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

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(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.