C+轰击铍的分子动力学模拟

使用分子动力学模拟方法研究了入射能量对C⁺离子与Be样品表面相互作用的影响。模拟结果表明,随着C⁺离子的入射能量增大,C⁺离子注入深度也增加,Be原子的溅射产额近似线性增加,而滞留在样品中的C原子数量变化不大,在C⁺离子轰击Be样品的初始阶段,样品中Be原子的溅射产额较大,而随着C⁺离子注入剂量的增加,Be原子的溅射产额逐渐减小并趋于稳定。在此作用过程中,在样品表面形成一个富C层,减缓了样品中Be原子的溅射速率,起到了保护Be样品的作用。     

Thickness induced magnetic anisotropic properties of Tb-Fe-Co thin films

The influence of Tb₂₅Fe₆₁Co₁₄ thin film thicknesses varying from 2 to 300 nm on the structural and magnetic properties has been systematically investigated by using of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, magnetization, and magneto-optic Kerr effect microscopy measurements. Thin film growth mechanism is pursued and controlled by ex-situ X-ray refractometry measurements. X-ray diffraction studies reveal that the Tb₂₅Fe₆₁Co₁₄ films are amorphous regardless of thin films thicknesses. The magnetic properties are found to be strongly related to thickness and preferred orientation. With an increase in film thickness, the easy axis of magnetization is reversed from in-plane to out-of-plane direction. The change in the easy axes direction also affects the remanence, coercivity and magnetic anisotropy values. The cause for the magnetic anisotropy direction change from in-plane to out-of-plane can be related to the preferred orientation of the thin film which depends on the large out-of-plane coercivity and plays an important role in deciding the easy axes direction of the films. According to our results, up to the 100 nm in-plane direction is dominated over the whole system under major Fe-Fe interaction region, after that point, the magnetic anisotropy direction change to the out-of-plane under major Tb-Fe/Tb-Co interaction region and preferred orientation dependent perpendicular magnetic anisotropic properties become more dominated with 2.7 kOe high coercive field values.     

The interactions of thiophene with polycrystalline UO2

We have studied the adsorption and desorption of thiophene on polycrystalline UO₂ as function of coverage, over the temperature range 100-640 K, using X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) and electron stimulated desorption (ESD). Thiophene is found to adsorb molecularly on stoichiometric UO₂. C 1s and S 2p XPS spectra are measured at different thiophene exposures and at different temperatures; they show no evidence for the presence of dissociation fragments, confirming that thiophene adsorbs and desorbs molecularly on a polycrystalline stoichiometric UO₂ surface. The variation of the S 2p and C 1s intensity as function of exposure, together with ESD measurements of O⁺ as function of exposure, can be connected to the growth mode of a thiophene film on UO₂; the thiophene film converts from a flat-lying configuration to an inclined structure as coverage increases. The effects of X-rays, UV, and electron irradiation on thiophene films have been studied in two different coverage regimes, monolayer and multilayer. Irradiation leads to a modification of thiophene films, and appreciable concentrations of species stable to 640 K are present on the surface for both regimes. The XPS results suggest that irradiation induces polymerization and oligomerization, as well as formation of thiolates and dissociation fragments of thiophene. The adsorption and reactivity of thiophene on defective UO₂ surfaces have also been studied. The O vacancies and defects in the oxide surface cause cleavage of C-H and C-S bonds leading to the dissociation of thiophene at temperatures as low as 100 K. These results illustrate the important role played by O vacancies in the chemistry of thiophene over an oxide surface.     

Fabrication techniques for colymer/Si optical waveguide

In this paper fabrication techniques were investigated for polymer/Si optical waveguide. The aluminum film was used as photolithographic mask instead of photoresist to improve waveguide profile. The influence of aluminum metal cladding produced by sputtering process on the optical character of the device was discussed. The absorption loss was calculated and measured by using effective index method and cut-back method, respectively. Optimized etching parameters were given in reactive ion etching using oxygen, such as radio frequency power and gas flow rate. Measured near-field mode pattern indicated fabrication waveguide achieved single-mode transmission at wavelength 1.55 μm.     

Growth and optical properties of Fe2O3 thin films: A study of quantum confinement effects by experiment and theory

Thin iron films in the thickness range 0.7–48 nm have been deposited on high quality Corning glass and Si(100) substrates by radio frequency magnetron sputtering. The films were then oxidized by annealing at temperatures of 400−450 °C in a furnace in air. X-ray diffraction experiments revealed the formation of single-phase α-Fe₂O₃. The films were continuous and present negligible surface roughness. Ultraviolet-visible light absorption spectroscopy has shown a blue shift of both, the indirect and direct band gaps of hematite. The experimental results are interpreted as evidences of quantum confinement effects. This is facilitated by theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation. The agreement between theory and experiment supports the quantum confinement interpretation.     

Sputtering of clusters from nickel-aluminium

A NiAl(1 1 1) single crystal was bombarded with 15 keV Ar⁺, and the resulting secondary neutrals were analysed by laser postionisation secondary neutral mass spectrometry. By measuring the individual cluster photoion intensity as a function of laser power, the sputter yields of 33 individual clusters were determined. The yield of Al_n clusters sputtered from NiAl falls with increasing cluster nuclearity as n^−8.7 while Ni_n and Al_m−nNi_n yields are proportional to n^−5.9 and n^−5.2, respectively. The distribution of thee yields of mixed Al_m−nNi_n clusters with n and m is found to diverge significantly from the expected distribution based on a random combinatorial approach, indicating that the energetics due to the chemical bonding in the clusters plays a significant role during cluster formation in the sputtering process.     

High thermoelectric power in a NaxCoO2 thin film prepared by sputtering with rapid thermal annealing

Na_xCoO₂ thin films were fabricated by means of RF-magnetron sputtering. We measured and analyzed the thermal properties and changes of the Na_xCoO₂ crystal structure by XRD, SEM, Raman spectra, and XPS analyses. Sodium ions diffused from the bulk of the thin film to the surface as the temperature increased. The diffused Na ions reacted with oxygen ions and Na₂O was formed on the surface of the thin film, resulting in a decrease of the carrier concentration and a change of the crystal structure from a layer to a spinel structure. The Seebeck coefficient of the Na_xCoO₂ thin film annealed at 550 °C is larger than the value (100 μV/K) for single crystal NaCo₂O_4.     

Substrate temperature dependence of the properties of scandium-doped ZnO films deposited by sputtering

Structural and optical properties of Sc-doped ZnO films grown by RF magnetron sputtering at different substrate temperatures were investigated. All the ZnO:Sc films are polycrystalline with the hexagonal wurtzite structure. X-ray diffraction patterns of the films showed that the doped-films have (0 0 2) as preferred orientation when the deposition temperature was increased from 250 °C to 300 °C. All the films are in a state of compressive stress, whereas the stress decreases gradually with increasing substrate temperature. The average transmittance of these films was above 90% in the wavelength range from 400 nm to 800 nm. The optical band gap of these films was determined. The optical constants of these films were determined using transmittance and reflectance spectra.     

The control of the diameter of the nanorods prepared by dc reactive magnetron sputtering and the applications for DSSC

The TiO₂ nanorod arrays, with about 1.8 μm lengths, have been deposited on ITO substrates by dc reactive magnetron sputtering at different target-substrate distances. The average diameter of these nanorods can be modified from about 45 to 85 nm by adjusting the target-substrate distance from 90 to 50 mm. These nanorods are highly ordered and perpendicular to the substrate. Both XRD and Raman measurements show that the nanorods prepared at different target-substrate distances have only an anatase TiO₂ phase. The nanorods prepared at the target-substrate distance less than 80 mm have a preferred orientation along the (2 2 0) direction. However, this preferred orientation disappears as the target-substrate distance is more than 80 mm. These TiO₂ nanorods have been used as the electrodes for dye-sensitized solar cells (DSSCs). The highest conversion efficiency, about 4.78%, has been achieved for TiO₂ nanorods prepared at 80 mm target-substrate distance.     

Influence of plasma pressure on the growth characteristics and ferroelectric properties of sputter-deposited PZT thin films

PZT thin films of thickness (320-1040) nm were synthesized on Si/SiO₂/Ti/Pt multilayered substrates by radio frequency magnetron sputtering. The influence of plasma pressure in the range of (0.24-4.9) Pa, during deposition, on the structural, electrical and ferroelectric properties of the PZT films was systematically studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and cross-sectional transmission electron microscopy (XTEM) were employed for structural study. Nano-probe Energy Dispersive (EDX) line scanning was employed to investigate the elemental distribution across the film-bottom electrode interface. I-V characteristics and polarization-electric field (P-E) hysteresis loop of the films were measured. The study reveals that the plasma pressure has a strong influence on the evolution and texture of the ferroelectric perovskite phase and microstructure of the films. At an optimum plasma pressure of 4.1 Pa, PZT films are grown with 93% perovskite phase with (1 1 1) preferred orientation and uniform granular microstructure. These films show a saturation polarization of 67 μC/cm², remnant polarization of 30 μC/cm² and coercive field of 28 kV/cm which, according to the literature, seem to be suitable for device applications.Transmission electron microscopy (TEM) study shows that at a plasma pressure of 4.1 Pa, the PZT/bottom Pt interface is sharp and no amorphous interlayer is formed at the interface. At a higher plasma pressure of 4.9 Pa, poor I-V and P-E hysteresis loop are observed which are interpreted as due to an amorphous interlayer at the film-bottom electrode interface which is possibly enriched in Pb, Zr, O and Pt.