Structural complexity of disordered surfaces: Analyzing the porous silicon SFM patterns

This paper introduces a relative structural complexity measure for the characterization of disordered surfaces. Numerical solutions of 2d+1 KPZ equation and scanning force microscopy (SFM) patterns of porous silicon samples are analyzed using this methodology. The results and phenomenological interpretation indicate that the proposed measure is efficient for quantitatively characterize the structural complexity of disordered surfaces (and interfaces) observed and/or simulated in nano, micro and ordinary scales.     

软X射线分光晶体KAP的反射率特性

弯晶谱仪是激光等离子体软X射线的有效诊断工具,KAP是弯晶谱仪的分光晶体之一.利用原子散射因子和结构因子分量,以及镶嵌晶体模型计算KAP的积分反射率,表明KAP的积分反射率与波长有关,先随波长增大而减小,后随波长增大而增大.此外,还计算了KAP的峰值反射率、半最大值宽度、能量宽度和能量分辨率,表明峰值反射率和能量分辨率随波长增大而减小.     

多孔硅在30~180℃温区光致发光谱的研究

对长期存放在空气中的多孔硅样品和即时制备的多孔硅样品分别在室温~180℃下进行了光致发光（PL）温度效应的研究.两类样品的PL呈现不同的变化规律.前者的PL还表现为双峰,且长波PL峰随温度升高蓝移;后者的PL表现为单峰,且PL峰位随温度升高红移.基于量子限制效应对后者进行了解释;而前者难以用分立的量子限制和表面发光中心模型来解释,实验结果表明两种机制之间可能有较复杂的耦合效应发生.     

Electrical and optical characteristics of porous silicon impregnated with LaF3 by a novel chemical bath technique

The structural, electrical and optical characteristics of porous silicon (PS) due to the impregnation of LaF₃ into PS by a novel chemical-bath deposition (CBD) technique have been investigated in this article. Without removing the PS from the anodization chamber the impregnation with LaF₃ has been done by reacting LaCl₃ with HF in the same chamber at room temperature. The impregnation of LaF₃ was confirmed by the SEM on the cross-section of the LaF₃/PS/Si system and EDX. The modification of PS surface by LaF₃ had direct influence on the electrical and optical properties of PS. Electrical properties of Ag/LaF₃/PS/p-Si/Ag structures were studied through the current-voltage (I-V) and capacitance-voltage (C-V) characteristics. Formation of metal-insulator-semiconductor (MIS) diode was evident whose forward current increased with annealing. A diode factor of about 2.4 has been obtained for the annealed heterostructure indicating a high density of trap states. The C⁻²-V curves of all samples showed negative flat band voltage of around −2 V confirming a large number of fixed positive charges in the LaF₃. The photoluminescence (PL) intensity of the LaF₃-impregnated PS showed aging for the as-deposited samples, but when annealed PS structure recovered the PL intensity. Experimental results show that the optimized chemical bath passivation process for the LaF₃ on porous silicon could enable the porous silicon to be an important material for photonic application.     

Hierarchically assembled porous ZnO microstructures and applications in a gas sensor

This paper presents a facile, low-cost and pollution-free route to prepare porous metal oxide nanomaterials. Hierarchically assembled ZnO microstructures with multi-scaled porosity were obtained by calcining the flower-like assembly of a basic zinc carbonate (BZC) precursor which was synthesized by a facile low-temperature (100 ^°C) homogenous precipitation without using any organic solvent or surfactant. A gas sensor based on the porous ZnO sample exhibited higher response to ethanol and formaldehyde gases than commercial ZnO powder. The facile preparation method and the improved property derived from the hierarchically porous microstructure are of great significance in the synthesis and application of nanomaterials.     

Preparation and characterization of Pt-supported porous graphite nanofibers

In this work, porous graphite nanofibers (PGNFs) were manufactured as promising catalyst supporter by a physical activation method for direct methanol fuel cells, and Pt nanoparticles were loaded on the PGNFs in order to prepare electrode materials by a chemical reduction method. The pore structures of the Pt/PGNFs were analyzed by N₂ adsorption isotherms at 77 K. Electrocatalytic activities of final products were investigated by voltammetry and conductivity measurements in a 1.0 M CH₃OH/0.5 M H₂SO₄. As a result, electrocatalytic activities of Pt/PGNFs were increased in the presence of Pt particles on the PGNFs and with increasing the specific surface area of the carbons.     

刚性衬底上铜铟硒纳米棒阵列的合成与表征

在覆盖有钨电极的硅衬底上利用多孔阳极氧化铝模板为生长掩膜电沉积合成垂直排列的铜铟硒纳米棒阵列. 多孔阳极氧化铝模板由阳极氧化磁控溅射制备的铝膜制成. 扫描电子显微镜结果表明,该纳米棒阵列结构致密,直径约100 nm长度约1μm,纵横比为10. X射线衍射、微区拉曼光谱和高分辨透射电子显微镜结果表明,真空条件下450 oC退火处理的铜铟硒纳米棒是多晶纯相的黄铜矿结构的铜铟硒,在纳米棒轴向方向上有比较大的晶粒尺寸. 能量色散X射线光谱表明,铜铟硒纳米棒的化学组成接近InSe₂的化学计量比,由吸收光谱分析推算铜铟硒纳米棒带隙为0.96 eV.     

Conciliating surface superhydrophobicities and mechanical strength of porous silicon films

Hydrophobic surfaces on Mechanical stable macroporous silicon films were prepared by electrochemical etching with subsequent octadecyltrichlorosilane (OTS) modification. The surface morphologies were controlled by current densities and the mechanical properties were adjusted by their corresponding porosities. Contrast with the smooth macroporous silicon films with lower porosities (34.1%) and microporous silicon with higher porosities (97%), the macroporous film with a rough three-dimension (3D) surface and a moderate pore to cross-section area ratio (37.8%, PSi2′) exhibited both good mechanical strength (Yong’ modulus, shear modulus and collapse strength are 64.2, 24.1 and 0.32 GPa, respectively) and surface superhydrophobicity (water contact angle is 158.4 ± 2° and sliding angle is 2.7 ± 1°). This result revealed that the surface hydrophobicities (or the surface roughness) and mechanical strength of porous films could be conciliated by pore to cross-section area ratios control and 3D structures construction. Thus, the superhydrophobic surfaces on mechanical stable porous films could be obtained by 3D structures fabrication on porous film with proper pore to cross-section area ratios.     

Stability analysis of a Maxwell fluid in a porous medium heated from below

Based on a modified-Darcy–Brinkman–Maxwell model, stability analysis of a horizontal layer of Maxwell fluid in a porous medium heated from below is performed. By solving the eigenvalue problems, the critical Rayleigh number, wave number and frequency for overstability are determined. It is found that the critical Rayleigh number for overstability decreases as the relaxation time increases and the elasticity of a Maxwell fluid has a destabilizing effect on the fluid layer in porous media. On the other hand, the critical Rayleigh number for overstability increases by increasing the porous parameter which acts to stabilize the system. In limiting cases, some previous results for viscoelastic fluids in nonporous media are recovered from our results.     

Effect of rapid thermal treatment on photoluminescence of surface passivated porous silicon

The photoluminescence of porous silicon with and without carbon deposition fabricated by plasma-enhanced chemical vapor deposition technique has been investigated. After the deposition, the rapid thermal processes in the temperature ranging from 500 to 1100 °C have been carried out. It was found that after the carbon deposition a new intense blue emission appeared. The rapid thermal processes at 800and 900 °C could enhance the blue emission, while the other rapid thermal processes quenched it. Finally, the mechanism for the effect of carbon deposition and rapid thermal processes on photoluminescence properties of porous silicon was discussed.