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RHEED intensity analysis of Si(001) 2 × 1 and 2 × 1-K surface structures
A34 54
Surface Science 242 (1991) 54-58 North-Holland
A study of the Si(111) ~-3 × ~3-Ag surface by transmission X-ray diffraction and X-ray diffraction topography Toshio Takahashi a, Shinichiro Nakatani a Naoko Okamoto a, Tetsuya Ishikawa b and Seishi Kikuta b a Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan b Department of Applied Physics, Faculty of Engineering University of Tokyo Hongo, Bunkyo-ku, Tokyo 113, Japan Received 21 May 1990; accepted for publication 15 June 1990 The adsorption site of Ag atoms with respect to the unreconstructed Si crystal was uniquely determined using transmission X-ray diffraction. The result is consistent with one of the two honeycomb-chained triangle models previously proposed by the authors using reflection X-ray diffraction. Next, the reconstruction of Si was analyzed; an Si trimer layer is about 0.8 ,~ below the Ag layer, and at least two double layers of Si are reconstructed, having the component of the honeycomb arrangement. Finally, the capability of surface X-ray diffraction topography was shown by observing the integral-order spot near the Bragg point.
Surface Science 242 (1991) 59-64 North-Holland
59
Surface structure of C1/Ni(lll) determined by surface EXAFS spectroscopy and soft X-ray standing-wave method M. Funabashi Research Development Corporation of Japan, 5-9.9 Tokodai, Tsukuba, Ibaraki 300-26, Japan
T. Yokoyama, Y. Takata, T. Ohta * Department of Materials Science, Faculty of Science, Hiroshima University, Naka-ku, Hiroshima 730, Japan
Y. Kitajima Photon Factory, National Laboratory for High Energy Physics, Oho, Tsukuba, lbaraki 305, Japan
H. Kuroda Department of Chemistry, Faculty of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan Received 16 May 1990; accepted for publication 4 June 1990 The surface structure of (¢r~ × vr~)R30oCI/Ni(lll) has been examined by the combination of polarization-dependent surface EXAFS spectroscopy and the soft X-ray standing wave (SW) method. The surface EXAFS analysis revealed that chlorine atoms locate at the three-fold hollow site with the CI-Ni bond distance of (2.33 -1-0.02)/~, corresponding to the spacing between CI and surface Ni layers of (1.83 + 0.02) ,~. The SW measurement allowed the determination of the displacement of CI; it is located 1!82 A above the N i ( l l l ) lattice plane. Consequently, surface relaxation is not accompanied by the adsorption of 1/3 of a monolayer (ML) of C1 atoms. The magnitudes of surface relaxation induced by S and CI adsorption on (100), (110) and (111) surfaces are compared and discussed. Surface Science 242 (1991) 65-68 North-Holland
65
RHEED intensity analysis of Si(001)2 × 1 and 2 x 1-K surface structures T. Makita, S. Kohmoto and A. Ichimiya Department of Applied Physics, School of Engineering, Nagoya University, Nagoya 464-01, Japan Received 21 May 1990; accepted for publication 6 June 1990 RHEED intensity rocking curves in the one-bemrn condition, for which the incident beam direction is 22.8 ° off from [110] azimuth, are measured for clean and potassium adsorbed Si(001)2 x 1 surfaces. Surface normal components of atomic positions are determined by analysis with RHEED dynamical calculations for both symmetrical and buckled dimer structures. The results reveal that the calculated curve for the buckled dimer model is in better agreement with the experimental curve than that for the symmetric
A35 one. For the best model the dimer layer is buckled, and the surface normal difference between upper and lower atomic positions of the dimer is 0.6 ,~. The second layer is also buckled and the surface normal difference is 0.2 ,/k. For Si(001)2 × 1-K structure, comparing calculated rocking curves with experimental ones, the double layer model gives better agreement than the single layer one. For the best model the surface normal difference between the upper and lower potassium positions is 1.25 ,~, and the upper potassium sits 2.3 A above the Si dimer array which is contracted 0.2 ~, into the surface normal direction.
Surface Science 242 (1991) 69-72 North-Holland
69
The direct observation of the Ge(001) dimer structure by high resolution UHV transmission electron microscopy M. Mitome and K. Takayanagi Department of Materials Science and Engineering, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 227, Japan Received 24 May 1990; accepted for publication 8 June 1990 The dimer structure of the (001) surfaces of the germanium particles and dynamical rearrangement are observed in real space and in real-time by high resolution UHV electron microscopy. From the computer simulation of the electron microscope images it is found that the dimers are asymmetric and change their dipole directions.
Surface Science 242 (1991) 73-80 North-Holland
73
Short range orders of an adsorbed layer: gold on the S i ( l l l ) 7 × 7 surface S. Takahashi, Y. Tanishiro and K. Takayanagi Tokyo Institute of Technology, Materials Science and Engineering, 4259 Nagatsuda, Midori-ku, Yokahama 227, Japan Received 3 July 1990; accepted for publication 9 August 1990 Ordered phases of 5 × 2, V'3 x ~ and 6 × 6 structures formed by gold deposition on a Si(lll)7 × 7 surface were observed by transmission electron diffraction (TED). Short-range orders of the V~ x v~ phase of low and high coverages are analyzed from diffuse TED intensities. Phasons which displace the adsorption site by a at every translation of 6a are found to be introduced in the V~ x ¢~ structure of the saturation coverage. The phasons, which create 2a correlation between gold clusters, prohibit formation of a completely ordered v/3 × v~ phase.
Surface Science 242 (1991) 81-89 North-Holland
81
REM and TEM studies of 2D A u - C u alloy adsorbates on a Si(111) surface I. Homma, Y. Tanishiro and K. Yagi Physics Department, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152, Japan Received 5 June 1990; accepted for publication 5 July 1990 Structures formed by co-deposition of Au and Cu on Si(lll)7 × 7 surfaces were studied by transmission and reflection electron microscopy (TEM and REM). A two-dimensional alloy adsorbate structure of ¢~ x v:3 was formed from the beginning of simultaneous deposition and by successive deposition of Au and Cu. The observed structure was different from those formed at the initial stage by deposition of individual metals. Dark field images due to reflections from the ¢'3 x ~ structure in TEM and REM showed domain structures, which indicated p3 symmetry of the ~ × v/3 structure instead of p31m.
Surface Science 242 (1991) 54-58 North-Holland
A study of the Si(111) ~-3 × ~3-Ag surface by transmission X-ray diffraction and X-ray diffraction topography Toshio Takahashi a, Shinichiro Nakatani a Naoko Okamoto a, Tetsuya Ishikawa b and Seishi Kikuta b a Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan b Department of Applied Physics, Faculty of Engineering University of Tokyo Hongo, Bunkyo-ku, Tokyo 113, Japan Received 21 May 1990; accepted for publication 15 June 1990 The adsorption site of Ag atoms with respect to the unreconstructed Si crystal was uniquely determined using transmission X-ray diffraction. The result is consistent with one of the two honeycomb-chained triangle models previously proposed by the authors using reflection X-ray diffraction. Next, the reconstruction of Si was analyzed; an Si trimer layer is about 0.8 ,~ below the Ag layer, and at least two double layers of Si are reconstructed, having the component of the honeycomb arrangement. Finally, the capability of surface X-ray diffraction topography was shown by observing the integral-order spot near the Bragg point.
Surface Science 242 (1991) 59-64 North-Holland
59
Surface structure of C1/Ni(lll) determined by surface EXAFS spectroscopy and soft X-ray standing-wave method M. Funabashi Research Development Corporation of Japan, 5-9.9 Tokodai, Tsukuba, Ibaraki 300-26, Japan
T. Yokoyama, Y. Takata, T. Ohta * Department of Materials Science, Faculty of Science, Hiroshima University, Naka-ku, Hiroshima 730, Japan
Y. Kitajima Photon Factory, National Laboratory for High Energy Physics, Oho, Tsukuba, lbaraki 305, Japan
H. Kuroda Department of Chemistry, Faculty of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan Received 16 May 1990; accepted for publication 4 June 1990 The surface structure of (¢r~ × vr~)R30oCI/Ni(lll) has been examined by the combination of polarization-dependent surface EXAFS spectroscopy and the soft X-ray standing wave (SW) method. The surface EXAFS analysis revealed that chlorine atoms locate at the three-fold hollow site with the CI-Ni bond distance of (2.33 -1-0.02)/~, corresponding to the spacing between CI and surface Ni layers of (1.83 + 0.02) ,~. The SW measurement allowed the determination of the displacement of CI; it is located 1!82 A above the N i ( l l l ) lattice plane. Consequently, surface relaxation is not accompanied by the adsorption of 1/3 of a monolayer (ML) of C1 atoms. The magnitudes of surface relaxation induced by S and CI adsorption on (100), (110) and (111) surfaces are compared and discussed. Surface Science 242 (1991) 65-68 North-Holland
65
RHEED intensity analysis of Si(001)2 × 1 and 2 x 1-K surface structures T. Makita, S. Kohmoto and A. Ichimiya Department of Applied Physics, School of Engineering, Nagoya University, Nagoya 464-01, Japan Received 21 May 1990; accepted for publication 6 June 1990 RHEED intensity rocking curves in the one-bemrn condition, for which the incident beam direction is 22.8 ° off from [110] azimuth, are measured for clean and potassium adsorbed Si(001)2 x 1 surfaces. Surface normal components of atomic positions are determined by analysis with RHEED dynamical calculations for both symmetrical and buckled dimer structures. The results reveal that the calculated curve for the buckled dimer model is in better agreement with the experimental curve than that for the symmetric
A35 one. For the best model the dimer layer is buckled, and the surface normal difference between upper and lower atomic positions of the dimer is 0.6 ,~. The second layer is also buckled and the surface normal difference is 0.2 ,/k. For Si(001)2 × 1-K structure, comparing calculated rocking curves with experimental ones, the double layer model gives better agreement than the single layer one. For the best model the surface normal difference between the upper and lower potassium positions is 1.25 ,~, and the upper potassium sits 2.3 A above the Si dimer array which is contracted 0.2 ~, into the surface normal direction.
Surface Science 242 (1991) 69-72 North-Holland
69
The direct observation of the Ge(001) dimer structure by high resolution UHV transmission electron microscopy M. Mitome and K. Takayanagi Department of Materials Science and Engineering, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 227, Japan Received 24 May 1990; accepted for publication 8 June 1990 The dimer structure of the (001) surfaces of the germanium particles and dynamical rearrangement are observed in real space and in real-time by high resolution UHV electron microscopy. From the computer simulation of the electron microscope images it is found that the dimers are asymmetric and change their dipole directions.
Surface Science 242 (1991) 73-80 North-Holland
73
Short range orders of an adsorbed layer: gold on the S i ( l l l ) 7 × 7 surface S. Takahashi, Y. Tanishiro and K. Takayanagi Tokyo Institute of Technology, Materials Science and Engineering, 4259 Nagatsuda, Midori-ku, Yokahama 227, Japan Received 3 July 1990; accepted for publication 9 August 1990 Ordered phases of 5 × 2, V'3 x ~ and 6 × 6 structures formed by gold deposition on a Si(lll)7 × 7 surface were observed by transmission electron diffraction (TED). Short-range orders of the V~ x v~ phase of low and high coverages are analyzed from diffuse TED intensities. Phasons which displace the adsorption site by a at every translation of 6a are found to be introduced in the V~ x ¢~ structure of the saturation coverage. The phasons, which create 2a correlation between gold clusters, prohibit formation of a completely ordered v/3 × v~ phase.
Surface Science 242 (1991) 81-89 North-Holland
81
REM and TEM studies of 2D A u - C u alloy adsorbates on a Si(111) surface I. Homma, Y. Tanishiro and K. Yagi Physics Department, Tokyo Institute of Technology, Oh-okayama, Meguro, Tokyo 152, Japan Received 5 June 1990; accepted for publication 5 July 1990 Structures formed by co-deposition of Au and Cu on Si(lll)7 × 7 surfaces were studied by transmission and reflection electron microscopy (TEM and REM). A two-dimensional alloy adsorbate structure of ¢~ x v:3 was formed from the beginning of simultaneous deposition and by successive deposition of Au and Cu. The observed structure was different from those formed at the initial stage by deposition of individual metals. Dark field images due to reflections from the ¢'3 x ~ structure in TEM and REM showed domain structures, which indicated p3 symmetry of the ~ × v/3 structure instead of p31m.