Effect of natural aging on photoluminescence of porous silicon

The influence of natural aging on the intensity and position of the photoluminescence (PL) peak in n-type porous silicon (por-Si) has been studied. Changes in the phase composition and relative content of the amorphous and oxide phases in por-Si during aging were determined by simulating the spectra of Si L _2,3 ultrasoft X-ray emission based on the reference spectra of the corresponding phases.     

多孔硅在高温退火过程中结构变化的研究

采用电化学腐蚀的方法制备了不同孔径的多孔硅薄膜样品,并在1050℃高温下进行了退火。采用扫描电镜和拉曼光谱对多孔硅退火前后结构的变化进行了观察,根据晶体形核理论分析了孔径变化的机理,并从热力学角度对其微观机制进行了讨论。实验和理论分析的结果均表明,多孔硅的初始孔径存在一个临界值,初始孔径小于此临界值时,孔在高温退火中有收缩的趋势;反之,初始孔径大于此临界值时,孔有变大的趋势。     

Photoluminescence and degradation properties of carbonized porous silicon

A promising new method of modifying the spectral characteristics of porous silicon and stabilizing its photoluminescence is proposed using high-temperature carbonization. Investigations have shown that carbonized samples exhibit stable photoluminescence and the spectral peak is shifted into the rf-blue range. Pis’ma Zh. Tekh. Fiz. 24, 24–30 (August 26, 1998)     

Transport properties of thermally oxidized porous silicon

The process of current transfer in thermally oxidized porous silicon has been studied. A model based on the combination of hopping and tunneling mechanisms of charge transport is proposed. The concentration of charge traps and the mobility of charge carriers are evaluated using the current-voltage characteristics measured at 100 and 300 K.     

硅树脂/二氧化硅高温相变及介电性能研究

采用氧乙炔喷枪对含有少量有机硅树脂的二氧化硅素坯进行单面烧蚀处理,利用XRD、SEM和SAED表征其高温物相变化.研究发现,高温烧蚀后的二氧化硅中有少量α-方石英析出,并伴有α-SiC、β-SiC新相生成,在此基础上研究了物态变化对材料高温介电性能的影响.     

The effect of adsorption complexes on the electron spectrum and luminescence of porous silicon

Effects of the surface atomic structures on the electron spectrum and luminescent properties of porous silicon (por-Si) were studied by methods of photoluminescence spectroscopy, UV photoelectron spectroscopy, and Fourier-transform IR spectroscopy. An analysis of evolution of the por-Si characteristics in the course of thermal treatment in vacuum revealed a correlation between the photoluminescence spectrum and intensity, on the one hand, and the electron spectrum and surface atomic structure, on the other hand. The thermodesorption of adsorbate from por-Si leads to atomic rearrangements on the sample surface, which is accompanied by changes in the electron structure and, hence, in the luminescent properties of the material.     

Formation and properties of porous silicon/titania nanostructures

Porous silicon/titania structures have been prepared for the first time by a sol-gel process in which a porous silicon layer was produced on single-crystal p-type silicon wafers and the titania was obtained from Ti-containing sol. The formation of TiO₂, predominantly in the form of anatase, on the porous silicon surface was demonstrated by X-ray diffraction and energy dispersive X-ray analysis. The porous layers were found to contain carbon in addition to the host elements (Si, Ti, and O). Increasing the pore volume through the thermal oxidation of the porous silicon and dissolution of the oxide layer had little effect on the final Ti content, whereas the average pore diameter increased twofold, and the photoluminescence intensity in the porous silicon increased by 20 times.     

Photoluminescence properties of erbium-doped single-crystal and porous silicon films

The features of the photoluminescence spectra of single-crystal and porous Si:Er films grown by molecular beam epitaxy are discussed. Pis’ma Zh. Tekh. Fiz. 25, 31–34 (May 26, 1999)     

Effects of hydrogenation and aging on the optical properties in porous Si layers

The effects of hydrogenation and aging on the optical properties in porous Si (PS) layers were investigated by using photoluminescence (PL) measurements. When the hydrogenated PS layers were aged in air, the intensity of the PL spectrum increased. The emission peak for the hydrogenated PS layers shifted to higher energy with decreasing H₂/N₂ ratio. The relation of the dehydrogenized states in the as-formed PS surface to the quantum states of Si nanoparticles with relatively small sizes is discussed. These results indicate that the optical properties of PS layers are significantly affected by hydrogenation and aging.     

Morphology and optical properties of titanium-doped porous silicon carbide layers

The effect of rapid thermal annealing (RTA) in oxygen on the properties of titanium-doped porous silicon carbide (por-SiC) layers has been studied. The data on the surface morphology and the photoluminescence (PL) spectra show that the high-temperature diffusion annealing is accompanied by the formation of titanium silicides, by an increase in the grain size of the material, and by the emergence of pores on the surface of the por-SiC-Ti sample. The results of PL measurements are consistent with data on the phase composition and the surface morphology of the samples. It is established that RTA leads to modification of the titanium-doped por-SiC structure.     

Investigation of opto-electronic properties on gradient-porosity porous silicon layer

Electrochemical etching with step-gradient current was applied to form gradient-porosity porous silicon (PS) layer on n-Si substrate and Al/gradient-porosity. PS/n-Si structure was fabricated to extract its opto-electronic properties using reflectivity, spectral response, and scanning electron microscopy. A conventional single-layer PS etched with constant-current was also compared. Compared to the single-layer PS, the absorption wavelength of gradient-porosity PS is blue-shifted due to a smaller quantum size, hence a wider band-gap. Such a wider band-gap leads to a larger barrier-height in Al/gradient-porosity PS than that in Al/single-layer PS one. More dangling bonds are found on the surface of gradient-porosity PS owing to inhomogeneous etching, thus a poor electronic property, though it has a lower broadband antireflection than single-layer PS.     

Mechanical properties of porous silicon by depth-sensing nanoindentation techniques

Porous silicon (PS) was prepared using the electrochemical corrosion method. Thermal oxidation of the as-prepared PS samples was performed at different temperatures for tuning their mechanical properties. The mechanical properties of as-prepared and oxidized PS were thoroughly investigated by depth-sensing nanoindentation techniques with the continuous stiffness measurements option. The morphology of as-prepared and oxidized PS was characterized by field emission scanning electron microscope and the effect of observed microstructure changes on the mechanical properties was discussed. It is shown that the hardness and Young's elastic modulus of as-prepared PS exhibit a strong dependence on the preparing conditions and decrease with increasing current density. In particular, the mechanical properties of oxidized PS are improved greatly compared with that of as-prepared ones and increase with increasing thermal oxidation temperature. The mechanism responsible for the mechanical property enhancement is possibly the formation of SiO₂ cladding layers encapsulating on the inner surface of the incompact sponge PS to decrease the porosity and strengthen the interconnected microstructure.     

氮化硅晶须对反应烧结氮化硅多孔陶瓷介电性能的影响

以硅粉和氮化硅晶须为原料,通过添加30%(质量分数)成孔剂球形颗粒,以聚乙烯醇作粘结剂,采用干压成型工艺,反应烧结制备了多孔氮化硅陶瓷,分析对比了氮化硅晶须对反应烧结氮化硅多孔陶瓷介电性能的影响.实验结果表明,随着氮化硅晶须加入量的升高,氮化硅多孔陶瓷的介电常数和介电损耗都升高,介电性能恶化.     

The synthesis and photoluminescence properties of selenium-treated porous silicon nanowire arrays

Here we prepared vertical and single crystalline porous silicon nanowire (SiNW) arrays using the silver-assisted electroless etching method. The selenization was carried out by annealing the samples in vacuum with selenium atmosphere. The selenization treatment at 700?°C is useful for investigating the photoluminescence (PL) properties of porous SiNWs, with an enhancement of 30 times observed. The observed PL peaks blue-shift to 650 nm and the decomposition of the spectrum reveals that three PL bands with different origins are obtained. It is proved that selenization treatment could remove the Si-H bonds on the surface and form Si-Se bonds, which could increase the absorbance of the SiNWs and also enhance the stability of the PL intensity. These Se-treated porous SiNWs may be useful as nanoscale optoelectronic devices.     

Electronic properties of microporous silicon under illumination and with the adsorption of ammonia

An electromotive force has been observed at contacts of porous silicon samples, its magnitude and sign varying with illumination and adsorption of ammonia. The samples exhibit characteristic nonuniformity of the porosity along the surface of the material. The physical mechanism for these effects is discussed. Pis’ma Zh. Tekh. Fiz. 23, 77–82 (June 12, 1997)     

表面金属化对多孔硅光特性的影响(英文)

在室温下使用过滤阴极真空电弧系统在多孔硅表面沉积大约10纳米左右厚度的铜、铝和钛薄膜,并且在真空下800度退火10分钟.多孔硅层是通过电化学腐蚀硅制得.X射线光电子谱、荧光谱,光吸收谱和X射线衍射谱的研究表明退火后,沉积铜和钛的样品出现明显的光吸收红移和硅2p电子能级移动.这是由于在多孔硅表面形成铜和钛的硅化物而引起的晶体场和电子传输变化所造成的.     

Theoretical and experimental studies of the porous structure and adsorption properties of carbofibrous materials

We have made theoretical and experimental studies of the porous structure and adsorption properties of activated carbon fibrous materials and granular activated carbon with respect to vapors of benzene, toluene, ethylacetate, and acetone. The parameters of the porous structure of adsorbents have been determined by the adsorption by them of the standard substance — benzene — and used to calculate their adsorption characteristics with respect to the investigated organic solvents. A good agreement between the calculated and experimental characteristics for all investigated adsorbents has been obtained. The dependence of adsorption properties of activated carbon fibrous adsorbents and granular activated carbon on the volume and size of adsorbing pores, as well as on the molecular polarizability of the adsorptive, has been established.