Microscopic Tunneling Properties of Adsorbed Surfaces

研究项目“有机分子在硅表面的电子态”：通过第一性原理计算，解释了五个苯环吸附在Si(001)2×1表面的并五苯分子的STM图像。我们的结论是，在由针尖-真空-有机分子-衬底组成的体系中，电子从有机分子-衬底系统的本征态通过真空隧道到针尖。研究项目富勒烯衍生物的电子态：我们考虑了碳片中的1，2，3和6个杂质五边形。计算1个五角形系统会再现STM图像。对于2个五边形，HOMO与C_(60)分子在Si(001)2×1表面上的HOMO非常相似。对于碳纳米管(CNT)尖端的模型--6个五边形，我们已经得到了初步的结果，并且还在继续计算中。尽管世界各地对碳纳米管的电子态进行了大量的研究，但所有碳纳米管的尖端都是开放的。从碳纳米管用于STM针尖的角度出发，我们得到了闭合的碳纳米管尖端的电子态，如果多个之字形的碳纳米管呈星状排列，则同核分子在6个五边形附近具有较高的电荷密度。因此，我们可以重现最近在Mie和早稻田大学获得的场发射显微镜(FE)图像。

Research item 'electronic states of organic molecule on Si surface' : By calculating from the first-principle, we explain STM images of pentacene molecules with five benzen rings adsorbed on Si (001) 2×1 surface. We conclude that in the system consisting of tip-vacuum-organic molecule-substrate, electrons tunnel from the eigen states of the organic molecule-substrate system to tip via the vacuum.Research item 'electronic states of fullerene derivatives' : we consider 1, 2, 3 and 6 impurity pentagons in carbon sheet. Calculation of 1 pentagon system reproduces STM images. For 2 pentagons, HOMOs quite resemble to those of C60 molecule on Si (001) 2×1 surface. For 3 pentagons, they also resemble to those of C60 on Si (111) 7×7 surface.For 6 pentagons which is the model of the tip of carbon nanotube (CNT), we have gotten primitive results at this stage and are continuing calculation. Although many researchs of electronic states of CNT have been done over the world, the tip ends of all of CNT are 'open'. From the view point to utilize CNT for STM tip, we obtain electronic states of tip apex of 'closed' CNT.If pentagons of multi zig-zag CNT are arranged stellately, HOMOs have high charge density around 6 pentagons. Thus, we can reproduce field emission microscope (FEM) images which are obtained quite recently at Mie and Waseda Universities.