Arunabhiram Chutia

Theoretical Study on Electronic and Electrical Properties of Nanostructural ZnO

The electronic and electrical properties of ZnO semiconductor single wall nanotube were investigated using periodic supercell approach within density functional theory combined with tight-binding quantum chemistry method. Armchair (10,10) and zigzag (10,0) nanotubes were considered. The lower strain energies required to roll up a ZnO graphitic sheet into a tube and the negative cohesive energies implied the possibility for the formation of ZnO single wall nanotubes. It was shown that the band gaps between the valence band maximum (VBM) and conduction band minimum (CBM) of nanotubes calculated by means of the two methods are similar and are larger than that of the bulk ZnO. It was found that the band gaps of ZnO nanotube are relatively insensitive to the chirality and diameter. According to the estimated electrical conductivities, the non-defect bulk and nanotube ZnO exhibited insulator properties, while they exhibited semiconductor properties when oxygen vacancies are introduced in the structures. The relative stability and band gap of fullerene-like ZnO clusters were also analyzed.

Influence of surface chemistry on the electronic properties of graphene nanoflakes

Abstract Spin polarized density functional theory was employed to investigate the influence of organic functional groups on the electronic properties of graphene nanoflakes (GNF). We found that for OH functionalized GNF, energy gap decreases as the number of layers is increased regardless of the stacking pattern (ABA and AAA). In the case of SH functionalized GNF the energy gap depends on the number of layers and on the stacking pattern. The observed trends were clarified in terms of interactions between π -electron rich beds. Our results bring new insights into engineering the properties of GNFs by modification of their surface chemistry and stacking conformation.

Theoretical Investigation on Electrical and Electronic Properties of Carbon Materials

The present work is focused on the theoretical investigation of the electronic and electrical properties of alkene chains with the general formula CnHn+2 (n=2, 4, 8, 10, 14, and 16). Preliminary investigation showed that with increasing chain lengths of these systems the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreases and the systems approach semiconducting behavior. Further, a novel methodology based on tight-binding quantum mechanics called Colors, which was developed in our laboratory, was used for the first time to theoretically estimate the electrical conductivity of these molecular systems. A study on doped C8H10 alkene chains was also carried out and it was observed that the electrical conductivity of the doped C8H10 system increased by a factor of ~109 times as compared with the undoped system.

Theoretical Simulation of Dielectric Breakdown by Molecular Dynamics and Tight-Binding Quantum Chemistry Methods

A novel methodology is addressed and employed to simulate dielectric breakdown process of the amorphous SiO2 (a-SiO2) under high electric fields, as well as the role of hydrogen and oxygen vacancy in the breakdown process. This methodology is based on classical molecular dynamics in conjunction with our original tight-binding quantum chemical molecular dynamics method. It is shown from the electronic structure that gap of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for a-SiO2 under no electric field at 300 K is calculated to be 7.5 eV and the orbital contributions to the valence band and conduction band are in line with experimental data. We have evaluated the electric field dependence of breakdown for a-SiO2 at 300 K and found that the insulator property shifts to conductor when electric field reached to a very high value of 5×1010 V/m. The result of this process can be ascribed to the decreasing of band gap induced by the destruction of geometry of a-SiO2 under very high electric field. Our results reveal that the conductivity of a-SiO2 increases with the increase of hydrogen or oxygen vacancy concentration in the oxide structure under the electric field. This supports the fact that defects play an important role in triggering breakdown process. Finally, a complex model has been build and used to simulate the influence of interface structure of Si and SiO2 under high electric field.

Development of A Seebeck Coefficient Prediction Simulator Using Tight-Binding Quantum Chemical Molecular Dynamics

Technologies oriented to the development of thermoelectric materials are of great interest because they can assist in directly tapping the vast reserves of currently underused thermal energy. To improve the rational design of high-performance thermoelectric materials, a new numerical procedure for prediction of Seebeck coefficient based on the electronic information from tight-binding quantum chemical molecular dynamics method, has been developed. The newly developed simulator can evaluate Seebeck coefficient theoretically. The simulator is used for the prediction of the Seebeck coefficients for Pt and Si that are the representative materials for metals and semiconductors, respectively. The results show that both coefficients are in quantitative agreement with experimental data, i.e. in the case of Pt metal the predicted value is 5.62 µV/K while the experimental is -4.45 µV/K. Similarly, in the case of Si semiconductor the predicted value is -324.48 µV/K while the experimental is 300–400 µV/K. This new developed simulator can be used to guide the rational design of high performance thermoelectric materials.

Influence of Organic Functional Groups on the Electrical Properties of Carbon Black: A Theoretical Study

In the present investigation methods based on tight-binding approximation (TBA) and density functional theory (DFT) were employed to investigate the electronic properties of carbon black. The influence of organic functional groups (OFGs) such as –OH and –CHO in the basic structural units (BSUs) of carbon black was studied. It was seen that with the substitution of OFGs in the pristine graphene layers the energy gaps decreased. The changes in energy gaps associated with the topological association of OFGs were also investigated. The change of energy gaps associated with the topological association among the OFGs and with the graphene moieties was seen to be marginal.

Electrochemical synthesis and characterization of stable colloidal suspension of graphene using two-electrode cell system

The present work reports the synthesis and characterization of graphene via electrochemical exfoliation of graphite rod using two-electrode system assisted by Sodium Dodecyl Sulphate (SDS) as a surfactant. The electrochemical process was carried out with sequence of intercalation of SDS onto the graphite anode followed by exfoliation of the SDS-intercalated graphite electrode when the anode was treated as cathode. The effect of intercalation potential from 5 V to 9 V and concentration of the SDS surfactant of 0.1 M and 0.01 M were investigated. UV-vis Spectroscopic analysis indicated an increase in the graphene production with higher intercalation potential. Transmission Electron Microscopy (TEM) analysis showed a well-ordered hexagonal lattice of graphene image and indicated an angle of 60° between two zigzag directions within the honeycomb crystal lattice. Raman spectroscopy analysis shows the graphitic information effects after the exfoliation process.

Development of Multi-Scale Electromigration Simulator using Ultra Accelerated Quantum Chemical Molecular Dynamics and a Kinetic Monte Carlo Method and its Application to Cu Interconnect

Tohoku Univ., Dept. of Appl. Chem., Grad. School of Eng. 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Phone: +81-22-795-7233 E-mail: miyamoto@aki.che.tohoku.ac.jp Tohoku Univ., NICHe, 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tohoku Univ., Dept. of Chem. Eng., Grad. School of Eng. 6-6-11-1302 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Tezpur Univ., Dept. of Chem. Sci., School of Sci. & Tech. Napaam 784028, Tezpur, Assam, India Tohoku Univ., FRI, Grad. School of Eng. 6-6-11-701 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan