硅纳米线拉曼光谱的研究

声子限制效应会引起本征硅纳米线拉曼光谱红移及不对称宽化,但研究发现其并非引起硅纳米线拉曼光谱改变的主要因素。研究表明,由于在拉曼光谱测量中,通常使用的入射激光功率都在5 mW以上,激光加热会导致很高的局部温度,从而引起拉曼光谱大幅度红移并对称宽化,这是硅纳米线拉曼光谱红移的主要影响因素。另外,激光功率很高时,由激光激发的载流子会与声子发生Fano型干涉,从而使硅纳米线拉曼光谱发生Fano型红移和不对称宽化。除此之外,对小直径本征硅纳米线,声子限制效应导致波矢选择定弛则弛豫,使不在布里渊区中心的声子也可以参与拉曼散射,因而其拉曼光谱中除常见的几个拉曼峰外还会出现新拉曼峰。     

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。     

碱液修饰对硅纳米线阵列电池光谱响应的影响

采用金属催化化学腐蚀法在p型(100)硅基底上制备了硅纳米阵列,然后用碱溶液对纳米线阵列进行修饰。分别研究了碱液修饰对硅纳米线阵列形貌、光电性质的影响。研究表明: 与绒面及纳米线阵列相比,碱修饰30 s硅纳米线阵列的表面分散均匀,反射率降低;光谱响应度显著提高,并且出现最大量子效率对应波长红移现象。最后,详细讨论了碱液修饰硅纳米线阵列电池对光谱响应的影响机制。     

氧化钨纳米线结构相变的拉曼光谱研究

本文利用拉曼光谱技术对氧化钨纳米线结构随激光功率改变而变化的情况进行了研究。研究结果表明氧化钨纳米线在一定功率的激光照射下被氧化成了三氧化钨纳米线;随着激光功率的进一步增大,纳米线温度进一步升高,三氧化钨纳米线由开始的单斜相向正交相结构过渡。实验证实三氧化钨纳米线的相变过程是可逆的,而之前的氧化过程是不可逆的。     

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。     

InGaN/GaN多量子阱热退火的拉曼光谱和荧光光谱

通过拉曼光谱及荧光光谱测量研究了采用低压金属有机化学沉积(MOCVD)方法生长的InGaN／GaN多量子阱高温快速热退火处理对量子阱光学性质的影响。观测到退火后InGaN／GaN量子阱的拉曼光谱E2,A1(LO)模式的峰位置出现了红移,而且该振动峰的半高宽也有微小变化。温度升高退火效果更明显。退火使量子阱内应力部分消除,同时In,Ga原子扩散出现相分离使拉曼谱表现出变化。在常温和低温下的光荧光谱表明,退火处理的量子阱发光主峰都出现了红移;而且低温退火出现红移,退火温度升高相对低温退火出现蓝移;同时在低温荧光光谱里看到经过退火处理后原发光峰中主峰旁边弱的峰消失了。讨论了退火对多量子阱光学性质的影响。     

人血红细胞傅里叶变换红外和近红外拉曼光谱

通过人血红细胞傅里叶变换近红外拉曼光谱和红外光谱研究,基本上确定了人血红细胞中特征官能团的归属, 发现不同拉曼频移的拉曼信号强度随激发光功率呈非线性变化规律。近红外激光拉曼光谱结合红外光谱信息,可作为研究人血红细胞结构的有效测试手段。     

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。     

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。     

光子晶体光纤中超连续谱产生的蓝移光谱分析

以理论和实验相结合的方法对光子晶体光纤中超连续谱产生的蓝移光谱进行了研究.实验研究了超连续谱蓝移光谱随入射激光的功率的变化,着重分析了光谱在短波方向展宽的机制.结果表明:在入射激光功率较低的情况下,利用包含色散、自相位调制、自变陡及脉冲内拉曼散射效应的非线性薛定谔方程可以准确地分析光谱的展宽情况,理论和实验结果一致;但是,当功率较高时,光谱展宽的蓝移部分理论和实验结果出现差别.因此,在理论和实验的基础上讨论了四波混频及交叉相位调制效应对超连续谱产生的影响,从而为超连续谱在短波方向的展宽提供了很好的实验和理论依据.     

Quantitative analysis of the phonon confinement effect in arbitrarily shaped Si nanocrystals decorated on Si nanowires and its correlation with the photoluminescence spectrum

Arrays of single‐crystalline Si nanowires (NWs) decorated with arbitrarily shaped Si nanocrystals (NCs) are grown by a metal‐assisted chemical etching process using silver (Ag) as the noble metal catalyst. The metal‐assisted chemical etching‐grown Si NWs exhibit strong photoluminescence (PL) emission in the visible and near infrared region at room temperature. Quantum confinement of carriers in the Si NCs is believed to be primarily responsible for the observed PL emission. Raman spectra of the Si NCs decorated on Si NWs exhibit a red shift and an asymmetric broadening of first‐order Raman peak as well as the other multi‐phonon modes when compared with that of the bulk Si. Quantitative analysis of confinement of phonons in the Si NCs is shown to account for the measured Raman peak shift and asymmetric broadening. To eliminate the laser heating effect on the phonon modes of the Si NWs/NCs, the Raman measurement was performed at extremely low laser power. Both the PL and Raman spectral analysis show a log‐normal distribution for the Si NCs, and our transmission electron microscopy results are fully consistent with the results of PL and Raman analyses. We calculate the size distribution of these Si NCs in terms of mean diameter (D₀) and skewness (σ) by correlating the PL spectra and Raman spectra of the as‐grown Si NCs decorated on Si NWs. Copyright © 2015 John Wiley & Sons, Ltd.     

Interplay between phonon confinement effect and anharmonicity in silicon nanowires

Getting light out of silicon is a difficult task since the bulk silicon has an indirect energy electronic band gap structure. It is expected that this problem can be circumvented by silicon nanostructuring, since the quantum confinement effect may cause the increase of the silicon band gap and shift the photoluminescence into the visible energy range. The increase in resulting structural disorder also causes the phonon confinement effect, which can be analyzed with a Raman spectroscopy. The large phonon softening and broadening, observed in silicon nanowires, are compared with calculated spectra obtained by taking into account the anharmonicity, which is incorporated through the three and four phonon decay processes into Raman scattering cross-section. This analysis clearly shows that the strong shift and broadening of the Raman peak are dominated by the anharmonic effects originating from the laser heating, while confinement plays a secondary role.     

Raman study of NiFe2O4 nanoparticles,bulk and films: effect of laser power

Nanoparticles, bulk and thin films of NiFe₂ O₄ compounds are studied by micro‐Raman spectroscopy. The effect of varying the incident laser power up to 40 mW was studied in all forms of the samples. The spectra showed a large magnitude of red shift and line broadening as a result of high incident laser power. It is shown that the inverse spinel structure remains robust, and no trace of laser‐induced oxidation was observed. The low‐temperature study of the bulk and nanoparticles has also been carried out for elucidating thermal effects due to the high incident laser power. The rise in temperature for maximum incident laser power of 40 mW was estimated to be ∼625 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

GaN直纳米线的光学性能

对 Ga N直纳米线的拉曼光谱及光致发光光谱进行了研究。拉曼光谱表明 ,与计算值相比 ,E2 ( high)声子频率在 560 cm- 1有 -9cm- 1的移动 ,这种声子频率显示出向低能带频移及带变宽的特征 ,是由于纳米尺寸效应所引起的结果。体系的光致发光光谱在 3 44 .8nm附近的近带隙发光 ,与文献报道的 Ga N体材料的数值3 65nm相比有一蓝移 ,这是由于量子限制效应造成的     

易解石族矿物的Raman光谱和光致发光谱研究

测定并讨论了中国白云鄂博矿区变生及退火晶态易解石族矿物Ｒａｍａｎ光谱和光致发光谱,与退火晶质矿物相比,变生态易解石的Ｒａｍａｎ光谱和光致发光谱的强度降低,谱线宽化弥散,说明在变生过程中,矿物的结构发生畸变,元素分布趋于无序。分析表明,易解石族矿物在５１４．５ｎｍ激光激发下的所有光致发光谱峰均出自Ｎｄ＾３＋的辐射跃迁。     

Effects of the agglomeration state on the Raman properties of Co3O4 nanoparticles

The features of the Raman spectra of Co₃O₄ 30‐nm nanoparticles depend strongly on their agglomeration state. When measured at low incident laser power, the spectrum of isolated nanoparticles corresponds to that found in bulk materials, whereas the agglomerated nanoparticles present a clear red‐shift and broadening of the Raman bands. On the other hand, when measured at even lower power, both agglomerated and isolated nanoparticles show the same spectrum of microscopic particles. These effects have been studied by variations of the 532‐nm laser power and the environmental temperature. The thermal dependence of Raman spectra of agglomerated nanoparticles is different to that of isolated nanoparticles but is comparable to the one of bulk material. The different behaviour of the nanoparticles at different agglomeration state is associated to the transmission of phonons among the particles. On the other hand, an increase of the laser power causes a larger number of acoustic phonons, producing a variation of the vibration anharmonicity of the nanoparticles. This increase is more pronounced in the agglomerated nanoparticles, due to the transmission of phonons, causing a much intense modification of the Raman spectrum produced by the laser power. These results clearly indicate that the agglomeration state of the nanoparticles affects their Raman properties. Copyright © 2012 John Wiley & Sons, Ltd.     

Photoluminescence blue shift of indium phosphide nanowire networks with aluminum oxide coating

This paper describes our finding that optical properties of semiconductor nanowires were modified by depositing a thin layer of metal oxide. Indium phosphide nanowires were grown by metal organic chemical vapor deposition on silicon substrates with gold catalyst resulting in three‐dimensional nanowire networks, and optical properties were obtained from the collective nanowire networks. The networks were coated with an aluminum oxide thin film deposited by plasma‐enhanced atomic layer deposition. We studied the dependence of the peak wavelength of photoluminescence spectra on the thickness of the oxide coatings. A continuous blue shift in photoluminescence spectra was observed when the thickness of the oxide coating was increased. The observed blue shift is attributed to the Burstein–Moss effect due to increased carrier concentration in the nanowire cores caused by repulsion from intrinsic negative fixed charges located at the inner oxide surface. Samples were further characterized by scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, and selective area diffractometry to better understand the physical mechanisms for the blue shift. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Confocal Raman spectromicroscopy for tin-core/carbon-shell nanowire heterostructure

High density heterostructures of carbon nanotubes encapsulated single crystalline tin nanowires have been characterized by Raman spectromicroscopy. The morphology, composition and structure of the synthesized nanoheterostructures were examined by using scanning electron microscopy, transmission electron microscopy. The Raman spectra obviously manifest the crystalline nano-graphite within amorphous carbon walls in the heterostructures. The Raman image reproduces the pristine heterostructures of the CNTs as seen in SEM image, which illustrate the single nanowires oriented uniformly grown on micro-graphitic fibers. It was found that the resultant heterostructures are luminescent which was attributed to crystalline nano-graphite embedded in the amorphous carbon matrix, which is a consequence of excitons localization within an increasing number of sp² rich clusters. The contrast in the Raman image reflects nonuniform distribution of the graphite cluster size which acts as the radiative centers. The luminescent property was reviewed. The enhanced Raman spectra and luminescent property by the well-defined tin nanowires inside the heterostructures was revealed.