Seebeck and resistivity measurements are made on thin film CdS and Zn_xCd_1-xS samples in an apparatus of original design over a temperature range from near liquid nitrogen temperature to room temperature. The temperature dependence of mobility and carrier concentration is studied in CdS films of varying thicknesses (3 µm to 14.0 µm) and in Zn_xCd_1-xS films of varying zinc content (0 ≤ x ≤ .35) . Scattering is found to be grain boundary dependent in all films except the thinest CdS film measured (3.0 µm) in which lattice scattering dominates. The grain boundary barrier height increases with film thickness in CdS films due to a decrease in carrier concentration as film thickness increases making electron traps at the grain boundary influential. As the zinc concentration is increased the carrier concentration decreases and the grain boundary barrier height increases as seen in the CdS films. / Master of Science

No description available.

No description available.

No description available.

No description available.

A novel in-situ stress measurement technique to study the formation kinetics of multi component oxide thin films was developed and was applied to PbTiO₃. Single phase PbTi 0₃ thin films were formed from the reaction between films in the deposited PbO ITi0₂ multilayer. The film stoichiometry was accurately controlled by depositing individual layers of the required thickness. Development of film stresses associated with the formation of the product layer at the PbO/Ti0₂ interface of the multilayers was used to monitor growth rate of the PbTiO₃ layer. It was found that growth of the PbTiO₃ phase obeyed the parabolic law and the effective activation energy was estimated to be 108 kJ/mole. It is believed that the mechanism of this reaction was dominated by grain boundary diffusion of the participating cations. / Ph. D.

This dissertation focuses on identifying and analyzing the mechanism of solid nucleation in liquid thin films. In doing so, we identify and describe a previously unrecognized mechanism of nucleation in condensed systems referred to as transmorphic nucleation. This cluster-shape-change-based mechanism is revealed as a general heterogeneous nucleation mechanism applicable to discontinuous phase transformations occurring in continuous or pre-patterned thin films, as well as in numerous materials systems that possess morphologically and chemically non-trivial heterogeneous-nucleation-catalyzing interfaces (e.g., polycrystalline materials, embedded nano-crystals, and materials with structured interfaces). Identifying, deciphering, and modeling the nature and details associated with how a new phase can nucleate in thin-film materials can be both scientifically meaningful for understanding discontinuous phase transformations in general, and technologically important for engineering various thin-film-based and nano-material-based applications and devices in particular. Classical nucleation theory (CNT) has long been established and regarded as the most practicable treatment that captures the thermodynamic and kinetic essence of the nucleation phenomenon in condensed systems in the simplest and most effective manner. Through a close examination of the theory, we identify and propose morphological equilibrium hypothesis (MEH) as an essential element of CNT. Our shape-transition-based model for transmorphic nucleation in thin films presented in this thesis illustrates that this hypothesis can be violated. As such, the CNT formulation is lacking in capturing the occurrence of the MEH-deviating shape evolution of the clusters, as for instance encountered during the process of transmorphic nucleation. In this dissertation, we conceptually, theoretically, and numerically examine and analyze the kinetic pathway through which nucleation of solids takes place in encapsulated liquid thin films. This example was selected for investigation because it is a particularly simple system, which in turn permits one to make clear, definitive, and general conclusions. A new nucleation mechanism of transmorphic nucleation is discovered in the process. This mechanism is defined generally as the nucleation mechanism through which supercritical clusters are generated from subcritical clusters during an irreversible and morphological-equilibrium-deviating shape evolution initiated when the fluctuating embryos encounter a local growth-inducing element in the catalyzing interface. Both thermodynamic and kinetic analyses in accordance with our transmorphic nucleation mechanism are carried out using a novel adaptation of established theoretical formulations and numerical modeling methods. The kinetic pathway of transmorphic nucleation is described, and transmorphic nucleation temperature window is thermodynamically identified. The kinetic aspect of transmorphic nucleation in thin films is uniquely captured by keeping track of two coupled population distribution profiles of equilibrium-morphology-adhering cluster shapes. Overall, the thesis starts with critical and deconstructive examination of CNT. It builds on our theory of phase initiation and evolution in condensed systems, i.e., Gibbs-Thomson variation (GTV) and Gibbs-Thomson function (GTF), and our interpretation of CNT to investigate steady-state and transient transmorphic nucleation in thin films. The thesis also examines and analyzes all other modes of shape-transition-affected nucleation in thin films outside the transmorphic nucleation domain to provide the comprehensive description of the entire map of nucleation mechanisms in thin-film systems. As far as the implications of the current work on the classical theory of nucleation is concerned, we illustrate how the phenomenon of transmorphic nucleation which violates MEH that forms the basis of CNT, reveals this previously unrecognized limitation of the current formulation of the classical theory of nucleation. The results presented in this dissertation further show that the GTV-based approach, which we identify as the foundation upon which CNT is formulated, can address the MEH-violating shape evolution of subcritical to supercritical clusters. Moreover, the aforementioned reformulation of cluster evolution in this dissertation can be of value for understanding and manipulating phase initiation and evolution involving all of the three Gibbs-Thomson phenomena (i.e., nucleation, coexistence, and free growth) in small, controlled materials systems for optimizing various confined and interface-rich materials that are increasingly becoming technologically important.

The Thermal Radiation Group at Virginia Polytechnic Institute and State University has been developing analytical and numerical heat transfer models for NASA's Langley Research Center for more than 25 years. Recent versions of these models are being used in the design of the next-generation thermal radiation detectors intended for Earth radiation budget campaigns. The current investigation presents three models for the absorption of electromagnetic radiation in thin films. The first assumes a surface heating boundary condition. The second model, derived from electromagnetic theory, is an analytical volumetric heat generation model. This model can be applied to a semi-infinite medium or to a thin-film absorber layers behaving as a second-surface mirror; that is, a semi-transparent coating deposited on top of a reflective surface. The third model is a statistical volumetric heat generation model that is derived using the Monte Carlo ray-trace (MCRT) method. These models are compared by using them to predict the transient temperature response of a generic thermal radiation detector. Results are presented for absorber layers in which the index of refraction is equal to the extinction coefficient. It was found that both of the volumetric heat generation models produce identical results. It was also found that the response of the detector due to shorter wavelengths deviates less from the surface absorption model than at longer wavelengths. A second-surface mirror reflection model for the absorber layer of the thermal radiation detector is also presented in this thesis. / Master of Science

There is a critical need for materials with very high dielectric constant to be integrated in the next generation of 64- and 256-Mb ULSI DRAMs. Materials in the Pb-based perovskite family have high relative permittivities and have consequently attracted a world wide attention. Cubic Lead Lanthanum Titanate (PLT) is one of the prime candidates in this respect and its structure and properties in the thin film form were investigated in the present study, for potential application in the ULSI DRAMs. Thin films of Lead Lanthanum Titanate corresponding to 28 atomic percentage of lanthanum were prepared by metalorganic decomposition (MOD) process. Solutions were prepared from lead acetate, lanthanum acetate and titanium iso-propoxide and thin films were then spin-coated from these solutions on PtlTilSi0₂/Si and sapphire substrates. The films were fabricated from two solutions of different compositions. The composition of the first solution was determined assuming that the incorporation of La³⁺ in the PbTi0₃ structure gives rise to A-site or Pb vacancies whereas for the composition of the other solution the creation of B-site or Ti vacancies was assumed. The effect of excess lead on the structure and the properties was also studied for 0% to 20% of excess PbO. The x-ray diffraction patterns of all films at room temperature indicated a cubic structure with lattice constant of 3.92 A. Optical and electrical measurements showed that the films made assuming B-site vacancies had better properties. In general, excess PbO was found to improve the optical as well as the electrical properties of films. However, in films with Bsite vacancies this improvement occurred only up to 5-10% of excess PbO, while higher PbO additions had a deleterious effect. The films had high resistivity, good relative permittivity, low loss, very low leakage current density, and high charge storage density. A type-B film with 10 % excess Pb had a permittivity of 1336 at 100 kHz. It also had a charge storage density at room temperature of around 16.1 μC/cm² at a field of 200 kV/cm and no sign of polarization loss or breakdown was observed up to 10¹⁰ cycles under the accelerated degradation breakdown test. / Master of Science

The work function of hydrogen-terminated, polycrystalline diamond was studied using ultraviolet photoelectron spectroscopy. Polycrystalline diamond films were deposited onto molybdenum substrates by electrophoresis for grain sizes ranging from 0.3 to 108 microns. The work function and electron affinity were measured using 21.2 eV photons from a helium plasma source. The films were characterized by x-ray photoelectron spectroscopy to determine elemental composition and the sp2/sp3 carbon fraction. The percentage of (111) diamond was determined by x-ray diffraction, and scanning electron microscopy was performed to determine average grain size. The measured work function has a maximum of 5.1 eV at 0.3 microns, and decreases to 3.2 eV at approximately 4 microns. Then the work function increases with increasing grain size to 4.0 eV at 15 microns and then asymptotically approaches the 4.8 eV work function of single crystal diamond at 108 microns. These results are consistent with a 3-component model in which the work function is controlled by single-crystal (111) diamond at larger grain sizes, graphitic carbon at smaller grain sizes, and by the electron affinity for the intervening grain sizes.