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The surface structure of V(100)
Al49 Surface Science 116(1982) 66-84 North-Holland Publishing Company
66
THE
SURF’ACJZ STRUCTURE
V. JENSEN, J.N. ANDERSEN,
OF V(100)
H.B. NIELSEN and D.L. ADAMS
Insrittmte of Physics, University of Aorhur, DK-8ooO Aorhw C, Denmark Received 24 November 198I The structure of the clean V( 100)-( 1 X 1) surface is determined, based on an r-factor comparison of experimental LEJZDintensity-energy spectra with the results of multiple-scattering model calculations. Mkimiaation of the r-factor with respect to the calculational variables leads to optin$m values of the first and second interlayer spacings of d, = 1.41rtO.01 A and d2 = 1.53* 0.01 pi, corresponding respectively to a contraction of 7% and an expansion of I % with respect to the bt# value of da = I .5 141 A. Preliminary studies of the adsorption of 0, and CO confirm that the V( 100)- (5 X I) structure observed during the process of cleaning the crystal is not characteristic of the clean surface, as suggested recently by Davies and Lambert (Surface Science 107 (1981) 391), but rather is associated with the presence of a significant concentration of oxygen in the surface region.
85
Surface Science I I6 (1982) 85-103 North*Holland Publishing Company EVIDENCE FOR THE STRUCTURES FROM
FORMATION OF STABLE C, AND C, UNSATURATED
ALKYLIDYNE HYDROCARBONS
ADSORBED
I’t(lll)
SURFACE
ON THE
R.J. kOESTNER, G.A. SOMORJAI
SINGLE
CRYSTAL
J.C. FROST **, P.C. STAIR***,
*
M.A. VAN HOVE and
Materials ond Molecular Research Division, Lawrence Berkelqv L.abvrototy Chemistry, Universiry of California, Berkeley, Cali/ornia 94720, USA
and Deportment
of
Received 14 October I98 1f accepted for publication 22 December 198I
C, and C, hydrocarbon (methylacetylene, propylene, and the 2-butenes) adsorption on the Pt( 1I I) face was studied by observing the LAZEDpatterns that formed and by measuring the intensity versus voltage spectra for each structure. Two phases exist for each of these molecules adsorb@ on the Pt( 1I I) surface. At low temperatures, the unsaturated C-C group forms a di-a bond to two Pt atoms. Upon warming to about room temperature, and in the presence of hydrogen for the’alkynes, a conversion takes place to an alkylidyne species that is bonded to three Pt atoms and has its C-C bond nearest to the metal substrate oriented perpendicularly to the surface. The butylidyne species is shown to order its ethyl group into an (8 X 8) or (26 X 2fi)R30” superlattice when the hydrocarbon exposure is increased; this ordering is probably a natural consequence of the steric hindrance among neighboring ethyl groups as the hydrocarbon coverage ?&eases slightly with larger exposures.
66
THE
SURF’ACJZ STRUCTURE
V. JENSEN, J.N. ANDERSEN,
OF V(100)
H.B. NIELSEN and D.L. ADAMS
Insrittmte of Physics, University of Aorhur, DK-8ooO Aorhw C, Denmark Received 24 November 198I The structure of the clean V( 100)-( 1 X 1) surface is determined, based on an r-factor comparison of experimental LEJZDintensity-energy spectra with the results of multiple-scattering model calculations. Mkimiaation of the r-factor with respect to the calculational variables leads to optin$m values of the first and second interlayer spacings of d, = 1.41rtO.01 A and d2 = 1.53* 0.01 pi, corresponding respectively to a contraction of 7% and an expansion of I % with respect to the bt# value of da = I .5 141 A. Preliminary studies of the adsorption of 0, and CO confirm that the V( 100)- (5 X I) structure observed during the process of cleaning the crystal is not characteristic of the clean surface, as suggested recently by Davies and Lambert (Surface Science 107 (1981) 391), but rather is associated with the presence of a significant concentration of oxygen in the surface region.
85
Surface Science I I6 (1982) 85-103 North*Holland Publishing Company EVIDENCE FOR THE STRUCTURES FROM
FORMATION OF STABLE C, AND C, UNSATURATED
ALKYLIDYNE HYDROCARBONS
ADSORBED
I’t(lll)
SURFACE
ON THE
R.J. kOESTNER, G.A. SOMORJAI
SINGLE
CRYSTAL
J.C. FROST **, P.C. STAIR***,
*
M.A. VAN HOVE and
Materials ond Molecular Research Division, Lawrence Berkelqv L.abvrototy Chemistry, Universiry of California, Berkeley, Cali/ornia 94720, USA
and Deportment
of
Received 14 October I98 1f accepted for publication 22 December 198I
C, and C, hydrocarbon (methylacetylene, propylene, and the 2-butenes) adsorption on the Pt( 1I I) face was studied by observing the LAZEDpatterns that formed and by measuring the intensity versus voltage spectra for each structure. Two phases exist for each of these molecules adsorb@ on the Pt( 1I I) surface. At low temperatures, the unsaturated C-C group forms a di-a bond to two Pt atoms. Upon warming to about room temperature, and in the presence of hydrogen for the’alkynes, a conversion takes place to an alkylidyne species that is bonded to three Pt atoms and has its C-C bond nearest to the metal substrate oriented perpendicularly to the surface. The butylidyne species is shown to order its ethyl group into an (8 X 8) or (26 X 2fi)R30” superlattice when the hydrocarbon exposure is increased; this ordering is probably a natural consequence of the steric hindrance among neighboring ethyl groups as the hydrocarbon coverage ?&eases slightly with larger exposures.