アルカリハライド上におけるAuの初期成長 : ―化学結合論的視点から―

概要

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Novel quantitative interpretations are presented for the heteroepitaxy of Au deposited onto UHV-cleaved surfaces of NaCl and KBr. Although Au adsorption processes in the (100) surface of alkali-halide crystals have been regarded as physisorption so far, the result of simulation by the discrete variational Xα cluster method confirms that a Au atom adsorbs to make chemically bonding states on both the NaCl (100) and KBr (100) surfaces. The present well-controlled UHV deposition experiments offer the following results : In the Au/ NaCl system, multiply twinned particles (MTPs) are formed; on the other hand, in the Au/ KBr system, pyramidal particles which are a single crystal are formed. This result suggests that the Au atom is more strongly bonded on the KBr surface than the NaCl one. However, the simulated results are opposite. Therefore, it is proposed that in the heteroepitaxy of a metal/alkali-halide system the strength of chemical bonding is not a decisive parameter, but the geometric factors such as surface dangling bond and symmetry of the atomic arrangements of a substrate play an important role.