Surface structure, chemical composition, bonding configuration, film polarity, and electronic properties of InN layers grown by high pressure chemical vapor deposition (HPCVD) have been investigated. Sputtering at an angle of 50-70 degrees followed by atomic hydrogen cleaning (AHC) was successful in removing the carbon contaminants. AHC is found to be the most effective cleaning process to remove oxygen contaminants from InN layers in an ultrahigh vacuum (UHV) system and produced a well ordered surface. Auger electron spectroscopy (AES) confirmed the cleanliness of the surface, and low energy electron diffraction (LEED) yielded a 1×1 hexagonal pattern demonstrating a well-ordered surface. High resolution electron energy loss spectra (HREELS) taken from the InN layers exhibited loss features at 550 cm-1, 870 cm-1 and 3260 cm-1 which were assigned to Fuchs-Kliewer phonon, N-H bending, and N-H stretching vibrations, respectively. Assignments were confirmed by observation of isotopic shifts following atomic deuterium dosing. No In-H species were observed indicating N-termination of the surface and N-polarity of the film. Broad conduction band plasmon excitations were observed centered at 3100 cm-1 to 4200 cm-1 in HREEL spectra acquired with 25 eV electrons, for a variety of samples grown with different conditions. Infrared reflectance data shows a consistent result with HREELS for the bulk plasma frequency. The plasmon excitations are shifted about 300 cm-1 higher in HREEL spectra acquired using 7 eV electrons due to the higher plasma frequency and carrier concentration at the surface than in the bulk, demonstrating a surface electron accumulation. Hydrogen completely desorbed from the InN surface upon annealing for 900 s at 425 ºC or upon annealing for 30 s at 500 ºC. Fitting the coverage versus temperature for anneals of either 30 or 900 s indicated that the desorption was best described by second order desorption kinetics with an activation energy and pre-exponential factor of 1.3±0.2 eV and 10-7.3±1.0 cm2/s, respectively. Vibrational spectra acquired from HREEL can be utilized to explain the surface composition, chemical bonding and surface termination, and film polarity of InN layers. The explanation of evidence of surface electron accumulation and extraction of hydrogen desorption kinetic parameters can be performed by utilizing HREEL spectra.

In order to truly understand the process-property behavior of polymer systems it is essential to identify the three dimensional structure of the materials fabricated. For heterogeneous polymer systems such as nanoparticle filled systems, determination of the three dimensional optical properties are particularly difficult. Such information is essential, however, if the behavior of these systems are to be understood and formalized. The purpose of the present research was to develop methods for measuring the optical characteristics of heterogeneous polymer systems nondestructively, in order to characterize their three dimensional behavior. The thesis contains three parts: Part A: Study of an Oriented Uniformly Distributed System: Stretched Isotactic Polypropylene- nano Carbon Black Films (IPP-CB). Three nondestructive optical methods: optical waveguide coupling, Fourier Transform Infrared (FTIR) spectroscopy and x-ray diffraction, were used to investigate the effect of the carbon black on the phase behavior and orientation of the films. It was found that the carbon black has little effect on the crystal form and crystallinity, but has a significant effect on the three dimensional orientation behavior of the polypropylene in the IPP-CB systems. Part B: Study of a non-Uniformly Distributed System: Compression Molded Poly (Methyl Methacrylate) with Nano Indium Tin Oxide (PMMA-ITO) The PMMA-ITO sample is an un-oriented and non-uniformly mixed system which has a grain structure. A unique Break Point Waveguide Method was developed to deal with this problem. It was found that both the refractive index and the extinction coefficient increased with ITO concentration and the samples were three dimensionally random. Part C: Development of Computational Improvements in System Operations Four methods were developed to improve the accuracy of the waveguide methods. They are the Bootstrap Method, the Two-Line Method, the Big Area Method and the Modified Knee method. In conclusion, the three dimensional optical characteristics of two different kinds of heterogeneous polymer systems, oriented uniformly distributed IPP-CB films and non-uniformly distributed PMMA-ITO composites, are obtained and their structures evaluated. Further, several new methods were developed to improve the accuracy of the current optical waveguide methods.

In this dissertation, the electrical characteristics of generally used hydrogenated amorphous silicon (a-Si:H) TFTs in LCD and newly risen amorphous indium-gallium-zinc oxide (a-IGZO) TFTs were studied. For modern mobile display and large-size flat panel display application, the traditional thin-film transistor-liquid crystal display (TFT-LCD) technology confronts with a lot of challenges and problems. In general, flexible displays must exhibit some bending ability; however, bending applies mechanical strain to electronic circuits and affects device characteristics. Therefore, the electrical characteristics of a-Si:H TFTs fabricated on stainless steel foil substrates with uniaxial bending were investigated at different temperatures. Experimental results showed that the on-state current and threshold voltage degraded under outward bending. This is because outward bending will induce the increase of band tail states, affecting the transport mechanism at different temperatures. In addition, for practical operation, the electrical characteristics of a-Si:H TFTs under flat and bending situations after AC/DC stress at different temperatures were studied. It was found that high temperature and mechanical bending played important roles under AC stress. The dependence between the accumulated sum of bias rising and falling time and the threshold voltage shifts under AC stress was also observed. Because a-Si:H is a photosensitive material, the high intensity backlight illumination will degrade the performance of a-Si:H TFTs. Thus, the photo-leakage current of a-Si:H TFTs under illumination was investigated at different temperatures. Experimental results showed that a-Si:H TFTs exhibited a pool performance at lower temperatures. The indirect recombination rate and the parasitic resistance (Rp) are responsible for the different photo-leakage-current trends of a-Si:H TFTs under varied temperature operations. To investigate the photo-leakage current, the a-Si:H TFTs were exposed to ultraviolet (UV) light irradiation. It was found that the photo current of a-Si:H TFTs was reduced after UV light irradiation. The detail mechanisms on reducing/increasing photo-leakage current by UV light irradiation were discussed. Recently, the oxide-based semiconductor TFT, especially a-IGZO TFT, is considered as one of promising candidates for active matrix flat-panel display. However, the a-IGZO TFT exists significant electrical instability issue and manufacturing problems. As a consequence, we investigated the effect of hydrogen incorporation on a-IGZO TFTs to reduce interface states between active layer and insulator. Experimental results showed that the electrical characteristics of hydrogen-incorporated a-IGZO TFTs were improved. The threshold voltage shift (£GVth) in hysteresis loop is suppressed from 4 V to 2 V due to the hydrogen-induced passivation of the interface trap states. Finally, we reported the effect of ambient environment on a-IGZO TFT instability. As a-IGZO TFTs were stored in atmosphere environment for 40 days, the transfer characteristics accompanying strange hump were observed during bias-stress. The hump phenomenon is attributed to the absorption of H2O molecule. Additionally, the sufficient electric field is also necessary to cause this anomalous transfer characteristic.

Ternary chalcopyrite compounds are the semiconductors with suitable properties to be used as absorber materials in thin film solar cells. AgInSe2 is a promising candidate with its several advantages over the widely used CuInSe2. The purpose of this study was to optimize the physical properties of the Ag-In-Se (AIS) thin films that were deposited by e-beam evaporation of Ag3In5Se9 single crystal powder for solar cell applications by means of post-annealing process under nitrogen atmosphere. The as-grown AIS thin films were annealed at 200, 300 and 400oC and their structural, optical, electrical and photoelectrical properties were examined to observe the effects of post-annealing process. Structural characterization of the films was performed by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses. Optical properties of the films were investigated by optical transmittance measurements. Electrical and photoelectrical properties of the films were examined by temperature dependent conductivity, photoconductivity under different illumination intensities and spectral photoresponse measurements. It was discovered that the annealing of AIS thin films at 200oC resulted in the best physical properties for solar cell applications. The obtained films were polycrystalline with mixed binary and ternary crystalline phases, such as Ag3In5Se9, AgInSe2 and InSe, and showed n-type conductivity with room temperature conductivity value of 2.3x10-6 (Ohm&shy / cm)-1. The band gap energy of the 200oC-annealed films was determined as 1.68 eV from spectral photoresponse measurements. The results of the study revealed that the inadequate Ag incorporation and segregation and/or reevaporation of Se atoms at high annealing temperatures were the major problems encountered in producing single phase polycrystalline AgInSe2 thin films. The required stoichiometry of thin films should be maintained during the growth of the films by means of an alternative deposition procedure and the films should be selenized during post-annealing process.

The objective of the research was to develop high quality GaN epitaxial growth on alternative substrates that could result in higher external quantum efficiency devices. Typical GaN growth on sapphire results in high defect materials, typically 10⁸⁻¹⁰cm⁻², due to a large difference in lattice mismatch and thermal expansion coefficient. Therefore, it is useful to study epitaxial growth on alternative substrates to sapphire such as ZnO which offers the possibility of lattice matched growth. High-quality metalorganic chemical vapor deposition (MOCVD) of GaN on ZnO substrate is hard to grow due to the thermal stability of ZnO, out-diffusion of Zn, and H₂back etching into the sample. Preliminary growths of GaN on bare ZnO substrates showed multiple cracks and peeling of the surface. A multi-buffer layer of LT-AlN/GaN was found to solve the cracking and peeling-off issues and demonstrated the first successful GaN growth on ZnO substrates. Good quality InGaN films were also grown showing indium compositions of 17-27% with no indium droplets or phase separation. ZnO was found to to sustain a higher strain state than sapphire, and thereby incorporating higher indium concentrations, as high as 43%, without phase separation, compared to the same growth on sapphire with only 32%. Si doping of InGaN layers, a known inducer for phase separation, did induce phase separation on sapphire growths, but not for growths on ZnO. This higher strain state for ZnO substrates was correlated to its perfect lattice match with InGaN at 18% indium concentration. Transmission electron microscopy results revealed reduction of threading dislocation and perfectly matched crystals at the GaN buffer/ZnO interface showing coherent growth of GaN on ZnO. However, Zn diffusion into the epilayer was an issue. Therefore, an atomic layer deposition of Al₂O₃was grown as a transition layer prior to GaN and InGaN growth by MOCVD. X-ray and PL showed distinct GaN peaks on Al₂O₃/ZnO layers demonstrating the first GaN films grown on Al₂O₃/ZnO. X-ray photoelectron spectroscopy showed a decrese in Zn diffusion into the epilayer, demonstrating that an ALD Al₂O₃layer was a promising transition layer for GaN growth on ZnO substrates by MOCVD.

In general, the bearing alloys have two types of microstructure i.e., either a soft matrix with discrete hard particles or a continuous matrix of the harder metal with small amount of the softer metal finely dispersed in it. The aluminium and copper based bearing alloys which are widely studied fall in the second category. However, the bearing materials which have been studied have micron sized dispersoids. In recent times, it is possible to produce nanoscale dispersoids in a hard matrix by the novel processing route of rapid solidification. This offers an opportunity to study the small length scale effect on tribological processes. In this thesis, we deal with aluminium alloys where nanoscaled dispersions of lead, bismuth and indium are produced by rapid solidification processing. Chapter 1 of the thesis is an introduction, followed by Chapter 2, which reviews the literature on nanomaterials. Special attention is given to the monotectic system, followed by a brief description on friction and wear of materials which is necessary for our present investigation. The details of experimental and characterisation techniques are given in Chapter 3. In Chapter 4, we present a brief study of white metal bearings (babbit). Tin-based babbit of composition, Sn-6wt% Cu-llwt% Sb was studied. The study of babbit was mainly carried out with the idea that it could serve as a benchmark for subsequent studies in aluminium alloys, in terms of tribological properties. In particular, we have carried out a detailed electron microscopic investigation on the phases present in the bearing alloy. The friction and wear behaviour of this material confirms the proper calibration of our setup for wear studies. This is followed by a detailed study on the synthesis, microstructure and tribological behaviour of nanodispersed aluminium alloys, Al-6wt% Pb and Al-10wt% Pb in Chapter 5. For comparison, we have also studied melt-spun aluminium without dispersoids. Detailed electron microscopic characterisation indicates that lead has a cube on cube orientation relationship with the aluminium matrix, and the particles exhibit a lognormal distribution with the mode of the particle size distribution being 15 nm. The pin on disc results suggest a distinct lowering of coefficient of friction corresponding to pure aluminium (μ= 0.40) and as cast aluminium-lead alloys (μ= 0.41). Detailed SEM studies indicate a tribolayer consisting primarily of Al, Pb and Fe. The later comes from the counterface material. Our results clearly indicate that at an early stage, little or no oxidation takes place at the sliding interface. TEM observations indicate significant deformation of lead particles in the sub-surface region. The observations suggest spreading of the lead, which acts as a lubricating layer. Wear behaviour is primarily adhesive and follows Archard's wear law. However, the rate of wear is less than that reported by other investigators on micronsized lead dispersions in aluminium. In Chapter 6, we present the results for alloys dispersed with nanosized indium and bismuth. We show that indium particles on melt-spinning exhibit both cubic and tetragonal crystal structure. The indium particles are coarser (with a mode of 25 nm) than the lead and bismuth particles (which have mode of 15nm). The bismuth containing alloys have a lower wear rate and coefficient of friction compared to lead and indium alloys. However, both indium and bismuth particles do not follow Archard's wear law and the wear vs load graph shows a non-linear behaviour. The results are discussed in terms of known mechanisms of the coefficient of friction and wear. Chapter 7 gives the salient conclusions while in Chapter 8 we discuss some of the unanswered questions and the potential for future work in this field.

This dissertation presents thermal and thermoelectric measurements of nanostructures. Because the characteristic size of these nanostructures is comparable to and even smaller than the mean free paths or wavelengths of electrons and phonons, the classical constitutive laws such as the Fourier’s law cannot be applied. Three types of nanostructures have been investigated, including nanoscale constrictions patterned in a sub-100 nm thick silicon film, monatomic thick graphene ribbons supported on a silicon dioxide (SiO₂) beam, and indium antimonide (InSb) nanowires. A suspended measurement device has been developed to measure the thermal resistance of 48-174 nm wide constrictions etched in 35-65 nm thick suspended silicon membranes. The measured thermal resistance is more than ten times larger than the diffusive thermal resistance calculated from the Fourier’s law. The discrepancy is attributed to the ballistic thermal resistance component as a result of the smaller constriction width than the phonon-phonon scattering mean free path. Because of diffuse phonon scattering by the side walls of the constriction with a finite length, the phonon transmission coefficient is 0.015 and 0.2 for two constrictions of 35 nm x 174 nm x220 nm and 65 nm x 48 nm x 50 nm size. Another suspended device has been developed for measuring the thermal conductivity of single-layer graphene ribbons supported on a suspended SiO₂ beam. The obtained room-temperature thermal conductivity of the supported graphene is about 600 W/m-K, which is about three times smaller than the basal plane values of high-quality pyrolytic graphite because of phonon-substrate scattering, but still considerably higher than for common thin film electronic materials. The measured thermal conductivity is in agreement with a theoretical result based on quantum mechanical calculation of the threephonon scattering processes in graphene, which finds a large contribution to the thermal conductivity from the flexural vibration modes. A device has been developed to measure the Seebeck coefficients (S) and electrical conductivities ([sigma]) of InSb nanowires grown by a vapor-liquid-solid process. The obtained Seebeck coefficient is considerably lower than the literature values for bulk InSb crystals. It was further found that decreasing the base pressure during the VLS growth results in an increase in the Seebeck coefficient and a decrease in the electrical conductivity, except for a nanowire with the smallest diameter of 15 nm. This trend is attributed to preferential oxidation of indium by residual oxygen in the growth environment, which could cause increased n-type Sb doping of the nanowires with increasing base pressure. The deviation in the smallest diameter nanowire from this trend indicates a large contribution from the surface charge states in the nanowire. The results suggest that better control of the chemical composition and surface states is required for improving the power factor of InSb nanowires. On approach is to use Indium-rich source materials for the growth to compensate for the loss of indium due to oxidation by residual oxygen. / text

There has been growing interest in developing colloidal metal and semiconductor nanocrystals as biomedical imaging contrast agents and therapeutics, since light excitation can cause the nanocrystals to fluoresce or heat up. Recent advances in synthetic chemistry produced fluorescent 2-4 nm diameter silicon and 1-2 nm diaemeter CuInSSe nanocrystals, as well as 16 nm diameter copper selenide (Cu₂₋[subscript x]Se) nanocrystals exhibiting strong absorbance of near infrared light suitable for biomedical applications. However, the syntheses yield nanocrystals that are stabilized by an adsorbed layer of hydrocarbons, making the nanocrystals hydrophobic and non-dispersible in aqueous solution. Encapsulating these nanocrystals in amphiphilic polymer micelles enables the nanocrystals to disperse in water. Subsequently, the Si nanocrystals were injected into tissue to demonstrate fluorescence imaging, the photothermal transduction efficiency of copper selenide nanocrystals was characterized in water, and the copper selenide nanocrystals were used enhance the photothermal destruction of cancer cells in vitro. The polymer-encapsulated copper selenide nanocrystals were found to have higher photothermal transduction efficiency than 140 nm diameter Au nanoshells, which have been widely investigated for photothermal therapy. Combining the optical properties of metal and semiconductor nanocrystals with the drug-carrying capability of lipid vesicles has received attention lately since it may create a nanomaterial capable of performing simultaneous drug delivery, optical contrast enhancement, and photo-induced therapy. Hydrophobic, dodecanethiol-coated Au nanocrystals were dispersed in water with phosphatidylcholine lipids and characterized using cryo transmission electron microscopy. 1.8 nm diameter Au nanocrystals completely load the bilayer of unsaturated lipid vesicles when the vesicles contain residual chloroform, and without chloroform the nanocrystals do not incorporate into the vesicle bilayer. 1.8 nm Au nanocrystals dispersed in water with saturated lipids to form lipid-coated nanocrystal agglomerates, which sometimes adhered to vesicles, and the shape of the agglomerates varied from linear nanocrystal chains, to flat sheets, to spherical clusters as the lipid fatty acid length was increased from 12 to 18 carbons. Including squalene formed lipid-stabilized emulsion droplets which were fully loaded with the Au nanocrystals. Results with 4.1 nm Au and 2-3 nm diameter Si nanocrystals were similar, but these nanocrystals could not completely load the bilayers of unsaturated lipids. / text

This thesis focuses on the use of surface modifiers to tune the properties of both metals and metal oxides. Particular attention is given to examine the modification of transparent conducting oxides (TCOs) including indium tin oxide and zinc oxide both through the use of phosphonic acids as well as organic and metal-organic dopants. In this thesis a variety of known and new phosphonic acids are synthesized. A subset of these molecules are then used to probe the relationship between the ability of a phosphonic acid to tune the work function of ITO and how that interrelates with the coverage and molecular orientation of the modifier on the surface. Experimental techniques including XPS, UPS, and NEXAFS are coupled with theoretical DFT calculations in order to more closely examine this relationship. Literature surrounding the modification of zinc oxide with phosphonic acids is not as prevalent as that found for the modification of ITO. Thus, effort is placed on attempting to determine optimal modification conditions for phosphonic acids on zinc oxide. As zinc oxide is already a low work function metal oxide, modifiers were synthesized in an attempt to further decrease the work function of this substrate in an effort to minimize the barrier to carrier collection/injection. Etching of the substrate by phosphonic acids is also examined. In a related technique, n- and p-dopants are used to modify the surfaces of ITO, zinc oxide, and gold and it was found that the work function can be drastically altered, to approximately 3.3 – 3.6 eV for all three of the substrates examined. Surface reactions are straightforward to conduct typically taking only 60 s to achieve this change in work function.

This dissertation has focused on i) optimizing charge transfer rates at indium-tinoxide (ITO) electrodes, and ii) characterization of the supramolecular structure and properties of ultra thin surface modifier films on modified electrodes for various device applications. Commercial ITO surfaces were modified using conducting polymer thin film architectures with and without various chemical activation procedures. Ferrocene derivatives were used as redox probes, which showed dramatic changes in electron transfer rate as the SA-PANI/PAA layers were added to the ITO surface. Highest rates of electron transfer were observed for DMFc, whose oxidation potential coincides with the potential region where these SA-PANI/PAA films reach their optimal electroactivity. Apparent heterogeneous electron transfer rate constants, kS, measured voltammetrically, were ca.10 x higher for SA-PANI/PAA films on ITO, versus clean ITO substrates. These films also showed linear potentiometric responses with retention of the ITO transparency with the capability to create smoothest films using an aqueous deposition protocol, which proved important in other applications. ITO electrodes were also modified via chemisorption of carboxy functionalized EDOTCA and electropolymerization of PEDOTCA/PEDOT copolymers, when properly optimized for thickness and structure, enhance voltammetrically determined electron transfer rates (kS) to solution probe molecules, such as dimethylferrocene (DMFc). Values of kS ≥ 0.4 cm•sec⁻¹, were determined, approaching rates seen on clean gold surfaces. ITO activation combined with formation of these co-polymer films has the effect of enhancing the electroactive fraction of electrode surface, versus a non-activated, unmodified ITO electrode, which acts as a “blocked” electrode. The electroactivity and spectroelectrochemistry of these films helped to resolve the electron transfer rate mechanism and enabled the construction of models in combination with AFM, XPS, UPS and RAIRS studies. The surface topography, structure, composition, work function and contact angle, also revealed other desirable properties for molecular electronic devices. The carboxylic functionality of the EDOTCA molecule adds more desirable properties compared to normal PEDOT films, such as favoring the deposition of smooth films, increasing the optical contrast, participating in hydrogen-bonding, chemisorption to oxide surface, self-doping and providing a linker for incorporation of different functional groups, new molecules, or nanoparticles. Periodic sub-micron electrode arrays can be created using micro-contact printing and electropolymerization. The sinusoidal modulation of the refractive index of such confined conducting polymer nanostructures or nanoparticle stripes allows efficient visible light diffraction. The modulation of the diffraction efficiency at PANI and PEDOT gratings in the presence of an analytical stimulus such as pH or potential demonstrate the sensing capability at these surfaces. The template stripped gold surfaces that are being developed in our lab demonstrate several advantages over commercially available evaporated gold films especially for nanoscale surface modification.