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Debnarayan Jana

Other affiliations: National Taiwan University
Bio: Debnarayan Jana is an academic researcher from University of Calcutta. The author has contributed to research in topic(s): Graphene & Density functional theory. The author has an hindex of 23, co-authored 127 publication(s) receiving 2328 citation(s). Previous affiliations of Debnarayan Jana include National Taiwan University.

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Journal ArticleDOI
Abstract: In this short topical review, a brief account of the evolution of defects due to controlled changes in polycrystalline zinc oxide has been presented. X-ray diffraction, Positron annihilation spectroscopy and optical absorption spectroscopy has been employed to understand various defective states of ZnO. Thermogravimetric analysis, room temperature resistivity and photoluminescence measurements (just mentioned) have been used to throw more light on this topic. A coherent scenario in the light of previous works in this field has been discussed. At the end discussion on the magnetic studies on ZnO-based systems has been added in short.

263 citations

Journal ArticleDOI
Abstract: This review covers the electronic, optical and electrochemical properties along with electronic behaviors of boron (B) and nitrogen (N) substituted Single Wall Carbon Nanotubes (SWCNTs) underlying density functional theory (DFT) simulations. It is intended to be of interest for both experimentalists and theorists to expand application in the fields of SWCNTs. In particular, this article will focus on the electronically driven optical properties of CxNy nanotubes as a function of N concentration and BxCy nanotubes as a function of B under the action of a uniform electric field with various polarization directions through relaxed C–C bond length ab initio DFT. The link between the electronic band structure and the peak of the loss function will be highlighted. Within the formalism of DFT, we also consider the aspects of vacancy-defected SWCNTs. The effect of nitrogen incorporation is quite pronounced in enhancing the electrochemical properties of CNTs. In fact, this is a growing field due to the need of developing next-generation H-based energies. Finally, an attempt will be made for a comparative study of these theoretical results with experimental ones. Although there are ample experimental reports of N incorporation, at least less than 10%, in the nanostructured carbon, the experimental results on B-alloyed and N-alloyed SWCNTs are scarce. The review concludes with an outlook on the technological potential of these nano-composite systems as optical devices and nano-sensors.

214 citations

Journal ArticleDOI
01 Jul 2014-Carbon
Abstract: Graphene nanosheet has been doped with nitrogen, boron and nitrogen–boron pair of different concentrations. Modifications of electronic and optical properties due to nitrogen, boron and nitrogen–boron codoping in graphene nanosheet have been explored in the frame work of ab-initio density functional theory. Band gap opening has been observed and besides, its magnitude increases with the doping concentration of three different species of adatoms. The static dielectric constant in the long wave length limit for parallel polarization of electric field increases with the doping concentration, whereas for perpendicular polarization it remains almost constant with respect to the doping concentration and specific types. Moreover, in case of nitrogen doped systems, a new electron energy loss spectra peak emerges around ∼2.4 eV for parallel polarization of applied external electric field vector. This peak height increases with the doping concentration. The maximum value of the reflectivity is enhanced with nitrogen concentration while for boron and nitrogen–boron pair concentration, a decreasing tendency is noticed.

138 citations

Journal ArticleDOI
TL;DR: The results obtained so far from experimental and theoretical studies in understanding silicene have shown enough significant promising features to open a new direction in the silicon industry, silicon based nano-structures in spintronics and in opto-electronic devices.
Abstract: Inspired by the success of graphene, various two dimensional (2D) structures in free standing (FS) (hypothetical) form and on different substrates have been proposed recently. Silicene, a silicon counterpart of graphene, is predicted to possess massless Dirac fermions and to exhibit an experimentally accessible quantum spin Hall effect. Since the effective spin-orbit interaction is quite significant compared to graphene, buckling in silicene opens a gap of 1.55 meV at the Dirac point. This band gap can be further tailored by applying in plane stress, an external electric field, chemical functionalization and defects. In this topical theoretical review, we would like to explore the electronic, magnetic and optical properties, including Raman spectroscopy of various important derivatives of monolayer and bilayer silicene (BLS) with different adatoms (doping). The magnetic properties can be tailored by chemical functionalization, such as hydrogenation and introducing vacancy into the pristine planar silicene. Apart from some universal features of optical absorption present in all these 2D materials, the study on reflectivity modulation with doping (Al and P) concentration in silicene has indicated the emergence of some strong peaks having the robust characteristic of a doped reflective surface for both polarizations of the electromagnetic (EM) field. Besides this, attempts will be made to understand the electronic properties of silicene from some simple tight-binding Hamiltonian. We also point out the importance of shape dependence and optical anisotropy properties in silicene nanodisks and establish that a zigzag trigonal possesses the maximum magnetic moment. We also suggest future directions to be explored to make the synthesis of silicene and its various derivatives viable for verification of theoretical predictions. Although this is a fairly new route, the results obtained so far from experimental and theoretical studies in understanding silicene have shown enough significant promising features to open a new direction in the silicon industry, silicon based nano-structures in spintronics and in opto-electronic devices.

124 citations

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Abstract: Mechanical milling and subsequent annealing in air at temperatures between 210 and 1200°C have been carried out on high purity ZnO powder to study the defect generation and recovery in the material. Lowering of average grain size (from 76±1to22±0.5nm) as a result of milling has been estimated from the broadening of x-ray lines. Substantial grain growth in the milled sample occurs above 425°C annealing temperature. Positron annihilation lifetime (PAL) analysis of the samples shows a distinct decrease of the average lifetime of positrons very near the same temperature zone. As indicated from both x-ray diffraction (XRD) and PAL results, high temperature (>700°C) annealed samples have a better crystallinity (or lower defect concentration) than even the nonmilled ZnO. In contrast, the measured optical band gap of the samples (from absorption spectroscopy) does not confirm lowering of defects with high temperature annealing. Thermally generated defects at oxygen sites cause significant modification of the optical absorption; however, they are not efficient traps for positrons. Different thermal stages of generation and recovery of cationic as well as anionic defects in granular ZnO are discussed in the light of XRD, PAL, and optical absorption studies.

116 citations

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Proceedings Article
14 Jul 1996
TL;DR: The striking signature of Bose condensation was the sudden appearance of a bimodal velocity distribution below the critical temperature of ~2µK.
Abstract: Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

3,409 citations

01 Sep 1955
Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

2,654 citations

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Abstract: The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

1,240 citations