Atomic scale control of work function by means of molecular beam techniques

（a）原子尺度的表面改性已经发现，超音速甲烷束与Pt（111）的碰撞根据平移能诱导生成乙叉、烃和石墨。它也清楚地表明，吸附这样一个小的覆盖范围的Cs为0.006 ML增加了约200 meV的反应的势垒，导致反应的终止。这些事实表明，基于入射分子的平移能控制表面反应的可能性。（B）原子尺度下的功函数观测我们提出了一种利用扫描隧道显微镜（STM）定量讨论原子尺度下的功函数的方法。综上所述，由于电负性的差异以及电偶极周围的功函数的非局部降低，Cs原子的吸附诱导了电偶极。此外，通过非接触式原子力显微镜对京都大学制备的过渡金属氮化物的功函数进行显微观察，揭示了取决于制备方法的微观特征的差异。（c）分子束装置与STM的组合我们开发了分子束装置与STM的组合系统。此外，从氦原子散射，非局部效应的功函数降低，由于吸附被证实。虽然甲烷束的动能略大于阈值能量的表面反应终止后，少量的碳相关物种的吸附，与500 meV的平移能量的甲烷束的入射完成单层石墨完全覆盖的表面。更高能量的束诱导良好取向的单层石墨。结果表明，基于动能的吸附物的精确控制的可能性。

(a)Atomic-scale surface modification It was found that the collision of supersonic methane beams onto Pt (111) induces the generation of ethylidine, hydrocarbon and graphite, depending on the translational energy. It was also made clear that adsorption of such a small coverage of Cs as 0.006 ML increases the potential barrier for the reaction by about 200 meV, resulting in the termination of the reaction. These facts suggest the possibility of the control of surface reaction based on the translational energy of incident molecules.(b)Work function observation in an atomic scale We have proposed a procedure to quantitatively discuss the work function in an atomic scale by means of a scanning tunneling microscope (STM). In conclusion, the adsorption of Cs atoms induces the electric dipole due to the difference in electronegativity as well as the non-local reduction in work function around the dipole. Furthermore, the microscopic observations of work function of transition metal nitrides prepared in Kyoto university by means of a non-contact atomic force microscope reveal the difference in microscopic features, depending on the preparation method.(c)Combination of molecular beam apparatus and STM We have developed the combined system of molecular beam apparatus and STM. Also from helium atom scatterings, the non-local effect of the work function reduction due to adsorption was confirmed. Although the surface reaction of methane beams with a kinetic energy a little larger than the threshold energy is terminated after a small amount of adsorption of carbon related species, the incidence of the methane beam with a translational energy of 500meV completed monolayer graphite fully covering the surface. Further higher energy beams induces well-oriented monolayer graphite. The results demonstrate the possibility of precise control of adsorbates based on the kinetic energy.