The structural properties and local contact potential difference of Au on Si(111)-(7×7) surface were studied by self-made ultra-high vacuum non-contact Kelvin probe force microscope. Although scanning tunneling microscopy has been widely used to study metal adsorbed semiconductor surfaces on the atomic scale, the tunnel current measured by scanning tunneling microscopy is easy to lead to accidental switching of charge states in the measurement process, and it is only limited to the observation of metal and semiconductor surfaces. Kelvin probe force microscope allows us to directly measure the charges at different positions of various flat surfaces by local contact potential difference at the atomic scale, which has become a more convenient and accurate means of charge characterization. In this paper, the topography and local contact potential difference atomic scale of Au adsorbed Si(111)-(7×7) surface were measured by Kelvin probe force microscope at room temperature, and the corresponding adsorption model and first principle calculation were established. The differential charge density distribution of the stable adsorption position of Au/Si(111)-(7×7) was obtained, and the local contact potential difference relationship of the stable adsorption position of Au on Si surface was given, The mechanism of charge transfer between Au atom and Si(111)-(7×7) surface during adsorption was analyzed. The experimental results show that at room temperature, single Au atom will form triangular delocalized adsorption state in the half unit cells of Si(111)-(7×7). The delocalized adsorption state are due to the moving speed of a single Au atom in the HUC is faster than the scanning speed of Kelvin probe force microscope, and the local contact potential difference measurement of Au/Si(111)-(7×7) adsorbed surface can effectively identify Au and Si atoms. Obviously, this research is of great significance to promote the development of surface charge precision measurement, and is expected to provide some insights into the charge properties of metal adsorbed semiconductor surfaces.

Magnetic properties of several potential rocksalt half-metallic ferromagnets based on the first-principles calculations *Liu Jun( ) a) † , Zhan Rui( ) b) , Li Li( ) a) , and Dong Hui-Ning( ) a)

The possible high pressure modifications of Lithium Iodate (LiIO3) were surveyed in the high pressure and high temperature ranges up to 40 kbar and 750℃. Two high pressure modifications have been observed. The first is found in the range of 1.5-4.9 kbars and 310-450℃, while another appears in the pressure range above 15 kbars. The phase boundries were determined by DTA and quenching method. The diagram published abroad in 1969 have been corrected and the stability of each phase at high pressures and high temperatures has been discussed.

No abstract

The geometrical structures of Cd0.75TM0.25Se (TM = Ti, V, Cr and Mn) are optimized, and then their electric and magnetic properties are investigated by performing first-principles calculations within the generalized gradient approximation for the exchange-correlation function based on density functional theory. Cd0.75TM0.25Se (TM = Ti and V) are found to have high spin-polarization near 100% at the Fermi level. Cd0.75TM0.25Se (TM = Cr and Mn) are half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely +100%. The supercell magnetic moments of Cd0.75Cr0.25Se and Cd0.75Mn0.25Se are 4.00 and 5.00 μB, which arise mainly from Cr-ions and Mn-ions, respectively. The half-metallicity of Cd0.75Cr0.25Se is more stable than that of Cd0.75Mn0.25Se. The electronic structures of Cr-ions and Mn-ions are Cr e2g↑t22g↑ and Mn e2g↑t32g↑, respectively.