of technological devices and also to the understanding of many natural phenomena. In this thesis I examine the way in which micro and nano patterning can alter optical properties across a large range of wavelength scales and how these novel phenomena can be utilised. Micro patterned electrodes can tune the geometry of radio frequency electric fields to generate dielectrophoretic microfluidic devices. These devices use the dielectrophoretic force to sort, position and characterise the properties of micro and nano particles. I develop a new image processing algorithm that radically improves experimental efficiency allowing for real-time supervisor free dielectrophoretic characterisation of nanoparticles. Metamaterials are composite structures that have repeating units that are much smaller than the wavelength of radiation they are designed to work with. The optical properties of the materials are derived from these units rather than the bulk characteristics of the materials they are composed of. I demonstrate the development of novel THz metamaterial absorber devices. These devices provide a means to design and control the absorption of THz radiation, modulating bandwidth, polarization dependence and frequency in a form that is readily integrable with other standard fabrication processes. Finally by periodically patterning materials on the nanometer scale I demonstrate the development of novel photonic crystal devices and complementary optical components. In these devices the periodicity of the electromagnetic wave is modulated by the periodicity of the structures themselves resulting in band gaps and resonances analogous to the band gaps and defect states found commonly in semi-conductor physics. I demonstrate the theory, fabrication and measurement of these devices using novel broadband supercontinuum sources and propose a future application for biosensing. Further topics covered in the appendix include the development of a spin out technology, a $100 open source atomic force microscope developed while spending time in China. Finally I examine the role of patterning for optimising the performance of nanomechanical cantilever biosensors, and show how geometrical effects on the microscopic scale are crucial to understanding the workings of the vancomycin family of antibiotics, as screened using microcantilevers. Portions of this report are edited extracts from published articles resulting from this work, a full list of which is given in Appendix A.

Solution chemistry is a versatile and powerful tool in the synthesis of designed, complex nano-level high-tech materials. Normally, the technique is considered too expensive for large-scale production of complex multi-component ceramic materials. This thesis describes the expansion of the useful area of solution processing to multi-component bulk materials such as ZnO-based high-field varistors and WC–Co cutting tools, by developing novel techniques for solution-based coating of conventionally prepared metal and ceramic powders. The chemistry and microstructure development in the preparation of coatings, and the sintering of the coated powders to compacts, were studied in detail by SEM-EDS, TEM-EDS, XRD, IR-spectroscopy, dilatometry, TGA and DSC chemical analysis.

ZnO powder with a ca 20 nm thick, homogeneous oxide coat of Bi–Sb–Ni–Co–Mn–Cr–Al oxide was prepared. After sintering to dense varistor bodies, much improved microstructures with much reduced ZnO-grain sizes were obtained. This shows that the oxides added as liquid sintering aid and grain-growth inhibitor become much more active when added homogeneously as a skin on the ZnO powder.

After sintering of cobalt-coated WC, much improved micro-structures were obtained with a much more narrow WC grain-size distribution than that obtained from starting powders mixed by a conventional milling route. Coated powders also obviate the need for the extensive milling of WC and Co powders used in conventional mixing.

The novel solution route was also applied to preparation of porous sponges and thin films on metal, glass and Al₂O₃ of sub 20 nm sized Co- or Ni-particles.

This thesis addresses novel nanocomposite materials by incorporating quantum dots, and other nanoentities, into polymer and sol-gel derived matrices, aiming to produce integrated photonic structures. Its objectives embrace the synthesis and the investigation of photonic materials, together with alternative fabrication methodologies enabling the effective integration of functional nanocomposite photonic structures, such as active waveguides, micro-ring structures and diffractive optical elements for sensing applications. Design, synthesis and characterization of nanocomposite materials in this context, involves QD incorporation in tailored-made polymers, synthesized using radical polymerization as well as QD embedment in titania matrices synthesized via sol-gel methods. Low cost sol-gel derived silica incorporating NiCl2 ¬ nanoentities was exploited in the proposed scheme of remote point sensing for ammonia detection. Commercially available hybrid organic/inorganic materials of the ORMOCER family are also used for structure fabrication. Further to microscopy, characterization of the materials mainly includes spectroscopic studies and refractive index measurements using reflectance interferometry. For the demonstration of complex photonic structures by using nanocomposites elaborated studies are presented here focusing on two fabrication methods: a) direct laser ablative microfabrication using ArF excimer radiation at λ=193 nm and, b) soft lithography. To achieve this, a fully automated ArF excimer laser microfabrication station was established comprising computer controlled nanopositioning and laser beam control, as well as various prototype materials synthesis and fabrication devices. QD/polymer computer generated holograms, waveguides and micro-ring structures were simulated, designed and fabricated. Specific protocols and method were established. A modified solvent-assisted soft lithography method was also used for micropatterning and fabrication of photonic structures using QD/polymer and QD/titania films in conjunction to common UV and thermally curable materials. A solvent vapor smoothing process was found to significantly enhance the quality of the structures as observed with scanning electron microscopy. QD/polymer computer generated holograms, diffractive optical elements, micro-ring structures, vertical cavity resonators and other advanced photonic structures comprising quantum dot nanocrystals and nano-entities are investigated. A new photonic sensing scheme is proposed and demonstrated here for remote, spatially-localized sensing. It comprises a low cost diffractive thin film of a sensing material remotely interrogated by use of light beams. A silica/NiCl2 system fabricated via the sol-gel methods and micropatterned using the direct laser ablative microfabrication method is demonstrated, to allow detection of as low as 1 ppm of ammonia. Finally, the merits of incorporating epitaxially grown quantum dots in highly resonant structures for signal amplification, namely vertical cavity semiconductor optical amplifier and micro-ring semiconductor optical amplifiers, are discussed. Such devices are demonstrated to lack a laser threshold if designed properly allowing for the full exploitation of the fast carrier dynamics of quantum dots by driving them at high currents, for amplification of high-bit-rate signals of up to 100 Gb/s. A rate equation theoretical model was developed which provides both performance prediction of the devices under discussion and design guidelines for threshold-less operation. This doctoral thesis served, as a whole, its main scope of providing a palette of materials and methods as well as some useful concepts for the fabrication of functional photonic structures and devices based on advanced nanocomposites.
Στην παρούσα διδακτορική διατριβή μελετώνται νανοδομημένα υλικά με ενσωματωμένες κβαντικές ψηφίδες και άλλες νανο-οντότητες σε πολυμερή και ανόργανες μήτρες μέσω της μεθόδου sol-gel, στοχευοντας στην κατασκευή δομών ολοκληρωμένων φωτονικών κυκλωμάτων. Οι στόχοι της διατριβής επικεντρώνονται στην σύνθεση και μελέτη φωτονικών υλικών και στον συνδυασμό τους με εναλλακτικές μεθόδους κατασκευής φωτονικών δομών. Τα νανοσύνθετα υλικά που μελετήθηκαν παρουσιάζουν μια σειρά από φωτονικές ιδιότητες για την υλοποίηση φωτονικών δομών διαφόρων λειτουργικοτήτων όπως ενεργοί οπτικοί κυματοδηγοί, ενεργοί συντονιστές μικροδακτυλίου και περιθλαστικά οπτικά στοιχεία για φωτονικές εφαρμογές. Στα πλαίσια της σχεδίασης, σύνθεσης και χαρακτηρισμού αυτών των νανοδομημένων υλικών κβαντικές ψηφίδες ενσωματώθηκαν σε πολυμερικές μήτρες ειδικά σχεδιασμένες για τον σκοπό αυτό καθώς και σε ανόργανες μήτρες παρασκευασμένων με την μέθοδο sol-gel. Μελετήθηκαν ακόμα υλικά διοξειδίου του πυριτίου εμπλουτισμένα με νανο-οντότητες χλωριούχου νικελίου του για χρήση σε φωτονικούς αισθητήρες. Τα υλικά αυτά συνετέθησαν με μεθόδους χαμηλού κόστους και χρησιμοποιήθηκαν σε καινοτόμες διατάξεις φωτονικών αισθητήρων που περιγράφονται εδώ. Επιπλέον μελετήθηκαν υβριδικά οργανικά/ανόργανα υλικά ORMOCER για την κατασκευή μιας σειράς φωτονικών διατάξεων. Ο χαρακτηρισμός των υλικών που περιγράφονται εδώ πραγματοποιήθηκε με φασματοσκοπικές μεθόδους ενώ ο δείκτης διάθλασης τους μετρήθηκε με την τεχνική της ανακλαστικής συμβολομετρίας. Η κατασκευή και επίδειξη σύνθετων νανοδομημένων φωτονικών διατάξεων πραγματοποιήθηκε με δύο μεθόδους: α) την μέθοδο φωτο-εκρηκτικής αποδόμησης με χρήση excimer laser σε μήκος κύματος λ=193 nm και β) με την μέθοδο soft lithography. Για τον σκοπό αυτό αναπτύχθηκε μια πλήρως αυτοματοποιημένη διάταξη μικροκατασκευής με χρήση ArF excimer laser στην οποία τόσο η πηγή laser όσο και η νανομετρική πλατφόρμα για την κίνηση του υπό διαμόρφωση δείγματος ελέγχονται από υπολογιστή. Η διάταξη αυτή χρησιμοποιήθηκε για την κατασκευή διαφόρων διατάξεων σε πολυμερικά υμένια με ενσωματωμένες κβαντικές ψηφίδες όπως υπολογιστικά σχεδιασμένων ολογραμμάτων, κυματοδηγοί και συντονιστές μικροδακτυλίου με γεωμετρικά χαρακτηριστικά που προκύπτουν από θεωρητικές προσομοιώσεις. Ακόμα αναπτύχθηκε μια παραλλαγή της μεθόδου soft lithography για την υποβοηθούμενη από χημικό διαλύτη φωτονικών δομών πολυμερικών μητρών και μητρών τιτανίας με ενσωματωμένες κβαντικές ψηφίδες σε συνδυασμό με κοινά υλικά σχεδιασμένα για την μέθοδο soft lithography και τα οποία διαμορφώνονται με έκθεση σε υπεριώδη ακτινοβολία. Στην διατριβή αυτή παρουσιάζεται ακόμα μια καινοτόμα σχεδίαση φωτονικών αισθητήρων για την τοπική ανίχνευση διαφόρων χημικών ή φυσικών παραγόντων από απόσταση. Οι αισθητήρες αυτοί αποτελούνται από περιθλαστικές δομές κατασκευασμένες σε υμένα κατάλληλων υλικών, οι οπτικές ιδιότητες των οποίων ανιχνεύονται με τη χρήση δέσμης laser. Ένας τέτοιος περιθλαστικός αισθητήρας αμμωνίας υμενίου διοξειδίου του πυριτίου με ενσωματωμένες νανο-οντότητες χλωριούχου νικελίου παρουσιάζεται εδώ, του οποίου η περιθλαστική δομή κατασκευάστηκε με τη μέθοδο της φωτο-εκρηκτικής αποδόμησης με laser. Ο αισθητήρας αυτός παρουσιάζει εξαιρετική επίδοση και ικανότητα ανίχνευσης αμμωνίας συγκέντρωσης μόλις 1 ppm. Τέλος, συζητούνται τα πλεονεκτήματα της χρήσης κβαντικών ψηφίδων αναπτυγμένων με την επιταξιακές μεθόδους σε δομές οπτικών ενισχυτών ισχυρού συντονισμού, συγκεκριμένα σε οπτικούς ενισχυτές ημιαγωγού κάθετης κοιλότητας και οπτικούς ενισχυτές ημιαγωγού μικροδακτυλίου. Συγκεκριμένα, επιδεικνύεται με τη χρήση ενός θεωρητικού μοντέλου που αναπτύχθηκε εδώ πως με τον κατάλληλο σχεδιασμό είναι δυνατόν στις διατάξεις αυτές να αποτρέπεται πλήρως η λειτουργία laser με την απουσία ρεύματος κατωφλίου. Η ιδιαιτερότητα αυτή επιτρέπει την χρήση μεγάλων ρευμάτων και την συνεπακόλουθη εκμετάλλευση της γρήγορης δυναμικής των φορέων στις κβαντικές ψηφίδες για την αποτελεσματική ενίσχυση σημάτων υψηλών ταχυτήτων (μεχρι 100 Gb/s). Η Διαδακτορική διατριβη, υπηρετεί συνολικά τον κύριο σκοπό της προσφέροντας μια παλέττα υλικών και μεθόδων για την ανάπτυξη λειτουργικών φωτονικών δομών και διατάξεων βασισμένων σε προηγμένα νανοσύνθετα υλικά.

Silicon based 3D fin structure is believed to be the potential future of current semiconductor technology. However, there are significant challenges still exist in realizing a manufacturable fin based process. In this work, we have studied the effects of hydrogen anneal on the structural and electrical characteristics of silicon fin based devices: tri-gate, finFET to name a few. H₂ anneal is shown to play a major role in structural integrity and manufacturability of 3D fin structure which is the most critical feature for these types of devices. Both the temperature and the pressure of H₂ anneal can result in significant alteration of fin height and shape as well as electrical characteristics. Optimum H₂ anneal is required in order to improve carrier mobility and device reliability as shown in this work. A new hard-mask based process was developed to retain H₂ anneal related benefit while eliminating detrimental effects such as reduction of device drive current due to fin height reduction. We have also demonstrated a novel 1T-1C pseudo Static Random Access Memory (1T-1C pseudo SRAM) memory cell using low cost conventional tri-gate process by utilizing selective H₂ anneal and other clever process techniques. TCAD-based simulation was also provided to show its competitive advantage over other types of static and dynamic memories in 45nm and beyond technologies. A high gain bipolar based on silicon fin process flow was proposed for the first time that can be used in BiCMOS technology suitable for low cost mixed signal and RF products. TCAD-based simulation results proved the concept with gain as high 100 for a NPN device using single additional mask. Overall, this work has shown that several novel process techniques and selective use of optimum H₂ anneal can lead to various high performance and low cost devices and memory cells those are much better than the devices using current conventional 3D fin based process techniques.
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碩士
國立中山大學
電機工程學系研究所
103
In this thesis, we propose two novel capacitorless 1T-DRAMs, with the multi-gate and nano-pillar structures : The first type is a double-gate Nanowire TFT, with the fin-gate and pillar-body structure (FGPB). The second type is a vertical current bridge MOSFET, with the gate-all-around and nano-pillar structure (GAANP). We adopt the GIDL mechanism as 1T-DRAM programming method, and use the Sentaurus TCAD 12.0 simulation tool to confirm the memory performance. Compared with the conv. DG-NTFT, the FGPB device has nano-pillar structure, which can increase the pseudo neutral region without additional occupied area. This structure can improve the band-to-band tunneling, and keep the holes away from the P-N junction. The GIDL current is improved about 274.33 %. With fin-gate to control the excess hole efficiently, this structure can also overcome the SRH recombination influence indirectly. In terms of the low-power application, and the power consumption can maintained below 0.8 μW/μm. Compared with the lateral current bridge 1T-DRAMs, the GAANP SOI/Bulk-Silicon device has surrounding gate, which can enhance the excess hole control-ability; the vertical channel not only keeps the device in long-channel, but also maintains at a certain level of memory performance. In terms of the current bridge devices benchmark comparison, the GAANP SOI 1T-DRAM PW is improved at least about 238.54 %. The RT at 358 K is improved about 6.91 %. Two novel devices not only achieve low-power consumption, but also have sufficient operating endurance and disturbance immunity. We provide two excellent candidates for future 1T-DRAM applications.

In the first part of this dissertation, we study mainly novel boron structures and their electronic and mechanical properties, using ab initio calculations. The electronic structure and construction of the boron buckyball B80, and boron nanotubes as the α-sheet wrapped around a cylinder are studied. The α-sheet is considered so far to be the most stable structure energetically out of the two dimensional boron assemblies. We will argue however that there are other sheets close in energy, using cluster expansion method. The boron buckyball is shown to have different possible isomers. Characterization of these isomers according to their geometry and electronic structure is studied in detail. Since the B80 structure is made of interwoven double-ring clusters, we also investigate double-rings with various diameters. We investigate the properties of nanotubes obtained from α-sheet. Computations confirm their high stability and identify mechanical stiffness parameters. Careful relaxation reveals the curvature-induced buckling of certain atoms off the original plane. This distortion opens up the gap in narrow tubes, rendering them semi-conducting. Wider tubes with the diameter d  1.7 nm retain original metallic character of the α-sheet. We conclude this part by investigation into hydrogen storage capacity of boron-rich compounds, namely the metallacarboranes. In the second part of dissertation, we switch our focus to electronic and transport properties of carbon nano-structures. We study the application of carbon nanotubes as electro-chemical gas sensors. The effect of physisorption of NO2 gas molecules on electron transport properties of semi-conducting carbon nanotubes is studied using ab initio calculations and Green’s function formalism. It is shown that upon exposure of nanotube to different concentrations of gas, the common feature is the shift in conductance towards lower energies. This suggests that physisorption of NO2 will result in a decrease (increase) in conductance of p-type (n-type) nanotubes with Fermi energies close to the edge of valence and conduction band. Finally we study the effect of torsion on electronic properties of carbon nano-ribbons, using helical symmetry of the structures.

碩士
國立交通大學
材料科學與工程學系
99
This thesis contains two main topics: heterojunction nano-structures and photocatalysts. First, a series of novel p-type Cu2O and CuO, n-tpye ZnO, and their mixed p-n heterojunction nano-structures were newly prepared mainly by chemical reduction method. Second, the nano-structures obtained were applied as photocatalysts and the nano-structural influence on photocatalytic performance was compared and discussed. Cu2O was prepared by spontaneous oxidation of spherical Cu nano-particles (~5 nm in diameter) in water at room temperature. Several novel CuO nano-structures were then simply synthesized by the further oxidation of the prepared Cu2O nano-particles in aqueous solutions. Accompanying with the oxidation process, a distinct morphological transformations from zero-dimensional (Cu2O) to one-dimensional or two-dimensional (CuO) was found and its mechanism is considered as the key point to produce such a variety of CuO nanostructures including buckhorn-like rods, short rods, and flakes, in this work. In addition, one-dimensional Cu(OH)2 nano-structures (~100 nm long and 15 nm in width) can also be found under some oxidation conditions. ZnO nano-structures including one-dimensional single crystal rods, octahedra and three-dimensional flower-like assemblies were synthesized. In addition, using suspended Cu2O nano-particles as substrates, ZnO nano-structures could directly grow on Cu2O to form a p-n heterojunction ZnO/CuO composite. Our photocatalytic experiment has proved that the p-n heterojunction ZnO/CuO composite prepared indeed presents at least 45% enhancement of the degradation efficiency of organic dye, Rhodamine B, comparing with the simple mixture of CuO and ZnO nano-structures. Nano-structures generally demonstrate a variety of morphologies in comparison with bulk materials. In this thesis, we illustrated a series of XRD analysis with theoretical calculations to distinguish some frequently observed morphologies of nano-particles, including cube, sphere, decahedron and icosahedron for metals and sphere, cube and rod for oxides.

碩士
國立中山大學
化學系研究所
101
“Aerosols”, suspensions of ultrafine particulates in a gas, play significant roles in a number of important research fields, including the atmospheric chemistry, planetary sciences, environmental sciences as well as the biomedical sciences and therapeutic administration. Since aerosols have various size, shape, composition and architecture, it is crucial to understand the fundamental physical, chemical and optical properties of aerosols from the atomic and molecular level. In order to address these issues, we have recently constructed a novel multi-functional aerosol instrument. This new multi-functional aerosol instrument is composed of three main parts, including (I) a long- path, temperature adjustable aerosol chamber coupled with the rapid-scan Fourier transform infrared spectrometer, (II) an adjustable aerodynamic lens system to produce a focused and size-selected aerosol particle beam, and (III) an aerosol ultraviolet photoelectron spectrometer (UPS) chamber with a high-resolution hemispherical electron energy analyzer. Aerosols are generated either by an atomizer or formed in-situ in the long-path aerosol chamber under well-controlled conditions. The aerosol size distribution and concentration are characterized via a scanning mobility particle sizer (SMPS). The performance of this newly developed aerosol instrument and some preliminary results of each part will be discussed.