Tatsuya Ohira

Molecular Dynamics Simulation of Hydrogenated Amorphous Silicon with Tersoff Potential

A Molecular dynamics method with a Many-body Tersoff-type interatomic potential has been being applied to analyses of hydrogenated Amorphous silicon ( a-Si:H ) thin-film growth processes. As a first step toward film growth simulations, Molecular dynamics simulations of SiH3 radical, which would be a significant precursor for the a-Si:H thin-film growth processes, and a-Si:H formation with a rapid quenching method have been performed by developing new Tersoff-type interatomic potential between Si and H in this study. Visualization of SiH3 radical dynamics by computer graphics has made it possible to observe the inversion and rotation of SiH3 radical, which had been predicted by infrared diode-laser spectroscopie measurement in other group. In addition, visualization of the a-Si:H sample has helped us to find that there are some microcavities in the sample and that there are two kinds of hydrogen in the sample, gathering closely together while lying scattered, which had been predicted in IR absorption experimental results.

Molecular dynamics simulation of amorphous silicon with Tersoff potential

We have performed molecular dynamics simulation of amorphous silicon (a-Si) by rapid quenching, with empirical interatomic potential (Tersoff potential) as a first step toward hydrogenated amorphous silicon film growth simulations. The numerical results on structural properties showed fairly good agreement with experimental data or numerical results from ab-initio molecular dynamics in other groups. In our a-Si sample, the average coordination is 4.2 and approximately 18% of the atoms have a coordination number of 5. In addition, visualization of the a-Si sample by computer graphics made it possible to see that there are some microcavities in the sample, which was predicted in experimental data.

Atomistic Simulations of the Work of Adhesion at Metal Oxide Interfaces

In this work we have studied magnetite scale adhesion on a tube made from some different type materials, and treated metal oxide interfaces between magnetite scales (Fe 3 O 4 ) and stainless steel tube surface oxides (NiFe 2 O 4 ) or chromium coating tube surface oxides (Cr 2 O 3 , FeCr 2 O 4 ). In this paper we have defined new MEAM (Modified Embedded Atom Method) parameters for Fe-O, Cr-O, Ni-O, Fe-Ni, and Fe-Cr pair interactions based on experimental information such as lattice constants, cohesive energies, bulk moduli of those metal oxides, and have calculated the work of adhesion at Fe 3 O 4 (110) / Fe 3 O 4 (110), NiFe 2 O 4 (110), Cr 2 O 3 (110), Cr 2 O 3 (100), FeCr 2 O 4 (110) interfaces where a cluster-surface interfacial model is adopted. As the results of the calculation, it was found that there is an energy barrier, which prevents scales from approaching a tube surface, in a potential energy curve vs. a separation between scales and chromium coating surfaces. We further discuss the effect of surface directions at interfaces on the work of adhesion.