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

点击翻译按钮获取中文摘要

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.