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Adsorption studies of Ni on MoS2 and O2 on Ni-covered MoS2
A729 Surface Science 164 (1985) 353--366 North-Holland, Amsterdam
353
A D S O R P T I O N S T U D I E S OF Ni ON M o S 2 AND O 2 ON Ni-COVERED MoS 2 C. PAPAGEORGOPOULOS and M. K A M A R A T O S Department of Pl~vstcs. Unicerst(v of loanmna. GR-453 32 loanmna. (;ree~e Received 26 November 1984; accepted for publication 5 August 1985 Deposition of Ni on the basal plane of MoS 2 and the interaction of this system with subsequently adsorbed oxygen have been studied in an UIIV system with LEED, AES, EELS and WF measurements. For substrate temperatures at or below room temperature the deposited Ni forms small islands, which change to 3f) particles on heating. At elevated substrate temperature (450 K), Ni grows to 3D particles from the early stages of its deposition. The Ni adatoms do not interact with the surface S atoms of MoS, as Fe doe's. The Ni particles thus remain clean on MoS 2, which is promising in heterogeneous catalysis. When the MoS 2 -Ni system is exposed to oxygen the latter is adsorbed only on Ni. The interaction of the Ni adsorbate with oxygen is quite similar to that of oxygen with metallic Ni substrates.
Surface Science 164 (1985) 367-392 North-Holland. Amsterdam
367
S T R U C T U R E ANALYSIS OF Si(l 1 I)-7 × 7 R E C O N S T R U C T E D SURFACE BY T R A N S M I S S I O N ELECTRON DIFFRACTION Kunio T A K A Y A N A G I , Yasumasa TANISHIRO, Shigeki TAKAHASHI and Masaetsu T A K A H A S H I Phwtc~' Department, Tokyo Institute of Technology, Oh-okavama, Meguro-ku, Tol, w~. 152 Japan Received 27 May 1985; accepted for publication I August 1985 The atomic structure of the 7 × 2 reconstructed Si(1 ! I ) surface has been analysed b) ultra-high vacuum ( U H V ) transmission electron diffraction (TED). A possible projected structure of the surface is deduced from the intensity distribution in T E D patterns of normal electron incidence and from Patterson and Fourier syntheses of the intensities. A new three-dimensional structure model, the DAS mc',del, is proposed: "['he model consists of 12 adatoms arranged kx:all'~ in the 2 × 2 structure, a stacking fault layer and a layer with a vacancy at the corner and 9 dimers on the sides of each of the two triangular subcells of the 7 × 7 unit cell. '['he silicon layers in one subcell are stacked with the normal sequence, CcAaB ~ adatoms, while those in the other subcell are stacked with a faulted sequence, CcAa/C + adatoms. The model has only 19 dangling bonds, the smallest number among models so far proposed. Previously proposed models are tested quantitatively by the T E D intensity. Advantages and limits of the T | ' D analysis are discussed.
353
A D S O R P T I O N S T U D I E S OF Ni ON M o S 2 AND O 2 ON Ni-COVERED MoS 2 C. PAPAGEORGOPOULOS and M. K A M A R A T O S Department of Pl~vstcs. Unicerst(v of loanmna. GR-453 32 loanmna. (;ree~e Received 26 November 1984; accepted for publication 5 August 1985 Deposition of Ni on the basal plane of MoS 2 and the interaction of this system with subsequently adsorbed oxygen have been studied in an UIIV system with LEED, AES, EELS and WF measurements. For substrate temperatures at or below room temperature the deposited Ni forms small islands, which change to 3f) particles on heating. At elevated substrate temperature (450 K), Ni grows to 3D particles from the early stages of its deposition. The Ni adatoms do not interact with the surface S atoms of MoS, as Fe doe's. The Ni particles thus remain clean on MoS 2, which is promising in heterogeneous catalysis. When the MoS 2 -Ni system is exposed to oxygen the latter is adsorbed only on Ni. The interaction of the Ni adsorbate with oxygen is quite similar to that of oxygen with metallic Ni substrates.
Surface Science 164 (1985) 367-392 North-Holland. Amsterdam
367
S T R U C T U R E ANALYSIS OF Si(l 1 I)-7 × 7 R E C O N S T R U C T E D SURFACE BY T R A N S M I S S I O N ELECTRON DIFFRACTION Kunio T A K A Y A N A G I , Yasumasa TANISHIRO, Shigeki TAKAHASHI and Masaetsu T A K A H A S H I Phwtc~' Department, Tokyo Institute of Technology, Oh-okavama, Meguro-ku, Tol, w~. 152 Japan Received 27 May 1985; accepted for publication I August 1985 The atomic structure of the 7 × 2 reconstructed Si(1 ! I ) surface has been analysed b) ultra-high vacuum ( U H V ) transmission electron diffraction (TED). A possible projected structure of the surface is deduced from the intensity distribution in T E D patterns of normal electron incidence and from Patterson and Fourier syntheses of the intensities. A new three-dimensional structure model, the DAS mc',del, is proposed: "['he model consists of 12 adatoms arranged kx:all'~ in the 2 × 2 structure, a stacking fault layer and a layer with a vacancy at the corner and 9 dimers on the sides of each of the two triangular subcells of the 7 × 7 unit cell. '['he silicon layers in one subcell are stacked with the normal sequence, CcAaB ~ adatoms, while those in the other subcell are stacked with a faulted sequence, CcAa/C + adatoms. The model has only 19 dangling bonds, the smallest number among models so far proposed. Previously proposed models are tested quantitatively by the T E D intensity. Advantages and limits of the T | ' D analysis are discussed.