Dissertations / Theses on the topic 'Chemical vapour deposition (CVD)'

Chalcogenide glasses, especially sulphide glasses, are becoming more and more important for the fabrication of optoelectronic devices in part because of the high nonlinearity, strong photosensitivity and several other unique properties they have. Chalcogenide glasses are normally fabricated by a conventional melt-quenching method. The glasses are then further processed to form, for example, thin films, optical fibre and optoelectronic devices. /°C. The purity of germanium sulphide bulk glass bas been determined by a glow discharge mass spectrometry (GDMS) technique and an exceptionally low level of transition metal impurities in this glass have been achieved.

The chemical vapour deposition (CVD) of graphene is the most promising route for production of large-area graphene films. However there are still major challenges faced by the field, including control of the graphene coverage, quality, and the number of layers. These challenges can be overcome by developing a fundamental understanding of the graphene growth process. This thesis contributes to the growing body of work on graphene CVD by uniquely exploring the gas phase chemistry and fluid flow in the hot-wall graphene CVD reactor. Firstly the reported parameter space for the hot-wall CVD of graphene on copper was mapped, informing the subsequent work and providing a resource for the wider community. A CVD reactor was constructed to extend this parameter space to lower pressures using methane as a carbon source, and the films were categorised using scanning electron microscopy, Raman spectroscopy and optical dark field microscopy. The latter showed particular promise as a rapid and non-destructive characterization technique for identifying graphene films on the deposition substrate. The gas phase equilibrium compositions were calculated across the parameter space, and correlations between the stabilities of various chemical species and the types of deposition were drawn. This laid a foundation for the remainder of the experimental work, which explored the effect of diluent gases and different feedstocks on the growth to understand the importance of the identified correlations. Diluent gases (argon and nitrogen) were added to the experimental conditions and the thermodynamic model, and were found to reduce the degree of coverage of the graphene films. This result shows that the CVD of graphene is sensitive to factors other than the thermodynamic state parameters, such as the fluid flow profile in the reactor and inelastic collisions between the higher mass diluent gases and the methane/hydrogen/copper system. Using a nitrogen diluent raises the equilibrium carbon vapour pressure and seems to allow larger graphene grains to form. This suggests that thermodynamic factors can contribute to the nucleation of graphene films. Varying the hydrocarbon feedstock and the process conditions indicated that the structure of the deposited carbon is closely related to the nucleation kinetics. Three nucleation regimes are associated with different types of deposition: homogeneous nucleation with amorphous carbon or soot; uncatalysed nucleation with multilayer deposition; and nucleation processes controlled by the copper substrate withpredominantly monolayer deposition. Changing the feedstock from methane to acetylene resulted in poorer graphene coverage, showing that thermodynamic control does not apply in the portion of the parameter space at the high temperatures and lowpressures most successfully used for the deposition of continuous graphene monolayers.

Chemical Vapour Deposition (CVD) diamond detectors were modelled for dosimetry of radiotherapy beams. This was achieved by employing the EGSnrc Monte Carlo (MC) method to investigate certain properties of the detector, such as size, shape and electrode materials. Simulations were carried out for a broad 6 MV photon beam, and water phantoms with both uniform and non-uniform voxel dimensions. A number of critical MC parameters were investigated for the development of a model that can simulate very small voxels. For a given number of histories (100 million), combinations of the following parameters were analyzed: cross section data, boundary crossing algorithm and the HOWFARLESS option, with the rest of the transport parameters being kept at default values. The MC model obtained with the optimized parameters was successfully validated against published data for a 1.25 MeV photon beam and CVD diamond detector with silver/carbon/silver structure with thicknesses of 0.07/0.2/0.07 cm for the electrode/detector/electrode, respectively. The interface phenomena were investigated for a 6 MV beam by simulating different electrode materials: aluminium, silver, copper and gold for perpendicular and parallel detector orientation with regards to the beam. The smallest interface phenomena were observed for parallel detector orientation with electrodes made of the lowest atomic number material, which was aluminium. The simulated percentage depth dose and beam profiles were compared with experimental data. The best agreement between simulation and measurement was achieved for the detector in parallel orientation and aluminium electrodes, with differences of approximately 1%. In summary, investigations related to the CVD diamond detector modelling revealed that the EGSnrc MC code is suitable for simulation of small size detectors. The simulation results are in good agreement with experimental data and the model can now be used to assist with the design and construction of prototype diamond detectors for clinical dosimetry. Future work will include investigating the detector response for different energies, small field sizes, different orientations other than perpendicular and parallel to the beam, and the influence of each electrode on the absorbed dose.

In this thesis, a numerical and theoretical investigation of the Pulsed Pressure Chemical Vapour Deposition (PP-CVD) progress is presented. This process is a novel method for the deposition of thin films of materials from either liquid or gaseous precursors. PP-CVD operates in an unsteady manner whereby timed pulsed of the precursor are injected into a continuously evacuated reactor volume. A non-dimensional parameter indicating the extent of continuum breakdown under strong temporal gradients is developed. Experimental measurements, supplemented by basic continuum simulations, reveal that spatio-temporal breakdown of the continuum condition occurs within the reactor volume. This means that the use of continuum equation based solvers for modelling the flow field is inappropriate. In this thesis, appropriate methods are developed for modelling unsteady non-continuum flows, centred on the particle-based Direct Simulation Monte Carlo (DSMC) method. As a first step, a basic particle tracking method and single processor DSMC code are used to investigate the physical mechanisms for the high precursor conversion efficiency and deposition uniformity observed in experimental reactors. This investigation reveals that at soon after the completion of the PP-CVD injection phase, the precursor particles have an approximately uniform distribution within the reactor volume. The particles then simply diffuse to the substrate during the pump-down phase, during which the rate of diffusion greatly exceeds the rate at which particles can be removed from the reactor. Higher precursor conversion efficiency was found to correlate with smaller size carrier gas molecules and moderate reactor peak pressure. An unsteady sampling routine for a general parallel DSMC method called PDSC, allowing the simulation of time-dependent flow problems in the near continuum range, is then developed in detail. Nearest neighbour collision routines are also implemented and verified for this code. A post-processing procedure called DSMC Rapid Ensemble Averaging Method (DREAM) is developed to improve the statistical scatter in the results while minimising both memory and simulation time. This method builds an ensemble average of repeated runs over small number of sampling intervals prior to the sampling point of interest by restarting the flow using either xi a Maxwellian distribution based on macroscopic properties for near equilibrium flows (DREAM-I) or output instantaneous particle data obtained by the original unsteady sampling of PDSC for strongly non-equilibrium flows (DREAM-II). The method is validated by simulating shock tube flow and the development of simple Couette flow. Unsteady PDSC is found to accurately predict the flow field in both cases with significantly reduced run-times over single processor code and DREAM greatly reduces the statistical scatter in the results while maintaining accurate particle velocity distributions. Verification simulations are conducted involving the interaction of shocks over wedges and a benchmark study against other DSMC code is conducted. The unsteady PDSC routines are then used to simulate the PP-CVD injection phase. These simulations reveal the complex flow phenomena present during this stage. The initial expansion is highly unsteady; however a quasi-steady jet structure forms within the reactor after this initial stage. The simulations give additional evidence that the collapse of the jet at the end of the injection phase results in an approximately uniform distribution of precursor throughout the reactor volume. Advanced modelling methods and the future work required for development of the PP-CVD method are then proposed. These methods will allow all configurations of reactor to be modelled while reducing the computational expense of the simulations.

Silicon is widely used in optoelectronic devices, including solar cells. In recent years new forms of silicon have become available, including amorphous, microcrystalline and nano-crystalline material. These new forms have great promise for low cost, thin film solar cells and the purpose of this work is to investigate their preparation and properties with a view to their future use in solar cells. A Hot Wire-Deposition Chemical Vapour Deposition CVD (HW-CVD) system was constructed to create a multi-chamber high vacuum system in combination with an existing Plasma Enhanced Chemical Vapour Deposition (PECVD) system; to study the amorphous to crystalline transition in silicon thin films. As the two chambers were linked by a common airlock, it was essential to construct a transfer mechanism to allow the transfer of the sample holder between the two systems. This was accomplished by the incorporation of two gate valves between the two chambers and the common airlock as well as a rail system and a magnetic drive that were designed to support the weight of, and to guide the sample holder through the system. The effect of different deposition conditions on the properties and structure of the material deposited in the combined HW-CVD:PECVD system were investigated. The conditions needed to obtain a range of materials, including amorphous, nano- and microcrystalline silicon films were determined and then successfully replicated. The structure of each material was analysed using Transmission Electron Microscopy (TEM). The presence of crystallites in the material was confirmed and the structure of the material detected by TEM was compared to the results obtained by Raman spectroscopy. The Raman spectrum of each sample was decoupled into three components representing the amorphous, intermediate and crystalline phases. The Raman analysis revealed that the amorphous silicon thin film had a dominant amorphous phase with smaller contribution from the intermediate and crystalline phase. This result supported the findings of the TEM studies which showed some medium range order. Analysis of the Raman spectrum for samples deposited at increasing filament temperatures showed that the degree of order within the samples increased, with the evolution of the crystalline phase and decline of the amorphous phase. The Selected Area Diffraction (SAD) patterns obtained from the TEM were analysed to gain qualitative information regarding the change in crystallite size. These findings have been confirmed by the TEM micrograph measurements. The deposition regime where the transition from amorphous to microcrystalline silicon took place was examined by varying the deposition parameters of filament temperature, total pressure in the chamber, gas flow rate, deposition time and substrate temperature. The IR absorption spectrum for ƒÝc-Si showed the typical peaks at 2100cm-1 and 626cm-1, of the stretching and wagging modes, respectively. The increase in the crystallinity of the thin films was consistent with the evolution of the 2100cm-1 band in IR, and the decreasing hydrogen content, as well as the shift of the wagging mode to lower wavenumber. IR spectroscopy has proven to be a sensitive technique for detecting the crystalline phase in the deposited material. Several devices were also constructed by depositing the ƒÝc-Si thin films as the intrinsic layer in a solar cell, to obtain information on their characteristics. The p- layer (amorphous silicon) was deposited in the PECVD chamber, and the sample was then transferred under vacuum using the transport system to the HW-CVD chamber where the i-layer (microcrystalline silicon) was deposited. The sample holder was transferred back to the PECVD chamber where the n-layer (amorphous silicon) was deposited. The research presented in this thesis represents a preliminary investigation of the properties of ƒÝc-Si thin films. Once the properties and optimum deposition characteristics for thin films are established, this research can form the basis for the optimization of a solar cell consisting of the most efficient combination of amorphous, nano- and microcrystalline materials.

This thesis analyzes the chemical vapour deposition (CVD) growth of vertically aligned carbon nanotube (CNT) forests in order to understand how CNT forests grow, why they stop growing, and how to control the properties of the synthesized CNTs. In situ kinetics data of the growth of CNT forests are gathered by in situ optical microscopy. The overall morphology of the forests and the characteristics of the individual CNTs in the forests are investigated using scanning electron microscopy and Raman spectroscopy. The in situ data show that forest growth and termination are activated processes (with activation energies on the order of 1 eV), suggesting a possible chemical origin. The activation energy changes at a critical temperature for ethanol CVD (approximately 870°C). These activation energies and critical temperature are also seen in the temperature dependence of several important characteristics of the CNTs, including the defect density as determined by Raman spectroscopy. This observation is seen across several CVD processes and suggests a mechanism of defect healing. The CNT diameter also depends on the growth temperature. In this thesis, a thermodynamic model is proposed. This model predicts a temperature and pressure dependence of the CNT diameter from the thermodynamics of the synthesis reaction and the effect of strain on the enthalpy of formation of CNTs. The forest morphology suggests significant interaction between the constituent CNTs. These interactions may play a role in termination. The morphology, in particular a microscale rippling feature that is capable of diffracting light, suggest a non-uniform growth rate across the forest. A gas phase diffusion model predicts a non-uniform distribution of the source gas. This gas phase diffusion is suggested as a possible explanation for the non-uniform growth rate. The gas phase diffusion is important because growth by acetylene CVD is found to be very efficient (approximately 30% of the acetylene is converted to CNTs). It is seen that multiple mechanisms are active during CNT growth. The results of this thesis provide insight into both the basic understanding of the microscopic processes involved in CVD growth and how to control the properties of the synthesized CNTs.

This dissertation summarises the study of different aspects of the aerosol-assisted chemical vapour deposition (AACVD) technique for the production of multi-wall carbon nanotubes (MWCNTs). Upscaling the synthesis while retaining the quality of MWCNTs has been a prime objective throughout the work. A key aspect of this work was the study of different growth parameters and their influence on the homogeneity of the products across the reactor. The effect of the precursor composition on the yield and quality of MWCNTs were also investigated. It was shown that the synthesis rate can be significantly (60 – 80 %) increased by tuning the composition of the precursor. Moreover, by optimising the synthesis recipe and using a larger reactor, the synthesis rate and efficiency of the precursor were increased fivefold (up to 14 g/hr) and twice (up to 88 %) respectively. Large area (up to 90 cm²), mm-thick carpets of MWCNTs which were both free-standing and on substrate were produced. The carpets could withstand normal handlings without tearing apart, making them suitable for macroscopic characterisations and applications. By in-situ qualitative and quantitative gas analysis of the atmosphere of the reactor, the thermocatalytic cracking behaviour of 25 precursors was investigated and a mechanism for successive formation of different hydrocarbon fragments inside the reactor was proposed. A number of dedicated gas analysis methods and apparatuses such as a probe for zone-by-zone gas analysis of reactor and a heated chamber for preparation of standard gas analysis samples were developed to explore some of the least investigated aspects of the thermocatalytic cracking of precursors. Mapping the reactor revealed that some single-wall and double-wall carbon nanotubes (SWCNTs and DWCNTs) were also produced near the exhaust of the reactor. The SWCNTs were partly covered by fullerene-like species and resembled different forms of carbon nanobuds. In addition, the effect of the electron beam on the interaction of the SWCNTs and the fullerene-like species was studied in situ using high-resolution transmission electron microscopy (HRTEM).

The objective of this thesis is to develop an easy-to-use and computationally economical numerical tool to investigate the flow field in the Pulsed Pressure Chemical Vapour Deposition (PP-CVD) reactor. The PP-CVD process is a novel thin film deposition technique with some advantages over traditional CVD methods. The numerical modelling of the PP-CVD flow field is carried out using the Quiet Direct Simulation (QDS) method, which is a flux-based kinetic-theory approach. Two approaches are considered for the flux reconstruction, which are the true directional manner and the directional splitting method. Both the true directional and the directional decoupled QDS codes are validated against various numerical methods which include EFM, direct simulation, Riemann solver and the Godunov method. Both two dimensional and axisymmetric test problems are considered. Simulations are conducted to investigate the PP-CVD reactor flow field at 1 Pa and 1 kPa reactor base pressures. A droplet flash evaporation model is presented to model the evaporation and transport of the liquid droplets injected. The solution of the droplet flash evaporation model is used as the inlet conditions for the QDS gas phase solver. The droplet model is found to be able to provide pressure rise in the reactor at the predicted rate. A series of parametric studies are conducted for the PP-CVD process. The numerical study confirms the hypothesis that the flow field uniformity is insensitive to the reactor geometry. However, a sufficient distance from the injection inlet is required to allow the injected precursor solution to diffuse uniformly before reaching the substrate. It is also recommended that placement of the substrate at the reactor’s centre axis should be avoided.

Carbon nanotubes (CNTs) were successfully grown on the surface of carbon fibre reinforcements in carbon fibre architecture through in-situ catalytic chemical vapour deposition (CCVD). Success was also implemented on powders of oxides and non-oxides, including Y-TZP powder, ball milled alumina powder, alumina grits, silicon carbide powder. Preliminary results have been achieved to demonstrate the feasibility of making ceramic composites consisting of CNTs reinforcements.

Field-effect transistors (FET) based on graphene as channel has extraordinaryproperties in terms of charge mobility, charge carrier density etc. However, there aremany challenges to graphene based FET due to the fact graphene is a monolayer ofatoms in 2-dimentional space that is strongly influenced by the operating conditions.One issue is that the Dirac point, or K-point, shifts to higher gate voltage whengraphene is exposed to atmosphere. In this study graphene field-effect transistors(GFET) based on commercially available CVD graphene are electrically characterizedthrough field effect gated measurements. The Dirac point is initially unobservable andlocated at higher gate voltages (>+42 V), indicating high p-doping in graphene.Different treatments are tried to enhance the properties of GFET devices, such astransconductance, mobility and a decrease of the Dirac point to lower voltages, thatincludes current annealing, vacuum annealing, hot plate annealing, ionized water bathand UV-ozone cleaning. Vacuum annealing and annealing on a hot plate affect thegated response; they might have decreased the overall p-doping, but also introducedDirac points and non-linear features. These are thought to be explained by localp-doping of the graphene under the electrodes. Thus the Dirac point of CVDgraphene is still at higher gate voltages. Finally, the charge carrier mobility decreasedin all treatments except current – and hot plate annealing, and it is also observed that charge carrier mobilities after fabrication are lower than the manufacturer estimatesfor raw graphene on SiO2/Si substrate.

Boron carbide was produced on tungsten substrate in a dual impinging-jet CVD reactor from a gas mixture of BCl3, CH4, and H2. The experimental setup was designed to minimise the effect of mass transfer on reaction kinetics, which, together with the on-line analysis of the reactor effluent by FTIR, allowed a detailed kinetic investigation possible. The phase and morphology studies of the products were made by XPS, XRD,micro hardness and SEM methods. XPS analysis showed the existence of chemical states attributed to the boron carbide phase, together with the existence of oxy-boron carbide species. SEM pictures revealed the formation of 5-fold icosahedral boron carbide crystals up to 30 micron sizes for the samples produced at 1300oC. Microhardness tests showed change of boron carbide hardness with the temperature of tungsten substrate. The hardness values (Vickers Hardness) observed were between 3850 kg/mm2 and 4750 kg/mm2 corresponding to substrate temperatures of 1100 and 1300 C, respectively. The FTIR analysis of the reaction products proved the formation of reaction intermediate BHCl2, which is proposed to occur mainly in the gaseous boundary layer next to the substrate surface. The experimental parameters are the temperature of the substrate, and the molar fractions of methane and borontrichloride at the reactor inlet. The effects of those parameters on the reaction rates, conversions and selectivities were analysed and such analyses were used in mechanism determination studies. An Arrhenius type of a rate expression was obtained for rate of formation of boron carbide with an energy of activation 56.1 kjoule/mol and the exponents of methane and boron trichloride in the reaction rate expression were 0.64 and 0.34, respectively, implying complexity of reaction. In all of the experiments conducted, the rate of formation of boron carbide was less than that of dichloroborane. Among a large number of reaction mechanisms proposed only the ones considering the molecular adsorption of boron trichloride on the substrate surface and formation of dichloroborane in the gaseous phase gave reasonable fits to the experimental data. Multiple non-linear regression analysis was carried out to predict the deposition rate of boron carbide as well as formation rate of dichloroborane simultaneously.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 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 48-50).
Graphene has been regarded as a good candidate to make a breakthrough in various applications including electronics, sensors and spintronics due to its exceptional physical properties. To realize those practical applications, a high quality homogeneous wafer-scale graphene is required. Among various synthesis methods, chemical vapor deposition (CVD) has been a focus of attention as the most promising and cost-efficient deposition techniques, with advantages of its excellent repeatability and controllability, to produce large area graphene crystals on transition metal catalyst substrates. In particular, Cu with low carbon solid solubility is suitable to obtain uniform single layer deposition of graphene over large areas. Here, we report reliable method to grow high-quality continuous graphene film by CVD. Their surface properties and electrical transport characteristics are explored by several characterization techniques. In CVD process, furthermore, a subsequent transfer process to a substrate of interest is required for a wide variety of applications, especially in electronics and photonics, because the metal substrates necessary to catalyze the CVD graphene growth cannot be used. It is important not only to improve quality of as-grown graphene by optimizing growth system but also to develop transfer methods to prevent degradation in quality while transferring as-grown graphene to target substrates. In the case of wet transfer, surface tension of the liquid such as an etching agent or water contributes to make inevitable ripples, wrinkles and cracks. In this regard, we demonstrate new transfer methods by selecting a new polymeric support materials in order to reduce the number of winkles, defects and residues.
by Seong Soon Jo.
S.M.

Paramagnetic defects in free standing polycrystalline diamond films made by chemical vapour deposition (CVD) have been studied using electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and infrared absorption. EPR experiments at a range of frequencies (1-35 GHz) confirm the ¹H hyperfine parameters for the recently identified H1 defect (Zhou et al., Phys. Rev. B, 54:7881 (1996)). In the samples studied here, H1 is always accompanied by another defect at g=2.0028(1). Saturation recovery measurements are consistent with two defects centred on g=2.0028. The spin-lattice relaxation rate of H1 is a factor of 10-100 times more rapid than the single substitutional nitrogen centre (N⁰_S), which is known to be incorporated into the bulk diamond. ¹H matrix ENDOR measurements indicate that the H1 centre is in an environment with hydrogen atoms 2-10 A distant from the centre. The near neighbour hydrogen identified by the EPR was not detected in the ENDOR experiments. The concentration of H1 correlates with the total integrated C-H stretch absorption in the samples studied here. All the evidence is consistent with H1 being located at hydrogen decorated grain boundaries (or in intergranular material) rather than in the bulk diamond. The affect of annealing the films in vacuo up to 1900 K has been studied. On annealing at 1700 K it was found that some of the hydrogen on internal grain boundaries became mobile but was not lost from the sample, and the intensity of the EPR absorption at g=2.0028 decreased. Annealing at 1900 K severely degraded the optical properties of the samples, and a new defect with g=2.0035(2) was created. Infrared measurements show that hydrogen is lost from most CVD diamond samples when annealed to 1900 K for four hours. An EPR imaging (EPRI) probe was designed and built. This comprised a 3-loop, 2-gap loop-gap resonator and a pair of anti-Helmholtz coils providing a magnetic field gradient ∂B_z/∂z. Using this probe the distribution of N⁰_S was measured in the growth direction of four CVD diamonds to a resolution of 20 μm. The distribution of N⁰_S is shown to be different to the distribution of defects with g=2.0028. Two-dimensional images of the spin density of N⁰_S in single crystal type Ib diamonds made by the high temperature and pressure (HTP) method have been generated, demonstrating a resolution of 100 μm. A two-dimensional image of the spin density of g=2.0028 defects in a CVD sample is compared to a photograph of the same sample, showing the correlation between the distribution of the defects with the distribution of non-diamond material in the sample. The distribution of the [N-N]⁺ defect in a natural diamond has been examined using ∂B_z/∂B_ϰ field gradient coils.

Thesis (M.S.)--Southern Illinois University Carbondale, 2008.
"Department of Mechanical Engineering and Energy Processes." Includes bibliographical references (pages 117-119). Also available online.

ABSTRACT PRODUCTION OF CARBON NANOTUBES BY CHEMICAL VAPOR DEPOSITION Ayhan, Umut BariS M.S., Department of Chemical Engineering Supervisor: Prof. Dr. Gü
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z Co-Supervisor: Assoc. Prof. Dr. Burhanettin Ç
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ek July 2004, 75 pages Carbon nanotubes, which is one of the most attractive research subject for scientists, was synthesized by two different methods: Chemical vapor deposition (CVD), a known method for nanotube growth, and electron beam (e-beam), a new method which was used for the first time for the catalytic growth of carbon nanotubes. In both of the methods, iron catalyst coated silica substrates were used for the carbon nanotube growth, that were prepared by the Sol-Gel technique using aqueous solution of Iron (III) nitrate and tetraethoxysilane. The catalytic substrates were then calcined at 450 °
C under vacuum and iron was reduced at 500°
C under a flow of nitrogen and hydrogen. In CVD method the decomposition of acetylene gas was achieved at 600 °
C and 750 °
C and the carbon was deposited on the iron catalysts for nanotube growth. However, in e-beam method the decomposition of acetylene was achieved by applying pulsed high voltage on the gas and the carbon deposition on the silica substrate were done. The samples from both of the methods were characterized using transmission electron microscopy (TEM) and Raman spectroscopy techniques. TEM images and Raman spectra of the samples show that carbon nanotube growth has been achieved in both of the method. In TEM characterization, all nanotubes were found to be multi-walled carbon nanotubes (MWNT) and no single-walled carbon nanotubes (SWNT) were pictured. However, the Raman spectra show that there are also SWNTs in some of the samples.

A series of ruthenium complexes of the general type Ru(CO)2(P(n-Bu)3)2(O2CR)2 (4a, R = Me; 4b, R = Et; 4c, R = i-Pr; 4d, R = t-Bu; 4e, R = CH2OCH3; 4f, R = CF3; 4g, R = CF2CF3) was synthesized by a single-step reaction of Ru3(CO)12 with P(n-Bu)3 and the respective carboxylic acid. The molecular structures of 4b, 4c and 4e–g in the solid state are discussed. All ruthenium complexes are stable against air and moisture and possess low melting points. The physical properties including the vapor pressure can be adjusted by modification of the carboxylate ligands. The chemical vapor deposition of ruthenium precursors 4a–f was carried out in a vertical cold-wall CVD reactor at substrate temperatures between 350 and 400 °C in a nitrogen atmosphere. These experiments show that all precursors are well suited for the deposition of phosphorus-doped ruthenium layers without addition of any reactive gas or an additional phosphorus source. In the films, phosphorus contents between 11 and 16 mol% were determined by XPS analysis. The obtained layers possess thicknesses between 25 and 65 nm and are highly conformal and dense as proven by SEM and AFM studies
Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Diamond is an important material in many industrial applications (e.g., machining of hard materials, bio-electronics, optics, electronics, etc.) because of its exceptional properties such as hardness, tolerance to aggressive environments, compatibility with human tissues, and high carrier mobility. However, a highly controlled method for growing artificial high-purity diamond on a range of different substrates is needed to exploit these exceptional properties. The Chemical Vapour Deposition (CVD) method is a useful tool for this purpose, but the process still needs to be developed further to achieve better control of growth. In this context, the introduction of dopant species into the gas phase has been shown to strongly influence growth rate and surface morphology. Density Functional Theory (DFT) methods are used to deepen our atomic-level understanding of the effect of dopants on the mechanism for CVD growth on diamond. More specifically, the effect of four dopants (N, P, B and S) has been studied on the important reaction steps in the growth mechanism of diamond. Substitution of N into the diamond lattice has generally been found to disfavour critical reaction steps in the growth of the 100-face in diamond. This negative effect has been related to electron transfer from the N dopant into an empty surface state, e.g., a surface carbon radical. In addition, strong surface stabilization is observed for N substitution in certain sites via a beta-scission reconstruction, with the formation of sp2 carbon. These observations correlate well with observed surface degradation and decrease in growth rate when a high concentration of nitrogen gas is introduced into the CVD growth process. The effect of co-adsorbed P, S and B onto the diamond surface has also been investigated for two reaction steps: CH3 adsorption and H abstraction. While P and B are observed to influence these reaction steps, the effect of S is rather limited.

This diploma thesis is mainly focused on the fabrication of graphene layers on the copper foil by the Chemical Vapor Deposition (CVD). For this purpose the high-temperature chamber for the production of the graphene was completed and fully automated. The production of the high area graphene on the copper foil was experimentally achieved. The Raman microscopy and X-ray photoelectron spectroscopy measurements proved that the produced graphene is mostly a monolayer. Graphene layer was transferred on non-conductive substrate.

Carbon nanotubes present enormous potential for future nanoelectronic applications. This study details one method for producing such nanotubes via chemical vapor deposition (CVD) of methane gas at high temperatures. This method represents the best known way to selectively place nanotubes, as will be needed for complex electronic structures. Various growth conditions are manipulated and the effects on the resulting nanotubes are recorded.

En esta tesis doctoral, se ha investigado y desarrollado un nuevo método de CVD asistido por aerosol (AACVD), que permite el crecimiento de nanoestructuras de WO3 intrínsecas y funcionalizadas con Au. Así mismo se han depositado capas policristalinas de SnO2 para aplicaciones de detección de gases. La síntesis de materiales nanoestructurados, la fabricación de dispositivos y sus propiedades de detección de gases, han sido estudiadas. El método AACVD fue utilizado para la síntesis y la deposición directa de capas activas encima de sustratos de alúmina y también sobre substratos micromecanizados (microhotplates), lo que demuestra la compatibilidad entre la tecnología de silicio y la deposición de la capas activas nanoestructuradas. En la tesis se ha demostrado que las capas nanoestructuradas de WO3 funcionalizadas con oro tienen una sensibilidad mejor que las intrínsecas frente a algunos gases relevantes y al mismo tiempo se ha producido un cambio de selectividad.
In this doctoral thesis, it has been investigated and developed the Aerosol Assisted Chemical Vapour Deposition (AACVD) method for direct in-situ growth of intrinsic and Au-functionalised nanostructured WO3, as well as SnO2-based devices for gas sensing applications. The nanostructured material synthesis, device fabrication and their gas sensing properties have been studied. AACVD method was used for synthesis and direct deposition of sensing films onto classical alumina and microhotplate gas sensor substrates, demonstrating the compatibility between the microhotplate fabrication process and the sensing nanostructured layer deposition. The effect of Au nanoparticles on the gas sensor’s response was measured and presented in this thesis. The test results revealed that the addition of Au nanoparticles to the WO3 nanoneedles has increased the sensor’s response towards the tested gases (i.e. EtOH). It was therefore demonstrated that the Au-functionalisation has an enhancing effect on the gas sensing properties of WO3 nanoneedles

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006.
Lackey, W. Jack, Committee Chair ; Cochran, Joe K., Committee Member ; Danyluk, Steven, Committee Member ; Fedorov, Andrei G., Committee Member ; Rosen, David W., Committee Member ; Wang, Zhonglin, Committee Member.

This thesis details an investigation of the suitability of commercially-available single crystal and polycrystalline diamond films made via chemical vapor deposition (CVD) that were not studied previously for use in radiotherapy dosimetry. Novel sandwich-type detectors were designed and constructed to investigate the dosimetric response of diamond films under clinical conditions. Relatively inexpensive diamond films were obtained from three manufacturers: Diamonex, Diamond Materials GmbH and Element Six. Spectrophotometry, Raman spectroscopy and bulk conductivity studies were used to characterize these films and correlate crystalline quality with detector performance. Novel detectors were designed and constructed to investigate detectors under clinical conditions, including Perspex encapsulations and PCBs to minimize fluence perturbations. The dosimetric response of these diamond detectors was examined using a 6 MV beam from a Varian Clinac 600C linear accelerator. Diamond detectors were evaluated by measuring a number of response characteristics. Polycrystalline CVD diamond films from Diamonex (100, 200, 400-μm thicknesses) were considered unsuitable for dosimetric applications due to their lack of stability, low sensitivity, high leakage currents, high priming dose and dependence on dose rate. High-quality polycrystalline diamond films from Diamond Materials (100, 200, 400-μm thicknesses) displayed characteristics that varied with film thickness. A 100-μm film featured slow response dynamics and high priming doses. Thicker films featured suitable dosimetric characteristics, e.g. negligible leakage currents, low priming doses, fast response dynamics and good sensitivity with small sensitive volumes. Element Six single crystal CVD diamond films (500-μm thicknesses) with small sensitive volumes (0.39 mm³) exhibited suitable characteristics for dosimetry. These films showed negligible leakage currents (< 1.25 pA), low priming doses (1–10 Gy), quick response dynamics, high sensitivity (47–230 nC Gy⁻¹) and were weakly dependent on dose rate and directional dependence (±1%). A relatively inexpensive single crystal CVD diamond film from Element Six that exhibited high sensitivity (230 nC Gy⁻¹ at 0.5 V μm⁻¹), amongst other favourable characteristics, was selected for further analyses. An appropriate operating voltage was determined before further clinically relevant measurements could be conducted. This included how changes in an applied electric field affected detector response, and determined whether an optimal operating voltage could be realized within the parameters of conventional instrumentation used in radiation therapy. The results of this study indicated a preference towards using 62.5 V (at ~0.13 V μm⁻¹) out of a range of 30.8–248.0 V for temporal response as required for modulated beams due to its minimal rise time (2 s) and fall time (2 s) yet sufficient sensitivity (37 nC Gy⁻¹) and weak dependence on polarity (±1.5%). Investigations were then performed on the same diamond detector to evaluate its performance under more clinically relevant conditions. Repeatability experiments revealed a temporary loss in sensitivity due to charge detrapping effects following irradiation, which was modelled to make corrections that improved short-term precision. It was shown that this detector could statistically distinguish between dose values separated by a single Monitor Unit, which corresponded to 0.77 cGy. Dose rate dependence was observed when using low, fixed doses in contrast to using stabilized currents and higher doses. Depth dose measurements using this detector compared well with ion chambers and diode dosimeters. Comparisons of initial measurements with values in the literature indicate encouraging results for fields sizes < 4 x 4 cm², but further measurements and comparisons with Monte Carlo calculations are required. Using this detector to make off-axis measurements in the edge-on orientation reduced perturbation of the beam due to its sandwich configuration and thin 150 nm Ag contacts. This diamond detector was found to be suitable for routine dosimetry with conventional radiotherapy instrumentation with a materials cost of < NZ$200.

Thesis (M.S.)--Southern Illinois University Carbondale, 2005.
"Department of Mechanical Engineering and Energy Processes." Includes bibliographical references (leaves 51-53). Also available online.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.
Includes bibliographical references (p. 179-181).
A systematic investigation of the microstructure produced in ion-induced chemical vapor deposition (11-CVD) of copper from copper(I)hexafluoroacetylacetonatevinyltrimethylsilane (Cu(I)hfacVTMS) gas precursor is reported. II-CVD involves the ion-driven decomposition of Cu(l)hfacVTMS and subsequent deposition of copper films at ambient temperature. The thin films were grown with the aid of a broad beam Kaufman source in a "multibeam apparatus", which allowed monitoring of experimental conditions - growth rate, temperature, ion beam flux, ion beam energy and gas precursor flux. Deposition temperatures ranged from room temperature to 100⁰C. The desirable operation range is the "ion-flux-limited regime", in which sufficient precursor flux allows the growth rate to scale with the ion flux. Plan-view TEM and cross-sectional TEM (XTEM) show that the film develops a characteristic cellular microstructure of continuous crystalline copper columns (15 nm diameter) surrounded by an amorphous phase containing both carbon impurity and copper. The column diameter increases with temperature but is not affected by the growth rate for temperatures up to 60⁰C. At higher temperatures, the growth mechanism is not purely ion driven due to the onset of thermal CVD. However, quantitative XPS (x-ray photoelectron spectroscopy) shows that the film purity not only increases with substrate temperature, but also increases with decreasing growth rate due to the kinetics of byproduct desorption. STEM-EDS (scanning transmission electron microscopy - energy dispersive x-ray spectroscopy) shows that the intercolumnar spaces contain more copper at lower growth rates for a given substrate temperature. Hydrogen-atom-assisted II-CVD effectively removed all carbonaceous impurity to within the detection limit of XPS. The cellular microstructure is not observed in these films; however, deposition at 100⁰C produces films that still retain a columnar structure even though the atomic fraction of carbon is only [approximately] 0.5%. This high temperature growth process has a mixed mechanism where the ion beam flux also enhances the kinetics of the thermal CVD process. The microstructure evolution is modeled as a cellular growth process that is controlled by surface transport of carbon impurity. The cellular mechanism is corroborated by the sharp transitions
(cont.) observed in XTEM for a change in deposition conditions. The surface diffusion is not only a function of temperature but also the ion flux. This explains why the column diameter remains independent of growth rate at constant temperature. The model assumes an approximately linear dependence of the diffusion constant's pre-exponential factor with ion the flux. The model predicts column diameters that are in good agreement with experimental data. The model was designed to integrate with Chiang's kinetic model to provide a foundation for depositing controlled microstructures using I-CVD. The work presented here demonstrates the possibility of growing controlled nano-cellular microstructures using a low voltage broad ion beam at or near ambient temperature. Films with such nano-cellular structures are expected to have highly anisotropic properties that could be used in a variety of applications, including magnetics ...
by Francis L. Ross, III.
Ph.D.

Hot-wire chemical vapour deposition (HWCVD) is a promising technique that permits polycrystalline silicon films with grain size of nanometers to be obtained at high deposition rates and low substrate temperatures. This material is expected to have better electronic properties than the commonly used amorphous hydrogenated silicon (a-Si:H).

In this work, thin-film transistors (TFTs) were fabricated using nanocrystalline hydrogenated silicon film (nc-Si:H), deposited by HWCVD over thermally oxidized silicon wafer. The employed substrate temperature during the deposition process permits inexpensive materials as glasses or plastics to be used for various applications in large-area electronics. The deposition rate was about one order of magnitude higher than in other conventionally employed techniques. The deposited nc-Si:H films show good uniformity and reproducibility. The films consist of vertically grown columnar grains surrounded by amorphous phase. The columnar grains are thinner at the bottom (near the oxide interface) and thicker at the top of the film. Chromium layer was evaporated over the nc-Si:H in order to form drain and source contacts. Using photolithography techniques, two types of samples were fabricated. The first type (simplified) was with the chromium contacts directly deposited over the intrinsic nc-Si:H layer. No dry etching was involved in the fabrication process of this sample. The transistors on the wafer were not electrically separated from each other. Doped n+ layer was incorporated at the drain and source contacts in the second type of samples (complete samples). Dry etching was employed to eliminate the nc-Si:H between the TFTs and to isolate them electrically from each other.

The electrical characteristics of both types of nc-Si:H TFTs were similar to a-Si:H based TFTs. Nevertheless, some significant differences were observed in the characteristics of the two types of samples. The increasing of the off-current in the simplified structure was eliminated by the n+ layer in the second type of samples. This led to the improving of the on/off ratio. The n+ layer also eliminated current crowding of the output characteristics. On the other hand, the subthreshold slope, the threshold voltage and the density of states were slightly deteriorated in the samples with incorporated n+ layer. Surface states created by the dry etching could be a possible reason. Other cause could be a bad quality of the nc-Si:H/SiO2 interface. The TFTs with incorporated n+ contact layer and electrically separated on the wafer were used in the further studies of stability and device modelling.

The nc-Si:H TFTs were submitted under prolonged positive and negative gate bias stress in order to study their stability. We studied the influence of the stressing time and voltage on the transfer characteristics, threshold voltage, activation energy and density of states. The threshold voltage increased under positive gate bias stress and decreased under negative gate bias stress. After both positive and negative stresses, the threshold voltage recovered its initial values without annealing. This behaviour indicated that temporary charge trapping in the channel/gate insulator interface is the responsible process for the device performance under stress. Measurements of space-charge limited current confirmed that bulk states were not affected by the positive nor by negative stress.
Analysis of the activation energy and the density of states gave more detailed information about the physical processes taking place during the stress. Typical drawback of the nc-Si:H films grown by HWCVD with tungsten (W) filament is the bad quality of the bottom, initially grown, interfacial layer. It is normally amorphous and porous. We assume that this property of the nc-Si:H film is determining for charge trapping and the consecutive temporary changes of the TFT's characteristics. On the other hand, the absence of defect-state creation during the gate bias stress demonstrates that the nc-Si:H films did not suffer degradation under the applied stress conditions.

The electrical characteristics and the operational regimes of the nc-Si:H TFTs were studied in details in order to obtain the best possible fit using the Spice models for a-Si:H and poly-Si TFTs existing until now. The analysis of the transconductance gm showed behaviour typical for a-Si:H TFTs at low gate voltages. In contrast, at high gate voltages unexpected increasing of gm was observed, as in poly-Si TFTs. Therefore, it was impossible to fit the transfer and output characteristics with the a-Si:H TFT model neither with poly-Si TFT model.
We performed numerical simulations using the Silvaco's Atlas simulator of semiconductor devices in order to understand the physical parameters, responsible for the device behaviour. The simulations showed that the reason for this behaviour is the density of acceptor-like states, which situates the properties of nc-Si:H TFTs between the amorphous and the polycrystalline transistors. Taking into account this result, we performed analysis of the concentrations of the free and the trapped carriers in nc-Si:H layer. It was found that nc-Si:H operates in transitional regime between above-threshold and crystalline-like regimes. This transitional regime was predicted earlier, but not experimentally observed until now. Finally, we introduced new equations and three new parameters into the existing a-Si TFTs model in order to account for the transitional regime. The new proposed model permits the shapes of the transconductance, the transfer and the output characteristics to be modelled accurately.

Graphene receives enormous attention owing to its distinctive physical and chemical prosperities. Growing and transferring graphene to different substrates have been investigated. The graphene growing on the copper substrate has an advantage of low solubility of carbon on the copper which allow us to grow mostly monolayer graphene. Graphene sheet of few centimeters can be transferred to 300nm silicon oxide and quartz crystal pre-deposited with metal like Cu and Ru. Characterization of the graphene has been done with Raman and contact angle measurement and recently quartz crystal microbalance (QCM) has been employed. The underpotential deposition (UPD) process of Bi on Ru metal surface is studied using electrochemical quartz crystal microbalance (EQCM) and XPS techniques. Both Bi UPD and Bi bulk deposition are clearly observed on Ru in 1mM Bi (NO3)3/0.5M H2SO4. Bi monolayer coverage calculated from mass (MLMass) and from charge (MLCharge) were compared with respect to the potential scanning rates, anions and ambient controls. EQCM results indicate that Bi UPD on Ru is mostly scan rate independent but exhibits interesting difference at the slower scan. Bi UPD monolayer coverage calculated from cathodic frequency change (ΔfCathodic) is significantly smaller than the monolayer coverage derived from integrated charge under the cathodic Bi UPD peak when scan rate is at least 5 mV/s. XPS is utilized to explore the detailed chemical composition of the observed interfacial process of Bi UPD on Ru.

Orientador: Abner de Siervo
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-31T16:48:10Z (GMT). No. of bitstreams: 1 Ferreira_RodrigoCezardeCampos_M.pdf: 12900994 bytes, checksum: 7f4ff602b7e6aae7e2d8890e9f8d0a2b (MD5) Previous issue date: 2016
Resumo: O grafeno é um alótropo bidimensional do carbono com hibridização do tipo sp2. Suas notáveis propriedades eletrônicas e estruturais provocaram um enorme interesse científico e tecnológico para o material na última década. Grafeno pode ser crescido em certos metais de transição através da técnica bem conhecida Chemical Vapor Deposition (CVD). A estabilidade do grafeno nesses substratos é garantida, porém as interações químicas entre eles modificam suas exóticas propriedades eletrônicas e estruturais. É possível sintetizar grafeno sobre Ir(111) sem defeitos estruturais substanciais e em um único domínio, quando realizado sob condições específicas de temperatura do substrato e da pressão do gás precursor (propileno). Na tentativa de isolar o grafeno do substrato, seja fisicamente ou eletricamente, existe a possibilidade da intercalação de diversas espécies, tais como gases, metais ou nanopartículas. Realizando tal procedimento, além da suspensão do material, é possível também dopar a banda eletrônica ou induzir abertura de gap. Neste contexto, o objetivo deste trabalho é estudar a dinâmica de crescimento e intercalação do ferro em Gr/Ir(111), seguindo os parâmetros termodinâmicos envolvidos e observando principalmente os deslocamentos químicos usando espectroscopia de fotoelétrons de raio-x (XPS) de alta resolução com síncrotron. Em paralelo, também usamos o microscópio de varredura por tunelamento (STM) para acompanhar a formação e intercalação das estruturas na superfície durante os ciclos de evaporação do ferro. Os resultados mostraram que, com o substrato à temperatura ambiente, o Fe interage fortemente com o grafeno e ocorre intercalação parcial. No caso de evaporação à temperaturas moderadas, houve intercalação total do Fe que permaneceu protegido pela folha de grafeno, indicando ser possível crescer um filme fino intercalado na superfície
Abstract: Graphene is a 2D carbon allotrope having sp2 hybridized atoms in a single-layer. Its remarkable electronic and structural properties attract an enormous scientific and technological interest to the material in the last decade. Graphene can be grown on certain transition metals by the well-known Chemical Vapor Deposition (CVD) technique. The stability of graphene in these substrates is guaranteed, but the chemical interactions between them modify its exotic electronic and structural properties. It is possible to grow graphene on the Ir(111) surface without substantial structural defects and withsingle domain, whenspecific conditions of substrate temperature and pressure of the precursor gas (propylene) are applied. While trying to retrieve the characteristic properties, the scientific community has been trying to isolate graphene from the metallic substrate, either physically or electrically, by intercalation of various species such as gases, metals or nanoparticles. By performing such procedures, it is possible, besides the desired suspension of the material, to induce changes such as gap opening and doping of the electronic band structures. In this context, the aim of this work is to study the dynamics of iron growth and intercalation in Gr/Ir(111), following the thermodynamic parameters involved and observing mainly the chemical shifts using high resolution x-ray photoelectron spectroscopy (XPS). In parallel, we also used the scanning tunneling microscope (STM) to follow the formation of Fe surface structures during the evaporation cycles and intercalation. The results show that at room temperature, Fe interacts strongly with graphene with partial intercalation. In the case of evaporation at moderate temperatures, there was full intercalation of Fe which remained protected by the graphene sheet
Mestrado
Física
Mestre em Física
1423605/2014
CAPES

Thesis (Ph.D.)--University of Cincinnati, 2008.
Committee/Advisors: Raj N. Singh PhD (Committee Chair), Relva C. Buchanan PhD (Committee Member), Rodney Roseman PhD (Committee Member), Donglu Shi PhD (Committee Member). Title from electronic thesis title page (viewed Sep.3, 2008). Keywords: Boron nitride nanotube (BNNT); boron nanowire (BNW); chemical vapor deposition (CVD). Includes abstract. Includes bibliographical references.

This work uses a modification of the chemical vapor deposition (CVD) technique to study the effects of source gas flow geometry (and the corresponding parameters) on carbon nanotube growth. Our approach is to flow the carbon-containing source gas through a nozzle, projecting the gas stream onto targeted regions of the substrate. This technique not only allows the potential for localized nanotube growth, but also offers an interesting opportunity to provide an experimental test of theoretical nanotube growth models.

Doutoramento em Nanociências e Nanotecnologia
The present work is aimed to provide description of experimental part of graphene and two-dimensional structures. State-of-the-art techniques employing chemical vapor deposition (CVD) were used to deposit graphene and two-dimensional structures for their multidisciplinary applications including nano-electronics and semi-conducting industries. All the problems, suggestions and other important issues related to the growth and parameterizing the optimum condition for strictly monolayer to few layers have been briefly discussed. This may give double benefits such as realizing 2D electronic devices with high carrier motilities and understanding the behaviour of these 2D materials upon small ion intercalation. The as synthesized graphene grown on copper (Cu) substrate showed the ideal Raman spectrum with least defect concentration. The presence of very small D peaks confirmed the high quality of graphene crystals with strictly monolayer to few layers. Moreover, High Resolution X-rays Spectroscopy (HR-XPS) analysis showed the high quality graphene with C 1s in sp2 configuration (with binding energy at ~284.8 eV). The absence of other components resembled the purity of graphene and again reconfirmed the good quality of synthesized graphene. The Raman image mapping, demonstrated the full coverage of large area graphene on copper substrate. Additionally, the High Resolution Transmission Electron Microscopy (HRTEM) results reconfirmed that the high crystalline nature with two-type of rotational planes, which may attributed to the presence of wrinkles formed during the transfer of graphene sheet on TEM grids. This thesis is also devoted to the heteroatom doping in order to tune the electronic properties of graphene. Ammonia (NH3) was used herein to provide nitrogen (N) as a source for foreign atom for the doping of pure graphene. Here again, efforts were made to discuss all the problems, suggestions and other important issues related to growth and parameterizing the optimum conditions for in-situ ammonia doping of graphene on Cu. The substrate (thickness of films) playing role in the defect creations was also discussed. Raman results showed the enhanced D and D’ peaks, which confirmed the doping of graphene by NH3. HRXPS showed the C 1s core level centred at a BE of 284.5 eV, ascribed to C sp2 can be co-related with the good quality of C. Thus, in context with the XPS, the graphene grown on 20 µm Cu substrate showed the better nitrogen intercalation in the graphene sheets under the same growing conditions. Two components (substitutional at BE of 401.7 eV and pyridinic at BE of 398.5 eV) were clearly distinguished in the respective N 1s core level. The doping with substitutional type of configuration, involves three nitrogen valence electron forming three σ– bonds, one electron filling the π–states, and the fifth electron entering the π*–states of the conduction band, and altogether provide a strong doping effect. The presented work also reported a study demonstrating an in-situ method for the quantitative characterization of nanoscale electrostatic properties of as-grown multilayer-graphene (MLG) sheets on nickel (Ni) by combining atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). Large area epitaxial MLG sheets were grown on Ni by using CVD technique. The high crystalline nature of MLG sheets on Ni was confirmed by Raman spectroscopy with the FWHM value as low as ~20 cm-1 for G peak. We performed the charge injection (and subsequent charge diffusion over time) on the as synthesized graphene on Ni. The results unveiled that: (i) MLG surface can be either positively or negatively charged through injection process using Pt coated Si-based AFM probes; (ii) the charges can be accumulated and eventually reached to saturated concentrations of (+4.45±0.1) μC/m2 and (−1.3±0.1) μC/m2 , respectively; and (iii) the charge diffusion coefficients on graphene surface were measured to be (1.50±0.05) × 10−16 m2 /s and (0.64±0.05) × 10−16 m2 /s for the positive and the negative charges, respectively. The concerned experiment related to the discovery of charge injection in MLG may pave the way for designing a new class of energy harvesting devices. In addition to this, study also demonstrated a technique for nano-patterning/charge lithography of surface charges by contact electrification, which could be a promising application to create charged nanostructures for next generation graphene based nano-electronic devices. A brief description on the quality of transferred substrate has also been noted. Various substrates such as SiO2/Si and Au substrate have been used. A relative quality comparison between before and after transfer of graphene has been critically described. Results from HRXPS show the iron monolayer interaction with graphene. Lastly, this research also showed the major parameterizing and synthesizing steps, and the work flow for the high quality TMDs materials (such as MoS2) by modifying the current CVD equipment. A thorough review of the fundamental properties as well as methods of synthesis, properties and problems related to the growth of 2D materials was also highlighted. The effect of pressure and other conditions for the growth of high quality were fully described. This study found 50mbar as an optimum pressure for the growth of large area MoS2 having a direct bandgap of 1.6eV. Micro-Raman results clearly showed distinguish E1 2g and A1 g peaks and HRXPS re-confirmed its high quality by the different Mo and S core-level peaks. Additionally, employing Focused ion beam equipped with SEM (scanning electron microscopy) technique (FIB), the present study prepared platinum (Pt) electrodes required for the electrical measurements. The result showed: (i) the ohmic and semi-conducting behavior of the crystals; (ii) the importance of high-quality singlelayer (SL) MoS2 in the semi-conducting industries; and (iii) the potential of high quality SL MoS2 for replacing graphene in near future.
O presente trabalho, tem com objetivo promover a descrição da parte experimental da síntese de grafeno e de estruturas bidimensionais (2D). Foram usadas as técnicas já existentes, que aplicam deposição química na fase de vapor (CVD), para a síntese de grafeno e estruturas bidimensionais com aplicações multidisciplinares, como indústrias de nano-eletrónicos e de semicondutores. Todos os problemas, sugestões e questões importantes relacionados com o crescimento e parametrização da condição ótima para formação de estritamente monocamadas a pequenas camadas foram brevemente discutidas. Isto pode trazer benefícios duplos como a produção de dispositivos eletrónicos 2D com altas motilidades de transporte e o entendimento do comportamento dos materiais 2D sujeitos a intercalação iónica. Os grafenos sintetizados no substrato cobre (Cu) apresentaram um espectro ideal de Raman com uma concentração de defeitos menor. A presença de pequenos picos D confirmou a elevada qualidade dos cristais de grafeno com estritamente monocamadas a pequenas cadeias. Além disso, a espectroscopia de Raios-X de alta resolução (HR-XPS) mostrou o grafeno de elevada qualidade com C 1s em configuração sp2 (com energia de ligação a ~284.8 eV). A ausência de outros componentes reforça a pureza e a qualidade do grafeno sintetizado. As imagens de mapping Raman demonstraram a cobertura total do grafeno de elevada área no substrato cobre. Adicionalmente, os resultados de microscopia de transmissão eletrónica de alta resolução (HRTEM) confirmaram a elevada natureza cristalina com dois tipos de planos rotacionais que podem ser atribuídos à presença de rugas durante a transferência de folhas de grafeno nas grelhas de TEM. Esta tese dedica-se também à dopagem heteroatómica do grafeno com o objetivo de alterar as suas propriedades eletrónicas. A amónia (NH3) foi usada como fonte de azoto (N) como átomo externo para a dopagem do grafeno puro. Mais uma vez, foram feitos esforços para discutir todos os problemas, sugestões e outras questões importantes relacionadas com o crescimento e parametrização das condições ótimas para a dopagem in-situ de amónia do grafeno no cobre. O papel do substrato (espessura do filme) na criação de defeitos foi também discutida. Os resultados de Raman mostram o aumento dos picos D e D’, o que confirma a dopagem do grafeno por NH3. Os dados de HRXPS mostraram o pico C 1s centrado a uma energia de ligação (BE) de 284.5 eV, atribuído ao C sp2 que pode ser correlacionado com a boa qualidade do C. Então, de acordo com o XPS, o grafeno que cresceu no substrato Cu 20 µm apresentou uma melhor intercalação do azoto nas folhas de grafeno sob as mesmas condições de crescimento. As duas componentes (substitucional a BE de 401.7 eV e piridínica de 398.5 eV) foram claramente distinguidas no respetivo pico N 1s. A dopagem com o tipo de configuração substitucional envolve três eletrões de valência do nitrogénio formando três ligações σ, um eletrão a preencher os estados π e o quinto eletrão no estado π* da banda de condução que conduzem, no total, a um forte efeito de doping. O presente trabalho também reporta um método in-situ para a caraterização quantitativa das propriedades eletrostáticas na escala nano das folhas de grafeno multicamada (MLG) crescidas no níquel (Ni) por combinação de dados de microscopia de força atómica (AFM) e microscopia de força atómica Kelvin (KPFM). Folhas MLG de larga área epitaxial cresceram no Ni usando a técnica CVD. A elevada natureza cristalina das folhas MLG no níquel foi confirmada por espectroscopia Raman com valor de FWHM tão baixo como ~20 cm-1 para o pico G. Foi feita a injeção de carga (e subsequente difusão de carga com o tempo) no recém sintetizado grafeno no Ni. Os resultados revelaram que : (i) a superfície MLG pode ser carregada quer positivamente quer negativamente pelo processo de injeção usando sondas de Si revestidas de Pt; (ii) as cargas podem ser acumuladas e eventualmente atingir concentrações de saturação de (+4.45±0.1) μC/m2 e (−1.3±0.1) μC/m2 , respetivamente; e (iii) os coeficientes de difusão de carga na superfície medidos foram de (1.50±0.05) × 10−16 m2 /s e (0.64±0.05) × 10−16 m2 /s para as cargas positivas e negativas, respetivamente. As experiências relacionadas com a descoberta de injeção de carga no MLG podem conduzir a uma maneira de desenhar uma nova classe de dispositivos de recolha de energia. Além disso, este estudo também demonstra uma técnica para nano-modelação/litografia de carga das superfícies de carga por eletrificação do contacto, que pode vir a ser uma aplicação promissora para criar nanoestruturas carregadas para a próxima geração de dispositivos nanoeletrónicos baseados em grafeno. Uma breve descrição da qualidade dos substratos transferidos foi também explorada. Foram usados vários substratos, como SiO2/Si e Au. Uma comparação qualitativa da qualidade entre a transferência do grafeno antes e depois foi criticamente descrita. Os resultados de HRXPS mostram a interação da camada de ferro com o grafeno. Por fim, esta pesquisa também mostrou as principais etapas de parametrização e síntese, e o fluxo de trabalho para materiais de elevada qualidade TMDs (como MoS2), por modificação do actual aparelho de CVD. Uma revisão completa das propriedades fundamentais, assim como do método de síntese, propriedades e problemas relacionados com o crescimento de materiais 2D foram também salientados. O efeito da pressão e outras condições para o crescimento de elevada qualidade foram completamente descritos. Este estudo indica que a pressão ótima para o crescimento de uma larga área MoS2 com uma bandgap direta de 1.6 eV é de 50 mbar. Os resultados de micro-Raman mostram claramente a distinção de picos E1 2g e A1 g picos e os dados de HR-XPS reconfirmam a sua elevada qualidade através de diferentes picos de nível interno de Mo and S. Além disso, através do uso da técnica microscopia eletrónica de varrimento (SEM) com feixe de iões focalizados (FIB), foram preparados elétrodos de platina necessários para medidas elétricas. O resultado mostrou: (i) o comportamento óhmico e semi-condutor dos cristais; (ii) a importância das monocamadas de elevada qualidade (SL) MoS2 nas indústrias de semi-condutores e (iii) o potencial das SL MoS2 de elevada qualidade para substituir o grafeno num futuro próximo.

Chemical Vapor Deposition (CVD) Diamond is a promising technology for the passive cooling of high power Gallium Nitride (GaN) semiconductor devices. The high thermal conductivity diamond can be placed near the junction of the GaN transistor either by direct growth on the backside of the GaN or by bonding it to the GaN. In both cases, the thermal resistance near the interface with the diamond and any semiconductor it is attached to has the potential for large thermal resistance that limits the effectiveness of the diamond layer. In this work, several techniques are developed to understand the thermal conductivity of thin diamond films and the thermal boundary resistance with Si and GaN substrates. Anisotropic thermal conductivity measurements are made using Raman spectroscopy temperature mapping along with electric resistance heating. For devices, the thermal boundary resistance is measured using transistors as the heat source and thermal mapping using Raman spectroscopy. Quick screening methods based on Raman, Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS) are also correlated with the thermal properties of the films. Based on this work, the properties of CVD diamond films near the interface of semiconductor substrates is revealed for layers less than 5 µm in thickness and their impact or limitations on thermal management shown through simulations.