Millimeter size single crystals of double perovskite La2NiMnO6 (LNMO) were grown by the High Temperature Solution Growth Method. The magnetic measurements and polarized Raman spectra between 5 and 350K provide evidence that the crystals have high degree of Ni(2+)/Mn(4+)ordering, small amount of lattice defects and highest Tc = 288K reported so far for ferromagnetic double perovskites. At a microscopic level the crystals are heavily twinned and the effect of twinning on the Raman spectra is analyzed in detail.
We report crystal growth and Raman spectroscopy characterization of pure and mixed bulk topological insulators. The series comprises of both binary and ternary tetradymite topological insulators. We analyzed in detail the Raman peaks of vibrational modes as out of plane Ag, and in plane Eg for both binary and ternary tetradymite topological insulators. Both out of plane Ag exhibit obvious atomic size dependent peak shifts and the effect is much lesser for the former than the latter. The situation is rather interesting for in plane Eg, which not only shows the shift but rather a broader hump li…
Graphene layers placed on SrTiO3 single-crystal substrates were investigated using temperature-dependent confocal Raman spectroscopy. This approach successfully resolved distinct Raman modes of graphene that are often untraceable in conventional measurements due to the strong Raman scattering background of SrTiO3. Information on defects and strain states was obtained for a few graphene/SrTiO3 samples that were synthesized by different techniques. This confocal Raman spectroscopic approach can shed light on the investigation of not only this graphene/SrTiO3 system but also various two-dimension…
Comment on "Raman spectroscopy study of NaxCoO2 and superconducting NaxCoO2 yH2O"
讨论了热分子钴酸盐表面降解对拉曼光谱的影响，并与Co_3O_4单晶的实验结果进行了比较。我们得出结论，在NaCl助熔剂生长的NaxCoO 2晶体上容易形成Co 3 O 4的表面层，这导致观察到约700 cm-1的强声子[Phys.Rev.B70，052502（2004）]。来自光学浮区炉的新切割晶体上的拉曼光谱没有显示出这种效应，并且在约600 cm-1处具有高频声子截止[Phys. Rev. Lett 96，167204（2006）]。讨论了热分子钴酸盐的结构维数、电子关联与高频声子截止的关系。
Recently, phonons with chirality (chiral phonons) have attracted significant attention. Chiral phonons exhibit angular and pseudo-angular momenta. In circularly polarized Raman spectroscopy, the peak split of the $Γ_3$ mode is detectable along the principal axis of the chiral crystal in the backscattering configuration. In addition, peak splitting occurs when the pseudo-angular momenta of the incident and scattered circularly polarized light are reversed. Until now, chiral phonons in binary crystals have been observed, whereas those in unary crystals have not been observed. Here, we observe ch…
Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are promising candidates for optoelectronic applications due to their efficient light emission properties, and strong dielectric confinement effects. Raman spectroscopy is a versatile, non-contact and often non-destructive technique, widely used to characterize crystalline materials. However, the inherently weak phonon scattering, strong background, and complex nature of the Raman signals from HOIPs present challenges in obtaining reliable signals. Further, the fragile nature of the 2D HOIP crystals results in rapid degradation …
We report on Raman and photoluminescence spectroscopic studies on oxygen vacancy induced structural disorder in Gd2Ti2O7-d single crystals grown by optical floating zone technique under argon atmosphere. The oxygen vacancies in Gd2Ti2O7-d wafers decrease with thermal annealing in an air atmosphere. The full width at half maximum of X-ray diffraction rocking curve decreases from 245 to 157 arc-second and the optical transmittance increases from 23 to 87 % (at 1000 nm) upon post growth thermal annealing. Raman spectroscopic studies reveal a monotonic increase in intensity of O-Gd-O (Eg) and Ti-O…
Tungsten, a plasma-facing material for future fusion reactors, may be exposed to air during abnormal operation or accidents. Only limited information is available on the evolution of related oxide phases. This work addresses the effect of substrate orientation on structural variations of tungsten oxides. Annealing experiments in an argon-oxygen atmosphere have been conducted at T = 400 °C under varying oxygen partial pressure and oxidation time. A combination of EBSD, Raman spectroscopy and confocal microscopy shows preferential oxidation initially on {111} base material planes. The oxide scal…
Recent Raman data on diamond and crystalline Si nanopowders are analyzed with the use of a microscopic theory of Raman scattering in ensembles of disordered nonpolar nanocrystals. The large width of the Raman peak in nanoparticles as compared to the corresponding peak in bulk materials and the peak inverse dependence on the particle size observed experimentally are explained within the framework of the theory. It is shown that this theory is capable to extract confidently from the Raman data four important microscopic characteristics of the nanopowder including the mean particle size, the vari…
A detailed high pressure study is carried out on 1T$^\prime$ MoTe$_{2}$ using X-ray diffraction(XRD) and Raman spectroscopy measurements upto about 30.5 GPa. High pressure XRD measurements show no structural transition. All the lattice parameters exhibit anomalous changes in the pressure region 8.4 to 12.7 GPa. Compressibility of the sample is found to be reduced by almost four times above 12.7 GPa with respect to that below 8.4 GPa. The anomalies in the Raman mode corresponding to the out of plane vibrations of Mo atoms sitting in the unit cell surface indicate a strong electron phonon coupli…
BaZrO3 is a perovskite that remains in the simple cubic phase at all temperatures, hence with no first-order Raman-active phonon mode allowed by symmetry. Yet, it exhibits an intense Raman spectrum with sharp and well-defined features. Here, we report the evolution of the Raman spectrum of BaZrO3 single crystals in a broad temperature range (4--1200~K) and discuss its origin with the support of detailed first-principle calculations of the lattice dynamics. Phonon calculations are performed not only for the cubic phase of BaZrO3, but also for the low-symmetry phases with octahedra tilts that ha…
We report the growth of thickness-controlled rotationally faulted multilayer graphene (rf-MLG) on Ni foils by low-pressure chemical vapor deposition and their characterization by micro-Raman spectroscopy. The surface morphology and thickness were investigated by scanning electron microscope, X-ray diffraction, and transmittance measurements. These results have revealed that the thickness of rf-MLG can be effectively controlled by the thickness of the Ni foil rather than the flow rate of CH$_4$, H$_2$, Ar. In the Raman spectroscopy measurements, we observed most Raman peaks of the graphitic mat…
On the Raman Spectrum of Plutonium dioxide: vibrational and crystal electric field modes
从理论和实验两方面研究了二氧化钚的拉曼光谱。特别注意的是，已专门用于识别的高能量模式在$2120$厘米$^{-1}$和$2625$厘米$^{-1}$，其中的归属到目前为止一直有争议。这两种模式的温度依赖性表明电子起源。晶体场（CF）计算表明，这两种模式分别归属于$^{5}I_{4}$流形中的$Γ_{1}$-$\rightarrow$-$Γ_{5}$和$Γ_{1}$-$\rightarrow $-$Γ_{3}$ CF跃迁.这两个模式，连同唯一的振动线预见的群论的Fm ${-3}$ m PuO $_{2}$对称性，T $_{2g}$ PuO伸缩模式在$478$ cm $^{-1}$，因此可以被用作拉曼指纹的fcc二氧化钚。
Probing the anisotropic behaviors of black phosphorus by transmission electron microscope, angular-dependent Raman spectra and electronic transports measurements
LiBC by polarized Raman spectroscopy: Evidence for lower crystal symmetry ?
本文介绍了偏振拉曼散射研究的几个微米大小的微晶LiBC与自然的面孔。对生长样品的实验显示出四种晶格模式，频率分别为1276 cm ^-1、830 cm ^-1、546 cm ^-1和170 cm ^-1。观察到的拉曼线的数量和它们的选择规则与假设的D6h对称性不相容。1276 cm ^-1和170 cm ^-1处的模式对应于预期的拉曼活动模式。与超导化合物MgB 2相比，B-C键伸缩模（在1276 cm ^-1处）具有相当小的阻尼。随后的热处理后，两个"禁戒"模（830 cm ^-1和546 cm ^-1）消失。
Charge density wave (CDW) is a unique phenomenon mostly realized in two-dimensional (2D) metallic layered transition metal dichalcogenides (TMDCs). Here, we report on Raman spectroscopy of single crystal 1T-VSe2 and observed signature of commensurate CDW (C-CDW) and incommensurate (I-CDW) transition, in the temperature range of 50-120 K. The room temperature Raman spectra showed a sharp A1g mode ~ 206 cm-1 along with two new weak and broad Raman modes associated to Eg mode ~ 257 cm-1 and two-phonon mode (2ph) ~ 332 cm-1. The onset of I-CDW and C-CDW is estimated from resistance measurements su…
[Fe(phen)2(NCS)2] is a prototype transition metal complex material, which undergoes a phase transition between low-spin (LS) and high-spin (HS) phases, induced by temperature, pressure or light. Vibrational modes play a key role for spin-state switching both in thermal and photo-induced cases, by contributing to vibrational entropy for thermal equilibrium transitions or driving the fast structural trapping of the photoinduced high spin state. Here we study the crystal phonon modes of [Fe(phen)2(NCS)2], by combining THz, IR, and Raman spectroscopies sensitive to modes in different frequency ran…
We calculate the eigenstates of a diatomic molecule in a range of model mean-field potentials, and evaluate the evolution of their associated Raman spectra with field strength. We demonstrate that dramatic changes in the appearance of the Raman spectrum for a diatomic molecule occur without any associated change in the symmetry of the surrounding potential. The limiting cases of the quantum eigenstates correspond, in the classical sense, to free rotation, and libration of well-oriented molecules. However, there are also many mixed modes which are neither rotons nor librons. The consequence for…
The lattice dynamics of preferentially aligned nanocrystals formed upon drying of aqueous Ba(NO$_3$)$_2$ solutions in a mesoporous silica glass traversed by tubular pores of approximately 12 nm are explored by Raman scattering. To interpret the experiments on the confined nanocrystals polarized Raman spectra of bulk single crystals and X-ray diffraction experiments are also performed. Since a cubic symmetry is inherent to Ba(NO$_3$)$_2$, a special Raman scattering geometry was utilized to separate the phonon modes of A$_g$ and E$_g$ species. Combining group-theory analysis and \textit{ab initi…
