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Ranjan K. Singh

Bio: Ranjan K. Singh is an academic researcher from Banaras Hindu University. The author has contributed to research in topics: Raman spectroscopy & Liquid crystal. The author has an hindex of 20, co-authored 134 publications receiving 1465 citations. Previous affiliations of Ranjan K. Singh include Schiller International University & University of Würzburg.


Papers
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Journal ArticleDOI
TL;DR: In this article, the stable-metastable phase transition in the Raman spectra of TB10A was attributed to a previously unseen stable-measureable transition transition.
Abstract: Raman spectra of TB10A were recorded in the regions, 925-1000 and 1140-1220cm-1 from room temperature down to 20 K, during cooling and heating cycles. The subtle changes in the spectral features of the bands at 975 and 1195cm-1 at 47 K were attributed to a hitherto unreported stable-metastable phase transition in TB10A. The dynamics of the new phase transition have been explained in terms of splitting of the non-planar mode at 975cm-1 owing to strong intermolecular interaction due to close molecular packing in the low temperature phase. The spectral anomaly of the 975cm-1 band, in terms of variation of relative intensity with respect to temperature, also shows the hysterisis linked with the process of stable-metastable-stable modification in TB10A.

3 citations

Journal ArticleDOI
TL;DR: The present work shows that SERS can be used to study intermolecular H-bonding of molecules at very low concentrations.
Abstract: In the present study, low-frequency SERS is reported for the first time to investigate intermolecular interactions. Low-frequency SERS in the THz region (>50 cm−1) and the mid-IR region is used to probe the H-bonding interaction in 2-mercaptobenzoic acid (2-MBA) molecules adsorbed on the surface of ZnO nanoparticles. The self-association due to H-bonding leads to dimer formation of 2-MBA through carboxylic acid groups. The characteristic Raman bands of the 2-MBA dimer, H-bonded O–H stretching and out-of-plane O–H bending modes, are observed. Subsequently, this dimer formation causes the evolution of two new low-frequency modes at 90 cm−1 (shear dimer in-plane bending) and 110 cm−1 (shear dimer stretching) of intermolecular H-bonding and a blue-shift of the torsional mode of (–COOH) + (–SH). In the THz region (50–200 cm−1) the vibrational modes are blue-shifted, while in the mid-IR region the symmetric out-of-plane O–H bending is red-shifted. The present work shows that SERS can be used to study intermolecular H-bonding of molecules at very low concentrations.

3 citations

Journal ArticleDOI
TL;DR: In this article, the anomalous intensity enhancement mechanism was explained by invoking an interference effect between a weak dipole-forbidden excited state and a nearby strong electronic level via vibrational modes.
Abstract: Pre-resonance Raman spectra of certain liquid crystalline compounds, TB4A, TB7A and TB10A, are reported. The anomaly observed in the pre-resonance Raman spectra in the three compounds was initially explained by the Albrecht-Hutley Model, but its failure leads us to explain the anomalous intensity enhancement mechanism by invoking an interference effect between a weak dipole-forbidden excited state and a nearby strong electronic level via vibrational modes. The presence of a 21Ag dipole-forbidden excited state in TB4A and TB10A is deduced after an elaborate discussion of their centro-symmetric structure. The structural difference of TB7A in comparison with TB4A and TB10A is also discussed by taking their X-ray data into consideration.

3 citations


Cited by
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Journal ArticleDOI
TL;DR: The limit of sensitivity in SERS is introduced in the context of single-molecule spectroscopy and the calculation of the ‘real’ enhancement factor, which illustrates the broad applications of this powerful technique.
Abstract: Surface-enhanced Raman spectroscopy (SERS) combines molecular fingerprint specificity with potential single-molecule sensitivity. Therefore, the SERS technique is an attractive tool for sensing molecules in trace amounts within the field of chemical and biochemical analytics. Since SERS is an ongoing topic, which can be illustrated by the increased annual number of publications within the last few years, this review reflects the progress and trends in SERS research in approximately the last three years. The main reason why the SERS technique has not been established as a routine analytic technique, despite its high specificity and sensitivity, is due to the low reproducibility of the SERS signal. Thus, this review is dominated by the discussion of the various concepts for generating powerful, reproducible, SERS-active surfaces. Furthermore, the limit of sensitivity in SERS is introduced in the context of single-molecule spectroscopy and the calculation of the 'real' enhancement factor. In order to shed more light onto the underlying molecular processes of SERS, the theoretical description of SERS spectra is also a growing research field and will be summarized here. In addition, the recording of SERS spectra is affected by a number of parameters, such as laser power, integration time, and analyte concentration. To benefit from synergies, SERS is combined with other methods, such as scanning probe microscopy and microfluidics, which illustrates the broad applications of this powerful technique.

706 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented an Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development (NFthis paper ) supported by the OMV Group, the EPSRC (DTA studentships for D.W. and T.E.O.), the World Premier Institute Research Center Initiative (WPI), MEXT, Japan (to K.L., GAN 701192 - VSHER), the German Research Foundation (to M.F.
Abstract: This work was supported by the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development), the OMV Group (to E.R.), the EPSRC (DTA studentships for D.W.W. and T.E.R), the Isaac Newton Trust, the German Research Foundation (to M.F.K.), the World Premier Institute Research Center Initiative (WPI), MEXT, Japan (to K.L.O.) and a Marie Curie Research fellowship (to K.H.L., GAN 701192 - VSHER).

383 citations

Reference BookDOI
08 Oct 2018
TL;DR: Xerographic photoreceptors charge acceptance and dark discharge photoinduced discharge photogeneration theories photogengeneration in organic solids charge transport theories charge transport in polymers and related materials experimental techniques photoreceptor preparation photoresceptors fatigue summary and future requirements.
Abstract: Xerographic photoreceptors charge acceptance and dark discharge photoinduced discharge photogeneration theories photogeneration in organic solids charge transport theories charge transport in polymers and related materials experimental techniques photoreceptor preparation photoreceptors fatigue summary and future requirements.

378 citations

Journal ArticleDOI
26 Nov 1994-BMJ
TL;DR: In the future of all-conquering genetic technology, who should be screened for what and by whom?
Abstract: Ed Lori B Andrews, Jane E Fullarton, Neil A Holtzman, Arno G Motulsky National Academy Press, £28.95, pp 338 ISBN 0-309-04798-6 Genetic screening tends to serve as a flypaper on which our hovering fears of a Brave New World alight and stick. In the future of all-conquering genetic technology, who should be screened for what and by whom? Here is a dense report, compiled by a committee of the great and the good, with hundreds of recommendations for action and inaction. How much …

332 citations

Journal ArticleDOI
01 May 2019-Talanta
TL;DR: CQDs, their structure, and PL characteristics are introduced and recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

286 citations