Changes In Film Orientation Research Articles

Sputtering gas pressure and target power dependence on the microstructure and properties of DC-magnetron sputtered AlB2-type WB2 films

The study is mainly to optimize the process parameters (sputtering pressure and sputtering power) of the AlB2-type WB2 films deposited by DC magnetron sputtering by comparing their microstructure, elemental composition, and tribo-mechanical properties. As the argon pressure (PAr) increases (0.3–1.0 Pa), the particle density increases first and then decreases, with a corresponding decrease for particle energy. Under this condition, both the deposition rate and the B/W atomic ratio of the WB2 films increase first and then decrease under the competition effect between the sputtering and scattering process, the film orientation changes from (0 0 1) to (1 0 1), the microstructure changes from dense fine-fiber to porous column coupled with the stress evolution from compressive stress to increased tensile stress. Consequently, films deposited at PAr > 0.5 Pa have the poor hardness and wear-resistance. As the sputtering power increases (150–310 W), both the particle density and particle energy increase. Thus, the deposition rate increases greatly, the B/W atomic ratio declines slightly due to the resputtering process, the film structure becomes dense but rough by the particle bombardment causing the stress change from tensile stress to enhanced compressive stress, and the film orientation changes from the well-crystallized (0 0 1) to poor-crystallized (1 0 1). In conclusion, films with (0 0 1) orientation, high B/W atomic ratio, dense structure and proper compressive stress, which can be deposited at PAr = 0.5 Pa and sputtering current 0.5 A (corresponding to target power about 150 W), show the excellent tribo-mechanical properties with high hardness about 39.4 GPa and low wear rate of 2.2 × 10−7 mm3/mN.

Epitaxial growth of Bi thin films on Ge(1 1 1)

We investigated Bi thin film growth on Ge(1 1 1) by using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). In the submonolayer regime, adsorbed Bi atoms form patches of the ( 2 × 1 ) structure. However, the structure does not grow to a long-range order. Following the formation of a ( 1 × 1 ) monolayer (ML) film, two-dimensional (1 1 0)-orientated Bi islands grow. The film orientation changes from (1 1 0) to (1 1 1) at 6–10 ML. The (1 1 0)-oriented Bi film shows a six-domain LEED pattern with missing spots, associated with a glide-line symmetry. The hexagonal (1 1 1) film at 14 ML has a lattice constant 2% smaller than bulk Bi(1 1 1).

Structural Properties of CdTe Thin Films for Solar Cell Applications Deposited on Flexible Foil Substrates

AbstractCadmium telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal band gap of 1.45 eV and its high optical absorption coefficient. The typical CdTe thin film solar cell is of the superstrate configuration where a window layer (CdS), the absorber (CdTe), and a back contact are deposited onto a glass slide coated with a transparent electrode. Substrate CdTe solar cells where the above listed films are deposited in reverse order are not common. In this study, the growth of CdTe thin films deposited on foil substrates by the close-spaced sublimation (CSS) has been investigated for the purpose of fabricating substrate based CdTe solar cells. The CdTe films were deposited at substrate temperatures (TSUB) in the range of 300 to 600°C, and source temperatures (TSRC) in the 600 to 650°C range. The effect of the substrate-source temperature variations on the growth rate, film structure and morphology were studied using XRD and SEM. It was found that for low substrate temperature and as the growth rate increases, grain size was the same but the films appeared to be more uniform and more densely packed with less or no pinholes. The growth rate increased as the source temperature increased. The substrate temperature clearly influences the grain growth and the preferred orientation. As the substrate temperature increased the growth rate decreased and the grain size varied from 2 to 6 μm. XRD analysis showed that with the increase in substrate temperature film orientation changes from preferential along the (111) direction to a mix of (111) (220) and (311).

Preparation and characterization of highly conducting and transparent Al doped CdO thin films by pulsed laser deposition

Highly conducting and transparent aluminum doped CdO thin films were deposited using pulsed laser deposition technique. The effect of growth temperature on structural, electrical, and optical properties was studied. It is observed that the film orientation changes from preferred (1 1 1) plane to (2 0 0) plane with increase in growth temperature. The electrical resistivity of the films was found to increase with increase in growth temperature. The low resistivity of 4.3 × 10 −5 Ω cm and high transparency (∼85%) was obtained for the film grown at 150 °C. The band gap of the films varies from 2.74 eV to 2.84 eV.

Structural and ferroelectric properties of yttrium substituted bismuth titanium thin films

Yttrium substituted Bi 4− x Y x Ti 3O 12 ( x = 0.00, 0.10, 0.30, 0.50, 0.75, 1.00) polycrystalline thin films were synthesized by metal-organic decomposition method. Ferroelectric measurements revealed that the Bi 4Ti 3O 12 (BTO) films substituted by Y with appropriate ratios could have higher remnant polarization and significantly improved fatigue behavior compared with BTO. The remnant polarization of the Bi 3.50Y 0.50Ti 3O 12 capacitor reached 10 μC/cm 2 at an applied field about 120 kV/cm with nearly fatigue free property up to 10 10 cycles. By using Raman spectra, X-ray diffraction, and scanning electron microscope to analyze the structure and composition of the films, it was found that the Y substitution of Bi at A-site induces changes in film orientation and the lattice distortion that are probably responsible for the improved ferroelectric properties. The microstructure and its relation with the leakage behavior of these thin films were also discussed.

Determination of the polarity of ZnO thin films by electron energy-loss spectroscopy

The polarity of the ZnO film grown on sapphire using an ultra-thin Ga wetting layer has been investigated by electron energy-loss spectroscopy (EELS). The intensity of the oxygen K-edge in electron energy-loss spectrum from the ZnO film shows a prominent difference when the film orientation changes from the (0002) Bragg condition to the (000 2 ̄ ) Bragg condition. The EELS study reveals that the ZnO film with very thin Ga wetting layer has the [0001] polarity, which is further confirmed by the conventional convergent beam electron diffraction method.

Fabrication and characterization of double-sided YBCO superconducting thin films using laser ablation

Abstract Epitaxial growth of double-sided high- T c superconducting (HTSC) thin film has been systematically investigated since it is important for microwave applications as well as for fundamental research. We have fabricated highly c -axis oriented YBa 2 Cu 3 O 7− x (YBCO) superconducting thin films on (100) MgO substrates by pulsed laser deposition(PLD), because devices like microwave stripline filters for communication systems require high-quality HTSC thin films on both sides of single crystal wafers. To use one-sided film as a low-loss ground plane, we have used a halogen lamp to heat the substrate without silver paste to preserve its backside for the fabrication of double-sided superconducting thin films. The electrical property and the structural characteristics of YBCO films have been studied by R – T measurement and X-ray diffraction. We have observed by X-ray diffraction the film orientation changes from c -axis to a -axis as the film thickness increases. Glancing-angle X-ray diffraction revealed that the film orientation was changed from fully c -axis near the substrate/film interface to a mixture of a -axis and c -axis near the film surface. This should be considered in the manufacture of superconducting microwave devices. By optimizing the thickness and the deposition temperature of YBCO thin films, highly c -axis-oriented double-sided YBCO thin films have been fabricated. The transition temperature of these films has been shown to be about 88 K.

ＴｉＮイオンプレーティング皮膜の配向性におよぼす基板の影響

TiN films were prepared on SK 5 and glass substrates by RF ion plating at various values of nitrogen pressure, bias voltage and RF power. The effects of these process parameters on the X-ray intensity and composition data of the films were studied using X-ray diffraction and X-ray photoelection spectroscopy (XPS).At higher nitrogen pressure, the TiN film surface was predominantly parallel to (200) for steel substrates and to (111) for glass. At lower bias voltage and lower RF power, the (111) orientation was strongly preferred for both substrates, while at higher bias voltage and higher RF power, the film surface was predominantly parallel to (200) for steel substrates and (111) for glass. It was found that these changes in film orientation can be explained by a gas adsorptive inhibition model, even for insulating substrates.

Spectroscopic ellipsometry studies of YBa2Cu3O7−δ deposited on SrTiO3

The dielectric function ε=ε1−iε2 of the YBa2Cu3O7−δ high-Tc superconducting films grown on (100) SrTiO3 (c-axis oriented) and (110) SrTiO3 (ab-oriented) substrate was measured by spectroscopic polarization modulation ellipsometry (SPME) and changes in film orientation were studied by comparing films of various thicknesses. The films deposited on SrTiO3 (100) substrates demonstrated an isotropic ε1 that changed with film thickness. It is observed that the decrease in the metallic dielectric behavior associated with the increase in the thickness of the films grown on (100) SrTiO3 substrates is mainly due to a change in the orientation of the films. The films deposited on SrTiO3 (110) showed anisotropic dielectric behavior when the plane of polarization is parallel and perpendicular to the c-axis of the film. These studies show that for this high-temperature superconductor with anisotropic dielectric behavior, SPME is a highly sensitive technique capable of measuring small changes in the film orientation.