多孔硅的拉曼光谱研究

本文研究了多孔硅的拉曼光谱随激发激光功率的变化 ,发现当激发光的功率较低时 ,多孔硅的拉曼光谱在 5 2 0cm- 1附近为一单峰。随着激光功率的增加 ,该单峰向低波数移动且半高宽增大 ,当继续增大激光功率时 ,该单峰分裂为双峰 ,位于低波数一侧的拉曼峰随着激光功率的增大而进一步向低波数移动。多孔硅的拉曼光谱随着激光功率的变化是一个可逆的过程。这一结果表明 ,低波数拉曼峰的位置既不能作为多孔硅颗粒尺寸的量度 ,也不能只把低波数的拉曼峰作为多孔硅的特征。我们认为激光诱导多孔硅中LO和TO声子模的简并解除是观察到双峰的主要原因。     

多孔硅拉曼光谱随激发功率变化的研究

用阳极氧化法新制备了多孔硅样品,以457．5nm固体激光器为激发光源,在不同激发功率下,获得了拉曼谱图和一些谱峰参量随激光功率的变化关系。解释了520cm^-1和300cm^-1附近拉曼峰随功率变化的一系列可逆的实验现象：随激光功率升高出现的红移和非对称性展宽,主要是由于样品局域平均粒径变小而受量子限域效应的影响导致的;样品局域平均粒径在表面上的二维减小与随激光功率升高而导致的局域温升并不违背基本的热力学定律;高功率时520cm^-1附近双峰的出现是由于多孔硅样品局域平均粒径达到一定阈值而导致的纵模和横模双声子模的分裂。     

发射可见光多孔硅的拉曼光谱

本文报导了多孔硅的拉曼散射和光致发光的研究。给出了多孔硅的拉曼和光致发光谱之间的对应关系,根据拉曼峰的移动,估算了多孔硅量子线横截面的平均尺度为2.1～4.2nm。     

激发光强度对多孔硅拉曼光谱的影响①

报道了经较强激发光辐照后的多孔硅呈现出的独特拉曼光谱性质,其一阶拉曼峰随着激发光功率的不同而变化。当激发光功率增大时,其峰位逐渐红移,同时峰的宽度变大,这种变化是可逆的。我们讨论了产生该现象可能机制。     

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。     

多孔硅纳向分辨拉曼及光致发光研究

运用高灵敏度的共焦显微拉曼系统研究了多孔硅在纵的拉曼效应和光致发光的性质。研究结果表明多孔硅在形成的初期和后的反应机制不相同。反应初期,外表面的颗粒尺寸比内同大,而经过长时间刻蚀而获得得的多孔硅,其相表面颗粒尺寸比 小。我们认为反应的初期主要表面不均匀电场的影响,而随着表面多孔层的增厚和颗粒的细化,刻蚀反应逐渐变成受传质过程和量子尺寸约束的控制。     

多孔硅纵向分辨拉曼及光致发光研究

运用高灵敏度的共焦显微拉曼系统研究了多孔硅在纵向的拉曼效应和光致发光的性质。研究结果表明多孔硅在形成的初期和后期的反应机制不相同。反应初期,外表面的颗粒尺寸比内表面的大,而经过长时间刻蚀而获得的多孔硅,其外表面颗粒尺寸比内表面的小。我们认为反应的初期主要受表面不均匀电场的影响,而随着表面多孔层的增厚和颗粒的细化,刻蚀反应逐渐变成受传质过程和量子尺寸约束的控制。     

多孔硅光致发光的温度效应研究

通过对多孔硅光致发光峰随测量温度变化的研究，发现随测量温度的下降，光致发光峰位有两种截然不同的移动方向：发光峰中心波长较长的样品，主峰向低能方向移动(即红移)；而发光峰位波长较短的样品则向高能方向移动(即蓝移).根据多孔硅光致发光峰的温度效应，定性地给出了发光效率随波长变化的模拟曲线，并由此能较好地解释多孔硅光致发光峰位随温度变化而移动的实验现象. 关键词：     

Fano resonance in heavily doped porous silicon

Unexpectedly, the Fano resonance caused by the interference of continuum electron excitations with the longitudinal optical (LO) phonons was observed in random porous Si by Raman scattering. The analysis of the experimental data shows that the electron states trapped at the Si SiO₂ interface dominate in the observed Raman scattering. The gap energy associated with the interface states was determined. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

Phonon confinement effects in Raman spectra of porous silicon at non‐resonant excitation condition

Light emitting porous silicon samples with different porosities, i.e. crystalline sizes, were produced from the low level doped p‐type silicon wafers by the anodization process. The effects of strong phonon confinement, redshift and broadening, were found on the O(Γ) phonon mode of the Raman spectra recorded at non‐resonant excitation condition using a near infrared 1064 nm laser excitation wavelength. Similarly, the blueshift of the photoluminescence peak was observed by reducing the crystalline sizes. Vibrational and optical findings were analysed within the existing models of confinement on the vibrational and electronic states of silicon nanocrystals. Since the energy of the photoluminescence peak of small nanocrystals also depends on the oxygen content on the surface of nanocrystals, the surface oxidation states were examined using infrared and energy dispersive spectroscopy. The partial coverage of the surface of nanocrystals was found due to the sample exposure to air. As a consequence, the photoluminescence energy did not increase as would be expected from the quantum confinement model. These results further indicate that the oxygen passivation along with the quantum confinement determines the electronic states of the silicon nanocrystals in porous silicon. Copyright © 2014 John Wiley & Sons, Ltd.     

用拉曼光谱测定CCl_4散射介质的温度

作者发展了测量散射体温度的拉曼光谱方法,选用CCl4液体做散射介质,对它的217、315和459等三个散射带进行观测,分别记录它们的Stokes和AntiStokes分量的光谱强度,测量得到CCl4液体散射体的温度。实验结果显示,这种非接触光谱测量法具有重要的实用价值。     

基于多孔硅Bragg反射镜的液体浓度测量方法

提出了一种利用多孔硅Bragg反射镜(简称PSBR)的反射谱来测量液体浓度的新方法。当在PSBR的孔内浸入不同浓度的液体时,多孔硅的有效折射率会发生变化,从而引起PSBR反射谱峰位发生变化。利用脉冲腐蚀法制备PSBR,采用正交参数设计法优化实验参数。对其进行了浓度测量实验和验证实验,测量误差小于0.14%。     

多孔硅的时间延迟光谱

利用时间延迟光谱技术测量了多孔硅的发光光谱. 实验结果表明,多孔硅的发光是复杂的动力学发光弛豫过程,时间延迟光谱测量技术在研究复杂动力学发光过程方面比稳态光谱测量方法更有效.