第一原理計算によるナノ結晶ダイヤモンドの非sp^3結合領域の構築とその弾性特性に及ぼす影響の解析

Abstract

In this paper, we propose a diamond structure including stacking faults as a candidate atomicscale model for nanocrystalline diamond (NCD) with a small amount of non-sp^3 bonded region. The previous work reveals that NCD thin films show unusual elastic behavior, where the diagonal elastic constants decrease and the off-diagonal elastic constants increase as the grain size decreases. Using ab-initio calculations, the stable stacking-fault structures are obtained, whose partial density of states (PDOS) of the 2p_z orbital of the carbon atoms facing stacking faults behave as those of non-sp^3 bonded atoms. Elastic constants of these structures are calculated from changes in the total energy by applying strains, which consistently explain the unusual elastic behavior of NCD films. This result shows that a combination of measurement and theoretical calculation is effective to analyze the relationship between microscopic structures and macroscopic property.