"In the past decade nanomaterials have attracted the interest of scientists and engineers all over the world due to their unique properties. Through their devoted experimental efforts, limited advances have been made on the synthesis of nanomaterials, the integration of nanomaterials into the structures of larger scales, and the property study of nanomaterials to explore possible applications. Despite the huge amount of money, resources, and effort invested in nanomaterials, several challenges still remain as obstacles on the way towards the successful large scale use of nanomaterials to benefit human life and society. For example, the need for low-cost, robust, and highly productive manufacturing methods and the demand for efficient integration of nanomaterials with materials and devices of larger length scales are still left unmet. The objective of this work was to utilize cost-efficient nanofabrication methods such as template-assisted fabrication, electrodeposition, and chemical vapor deposition to fabricate nanomaterials, integrate nanomaterials with larger structures to form a hierarchical composite, and explore the application of unique nanostructured electrode in lithium-ion batteries. Thus the thesis consists of three main parts: (1) fabrication of one-dimensional inorganic nanomaterials such as metal nanowires, metal nanorods, and carbon nanotubes with good control over shape and dimension; (2) synthesis of hierarchical carbon nanofibers on carbon microfibers and/or glass microfibers; and (3) development of nanostructured anodes to improve high-rate capability of lithium-ion batteries by adapting nanorod arrays as miniature current collectors. "

O presente trabalho estuda a produção e modificações físico-químicas do grafeno frente a tratamentos térmicos. Em uma primeira etapa, foi investigada a síntese de grafeno pela técnica de Deposição Química a partir da fase Vapor (CVD) sobre fitas de cobre. Nós variamos quatro parâmetros que influenciam no crescimento de grafeno: fluxo de metano (CH4), fluxo de hidrogênio (H2), tempo de crescimento e grau de pureza do cobre. Usando as técnicas de caracterização de espectroscopia Raman e microscopia óptica, observamos que fluxo menor de H2 e fluxo intermediários de CH4 favorecem o crescimento de grafeno de alta qualidade. Além disso, vimos que 15 minutos de crescimento de grafeno é suficiente para cobertura do substrato de cobre com grafeno. Por fim, foi visto que o maior grau de pureza do cobre permite a produção de monocamadas de grafeno mais homogêneas. Numa segunda etapa, foi realizado um estudo com objetivo de entender a interação de hidrogênio com monocamadas de grafeno. Nós usamos amostras de grafeno depositadas em filmes de SiO2 (285 nm)/Si e tratadas termicamente em atmosfera controlada de deutério (99,8%) em temperaturas entre 200 e 800 °C. Nós também investigamos a dessorção de hidrogênio do grafeno usando amostras previamente tratadas em deutério a 600 °C e depois tratadas em atmosfera controlada de nitrogênio em temperaturas entre 200 e 800 °C. Após os tratamentos, análise por reação nuclear (NRA) foi realizada para quantificar o deutério, onde nós observamos uma grande incorporação de deutério no grafeno acima de 400 °C, tendo um aumento moderado até 800 °C. Nós também observamos que a dessorção do deutério do grafeno ocorre apenas em 800 °C, embora a dessorção de deutério do óxido de silício ocorra a partir de 600°C. Espectroscopia Raman também foi realizada após cada tratamento térmico. Os resultados mostram que os defeitos na estrutura do grafeno têm um grande aumento para as etapas de maior temperatura na incorporação de deutério. Análises realizadas com Espectroscopia de Fotoelétrons Induzidos por Raios X (XPS) mostraram que a incorporação de deutério para maiores temperaturas causa o "etching" do grafeno. Por fim, caracterizações usando Espectroscopia de Absorção de Raios X (NEXAFS) mostraram que o deutério liga-se ao grafeno sem orientação preferencial. / The present work studies the production and physical-chemical modifications of the graphene under thermal annealings. In a first study, the graphene synthesis by Chemical Vapor Deposition (CVD) on copper foils was investigated. We varied four parameters that influence the growth of graphene: methane flow (CH4), hydrogen flow (H2), growth time and copper purity. Using Raman spectroscopy and optical microscopy, we observed that lower flux of H2 and intermediate flux of CH4 leads to the growth of high quality graphene. In addition, we observed that 15 minutes growth of graphene is sufficient to cover the copper substrate. A higher copper purity allows the production of homogeneous graphene monolayers. In a second step, a study was carried out to understand the interaction of hydrogen with graphene monolayers. We used graphene samples deposited on SiO2 (285 nm)/Si films and annealed in a controlled atmosphere of deuterium (99.8%) at temperatures between 200 and 800 °C. We also investigated the hydrogen desorption of graphene using samples previously treated in deuterium at 600 °C and then annealed in a controlled atmosphere of nitrogen at temperatures between 200 and 800 °C. After the annealings, nuclear reaction analysis (NRA) was performed to quantify the deuterium, where we observed a large incorporation of deuterium in graphene above 400 °C, with a moderate increase up to 800 °C. We also observed that desorption of deuterium occurs only at 800 °C, although deuterium desorption from silicon oxide occurs at 600 °C. Raman spectroscopy was also performed after each annealing. The results show that defects in the structure of graphene have a large increase for deuterium incorporation. Analyzes carried out with X-ray Photoelectron Spectroscopy (XPS) showed that the deuterium incorporation at higher temperatures leads to graphene etching. Finally, characterizations using X-ray Absorption Spectroscopy (NEXAFS) showed that deuterium binds to graphene without preferential orientation.

"August 1999." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

This thesis describes studies of a two-dimensional (2D), hexagonal arrangement of carbon atoms, graphene. Because of graphene’s reduced dimensionality, the 2D material possesses many desirable mechanical and electrical properties compared to its three-dimensional (3D) counterpart, graphite. In fact, its mechanical strength and electrical mobility are one of the strongest and fastest in the world, prompting much excitements from science and engineering communities alike ever since its first experimental demonstration in 2004. The first part of this thesis deals with graphene in material level. Chapter 1 provides an introduction to graphene. Chapter 2 describes chemical vapor deposition (CVD) synthesis of graphene and various transfer techniques. Chapter 3 describes characterization of graphene using optical inspection, oxidation test, Raman spectroscopy, and electrical transport. The second part of this thesis concerns graphene in device level, electro-mechanical implementation in particular. Chapter 4 gives an introduction to graphene nano-electro- mechanical systems (GNEMS), where the material’s mechanical and electrical prowess can best be combined, and describes fabrication process as well as transduction mechanism. Chapter 5 shows how GNEMS can be used to build a pressure sensor or an accelerometer. Chapter 6 is a study of the graphene resonators for signal processing such as in RF filters or oscillators. Chapter 7 describes the graphene - silicon nitride heterostructure resonators. The third part of this thesis considers the integration of GNEMS at a system level. Chapter 8 depicts integration of graphene resonators onto a taped-out CMOS die using post-processing. This work, in conjunction with numerous other work done by fellow researchers in the field, tries to provide an overview - from the material synthesis to device fabrication and characterization, and further to system level integration - in utilizing graphene, and graphene NEMS in particular, for sensing and signal processing applications.

Electrical and optical properties of the (N,Ga)-doped ZnO films have been studied. Three growth regions were identified to obtain ZnO films with different conduction types depending on the N/Ga flux ratio in doping process. The PL spectra show evident competition between neutral-donor bound exciton (D0X) and neutral-acceptor bound exciton (A0X) according to the N/Ga ratio. From the temperature-dependent PL spectra, the nitrogen acceptor level was identified to be about 126 meV in (N,Ga)-doped p-type ZnO. / For nitrogen doping of ZnO thin films, DMHy was used as the nitrogen dopant source. A narrow temperature window from about 500°C to 550°C for efficient nitrogen doping was identified. However, p-type ZnO was not obtained by nitrogen mono-doping, which results from the low solubility of N and the self-compensating effect of native defects, and/or N-induced complexes. By co-doping N with Ga in proper ratios, p-type ZnO films were successfully achieved with a high hole concentration of 3.51 x 1017 --2.41 x 1018cm-3, Hall mobility of 1.1 --4.29 cm2/V-s and resistivity of 0.6 -- 16.2 O cm. But the conduction type critically depends on the growth conditions. Based on the successfully fabrication of (N,Ga)-doped p-type ZnO, a p-ZnO:(N,Ga)/n-ZnO homojunction was fabricated. The I-V measurement shows clear rectifying behavior with a turn-on voltage of about 3.7 V. / Further investigation of the effect of N/Ga doping ratios on the conduction type of ZnO samples reveals that successful doping depends much on engineering a stable local chemical bonding environment. Under mono-doping conditions (via N-Zn4), nitrogen solubility is limited and nitrogen acceptors are readily compensated by native donors and/or N-related donors; under appropriate N/Ga flux ratios, cluster-doping (via Ga-N3O and Ga-N4) can be realized to achieve p-type ZnO; while excessively high N/Ga ratios cause the doped ZnO n-type conductivity again, which may be because that under excessively high N/Ga ratio range, N-Zn4 configuration dominates and thus cause more N-related donors and degrade the ZnO film quality, similar as the mono-doping case. By tuning the N/Ga ratio in doping, it is expected to create appropriate chemical environments to enhance the formation of desired dopant species for stable p-type ZnO. / In this work, Metal-organic chemical vapour deposition (MOCVD) growth of ZnO and its p-type doping have been studied. The group V element N was used as primary dopant to make ZnO p-type. In the growth of ZnO by MOCVD, it was found that the structural and morphological properties of deposited ZnO strongly depend on growth conditions. Low VI/II ratio and high growth rate favor the growth of ZnO nanostructures (nanowires, nanobelts); while high VI/II ratio and low growth rate favor the growth of ZnO thin films. / The semiconductor ZnO is currently gaining intense interest in the research community because of its prospect in optoelectronic applications, such as blue/ultraviolet emitters and detectors, and high speed electronic devices. However, making reliable and reproducible p-type ZnO is still a bottleneck, which impedes the practical application of ZnO-based devices. The difficulty is mainly due to the self-compensation effect of native defects and the low solubility limit of acceptor dopants. Although substantial research is currently being carried out worldwide towards this goal, the effective p-type dopant and its doping process have not yet been identified. / Wang, Hui. / "Apr 2008." / Adviser: Aaron H. P. Ho. / Source: Dissertation Abstracts International, Volume: 70-03, Section: B, page: 1860. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Neste trabalho, foi realizado o crescimento de nanotubos de carbono pela técnica de deposição química a vapor (CVD) térmica catalítica, utilizando-se filmes finos de níquel como material catalisador, gás metano (CH4) como fonte de hidrocarboneto e nitrogênio (N2) como gás de arraste. Amostras processadas sobre filmes de Ni de 15 nm de espessura, depositados sobre substrato de óxido de silício (SiO2), com temperatura de processo de 900 ºC e tempo de 15 minutos promoveram uma maior densidade de síntese de nanotubos de carbono, utilizando-se um fluxo na proporção de 2 partes de N2 para 1 parte de CH4. Comprovou-se sua síntese através da visualização de sua morfologia por microscopia eletrônica de varredura (SEM) e microscopia eletrônica de transmissão (TEM), além da extração de seu espectro característico por espectroscopia Raman e espectroscopia de dispersão de raio-X (EDS). Em um segundo estudo, depositaram-se sobre substratos de vidro filmes transparentes e condutores (TCF) à base de nanotubos de carbono de paredes múltiplas (MWCNT) comerciais, pela técnica de dip coating. Para isso, realizou-se a dispersão dos nanotubos sob diversas concentrações em água deionizada (DI) com o auxílio do surfactante dodecil sulfato de sódio (SDS), com posterior funcionalização através do ataque químico por ácido nítrico (HNO3), visando sua aplicação na fabricação de células solares. Foram utilizados os equipamento de quatro pontas e curva corrente x tensão (IV) para caracterização elétrica, transmitância por espectrofotometria para caracterização óptica, SEM para a visualização de sua morfologia e espectroscopia Raman para a análise química de suas estruturas. Valores de resistência de folha de 2x105 W/ e transmitância de 65% foram obtidos nas amostras mais concentradas, com 0,2 mg de nanotubos por ml de água DI. Uma etapa de limpeza em água DI pós deposição foi feita para remoção do excesso de surfactante presente no filme, o que prejudica tanto as características elétricas e ópticas, por ser um dielétrico e não ser transparente. Essa limpeza melhorou o valor de transmitância, porém aumentou a resistência de folha, devido à remoção parcial dos nanotubos presentes no filme, interrompendo em certos pontos a malha que promovia a passagem de corrente elétrica. O ataque químico por HNO3 promoveu a criação de algumas quebras na estrutura do carbono, o que é verificado pelo aumento da banda D, característico da presença de defeitos. / In this work, the growth of CNTs was investigated, using chemical vapor deposition (CVD) thermal catalytic technique, carried out by utilizing thin films of nickel as catalyst material, methane (CH4) as hydrocarbon source and nitrogen (N2) as carrier gas. Samples processed onto 15 nm thick Ni films, deposited on silicon oxide (SiO2) substrates, at a temperature of 900 °C for 15 minutes, promoted a higher density of carbon nanotubes, using a gas mixture at the ratio of 2 parts of N2 and 1 part of CH4. This was verified by analysing the nanotubes morphology by scanning electron microscopy (SEM) and transmission electronic microscopy (TEM) and by the extraction of its characteristic spectrum by Raman spectroscopy and energy dispersive spectroscopy (EDS). In a second study, transparent conductive films (TCF) based on commercial multi-walled carbon nanotubes (MWCNT) were deposited on glass substrates by the dip coating technique. To do so, carbon nanotubes (CNTs) with different concentrations were dispersed in deionized water (DI) with the addition of the surfactant sodium dodecyl sulfate (SDS), and subsequent functionalization through chemical attack by nitric acid (HNO3), aiming their application in solar cell fabrication. The four point probe equipment and current x voltage curve (IV) was used for electrical characterization, transmittance for optical characterization, SEM to visualize their morphology and Raman spectroscopy for chemical analysis of their structures. Sheet resistance values of 2x105 W/ and transmittance of 65% were obtained in the most concentrated samples, with 0.2 mg per ml of nanotubes in deionized water (DI). A cleaning stage in DI water after deposition was taken for removal of surfactant excess in the film, which harms both the electrical and optical characteristics, as it is a dielectric and not transparent. This cleaning improved the transmittance value, but increased the sheet resistance due to partial removal of the nanotubes in the film, interrupting at certain points the mesh of CNTs that promoted the passage of electric current. The chemical attack by HNO3 promoted the functionalization by creating some breaks in the carbon structure, which is checked by the observation of the increasing in D band, which is characteristic of defects.

Ultramicroelectrodes (UMEs) (limiting dimensions <~25 μm) and nanoelectrodes (<~100 nm) exhibit enhanced electrochemical properties compared to macroscopic electrodes. Their small sizes and enhanced properties make them well-suited for various interesting and important applications such as measuring redox-active species in nonaqueous solvents, studying intermediates of fast electrochemical reactions, and investigating electrochemical and electrocatalytic properties of single nanoparticles. While UMEs are commercially available, nanoelectrode fabrication is still largely confined to research labs. Various methods for constructing nanoelectrodes have been reported and continue to be developed, but most require considerable expertise, and comparisons between different fabrication processes are lacking. In this work, a comparison of laser-assisted pulling and chemical vapor deposition (CVD) methods of electrode fabrication is made with the aim of optimizing production of carbon nanoelectrodes for single nanoparticle electrochemical measurements. By examining effects of pulling parameters, post-pulling treatments, and CVD processing, electrodes as small as ~50 nm were successfully produced.

Diamond is widely known for its extraordinary properties, such as high thermal conductivity, energy bandgap and high material hardness and durability making it a very attractive material for microelectronic and mechanical applications. Synthetic diamonds produced by chemical vapor deposition (CVD) methods retain most of the properties of natural diamond. Within this class of material, nanocrystalline diamond (NCD) is being developed for microelectronic and microelectromechanical systems (MEMS) applications. During this research, intrinsic and doped NCD films were grown by the microwave plasma enhanced chemical vapor deposition (MPECVD) method using CH4/Ar/H2 gas mixture and CH4/Ar/N2 gas chemistries respectively. The first part of research focused on the growth and characterization of NCD films while the second part on the application of NCD as a structural material in MEMS device fabrication. The growth processes were optimized by evaluating the structural, mechanical and electrical properties. The nature of chemical bonding, namely the ratio of sp²:sp³ carbon content was estimated by Raman spectroscopy and near edge x-ray absorption fine structure (NEXAFS) techniques. The micro-structural properties were studied by x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The mechanical properties of the pure NCD films were evaluated by nano-indentation. The electrical properties of the conductive films were studied by forming ohmic as well as schottky contacts. In second part of this study, both free-standing and membrane capped field emitter devices were fabricated by a silicon mold technique using nitrogen incorporated (i.e., doped) NCD films. The capped field emission devices act as a prototype vacuum microelectronic sensor. The field emission tests of both devices were conducted using a diode electrical device model. The turn-on field and the emission current of free-standing emitter devices was found to be approximately 0.8 V/µm and 20 µA, respectively, while the turn-on fields of capped devices increased by an order of magnitude. The emission current in the field emission sensor changed from 1 µA to 25 µA as the membrane was deflected from 280 µm to 50 µm from the emission tip, respectively.

Silicon Carbide has been a semiconductor material of interest as a high power and temperature replacement for Silicon (Si) in harsh environments due to the higher thermal conductivity and chemical stability of SiC. The cost, however, to produce this material is quite high. There are also defects in the substrate material (SiC) that penetrate into the active devices layers which are known device killers. Silicon is a material that provides a low cost substrate material for epitaxial growth and does not contain the defects that SiC substrates have. However, the large (~22%) lattice mismatch between Si and SiC creates dislocations at the SiC/Si interface and defects in the SiC epitaxial layer. These defects result in high leakage currents in 3C-SiC/Si devices. The main focus of the this research was to reduce or eliminate these defects using novel Si substrates. First a 3C-SiC on Si baseline process was developed under atmospheric pressure conditions consisting of 3 steps - an in-situ hydrogen etch to remove the native oxide, a carbonization step to convert the Si surface to SiC, and finally a growth step to thicken the SiC layer to the desired value. This process was then modified to establish a high-quality, low-pressure 3C-SiC CVD growth process. This LPCVD process was then used to grow 3C-SiC on numerous novel Si substrates, including porous Si, porous 3C-SiC "free-standing" substrates and SOI substrates which consisted on thin Si films bonded to poly-crystalline SiC plates. The results of these experiments are presented along with suggestions for future work so that device-grade films of 3C-SiC can be developed for various applications.

Metal oxide thin films are dynamic materials that have revolutionised the nature of semiconductor and electronic thin film devices. Recently, progress has stagnated in some aspects due to the increasingly complex deposition apparatus required, and the dearth of suitable precursor complexes of certain ???difficult??? metals. This thesis seeks to address both of these issues. The application of a precursor complex, Mg6(O2CNEt2)12 to the SSCVD of MgO thin films delivered the highest quality films ever reported with this technique. The resultant films were found to be of purely (111) orientation. Due to the nature of the precursor, the chemical reactions occurring at the surface during SSCVD growth result in a high growth rate, low flux environment and films of (111) orientation have been achieved without the amorphous underlayer. This finding has important implications for buffer layers in perovskite thin film devices. The unprecedented precursor chemistry has been used as a basis for the extremely high quality material produced, along with the unusual, yet beneficial structural morphology it possesses. A new range of barium complexes with single encapsulating ligands have been prepared for use in chemical vapour deposition (CVD) of BaTiO3 thin films. A novel pathway to an unprecedented class of barium carbamates is reported, and also new dianionic bis ??-ketoesterates and their barium, strontium, and calcium analogues were synthesised. High resolution mass spectrometry showed the barium bis ??-ketoesterate derivatives to be monomeric, and preliminary testing indicated some volatility in these species. Insights were gained into the likely successful pathways to building a volatile heterobimetallic precursor complex containing an alkaline earth metal. The knowledge of intimate mixing in heterobimetallic precursor complexes was extended by some novel chemistry to develop the first mixed Zn/Mg carbamato cluster complexes. These complexes were found to be excellent SSCVD precursors for ZnxMg1-xO thin films. Thin films were deposited with these precursors and exhibited a single preferred orientation, with a constant amount of magnesium throughout the bulk of the films. Investigation of the light emission properties of the films revealed significant improvements in the structural order commensurate with the incorporation of magnesium, and the formation of the ZnxMg1-xO alloy.