Successful operation of Nano-ElectroMechanical Systems (NEMS) critically depends on their working environment and component materials' electromechanical properties. It is equally important that ambient or liquid environment to be seriously considered for NEMS to work as high sensitivity sensors with commercial viabilities. Firstly, to understand interaction between NEMS oscillator and fluid, transfer function of suspended gold nanowire NEMS devices in fluid was calculated. It was found that NEMS's resonance frequency decreased and energy dissipation increased, which constrained its sensitivity. Sensitivity limit of NEMS oscillators was also considered in a statistical framework. Subsequently, suspended gold nanowire NEMS devices were magnetomotively actuated in vacuum and liquid. Secondly, electromechanical properties of gold nanowires were carefully studied and the observed size effect was found to agree with theory, which predicted small changes of electromechanical property compared with bulk gold materials. Finally, it is well recognized that continuous development of new NEMS devices demands novel materials. Mechanical properties of new two-dimensional hexagonal Boron Nitride films with a few atomic layers were studied. Outlook of utilizing ultrathm BN films in next generation NEMS devices was discussed.

Several nanomaterials systems, both inorganic and organic in nature, have been extensively investigated by a number of characterization techniques including atomic force microscopy (AFM), electron microscopy, Fourier transform infrared spectroscopy (FTIR), and energy dispersive x-ray spectroscopy (EDX). The first system consists of boron nitride nanotubes (BNNTs) synthesized via two different methods. The first method, silica-assisted catalytic chemical vapour deposition (SA-CVD), produced boron nitride nanotubes with different morphologies depending on the synthesis temperature. The second method, growth vapour trapping chemical vapour deposition (GVT-CVD), produced multiwall boron nitride nanotubes (MWBNNTs). The bending modulus of individual MWBNNTs was determined using an AFM three-point bending technique, and was found to be diameter-dependent due to the presence of shear effects. The second type of nanomaterial investigated is the biomineralized calcareous shell of the serpulid Hydroides dianthus. This material was found to be an inorganic-organic composite material composed of two different morphologies of CaCO3, collagen, and carboxylated and sulphated polysaccharides. The organic components were demonstrated to mediate the mineralization of CaCO3 in vitro. The final system studied is the proteinaceous cement of the barnacle Amphibalanus amphitrite. The secondary structure of the protein components was investigated via FTIR, revealing the presence of β-sheet conformation, and nanoscale rod-shaped structures within the cement were identified as β-sheet containing amyloid fibrils via chemical staining. These rod-shaped structures exhibited a stiffer nature compared with other structures in the adhesive, as measured by AFM nanoindentation.

A framework for constructing kinetic monte carlo (KMC) simulations of diffusive events on a lattice was developed. This code was then tested by running simulations of Fe adatom diffusion on graphene and graphene-boron nitride surfaces. The results from these simulations was then used to show that the modeled diffusion adheres to the laws of brownian motion and generates results similar to recent research findings.

The structural properties of the group III-nitrides including AlN, Ga1-xMnxN, GaN:Cu, and InN were investigated by Raman spectroscopy. Absorption and photoluminescence spectroscopy were utilized to study the optical properties in these materials. The analysis of physical vapor transport grown AlN single crystals showed that oxygen, carbon, silicon, and boron are the major impurities in the bulk AlN. The Raman analysis revealed high crystalline quality and well oriented AlN single crystals. The absorption coefficient of AlN single crystals were assessed in the spectral range from deep UV to the FIR. The absorption and photoluminescence analysis indicate that, in addition to oxygen, carbon, boron, and silicon, contribute to the optical properties of bulk AlN crystals. In situ Cu-doped GaN epilayers with Cu concentrations in the range of 2x10^16 cm-3 - 5x1017 cm-3, grown on sapphire substrate by metal organic chemical vapor deposition, were investigated by Raman and PL spectroscopy. The Raman study revealed high crystalline GaN:Cu layers with minimal damage to the hexagonal lattice structure due to the Cu incorporation. A strong Cu related emission band at 2.4 eV was assigned to Cu induced optical transitions between deep Cu states and shallow residual donor states. Compensation of Cu states by residual donors and poor activation probability of deep Cu states are responsible for semi-insulating electrical conductivity. Ferromagnetic Ga1-xMnxN epilayers, grown by MOCVD with Mn concentration from x = 0 to x = 1.5, were optically investigated by Raman, PL, and transmission spectroscopy. The Raman studies revealed Mn-related Raman peaks at 300 cm-1, 609 cm-1, and 669 cm-1. Mn-related absorption and emission bands in Ga1-xMnxN were observed at 1.5 eV and 3.0 eV, respectively. The structural properties of InN layers, grown by high pressure-CVD with different free carrier concentrations, were analyzed by Raman spectroscopy. The Raman results show that the InN layers have high crystalline quality. The free carriers in layers were calculated by using the Lindhard-Mermin dielectric function taking into account finite wave vectors for various scattering processes including forbidden Frohlich, deformational potential associated with allowed electro-optic, and charge density fluctuation, mechanisms. The free carrier concentrations in the layers are below 1x10^20 cm-3.

The effect of silicon doping on the strain in c-plane InN films grown on c-plane GaN by plasma-assisted molecular beam epitaxy is investigated. Strain is measured by x-ray reciprocal space mapping and Raman spectroscopy. The silicon doping concentration of our sample is about 1018 cm-3 by Hall measurement. Relation between the strain and the silicon concentration is obtained. To understand the increase in tensile stress caused by Si doping is discussed in terms of a crystallite coalescence model.

Aluminum nitride (AlN) thin film is a promising material as buffer layer in GaN-based optoelectronic and electronic devices or as a substrate to fabricate Surface Acoustic Wave (SAW) and Film Bulk Acoustic wave Resonant (FBAR) devices in high frequency in wireless (>1GHz) communication technology. Aluminum nitride, thin film with the c-axis normal to the film is favored in a low energy deposition condition because it places the packed hexagonal basal plane parallel to the substrate surface. Grains of this orientation have a low surface energy which favors rapid growth in a columnar structure. In this experiment r.f. dual ion beam sputtering (DIBS) system is used to prepare the AlN films on Si (100) substrate. Various processing variable were tested to deposit AlN films with desirable properties. After systematic testing, a high quality film with preferred c-axis orientation was grown successfully on Si (100) substrate with Al target under the process parameters of 700 ev energy flux; 55% N2 / (N2+Ar) ratio; 4X10 - 4 torr working pressure with no heating of substrate. The AlN target is also used. The results show the great sensitivity of the films to oxygen-containing environments. Only under low residual oxygen pressure, could aluminum nitride be grown well. The deposited AlN thin film characteristic were studied by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Secondary Ion Mass Spectrometry (SIMS) and Electron Spectroscopy for Chemical Analysis (ESCA).

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In this study, highly C-axis oriented AlN thin films stacked upon Al bottom electrode on Si and Glass substrate are deposited with Reactive RF magnetron sputtering Technique. Three different sputtering systems were utilized to evaluate the optimized growth parameters. Room temperature growth was applied to the all system. During thin film growing , the substrate bias condition, sputtering work pressure, sputtering power and the N2 concentration are those key parameters to be adjusted in order to gain smooth surface morphology and highly C-axis prefer orientation AlN thin films. The crystallography of the deposited films was analyzed by x-ray diffraction (XRD). Film surface morphology was characterized by scanning electron microscopy (SEM). Meanwhile, transmission electron microscopy (TEM) was adopted to observe the microstructure and determine the grain size of the film. The results of the XRD patterns showed that in a 17cm long sputtering working distance condition, the AlN (002) can be obtained and the peak intensity can be increased when the sputtering power was fixed meanwhile reduced the working pressure and applied the negative bias on the substrate. The surface morphology can be improved with long working sputtering distance. The micrography of the TEM reveals that there is a transition region between Al metal and AlN film. Fine column structures can be observed in the initial growth stage. The size of the grain increased as the film became thicker. Strong AlN (002) ring pattern was obtained from the region of the top of the film. It indicates that the AlN (002) will not appear till the thickness of the film reach the critical thickness.

The failure mechanisms of the tantalum-based nitride diffusion barrier using between copper metal and the SiGe/Si layers grown with UHV/CVD have been studied. The TaN and Cu films were deposited with RF sputtering technique. The structure of these films was analyzed by X-ray diffraction. The stoichiometry of TaN was characterized by XPS (X-ray photoelectron spectroscopy). The morphology of the films was examined with SEM and the microstructure of the interface between several layers was observed with TEM. With comparing the XRD patterns of the samples which were annealed in the different temperatures, the failure temperature of the TaN barrier layer can be identified and the failure mechanism of this barrier layer cab be elucidated with TEM observation. The results revealed that the deposited TaN film with low sputtering power had better performance for preventing the Cu atoms diffusing into the SiGe layer. The high composition of Ge in the SiGe alloy degraded the blocking ability of the TaN barrier layer due to the released the existed strain between the SiGe and Si. When the failure temperature was reached, The Cu3Si phase was formed first in the interface of the TaN/SiGe and inside the TaN film. If the annealed temperature went higher, the TaSi2 phase also was formed. Compared with SiGe/Si and Si substrate, the TaN diffusion barrier layer has a higher failure temperature in Si than those in SiGe layer.

In this thesis, the aluminum nitride (AlN) thin film was selected as a sensing membrane for the H+ ion-sensitive field-effect transistor (ISFET). The AlN thin films were prepared by a rf sputtering technology on the reference electrode/electrolyte /AlN /SiO2/p-Si/Al structure. The capacitance-voltage (C-V) measurement was used to detect the H+ ion concentration and the C-V characteristic curves were obtained in the different pH buffer solutions. On the other hand, AlN thin films were also prepared on the double layer structure of AlN/SiO2 gate ISFET devices. After packaging, the current-voltage (I-V) measurement with a PID temperature controller was utilized to measure a series of the I-V characteristic curves. The threshold voltage can be obtained to evaluate the pH sensitivity in the different pH buffer solutions. Additionally, the effects of non-ideal factors, such as temperature effect, drift and hysteresis phenomenon on the characteristics of the ISFET are also measured, analyzed and compared with other sensing materials. According to the experimental results, it can be found that the ISFET based on aluminum nitride thin film has a superior high pH sensitivity of approximately 50~58 mV/pH at 25¢J. The drift and hysteresis are dependent on the H+ ion concentration in pH=1~11, in which the drift rate increases with the pH value increased and the hysteresis magnitude depends on the measuring time and route. It is found that the hysteresis widths measured in pH=7®3®7®11®7 cycle at 960s, 1920s and 3840s loop time are 1.0, 1.5 and 4.5 mV, respectively. When the temperature effect was considered, it was found that the ISFET could be operated at 5~65¢J, in which, the pH sensitivity increased as the ambient temperature increased with the temperature coefficient of sensitivity of about 0.13 mV/pH¢J. In addition, the output voltage of AlN pH-ISFET can be obtained by a constant current constant voltage (CCCV) read out circuit with a fairly linear response, stability and reproducibility in the pH measuring cycle. From the characteristics mentioned above, the AlN thin film can be as a sensing membrane for pH-ISFET applications.