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Copper intercalation in 1TTaS2
A344 Surface Science 251/252 (1991) 561-567 North-Holland
The surface structure of a c(2 × 2) potassium overlayer on Co{
10i0}
C.J. Barnes, P. Hu, M. Lindroos 1 and D.A. King Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 IEW, UK Received 1 October 1990; accepted for publication 2t December 1990 The surface structure of the clean Co(1010} surface and a c(2 × 2) potassium overlayer have been determined by quantitative low energy electron diffraction. The Co{10i0} sample has been shown to be laterally unreconstructed with the surface being uniquely terminated by an outermost closely packed double layer (dzl2 = 0.68 ~,). A damped oscillatory relaxation of the outermost three atomic layers occurs, with relaxations A dz12 = - 6.5 _+ 2% and A dz23 = + 1.0 _+ 2%. The c(2 x 2) overlayer formed at a coverage of 0.5 ML was subjected to a full I - V analysis. A range of adsorption sites were tested including fourfold hollow, on-top, and both long and short bridge sites in combination with both "long" and "short', cobalt interlayer terminations. A clear preference was found for adsorption in the maximal coordination fourfold hollow site. No switching of surface termination occurs. The potassium adatoms reside in the [1210] surface channels directly above second layer cobalt atoms with a potassium to outermost cobalt interlayer separation of 2.44 _+ 0.05 ~.. Potassium-cobalt bond lengths of 3.40 +_ 0.05 and 3.12 + 0.05 A between the four (one) outermost (second) layer nearest-neighbour substrate atoms suggests a potassium effective radius of 1.87 + 0.05 A, somewhat smaller than the Pauling covalent radius and considerably larger than the ionic radius (1.38 A). The alkali-surface bonding is thus predominantly " c o v a l e n t " / " metallic".
568
Surface Science 251/252 (1991) 568-572 North-Holland
LEED investigation and analysis of P b / S i ( l l l ) Timothy N. Doust and Steven P. Tear Department of Physics, University of York, Heslington, York YOI 5DD, UK Received 1 October 1990; accepted for publication 16 December 1990 The adsorption process of Pb onto clean Si(111)-7 × 7 substrates over a wide range of deposition doses and deposition/annealing temperature has been studied using LEED intensity (I(V)) spectra. Two ~/3 x ~/3-R30 ° phases have been observed. For fixed substrate temperature only one of these phases is present independent of the adsorbed dose. There is an irreversible phase change between the two surfaces at - 350 o C. Using Tensor LEED the high temperature phase has been analysed and adsorption shown to I occur at the T4 site for this phase with a saturation coverage of ~ ML.
Surface Science 251/252 (1991) 573-578 North-Holland
573
Low temperature growth mechanism of cobalt on Pt(ll0)(1 × 2) J. Fusy, M. Alnot, H. Abouelaziz and J.J. Ehrhardt CNRS, Laboratoire Maurice Letort, Route de Vandoeuvre, F-54600 Villers les Nancy, France Received 1 October 1990; accepted for publication 24 November 1990 Cobalt deposition on Pt(ll0X1 x 2) at 100 K has been studied by photoemission of adsorbed xenon, work function measurements, Auger electron spectroscopy and LEED. Since the AES peak to peak heights for Pt as a function of the cobalt exposure can be fitted with a Beer-Lambert attenuation taw, it is believed that the growth of the first layers proceeds through a pseudo layer by layer mechanism. This gives a calibration for cobalt fluxes. The work function passes through a minimum at the completion of the monolayer. Photoemission of adsorbed xenon reveals mixed adsorption sites in the range of a quarter to half of a monolayer of cobalt that could be associated with the filling of the valleys of the Pt(ll0)(1 x 2) by cobalt atoms. The tack of any LEED superstructure whatever the coverage, as well as the large width of the Xe 5p peaks are consistent with the formation of a rather disordered deposit.
The surface structure of a c(2 × 2) potassium overlayer on Co{
10i0}
C.J. Barnes, P. Hu, M. Lindroos 1 and D.A. King Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 IEW, UK Received 1 October 1990; accepted for publication 2t December 1990 The surface structure of the clean Co(1010} surface and a c(2 × 2) potassium overlayer have been determined by quantitative low energy electron diffraction. The Co{10i0} sample has been shown to be laterally unreconstructed with the surface being uniquely terminated by an outermost closely packed double layer (dzl2 = 0.68 ~,). A damped oscillatory relaxation of the outermost three atomic layers occurs, with relaxations A dz12 = - 6.5 _+ 2% and A dz23 = + 1.0 _+ 2%. The c(2 x 2) overlayer formed at a coverage of 0.5 ML was subjected to a full I - V analysis. A range of adsorption sites were tested including fourfold hollow, on-top, and both long and short bridge sites in combination with both "long" and "short', cobalt interlayer terminations. A clear preference was found for adsorption in the maximal coordination fourfold hollow site. No switching of surface termination occurs. The potassium adatoms reside in the [1210] surface channels directly above second layer cobalt atoms with a potassium to outermost cobalt interlayer separation of 2.44 _+ 0.05 ~.. Potassium-cobalt bond lengths of 3.40 +_ 0.05 and 3.12 + 0.05 A between the four (one) outermost (second) layer nearest-neighbour substrate atoms suggests a potassium effective radius of 1.87 + 0.05 A, somewhat smaller than the Pauling covalent radius and considerably larger than the ionic radius (1.38 A). The alkali-surface bonding is thus predominantly " c o v a l e n t " / " metallic".
568
Surface Science 251/252 (1991) 568-572 North-Holland
LEED investigation and analysis of P b / S i ( l l l ) Timothy N. Doust and Steven P. Tear Department of Physics, University of York, Heslington, York YOI 5DD, UK Received 1 October 1990; accepted for publication 16 December 1990 The adsorption process of Pb onto clean Si(111)-7 × 7 substrates over a wide range of deposition doses and deposition/annealing temperature has been studied using LEED intensity (I(V)) spectra. Two ~/3 x ~/3-R30 ° phases have been observed. For fixed substrate temperature only one of these phases is present independent of the adsorbed dose. There is an irreversible phase change between the two surfaces at - 350 o C. Using Tensor LEED the high temperature phase has been analysed and adsorption shown to I occur at the T4 site for this phase with a saturation coverage of ~ ML.
Surface Science 251/252 (1991) 573-578 North-Holland
573
Low temperature growth mechanism of cobalt on Pt(ll0)(1 × 2) J. Fusy, M. Alnot, H. Abouelaziz and J.J. Ehrhardt CNRS, Laboratoire Maurice Letort, Route de Vandoeuvre, F-54600 Villers les Nancy, France Received 1 October 1990; accepted for publication 24 November 1990 Cobalt deposition on Pt(ll0X1 x 2) at 100 K has been studied by photoemission of adsorbed xenon, work function measurements, Auger electron spectroscopy and LEED. Since the AES peak to peak heights for Pt as a function of the cobalt exposure can be fitted with a Beer-Lambert attenuation taw, it is believed that the growth of the first layers proceeds through a pseudo layer by layer mechanism. This gives a calibration for cobalt fluxes. The work function passes through a minimum at the completion of the monolayer. Photoemission of adsorbed xenon reveals mixed adsorption sites in the range of a quarter to half of a monolayer of cobalt that could be associated with the filling of the valleys of the Pt(ll0)(1 x 2) by cobalt atoms. The tack of any LEED superstructure whatever the coverage, as well as the large width of the Xe 5p peaks are consistent with the formation of a rather disordered deposit.