Yoichiro Yagi

Theory of short range order of Li on Cu(100)

Abstract The short range order of incommensurate structures of Li adsorbed on Cu(100) is discussed. According to the LEED measurements, the Li atoms form linear incommensurate chains pretty well ordered in the missing rows induced by the Li adsorption and the short range order between the Li atom chains is weaker. A one-dimensional classical XY -model is proposed for this system where the pretty well ordered linear chain is represented by a spin and the nearest neighbor spins couple. This model can be easily solved and the results are in satisfactory agreement with the experimental ones.

Correlation function of adsorbed Au chain on Si(111) surface

Abstract The surface structure of Au-adsorbed Si(111)-5 × 2 with short-range order has been observed through STM measurements. Particularly, the one-dimensional chains consisting of adsorbed Au atoms are clearly observed. A one-dimensional lattice model is constructed for this chain, with repulsive interactions and some assumed irregularity corresponding to STM observation. The theoretical positional correlation function of the adsorbed Au is obtained by a Monte Carlo simulation with fitting parameters of the repulsive interaction and of the irregularity of the experimental positional correlation function. Almost complete fitting is obtained, from which reasonable values of the repulsive interaction and concentration of the irregularity are obtained. A rigorous analysis is also made of another one-dimensional model to describe the inter-chain correlation on this surface, and is compared with experimental findings.

Semi-phenomenological Model for (4×1) to (8ד2”) Phase Transition of In-adsorbed Si(111) Surface

An Indium adsorbed Si(111) (4×1) reconstructed surface seems to undergo a structural phase transition to (8ד2”) at approximately 130 K with decreasing temperature. On the basis of existing experimental and the first principles theoretical results, a simple semi-phenomenological model, using the Ising spin scheme, is presented for this surface system. Its analysis by Monte Carlo simulation shows that the model can account for this peculiar phase transition well.

Theoretical analysis of coverage-dependent rotational hindrance of PF3 adsorbed on Ru(001)

Distribution of the azimuthal orientation of PF 3 molecules adsorbed on Ru(001) measured by ESDIAD shows interesting temperature and coverage dependences. It is interpreted in this analysis as due to the short range order in the locative distribution of the PF 3 molecules. Monte Carlo simulations are performed to obtain the temperature and coverage-dependent distribution of the adsorbed molecules. The distribution of the azimuthal orientation of the molecule is discussed on the basis of the obtained locative distribution of the molecules by using simple models for rotational hindrance to be compared with the experimental results.

Excitation spectra of incommensurate Li chains on a Cu(100) surface

According to low energy electron diffraction (LEED) measurements, Li atoms form linear incommensurate chains in the missing rows induced by Li adsorption on a Cu(100) surface at room temperature and in the coverage range from 0.375 to 0.4. The motions of these Li atoms in the chains are discussed by the classical molecular dynamics calculation. The vibrational excitation spectra of this system are also calculated. Li atoms are assumed to move not only parallel to the surface but also perpendicular to the surface in the missing row by the periodic potential from the substrate Cu atoms. This situation is treated in an approximate manner to show that the spectra obtained may be observed by spectroscopy measurements such as those made by high resolution electron energy loss spectroscopy.

Step-induced short range order on Si(100) reconstructed surfaces

Two kinds of interaction model are proposed to the asymmetric dimer model of the Si(100) reconstructed surface. One is the short range interaction model, and the other is the one including the longer range electric dipolar interaction. Short range order structures at step edges are examined for the two kinds of interaction model, and some differences are found. An attempt is made to compare the results with the STM images.

Atomic displacements and electronic properties for 4 ? 1?8 ? 2 phase transition of In-adsorbed Si(111) surface

The In-adsorbed Si(111) 4×1 reconstructed surface is known to undergo a phase transition to an 8×2 structure at approximately 130 K. This structural transition accompanies a metal-insulator transition known as the Peierls transition or charge density wave (CDW) transition. We construct a continuous displacement model and discuss the surface electronic states using a tight-binding model based on the first principles calculations. We performed Monte Carlo simulations, estimated the atomic displacement, and calculated the surface electronic properties around the transition temperatures, in terms of the density of states projected into the reciprocal space (RDOS). The results show that the nature of the transition can be understood as the order-disorder transition of an Ising system.

Short Range Order of Au/Si(111)5×2 Surface

固体の表面では表面再構成によりもとの結晶面とは著しく異なる二次元の異方性をもつものが多い。それらの中でも特に大きな異方性をもつ表面として金原子が吸着したシリコン(111)表面の5×2再構成表面系が挙げられる。金原子吸着シリコン(111)5×2再構成表面は,温度と金原子の吸着量のある範囲内で,吸着金原子から成る一次元鎖構造をとることが知られている。この非常に異方的な短距離秩序をもつ表面に対して,二つの異なる一次元模型を組み合わせて適用することによって表面吸着金原子の短距離秩序配列を説明した。まず,一次元鎖方向に関しては,吸着金原子の吸着位置に,あるirregularityを導入した一次元格子ガス模型を設定した。モンテカルロシミュレーションにより,吸着金原子の位置相関関数を計算した結果,STM像から得られた位置相関関数をほぼ完全に再現できた。一次元鎖間方向に関しては,一次元鎖間の位相差を4段階に不連続にした一次元XY模型を設定することで,一次元鎖間の弱い相関を説明できた。