Browsing by Author "Animesh K. Ojha"

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A new approach to explain concentration-dependent changes of isotropic Raman line width in the associated binary mixtures
(2006) Animesh K. Ojha; Sunil K. Srivastava; Ranjan K. Singh; B.P. Asthana
We report on a new empirical relationship to explain the concentration-dependent isotropic Raman line width changes of a vibrational mode in uniform binary mixtures. The factors contributing to the intrinsic line width and several other broadening mechanisms are, in general, concentration-dependent. Concentration fluctuation in a microscopic volume and microviscosity are the two factors that are known to cause a concentration-dependent line width variation. These two factors combined in a specific manner successfully explain the variation of the line width with concentration strongly associated with binary systems. A readily usable empirical relationship for line width is suggested. It has been demonstrated that it can successfully explain the line width variation with concentration in a given class of hydrogen-bonded systems taking some representative binary mixtures. © 2006 American Chemical Society.
Amino acids assisted growth of methylammonium lead iodide cuboidal crystals for solar cell applications
(Elsevier B.V., 2023) Saurav K. Ojha; Divya Singh; Aditya Kumar; Arvind Singh; Ranjan K Singh; Animesh K. Ojha
The cuboidal crystals of methylammonium lead iodide (MAPbI3) with controlled shapes and sizes are successfully synthesized by monitoring their growth in the precursor solution using different α-amino acids. The directional growth of MAPbI3 crystals is carried out by promoting crystallization at molecular level in the presence of an optimum concentration of α-amino acids. Alanine (ALA), having relatively larger value of dipole moment, induces directional growth to the MAPbI3 crystals at low concentration. The optical and electrical properties of the thin films formed by the grown MAPbI3 crystals are also enhanced. The dipole moment of the amino acids plays an important role in directional growth of MAPbI3 crystals. The least area of I-V hysteresis curve in the thin film prepared with 1.5 wt% of isoleucine (ISO) indicates minimum loss of energy which makes it suitable for application in perovskite solar cells (PSCs). © 2023 Elsevier B.V.
Complex formation of HCONH2 in CH3OH environment and investigation of linewidth changes of ν(C{double bond, long}O) stretching and NH2 bending modes
(2007) Animesh K. Ojha; Sunil K. Srivastava; Ranjan K. Singh; W. Kiefer; B.P. Asthana
The isotropic part of the Raman bands corresponding to NH2 bending and ν(C{double bond, long}O) stretching modes of formamide (HCONH2) at ∼1593 and 1668 cm-1, respectively, in neat HCONH2 as well as in binary mixtures with methanol (CH3OH) were reinvestigated. Variations of their linewidths exclusively with mole fractions of HCONH2, in the range C = 0.1-0.9 were studied. The linewidth variation of the NH2 bending mode shows a departure from the trend expected on the basis of concentration fluctuation model and this has been explained using a recently suggested empirical model by invoking the concept of microviscosities of the solute, HCONH2 and the solvent, CH3OH. The other peak at ∼1668 cm-1 shows a peculiar variation of the linewidth with concentration having two minima at C = 0.8 and 0.4, which have been explained in terms of formation of hydrogen bonded complexes, NH2HCO⋯HOCH3, and NH2HCO⋯(HOCH3)2 and the two phenomena, namely motional narrowing and diffusion dynamics being simultaneously operative. The equilibrium constants have been evaluated from the spectral data and their variation with total molar concentration has been presented. © 2006 Elsevier B.V. All rights reserved.
Concentration dependent wavenumber shifts and linewidth changes of some prominent vibrational modes of C4H8O investigated in a binary system (C4H8O+H2O) by polarized Raman study and ab initio calculations
(2005) Animesh K. Ojha; Sunil K. Srivastava; N. Peica; S. Schlücker; W. Kiefer; B.P. Asthana
Raman spectra of neat tetrahydrofuran (hereinafter, frequently referred to as THF; C4H8O) and its binary mixtures in aqueous (H2O) media were investigated using a rather sensitive scanning multichannel detection scheme. The spectra were recorded in the region, 800-1000 cm-1 for the neat liquid, C4H8O, and mixtures with varying mole fractions of C4H8O from 0.1 to 0.9. The spectra were, however, analyzed in two different regions, 800-1000 and 975-1100 cm-1. The spectra in the former region show an asymmetric peak also in neat liquid and were deconvoluted to two Raman line profiles having peaks at ∼910 and ∼914 cm-1, corresponding to ν(C-O) and ν(C-C) stretchings, respectively. At other concentrations, the spectra were analyzed for three Raman line profiles and the concentration dependence of wavenumber position and the linewidth (FWHM) for an additional peak at ∼896 cm-1 (at mole fraction of C4H8O, C=0.9) exhibited a peculiar trend, which has been explained by using the indirect dephasing model. The spectra in the latter region show two Raman peaks, an intense one at ∼1030 cm-1 and a relatively less intense at ∼1071 cm-1 in neat liquid. A striking feature is that their separation goes on decreasing with dilution. The optimized geometries and vibrational wavenumbers for various normal modes for neat THF as well as hydrogen bonded complexes were calculated using ab initio theory at the MP2 level and the results have been used to understand the changes in the spectral features with the varying concentration of the two components in the binary mixture (C4H8O+H2O). © 2004 Elsevier B.V. All rights reserved.
Concentration-dependent Raman study of noncoincidence effect in the NH 2 bending and C=O stretching modes of HCONH2 in the binary mixture (HCONH2+CH3OH)
(John Wiley and Sons Ltd, 2007) Animesh K. Ojha; Sunil K. Srivastava; B.P. Asthana; Ranjan K. Singh
The isotropic and anisotropic parts of the Raman spectra of NH2 bending and ν(C=O) stretching modes of HCONH2 in a hydrogen-bonding solvent, methanol, at different concentrations have been analyzed carefully in order to study the noncoincidence effect (NCE). In neat HCONH2, the experimentally measured values of noncoincidence Δνnc are ∼11 and ∼18 cm-1 for the NH 2 bending and ν(C=O) stretching modes, which reduce to 0.45 and 1.14 cm-1, respectively at the concentration of HCONH2 in mole fraction, χm = 0.1. The experimental results have been explained on the basis of two models, namely, the microscopic prediction of Logan and the macroscopic model of Mirone and Fini. The relative success of the two models in explaining the experimental data for both the modes have been discussed. It has been observed that in case of the ν(C=O) stretching vibrational mode the Logan model can reproduce the experimental data rather precisely, whereas in the case of the NH2 bending mode, Mirone and Fini model yields more accurate results. Copyright © 2006 John Wiley & Sons, Ltd.
Concentration-dependent surface-enhanced Raman scattering and molecular dynamic study of dimethyl formamide
(John Wiley and Sons Ltd, 2007) Shivangi Mishra; Animesh K. Ojha; Deepa Singh; Rajeev R. Prasad; Sunil K. Srivastava; Ranjan K. Singh
A concentration-dependent Raman study of dimethyl formamide (DMF) in Ag nanocolloidal solution was carried out in order to observe the effect of concentration on the surface enhancement mechanism. The Raman spectra in the region 900-2200 cm-1 comprising four prominent Raman modes were measured experimentally and analyzed at five different concentrations: 1, 3, 5, 7, 10 mM, and in neat DMF. In order to find the possible configurations of DMF + Ag complexes, density functional theory (DFT) calculations were carried out taking one, three and five Ag atom clusters. The Raman spectra of unconjugated DMF, DMF + Ag and DMF + 3Ag complexes were calculated theoretically to assign the vibrational modes under consideration more accurately and to understand the wavenumber shift and change in intensity observed in experimental measurements. Water present in the colloidal solution may also conjugate with DMF and its complexes with Ag. In order to see the influence of water on the wavenumber shift and intensity changes, we have also obtained the optimized structures and Raman modes of DMF + water and DMF + water + Ag complexes. Good agreement between the experimental and theoretical wavenumber shifts has been obtained by using B3LYP functional theory and CEP-31G basis set for the DMF + Ag complex. The experimental results suggest that the SERS enhancement is concentration-dependent. The concentration-dependent linewidth shows the existence of the phenomena of motional narrowing and diffusion dynamics in the colloidal solution. Copyright © 2007 John Wiley & Sons, Ltd.
Controlled synthesis and magnetic properties of monodispersed ceria nanoparticles
(American Institute of Physics Inc., 2015) Sumeet Kumar; Manish Srivastava; Jay Singh; Samar Layek; Madhu Yashpal; Arnulf Materny; Animesh K. Ojha
In the present study, monodispersed CeO2 nanoparticles (NPs) of size 8.5 ± 1.0, 11.4 ± 1.0 and 15.4 ± 1.0 nm were synthesized using the sol-gel method. Size-dependent structural, optical and magnetic properties of as-prepared samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscopy (HR-TEM), ultra-violet visible (UV-VIS) spectroscopy, Raman spectroscopy and vibrating sample magnetometer (VSM) measurements. The value of optical band gap is calculated for each particle size. The decrease in the value of optical band gap with increase of particle size may be attributed to the quantum confinement, which causes to produce localized states created by the oxygen vacancies due to the conversion of Ce4+ into Ce3+ at higher calcination temperature. The Raman spectra showed a peak at ∼461 cm-1 for the particle size 8.5 nm, which is attributed to the 1LO phonon mode. The shift in the Raman peak could be due to lattice strain developed due to variation in particle size. Weak ferromagnetism at room temperature is observed for each particle size. The values of saturation magnetization (Ms), coercivity (Hc) and retentivity (Mr) are increased with increase of particle size. The increase of Ms and Mr for larger particle size may be explained by increase of density of oxygen vacancies at higher calcination temperature. The latter causes high concentrations of Ce3+ ions activate more coupling between the individual magnetic moments of the Ce ions, leading to an increase of Ms value with the particle size. Moreover, the oxygen vacancies may also produce magnetic moment by polarizing spins of f electrons of cerium (Ce) ions located around oxygen vacancies, which causes ferromagnetism in pure CeO2 samples. © 2015 Author(s).
DFT study of hydrogen bond bridging mode of pyridine and diazenes in water environment
(2007) Deepa Singh; Sunil K. Srivastava; Animesh K. Ojha; B.P. Asthana; Ranjan K. Singh
Optimized geometries and vibrational spectra of pyridine (Py), pyridazine (Py1,2), pyrimidine (Py1,3), pyrazine (Py1,4) and their complexes with water molecules have been calculated with a view to look into the strength of hydrogen bonds, binding energies and vibrational wavenumbers of hydrogen bond bridging modes. The counterpoise corrected binding energies for different complexes are also calculated. The results of DFT calculations have been used to draw the potential energy curve and to calculate the amplitude of stretching vibration of hydrogen bond bridging modes. The three types of hydrogen bonds: N...H{single bond}O, O...H{single bond}O, and O...H{single bond}C have been studied. The relative hydrogen bond strengths and vibrational wavenumbers of these bridging modes have been explained in terms of redistribution of electronic charges on individual atoms. © 2007 Elsevier B.V. All rights reserved.
Dynamics and mechanism of the Crystal II → smecticG phase transition in TB7A by a temperature-dependent micro-Raman study and DFT calculations
(John Wiley and Sons Ltd, 2009) K. Vikram; Sunil K. Srivastava; Animesh K. Ojha; S. Schlücker; W. Kiefer; Ranjan K. Singh
The solid to smecticG (SmG) phase transition in a Schiff base liquid crystalline compound, terepthal-bis-heptylaniline (TB7A), is monitored in situ by temperature-dependent Raman microspectroscopy, using the band of a C-H in-plane bending mode as a marker. Contrary to the earlier report of a sudden wavenumber shift, the in situ measurement shows very clearly that a new Raman band at ~1160 cm-1 appears at the Crystal II → SmG transition. The dynamics of this phase transition is discussed in terms of a triple well potential below 210 K and a double well potential above 210 K. The phase transition essentially takes place as a result of intra-molecular rotation about the long molecular axis. The optimization energy at various fixed dihedral angles, (-C-C-C = N - ) are calculated using density functional theory (DFT) at the B3LYP/6-31G* level of theory. The relative energy at each dihedral angle is calculated relative to optimization energy obtained without any constraints and plotted as a function of dihedral angle (φ) between the adjacent phenyl ring planes, which also shows a double well potential at room temperature. © 2009 John Wiley & Sons, Ltd.
Hydrogen bonding in different pyrimidine-methanol clusters probed by polarized Raman spectroscopy and DFT calculations
(John Wiley and Sons Ltd, 2011) Dheeraj K. Singh; Shivangi Mishra; Animesh K. Ojha; Sunil K. Srivastava; S. Schlücker; B.P. Asthana; J. Popp; Ranjan K. Singh
We report on the hydrogen bonding between pyrimidine (Pd) and methanol (M) as H-donor in this study. Hydrogen bonds between pyrimidine and methanol molecules as well as those between different methanol molecules significantly influence the spectral features at high dilution. The ring-breathing mode ν1 of the reference system Pd was chosen as a marker band to probe the degree of hydrogen bonding. Polarized Raman spectra in the region 970-1020 cm-1 for binary mixtures of (pyrimidine + methanol) at 28 different mole fractions were recorded. A Raman line shape analysis of the isotropic Raman line profiles at all concentrations revealed three distinct spectral components at mole fractions of Pd below 0.75. The three components are attributed to three distinct groups of species: 'free Pd' (pd), 'Pd with low methanol content' (pd1) and 'Pd with high-methanol content' (pd2). The two latter species differ considerably in the pattern and the strengths of the hydrogen bonds. The results of density functional theory calculations on structures and vibrational spectra of neat Pd and eight Pd/M complexes with varying methanol content support our interpretations of the experimental results. A nice spectra-structure correlation for the different cluster subgroups was obtained, similar to earlier results obtained for Pd and water. Apart from N⋯H and O⋯H hydrogen bonds between pyrimidine and methanol, O⋯H hydrogen bonds formed among the methanol molecules in the cluster at high methanol content also play a crucial role in the interpretation of the experimental results. Vibrational spectroscopic analysis on hydrogen bonding between pyrimidine (Pd) with methanol (M) comprises both experimental Raman spectra and density functional theory (DFT) calculations on structures and vibrational spectra of various Pd/M complexes with varying solvent content. Polarized Raman spectra in the region 970-1020 cm-1 for binary mixtures of (Pd + M) at 28 different mole fractions were recorded. The results of DFT calculations on structures and vibrational spectra of neat Pd and eight Pd/M complexes were used for interpreting the experimental results. Finally, a spectra-structure correlation for different cluster subgroups was obtained. Copyright © 2010 John Wiley & Sons, Ltd.
Improper hydrogen bonding and motional narrowing in binary mixtures of 2- and 3-bromopyridine in methanol probed by polarized Raman study and DFT calculations
(John Wiley and Sons Ltd, 2007) Animesh K. Ojha; Sunil K. Srivastava; S. Schlücker; W. Kiefer; B.P. Asthana; Ranjan K. Singh
A concentration-dependent Raman study of the ν(C-Br) stretching and trigonal bending modes of 2- and 3-Br-pyridine (2Br-p and 3Br-p) in CH 3OH was performed at different mole fractions of the reference molecule, 2Br-p/3Br-p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen-bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm-1 in the case of 2Br-p and at ∼618 cm-1 in the case of 3Br-p compared to neat bromopyridine derivatives were attributed to specific hydrogen-bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br-p and 3Br-p and a series of hydrogen-bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(C-Br) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion-causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd.
Influence of self-association and inter-molecular hydrogen bonding on the ν(C≡N) stretching mode of CH3C≡N and C 2H5C≡N in binary mixtures with CH3OH - A comparative study via concentration-dependent polarized Raman study and ab initio calculation
(John Wiley and Sons Ltd, 2006) Sunil K. Srivastava; Animesh K. Ojha; P. Raghuvansh; W. Kiefer; B.P. Asthana
A Raman study of neat CH3C≡N and C2H 5C≡N and their binary mixtures (CH3C≡N + CH3OH) and (C2H5C≡N + CH3OH) has been made using a scanning multichannel detection technique, which is also more precise, especially when the observed Raman line profile has multiple components. The spectra in the ν(C≡N) stretching region (2220-2280 cm-1) for both the reference systems were recorded with varying mole fractions of the reference molecule, CH3C≡N/C2H 5C≡N, from 0.9 to 0.1. Ab initio calculations on the optimized structure and wavenumber position of the ν(C≡N) stretching mode of neat CH3C≡N and C2H5C≡N and their self-associated and hydrogen-bonded complex reveal that the wavenumber position of the ν(C≡N) stretching mode is shifted towards higher Raman wavenumbers because of both self-association and the hydrogen-bonded complex. This shift has been explained in terms of the repulsive interaction between the solute and solvent molecules. The dephasing of ν(C≡N) stretching mode with concentration shows that the viscosity dependent contribution is much more prominent than that due to concentration fluctuation. Copyright © 2006 John Wiley & Sons, Ltd.
Investigation of hydrogen bonding and self-association in neat HCONH 2 and the binary mixture (HCONH2+CH3OH) by concentration dependent Raman study and ab initio calculations
(2004) Animesh K. Ojha; Sunil K. Srivastava; J. Koster; M.K. Shukla; J. Leszczynski; B.P. Asthana; W. Kiefer
Raman spectra of neat formamide (HCONH2) and its binary mixture (HCONH2+CH3OH) with hydrogen donor solvent, methanol (CH3OH) were investigated using a sensitive scanning multichannel detection scheme, which is simultaneously more precise also, especially when the observed Raman line profile has multiple component bands. The spectra in the two regions, namely 1200-1500 and 1500-1800 cm-1 were recorded with varying mole fractions of the reference molecule, HCONH2, from 0.1 to 0.9. The spectra in the region 1200-1500 cm-1 show a broad band at ∼1312 cm-1, which shows a peculiar concentration dependence, and a relatively sharp peak at ∼1392 cm-1, whose peak position is not influenced by concentration. The spectra in the region 1500-1800 cm-1 also show two peaks, one at ∼1593 cm-1 and the other one at ∼1668 cm-1 which are assigned to NH 2 bending and ν(C=O) stretching vibrations, respectively. Both these Raman bands show an appreciable upshift of ∼15-20 cm-1 and the one at ∼1668 cm-1 has also a distinct asymmetry towards higher wavenumber. The optimized geometries and vibrational wavenumbers of various normal modes for neat formamide as well as its hydrogen-bonded complexes were also calculated using ab initio theory at the MP2 level. The results have been used to understand and explain the concentration dependent changes in the spectral features in terms of hydrogen bonding and self-association. © 2003 Elsevier B.V. All rights reserved.
Investigation of ν(N-H) and ν(C-N) stretching modes of propylamine (C3H7NH2) in a binary system C 3H7NH2 + CH3OH via concentration dependent Raman study and ab initio calculations
(2005) Sunil K. Srivastava; Animesh K. Ojha; W. Kiefer; B.P. Asthana
Raman spectra of propylamine (C3H7NH2) and its binary mixtures, C3H7NH2 + CH 3OH with varying mole fractions of the reference system, C 3H7NH2, C were recorded in two widely apart wavenumber regions, 3100-3600 cm-1 and 1225-1325 cm-1. In the former region, the two Raman bands at ∼3305 and ∼3326 cm -1, obtained after the line shape analysis, which were assigned to symmetric ν(NH) and anti-symmetric ν(NH) stretching modes, respectively, show a downshift upon dilution. However, whereas the ν(NH) anti-symmetric mode shows a shift of 18.6 cm-1, the ν(NH) symmetric mode shows a much smaller shift (5.7 cm-1) between neat liquid and high dilution, C = 0.1. This aspect has been explained using the optimized geometries calculated employing ab initio theory (MP2 level) for the neat C 3H7NH2 and its different hydrogen-bonded complexes. The linewidth versus concentration plot for the ν(NH) anti-symmetric stretching mode, however exhibits a distinct maxima at C = 0.4, which has been explained as a slight departure from the concentration fluctuation model. In the latter region, a symmetric peak is observed, which corresponds to ν(CN) stretching mode, which shows an upshift upon dilution and an almost linear concentration dependence. This has also been explained in terms of the parameters obtained from the optimized geometries of the different hydrogen-bonded complexes. © 2004 Elsevier B.V. All rights reserved.
Investigation on bonding interaction of benzonitrile with silver nano particles probed by surface enhanced Raman scattering and quantum chemical calculations
(2009) Shivangi Mishra; Ranjan K. Singh; Animesh K. Ojha
The Raman spectra of benzonitrile (Bz) in silver colloidal solution have been recorded at different millimolar concentrations of benzonitrile in the spectral range, 400-2300 cm-1 and the spectral parameters of prominent bands in the region are discussed as a function of concentration. The binding interactions between the benzonitrile and one/two silver atom complexes, [Bz + 1(2)Ag]0 and [Bz + 1(2)Ag]+1 have been investigated using DFT calculations at B3LYP level employing three basis sets, Lanl2DZ, SDD and CEP-31G. The Bz molecule seems to be adsorbed in end-on orientation. The binding energy of [Bz + 2Ag]0 complex is greater than that of [Bz + 1Ag]0 complex. Some bands of benzonitrile show red shift upon surface coordination while some are blue shifted. The red shift in ν(C{triple bond, long}N) vibrational mode is discussed in terms of shortening of C-CN bond due to metal-adsorbate back donation. © 2008 Elsevier B.V. All rights reserved.
Isotopic dilution, self-association, and Raman non-coincidence in the binary system (CH3)2C=O + (CD3)2C=O reinvestigated by polarized Raman measurement and ab initio calculations
(Elsevier, 2003) Sunil K. Srivastava; Animesh K. Ojha; J. Koster; M.K. Shukla; J. Leszczynski; B.P. Asthana; W. Kiefer
Raman spectra of the binary system (CH3)2C=O (acetone)+(CD3)2C=O (acetone-d6) were reinvestigated employing a more precise and sensitive scanning multichannel detection scheme. The I∥ and I⊥ components of the Raman scattered radiation were recorded in the C=O stretching region, 1600-1800 cm-1 as well as in the C-D and C-H stretching regions, 2000-2300 and 2800-3100 cm-1, respectively, in different mixtures with the varying mole fractions of the reference system. A careful Raman line shape analysis yielded after fit Δνnc due to Raman non-coincidence effect (NCE) in acetone and acetone-d6 as 4.87±0.01 and 4.49±0.01 cm-1, respectively. The optimized geometries and wavenumbers of the neat acetone molecule and its self-associated structure were calculated using ab initio method at the MP2 level using 6-31++G(d,p) basis set. The influence of self-association and NCE together were examined. A systematic study of Raman line shape analysis led to a hitherto unexplored aspect, the wavenumber shift and linewidth variation of the ν1(C-H) stretching mode of acetone upon isotopic dilution. The linewidth variation with the mole fraction of the reference system shows an excellent agreement with the corresponding linewidths derived from the T 2 values obtained by three color fs-CARS study reported earlier. © 2003 Elsevier B.V. All rights reserved.
Novel conducting lithium ferrite/chitosan nanocomposite: Synthesis, characterization, magnetic and dielectric properties
(Elsevier, 2014) Manish Srivastava; Jay Singh; Rajneesh K. Mishra; Manish K. Singh; Animesh K. Ojha; Madhu Yashpal; Srivastava Sudhanshu
A study on Lithium ferrite/chitosan nanocomposite (LFCN), easily moldable into arbitrary shapes, as the conducting polymer and ferromagnetic characteristics is presented. The composite material is produced in the presence of Li0.5Cr0.1Fe2.4O4 and Li 0.5Co0.1Fe2.4O4 nanoparticle by ex-situ polymerizations process. Various characterizations techniques have been used to explore the characteristic of the synthesized products. The frequency dependent dielectric properties and electrical conductivity of all the samples have been measured through complex impedance plot in the frequency range of 1 kHz-6 MHz at room temperature. It was observed that in case of (LFCN), fluctuation in value of (ε′) and (ε″) is ceased over the frequency range of 4 Mz which can be attributed to the steady storage and dissipation of energy in the nanocomposite system. Moreover, it is also observed that electrical conductivity of (LFCN) increases with frequency and its value was found to be (0.032-0.048) (ohm-cm)-1 in frequency range of 1 kHz-6 MHz. Due to its low cost, a simple synthesis process and high flexibility, the proposed LFCN may find applications in various types of electronic components. © 2014 Elsevier B.V. All rights reserved.
Optical absorption spectra of coinage metals (Cu, Ag, Au) nanorods: A theoretical study
(2008) Animesh K. Ojha; Ranjan K. Singh
Gold nanorods of average aspect ratio 3.1 have been synthesized. The nanorod solution has been characterized with UV-visible absorption spectra and TEM. UV-visible spectra of gold nanorods solution exhibit two plasmon modes, called transverse and longitudinal modes. Transverse and longitudinal plasmon modes of Cu, Ag and Au nanorods have been simulated on the basis of Gan's model for different aspect ratio keeping medium dielectric constant fixed and for different medium dielectric constant keeping aspect ratio fixed. Simulated result shows that the absorption maximum of longitudinal mode depends linearly on aspect ratio of nanorods, medium dielectric constant and type of metals. Empirical relations to obtain peak longitudinal plasmon frequency in terms of aspect ratio and medium dielectric constant for Cu, Ag and Au have been suggested. Vibrational dephasing time of Cu, Ag and Au for different resonance energy is also calculated. Copyright © 2008 American Scientific Publishers All rights reserved.
Optical absorption spectra of coinage metals (Cu, Ag, Au) nanorods: A theoretical study
(American Scientific Publishers, 2008) Animesh K. Ojha; Ranjan K. Singh
Gold nanorods of average aspect ratio 3.1 have been synthesized. The nanorod solution has been characterized with UV-visible absorption spectra and TEM. UV-visible spectra of gold nanorods solution exhibit two plasmon modes, called transverse and longitudinal modes. Transverse and longitudinal plasmon modes of Cu, Ag and Au nanorods have been simulated on the basis of Gan's model for different aspect ratio keeping medium dielectric constant fixed and for different medium dielectric constant keeping aspect ratio fixed. Simulated result shows that the absorption maximum of longitudinal mode depends linearly on aspect ratio of nanorods, medium dielectric constant and type of metals. Empirical relations to obtain peak longitudinal plasmon frequency in terms of aspect ratio and medium dielectric constant for Cu, Ag and Au have been suggested. Vibrational dephasing time of Cu, Ag and Au for different resonance energy is also calculated. Copyright © 2008 American Scientific Publishers. All rights reserved.
pH dependent surface enhanced Raman study of Phe + Ag complex and DFT calculations for spectral analysis
(2006) Animesh K. Ojha; Achintya Singha; Swagata Dasgupta; Ranjan K. Singh; Anushree Roy
Surface enhanced Raman spectra of Phenylalanine (Phe) in Ag colloidal solution have been recorded for Phe solutions at different pH. Spectral line-shape analyses of three enhanced modes have been carried out between pH 4.5 and 10.5. The variation of line-width with pH reveals two mechanisms in solution: (i) the fluctuation of pH in microscopic volume and (ii) the motional narrowing caused by the intermolecular ionic interaction. The different charge states of the reference molecule are responsible for the observed bond softening with decrease in pH. The 'Raman shift' and the 'Raman activity' of the vibrational modes with maximum enhancement have been explained by carrying out DFT calculations. © 2006 Elsevier B.V. All rights reserved.