Preparation and investigation of VOx thin films of n- and p-types

In this work we present first results on the synthesis of vanadium oxide semi-transparent conducting thin films of p- and n-types. The films were deposited by thermal evaporation method in vacuum, on: silicon, glass, sapphire, and gold substrates. Temperature of substrate during deposition was set around 250 °C. As deposited films were of a p-type of conductivity. Thermal annealing at 420 °C of as-deposited films in air at atmospheric pressure resulted in a change in the conductivity type.Optical, electrical and thermal properties of the deposited films were studied. The topography of the films was studied using AFM microscope. P-N structures were created using VO_x films on silicon and glass substrates. Electrical measurements had shown a non-linear behaviour of the samples.     

Characterization of electron irradiated GaN n-p diode

Electron-beam irradiated GaN n⁺-p diodes were characterized by deep level transient spectroscopy (DLTS) and optical responsivity measurements. The GaN n⁺-p diode structures were grown by metal organic chemical vapor deposition technique, and the electron irradiation was done by the energies of 1 MeV and 2 MeV with dose of 1 × 10¹⁶ cm^− 2. In DLTS measurement, the defect states of E_c − 0.36 eV and E_c − 0.44 eV in the electron irradiated diodes appeared newly. The optical responsivity of GaN n⁺-p diode was characterized in ultra-violet region, and then the maximum optical responsivity at 350 nm was decreased after electron-beam irradiation.     

Effects of deposition parameters on SiCln (n=0-2) densities in SiCl4 glow discharge plasma

The relative densities of SiCl_n (n=0-2) in SiCl₄ radio frequency (rf) glow discharge plasma are measured by mass spectrometry. The effects of discharge parameters, including rf power, discharge pressure, substrate temperature and SiCl₄ flow rate on the relative densities of SiCl_n (n=0-2) are investigated in detail. The experimental results demonstrate that the relative densities of SiCl_n (n=0-2) in SiCl₄ plasma are dependent strongly on these discharge parameters. An optimum configuration of discharge parameters (low rf power, high discharge pressure, low substrate temperature and low flow rate), which enhanced the formation of SiCl_n (n=0-2) radicals, was searched. Further, researching of SiCl_n (n=0-2) spatial distribution for seeking a suitable deposition condition is beneficial for understanding the deposition mechanism of thin films.     

Study of electric dipole and space charge characteristics of Al/C12TCNQ/Al by means of thermally stimulated current measurements

Electric dipole and space charge characteristics of Al/2-dodecyl-7, 7, 8, 8-tetracyanoquinodimethane (C₁₂TCNQ)/Al were studied by means of thermally stimulated current (TSC) measurements. The TSC curve of Al/C₁₂TCNQ/Al had two peaks, one at a temperature below 80 °C, which is due to the depolarization of electric dipoles, and the other, at a temperature above 80 °C, which is due to the movement of space charges in the C₁₂TCNQ Langmuir-Blodgett (LB) films. The polarization direction of the electric dipoles in the C₁₂TCNQ LB films was from the hydrophilic group to the hydrophobic group.     

Enhanced conductivity of pulsed laser deposited n-InGaZn6O9 films and its rectifying characteristics with p-SiC

Wide band gap InGaZn₆O₉ films of thickness ~ 350 nm were deposited on sapphire (0001) at room temperature by using the pulsed laser deposition technique. The transparent films showed the optical transmission of > 80% with the room temperature Hall mobility of ~ 10 cm²/V s and conductivity of 4 × 10² S/cm at a carrier density > 10²⁰ cm^− 3. The electrical properties as a function of deposition temperatures revealed that the conductivity and mobility almost retained up to the deposition temperature of 200 °C. The films annealed in different atmospheres suggested oxygen vacancy plays an important role in determining the electrical conductivity of the compound. Room temperature grown heterostructure of n-InGaZn₆O₉/p-SiC showed a good rectifying behavior with a leakage current density of less than 10^− 9 A/cm², current rectifying ratio of 10⁵ with a forward turn on voltage ~ 3 V, and a breakdown voltage greater than 32 V.     

Numerical simulation of transient waves in a heterogeneous soil layer

The passage of elastic waves through the upper soil strata is modeled by a rather simple solution based on freely propagating waves in a continuously heterogeneous material with amplitude dependence on a single coordinate corresponding to the direction of propagation. Specifically, pseudo-dilational and pseudo-rotational waves are developed for an elastic medium with position-dependent density and thus position-dependent pressure (P) and shear (S) wavespeeds, although in a strict sense these no longer exist as such due to coupling through the material heterogeneity. Time harmonic conditions are assumed to hold at the fundamental solution level and transient signal generation is achieved through Fourier synthesis. Numerical examples for the square root of linear in the depth coordinate wavespeed profiles are used in modeling the passage of impulsively-generated signals in a soft soil deposit under two-dimensional conditions.     

Characterisation of carbon fibres recycled from carbon fibre/epoxy resin composites using supercritical n-propanol

Three different PAN based carbon fibres (Toray T600S, T700S and Tenax STS5631) were recycled from epoxy resin/carbon fibre composites using supercritical n-propanol. The recycled carbon fibres were characterised using single fibre tensile tests, SEM, XPS and micro-droplet test. The tensile strength and modulus of the recycled carbon fibre was very similar to the corresponding as-received carbon fibres. However, the surface oxygen concentration decreased significantly, which caused a reduction of the interfacial shear strength with epoxy resin.     

Growth and properties of transparent p-NiO/n-ITO (In2O3:Sn) p-n junction thin film diode

We have grown “all oxide” transparent p-n junction thin film nanostructure device by using chemical solution deposition and E-beam evaporation onto SiO₂ substrate. Combined grazing incidence X-ray diffraction and atomic force microscopy confirm phase pure, mono-disperse 30 nm NiO and 2 at. wt.% Sn doped In₂O₃ (ITO) nanocrystallites. Better than 70% optical transparency, at a wavelength of 600 nm, is achieved across 160 nm thick p-n junction. The optical band gap across the junction was found to decrease as compared to the intrinsic ITO and NiO. The current-voltage (I-V) characteristics show rectifying nature with dynamic transfer resistance ratio of the order of 10³ in the forward bias condition. Very small reverse leakage current with appreciable breakdown was observed under the reverse bias condition. The observed optical and electrical properties of oxide transparent diode are attributed to the heteroepitaxial nature and carrier diffusion at the junction interface.     

Study of space charge in gallium nitride by the thermal step method

In this paper, we report the electric investigation of thin nitride gallium films by the capacitance voltage technique and the thermal step method (TSM). The C–V analysis at 1 MHz of Au/GaN diode reveals MOS behaviour and shows strong capacitance hysteresis.

This may be due to the presence of trapped charge in this structure. The space charge dynamics is studied by thermal step method at different applied voltages. The TS currents are reverted from negative ones to positive ones above inversion threshold of +0.2 V. This change corresponds to charge modulation from accumulation to the inversion one, in good agreement with the C–V characteristics. The stored charge in this sample is related to the nature of gallium nitride and to the manufacturing processes. The results confirm the possibility to apply the TSM for the measurement of the space charge in the semiconductor materials.     

EDTA-assisted hydrothermal synthesis,characterization, and luminescent properties of YPO4·nH2O:Eu (n = 0, 0.8) microflakes and microbundles

In this paper, the YPO₄:Eu³⁺ (5%) microflakes and YPO₄·0.8H₂O:Eu³⁺ (5%) microbundles have been synthesized by a simple EDTA-assisted hydrothermal method. The X-ray powder diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and photoluminescence (PL) were employed to characterize the as-obtained products. It was found that the composition of the product could be changed from YPO₄:Eu³⁺ (5%) to YPO₄·0.8H₂O:Eu³⁺ (5%) with a further increase in the amount of EDTA 0.5–1.0 g. The YPO₄:Eu³⁺ (5%) presented the pure tetragonal phase and flake-like microstructure, while the YPO₄·0.8H₂O:Eu³⁺ (5%) exhibited the hexagonal phase and bundle-like morphology. The possible formation mechanisms of the two architectures were put forward on the basis of different EDTA amount-morphology experiments. A detailed investigation on the photoluminescence of YPO₄·nH₂O:Eu³⁺ (5%) different samples indicated that the luminescent properties of products were strongly dependent on the compositions, morphologies, coordination environment and crystal field symmetry.     

电子束辐照后聚甲基丙烯酸甲酯的电荷特性

用电子束辐照的方法将电荷引入聚甲基丙烯酸甲酯中,研究了电子束辐照对样品电导率、介电常数的影响,以及电荷脱阱对样品的破坏行为.结果表明,电介质的击穿并不总是发生在电荷的注入过程中,也可以发生在空间电荷的脱阱过程中.同时探讨了注入电荷在样品内的输运情况和空间电荷脱阱对样品的破坏机理.     

Plasma deposition of n-SiOx nanocrystalline thin film for enhancing the performance of silicon thin film solar cells

In this paper, we firstly optimized the properties of n-SiO_x nanocrystalline thin film through tuning deposition parameters by plasma enhanced chemical vapor deposition, so that we can actively control the properties of materials obtained. Secondly, we proposed using n-SiO_x/Al as back reflector for amorphous silicon (a-Si:H) solar cells. Compared to Al single-layer as back reflector, adding an n-SiO_x layer into the back reflector could improve the solar cell performance, which not only enhances the short circuit current density by an improvement of spectral response in the wavelength range of 550-750 nm, but also improves the open circuit voltage. With an optimized n-SiO_x/Al back reflector, a-Si:H solar cells with an intrinsic layer thickness of 270 nm show 13.1% enhancement in efficiency. In addition, a-Si:H/μc-Si:H tandem solar cells with n-SiO_x as intermediate reflector were also researched. As a result, it evidently balanced the current matching between top and bottom cell.     

A study of atomic layer deposited LiAlxOy films on Mg-Li alloys

LiAl_xO_y films with thicknesses of 65-200 nm were deposited by the atomic layer deposition (ALD) technique on the LZ101 Mg-Li alloy. The ALD-deposited LiAl_xO_y films exhibit an amorphous structure and have an atomic ratios of Li:Al:O = 1:1:2. The potentio-dynamic polarization tests show that the corrosion resistance of Mg-Li alloys can be significantly improved due to the dense and pinhole-free structure as well as the excellent coverage and conformity of the ALD-deposited LiAl_xO_y films.     

A n-order shear deformation theory for free vibration of functionally graded and composite sandwich plates

In the present paper, a n-order model for functionally graded and composite sandwich plate is developed. This model uses the n-order polynomial term to represent the displacement field. Zero transverse shear stress boundary conditions at the top and bottom of the plate are satisfied. The third-order theory of Reddy [8] can be considered as a special case of present n-order theory. Natural frequencies of the functionally graded and composite plates with various side-to-thickness ratios, material properties are computed by present n-order theory with different n values. The results are compared with available published results which demonstrate the accuracy and efficiency of present n-order theory.     

分段装药结构爆破效果的数值模拟研究

基于大型非线性动力分析软件LS-DYNA,选用弹塑性模型*MAT_PLASTIC_KINEMATIC和JWL方程,建立无限岩体介质中中深孔爆破时连续装药结构和分段装药结构三维模型,并进行了数值模拟,再现了两种装药结构爆破过程中的应力发展过程,对比分析了它们在Von Mises有效应力分布、自由面有效应力峰值、孔壁压力分布及加速度等衰减上的差异。结合工程现场爆破实践验证了分段装药结构可以明显改善爆破效果。     

An organic nonvolatile memory using space charge polarization of a gate dielectric

We realize a nonvolatile and rewritable memory effect in an organic field-effect transistor (OFET) structure using polymethylmethacryrate (PMMA) dispersed with 10-methyl-9-phenylacridinium perchlorate (MPA⁺ClO₄⁻) as a gate dielectric. Applying a voltage between a top source-drain electrode and a bottom gate electrode induces electrophoresis of two ions of MPA⁺ and ClO₄⁻ towards the corresponding electrodes in the memory devices. The drain currents of the memory devices markedly increase from 10^− 9 A to 10^− 2 A under no gate voltage condition due to the strong space charge polarization effect. Our memory devices have excellent electrical bistability and retention characteristics, i.e. the memory on/off ratio reached 10⁷ and the drain current maintained 40% of the initial value after 10⁴ s.     

乳化炸药聚能射流侵彻靶板的数值仿真

为了研究聚能射流侵彻靶板的过程,采用乳化炸药对半球形药型罩聚能射流侵彻靶板实验,控制炸高为9cm,药型罩采用铜质材料。利用AUTODYN软件对聚能射流的形成、侵彻铝板的过程进行数值仿真,并且对多物质EULER算法求解得到的模拟结果进行分析,仿真结果与实验结果基本一致。     

Influence of oxygen/argon pressure ratio on the morphology, optical and electrical properties of ITO thin films deposited at room temperature

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO) thin films onto glass substrates are widely used as transparent and conductive electrodes for a variety of technological applications including flat panel displays, solar cells, smart windows, touch screens, etc.ITO films on glass and polycarbonate (PC) substrates were prepared at room temperature (RT) and at different PO₂. The films were characterized in terms of the surface roughness (δ), sheet resistance, the refractive index (n) and extinction coefficient (k). The free carrier density (n_c) and the carrier mobility (μ) of the ITO (In₂O₃:Sn) films were measured and studied. The n_c and μ values vary in different ratio of oxygen partial pressure (PO₂) of ITO deposition. The observed changes in the ITO film resistivity are due to the combined effect of different parameter values for n_c and μ. From AFM analysis and spectra calculations, the surface roughness values of the ITO films were studied and it was observed that the δ values were lower than 15 nm. The energy band gap E_g ranges from 3.26 eV to 3.66 eV as determined from the absorption spectrum. It was observed an increase on the energy band gap as the PO₂ decrease in the range of 20-2% PO₂. The Lorentz oscillator classical model has also been used to fit the ellipsometric spectra in order to obtain both refractive index n and extinction coefficient κ values.     

Effects of low-energy ion beam glancing angle nitridation on nGaAs surface and Co-nGaAs Schottky contact properties

In this research, effects of low-energy nitrogen and argon ion beam irradiation at a glancing angle on chemical composition and morphology of the GaAs surface as well as electrical properties of Co-nGaAs Schottky contact are studied. Substantial reduction of the effective barrier height was observed. This reduction was explained by formation of the irradiation-induced thin n⁺ layer. This revealed that low effective barrier height and low noise Co-nGaAs Schottky contacts can be fabricated on GaAs by low-energy nitrogen ion beam irradiation of surface. On the other hand, GaAs surface irradiation by low-energy noble gas (argon) ion beam resulted in substantial increase of the low-frequency noise at liquid nitrogen temperature. Formation of a thin GaN layer as a result of the GaAs surface irradiation by low-energy nitrogen ion beam was observed by XPS. Experimentally registered decrease of the low-frequency noise (in the case of nitrogen irradiation) was explained in terms of the screening of irradiation-induced defects, passivation of dangling bonds at the GaAs surface nGaAs and increased surface and Schottky contact homogeneity due to the ion beam nitridation.     

Antireflective characteristics of Ge1−xCx films on sub-wavelength structured ZnS surfaces

Antireflective sub-wavelength structures (SWSs) combined a Ge_1−xC_x coating on Zinc sulfide (ZnS) can enhance the long-wave infrared transmission and durability of ZnS, which have the potent for practical applications. We have investigated the antireflective characteristics of Ge_1−xC_x sub-wavelength periodic hole structures on ZnS through the Fourier modal method (FMM) for application with normally incident, randomly polarized, 10.6 μm wavelength. Then according to the results, we have successfully fabricated the sub-wavelength periodic square hole structures with Ge_0.05C_0.95 films on one side of ZnS. A substantial transmittance improvement for bare ZnS in the 8-12 μm spectral region was obtained.