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FI-STM study of alkali metal adsorption on Si surfaces
A169 Surface Science 246 (1991) 177-182 North-Holland
177
A FIM investigation of high temperature superconducting Bi 2(Sr, Ca) 3Cu 2Oy D.M. Ren a, W. Liu b, B.Y. Hu b, G.E. Zhou
a
and J.H. Qin a
" Center of Fundamental Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China b Physics Department, Huazhong Normal University, Wuhan, Hubei 430070, People's Republic of China Received 31 July 1990; accepted for publication 7 September 1990 By using FIM, high-transition-temperature superconducting Bi2(Sr, Ca)3Cu2Oy has been examined with H 2 and Ar imaging gases. Two kinds of F1M images, lines and spots, have been observed and analyzed. Both patterns convincingly show the lamellate structure of the specimens. The periodicity of the FIM image patterns is consistent with the proposed models, and some new patterns are observed and discussed.
Surface Science 246 (1991) 183-188 North-Holland
183
Electronic properties of high-T~ superconductors below and above the Fermi energy N. Ernst, W.A. Schmidt, G. Bozdech, M. Naschitzki Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14,'-1000Berlin 33, Germany
and A.J. Melmed Custom Probes Unlimited, Box 3938, Gaithersburg, MD 20878, USA Received 30 July 1990; accepted for publication 27 August 1990 Successful attempts to establish quantum-mechanical transparency for tunneling electrons in YBaCuO and BiSrCaCuO surfaces are reported. Depending on surface pretreatments, field electron and field ion energy distributions were initially shifted by several electron volts, referenced to the Fermi level, E F, of the metal support. This behavior is probably caused by a voltage drop in a dielectric layer at the surface. With the polarity for field electron emission, an "activation" of this layer towards metallic properties was observed. Electron and ion energy distributions measured after activation displayed sharp cut-offs at E F, in agreement with recent photoemission and inverse photoemission results. Metallic-like (possibly superconducting) surfaces were created through electric-field induced " t e a r - o f f ' of a collection of surface atomic layers. Different electronic densities of states above E F appear to be responsible for peak structures found in the ion energy distributions from BiCaSrCuO specimens.
Surface Science 246 (1991) 189-194 North-Holland
189
FI-STM study of alkali metal adsorption on Si surfaces T. Hashizume a, y. Hasegawa b, I. Sumita a,l and T. Sakurai
a
" Institute for Materials Research (IMR), Tohoku University, Sendal 980, Japan h Institute for Solid State Physics (ISSP), The University of Tokyo, Tokyo 106, Japan Received 31 July 1990; accepted for publication 12 September 1990 Alkali metal ( C s / K ) adsorption on the Si(lll)7 x 7 and Si(100)2 x 1 surfaces was investigated with the FI-STM. At the initial coverage on the Si(111 )7 × 7 surface, Cs(K) atoms adsorb at the on-top site of the center adatoms and are almost completely ionized. When heated at 3 0 0 ° C , a new 1 ~< 3 phase with misfit defects is formed. On the Si(100)2 × 1 surface, Cs atoms occupy the off-centered valley bridge site at the initial coverage. These results, together with L i / K adsorption, can be well understood based on the strong interaction between the directional Si dangling bonds and active alkali metal atoms.
177
A FIM investigation of high temperature superconducting Bi 2(Sr, Ca) 3Cu 2Oy D.M. Ren a, W. Liu b, B.Y. Hu b, G.E. Zhou
a
and J.H. Qin a
" Center of Fundamental Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China b Physics Department, Huazhong Normal University, Wuhan, Hubei 430070, People's Republic of China Received 31 July 1990; accepted for publication 7 September 1990 By using FIM, high-transition-temperature superconducting Bi2(Sr, Ca)3Cu2Oy has been examined with H 2 and Ar imaging gases. Two kinds of F1M images, lines and spots, have been observed and analyzed. Both patterns convincingly show the lamellate structure of the specimens. The periodicity of the FIM image patterns is consistent with the proposed models, and some new patterns are observed and discussed.
Surface Science 246 (1991) 183-188 North-Holland
183
Electronic properties of high-T~ superconductors below and above the Fermi energy N. Ernst, W.A. Schmidt, G. Bozdech, M. Naschitzki Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14,'-1000Berlin 33, Germany
and A.J. Melmed Custom Probes Unlimited, Box 3938, Gaithersburg, MD 20878, USA Received 30 July 1990; accepted for publication 27 August 1990 Successful attempts to establish quantum-mechanical transparency for tunneling electrons in YBaCuO and BiSrCaCuO surfaces are reported. Depending on surface pretreatments, field electron and field ion energy distributions were initially shifted by several electron volts, referenced to the Fermi level, E F, of the metal support. This behavior is probably caused by a voltage drop in a dielectric layer at the surface. With the polarity for field electron emission, an "activation" of this layer towards metallic properties was observed. Electron and ion energy distributions measured after activation displayed sharp cut-offs at E F, in agreement with recent photoemission and inverse photoemission results. Metallic-like (possibly superconducting) surfaces were created through electric-field induced " t e a r - o f f ' of a collection of surface atomic layers. Different electronic densities of states above E F appear to be responsible for peak structures found in the ion energy distributions from BiCaSrCuO specimens.
Surface Science 246 (1991) 189-194 North-Holland
189
FI-STM study of alkali metal adsorption on Si surfaces T. Hashizume a, y. Hasegawa b, I. Sumita a,l and T. Sakurai
a
" Institute for Materials Research (IMR), Tohoku University, Sendal 980, Japan h Institute for Solid State Physics (ISSP), The University of Tokyo, Tokyo 106, Japan Received 31 July 1990; accepted for publication 12 September 1990 Alkali metal ( C s / K ) adsorption on the Si(lll)7 x 7 and Si(100)2 x 1 surfaces was investigated with the FI-STM. At the initial coverage on the Si(111 )7 × 7 surface, Cs(K) atoms adsorb at the on-top site of the center adatoms and are almost completely ionized. When heated at 3 0 0 ° C , a new 1 ~< 3 phase with misfit defects is formed. On the Si(100)2 × 1 surface, Cs atoms occupy the off-centered valley bridge site at the initial coverage. These results, together with L i / K adsorption, can be well understood based on the strong interaction between the directional Si dangling bonds and active alkali metal atoms.