Polycrystalline Tetragonal Phase Research Articles

The free electron model and the electronic energy losses of protons at low velocities interacting with polycrystalline tantalum

In this letter, we report experimental data and theoretical work on the electronic energy loss and energy loss straggling of protons transmitted through self-supported thin films of tantalum in a polycrystalline tetragonal phase . Low-energy protons with energies below 10 keV and Ta films with nominal thickness of 6, 9 and 12 nm are used. The aim of this work is to understand the unexpected values of the Ta stopping power for low-energy proton backscattering reported recently, which are far from the prediction of the standard free electron gas model and semi-empirical approaches. This had led the authors to conclude the failure of the free electron model. Our transmission measurements confirm these experimental results. In this work, a qualitative discussion and quantitative explanation of our experimental results is given, using an approach based on the density functional theory within the framework of the free electron gas (FEG) model. We performed semiclassical deterministic trajectory simulations and employ the local density approximation model, using an inhomogeneous electron density distribution and the polycrystalline character of Ta samples.

Effect of Sm doping and annealing on magnetic and structural properties of sputter deposited SnO2 thin films

SmxSn1−xO2 thin films (with x = 0, 0.005, 0.02 and 0.04) were sputter deposited on Si (100) substrates and its physical properties were investigated. The as-deposited thin films were amorphous; however after electron beam rapid thermal annealing became polycrystalline tetragonal phase [JCPDS21-1250]. The preferred crystal growth orientation of the annealed thin films were along (101) plane, in contrast with its bulk where it is along (110) plane. However in both cases the crystallinity of SmxSn1−xO2 thin films reduced with increase in Sm dopant concentration. The annealed thin films showed continuous grain distribution, with linear increase in grain size from ∼12 to ∼52 nm with increase in Sm dopant concentration. Maximum magnetization of 0.031 emu was observed in annealed Sm0.04Sn0.96O2 thin film. The observed weak ferromagnetism in the thin films could have originated from the induced oxygen vacancies through Sm substitution and electron beam rapid thermal annealing in high vacuum. It was also observed that the optical absorption of doped SnO2 thin films (in 300 to 800 nm range) decreased by Sm doping. These observations suggest that Sm doped SnO2 thin films can be potentially used for dilute magnetic semiconductor and solar cell application.

Electrical Properties of Semiconducting YBa2Cu3O7-x Thin Film for Uncooled Infrared Detectors

Uncooled pyroelectric infrared based on semiconducting YBa2Cu3O6+x (YBCO) thin films have been investigated. YBCO precursor solutions were prepared by sol-gel method and YBCO films were fabricated by the spin coating method and structural and electrical properties with variation of annealing temperature were studied. As a result of the differential thermal analysis and thermogravimetry (DTA-TG) analysis, endothermic peak was observed at around 750°C due to the formation of the tetragonal phase. The crystal structure of the YBCO film annealed at 750°C was polycrystalline tetragonal phase. The thickness of all the films was approximately 0.26∼0.31 μm and average grain size of the YBCO film sintered at 750°C was about 60 nm. Temperature resistance coefficient (TCR), responsivity and detectivity of the YBCO film sintered at 750°C were 3.7%/K at room temperature, 14.47 V/W and 7.23 × 106 cm Hz1/2/W, respectively.

Laser and Thermal Vapor Deposition of Metal Sulfide (NiS, PdS) Films and in Situ Gas-Phase Luminescence of Photofragments from M(S2COCHMe2)2

NiS and PdS thin films are prepared at 10-2 Torr from the single-source precursors M(S2COCHMe2)2, M = Ni and Pd. Two different vapor deposition processes, photochemical and thermal, are employed. Gas-phase emission spectroscopy is used during the photochemical deposition to identify the two elemental components of the final materials, the metal atom and sulfur, in the gas phase. NiS and PdS thin films are grown by the thermal process at 300 and 350 °C, respectively, on Si and quartz substrates. The NiS films are highly oriented rhombohedral (γ) phase, and the PdS films are tetragonal-phase polycrystalline. The metal sulfide films are grown photolytically by 308 nm laser irradiation of the gas-phase precursors at lower temperatures (near the sublimation temperature). The NiS films show no X-ray diffraction patterns, but the PdS films are polycrystalline tetragonal phase. The films are analyzed by various surface analytical tools including scanning electron microscopy, X-ray photoelectron, and Rutherford ba...