G. P. Das

Band gap engineering by functionalization of BN sheet

From first principles calculations, we investigate the stability and physical properties of single layer h-BN sheet chemically functionalized by various groups viz. H, F, OH, CH3, CHO, CN, NH2 etc. We find that full functionalization of h-BN sheet with these groups lead to decrease in its electronic band gap, albeit to different magnitudes varying from 0.3 eV to 3.1 eV, depending upon the dopant group. Functionalization by CHO group, in particular, leads to a sharp decrease in the electronic band gap of the pristine BN sheet to ~ 0.3 eV, which is congenial for its usage in transistor based devices. The phonon calculations on these sheets show that frequencies corresponding to all their vibrational modes are real (positive), thereby suggesting their inherent stability. The chemisorption energies of these groups to the B and N atoms of the sheet are found to lie in the range of 1.5 -6 eV.

Ferromagnetism in Mn-doped GaN: From clusters to crystals

The magnetic coupling between doped Mn atoms in clusters as well as crystals of GaN has been studied from first principles using molecular orbital theory for clusters and linearized muffin tin orbital---tight binding formulation for crystals. The calculations, based on density functional theory and the generalized gradient approximation for exchange and correlation, reveal the coupling to be ferromagnetic with a magnetic moment ranging from

H-substituted anionic carbon clusters CnH− (n⩽10): Density functional studies and experimental observations

2.0{\ensuremath{\mu}}_{B}

h-BN monolayer on the Ni(111) surface: a potential catalyst for oxidation.

to

Strain-induced band-gap deformation of H/F passivated graphene andh-BN sheet

4.0{\ensuremath{\mu}}_{B}

Exploring semiconductor substrates for silicene epitaxy

per Mn atom depending on its environment. Mn atoms also tend to cluster and bind more strongly to N atoms than to Ga atoms. The significant binding of Mn to GaN clusters further indicates that it may be possible to increase the Mn concentration in GaN by using a porous substrate that offers substantial surface sites.

Quantum size effects in layered VX2 (X = S, Se) materials: Manifestation of metal to semimetal or semiconductor transition

We have studied the interaction of hydrogen with small neutral and anionic carbon clusters using density functional calculations. The geometry, stability, and electronic structure of these clusters show an odd–even alternation originating in the bonding nature of the carbon atoms. Our mass spectrometric measurements of the abundance of CnH− (n⩽10) cluster anions produced by gas-feed Cs sputtering from different crystallographic forms of carbon display similar odd–even alternation with the even-n clusters being relatively more abundant. The calculated trend in the adiabatic electron affinities shows a behavior similar to the experimental abundance pattern. We discuss a possible partial suppression of the chain-to-ring transformation (which normally occurs at n=10 in Cn−) in CnH− and compare it with our density functional calculations as well as observations in CnN−. We also observe that the size dependence of the abundance of CnH− clusters sputter ejected from a fullerene target exhibits a distinctly diffe...

Electronic structure of the 4H polytype of diamond

The hexagonal boron nitride (h-BN) is traditionally considered to be inert. In sharp contrast to the inert behavior of free-standing hexagonal boron nitride (h-BN), we propose the catalytic property of h-BN monolayer on Ni(111) substrate using first-principles density functional theory investigation. The interaction of O2 molecule with the h-BN/Ni(111) substrate results in nondissociative adsorption of the molecule along with elongation of the O-O bond. This can be considered as the activated state of the O2 molecule. Further interaction of this complex viz O2-h-BN/Ni(111) with an incoming CO molecule leads to the spontaneous formation of CO2. Interestingly, the CO adsorption on the h-BN/Ni(111) substrate was found to be unfavorable, thereby implying the oxidation of CO selectively through Eley-Rideal (ER) mechanism.

Novel properties of boron nitride nanotubes encapsulated with Fe, Co, and Ni nanoclusters

Strain induced band gap deformations of hydrogenated/fluorinated graphene and hexagonal BN sheet have been investigated using first principles density functional calculations. Within harmonic approximation, the deformation is found to be higher for hydrogenated systems than for the fluorinated systems. Interestingly, our calculated band gap deformation for hydrogenated/fluorinated graphene and BN sheets are positive, while those for pristine graphene and BN sheet are found to be negative. This is due to the strong overlap between nearest neighbor {\pi} orbitals in the pristine sheets, that is absent in the passivated systems. We also estimate the intrinsic strength of these materials under harmonic uniaxial strain, and find that the in-plane stiffness of fluorinated and hydrogenated graphene are close, but larger in magnitude as compared to those of fluorinated and hydrogenated BN sheet.

Ground state structural stability of ordered fcc- and bcc-based LiAl compounds under first and second nearest-neighbour pair approximation

We have carried out first-principles density functional theory based calculations on electronic properties of silicene monolayer on various (111) semi-conducting surfaces. We find that the relative stability and other properties of the silicene overlayer depend sensitively on whether the interacting top layer of the substrate is metal or non-metal terminated. The nature of silicene-monolayer on the metal terminated surface can be metallic or even magnetic, depending upon the choice of the substrate. The silicene overlayer undergoes n-type doping on metal terminated surface while it undergoes p-type doping on nonmetal terminated surfaces of the semiconductor substrates.