The incorporation of vacancies and H atoms into { 100}- and { 111 }-oriented diamond films during CVD growth in an atmosphere of H, H2, CH3, and C2H2 is simulated atomistically. The growing films are represented in three dimensions by a diamond cubic lattice, and the temporal evolution of the surfaces is accomplished by a kinetic Monte Carlo method. The dimer bonding of diamond atoms on the { 100} surface is treated explicitly. Growth begins on { 100}(2xl):H and { 11 }:H surfaces containing 288 and 300 atoms, respectively, in the surface plane, and the growth of approximately sixty atomic layers (18,000 atoms) is accomplished at each of fifteen substrate temperatures between 800 and 1500 K. The growth rates depend on the combined contributions to growth from CH3 and C2H2, whereas the point defect concentrations depend on the ratio of C2H2 to CH3 growth. The maximum { 100} growth rate is achieved at approximately 1200 K. Point defect concentrations are low at temperatures below 1300 K, but become high above 1300 K. Growth efficiency, defined as the ratio of growth rate to defect concentration, is maximum for both film orientations at substrate temperatures in the vicinity of 1100 to 1200 K.

Molecular dynamics simulations have been performed to investigate the chemical and structural processes which occur when molecular clusters of acetylene impact a non-rigid, hydrogenterminated diamond (111) surface at incident hyperthermal kinetic energies. The atoms are characterized by a realistic many-body empirical potential for hydrocarbon systems. The goal is to study the initial stages of thin film growth following impact. Important processes observed during the simulations include polymerization of the cluster molecules, and adsorption (tethering) of some polymer chains to the surface in the initial stages of thin film growth. Further simulations will be necessary to fully determine the characteristics of the film.

We study by using ab-initio methods the adsorption of As2-molecules on a Gaterminated GaAs(001) surface. We represent the GaAs crystal by a Ga5As2H8 cluster, which is large enough to resemble the crystal but sufficiently small to be tractable in a computer in a reasonable time. We calculate the reaction path along the symmetry axis C2 of this cluster and obtain the reaction path by minimizing the total energy of the system (cluster plus molecule). In the calculated positions above the cluster we account for the possibility of the As2-molecule to rotate around the C2 symmetry axis and for a change in the distance between the As-atoms. As a main result we obtain that for heights above the (001) surface less than about 3.5A we find a clear influence of the discrete atomic surface structure on the reaction path of the As2-molecule.

Recently, an energetic film growth technique was developed. In this process, an RF (radio frequency) plasma was ignited in an ambient atmospheric environment. An aqueous solution was excited into mist, which was then fed into the plasma reactor. After vaporization, films were formed on substrates outside the plasma. As a by-product, small amount of powders were collected in the plasma reactor. Films studied were indium-tin oxide (ITO), aluminum oxide (Al2O3), and lanthanum strontium manganite oxides (LaSrMnO). Films and powders were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX, EDS), and Ultraviolet-Visible (UV-Vis) transmission measurements. Morphology of a film surface was dependent on deposition conditions, such as chemical composition of the precursor materials, precursor feeding rate, and/or substrate temperature.

Epitaxial growth of CeO2 layers on silicon (100) substrates is studied using electron-beam evaporation under substrate bias application in an ultrahigh vacuum. Both negative and positive biases are proved to be effective for lowering the epitaxial temperature. Sample current characteristics are measured as a function of the bias voltage. Under negative bias conditions, as the bias voltage increases, the sample current varies from negative to positive with a transition point at -42 V and then reaches a saturation value of ∼ +4 μA above -60 V. Use of a negative bias of -60 V leads to epitaxial growth temperature lowering of ∼, 40°C. Under a positive bias, the sample current is negative and its absolute value increases with the bias voltage, where the sample current components are to be anions and electrons (46°) as determined by mass separation with a magnetic field application. It is experimentally clarified that the degree of enhancement of epitaxial growth is greater than that in the negative bias experiment (750°C at +60 V bias, i. e., epitaxial growth temperature lowering of 70°C) and the enhancement is attributed to the electron component. It is found that a negative current of ∼ -0.15 mA flows at zero bias, indicating that even in conventional evaporation, electrons somewhat promote epitaxial growth.

Atomic vapor transport has been investigated in the low vacuum (5 – 100 Pa) supersonic gas jets encountered in directed vapor deposition processes using a combination of Direct Simulation Monte Carlo (DSMC) techniques and a bimolecular collision model. The DSMC code generates the velocity vector, pressure, and temperature field for the carrier gas flow. This data is used as an input to a bimolecular collision model of atomic vapor transport in the flow. In the collision model, calculation of directed momentum loss cross-sections allows the location of carrier gas/vapor atom collisions to be deduced, and the vapor atom velocity vectors for individual vapor atoms to be tracked from source to substrate. For atoms arriving at the substrate, the impact location and velocity vector are obtained, making possible calculation of deposition efficiency, film thickness, adatom energy, and impact angle. These are the key inputs for simulations of resulting film microstructure/morphology evolution. Preliminary results for atomic transport of Cu vapor in supersonic He flows compare favorably with previously reported experimental observations.

Technologically interesting optical materials such as BaTiO3 and KnbO3 are difficult to grow as single crystals of large dimensions. Thin film techniques can overcome this problem by synthesizing these materials on commercially available substrates. We demonstrate the deposition of single crystalline BaTiO3 and KnbO3 on MgO, SrTiO3 and buffered MgO substrates by Pulsed Laser Deposition (PLD). The samples are characterized by Rutherford Backscattering Spectrometry / Channeling (RBS/C), X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). We found excellent crystalline quality, confirmed by RBS/C minimum yield values of 2 % and a FWHM of 0.36° of the BaTiO3(002) rocking curve. Even films of a few microns thickness have been grown without loss of crystalline perfection, and all films show very flat surfaces. The RMS roughness of a 950 nm BaTiO3 film was found to be 1.1 nm.

Low work function surfaces offer great promise as thermionic converters and neutral conversion surfaces due to the relative ease with which electrons may be removed. BaZrO3 surfaces were prepared using pulsed laser deposition (PLD) and their materials properties evaluated for potential use as a neutral conversion surface for space applications. Single layer films were fabricated at temperatures ranging from 110°C to 600°C, and as a function of background ambient pressure. The degree of crystallinity of the resulting films was measured using x-ray diffraction (XRD) and the surface morphology evaluated with atomic force microscopy (AFM). The film quality was found to be directly related to substrate temperature: an increase in grain size from ˜ 10 nm to >50 nm and improved crystal orientation with respect to the substrate were observed as the deposition temperature was increased from 110°C to 600°C.

During pulsed-laser deposition of La0.67Ca0.33MnO3 films on silicon substrates, a system that consists of visible optical-emission spectroscopy (OES) and Fourier transform infrared (FT-IR) spectroscopy is employed to perform in-situ diagnosis of the laser-induced plume and to monitor the substrate temperature and the film thickness. The effects of oxygen pressure, laser fluence, and distance from the target surface on emission spectra were studied. In FT-IR measurements, the slopes of the reflectance versus wavenumber curves were observed to increase with film thickness and hence with time, which provides end-point detection during the film growth. La0.67Ca0.33MnO3 films with (100), (110), and mixed orientations, depending on the substrate temperature, were deposited on yttria-stabilized zirconia (YSZ) buffered Si(100) and Si(111) substrates. In a magnetic field of 5 T, the maximum magnetoresistance (MR) values of 250% at 195 K and 164% at 140 K were observed in the as-deposited (110) and (100) films, respectively.

Cadmium Sulfide (CdS) thin films had been fabricated by a laser deposition technique. Our previous results indicated that the hexagonal structured films could be formed at a substrate temperature of 400 C or higher. Reducing the temperature to 200 C or lower, cubic dominant films had been fabricated. To further understand the effects of other deposition parameters, CdS films were deposited at 30 C in this study. Crystal structures of the films were analyzed by Xray diffraction (XRD) and Transmission Electron Microscopy (TEM). It was found that the processing windows for the cubic films were very limited. As revealed by optical transmission measurements, the optical absorption edge of the cubic film was different from that of the hexagonal film.

Laser Assisted Molecular Beam Deposition (LAMBD) utilizes a train of gas pulses to precisely control the flux of species generated by laser ablation. We have used the LAMBD technique to ablate Si, C or SiC and grow films on a variety of substrates. These films were deposited as a function of a variety of source growth parameters. Source emission spectra of the Si ablation showed atomic Si and Si+; C ablation showed C atoms. Flux control was implemented by a variation of the laser pulse energy. Flux rates were determined by ablation target mass differences. The films have been analyzed by Raman scattering, SEM, EDX, FTIR, ESCA and surface profile measurements to determine the film structure and composition. These results demonstrate the potential of using LAMBD sources as a means of depositing a variety of high quality single and multiple component films.

Pulsed laser deposition of Si on dihydride-terminated (l×1) Si (001) at low temperatures yields epitaxial layers, unlike molecular beam epitaxy. Si films were grown by ultrahigh vacuum pulsed laser deposition on the dihydride surface at substrate temperatures from 40 °C to 350 ° C. Epitaxial thickness and interface roughness were measured by high-resolution cross-sectional transmission electron microscopy and found to be comparable to known data for Si films grown by molecular beam epitaxy on monohydride-terminated (2×l) Si (001). Si films were grown at 200 °C by pulsed laser deposition on the dihydride surface at argon background pressures between 10− torr and 10−1 torr. Ion probe time of flight data was collected over the same pressure range. Comparison of the results suggests that loss of epitaxy is correlated with low incident energy. This, in conjunction with information on surface reconstruction obtained from reflection high-energy electron diffraction, suggests that the mechanism enabling epitaxy on the dihydride surface is Si subplantation, a mechanism only possible in growth with an energetic beam.

Thermodynamic functions of Co-Si and Au-Si systems were studied. The validity of these functions were confirmed by successfully calculating phase diagrams. It was revealed that the composition of the first nucleated compound is close to the concentration of the minimum free energy of the liquid alloy with respect to the two solid components (ΔG) of the binary systems. In addition, the minimum ΔG concentration was found to be located by interpolating the portion of the liquidus, where the liquid alloy is in equilibrium with the two solid constituents, into the central region of the diagram where compounds exist. The minimum ΔG concentration of other silicide and germanide systems were estimated by the suggested interpolation method. A new model for predicting the first nucleated compound in silicide as well as germanide systems was proposed based on the findings.

Epitaxial WS2 films have been grown on MoTe2 (0001) van der Waals faces using W(CO)6 and SnS2 as precursors. Despite a lattice mismatch of 10.3 % the film shows high crystalline quality. The interface is atomically abrupt and shows no interface dangling bonds as deduced from photoemission results (XPS, UPS). The growing overlayer nucleates on the flat (0001) terraces and not on steps as suggested from STM-measurements. For thin epilayers Moiré superstructures in LEED have been measured for the first time in semiconductor heteroepitaxy. From the intensity variation of the LEED spots with energy a corrugation of the overlayer film can be deduced. Based on these results a mechanism of van der Waals epitaxy is suggested.

The II-VI semiconductor CdS was grown by molecular beam epitaxy on the van der Waals faces of the layered semiconductor InSe. Chemical, electronic and morphological properties of the deposited films were investigated by means of low energy electron diffraction (LEED), soft x-ray photoelectron spectroscopy (SXPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). In contrast to observations made on other layered crystals, nucleation of CdS on InSe is possible also at elevated temperatures which is attributed to the small lattice mismatch. The growth front of CdS corresponds to the sulfur terminated polar (111)-B surface which has a strong tendency to form facets.

TiSe2/NbSe2 superlattices crystallized from elementally modulated films have been studied with a Scanning Transmission X-ray Microscope (STXM) at the Advanced Light Source. The samples exhibited structures in the plane of the film with sizes of the order of one micrometer. The chemical sensitivity of STXM allowed us to infer that the titanium in the superlattice exists predominantly in microcrystalline TiSe2, but that these microcrystals are interspersed with elemental titanium inclusions. The STXM images reflect the interfacial nucleation between the constituent layers characteristic of the kinetic trapping method.

A series of kinetically stable, crystalline superlattices containing an integral number of intergrown TiSe2 and NbSe2 layers have been synthesized by controlled crystallization of elementally modulated reactants. Theta-theta and rocking curve data were collected to study the evolution of the initially layered reactants into the crystalline superlattices as a function of temperature. Nucleation of the dichalcogenide structure occurs upon annealing at temperatures above 200°C with the c-axis oriented perpendicular to the substrate surface. The [00l] diffraction linewidths decrease with increased annealing time and temperature suggesting growth of the c-axis domain size. High quality c-axis oriented dichalcogenide crystalline superlattices result from extended annealing at the relatively low annealing temperature of 500°C. The large number of well resolved [00l] Bragg diffraction peaks confirm the well developed crystal structure of the product superlattices in this direction. Four probe electrical conductivity measurements were used to determine the variation of the superconducting critical temperature as a function of the number of TiSe2 and NbSe2 layers in the superlattice.

Cathode ray tube (CRT) technology remains the major display component for today's display technologies. The improvements from monochrome displays to today's full color displays have always been accompanied by improvements in the phosphors. The CRT type displays operate at very high voltages (over 10 keV) at relatively low currents, a few microamps/cm2. The phosphors and phosphor coating technology used in CRT based displays have been optimized for operation with these excitation conditions. However, the developments of field emitter displays based on microtip technology, or negative electron affinity technology require phosphors that operate at lower voltages, preferably 10 to 1500 eV at relatively higher current densities. Zn-rich zinc oxide (ZnO:Zn) powders have shown improved low voltage cathodoluminescence (CL) as compared to conventional ZnS based phosphors. ZnO:Zn thin film phosphors for cathodoluminescent displays, compared to conventional powder phosphors, can have the advantages of high electrical and thermal conductivity, high energy saturation limit, and high screen resolution. The photoluminescence (PL), Electroluminescence (EL), and CL from thin ZnO:Zn films were studied. The samples were prepared by Low Pressure Metal Organic Chemical Vapor Deposition (LP MOCVD) and post-annealed at temperatures from 700 °C to 1000 ° C. The PL, EL, and CL spectra have a peak centered at 590 nm that increases with annealing temperatures up to 1000 °C. The CL efficiencies are 0.12 Lm/W at electron voltages and currents as low as 500 V and 64 mA/cm2. The ZnO films have been characterized by X-ray Diffiractometry (XRD), and Sweep Electron Microscope (SEM). These PL, EL, and CL results from ZnO:Zn films show the promise for improved phosphors to meet Field Emitting Device (FED) challenges.

Film growth consists of two basic processes, deposition and surface relaxation, with opposing effects on the evolution of surface roughness. The pulsed-laser deposition (PLD) growth process has the unique feature of having periods of very high deposition rates on μs time scales followed by periods, on the order of seconds, with only surface relaxation. In this paper we report the first efforts towards exploiting this unique feature to study these two basic processes independently. Thin epitaxial films of ZnSe were grown using PLD on (001) GaAs and 2° miscut (001) GaAs substrates. For growth on both the singular and vicinal surfaces, RHEED patterns taken following growth showed clear, streaky first zone and sharp second zone spots, and well-defined Kikuchi lines; these features are indicative of a smooth growth surface and high quality film. No reconstruction of the growth surface was observed, in contrast to behavior observed in molecular beam epitaxy. Time-resolved RHEED measurements show that a single morphology developed during growth on singular (001) GaAs. However, during growth on miscut (001) GaAs, two morphologies developed, one transitory and one appearing to evolve towards steady state. When growth on the miscut substrate was stopped, recovery of the RHEED signal was observed. The rate of recovery could be attributed to two relaxation processes, as differentiated by their time constants. Potential origins of these observations are discussed.

The results of laser induced surface structure modifications utilizing time-resolved reflectivity measurements are presented for the pulsed laser irradiation (λ. = 1.06 μm and 0.53 μm) of thin polysilicon (poly-Si) layers of 0.1 μm, 0.45 μm and 1.0 μm in thickness on silicon substrates. It was shown that when the poly-Si layer of 0.1-0.45 thickness is totally molten, during a solidification, a large-grained structure having grain sizes exceeding the thickness of the molten Si layer is formed. At the same time, the time-resolved reflectivity changes its value nonmonotonically. This nonmonotonic behavior is due to the outcropping of growing grains onto the surface before the formation of a solid crystalline front as well as to the influence of the surface phenomena on the crystallization process.