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Structures of small hydrocarbons adsorbed on Si(001) and Si terminated ß-SiC(001)
A7 Surface Science 276 (1992) 156-165 North-Holland
Room-temperature adsorption of thiophene and related five-membered cyclic olefins on Si(111)7 x 7 by thermal desorption spectrometry C.D. MacPherson, D.O. Hu and K.T. Leung * Department of Chemistry, The University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 Received 24 February 1992; accepted for publication 28 May 1992 The room-temperature adsorption of a series of five-membered cyclic olefins including thiophene, furan, cyclopentadiene and cyclopentene on clean and modified Si(111)7 x 7 surfaces has been studied using thermal desorption spectrometry. In particular, two molecular desorption states were found for thiophene and furan while three states were observed for cyclopentadiene and cyclopentene on the clean 7 x 7 surface. In addition to molecular desorption, there was also evidence of a surface dehydrogenation of cyclopentene to cyclopentadiene. It was found that the adsorption states involved the carbon-carbon double bond(s) and, in the case of thiophene and furan, the lone-pair electrons of the hetero-atoms as well. Possible bonding geometries for these adsorption states were proposed. Post-exposure of molecular oxygen was found to have the effect of reducing molecular desorption of pre-adsorbed furan but not pre-adsorbed thiophene. The present work further demonstrated the "unexpected" surface reactivity of Si(111)7 x 7 towards (hetero-)cyclic olefins.
Surface Science 276 (1992) 166-173 North-Holland
Freezing of the 2 x 1 structure at commensurate Ag(100)-Si(100) interface Y. Kimura and K. Takayanagi Department of Materials Science and Engineering, Interdisc~olinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 227, Japan Received 20 December 1991; accepted for publication 9 June 1992 The growth process of Ag on the Si(100)2 x 1 surface is observed in situ by high-resolution reflection electron microscopy (HR-REM). A silver layer covers the Si(100) surface entirely at 1.5 ML (1 ML = 6.78 x 1014 atoms/one). Above 1.5 ML deposition, two-dimensional Ag islands are grown on the Ag layer of 1.5 ML at room temperature, while no islands are nucleated and grown on the layer at 480"C. Moir~ fringes appeared at the Ag islands seen in the HR-REM images and RHEED patterns show that the Ag islands after 3 ML deposition form a film with the (100) orientation and their (011) lattice planes are strained by 0.7% to be commensurate with the (011) Si lattice. The 2 x 1 structures of the Si(100) substrate are frozen at the Ag-Si interface, since the bright and dark contrast of the 2 x 1 domains of the clean surface is maintained.
Surface Science 276 (1992) 174-183 North-Holland
Structures of small hydrocarbons adsorbed on Si(001) and Si terminated/3-SIC(001) B.I. Craig Surveillance Research Laboratory, Defence Science and Technology Organisation, P.O. Box 1500, Salisbury, SA 5108, Australia
and
A8
P.V. Smith Department of Physics, University of Newcastle, Shortland, NSW 2308, Australia Received 13 March 1992; accepted for publication 5 June 1992 In this paper a theoretical examination of the adsorption of hydrocarbons atop Si(001) and silicon terminated /3-SIC(001) is presented. In each case the addition of a hydrocarbon species on top of each silicon dimer of the originally clean (2 × 1) silicon terminated substrate is examined. Both C2H 2 and C2H 4 species are considered. The total energies of the various potential candidate structures are determined to find the preferred structure. Each structure is obtained by varying the atomic positions in the first four layers of the appropriate unit cell to obtain the minimum total energy configuration for each proposed structure. The resulting structures are then compared to see whether one particular structure is strongly preferred or whether more than one structure may coexist. The results for the two substrates are compared and show that a c(2 × 2) arrangement of carbon dimers is strongly preferred for the SIC(001) substrate. However this structure is not determined for the Si(001) substrate, where the bridging of adjacent silicon atoms by carbon pairs is found to be more energetically favourable.
Surface Science 276 (1992) 184-199 North-Holland
Adsorption and thermal decomposition of N 2H4 and CH3N2H3 on Si(111)7 x 7 Y. Bu, D.W. Shinn and M.C. Lin Department of Chemistry, Emory University, Atlanta, GA 30322, USA Received 3 February 1992; accepted for publication 8 June 1992 The adsorption and thermal decomposition of N2H 4 and CHaN2H 3 on Si(111)7 × 7 were investigated using XPS, UPS and HREELS in the 120-1350 K surface temperature range. Both molecules were partially dissociated into N2H x or CH3N2H x (x = 2, 3) species with the N - N bond parallel or nearly parallel to the surface as they adsorbed on the surface at 120 K, especially at lower dosages (e.g., < 0.2 L) and more so for N2H 4 than CHaN2H 3. This was evidenced by the appearance of the Si-H vibration at 255 meV in the HREEL spectra and by the relatively larger FWHMs of the Nls XPS and the n +, n - molecular UPS peaks. When a ~ 0.4 L N2H 4 or CH3N2H 3 dosed sample was annealed to ~ 500 K, significant desorption of the molecules occurred as well as further dissociation of the N - H bonds. Above ~ 600 K the N - N bond began to break for both molecules. At ~ 730 K, the C-N bond dissociated to form CH x on the surface in the case of CH3N2H 3. Further annealing of the sample caused complete cracking of the N - H and C - H bonds until Si3N 4 or a mixture of Si-nitride and Si-carbide were formed for N2H 4 or CH3N2H 3, respectively.
Surface Science 276 (1992) 200-204 North-Holland
Carrier excitation by hyperthermal Xe collisions at a Si(lll):As surface J.W.P. Hsu *, C.C. Bahr, A. vom Felde t, D.R. Miller 2 and M.J. Cardillo AT& T Bell Laboratories, 600 Mountain Avenue, Murray Hill, NJ 97974, USA Received 9 April 1992; accepted for publication 15 June 1992 We measure the absolute yield of carrier excitation due to the collision of hyperthermal Xe atoms with As covered Si(lll) surfaces. The carrier lifetime of the samples was determined separately through photoconductivity experiments. We find the carrier excitation due to Xe atoms in the energy range of ~ 2-1t eV to be qualitatively consistent with a local hot spot model, i.e., the carrier excitation results from a thermal equilibration to a very high transient temperature of the few atoms near the collision site. We also discuss the implications of stronger atom-substrate interaction potential by comparing preliminary results of hyperthermal I atoms to Xe.
Room-temperature adsorption of thiophene and related five-membered cyclic olefins on Si(111)7 x 7 by thermal desorption spectrometry C.D. MacPherson, D.O. Hu and K.T. Leung * Department of Chemistry, The University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 Received 24 February 1992; accepted for publication 28 May 1992 The room-temperature adsorption of a series of five-membered cyclic olefins including thiophene, furan, cyclopentadiene and cyclopentene on clean and modified Si(111)7 x 7 surfaces has been studied using thermal desorption spectrometry. In particular, two molecular desorption states were found for thiophene and furan while three states were observed for cyclopentadiene and cyclopentene on the clean 7 x 7 surface. In addition to molecular desorption, there was also evidence of a surface dehydrogenation of cyclopentene to cyclopentadiene. It was found that the adsorption states involved the carbon-carbon double bond(s) and, in the case of thiophene and furan, the lone-pair electrons of the hetero-atoms as well. Possible bonding geometries for these adsorption states were proposed. Post-exposure of molecular oxygen was found to have the effect of reducing molecular desorption of pre-adsorbed furan but not pre-adsorbed thiophene. The present work further demonstrated the "unexpected" surface reactivity of Si(111)7 x 7 towards (hetero-)cyclic olefins.
Surface Science 276 (1992) 166-173 North-Holland
Freezing of the 2 x 1 structure at commensurate Ag(100)-Si(100) interface Y. Kimura and K. Takayanagi Department of Materials Science and Engineering, Interdisc~olinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 227, Japan Received 20 December 1991; accepted for publication 9 June 1992 The growth process of Ag on the Si(100)2 x 1 surface is observed in situ by high-resolution reflection electron microscopy (HR-REM). A silver layer covers the Si(100) surface entirely at 1.5 ML (1 ML = 6.78 x 1014 atoms/one). Above 1.5 ML deposition, two-dimensional Ag islands are grown on the Ag layer of 1.5 ML at room temperature, while no islands are nucleated and grown on the layer at 480"C. Moir~ fringes appeared at the Ag islands seen in the HR-REM images and RHEED patterns show that the Ag islands after 3 ML deposition form a film with the (100) orientation and their (011) lattice planes are strained by 0.7% to be commensurate with the (011) Si lattice. The 2 x 1 structures of the Si(100) substrate are frozen at the Ag-Si interface, since the bright and dark contrast of the 2 x 1 domains of the clean surface is maintained.
Surface Science 276 (1992) 174-183 North-Holland
Structures of small hydrocarbons adsorbed on Si(001) and Si terminated/3-SIC(001) B.I. Craig Surveillance Research Laboratory, Defence Science and Technology Organisation, P.O. Box 1500, Salisbury, SA 5108, Australia
and
A8
P.V. Smith Department of Physics, University of Newcastle, Shortland, NSW 2308, Australia Received 13 March 1992; accepted for publication 5 June 1992 In this paper a theoretical examination of the adsorption of hydrocarbons atop Si(001) and silicon terminated /3-SIC(001) is presented. In each case the addition of a hydrocarbon species on top of each silicon dimer of the originally clean (2 × 1) silicon terminated substrate is examined. Both C2H 2 and C2H 4 species are considered. The total energies of the various potential candidate structures are determined to find the preferred structure. Each structure is obtained by varying the atomic positions in the first four layers of the appropriate unit cell to obtain the minimum total energy configuration for each proposed structure. The resulting structures are then compared to see whether one particular structure is strongly preferred or whether more than one structure may coexist. The results for the two substrates are compared and show that a c(2 × 2) arrangement of carbon dimers is strongly preferred for the SIC(001) substrate. However this structure is not determined for the Si(001) substrate, where the bridging of adjacent silicon atoms by carbon pairs is found to be more energetically favourable.
Surface Science 276 (1992) 184-199 North-Holland
Adsorption and thermal decomposition of N 2H4 and CH3N2H3 on Si(111)7 x 7 Y. Bu, D.W. Shinn and M.C. Lin Department of Chemistry, Emory University, Atlanta, GA 30322, USA Received 3 February 1992; accepted for publication 8 June 1992 The adsorption and thermal decomposition of N2H 4 and CHaN2H 3 on Si(111)7 × 7 were investigated using XPS, UPS and HREELS in the 120-1350 K surface temperature range. Both molecules were partially dissociated into N2H x or CH3N2H x (x = 2, 3) species with the N - N bond parallel or nearly parallel to the surface as they adsorbed on the surface at 120 K, especially at lower dosages (e.g., < 0.2 L) and more so for N2H 4 than CHaN2H 3. This was evidenced by the appearance of the Si-H vibration at 255 meV in the HREEL spectra and by the relatively larger FWHMs of the Nls XPS and the n +, n - molecular UPS peaks. When a ~ 0.4 L N2H 4 or CH3N2H 3 dosed sample was annealed to ~ 500 K, significant desorption of the molecules occurred as well as further dissociation of the N - H bonds. Above ~ 600 K the N - N bond began to break for both molecules. At ~ 730 K, the C-N bond dissociated to form CH x on the surface in the case of CH3N2H 3. Further annealing of the sample caused complete cracking of the N - H and C - H bonds until Si3N 4 or a mixture of Si-nitride and Si-carbide were formed for N2H 4 or CH3N2H 3, respectively.
Surface Science 276 (1992) 200-204 North-Holland
Carrier excitation by hyperthermal Xe collisions at a Si(lll):As surface J.W.P. Hsu *, C.C. Bahr, A. vom Felde t, D.R. Miller 2 and M.J. Cardillo AT& T Bell Laboratories, 600 Mountain Avenue, Murray Hill, NJ 97974, USA Received 9 April 1992; accepted for publication 15 June 1992 We measure the absolute yield of carrier excitation due to the collision of hyperthermal Xe atoms with As covered Si(lll) surfaces. The carrier lifetime of the samples was determined separately through photoconductivity experiments. We find the carrier excitation due to Xe atoms in the energy range of ~ 2-1t eV to be qualitatively consistent with a local hot spot model, i.e., the carrier excitation results from a thermal equilibration to a very high transient temperature of the few atoms near the collision site. We also discuss the implications of stronger atom-substrate interaction potential by comparing preliminary results of hyperthermal I atoms to Xe.