共查询到20条相似文献,搜索用时 15 毫秒
1.
Volodymyr Dzhagan Nikolai Mel'nik Olexandra Rayevska Galyna Grozdyuk Viktor Strelchuk Olga Plyashechnik Stepan Kuchmii Mykhailo Valakh 《固体物理学:研究快报》2011,5(7):250-252
Resonant Raman scattering spectra of ultrasmall (<2 nm) magic‐size nanocrystals (NCs) are reported. The spectra of CdS and CdSx Se1‐x NCs, resonantly excited with 325 nm and 442 nm laser lines, correspondingly, reveal broad features in the range of bulk optical phonons. The relatively large width, ~50 cm‐1, and downward shift, ~20 cm‐1, of the Raman bands with respect to the longitudinal optical phonon in bulk crystals and large NCs are discussed based on the breaking of the translational symmetry and bond distortion in these ultrasmall NCs. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
E. S. Freitas Neto A. C. A. Silva S. W. da Silva P. C. Morais J. A. Gmez O. Baffa N. O. Dantas 《Journal of Raman spectroscopy : JRS》2013,44(7):1022-1032
Glass‐embedded Cd1−xCoxS quantum dots (QDs) with mean radius of R ≈ 1.70 nm were successfully synthesized by a novel protocol on the basis of the melting‐nucleation synthesis route and herein investigated by several experimental techniques. Incorporation of Co2+ ions into the QD lattice was evidenced by X‐ray diffraction and magnetic force microscopy results. Optical absorption features with irregular spacing in the ligand field region confirmed that the majority of the incorporated Co2+ ions are under influence of a low‐symmetry crystal field located near to the Cd1−xCoxS QD surface. Electron paramagnetic resonance data confirmed the presence of Co2+ ions in a highly inhomogeneous crystal field environment identified at the interface between the hosting glass matrix (amorphous) and the crystalline QD. The acoustic‐optical phonon coupling in the Cd1−xCoxS QDs (x ≠ 0.000) was directly observed by Raman measurements, which have shown a high‐frequency shoulder of the longitudinal optical phonon peak. This effect is tuned by the size‐dependent sp‐d exchange interaction due to the magnetic doping, causing variations in the coupling between electrons and longitudinal optical phonon. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
3.
A. G. Milekhin A. I. Toropov A. K. Bakarov S. Schulze D. R. T. Zahn 《JETP Letters》2006,83(11):505-508
Raman scattering by optical phonons in InxGa1 ? x As/AlAs nanostructures with quantum dots has been studied experimentally for compositions corresponding to x = 0.3?1 under out-resonance conditions. Features due to scattering by GaAs-and InAs-like optical phonons in quantum dots have been detected, and the phonon frequencies have been determined as a function of the dot composition. With increasing excitation energy, a red shift is observed in the frequency of the GaAs-like phonon in quantum dots, which testifies to Raman scattering selective by the size of quantum dots. Under resonant conditions, multiphonon light scattering by optical and interface phonons is observed up to the third order, including overtones of the first-order phonons of InGaAs and AlAs materials and their combinations. 相似文献
4.
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. 相似文献
5.
GexSi1−x nanostructures that can be manipulated through size reduction, geometry variation, and alloying, are considered as one of the key developments for next generation technologies, due to their easy processing, unique properties, and compatibility with the existent silicon-based microelectronic industry. In this review, we have thoroughly discussed the major advances in electronic structures and phonon properties of GexSi1−x nanocrystals (NCs). Experimental and theoretical characterization related to several main factors, for example, size, composition, strain, temperature, and interface and surface were presented with special emphasis in low-frequency Raman scattering. Current difficulties in explaining the Raman spectra are the assignment of the low-frequency modes because of the complexity of the environment around the NCs, thus different theoretical models are introduced in detail to deal with different properties of GexSi1−x alloy NCs including Lamb’s theory, complex-frequency (CF) model, core–shell matrix (CMS) model and spatial coherence effect model. 相似文献
6.
Xiaming Zhu Huizhen Wu Zijian Yuan Jinfang Kong Wenzhong Shen 《Journal of Raman spectroscopy : JRS》2009,40(12):2155-2161
Multiphonon resonant Raman scattering in N‐doped ZnO films was studied, and an enhancement of the resonant Raman scattering process as well as longitudinal optical (LO) phonon overtones up to the sixth order were observed at room temperature. The resonant Raman scattering intensity of the 1LO phonon in N‐doped ZnO appears three times as strong as that of undoped ZnO, which mainly arises from the defect‐induced Raman scattering caused by N‐doping. The nature of the 1LO phonon at 578 cm−1 is interpreted as a quasimode with mixed A1 and E1 symmetry because of the defects formed in the ZnO lattice. In addition, the previously neglected impurity‐induced two‐LO‐phonon scattering process was clearly observed in N‐doped ZnO. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
Harish Kumar Yadav K. Sreenivas Vinay Gupta R. S. Katiyar 《Journal of Raman spectroscopy : JRS》2009,40(4):381-386
We present X‐ray diffraction and Raman spectroscopy studies of Ni‐doped ZnO (Zn1−xNixO, x = 0.0, 0.03, 0.06, and 0.10) ceramics prepared by solid‐state reaction technique. The presence of the secondary phase along with the wurtzite phase is observed in Ni‐doped ZnO samples. The E2(low) optical phonon mode is seen to be shifted to a lower wavenumber with Ni incorporation in ZnO and is explained on the basis of force‐constant variation of ZnO bond with Ni incorporation. A zone boundary phonon is observed in Ni‐doped samples at ∼130 cm−1 which is normally forbidden in the first‐order Raman scattering of ZnO. Antiferromagnetic ordering between Ni atoms via spin‐orbit mechanism at low temperatures (100 K) is held responsible for the observed zone boundary phonon. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
8.
Antoine Reigue Baptiste Augui Pablo G. Etchegoin Eric C. Le Ru 《Journal of Raman spectroscopy : JRS》2013,44(4):573-581
The aim of this work is to illustrate the power of recently developed methods for measuring resonance Raman scattering (RRS) spectra of efficient fluorophores (using a standard continuous wave excitation and a charge‐coupled device (CCD)‐based Raman spectrometer), by applying them to a detailed study of a specific fluorophore: Nile Blue A. A combination of methods are used to measure the RRS properties of Nile Blue A in water (quantum yield (QY) of 4%) and ethanol (QY of 22%) at excitation wavelengths between 514 and 647 nm, thus covering both pre‐resonance and RRS conditions. Standard Raman measurements are used in situations where the fluorescence background is small enough to clearly observe the Raman peaks, while the recently introduced polarization‐difference RRS and continuously shifted Raman scattering are used closer to (or at) resonance. We show that these relatively straightforward methods allow us to determine the Raman cross‐sections of the most intense Raman peaks and provide an accurate measurement of their line‐width; even for broadenings as low as ∼ 4 cm − 1. Moreover, the obtained Raman excitation profiles agree well with those derived from the optical absorption by a simple optical transform model. This study demonstrates the possibility of routine RRS measurements using standard Raman spectrometers, as opposed to more complicated time‐resolved techniques. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
9.
E. S. F. Neto N. O. Dantas S. W. da Silva P. C. Morais M. A. Pereira da Silva 《Journal of Raman spectroscopy : JRS》2010,41(10):1302-1305
This work gives the evidence of the lattice contraction in CdSe nanocrystals (NCs) grown in a glass matrix. The CdSe NCs were investigated by atomic force microscopy (AFM), optical absorption (OA), and Raman spectroscopy. The average size of CdSe NCs can be estimated by AFM images. Using the OA spectra and the effective‐mass approximation, it was also possible to estimate the average sizes of CdSe NCs, which agree very well with the AFM data. These results showed that the CdSe NCs grow with increasing time of heat treatment. The blue shift of the longitudinal optical (LO) modes and surface optical (SO) phonon modes with an increase in the average radius of the NCs, shown in the Raman spectra, was explained by the lattice contraction in CdSe NCs caused by thermodynamic interactions at the interface with the host glass matrix. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
Santanu Bhattacharya Anindya Datta Sandip Dhara Dipankar Chakravorty 《Journal of Raman spectroscopy : JRS》2011,42(3):429-433
Raman scattering studies were performed in GaN nanoribbons grown along [1 0 0]. These samples were prepared inside Na‐4 mica nanochannels by the ion‐exchange technique and subsequent annealing in NH3 ambient. Detailed morphological and structural studies including the crystalline orientation were performed by analyzing the vibrational properties in these GaN nanoribbons. Pressure in the embedded structure was calculated from the blue shift of the E2(high) phonon mode of GaN. Possible red shift of optical phonon modes due to the quantum confinement is also discussed. In addition to the optical phonons allowed by symmetry, two additional Raman peaks were also observed at ∼633 and 678 cm−1 for these nanoribbons. Calculations for the wavenumbers of the surface optical (SO) phonon modes in GaN in Na‐4 mica yielded values close to those of the new Raman modes. The SO phonon modes were calculated in the slab (applicable to belt‐like nanoribbon) mode, as the wavenumber and intensity of these modes depend on the size and the shape of the nanostructures. The effect of surface‐modulation‐assisted electron–SO phonon scattering is suggested to be responsible for the pronounced appearance of SO phonon modes. A scaling factor is also estimated for the interacting surface potential influencing the observed SO Raman scattering intensities. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
11.
R. Y. Sato‐Berrú A. Vzquez‐Olmos A. L. Fernndez‐Osorio S. Sotres‐Martínez 《Journal of Raman spectroscopy : JRS》2007,38(9):1073-1076
We measured the Raman spectra of ZnO nanoparticles (ZnO‐NPs), as well as transition‐metal‐doped (5% Mn(II), Fe(II) or Co(II)) ZnO nanoparticles, with an average size of 9 nm. A typical Raman peak at 436 cm−1 is observed in the ZnO‐NPs, whereas Zn1−xMnxO, Zn1−xFexO and Zn1−xCoxO presented characteristic peaks at 661, 665 and 675 cm−1, respectively. These peaks can be related to the formation of Mn3O4, Fe3O4 and Co3O4 species in the doped ZnO‐NPs. Moreover, these samples were analyzed at various laser powers. Here, we observed new vibrational modes (512, 571 and 528 cm−1), which are specific to Mn, Fe and Co dopants, respectively, and ZnO‐NPs did not reveal any additional modes. The new peaks were interpreted either as disorder activated phonon modes or as local vibrations of Mn‐, Fe‐ and Co‐related complexes in ZnO. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
12.
Cristina Fornacelli Philippe Colomban Isabella Turbanti Memmi 《Journal of Raman spectroscopy : JRS》2015,46(11):1129-1139
CdSxSe1 − x quantum dots received considerable attention in academic studies and as cut‐off filters and indirect‐gap semiconductors. These later compounds have also been used for artistic purposes to produce colored glass since the 1920s thanks to their bright colors. Because non‐invasive conditions are now mandatory when considering objects belonging to the cultural heritage, the use of Raman and fiber optics reflectance spectroscopy has been identified as potential ones to obtain information about the nanostructure of six samples of historical glass produced between the late 1920s and modern days. The average elemental composition of the nanocrystals has been deduced processing both optical and vibrational data, and the result arising has been compared taking into account the several factors affecting the experimental results. The diffusion of zinc inside the nanocrystals has also been questioned by the shift caused on the CdS‐ and CdSe‐like phonon band wavenumber and on the absorption edge wavelength. An investigation of the size distribution and crystallinity of CdSxSe1 − x nanoparticles has been also performed considering those parameters that are mainly influenced by the disorder of the system, such as the extent of the Urbach tail and the Raman bandwidth. Thanks to the results obtained, discrimination between the more recent glass and the older Art Nouveau ones has been verified, leading to the identification of a useful analytical protocol for conservation purposes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
13.
Satyaprakash Sahoo S. Dhara V. Sivasubramanian S. Kalavathi A. K. Arora 《Journal of Raman spectroscopy : JRS》2009,40(8):1050-1054
1‐longitudinal optical (LO) phonons in free‐standing mixed Cd1−xZnxS nanocrystals, synthesized using chemical precipitation, are investigated using Raman spectroscopy. As expected for the nanocrystals, the 1‐LO modes are found to appear at slightly lower wavenumbers than those in the bulk mixed crystals and exhibit one‐mode behavior. On the other hand, the line broadening is found to be much more than that can be accounted on the basis of phonon confinement. From the detailed line‐shape analysis it turns out that the substitutional disorder in the mixed crystals contributes much more to the line broadening than the phonon confinement. The linewidth arising from these mechanisms are also extracted from the analysis. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
14.
利用325nm紫外光激发,对不同组分的InxGa1-xN薄膜的喇曼散射谱进行了研究.在光子能量大于带隙的情况下,观察到显著增强的二阶A1(LO)声子散射峰.二阶LO声子峰都从一阶LO声子的二倍处向高能方向移动,移动量随样品In组分的增加而增大,认为是带内Frhlich相互作用决定的多共振效应引起的.分析了一阶LO声子散射频率和峰型与In组分的关系.在喇曼谱中观察到样品存在相分离现象,并与X射线衍射的实验结果进行
关键词:
xGa1-xN合金')" href="#">InxGa1-xN合金
紫外共振喇曼散射
二阶声子
相分离 相似文献
15.
Raman spectra acquired from Si
x
Ge1−x
-nanocrystal-embedded SiO2 films show dependence of the Si–Si optical phonon frequency on Si content. The frequency upshifts, and peak intensity increases
as the silicon concentration increases. For a given Si content, the frequency remains unchanged with annealing temperature.
Spectral analysis and density functional theory calculation reveal that the optical Si–Si phonon is related to the formation
of localized Si clusters surrounded by Si/Ge atomic layers in the Si
x
Ge1−x
nanocrystals and the intensity enhancement arises from the larger cluster size. The synergetic effect of surface tensile
stress and phonon confinement determines the Si–Si optical phonon behavior. 相似文献
16.
Michael Bauer Alexander M. Gigler Andreas J. Huber Rainer Hillenbrand Robert W. Stark 《Journal of Raman spectroscopy : JRS》2009,40(12):1867-1874
Silicon carbide (SiC) is often used for electronic devices operating at elevated temperatures. Spectroscopic temperature measurements are of high interest for device monitoring because confocal Raman microscopy provides a very high spatial resolution. To this end, calibration data are needed that relate Raman line‐shift and temperature. The shift of the phonon wavenumbers of single crystal SiC was investigated by Raman spectroscopy in the temperature range from 3 to 112°C. Spectra were obtained in undoped 6H SiC as well as in undoped and nitrogen‐doped 4H SiC. All spectra were acquired with the incident laser beam oriented parallel as well as perpendicular to the c‐axis to account for the anisotropy of the phonon dispersion. Nearly all individual peak centers were shifting linearly towards smaller wavenumbers with increasing temperature. Only the peak of the longitudinal optical phonon A1(LO) in nitrogen‐doped 4H SiC was shifting to larger wavenumbers. For all phonons, a linear dependence of the Raman peaks on both parameters, temperature and phonon frequency, was found in the given temperature range. The linearity of the temperature shift allows for precise spectroscopic temperature measurements. Temperature correction of Raman line‐shifts also provides the ability to separate thermal shifts from mechanically induced ones. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
17.
S. Das R. K. Singha S. Manna S. Gangopadhyay A. Dhar S. K. Ray 《Journal of nanoparticle research》2011,13(2):587-595
We have grown Ge nanocrystals (NCs) (4.0–9.0 nm in diameter) embedded in high-k HfO2 matrix for applications in floating gate memory devices. X-ray photoelectron spectroscopy has been used to probe the local
chemical bonding of Ge NCs. The analysis of Ge–Ge phonon vibration using Raman spectroscopy has shown the formation of compressively
stressed Ge NCs in HfO2 matrix. Frequency dependent electrical properties of HfO2/Ge-NCs in HfO2/HfO2 sandwich structures have been studied. An anticlockwise hysteresis in the capacitance–voltage characteristics suggests electron
injection and trapping in embedded Ge NCs. The role of interface states and deep traps in the devices has been thoroughly
examined and has been shown to be negligible on the overall device performance. 相似文献
18.
The microstructures of (1 − x)(TeO2)–xPbF2, (x = 0.1, 0.15, and 0.25 mol) glasses were investigated by using the Raman spectroscopic technique. The effect of compositions on the TeO2 glass networks and the intensity ratios of the deconvoluted Raman peaks were determined. The results confirm that the addition of modifiers to the glass network former shifts the Raman intensity and the peak wavenumber values for each band in the 167–165, 652–645, and 747–755 cm−1 wavenumber regions. The structural evaluation was recognized from the Raman spectra, with the structural units described as [TeO3+1] polyhedra, [TeO3] trigonal pyramids, and [TeO4] trigonal bipyramids for this binary glass system. Heat‐treatment of the samples shows that the metastable crystalline phase of TeO2 known as γ‐TeO2 is formed only when the modifier content is 10 mol% in the glass matrix. Transparent glass properties were not realized when the TeO2 amount was decreased to less than 10 mol% content. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
19.
N. K. Karan R. S. Katiyar T. Maiti R. Guo A. S. Bhalla 《Journal of Raman spectroscopy : JRS》2009,40(4):370-375
This paper reports a systematic study of the composition and the temperature‐dependent‐Raman spectra of Zr4+‐rich BaZrxTi1−xO3 (BZT) ceramic compositions (0.50⩽x⩽1.00). On the basis of the dielectric behavior of Zr rich BZT ceramics, the observed relaxor behavior has been hypothesized as a result of increasing long‐range interactions of nanosized, Ti4+‐rich polar regions in a Zr4+‐rich nonpolar matrix. Beyond an optimum concentration of BaTiO3 (BT) in the nonpolar matrix of BaZrO3 (x⩽0.75), a critical size and density of the polar regions is reached when the polar clusters start showing the relaxor like behavior, which finally show classical relaxor behavior for compositions with x = 0.5 and 0.6. This hypothesis is strongly supported from the Raman data on Zr‐rich BZT presented in this paper. Well‐defined BT Raman spectra for 5% BT in BZT composition were recorded, which followed completely up to the 50% Ti addition in the BZT samples. The temperature‐dependent Raman spectra collected on the BZT ceramics far beyond the dielectric transition temperatures supported the existence of the nano‐polar BT regions, like in typical relaxor samples. The full width at half‐maximum (FWHM), integrated intensity of the peaks in the Raman spectra has been analyzed to further support the conclusions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
V. S. Vinogradov T. N. Zavaritskaya G. Karczewski I. V. Kucherenko N. N. Mel’nik W. Zaleszczyk 《Physics of the Solid State》2010,52(8):1757-1762
The Raman scattering and luminescence spectra of Zn1 − x
Mn
x
Te (0 ≤ x ≤ 0.6) quantum wires have been investigated. The quantum wires have been grown by molecular-beam epitaxy on the (100)GaAs
substrate with Au used as a catalyst. The spectrum of optical phonons in ZnMnTe quantum wires varies with a variation in x in accordance with an intermediate (between one- and two-mode) type of transformation. The optical phonon spectrum has been
analyzed in terms of the microscopic theory. It has been demonstrated that the experimental data can be brought in accord
with the theory by properly modifying the calculated density of phonon states for ZnTe. The spatial confinement has been found
to affect the electronic states in Zn1 − x
Mn
x
Te quantum wires. 相似文献