Development of an Analysis System of Gas-Surface Interaction using the Molecular Dynamics Method

近年来，工程技术的发展对稀薄气体流动的分析提出了更高的要求。例如，在制造半导体时，分析与膜表面相互作用的气体分子是重要的。我们的目标是开发一个更复杂的系统的气体-表面相互作用，如多原子分子-表面相互作用的分子动力学方法的分析系统。松本、松井等人在多原子分子相互作用或吸附物分子存在的情况下，对该系统进行了扩展，使用超级计算机和专用软件进行了计算。当吸附物分子存在时，通过将气体分子吸附到表面然后碰撞气体分子来完成模拟。在这种情况下，吸附物分子影响气体分子。我们选择了一个氧分子（双原子分子）来分析多原子气体分子与表面的相互作用。旋转自由度对气体原子和表面之间的能量交换过程产生影响。Shobatake等人使用石墨表面进行了气体-表面相互作用的实验。这些数据将有助于估计气体原子和表面原子之间的势的形式，这在进行分子动力学模拟时是必不可少的。此外，还获得了比较单原子分子和双原子分子散射分布的实验数据。

Recently, advances in engineering techniques gave more demands to analyze rarefied gas flows. The analysis of a gas molecule interacting with a surface of a film when manufacturing a semi-conductor, for example, is important. Our aim is to develop an analysis system of a more complicated system of gas-surface interaction such as a polyatomic molcule-surface interaction using the molecular dynamics method. With this system, data of adsorption rates or scattering distributions of a gas molecule are acquirable.Matsumoto, Matsui and others have expanded the system when polyatomic molecules interact or when adsorbate molecules exists, and has done calculations using a supercomputer and an exclusive software. When an adsorbate molecule exists, the simulation was done by adsorbing gas molecules to the surface and then colliding a gas molecule. At this situation, the adsorbate molecule influences the gas molecule. We have selected an oxygen molecule (diatomic molecule) to analyze the interaction of a polyatomic gas molecule and a surface. The rotational degree of freedom gave influence on the process of energy exchange between the gas atom and the surface.Shobatake and others have done experiments of gas-surface interaction using a graphite surface. The date will help estimate the from of the potential between the gas atom and the surface atom, which is essential when performing molecular dynamics simulations. Also, experimental data for comparing scattering distributions between monatomic molecules and diatomic molecules were obtained.