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On some properties of the (110) surfaces of GaAs
Classified
abstracts
3695-3769
Classified abstracts on this page 3695-3701
Editor’s note The label immediately following that at the end of each abstract
I. General I I. GASES
vacuum
science
the title of each item denotes country of origin of publication, indicates country of origin of work (where known).
and engineering
AND SOLIDS
II 3695. RHEED and AES studies of the reactions of chlorine on the dense faces of iron and chromium. (France) Epitaxial relationships of FeCl* and CrCI, have been investigated by rhe Rheed method, on low-index faces of iron and chromium and related to the structure of chemisorbed structures nucleated in the tirst steps of the chemical reaction. Epitaxial films are in the form of nuclei or continuous films according to the kinetics of reaction and were prepared either by gas-metal reaction either by a low-energy plasma of chlorine ions. We have shown the preponderant character of chlorine-chlorine chains of the structure in the interfacial networks of reaction products. It is shown that in the case of the (I IO) face of iron, the first chemisorbed structure observed is a p(I * I) chlorine and that a structure a( 2’i”
2:/‘)
R 30 is equally observed near
the saturation coverage. Thus, two types of chemisorbed structures of different symmetry are nucleated before the growth of (001) sheets of epitaxial FeCl,. In the case of the (210) face of iron, only one type of structure have been found -a( “is
’ 2:/T)
R 30. Auger
spectra
related to this structure indicate that the Auger transition Mz3 VV of iron is split in two peaks. Electron energyloss spectra have also been studied and are characteristic of the coverage of the metal surface with chemisorbed chlorine and three-dimensional nuclei. Chlorine reaction on (100) and (I I I) faces of chromium shows that the edification of the epitaxial three-dimensional film of CrC12 is preceded by the formation of a three-dimensional phase consisting ofan hexagonal stacking of chlorine atoms with chromium atoms located in the octaedralsites. D Vigner et al, Vide, 32 (I 87), 1977, 64-69 (in French). II 3696. On some properties of the (110) surfaces of GaAs. (France) We study the properties of clean surfaces (I IO) of GaAs. obtained by cleavage under- ultra-high vacuum, in the temperature .range 77400 K. The method used is the Kelvin Method comoleted bv LEED. AES measurements. After cleavage the samples are cooledio~lO0 i and contact potential variations in the dark are studied when the temperature is increased from 100 K to 400 K with or without illumination of the surface at 100 K. Variations of the work function 0,, with photons energy in vacuum, after oxygen adsorption or after electron bombardment are also studied. J Bonnet et al, Vide, 32 (I 88), 1977, 99-l 03 (in French). 11 3697. The influence of structural defects on the adsorption state of simple molecules on transition metals. (France) The influence of structural defects on the adsorption state of simple molecules on transition metals is illustrated by several examples already published in the literature and by carbon monoxide adsorption on Re (OOOI) and on Re 114 (OOOI) x (IO-II)1 studied in our laboratory. The results show that the CO/3 state is strongly related to the presence of steps on the surface which have an influence on the state populations and on the surface structure formation by adsorption at 550 K. R Ducros, Vide, 32 (I 89), 1977, 128-l 29 (in French). 11 3698. Influence of surface structure on the rate of O2 adsorption and CO oxidation on platinum. (France) The surface science approach to the investigation of the structure factor in chemisorption and catalysis is critically appraised by discussing recent data on the adsorption of O2 and the oxidation of CO
and
on Pt single crystal surfaces. The experimental data on O2 adsorption show that there is a substantial orientational structure effect, mostly due to reconstruction of.the Pt (100) surface. The effect of steps on O2 adsorption does not appear to be as significant as originally believed. Similar statements can be made for the rate of CO oxidation. However, these conclusions should not be considered as universally applicable since only a limited body of experimental results is available. (Germany) H P Bonzel and G Comsa, Vide, 32 (189). 1978, 130-134. I1 3699. Study of ESD from type 304 stainless steel in relation to CTR first wall applications. (USA) Electron stimulated desorption (ESD) of adsorbed species from type 304 stainless steel (SS) was studied, primarily from the standpoint of controlled thermonuclear fusion reactor ‘first wall’ applications. H + and F+ were, by far, the most predominant ESD ion species observed from ‘as is’ SS surfaces. O+. Cl+ and other ESD ions were also observed, but normally in much smaller quantities. The origin of the ESD ion signals are attributed to adsorbed HZ and/or Hz0 for ESD of H+, and fluorocarbon and/or alkali halide contaminants in the case of ESD of F+. Little or no temperature effects on the H+ and F+ ESD ion signals were observed over the SS sample temperature range from 23 to -450°C. The total cross-section for ESD of hydrogen was found to be -IO- I6 cm2 while that for ESD of fluorine was found to be -IO-” cm2. The ion energy distributions of both H+ and F+ ions were obtained and no observable changes were found over the bombarding electron energy range 300-4000 eV. The total cross-section for ESD of hydrogen from SS was investigated as a function of bombarding electron energy over the energy range 200-4000 eV. Relative cross-sections for ESD of H+ and F+ were investigated over the bombarding electron energy range 50-6000 eV. The cross-section behaviour for ESD vs electron energy was found to be very similar to the behaviour for electron-gas-phase molecule interaction cross-sections vs electron energy. The ESD cross-section maximum was observed to occur at an electron energy of several hundred eV. Above this energy the cross-section slowly decreased with increasing electron energy. The observed behaviour of ESD cross-section vs electron energy is attributed to the interaction of both primary and secondary electrons with the surface adsorbates. M J Drinkwine and D Lichtman, J Vuc Sci Technol, 15 (I ), 1978,74-75. II 3700. Localized substrate heating during ion implantation. (USA) The enhanced etching of ion-implanted silicon nitride in buffered hydrofluoric acid has been studied as a function of beam current in an ion implantation system using rotating mechanical scan. Reduction of the enhancement due to annealing has been observed under conditions where an earlier model of target heating during ion implantation would predict no annealing. The implication of this observation for future beam heating calculations is explored briefly. P D Parry, J Vat Sci Technol, 15 (I), 1978, I I l-l IS. II 3701. Photovoltaic properties of CdTe p-n junctions produced by ion implantation. (USA) A surface region about 0.22 pm thick of cadmium-annealed undoped ,r-type CdTe single crystal was converted top type by implantation of 60 keV As+ ions followed by a cadmium annealing. The electrical properties of the p-type layer were measured as well as the photovoltaic properties of thep-n junction formed in this way. For illumination by sunlight an open-circuit voltage of 0.84 V was found in a cell with a solar efficiency of 3.0%. The parameters of the junction were determined using a model designed to describe the spectral response of the cell. Muren Chu et al, J appl Phys, 49 (I), 1978, 322-326. 373
abstracts
3695-3769
Classified abstracts on this page 3695-3701
Editor’s note The label immediately following that at the end of each abstract
I. General I I. GASES
vacuum
science
the title of each item denotes country of origin of publication, indicates country of origin of work (where known).
and engineering
AND SOLIDS
II 3695. RHEED and AES studies of the reactions of chlorine on the dense faces of iron and chromium. (France) Epitaxial relationships of FeCl* and CrCI, have been investigated by rhe Rheed method, on low-index faces of iron and chromium and related to the structure of chemisorbed structures nucleated in the tirst steps of the chemical reaction. Epitaxial films are in the form of nuclei or continuous films according to the kinetics of reaction and were prepared either by gas-metal reaction either by a low-energy plasma of chlorine ions. We have shown the preponderant character of chlorine-chlorine chains of the structure in the interfacial networks of reaction products. It is shown that in the case of the (I IO) face of iron, the first chemisorbed structure observed is a p(I * I) chlorine and that a structure a( 2’i”
2:/‘)
R 30 is equally observed near
the saturation coverage. Thus, two types of chemisorbed structures of different symmetry are nucleated before the growth of (001) sheets of epitaxial FeCl,. In the case of the (210) face of iron, only one type of structure have been found -a( “is
’ 2:/T)
R 30. Auger
spectra
related to this structure indicate that the Auger transition Mz3 VV of iron is split in two peaks. Electron energyloss spectra have also been studied and are characteristic of the coverage of the metal surface with chemisorbed chlorine and three-dimensional nuclei. Chlorine reaction on (100) and (I I I) faces of chromium shows that the edification of the epitaxial three-dimensional film of CrC12 is preceded by the formation of a three-dimensional phase consisting ofan hexagonal stacking of chlorine atoms with chromium atoms located in the octaedralsites. D Vigner et al, Vide, 32 (I 87), 1977, 64-69 (in French). II 3696. On some properties of the (110) surfaces of GaAs. (France) We study the properties of clean surfaces (I IO) of GaAs. obtained by cleavage under- ultra-high vacuum, in the temperature .range 77400 K. The method used is the Kelvin Method comoleted bv LEED. AES measurements. After cleavage the samples are cooledio~lO0 i and contact potential variations in the dark are studied when the temperature is increased from 100 K to 400 K with or without illumination of the surface at 100 K. Variations of the work function 0,, with photons energy in vacuum, after oxygen adsorption or after electron bombardment are also studied. J Bonnet et al, Vide, 32 (I 88), 1977, 99-l 03 (in French). 11 3697. The influence of structural defects on the adsorption state of simple molecules on transition metals. (France) The influence of structural defects on the adsorption state of simple molecules on transition metals is illustrated by several examples already published in the literature and by carbon monoxide adsorption on Re (OOOI) and on Re 114 (OOOI) x (IO-II)1 studied in our laboratory. The results show that the CO/3 state is strongly related to the presence of steps on the surface which have an influence on the state populations and on the surface structure formation by adsorption at 550 K. R Ducros, Vide, 32 (I 89), 1977, 128-l 29 (in French). 11 3698. Influence of surface structure on the rate of O2 adsorption and CO oxidation on platinum. (France) The surface science approach to the investigation of the structure factor in chemisorption and catalysis is critically appraised by discussing recent data on the adsorption of O2 and the oxidation of CO
and
on Pt single crystal surfaces. The experimental data on O2 adsorption show that there is a substantial orientational structure effect, mostly due to reconstruction of.the Pt (100) surface. The effect of steps on O2 adsorption does not appear to be as significant as originally believed. Similar statements can be made for the rate of CO oxidation. However, these conclusions should not be considered as universally applicable since only a limited body of experimental results is available. (Germany) H P Bonzel and G Comsa, Vide, 32 (189). 1978, 130-134. I1 3699. Study of ESD from type 304 stainless steel in relation to CTR first wall applications. (USA) Electron stimulated desorption (ESD) of adsorbed species from type 304 stainless steel (SS) was studied, primarily from the standpoint of controlled thermonuclear fusion reactor ‘first wall’ applications. H + and F+ were, by far, the most predominant ESD ion species observed from ‘as is’ SS surfaces. O+. Cl+ and other ESD ions were also observed, but normally in much smaller quantities. The origin of the ESD ion signals are attributed to adsorbed HZ and/or Hz0 for ESD of H+, and fluorocarbon and/or alkali halide contaminants in the case of ESD of F+. Little or no temperature effects on the H+ and F+ ESD ion signals were observed over the SS sample temperature range from 23 to -450°C. The total cross-section for ESD of hydrogen was found to be -IO- I6 cm2 while that for ESD of fluorine was found to be -IO-” cm2. The ion energy distributions of both H+ and F+ ions were obtained and no observable changes were found over the bombarding electron energy range 300-4000 eV. The total cross-section for ESD of hydrogen from SS was investigated as a function of bombarding electron energy over the energy range 200-4000 eV. Relative cross-sections for ESD of H+ and F+ were investigated over the bombarding electron energy range 50-6000 eV. The cross-section behaviour for ESD vs electron energy was found to be very similar to the behaviour for electron-gas-phase molecule interaction cross-sections vs electron energy. The ESD cross-section maximum was observed to occur at an electron energy of several hundred eV. Above this energy the cross-section slowly decreased with increasing electron energy. The observed behaviour of ESD cross-section vs electron energy is attributed to the interaction of both primary and secondary electrons with the surface adsorbates. M J Drinkwine and D Lichtman, J Vuc Sci Technol, 15 (I ), 1978,74-75. II 3700. Localized substrate heating during ion implantation. (USA) The enhanced etching of ion-implanted silicon nitride in buffered hydrofluoric acid has been studied as a function of beam current in an ion implantation system using rotating mechanical scan. Reduction of the enhancement due to annealing has been observed under conditions where an earlier model of target heating during ion implantation would predict no annealing. The implication of this observation for future beam heating calculations is explored briefly. P D Parry, J Vat Sci Technol, 15 (I), 1978, I I l-l IS. II 3701. Photovoltaic properties of CdTe p-n junctions produced by ion implantation. (USA) A surface region about 0.22 pm thick of cadmium-annealed undoped ,r-type CdTe single crystal was converted top type by implantation of 60 keV As+ ions followed by a cadmium annealing. The electrical properties of the p-type layer were measured as well as the photovoltaic properties of thep-n junction formed in this way. For illumination by sunlight an open-circuit voltage of 0.84 V was found in a cell with a solar efficiency of 3.0%. The parameters of the junction were determined using a model designed to describe the spectral response of the cell. Muren Chu et al, J appl Phys, 49 (I), 1978, 322-326. 373