Immunosensor application based on Raman spectroscopy of porous silicon

Porous silicon (PS) suitable for optical detection of immunoreaction is fabricated. The structure of immunosensor is prepared by the following steps: oxidization, silanization, glutaraldehyde cross-linker, and covalent binding of antibody. When antigen is added into the immunosensor, the Raman intensity is estimated to be linearly reduced according to the concentration of the surface protective antigen protein A (spaA) of below 4.0 μg ml-1. The ultimate detection limit is 1.412 × 102 pg ml-1. Controlled experiments are also presented with non-immune antigen of the spaA, and results show that the immunosensor has high specificity. Compared with the conventional enzyme-linked immuno sorbent assay (ELISA), this method is quick, inexpensive, and label-free.     

Investigation of fatigue relaxation of luminescence in porous silicon by time-resolved spectroscopy

This paper describes the first investigations of how the intensities of various time-resolved components of the luminescence from porous silicon relax with time. A paradoxical correlation is observed between the macro-and microtemporal relaxation of luminescence from porous silicon under pulsed photoexcitation: namely, a relative increase in the rate of macrorelaxation for the slower components of the luminescence. Spectral investigations show that the difference in the rates of fatigue relaxation “tiredness” is maximum at the long-wavelength edge of the luminescence band. We propose a model that allows us to explain the observed effects starting from the assumption that photoexcitations drift toward radiative recombination centers. Fiz. Tverd. Tela (St. Petersburg) 39, 1165–1169 (July 1997)     

Study of porous silicon structure by Raman scattering

In this paper, the effect of etching time on light emitting porous silicon has been studied by using Raman scattering. Enhancement of Raman intensity by increasing the porosity is observed. Also there is a red shift, about 4 cm⁻¹, from the Raman peak of crystalline silicon to that of porous silicon. The phonon confinement model suggests the existence of spherical nanocrystalline silicon with diameter around 7 nm. But SEM images show that the samples have a sheetlike structure that confines phonons in one dimension. This should not cause any shift in their Raman spectra. It is suggested that the observed Raman peak shift is due to the spherical nanocrystals on the surface of these sheets.     

An application of Raman spectroscopy on the measurement of residual stress in porous silicon

The porous silicon film, at micron level, and the bulk silicon substrate is a basic structure in MEMS components. The residual stress, due to the lattice mismatch between the film and the substrate, exists on the interface and may cause cracking and damaging on the component. Micro-Raman spectroscopy is an optical measurement method that was rapidly applied into the fields of chemistry, physics, material science and mechanics. In this paper, the method is introduced and applied to the study of the stress problems in porous silicon as follows. (1) In the electrochemical etching technique for porous silicon preparation, the distribution of the tensile residual stress along the transitional region between etched and un-etched area is experimentally studied and the result reveals the stress is continuous across the region. In the etched region it reaches GPa level, and in the transition region the gradient of the stress is high. (2) In chemical etching preparation of porous silicon, the residual stress rises up seriously in the cracked area, up to 0.92 GPa. With the porosity increasing, the tensile stress on the porous silicon film increases accordingly. The appearance of the porous silicon film surface is also given by metalloscope and atomic force microscope. The structure of the micro-pores is expected to have a close relation with the distribution of the residual stress.     

Superheating of silicon nanocrystals observed by Raman spectroscopy

In the Raman spectra of silicon nanocrystals a new anomalous component was detected. Close to the usual first order Raman peak situated for a bulk crystal at 521 cm⁻¹ at room temperature, two peaks arise shifting towards lower energy and demonstrating a huge temperature increase, as measured by the ratio of the Stokes/anti-Stokes peak intensities. This behavior is dependent on the laser power and on the morphology of the nanocrystals. We can exclude, however, confinement effects, although surface enhanced phonon modes could be responsible of such superheating. Alternative explanations are also suggested and discussed.     

Spectra of second-order Raman scattering in porous silicon

Spectra of second-order Raman scattering in porous silicon are investigated. A band shift towards lower energies in second-order spectra is observed, as well as the correlation between the values of band shift in first-and second-order spectra. It is demonstrated that the observed effect cannot be interpreted using the conventional concepts of the mechanisms of scattering in microcrystalline samples. An interpretation of the revealed effect is suggested.     

Enhancement of Raman scattering intensity in porous silicon

An enhancement in inelastic light scattering intensity from porous-silicon quantum wires has been discovered. It is shown that this effect is caused by a decrease in the absorption coefficient of the optical medium formed by quasi-one-dimensional structures, with the crystal structure of the wires themselves remaining unchanged. Fiz. Tverd. Tela (St. Petersburg) 41, 1320–1322 (July 1999)     

多孔硅拉曼光谱的研究

采用电化学腐蚀的方法制备多孔硅。对不同实验条件下所得到的多孔硅的拉曼光谱进行了分析，确认多孔硅是具有纳米晶结构特征的材料，肯定了量子限制效应在多孔硅光致发光中的作用。     

Study of birefringence in porous silicon layers by IR Fourier spectroscopy

Birefringence in porous silicon layers prepared with different etching currents on a (110) substrate is studied by IR Fourier spectroscopy. The spectra exhibit beats in the intensity of transmitted and reflected radiation due to the summation of the intensities of the ordinary and extraordinary waves interfering in the porous layer. An analysis of the spectra shows the layers to exhibit properties of a negative uniaxial crystal with the optical axis lying in the layer plane. The difference between the refractive indices of the ordinary and extraordinary waves for a layer with a porosity of 80% reaches 18%. The experimental data are in agreement with the calculations based on the effective-medium approximation, which takes into account the anisotropy of silicon nanocrystal arrangement in a porous layer.     

Enhanced Raman scattering in multilayer structures of porous silicon

Multiple enhancement of the Raman scattering efficiency is observed in porous‐silicon‐based one‐dimensional photonic bandgap (PBG) structures with tunable reflection and dispersion under excitation at 1.06 µm. The experimental results are explained as being due to the resonant increase in the effective Raman susceptibility at light wavelengths close to the PBG edges. This effect is discussed in view of possible applications in the Raman spectroscopy of molecules embedded in porous media as well as in the Raman laser based on silicon. Copyright © 2011 John Wiley & Sons, Ltd.     

Steady-state and time-resolved spectroscopy of porous silicon

We present experimental data on steady-state properties, time-resolved properties and on polarization characteristics of porous silicon photoluminescence and models for the decay processes of the red-orange band. The manifold manifestation of inhomogeneous broadening of this band in emission, excitation, polarization, kinetics and degradation supports the model in which porous silicon is treated as a network of crystallites connected via an oxide interface. Spectral inhomogeneties of the red-orange band can be described in terms of varying shape and size of silicon clusters. The polarization of emission is explained by coexistence of dot-like and wire-like entities, i.e. spherical and non-spherical clusters. The relative weight of these species determines the polarization degree, whereas the kinetics are controlled by the transport of excitations among the clusters. The decay is modeled by a modified stretched exponential function with the local lifetime, the migration lifetime, and a scaling factor. The latter is determined by the dimensionality of the space available for migration which was found to be close to but less than unity. On the nanosecond range two distinct bands in the blue-green region are evaluated that need further studies for interpretation. Generally, arguments are proposed in favor of a quantum confinement origin of the red-orange band and a bridge between quantum-wire and quantum-dot models is provided.     

Investigation of thermal transport in n-type porous silicon by photo-acoustic technique

Non-destructive thermal and optical characterization of materials can be successfully performed by the photo-acoustic technique. In this work, this technique has been applied to the measure of thermal conductivity in porous silicon by considering the photo-acoustic response at fixed frequency of samples having the same porosity but different thicknesses. Experimental data are interpreted in terms of a model which takes into account both scattering effects and the contribution to the photo-acoustic signal of the interstitial gas expansion. The measured thermal conductivity is found to be lower than the one reported for crystalline silicon by two orders of magnitude. A discussion of the photo-acoustic signal dependence on the morphology of the porous medium is also presented.     

拉曼光谱法计算多孔硅样品的温度

利用457.5nm固体激光器作为激发光源，得到了在不同功率激发下的多孔硅样品的拉曼光谱以及一些谱峰参数随功率的变化关系. 在从前的理论研究中，认为是由于激光功率的增大导致样品局域温度升高，从而使样品局域粒径变小，并由此引起了一系列谱峰参数的变化. 分别由520cm^-1和300cm^-1附近得到的随功率变化的拉曼谱图，详细讨论并计算了激光功率对多孔硅样品局域温度的定量影响，为拉曼光谱用于样品温度的定量测量奠定了实验基础. 关键词： 拉曼光谱 多孔硅 激光功率 样品温度     

Anomalous polarization of Raman scattering spectra from porous silicon

A violation of the polarization selection rules for Raman scattering is observed in porous silicon. This effect is caused by a weak disorientation of the quasi-one-dimensional silicon wires, with the crystal structure of the wires themselves and the macroscopic homogeneity of the material in optical experiments remaining intact. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 95–100 (25 January 1998)     

单细胞拉曼光谱结合多元统计方法分析不同酿酒酵母菌株的成分差异

应用单细胞拉曼光谱技术结合多元统计方法分析比较了六株不同来源的酿酒酵母菌株的同步化细胞,从而获知菌株间细胞成分的差异.利用连续密度梯度离心法分离酿酒酵母同步化细胞,分别对六个酵母菌株的同步化单细胞进行拉曼信号收集,并结合主成分分析(PCA)、辨别函数分析(DFA)两种多元统计分析光谱差异.结果表明,细胞的拉曼光谱表征其...     

Local structure of porous silicon studied by means of X-ray emission spectroscopy

2,3 X-ray emission spectra of porous silicon (P-Si) and of spark-processed silicon (sp-Si). Both types of Si-structure display strong photoluminescence in the visible range of the spectrum. Porous samples were prepared by anodization of n^-- and p⁺-Si-wafers. Whereas for the P-Si processed from p⁺-Si the presence of some amorphous silicon is detected, the X-ray emission spectra of porous Si prepared from n^--Si display a higher content of SiO₂. For spark-processed Si the Si L_2,3 X-ray emission spectra reveal a much stronger degree of oxidation which extends to depths larger than 10000 Å. Furthermore, the chemical state of silicon atoms of sp-Si measured at the center of the processed area is close to that of silicon dioxide, and it has an influence on the photoluminescence energy. Specifically, green photoluminescent sp-Si shows a higher degree of oxidation than the blue luminescent specimen. However, the depth of oxidation consistently decreases in areas with weak or no PL. Possible origins of the observed photoluminescence are discussed. Accepted: 6 March 1997