Gautam Mukhopadhyay

Resonant coupling between localized plasmons and anisotropic molecular coatings in ellipsoidal metal nanoparticles

We present an analytic theory for the optical properties of ellipsoidal plasmonic particles covered by anisotropic molecular layers. The theory is applied to the case of a prolate spheroid covered by chromophores oriented parallel and perpendicular to the metal surface. For the case that the molecular layer resonance frequency is close to being degenerate with one of the particle plasmon resonances strong hybridization between the two resonances occurs. Approximate analytic expressions for the hybridized resonance frequencies, their extinction cross-section peak heights, and widths are derived. The strength of the molecular-plasmon interaction is found to be strongly dependent on molecular orientation and suggests that this sensitivity could be the basis for novel nanoparticle based bio- and chemo-sensing applications.

Strain-tunable band gap in graphene/h-BN hetero-bilayer

Abstract Using full-potential density functional calculations within local density approximation (LDA), we predict that mechanically tunable band-gap and quasi-particle-effective-mass are realizable in graphene/hexagonal-BN hetero-bilayer (C/h-BN HBL) by application of in-plane homogeneous biaxial strain. While providing one of the possible reasons for the experimentally observed gap-less pristine-graphene-like electronic properties of C/h-BN HBL, which theoretically has a narrow band-gap, we suggest a schematic experiment for verification of our results which may find applications in nano-electromechanical systems (NEMS), nano opto-mechanical systems (NOMS) and other nano-devices based on C/h-BN HBL.

Structural and Electronic Properties of Graphene and Silicene: An FP‐(L)APW+lo Study

We report here the structural and electronic properties of graphene and silicene (the silicon analogue of graphene) investigated using first‐principles calculations of their ground state energies employing full‐potential (linearized) augmented plane wave plus local orbital (FP‐(L)APW+lo) method. On structure optimization, we found that the graphene‐like honeycomb‐ structure of Si is buckled (buckling parameter Δ≃0.44 A) in contrast with graphene whose structure is planar (Δ = 0.0 A). In spite of the buckled‐structure, silicene has an electronic structure similar to that of graphene. The results are in agreement with previous reports based on other methods. We have also calculated the lower bounds of the lattice constant “a” of these 2D systems, within the present method of study which are our new results.

First‐Principles Study of Structural and Electronic Properties of Germanene

The ground state structural and electronic properties of germanene (the germanium analogue of graphene) are investigated using first‐principles calculations. On structure optimization, the grapheme‐like honeycomb structure of germanene turns out as buckled (buckling parameter Δ = 0.635 A) in contrast with graphene’s planar structure (buckling parameter Δ = 0.0 A). In spite of this, germanene has similar electronic structure as that of graphene. While corroborating the reported results, we newly predict the in‐plane contraction of hexagonal Ge with (thermal) stretching along the “c” axis, akin to a phenomenon observed in graphite.

Strain-tunable band parameters of ZnO monolayer in graphene-like honeycomb structure

Abstract We present ab initio calculations which show that the direct-band-gap, effective masses and Fermi velocities of charge carriers in ZnO monolayer (ML-ZnO) in graphene-like honeycomb structure are all tunable by application of in-plane homogeneous biaxial strain. Within our simulated strain limit of ± 10 % , the band gap remains direct and shows a strong non-linear variation with strain. Moreover, the average Fermi velocity of electrons in unstrained ML-ZnO is of the same order of magnitude as that in graphene. The results promise potential applications of ML-ZnO in mechatronics/straintronics and other nano-devices such as the nano-electromechanical systems (NEMS) and nano-optomechanical systems (NOMS).

Collective resonances of carbon onions

Abstract Based on a simple equation of motion for the induced density in a spherical carbon particle we demonstrate the existence of a rich spectrum of collective resonances as a function of the number of shells for n = 1 ( C 60 ), 2,10 and 40. We also present results for the photoabsorption cross section and discuss the nature of the collective resonances by examining the eigenmodes of the systems.

Graphene and some of its structural analogues: full-potential density functional theory calculations

Using full-potential density functional calculations we have investigated the structural and electronic properties of graphene and some of its structural analogues, viz., monolayer (ML) of SiC, GeC, BN, AlN, GaN, ZnO, ZnS and ZnSe. While our calculations corroborate some of the reported results based on different methods, our results on ZnSe, the two dimensional bulk modulus of ML-GeC, ML-AlN, ML-GaN, ML-ZnO and ML-ZnS and the effective masses of the charge carriers in these binary mono-layers are something new. With the current progress in synthesis techniques, some of these new materials may be synthesized in near future for applications in nano-devices.

Reliability of single and dual Layer Pt nanocrystal devices for NAND flash applications: A 2-region model for endurance defect generation

Nanocrystal (NC) based memory devices are considered a possible alternative for floating gate (FG) replacement below 30nm node. In this work, endurance reliability of Pt NC devices is investigated for single layer (SL) and dual layer (DL) structures. The degradation in the devices due to Program/Erase (P/E) stress is investigated. Relative improvement in reliability of DL structure over SL structure is shown. A physical model for defect generation in the gate stack is proposed which is able to explain endurance and post-cycling characteristics. Dual layer structure is shown to have better inherent reliability over single layer structure.

Collective Aspects of Atomic Dynamics

We give a brief review of the theories describing collective dynamics of atoms, and comment on the hydrodynamic approach as well as the manybody approach based on RPA. In particular we put forward a unified approach, combining the hydrodynamical and single-particle aspects in a single theoretical framework. Some general aspects of the theory are discussed as well as a simple application to the oscillations of a spherical shell.

On dynamic image potential

Abstract Self consistent calculations for the dynamic image potential are carried out, taking the finite acceleration of the incoming charge into account. Results indicate that the effect of the inclusion of acceleration is rather small, and the simpler self consistent approach neglecting the acceleration and using a local speed approximation seems to be adequate. Our theoretical framework also provides a mathematical justification of the latter simpler approach which was earlier employed by Ray and Mahan in an ad hoc manner.