Investigation of micropipes in 6H-SiC by Raman scattering

The spectra of 6H-SiC crystals including micropipes have been examined for the Si face using Raman scattering. The first-order Raman features reveal that the intensity of the transverse optical phonon band centered at ∼796 cm⁻¹ is sensitive to the micropipes. And the second-order Raman features of the micropipes in bulk 6H-SiC are well-defined using the selection rules for second-order scattering in wurtzite structure. It is found that there are some second-order peaks missing for the micropipe-including sample, which may be induced by the reduction of the incident laser intensity at around the micropipe, especially the uneven surface in the inner wall of the micropipe. These features might also be employed to characterize other structural defects such as screw-dislocations and threading edge dislocations.     

拉曼光谱研究n型4H-和6H-SiC晶体的载流子浓度

半导体材料的纵光学声子与等离子体激元耦合模(LOPC模)能够提供材料电学方面的相关信息。本文在室温下测得了n型4H-和6H-SiC的拉曼光谱,分析了掺入的杂质对于SiC晶体拉曼光谱的影响,通过拟合n型4H-和6H-SiC晶体的LOPC模的线型得到等离子体频率,并由此从理论上计算了载流子浓度。载流子浓度的理论计算值与霍尔测量的结果符合得很好。研究结果进一步证实了对于n型4H-和6H-SiC晶体,可以通过分析LOPC模的线形来较准确地给出相关材料的载流子浓度。     

皮秒激光抽运高压H_2的受激拉曼散射研究

利用Nd :YAG锁模序列脉冲激光 (10 6 4nm)抽运充有高压H2 的拉曼池 ,输出光束经棱镜分光后投射在屏上 ,在可见光及近紫外光区用彩色胶卷摄得 15个受激拉曼散射光斑 ;经 1m光栅摄谱仪摄谱 ,在 36 5— 6 0 5nm波长范围内得到 6 5条受激拉曼谱线 .通过实验结果与理论计算值的比较 ,证明除了H2 的振动拉曼频移量 4 15 4 6cm- 1 外 ,还有多个振动及转动拉曼频移量共同参与作用 ,从而产生了从紫外到红外众多波长的受激拉曼散射光 .     

无紫外光照射下n型15R-SiC及6H-SiC晶体的电化学腐蚀

本文在无紫外光照射下通过电化学腐蚀法制备了多孔n型15R-及6H-SiC,并用扫描电子显微镜(SEM),拉曼散射及X射线衍射仪(XRD)对多孔层的结构进行了分析。结果表明:晶体的晶型及氧化条件等因素对多孔结构有较大影响。首次观察到多孔n型15-SiC的半圆管状结构,其孔隙率约是66%。     

Optical and magnetic properties of InFeP layers prepared by Fe~+ implantation

InFeP layers are prepared by ion implantation of InP with 100-keV Fe＋ ions to a dose of 5 ×10^16 cm-2 and investigated by optical, magnetic, and ion beam analysis measurements. Photoluminescence measurements show a deep-level peak at 1.035 eV due to Fe in InP and two exciton-related luminescences at 1.426 eV and 1.376 eV in the implanted samples annealed at 400℃. Conversion electron Mossbauer spectroscopy reveals a doublet corresponding to Fe3＋ ions in the indium sites. Atomic force microscopy and magnetic force microscopy show that magnetic clusters are formed in the annealing process. The magnetization-field hysteresis loops show ferromagnetic properties persisting up to room temperature with a coercive field of 100 0e （10e = 79.5775 A-m-1）, saturation magnetization of 4.35 × 10-5 emu, and remnant magnetization of 4.4× 10 6 emu.     

Comparison of the formation epitaxial graphenes on Si- and process and properties of C-face 6H-SiC substrates

In this paper,the epitaxial graphene layers grown on Si-and C-face 6H-SiC substrates are investigated under a low pressure of 400 Pa at 1600 C.By using atomic force microscopy and Raman spectroscopy,we find that there are distinct differences in the formation and the properties between the epitaxial graphene layers grown on the Si-face and the C-face substrates,including the hydrogen etching process,the stacking type,and the number of layers.Hopefully,our results will be useful for improving the quality of the epitaxial graphene on SiC substrate.     

Optical planar waveguides in yb3＋-doped phosphate glasses produced by He＋ ion implantation

Optical planar waveguides in Yb 3+-doped phosphate glasses are fabricated by implanting triple-energy helium ions. The guiding modes and the near-field intensity distribution are measured by using the prism-coupling method and the end-face coupling setup with a He-Ne laser at 633 nm The intensity calculation method (ICM) is used to reconstruct the refractive index profile of the waveguide. The absorption and the fluorescence investigations reveal that the glass bulk features are well preserved in the active volumes of the waveguides, suggesting the fabricated structures for possible applications as waveguide lasers.     

He离子辐照6H-SiC引入缺陷的光谱研究

实验采用300 keV的He²⁺辐照6H-SiC,辐照温度分别为室温,450,600和750 ℃,辐照剂量范围为1×10¹⁵–1×10¹⁷ cm^-2,辐照完成后对样品进行拉曼散射和紫外可见透射光谱测试与研究. 这两种分析方法的实验结果表明,He离子辐照产生的缺陷以及缺陷的恢复与辐照剂量和辐照温度有着直接关系. 室温下辐照会使晶体出现非晶化,体现在拉曼特征峰消失,相对拉曼强度达到饱和(同时出现了较强的Si-Si峰);高温下辐照伴随着晶体缺陷的恢复过程,当氦泡未存在时,高温辐照很容易导致Frenkel对、缺陷团簇等缺陷恢复,当氦泡存在时,氦泡会抑制缺陷恢复,体现在相对拉曼强度和相对吸收系数曲线斜率的变化趋势上. 本文重点讨论了高温辐照情况下氦泡对缺陷聚集与恢复的影响,并与高温下硅离子辐照碳化硅结果进行了对比. 关键词： 6H-SiC 氦泡 拉曼散射光谱 紫外可见透射光谱     

120keV的N+注入SiC薄膜的光谱特性研究

文中主要研究了120keV的N⁺注入后SiC薄膜样品的光致发光谱(PL)和傅立叶红外光谱(FTIR)特性.从红外光谱可以看到有明显得碳氮单键、双键、三键等新结构生成.从PL光谱则发现365nm处的发光峰明显增强,这表明N⁺注入使得带隙中深的能级辐射中心复合的效率大幅度提高     

Optical spectroscopy study of damage induced in 4H-SiC by swift heavy ion irradiation

Single crystals of 4H-SiC were irradiated with swift heavy ions (332 MeV Ti, 106 MeV Pb and 2.7 GeV U) in the electronic energy loss regime. The resulting damage was investigated with UV-visible optical absorption spectroscopy and micro-Raman spectroscopy. The evolution of the Raman data with fluence shows an accumulation of isolated point defects without amorphization of the material and a partial recrystallization of the structure, but only at the lowest fluence. Furthermore, the longitudinal optical phonon-plasmon coupling mode disappears upon irradiation, suggesting a strong perturbation of the electronic structure. This evolution is consistent with the optical bandgap decrease and the Urbach edge broadening that was also previously observed for the irradiation with 4 MeV Au ions.     

Coherent optical phonons in alexandrite crystal studied by Optical Kerr Effect spectroscopy

Herewith, we report on the first observation of coherent phonons in alexandrite crystal obtained by means of the femtosecond Optical Kerr Effect spectroscopy. We have managed to observe dynamics of the Raman‐active modes with high resolution and to find their lifetimes in the temperature range between 263 K and 373 K. We have used the obtained temperature dependence of phonon lifetimes and frequencies for calculation of the anharmonic coupling constants. On the basis of our results, we have also calculated the widths of homogeneously broadened Raman lines. Our results prove that, in case of transparent samples, this experimental technique is a very good alternative to the commonly used transient reflection method. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman spectroscopy study of damage induced in fluorapatite by swift heavy ion irradiations

Raman spectroscopy was used to study the radiation damage of fluorapatite single crystals and sinters. Krypton and iodine ion irradiations were performed at high energies (∼1 MeV amu⁻¹) for fluences ranging between 1 × 10¹¹ and 5 × 10¹³ cm⁻². Evolution of the symmetric stretching mode of the PO₄³⁻ tetrahedral building blocks (strongest Raman mode observed at 965 cm⁻¹) versus ion fluence was investigated. After irradiation, this peak decreases in intensity and a second broader peak appears at lower wavenumber. The well‐resolved peak has been assigned to the crystalline phase, and the broader one to the amorphous phase. The integrated intensity ratios of these two peaks versus fluence are in good agreement with the damage fractions determined by X‐ray diffraction (XRD). Fits of the amorphous fraction versus fluence show that the amorphization mechanisms is dominated by a single‐impact process for iodine ions and by a double‐impact process for krypton ions in the case of single crystals and sinters. For both irradiations, complete amorphization could not be obtained. The amorphous fraction saturates at a maximum value of 88% for sinters and 72% for single crystals. This is attributed to a recrystallization effect which is more important in single crystals than in sinters. For both types of samples, the crystalline peak shifts slightly to a lower wavenumber with fluence, and then shifts back to its initial value for an amorphous fraction larger than 60%. This feature is attributed to a stress relaxation, as shown in the XRD data, which is accompanied by a decrease of the crystalline peak full‐width at half‐maximum. Copyright © 2011 John Wiley & Sons, Ltd.     

离子注入掺杂锐钛矿TiO2薄膜的光学性能

 在玻璃基体上,采用射频磁控溅射方法在不同的基体温度下制备了TiO₂薄膜,然后在薄膜中注入注量分别为5×1016, 1×1017和5×1017/cm2的N离子以制备N掺杂的TiO₂薄膜。X射线衍射结果表明：制备出的TiO₂薄膜为锐钛矿型。X射线光电子能谱研究结果表明：注入的N离子与TiO₂晶粒相互作用,形成了含氮的TiO_xN_2-x化合物,从而改变了TiO₂薄膜的吸收边;随N离子注量增加,吸收边移动更明显;同时,由于氮离子注入产生的辐照缺陷使TiO₂薄膜在紫外和可见光区的吸收也明显增强。     

Characterization of 4H-SiC substrates and epilayers by Fourier transform infrared reflectance spectroscopy

The infrared reflectance spectra of both 4H–SiC substrates and epilayers are measured in a wave number range from 400 cm 1 to 4000 cm 1 using a Fourier-transform spectrometer. The thicknesses of the 4H–SiC epilayers and the electrical properties, including the free-carrier concentrations and the mobilities of both the 4H–SiC substrates and the epilayers, are characterized through full line-shape fitting analyses. The correlations of the theoretical spectral profiles with the 4H–SiC electrical properties in the 30 cm 1 –4000 cm 1 and 400 cm 1 –4000 cm 1 spectral regions are established by introducing a parameter defined as error quadratic sum. It is indicated that their correlations become stronger at a higher carrier concentration and in a wider spectral region (30 cm 1 –4000 cm 1 ). These results suggest that the infrared reflectance technique can be used to accurately determine the thicknesses of the epilayers and the carrier concentrations, and the mobilities of both lightly and heavily doped 4H–SiC wafers.     

Optical spectroscopy study of modifications induced in cerium dioxide by electron and ion irradiations

UV-visible absorption spectroscopy and Raman spectroscopy were used to study damage production in cerium dioxide epitaxial films and polycrystalline sintered samples after irradiation with electrons for three energies to span the threshold displacement energies of cerium and oxygen atoms, and 2.4-MeV Cu ions. Neither amorphization nor specific colour-centre bands were detected. Evolutions of the refractive index were derived from the interference fringes in the optical transmission spectra of epilayers after irradiation. No significant change of the refractive index occurred for the 1.0-MeV electron irradiation, whereas a maximum decrease by 28?±?8% was deduced for the 1.4-MeV and 2.5-MeV energies. These modifications are consistent with ballistic damage on the cerium sublattice for high electron energies producing Ce³⁺ ions. However, no significant change of refractive index was found for the Cu ion irradiation. This likely stems from the high rate of Frenkel pair recombination in the collision cascades induced by more energetic recoils than for the electron irradiations, combined with electronic excitations and hole capture on Ce³⁺ ions. This study reveals modifications of the electronic structure upon irradiation that could take place in other non-amorphizable oxide systems.     

离子注入掺杂锐钛矿TiO2薄膜的光学性能

在玻璃基体上,采用射频磁控溅射方法在不同的基体温度下制备了TiO2薄膜,然后在薄膜中注入注量分别为5×1016, 1×1017和5×1017/cm2的N离子以制备N掺杂的TiO2薄膜。X射线衍射结果表明：制备出的TiO2薄膜为锐钛矿型。X射线光电子能谱研究结果表明：注入的N离子与TiO2晶粒相互作用,形成了含氮的TiOxN2-x化合物,从而改变了TiO2薄膜的吸收边;随N离子注量增加,吸收边移动更明显;同时,由于氮离子注入产生的辐照缺陷使TiO2薄膜在紫外和可见光区的吸收也明显增强。     

Ce3+注入对不同尺寸的nc-Si/SiO2 超晶格发光特性的影响

通过电子束蒸发方法以及高温退火处理,得到nc-Si/SiO₂超晶格。将样品分别注入剂量为2.0×10¹⁴ cm^-2和2.0×10¹⁵ cm^-2的Ce³⁺,再对其进行二次退火处理,获得多组样品。通过对样品光致发光光谱的分析发现,样品发光强度的变化不仅受到Ce³⁺注入剂量的影响,而且也受到nc-Si颗粒大小的影响。在相同注入计量和相同的二次退火处理温度下,nc-Si颗粒较大的样品经Ce³⁺注入后其发光强度增强较为明显。     

Applications of Raman spectroscopy in herbal medicine

Raman spectroscopic techniques are a group of chemical fingerprint detection methods based on molecular vibrational spectroscopy. They are compatible with aqueous solutions and are time saving, nondestructive, and highly informative. With complementary and alternative medicine (CAM) becoming increasingly popular, more people are consuming natural herbal medicines. Thus, chemical fingerprints of herbal medicines are investigated to determine the content of these products. In this study, I review the different types of Raman spectroscopic techniques used in fingerprinting herbal medicines, including dispersive Raman spectroscopy, resonance Raman spectroscopy, Fourier transform (FT)–Raman spectroscopy, surface-enhanced Raman scattering (SERS) spectroscopy, and confocal/microscopic Raman spectroscopy. Lab-grade Raman spectroscopy instruments help detect the chemical components of herbal medicines effectively and accurately without the need for complicated separation and extraction procedures. In addition, portable Raman spectroscopy instruments could be used to monitor the health and safety compliance of herbal products in the consumer market.     

Optical spectroscopy of Mn2+ ions in CaCl2 single crystals

Abstract

In the present investigation the excitation and fluorescence spectra and lifetimes of Mn²⁺ ions in calcium chloride, for various manganese concentrations and sample temperatures have been studied for the first time. The fluorescence spectrum consists of an asymmetric broad band, which upon lowering the sample temperature, shifts its maximum from 580 nm at 300 K to 596 nm at 11 K. This luminescence band was associated with the ⁴T_lg(⁴G)→⁶A_lg(⁶S) spin-forbidden transition in the manganese ions occupying Ca-sites in the lattice of CaCl₂. The excitation spectrum of the Mn²⁺ fluorescence revealed the features of manganese ions in octahedral coordination and consisted of nine excitation peaks which were associated with Mn²⁺-crystal-field-sensitive transitions. A crystal field analysis of the wavelength positions of these transitions by means of the model developed by Curie et al. allowed us to determine the magnitude of the cubic field splitting 10Dq, the reduced Racah parameter B', the Koide-Pryce covalency parameter ε and the spin transfer coefficients f _[sgrave] and f _σ. From the measurement of the temperature dependence of the Mn²⁺ fluorescence lifetime, we have also obtained information about the different mechanisms which are involved in the relaxation of excited Mn²⁺ ions in this host crystal in the temperature range (11–300 K).     

Structural evolution study of additions of Sb_2S_3 and CdS into GeS_2 chalcogenide glass by Raman spectroscopy

The structures of pseudo-binary GeS_2–Sb_2S_3, GeS_2–CdS, Sb_2S_3–CdS, and pseudo-ternary GeS_2–Sb_2S_3–CdS chalcogenide systems are systematically investigated by Raman spectroscopy. It is shown that a small number of [S_3Ge–GeS_3]structural units(SUs) and-S-S-/S8 groups exist simultaneously in GeS_2 glass which has a three-dimensional continuous network backbone consisting of cross-linked corner-sharing and edge-sharing [GeS_4] tetrahedra. When Sb_2S_3 is added into GeS_2 glass, the network backbone becomes interconnected [GeS_4] tetrahedra and [SbS_3] pyramids. Moreover, Ge atoms in[S_3Ge–GeS_3] SUs tend to capture S atoms from Sb_2S_3, leading to the formation of [S_2Sb–SbS_2] SUs. When CdS is added into GeS_2 glass, [Cd_4GeS_6] polyhedra are formed, resulting in a strong crystallization tendency. In addition, Ge atoms in[S_3Ge–GeS_3] SUs tend to capture S atoms from CdS, resulting in the dissolution of Ge–Ge bond. Co-melting of Sb_2S_3 or CdS with GeS_2 reduces the viscosity of the melt and improves the homogeneity of the glass. The GeS_2 glass can only dissolve up to 10-mol% CdS without crystallization. In comparison, GeS_2–Sb_2S_3 glasses can dissolve up to 20-mol% CdS,implying that Sb_2S_3 could delay the construction of [Cd_4GeS_6] polyhedron and increase the dissolving amount of CdS in the glass.