SiC Pore Surfaces: Surface Studies of 4H-SiC(1-102) and 4H-SiC(-110-2)

The morphology and atomic structure of 4H-SiC(1102) and 4H-SiC(1102) surfaces, i.e. the surfaces found in the triangular channels of porous 4H-SiC, have been investigated using AFM, LEED and AES. After hydrogen etching the surfaces show steps parallel and perpendicular to the caxis, yet drastically different morphologies for the two isomorphic orientations. Both surfaces immediately display a sharp LEED pattern. Together with the presence of oxygen in the AES spectra this indicates the development of an ordered oxide. Both surfaces show an oxygen free, well ordered surface after Si deposition and annealing.

ADSORPTION KINETICS OF POTASSIUM ON SrTiO3(100)

In this paper, we study the kinetics of potassium adsorption on SrTiO 3(100) surface at room temperature. The study took place in UHV using AES, EELS, LEED, TPD, and WF measurements. Potassium grows in two-dimensional islands with maximum coverage of 3.9 × 1014 at/cm2. During adsorption charge transfer from the K -4s to Ti -3d energy level has been observed. No K – O compound has been measured. After heating at 1050 K most of the adsorbed potassium desorbs and the SrTiO 3(100) (1 × 1) LEED pattern reappears. There is not any indication of potassium intercalation into the substrate, either at room or at elevated temperature.

Thin CuInS2 Films Prepared by MOMBE: Interface and Surface Properties

CuInS2 films were prepared on Si(111) by MOMBE using standard MBE Cu and In sources and Ditertbutyldisulfide (TBDS) as an organic sulfur precursor. The films were analyzed in situ by XPS, LEED and UPS. Deposition at 250°C yields chalcopyrite films [1] with admixtures of CuSi2 and CuIn alloys. Deposition at higher temperatures up to 550°C was used to clarify the feasibility of the process. High quality LEED diffraction patterns show epitaxial growth but CuSi2 precipitations are still observed for deposition on Si(111). A buffer layer of indiumsulfide showed no considerable effect on the interface morphology. The obtained LEED pattern are in accordance with the epitaxial relation Si{111}||CuInS2{112}. Even for temperatures as high as 550°C no incorporation of Carbon or residual hydrocarbons in the film or adsorbed at the surface were detected.

AN ORDERED MIXED STRUCTURE FORMED BY RESTRUCTURING TYPE COADSORPTION OF Na AND K ON Ag(001)

Coadsorption of Na and K on Ag(001) at room temperature has been studied by low energy electron diffraction (LEED). A 3 × 3 LEED pattern was observed irrespective of the order of adsorption. For this formation, it is necessary to deposit Na and K atoms with appropriate coverage. We have determined the 3 × 3 structure by a tensor LEED analysis. It is a restructured surface and is very similar to the previously determined 3 × 3 structure formed on Ag(001) by pure Na adsorption. In the coadsorption, Na and K atoms occupy preferable sites selectively, and construct an ordered mixed structure on Ag(001). That is, small Na atoms are located in the missing row sites, while large K atoms sit on the hollow sites of four-Ag-atom islands. The reason for the site selectivity of Na and K atoms in the mixed 3 × 3 structures is discussed.

An ISS Study of Ga-Dimer Arrangement in the GaP(001)-(4 × 2) Surface

A GaP(001) Ga-rich surface produced by ion sputtering followed by annealing exhibited a 4 × 2 LEED pattern with half streaks in the [110] direction. We have studied the structure of this surface by low-energy ion-scattering spectroscopy (ISS) using alkali ions ( Na +) .We have found a unit cell of the 4 × 2 structure consisting of two Ga dimers plus two dimer vacancies from the measured incidence-angle dependence of the scattered-ion intensity in the [Formula: see text] surface azimuth and an atomic separation in the Ga dimer being about 0.27 nm from that in the [110] surface azimuth. Evidence is presented showing the unit structures being arranged irregularly in the [Formula: see text] direction around the twofold positions.

Clustered, Terraced And Mixed Surface Phases Of The Al70Pd21Mn9 Quasicrystal

The five-fold surface of the Al70 Pd21 Mn9 quasicrystal has been studied using STM, LEED and AES. STM images from surfaces which have been sputtered and annealed to 875 K reveal 20-30 Å protrusions that have been identified by others as Mackay-type clusters. Higher-resolution images reveal substructures in these clusters having dimensions 2-3 Å. Longer annealing times at 875 K produced large areas having flat terraces which were imaged with atomic resolution. The LEED pattern from this surface has sharp spots on a low background, and AES indicates that the surface is deficient in Mn relative to the bulk. For surfaces annealed to 1050 K for less than 2 hours, STM images indicate that cluster and terrace phases coexist, and a third phase having aligned arrays of clusters is identified which appears to be intermediate between the cluster and terrace phases.