Temperature dependent phonon confinement in silicon nanostructures

Temperature dependent variation in Raman line-shape from silicon (Si) nanostructures (NSs) is studied here. Asymmetry and red-shift in room temperature Raman spectrum is attributed to phonon confinement effect. Raman spectra recorded at higher temperatures show increase in FWHM and decrease in asymmetry ratio with respect to its room temperature counterpart. Theoretical Raman line-shape analyses of temperature dependence of phonon confinement is done by incorporating the temperature dependence of phonon dispersion relation. Experimental and theoretical temperature dependent Raman spectra are in good agreement.     

On the contribution of nearly critical spin and charge collective modes to the Raman spectra of high-Tc cuprates

We discuss how Raman spectra are affected by nearly critical spin and charge collective modes, which are coupled to charge carriers near a stripe quantum critical point. We show that specific fingerprints of nearly critical collective modes can indeed be observed in Raman spectra and that the selectivity of Raman spectroscopy in momentum space may also be exploited to distinguish the spin and charge contribution. We apply our results to discuss the spectra of high-T_c superconducting cuprates finding that the collective modes should have masses with substantial temperature dependence in agreement with their nearly critical character. Moreover, spin modes should be more diffusive than charge modes indicating that in stripes the charge is nearly ordered, while spin modes are strongly overdamped and fluctuate with high frequency.     

具有四次幂交换作用的Heisenberg铁磁体的低温自旋波理论

本文讨论具有四次幂交换作用的Heisenberg铁磁体,用Малеев玻色变换,在低温区建立〈S_i^z〉的严格展式,正确地包括了动力学相互作用和运动学相互作用,得到自旋波谱和自发磁化的正确温度依赖关系。 关键词：     

LBO晶体的光散射研究

ＬＢＯ晶体的光散射研究王越，蒋毅坚，刘玉龙（北京工业大学应用物理系北京１０００２２）（中科院物理研究所北京１０００８０）ＳｔｕｄｙｏｎｏｎＬＢＯＣｒｙｓｔａｌｂｙＬｉｇｈｔＳｃａｔｔｅｒｉｎｇ￥Ｙ．Ｗａｎｇ￣１；Ｙ．Ｊ．Ｊｉａｎｇ￣１ａｎｄＹ，Ｌ．Ｌ...     

Spectral signatures of critical charge and spin fluctuations in cuprates

We discuss how Raman spectra of high temperature superconducting cuprates are affected by nearly critical spin and charge collective modes, which are coupled to charge carriers near a stripe quantum critical point. We find that specific fingerprints of nearly critical collective modes can be observed and that the selectivity of Raman spectroscopy in momentum space may be exploited to distinguish the spin and charge contribution. We apply our results to discuss the spectra of high-T_c superconducting cuprates finding that the collective modes should have masses with substantial temperature dependence in agreement with their nearly critical character. Moreover spin modes have larger masses and are more diffusive than charge modes indicating that in stripes the charge is nearly ordered, while spin modes are strongly overdamped and fluctuating with high frequency.     

一种基于荧光材料的聚合物白光发光二极管

制备了一种基于荧光聚合物共混的单发光层聚合物白光发光二极管.器件结构为铟锡氧化物/苯磺酸掺杂聚乙烯基二氧噻吩/发光层/ 1,3,5-三(N-苯基-2-苯并咪唑-2)苯41/Ba/Al,蓝光材料芴-氟化喹喔啉共聚物(PF-BPFQ5)、绿光材料苯基取代的聚对苯乙炔(P-PPV)和红光材料聚(2-甲氧基-5-(2′-乙基己氧基)-1,4-对苯乙炔)(MEH-PPV)共混为发光层.当PF-BPFQ5,P-PPV,MEH-PPV的质量比例为100∶06∶06时,获得标准的白光,色坐标为（033 关键词： 聚合物发光二极管 白光 共混     

n-SiC拉曼散射光谱的温度特性

测量了采用离子注入法得到掺N的n-SiC晶体从100—450 K的拉曼光谱. 研究了SiC一级拉曼谱、电子拉曼散射谱及二级拉曼谱的温度效应. 实验结果表明,大部分SiC一级拉曼峰会随温度升高向低波数方向移动,但声学模红移(峰值位置向低频方向移动)的幅度较光学模小. 重掺杂4H-SiC的纵光学声子等离子体激元耦合(LOPC)模频率随温度升高表现出先蓝移(峰值位置向高频方向移动)后红移的变化趋势,表明LOPC模的温度特性不仅会受到非简谐效应的影响,还与实际已离化杂质浓度有关. 电子拉曼散射峰线宽随温度升高而增 关键词： 碳化硅 温度 纵光学声子等离子体激元耦合模 电子拉曼散射     

Temperature dependence of infrared and Raman modes in polymeric RbC60

Temperature dependence of the intra-molecular vibrational modes of C₆₀ in the quasi-1D polymeric RbC₆₀, across the low temperature transition at ∼50 K, has been probed through infrared (IR) and Raman spectroscopies. With the lowering of temperature, the split IR modes of RbC₆₀ are seen to harden but below 50 K a small but definitive signature of an anomalous softening is observed. In addition, the background IR transmission shows an increase below 50 K with the opening of a well defined gap in the electronic spectrum. The implications of these results, along with those of Raman measurements, are discussed in terms of the interaction of intra-molecular phonons with electrons and spin excitations in the system.     

Light scattering by spin excitations in copper-oxide-based materials

In this paper we present a study of spin dynamics in CuO, Bi₂CuO₄and CuGeO₃single crystals using Raman spectroscopy. The measurements of polarized Raman scattering spectra are performed in the temperature region from 10 to 300 K in various frequency ranges. We found and assigned the lines in the spectra that belong to magnetically ordered phases. The origin of these excitations, based on the temperature dependence of their energies, linewidths and symmetry arguments, is given. Also, we present calculations of two-magnon intensities, based on the densities of states, and compare them with experimental data.     

Effect of temperature on IR-absorption of diphenyl

In this work, the temperature dependence of the intensities of the IR absorption bands corresponding to the fundamental vibrations, overtones and combination frequencies of diphenyl is presented. A thorough discussion of the interpretation of the fundamental modes of vibration has been made on the basis of the temperature dependence of the intensities of these absorption bands.The structure of the diphenyl molecule has been the subject of numerous investigations. Despite a considerable amount of work on the Raman(1), IR(3,4,5) and ultraviolet (2) spectra, the assignment of the fundamental frequencies has not yet been established with certainty, Some assistance can be obtained from the temperature dependence of the IR spectrum of this material.     

Theory of resonant Raman scattering from low-energy collective excitations of interacting electrons in quantum wires

The Raman spectra of quantum wires in the region of electronic intra-band excitations are investigated using one- and two-band models based on the Luttinger approximation with spin. Structures related to charge and spin density modes are identified, and analyzed with respect to their behavior with photon energy and temperature. It is found that the low-energy peaks in the polarized spectra, close to resonance that are commonly assigned to “single particle excitations”, can be interpreted as the signature of spin density excitations. A broad structure in the resonant depolarized spectrum is predicted above the frequency of the spin density excitations. This is due to simultaneous but independent propagation of spin and charge density modes. The results, when compared with experiment, show, that the electronic collective excitations of quantum wires at low energies are characteristic for a non-Fermi liquid. Received: 25 March 1998 / Accepted: 3 June 1998     

BaTiO3和Ce:BaTiO3单晶的高温喇曼散射研究

从室温至180℃测量了BaTiO₃和Ce:BaTiO₃单晶的偏振喇曼谱,在X(ZZ)Y几何配置下发现了三条频率分别为986,1204和1480cm^-1的新谱线.根据喇曼散射截面的温度依赖关系,确认这些新谱线对应二阶喇曼散射,而A₁(TO)谱中位于275和514cm^-1处的非对称宽峰则属于一阶喇曼散射.在此基础上,对立方相BaTiO₃的喇曼谱和结构相变机制进行了讨论.通过比较B     

An EPR study of solid solutions of ferric oxide in γ-Al2O3

The EPR spectra of solid solutions of ferric oxide in γ-alumina have been studied. The dilute samples show two different spectra which are attributed to isolated ferric ions in the A and B sites of the spinel lattice. From the intensity dependence of the spectra on the iron concentration an approximate value of the range of the exchange forces is deduced. The concentrated samples show an isotropic spectrum at g = 2·033 which is attributed to clusters of ferric ions coupled by exchange. The temperature dependence of the intensity of the associated ions spectrum is attributed to the increase of the average spin value of the clusters with T.     

From spin flip excitations to the spin susceptibility enhancement of a two-dimensional electron gas

The g-factor enhancement of the spin-polarized two-dimensional electron gas was measured directly over a wide range of spin polarizations, using spin flip resonant Raman scattering spectroscopy on two-dimensional electron gases embedded in Cd(1-x)Mn(x)Te semimagnetic quantum wells. At zero Raman transferred momentum, the single-particle spin flip excitation, energy Z*, coexists in the Raman spectrum with the spin flip wave of energy Z, the bare giant Zeeman splitting. We compare the measured g-factor enhancement with recent spin-susceptibility enhancement theories and deduce the spin-polarization dependence of the mass renormalization.     

低温下单壁碳纳米管拉曼光谱温度效应研究

在单壁碳纳米管的低温拉曼光谱测量过程中,发现径向呼吸模(RBM)和正切拉伸模(GM)的拉曼频移在低温下的温度效应和在高温时的温度效应存在着很大的区别,在低温下拉曼光谱的频移和温度并不呈线性关系。而且,在温度为210K时,单壁碳纳米管内部的振动结构可能发生了变化。在低温下单壁碳纳米管拉曼峰的强度的变化是不可逆的。     

Temperature dependence of the photoluminescence and phosphorescence time decay of magnesia-stabilized zirconia

Temperature dependence of photoluminescence (PL) spectra and time decay ranging from 90 to 330 K are investigated in magnesia-stabilized zirconia single crystals. The emission PL spectra can be decomposed into two bands. The prominent one is centered in the blue-green region of the spectrum whereas the secondary one is centered in the yellow-orange region. The temperature dependence of these bands are analyzed in terms of the so-called configuration coordinate model. The Huang-Rhys parameter for the prominent band is found near 40 and the effective phonon at about 0.030 eV. Thermal quenching energy is determined to be 0.24 eV from the decreasing part of the I(T) curve. Luminescent decays were satisfactorily fitted by two exponentials over the whole temperature range investigated. Total lifetime temperature dependence can be accounted for by assuming a radiative decay from two metastable levels with a separation energy of 0.073 eV. Results are discussed on the basis of the major defects, oxygen vacancies and complex defects.     

N.M.R. studies of liquid boron trifluoride

Previous ¹⁹F N.M.R. studies of liquid BF₃ have been extended by obtaining the ¹¹B spectrum of BF₃ and the ¹⁹F spectrum of ¹⁰BF₃ at various temperatures. Values for the B-F coupling constant and the boron relaxation times have been obtained by computer matching and visual matching of observed and calculated spectra. Relaxation times have the Arrhenius temperature dependence found previously. The temperature dependence of the B-F coupling constant is discussed. Some of the possible advantages of ‘high spin spectra’ are discussed.     

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.     

Utility of Raman Data in Studying Substituted Amines and Hydrazines

By utilizing the Raman spectra of gases, it is frequently possible m provide sufficient data to unequivocally assign the fundamental and several hot bands of the two torsional modes of two coupled methyl rotors which is illustrated by the Raman spectrum of gaseous dimethylamine. From these data V03 = V30, V33 and V‘33 terms have been obtained and their values are compared to those obtained from MP2/6 - 31G(d) ab initio calculations. Also if one of the conformers of an amine or hydrazine has a plane of symmetry and another one has no symmetry, it can be possible to determine the origin of the observed amino torsional mode with excited states from the Raman spectrum, i.e., ethylamine is an example. Since the NH stretches of substituted amines and hydrazines are frequently very weak in the infrared spectrum, the Raman spectra are necessary for the assignment of these fundamentals. Studies are in progress to use the “isolated” NH stretching frequencies to obtain the r0 distances for amines and hydrazinest     

共振拉曼效应和电子-声子耦合对线性多烯分子共振拉曼光谱的影响

线性多烯分子具有高强度且信息丰富的共振拉曼光谱,在生物学、光电材料和医学等方面都有一定应用.而含有共轭双键的短链β胡萝卜素分子是多烯分子中极具有代表性的分子.在激发光作用下π电子与CC键振动相互作用影响着吸收光谱和拉曼光谱,而共振拉曼效应和电子-声子耦合影响着共振拉曼光谱的强度、频率和线型.测量了β胡罗卜素分子在二氯乙...