Showing papers by "Debnarayan Jana published in 2019"

Acetylenic linkage dependent electronic and optical behaviour of morphologically distinct '-ynes'.

Abstract: We have critically examined the key role of acetylenic linkages (–CC–) in determining the opto-electronic responses of dynamically stable tetragonal (T) ‘-ynes’ with the help of a density functional theory method. The presence of –CC– between two tetra-rings invariably flips the electronic bands about the Fermi level. The underlying physics has been critically addressed with the help of a real space renormalization group (RSRG) scheme under a tight binding (TB) approximation. Besides, we have proposed an elegant approach to introduce and tune a band gap in the customarily metallic T graphene allotrope. The quantum dots of these systems exhibit diode like current–voltage (I–V) characteristics and can be used in negative differential resistance devices. In addition, the anisotropic optical properties evidently support the electronic states of the systems. In particular, the static dielectric constants for some of these ‘-ynes’ are enhanced compared to graphene and T graphene. The effective number of electrons participating in an interband transition shows saturation over 30 eV. Furthermore, electron energy loss spectra (EELS) peaks are consistent with the plasma frequencies of the corresponding systems. The intrinsic responses of the –CC– in these systems are extremely important for basic science and nanodevice research.

Strain induced electronic and magnetic properties of 2D magnet CrI3: a DFT approach

Abstract: In the post-graphene era, out of several monolayer 2D materials, Chromium triiodide ([Formula: see text]) has triggered an exotic platform for studying the intrinsic ferromagnetism and large anisotropy at the nanoscale regime. Apart from that, its strong spin-orbit coupling of I also plays a key role in tailoring the electronic properties. In this work, the composition of compressive and tensile strain (uniaxial as well as biaxial) upto 12% have been applied to study the variation of the electronic and magnetic properties of [Formula: see text] employing density functional theory in (LDA+U) exchange correlation scheme. The stability limits of the structures under the influence of strains have been carried out via the deformation potential (DP) and stress-strain relation. For compressive strains in specific directions, the down-spin band gap is seen to be decreasing steadily. The magnetic moment computed from the density of states (DOS) is enhanced significantly under the influence of compressive strain. However, it has been observed that after the application of strain in some specific crystal directions, the magnetic moment of monolayer [Formula: see text] remains almost unchanged. Thus, with the help of strain, the tunning band gap along with underlying characteristic ferromagnetism of this material can unfold a new avenue for potential usage in spintronic devices.

First-principles calculation of the electronic and optical properties of a new two-dimensional carbon allotrope: tetra-penta-octagonal graphene.

Abstract: A novel sp2 hybridized planar 2D carbon allotrope consisting of tetra, penta and octagonal (TPO) rings is proposed in this work. Its thermodynamic stability is confirmed by molecular dynamics in the canonical ensemble at 600 K and the analysis shows that it can also remain stable at 1000 K. The mechanical stability of this material has been estimated by the Born-Huang criterion. Its in-plane stiffness constants are found to be 85% of that of graphene ensuring its high strength quality. The investigation of the electronic properties reveals that the material is metallic in nature with a Dirac cone at 3.7 eV above its Fermi level at an asymmetric position in the conduction band. The study of its optical property for parallel and perpendicular polarization yields the absence of any plasma frequency. Besides, its absorption is mostly spread within 10-20 eV. Further electrical transport study shows negative differential resistance (NDR) above 3.5 V for one nano device. Nano ribbons made out of a TPO-graphene sheet exhibit metallic character. When the porous sheet of TPO-graphene is exposed to Li and S atoms, it is found that the Li atoms pass through the pores unlike the S atoms owing to the less barrier energy compared to S atoms. Substitutional doping with boron and nitrogen at different sites of TPO-graphene showed splitting of the Dirac feature. Also suitable B and N doping brings about semiconducting properties with tunability in band gap with a maximum band gap of 1.09 eV for an isoelectronic structure. All these theoretical predictions might trigger further new avenues involving this novel TPO graphene.

Electronic and optical properties of the supercell of 8-Pmmn borophene modified on doping by H, Li, Be, and C: a DFT approach

Abstract: Borophene nanosheet has been doped with lithium, beryllium, carbon, and hydrogen atom(s). Modification of electronic properties through the splitting and shifting of the Dirac point has been explored within the framework of ab initio density functional theory (DFT). Doping the Pmmn borophene structure with lithium, beryllium, carbon, and hydrogen atoms leads to semiconductor–metallic transitions as well as absorption of light within the different parts of the electromagnetic spectrum. Indirect band-gap opening is noticed when the system is doped with one hydrogen atom. But when the doping is made double, the system becomes metallic. For lithium and beryllium doping, the split Dirac point has been observed to be situated at the conduction band (CB). However, for single-site carbon atom doping, it is seen to be situated at the valence band (VB), while, for double doping, the system becomes semiconducting with an indirect bandgap of 528 meV. Optical properties calculations show that, for parallel and perpendicular polarization, the excitations have mainly occurred within the low- and high-energy regions, respectively. The effective number of valence electrons does not show any saturation effect for all the doped systems in parallel as well as for perpendicular polarizations.

Simple correction to bandgap problems in IV and III–V semiconductors: an improved, local first-principles density functional theory

Abstract: We report results from a fast, efficient, and first-principles full-potential Nth-order muffin-tin orbital (FP-NMTO) method combined with van Leeuwen-Baerends correction to local density exchange-correlation potential. We show that more complete and compact basis set is critical in improving the electronic and structural properties. We exemplify the self-consistent FP-NMTO calculations on group IV and III-V semiconductors. Notably, predicted bandgaps, lattice constants, and bulk moduli are in good agreement with experiments (e.g. we find for Ge 0.86 eV, 5.57 [Formula: see text], 75 GPa versus measured 0.74 eV, 5.66 [Formula: see text], 77.2 GPa). We also showcase its application to the electronic properties of 2-dimensional h-BN and h-SiC, again finding good agreement with experiments.

Multi-facets of kinetic roughening of interfaces

Abstract: Abstract In this review, the authors are going to explore the intriguing aspects of kinetic roughening of interfaces. Interface roughness dynamics connected with various physical processes have been studied through novel microscopic models in connection with experiments. The statistical properties of such rough interfaces appearing in wide range of physical systems are observed to belong to different universality classes characterized by the scaling exponents. With the advancement of characterization techniques, the scaling exponents of thin-film surface (or the morphological evolution of amorphous surfaces eroded by ion bombardment) are easily computed even in situ during the growing (erosion) conditions. The relevant key physical parameters during the dynamics crucially control the overall scaling behaviour as well as the scaling exponents. The non-universal nature of scaling exponents is emphasized on the variations of the physical parameters in experimental studies and also in theoretical models. Overall, this review containing both theoretical and experimental results will unfold some novel features of surface morphology and its evolution and shed important directions to build an appropriate theoretical framework to explain the observations in systematic and consistent experiments.