163 research outputs found
Brillouin scattering studies on charge-ordered manganites
Brillouin scattering studies were carried out for the first time on charge-ordered manganites, namely, Nd0.5Ca0.5MnO3 and Pr0.63Ca0.37MnO3. We observe surface and bulk magnetic excitations (magnons) in the Brillouin spectra with the characteristics of ferromagnetic magnons. The frequency and intensity of these magnons in the temperature range 300 to 25 K, covering both charge-ordering and antiferromagnetic transition, follow exactly the temperature dependence of the DC magnetic susceptibility. The study strongly suggests the presence of ferromagnetic inhomogeneities in the charge-ordered as well as antiferromagnetic phases
Conformational Analysis of Molecules: Combined Vibrational Spectroscopy and Density Functional Theory Study
Vibrational spectroscopy can be broadly classified into Raman and infrared (IR). These two techniques are complementary to each other as the mechanisms behind these are different. Vibrational spectroscopy provides detail information about the structure of molecules. The advantage of this technique over X‐ray diffraction is that it can be used to probe molecules in solid, liquid or gas phase. This is especially helpful for studying biomolecules as those molecules can be probed in their physiological environment. Over the last few decades, quantum mechanical calculation has become important tool to assign bands from vibrational spectra. Combination of these two techniques has been used widely in the field of chemistry and biochemistry. In this chapter, we review some of the works that combine both of these techniques. A brief theoretical background is given for understanding the principle of these two techniques
Pressure induced topological and topological crystalline insulators
[EN] Research on topological and topological crystalline insulators (TCIs) is one of the most intense and exciting topics due to its fascinating fundamental science and potential technological applications. Pressure (strain) is one potential pathway to induce the non-trivial topological phases in some topologically trivial (normal) insulating or semiconducting materials. In the last ten years, there have been substantial theoretical and experimental efforts from condensed-matter scientists to characterize and understand pressure-induced topological quantum phase transitions (TQPTs). In particular, a promising enhancement of the thermoelectric performance through pressure-induced TQPT has been recently realized; thus evidencing the importance of this subject in society. Since the pressure effect can be mimicked by chemical doping or substitution in many cases, these results have opened a new route to develop more efficient materials for harvesting green energy at ambient conditions. Therefore, a detailed understanding of the mechanism of pressure-induced TQPTs in various classes of materials with spin-orbit interaction is crucial to improve their properties for technological implementations. Hence, this review focuses on the emerging area of pressure-induced TQPTs to provide a comprehensive understanding of this subject from both theoretical and experimental points of view. In particular, it covers the Raman signatures of detecting the topological transitions (under pressure), some of the important pressure-induced topological and TCIs of the various classes of spin-orbit coupling materials, and provide future research directions in this interesting field.V R and C N would like to dedicate this review to Professor C N R Rao who has been a mentor and inspiration for us. V R and C N acknowledge the Department of Science and Technology (DST) and JNCASR, India, for financial support. FJM acknowledges project MALTA Consolider Team network (RED2018-102612-T), financed by MINECO/AEI/10.13039/501100003329, I+D+i project PID2019-106383GB-42 financed by MCIN/AEI/10.13039/501100011033, as well as projects PROMETEO/2018/123 (EFIMAT) and CIPROM/2021/075 (GREENMAT) financed by Generalitat Valenciana. We sincerely thank Professor Umesh V Waghmare, Theoretical Sciences Unit, JNCASR, Professor Kanishka Biswas, New Chemistry Unit, JNCASR, Professor Sebastian C Peter, New Chemistry Unit, JNCASR, and Dr Boby Joseph, Elettra Sincrotrone Trieste, Italy for the active collaboration and fruitful discussion on these topics of interest.Rajaji, V.; Manjón, F.; Narayana, C. (2022). Pressure induced topological and topological crystalline insulators. Journal of Physics Condensed Matter. 34(42):1-16. https://doi.org/10.1088/1361-648X/ac8906116344
Surface Enhanced Raman Spectroscopy of Proteins: Implications in Drug Designing
In this review article we present a general overview of the recent progress in the newly developing area of the study of protein‐ligand interaction by surface enhanced Raman spectroscopy (SERS). Since its first observation in 1977, SERS have been fast developing into an analytical tool for trace detection of molecular entities, particularly in the area of bio‐molecule sensing and characterization. Also, with the development of the ability to design a variety of plasmonic structures and to be able to control and tune their plasmonic properties, we have been able to use them as SERS substrates for probing complex materials. Here we describe yet another application of SERS, mainly protein‐ligand interaction and its future into drug designing. We start with a general description of the SERS phenomenon. Subsequently we discuss the key spectral features of amino acids, peptides and proteins, and their structural aspects that can be elucidated from the SERS spectra. In the final sections we discuss the application of SERS to the study protein‐ligand interaction and its potential role in the area of drug designing
Elastic and structural instability of cubic Sn3N4 and C3N4 under pressure
We use in-situ high pressure angle dispersive x-ray diffraction measurements
to determine the equation of state of cubic tin nitride Sn3N4 under pressure up
to about 26 GPa. While we find no evidence for any structural phase transition,
our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier
theoretical estimates and that of other group IV-nitrides. We corroborate and
understand these results with complementary first-principles analysis of
structural, elastic and vibrational properties of group IV-nitrides, and
predict a structural transition of Sn3N4 at a higher pressure of 88 GPa
compared to earlier predictions of 40 GPa. Our comparative analysis of cubic
nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while
it is structurally unstable and should not exist at ambient conditions.Comment: 5 pages, 4 figure
Brillouin Scattering Studies of La_{0.77}Ca_{0.23}MnO_3 Across Metal-Insulator Transition
Temperature-dependent Brillouin scattering studies have been carried out on
La_{0.77}Ca_{0.23}MnO_3 across the paramagnetic insulator - ferromagnetic metal
(I-M) transition. The spectra show a surface Rayleigh wave (SRW) and a high
velocity pseudo surface acoustic wave (HVPSAW) besides bulk acoustic waves
(BAW). The Brillouin shifts associated with SRW and HVPSAW show blue-shifts,
where as the frequencies of the BAW decrease below the I-M transition
temperature (T_C) of 230 K. These results can be understood based on the
temperature dependence of the elastic constants. We also observe a central peak
whose width is maximum at T_C.Comment: 7 pages, 8 figure
Optical nonlinearity and charge transfer analysis of 4-[(E)-2-(2,4,6-Trinitrophenyl) ethylidene] benzonitrile adsorbed on silver nanoparticles : Computational and experimental investigations
The search for a potential nonlinear optical (NLO) material has led to the investigation of an organic compound 4-[(E)-2-(2,4,6-Trinitrophenyl)ethylidene]benzonitrile (TEB), which has a possibility of enhancing the NLO properties by the charge transfer mechanism if metal atoms are adsorbed on it. The experimental characterization of TEB is done using Fourier Transform Infrared (FT-IR), Fr-Raman, Ultraviolet-visible (UV-Visible), Photoluminescence (PL), Thermogravimetric/Differential Thermal Analysis (TG/DTA) and Z-scan techniques. The third order NLO properties evaluated using Z-scan technique proves that the material can be used as a good optical limiter. TEB is attached with silver atoms and the theoretical studies including geometry optimization, NBO analysis and hyperpolarizability calculations are carried out. The TEB molecule with silver atoms adsorbed is found to have increased hyperpolarizability values. The charge transfer from the metal atom to the nitrile group of the molecule is evident from the Surface Enhanced Raman Scattering (SERS) spectra using the silver nanoparticles. (C) 2018 Elsevier Ltd. All rights reserved.Peer reviewe
A low-cost Raman spectrometer design used to study Raman scattering from a single-walled carbon nanotube
The paper discusses the design of a low cost Raman spectrometer. Singlewalled Nanotubes (SWNT) have been studied to demonstrate the reach of such a system. We observe both the Radial-breathing Mode (RBM) and the tangential mode from the SWNT. The tube diameters of the SWNT used in these experiments have been determined using RBM to be predominantly 1.4 and 1.6 nm. These are consistent with the TEM images taken of the same sample. The new method of producing SWNT using Ni-Y catalyst in electric-arc discharge method produces nanotubes with very small dispersion in diameter and high yields. The chirality of the SWNT can be deduced from their radial breathing modes and it suggests that they are metallic in nature
Griffiths phase-like behaviour and spin-phonon coupling in double perovskite TbNiMnO
The Griffiths phase-like features and the spin-phonon coupling effects
observed in TbNiMnO are reported. The double perovskite compound
crystallizes in monoclinic space group and exhibits a magnetic phase
transition at 111 K as an abrupt change in magnetization. A negative
deviation from ideal Curie-Weiss law exhibited by 1/ curves and
less-than-unity susceptibility exponents from the power-law analysis of inverse
susceptibility are reminiscent of Griffiths phase-like features. Arrott plots
derived from magnetization isotherms support the inhomogeneous nature of
magnetism in this material. The observed effects originate from
antiferromagnetic interactions which arise from inherent disorder in the
system. Raman scattering experiments display no magnetic-order-induced phonon
renormalization below in TbNiMnO which is different from the
results observed in other double perovskites and is correlated to the smaller
size of the rare earth. The temperature evolution of full-width-at-half-maximum
for the {\it stretching} mode at 645 cm presents an anomaly which
coincides with the magnetic transition temperature and signals a close
connection between magnetism and lattice in this material.Comment: 17 pages, 8 figures; accepted in J. Appl. Phy
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