S. Hongo

Adsorption structure and silicide formation of Ba on the Si(001) surface

The behaviour of Ba atoms on the Si(001) surface was investigated by low-energy electron diffraction (LEED). An epitaxial silicide formation was observed for surfaces obtained both by deposition onto a substrate kept at 700 C and by annealing at 600 C after deposition at room temperature. These surfaces show ( 4 8 0 16 ) and ( 4 4 0 8 ) oblique patterns which have a unit cell close to six times and three times, respectively, as large as that of the BaSi 2 (111) surface. In addition to the (2x3 ), (2x1) and (2x4) structures at submonolayer coverage, a c(2x6) pattern was found. The two-fold periodicities of the (2x4) and (2x3) superstructures were determined to be parallel to the dimer direction using a single-domain Si(001)-(2 x 1) substrate.

Adsorption structure of Ba on an Si(001)-(2 × 1) surface

Abstract The behaviour of Ba atoms on a Si(001) surface was investigated by means of Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), metastable-atom de-excitation spectroscopy (MDS) and thermal desorption spectroscopy (TDS). A 2D phase diagram of surface structures as a function of substrate temperature and Ba coverage was obtained. The existence of a saturation coverage of less than 1 ML with a corresponding LEED pattern, of (2 × 3), (2 × 1) and (2 × 4) dependent on a temperature higher than 800°C, was confirmed.

Structure of the K adsorbed Si(001)2 × 1 surface studied by LEED

Abstract The surface structures of K adsorbed Si(001))2 × 1 surfaces have been studied by the dynamical analysis of low-energy electron diffraction (LEED) beam intensity versus electron energy curves (the so-called I - V curves). A reliability factor ( R -factor) analysis has been carried out for three models of the site of the K atoms, that is, a pedestal site model (Levines model), a double layer model, and a cave site model. Although the difference of the numerical value of R is not so large among these models, the double layer model indicates the smallest value within a symmetric dimer model of the topmost Si atoms.

Structure analysis of an alkali metal adsorbed Si(001)(2×1) surface by tensor LEED

Abstract The structures of the alkali metal (K, Cs) adsorbed Si(001)(2 × 1) surface have been studied by tensor LEED. A reliability factor ( R factor) analysis has been carried out for models having different sites for the alkali atoms, that is, a pedestal site model (so called Levines model), a cave site model and a double-layer model. Although the difference between the numerical values of R is small for these models, the smallest R factor is obtained for the double-layer model with a symmetric dimer model for the topmost Si atoms.

UPS study of electronic states of Ba on Si(001) surface

Abstract The electronic states depending on the substrate temperature and the Ba coverage have been investigated by ultraviolet photoelectron spectroscopy (UPS). With the Ba deposition at the room temperature, the surface states of the clean Si(001) decrease and the valence band states of Ba adsorbate appear at 0.4 and 1.4 eV below the Fermilevel(E F ). With the substrate being annealed at 350°C after a few ML deposition, the peaks decrease and a signal due to the formation of barium-silicide appears at 2.9 eV. With the temperature elevated, this signal shifts to 2.7 eV in accordance with the phase transition from BaSi to BaSi2. This signal is removed completely at 800°C by the evaporation of Ba atoms in excess of 1 ML and a featureless broad spectrum is observed. This spectrum keeps up to 1000°C, above which the intensity of the spectrum is weakened. Above 1100°C, the surface states of the clean Si reappear. These features are related to various surface structures.

Domain wall structure of Te/Si(001) surface studied by LEED

Abstract Adsorbed structures of Te on Si(001) surface have been studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). As elevating the temperature after the deposition of Te onto the Si(001) single-domain 1×2 surface by a few monolayers at room temperature, 1×1, 2×1, 1×3 and double-domain 1×2 LEED patterns were observed at about 350°C, 600°C, 680°C and 800°C, respectively. During the phase transitions from 1×1 to 2×1 and from 1×3 to 1×2 clean surface, continuous shifts of diffraction spots were observed. This phenomenon is explained by the formation of the domain walls. We considered a one-dimensional chain of scatterers on the surface which had a statistical distribution of domain length, and calculated the structure factor with a simple kinematic scattering based on the theory proposed by J.E. Houston and R.L. Park. The results of calculated intensity distributions were in good agreement with experiment.

Experimental results of cascade static lens gauge

Abstract A new ionization gauge of the ‘cascade static lens (CSL) gauge’, which has high sensitivity (S) and operates with weak emission current (Ie), was studied. In the gauge, apertured electrodes forming a cascade electrostatic lens system areeinstalled between the cathode and the ion collector, allowing the electrons to oscillate many times between the cathode and the ion collector under the focusing effect of the lenses. Suitable electrode potentials were studied by computer simulation. The experimental value of S = 22.1 Pa−1 (2870 tor−1) with Ie = 4 μA was obtained rather easily, and the linearity was confirmed in the measured region (8 × 10−8 Pa ∼ 1.5 × 10−5 Pa).

New desorption state of D2 from deuterium-terminated Si(100) by potassium adsorption

Abstract Metastable deexcitation spectroscopy (MDS) and thermal desorption spectroscopy (TDS) were used to investigate how potassium adsorption affects deuterium binding to a Si(100) surface. Upon depositing potassium atoms on the deuteride silicon, some of the preadsorbed deuterium atoms bound to the Si-dangling bonds break the bonds to produce K + D − bonds with its D − end toward the vacuum. The new D 2 desorption peak related to the KD bonds was found at 140°C, which was supported by MDS and work function experiments.

LEED I-V curve analysis for the structure of iron films on Si(111) surfaces

Abstract Iron films deposited on Si(111)7×7 surfaces grow layer-by-layer and the structure of iron films of more than half a monolayer ( 1 2 ML) average thickness changes from a 1×1 to a 2×2 superstructure after annealing above 400°C. LEED I-V curves of several beams have been measured, and for a film of 1 ML average thickness, experimental curves are compared with curves obtained by dynamical calculations. Consequently, it is most probable for the 1×1 structure that iron atoms sit in 3-fold hollow sites on a Si substrate which is missing the topmost plane.

Thermal desorption study of potassium from K/deuterated Si(100)2 × 1

Abstract The shift of the low temperature portion of the potassium desorption spectrum for the K/D/Si(100)2 × 1 caused by the deuterium preadsorption was discussed by thermal desorption spectroscopy (TDS) and metastable deexcitation spectroscopy (MDS) data. When the SiD bonds are formed around the K atom, the K(4s) electrons are localized at the K atom. This localization leads to the reduction in the long range dipolar interaction. This explanation is the most plausible for the shift of the low temperature portion of the potassium desorption spectrum.