Control of thin-film growth by controlling the shape of 2-dimensional nucleus during initial stage

本文研究了台阶边势垒（存在于台阶边，阻止原子向下移动到较低平台的扩散势垒）的影响。对薄膜生长的影响。近年来的研究表明，台阶边势垒的大小取决于台阶边的方向。这表明了通过控制二维核的形状来控制薄膜生长的可能性，因此详细研究台阶边势垒对薄膜生长的影响具有重要意义。模拟中所用的扩散、离解、层间输运活化能是用场离子显微镜对Pt和Ir实验测得的活化能。发现层间输运（原子向低平台的输运）是一种非线性过程。很大程度上取决于屏障的位置。也就是说，通过将层间传输的势垒从边缘移开，这实际上是Pt的情况，层间传输的速率急剧降低。并五苯分子薄膜的生长也被研究为温度的函数。由于层间传输的增加，表面粗糙度随温度的变化而降低至-50 ° C。但是，表面粗糙度增加高于此温度，这是在普通的生长，其中的粗糙度单调下降。这是由于并五苯分子的解离的发病。总之，层间输运对生长的重要性得到证实，这表明通过控制二维核的形状来控制薄膜生长的可能性。核的形状主要由边缘扩散决定，边缘扩散是沿着阶梯边缘的扩散，观察这种扩散是很重要的。

In this research, the effect of step-edge barrier (A diffusion barrier which exists at the step-edge and prevents atoms to move down to a lower terrace.) on thin-film growth is investigated. In recent studies, it is proposed that the step-edge barrier depends on the orientation of step-edge. This suggests a possibility of controlling thin-film growth by controlling the shape of a 2-dimensional nucleus and therefore the importance of investigating the effect of step-edge barrier on growth in detail.A growth simulation is performed to investigate the effect of step-edge barrier on growth. Activation energies of diffusion, dissociation, interlayer transport used in the simulation are those which were experimentally measured for Pt and Ir by field-ion-microscope. It is found that the interlayer transport (A transport of atoms to a lower terrace.) depends strongly on the position of the barrier. That is by moving the barrier for interlayer transport away from the edge, which is actually the case for Pt, the rate of interlayer transport decreases dramatically. This will contain atoms on the nucleus, therefore induce 3-dimensional growth.The growth of pentacene molecular thin films is also investigated as a function of temperature. Because of the increase in interlayer transport, the surface roughness decreases up to -50 degree C as a function of temperature. But the surface roughness increases above this temperature, which is in contrast to ordinary growth where the roughness decreases monotonically. This is attributed to the onset of dissociation of pentacene molecules.In conclusion, the importance of interlayer transport on growth is confirmed which suggests a possibility of controlling thin-film growth by controlling the shape of a 2-dimensional nucleus. The shape of a nucleus is determined mainly by edge diffusion, which is a diffusion along step edge, and it will be important to look at this diffusion.