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Photoluminescence nonuniformity from self-seeding nuclei in CVD-grown monolayer MoSe.
Nanoscale
January 2018
State Key Laboratory of Luminescent Materials and Devices, Guangdong engineering Technology Research and Development Center of special Optical Fiber Materials and Devices, South China University of Technology, Wushan Road 381, Guangzhou 510641, PR China.
We present optical spectroscopy (photoluminescence and Raman spectrum) studies of monolayer transition metal dichalcogenide MoSe, with spatial location, temperature and excitation power dependence. The investigated spectra show location-dependent behavior with an increase in photoluminescence and Raman intensity and a blue-shift in photoluminescence peak position in the inner region. The observed behaviors of a large shift in the photoluminescence peak position at the edge and biexciton emissions in the inner region confirm that the monolayer MoSe crystals grow from nucleation centers during the CVD process.
View Article and Find Full Text PDFTwo-state model for nematic liquid crystals made of bent-core molecules.
Phys Rev E
August 2017
Raman Research Institute, C. V. Raman Avenue, Bengaluru 560080, India.
Nematic (N) liquid crystals made of bent-core molecules exhibit unusual physical properties such as an intermediate phase between the N and isotropic (I) phases, a very weak NI transition as inferred from magnetic birefringence measurements in a low field, which is apparently incompatible with a large shift in the NI transition temperature (T_{ni}) measured under a high field. Using our conformational studies on the aromatic cores, we propose that only conformers which are more straightened than those in the ground state (GS) form clusters with a few layers, which persist even in the isotropic phase, as inferred from x-ray and rheological experiments. We present a Landau-de Gennes theory of the medium, including an orientational coupling between the clusters and the GS molecules, which accounts for all the unusual properties.
View Article and Find Full Text PDFpKa determination of D-ribose by Raman spectroscopy.
J Phys Chem B
January 2014
Structural Biology and Bioinformatics Division, CSIR-Indian Institute of Chemical Biology, Council of Scientific and Industrial Research , 4, Raja S.C. Mullick Road, Kolkata 700032, India.
Determination of the pKa of OH groups present in D-ribose is crucial in order to elucidate the origin and mechanism of many catalytic processes that involve the ribose unit. However, there is hardly any reports about the experimental pKa of the OH group due to the lack of an appropriate method. In this study we investigated the protonation state of OH groups in D-ribose by introducing C-D labeling and measuring the changes in the isolated C-D frequency in several isotopologues of the compound with pH.
View Article and Find Full Text PDFOptical and photocatalytic properties of heavily F(-)-doped SnO2 nanocrystals by a novel single-source precursor approach.
Inorg Chem
June 2011
Materials Chemistry Group, Department of Chemistry, University of Delhi, Delhi 110 007, India.
Heavily F-doped SnO(2) nanocrystals were successfully prepared by a novel synthetic approach involving low-temperature oxidation of a Sn(2+)-containing fluoride complex KSnF(3) as the single-source precursor with H(2)O(2). The F-doped SnO(2) powder was characterized by powder X-ray diffraction, TG-MS, BET surface area, diffuse reflectance spectroscopy, XPS, PL, FTIR spectroscopy, Raman spectroscopy, EPR spectroscopy, SEM, and TEM. Broadening of the diffracted peaks, signifying the low crystallite size of the products, was quite evident in the powder X-ray diffraction pattern of SnO(2) obtained from KSnF(3).
View Article and Find Full Text PDFThe nature of in-plane skeleton Raman modes of P3HT and their correlation to the degree of molecular order in P3HT:PCBM blend thin films.
J Am Chem Soc
June 2011
Department of Physics and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, United Kingdom.
The nature of main in-plane skeleton Raman modes (C=C and C-C stretch) of poly(3-hexylthiophene) (P3HT) in pristine and its blend thin films with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) is studied by resonant and nonresonant Raman spectroscopy and Raman simulations. Under resonant conditions, the ordered phase of P3HT with respect to its disordered phase is identified by (a) a large shift in the C=C mode peak position to lower wavenumber (~21 cm(-1) shift), (b) a narrower fwhm of the C=C mode (~9 cm(-1) narrower), (c) a larger intensity of the C-C mode relative to the C=C mode (~56% larger), and (d) a very small Raman dispersion (~5 cm(-1)) of the C=C mode. The behavior of the C=C and C-C modes of the ordered and disordered phases of P3HT can be explained in terms of different molecular conformations.
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