Hideaki Aizawa

Asymmetric structure of the Si(111)-3×3-Ag surface

The atomic and electronic structures of the Si(111)-E3◊E3-Ag surface are studied by first-principles calculations based on the density functional theory. It is found that a structural model consisting of two inequivalent Ag triangles is energetically more favorable than the well-established honeycomb-chained-triangle (HCT ) model. The new structure should yield an empty-state STM image with a hexagonal-lattice pattern, rather than a honeycomb pattern, which is confirmed by low-temperature STM observations.

First-principles study of CO bonding to Pt(111) : validity of the Blyholder model

Abstract The chemisorption of CO molecules on Pt(111) is studied by first-principles calculations based on the local density functional formalism with a slab model to represent the extended metal surface. We have developed a population analysis scheme which is applicable to calculations with plane wave basis sets. By applying the scheme to CO Pt (111) , the 4σ and 1π orbitals of CO are found to be completely filled, showing that they do not play a role in the bonding of CO to the surface. On the other hand, the calculated populations of the 5σ and 2π orbitals indicate that there is substantial 5σ donation and 2π backdonation, supporting the Blyholder model of CO chemisorption, the validity of which has recently been questioned. These results also suggest that a molecular-orbital based picture such as the Blyholder model is appropriate for describing simply the chemisorption bond, in spite of the fact that the molecular orbitals of CO rehybridize with each other upon adsorption, as has been shown recently by X-ray emission spectroscopy.

First-principles investigation of photo-induced desorption of CO and NO from Pt(111)

Photo-induced desorption of CO and NO from Pt(111) is investigated by means of first-principles electronic structure calculations with the configuration interaction method for small clusters. We propose a mechanism in which the desorption process begins with an electronic excitation to an unoccupied level with some 5σ contribution, and proceeds according to the MGR-like mechanism. The mechanism is consistent with the observed low threshold energy for NO as compared to that for CO, as well as the substrate dependence of photodesorption processes. It is suggested that the Antoniewicz mechanism is unlikely to be operative.

Population analysis study of etching processes at Si(100) surfaces with adsorbed halogens and hydrogens

Abstract Etching processes at X/Si(100) 3×1 surfaces (XBr, Cl, and H) are studied by means of ab initio electronic structure calculations with the help of population analyses performed with a method proposed recently. It is shown that at the halogen-adsorbed surfaces etching is promoted by the following two factors: (1) a weakening of SiSi backbonds resulting from a decrease in their bond charge, and (2) structural strain caused by repulsive interactions between the adsorbates. Both factors are found to be insignificant at the hydrogen-adsorbed surface. Several interesting aspects of the population analysis scheme are also discussed.

Photo-induced desorption through non-adiabatic couplings

A mechanism describing photo-induced desorption triggered by substrate excitation is presented. In this mechanism adsorbate motion is described quantum mechanically and desorption is considered to occur due to energy transfer from the electronic to the nuclear degrees of freedom via non-adiabatic couplings. Considerable insight is gained into experiments on photo-induced desorption of NO and CO from transition metal surfaces.

Fourier Expansion Method for Noncontact Atomic Force Microscopy Image Simulations – Application to Si(111) √3×√3–Ag Surface

A Fourier expansion method is proposed to simulate noncontact atomic force microscopy images. The three-dimensional distribution of the tip-surface interaction force obtained by the first-principles density functional calculations is efficiently used for calculating frequency shifts of the resonant frequency. The two-dimensional periodicity of the surface, which is the basis of this method, can be rigorously described. For a case study of this method, we theoretically simulate noncontact atomic-force microscopy (NC-AFM) images of a Si(111) √3×√3 R 30°–Ag rigid surface with the first-principles density functional calculation. Force spectroscopies and AFM images for different tip heights are calculated.