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First-principle calculations of effective mass of silicon crystal with vacancy defects

Zhong S., Wu M., Lei X.

Materials Science Poland

2016

Vol. 34, No. 4

916--923

The energy band structures and electron (hole) effective masses of perfect crystalline silicon and silicon with various vacancy defects are investigated by using the plane-wave pseudopotential method based on density functional theory. Our results show that the effect of monovacancy and divacancy on the energy band structure of crystalline silicon is primarily reflected in producing the gap states and the local states in valence band maximum. It also causes breaking the symmetry of energy bands resulting from the Jahn-Teller effect, while only producing the gap states for the crystalline silicon with hexavacancy ring. However, vacancy point defects could not essentially affect the effective masses that are derived from the native energy bands of crystalline silicon, except for the production of defect states. Simultaneously, the Jahn-Teller distortions only affect the gap states and the local states in valence band maximum, but do not change the symmetry of conduction band minimum and the nonlocal states in valence band maximum, thus the symmetry of the effective masses. In addition, we study the electron (hole) effective masses for the gap states and the local states in valence band maximum.

The influence of boron on the adsorption of Ti and C on TiC surfaces

Fan X., Ding H., Chu K

Materials Science Poland

2014

Vol. 32, No. 1

112--120

The first-principles calculations have been performed to study the influence of boron on the adsorption of Ti and C on different TiC surfaces. It is found that boron can be adsorbed on both TiC (001) and (111) surfaces. When boron is present and carbon supply is high during the preparation of TiC, boron can bond with carbon atoms to form B–C clusters on (001) surface, but the formation of them is less favorable than that of Ti–C clusters. However, under the low carbon-supply condition, both B–B and Ti–Ti clusters can be formed, and, once being formed, B–B clusters are more stable than the Ti–Ti ones. On Ti-terminated (111) surfaces, boron adatoms are more likely to be moved to form B–B clusters. The study of the diffusion of the adatoms on the surfaces demonstrates that boron adatoms can be more easily migrated on (111) surfaces, which further confirms the above results.

Electronic mechanism of dehydrogenation of the Mg-Ge mixture during milling under hydrogen

Zhou D. W., Liu J. S., Zhang J., Huang Z. G., Peng P.

Materials Science Poland

2010

Vol. 28, No. 1

43--54

The energy and electronic structure of the hydride phase are calculated by using the first-principles plane-wave pseudopotential method to explain experimental results of milling of a Mg-Ge mixture under hydrogen. The electronic mechanism of dehydrogenation of the Ge alloying system is also considered. By calculating heats of formation of MgH2 and (MgGe)H2 solid solutions, it is found that the structural stability of the alloying system is reduced when a little Ge dissolves in MgH2. As the Ge content increases, Mg2Ge may be formed by the reaction: 2MgH2 + Ge - Mg2Ge + 2H2, at the same time, the dehydrogenating properties of the system are improved compared with that of MgH2, but are reduced by contrast with that of (MgGe)H2 solid solutions. Based on the analysis of the densities of states (DOS) of MgH2 before and after Ge alloying, it is found that the improvement of the dehydrogenating properties of MgH2 dissolved into a little Ge is attributed to the weakened bonding between magnesium and hydrogen caused by the interactions between Ge and Mg.