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Orientation dependence of oxygen adsorption on a cylindrical GaAs sample
A328 38 INELASTIC ADSORBED
Surface Science 120 (1982) 38-46 North-Holland Publishing Company SCATTERING OF SLOW ELECTRONS ON A SMALL METAL SPHERE
W. EKARDT
and D.B. TRAN
BY MOLECULES
THOAI
Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-IO00 Berlin 33, Fed. Rep. of Germany Received 18 March 1982; accepted for publication 19 May 1982 The differential cross section for inelastic scattering of slow electrons by dipole excitation of molecules adsorbed on a small metal sphere is calculated. The significance of the exact hard core wave functions in calculating the cross section is shown by comparison with the corresponding plane-wave result. A strong radius dependence is obtained for the cross section at low energies. We conclude from our results that the scattering process studied provides a promising testing ground for the quantum dynamics of slow electrons near a small metal sphere.
Surface Science 120 (1982) 47-66 North-Holland Publishing Company DIFFRACTION STEPS *
FROM
47
SURFACES
T.-M. LU and M.G. LAGALLY
WITH
RANDOMLY
DISTRIBUTED
**
Department of Metallurgical and Mineral Engineering and Materials Science Center, University of Wisconsin- Madison, Madison, Wisconsin 53706, USA Received 22 December 1981; accepted for publication 4 May 1982 A closed-form solution is obtained for the angular distribution of intensity in diffraction from a surface on which the terrace size distribution is given by the geometric distribution, i.e. a surface in which the occurrence of steps is random. Several distributions of step heights that are integral multiples of the monatomic step height are considered. It is shown that a random occurrence of monatomic steps will cause some multiatomic steps. If a very broad distribution of step heights is assumed, the beam width no longer oscillates with energy but approaches a constant value except at the characteristic energies of zero width. Comparisons are made with a previous model and with measurements on GaAs(110).
Surface Science 120 (1982) 67-89 North-Holland Publishing Company ORIENTATION DEPENDENCE CYLINDRICAL GaAs SAMPLE I. A u g e r m e a s u r e m e n t s W. RANKE
*, Y . R . X I N G
67 OF OXYGEN
ADSORPTION
ON A
and G.D. SHEN
Semiconductor Institute, Chinese Academy of Sciences, P.O. Box 650, Beijing, People's Republic of China Received 28 January 1982 The orientation dependence of oxygen adsorption has been investigated by AES on the surface of a cylindrically shaped GaAs single crystal with [ 170] being its axis. It thus exposes the main low
A329 index orientations (001), ( l l l ) G a , (110), and (lll)As, as well as all their vicinal surfaces and intermediate orientations on its surface. It is shown that it is possible to prepare all these orientations simultaneously and with reasonable quality by ion bombardment and annealing (IBA). The orientation dependence of the amount of adsorbed oxygen in the range (001)( l l l ) G a - ( l l 0 ) - ( l f f ) A s can be understood in terms of different sticking coefficients on the different types of terrace site and of enhanced adsorption on edge-adjacent sites. These edge-adjacent sites show saturation at about 4 × 10 s L. Starting from (110) towards (11 l)Ga, at first, steps one atomic layer high are found, changing to a height of two layers when approaching (331). This behaviour can be understood in terms of the known relaxation on (110). A deep minimum in the amount of adsorbed oxygen between (l l/)As and (00/) is interpreted to be due to an As stabilized low sticking coefficient phase between (112) and (! 15). Early saturation ( a t ~ 105 L) on (001) and (1 ll)As is consistent with the fact that these surfaces usually do not reach their room temperature equlfibrium phase upon preparation by IBA. Sudden and accidental oxygen induced composition changes towards As-richer substrate compositions further confirm this.
90
Surface Science 120 (1982) 90-102 North-Holland Publishing Company
STUDY ON TITANIUM CARBIDE FIELD EMITrERS BY FIELD-ION MICROSCOPY, FIELD-ELECTRON EMISSION MICROSCOPY, AUGER ELECTRON SPECTROSCOPY, AND ATOM-PROBE FIELD-ION MICROSCOPY M. FUTAMOTO,
I. Y U I T O
and U. KAWABE
Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185, Japan and O. NISHIKAWA,
Y. T S U N A S H I M A
and Y. HARA
Department of Materials Science and Engineering. The Graduate School at Nagatsuta, Tokyo Institute of Technology, Midori-ku, Yokohama 227, Japan Received 24 February 1982; accepted for publication 17 May 1982 Surface structure, composition, and some field-electron emission properties are examined for thermally annealed titanium carbide emitters. As a result of high temperature heating, low-index planes of {100} and {111} become facetted and are observed as dark areas in field-electron emission patterns. Electrons are emitted predominantly from the {110} planes. The surface composition becomes enriched with carbon when the carbon deficient titanium carbide, TiCo.Tm, is heated at high temperatures in vacuum better than 10 -7 Pa. The topmost (110) layer consists of both Ti and C atoms. The instability in the electron emission current of titanium carbide is conSidered to be due to the local work function change caused by an interaction between vacuum residual gases and chemically active titanium atoms on the emitter surface.
Surface Science 120 (1982) 38-46 North-Holland Publishing Company SCATTERING OF SLOW ELECTRONS ON A SMALL METAL SPHERE
W. EKARDT
and D.B. TRAN
BY MOLECULES
THOAI
Fritz-Haber-lnstitut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-IO00 Berlin 33, Fed. Rep. of Germany Received 18 March 1982; accepted for publication 19 May 1982 The differential cross section for inelastic scattering of slow electrons by dipole excitation of molecules adsorbed on a small metal sphere is calculated. The significance of the exact hard core wave functions in calculating the cross section is shown by comparison with the corresponding plane-wave result. A strong radius dependence is obtained for the cross section at low energies. We conclude from our results that the scattering process studied provides a promising testing ground for the quantum dynamics of slow electrons near a small metal sphere.
Surface Science 120 (1982) 47-66 North-Holland Publishing Company DIFFRACTION STEPS *
FROM
47
SURFACES
T.-M. LU and M.G. LAGALLY
WITH
RANDOMLY
DISTRIBUTED
**
Department of Metallurgical and Mineral Engineering and Materials Science Center, University of Wisconsin- Madison, Madison, Wisconsin 53706, USA Received 22 December 1981; accepted for publication 4 May 1982 A closed-form solution is obtained for the angular distribution of intensity in diffraction from a surface on which the terrace size distribution is given by the geometric distribution, i.e. a surface in which the occurrence of steps is random. Several distributions of step heights that are integral multiples of the monatomic step height are considered. It is shown that a random occurrence of monatomic steps will cause some multiatomic steps. If a very broad distribution of step heights is assumed, the beam width no longer oscillates with energy but approaches a constant value except at the characteristic energies of zero width. Comparisons are made with a previous model and with measurements on GaAs(110).
Surface Science 120 (1982) 67-89 North-Holland Publishing Company ORIENTATION DEPENDENCE CYLINDRICAL GaAs SAMPLE I. A u g e r m e a s u r e m e n t s W. RANKE
*, Y . R . X I N G
67 OF OXYGEN
ADSORPTION
ON A
and G.D. SHEN
Semiconductor Institute, Chinese Academy of Sciences, P.O. Box 650, Beijing, People's Republic of China Received 28 January 1982 The orientation dependence of oxygen adsorption has been investigated by AES on the surface of a cylindrically shaped GaAs single crystal with [ 170] being its axis. It thus exposes the main low
A329 index orientations (001), ( l l l ) G a , (110), and (lll)As, as well as all their vicinal surfaces and intermediate orientations on its surface. It is shown that it is possible to prepare all these orientations simultaneously and with reasonable quality by ion bombardment and annealing (IBA). The orientation dependence of the amount of adsorbed oxygen in the range (001)( l l l ) G a - ( l l 0 ) - ( l f f ) A s can be understood in terms of different sticking coefficients on the different types of terrace site and of enhanced adsorption on edge-adjacent sites. These edge-adjacent sites show saturation at about 4 × 10 s L. Starting from (110) towards (11 l)Ga, at first, steps one atomic layer high are found, changing to a height of two layers when approaching (331). This behaviour can be understood in terms of the known relaxation on (110). A deep minimum in the amount of adsorbed oxygen between (l l/)As and (00/) is interpreted to be due to an As stabilized low sticking coefficient phase between (112) and (! 15). Early saturation ( a t ~ 105 L) on (001) and (1 ll)As is consistent with the fact that these surfaces usually do not reach their room temperature equlfibrium phase upon preparation by IBA. Sudden and accidental oxygen induced composition changes towards As-richer substrate compositions further confirm this.
90
Surface Science 120 (1982) 90-102 North-Holland Publishing Company
STUDY ON TITANIUM CARBIDE FIELD EMITrERS BY FIELD-ION MICROSCOPY, FIELD-ELECTRON EMISSION MICROSCOPY, AUGER ELECTRON SPECTROSCOPY, AND ATOM-PROBE FIELD-ION MICROSCOPY M. FUTAMOTO,
I. Y U I T O
and U. KAWABE
Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185, Japan and O. NISHIKAWA,
Y. T S U N A S H I M A
and Y. HARA
Department of Materials Science and Engineering. The Graduate School at Nagatsuta, Tokyo Institute of Technology, Midori-ku, Yokohama 227, Japan Received 24 February 1982; accepted for publication 17 May 1982 Surface structure, composition, and some field-electron emission properties are examined for thermally annealed titanium carbide emitters. As a result of high temperature heating, low-index planes of {100} and {111} become facetted and are observed as dark areas in field-electron emission patterns. Electrons are emitted predominantly from the {110} planes. The surface composition becomes enriched with carbon when the carbon deficient titanium carbide, TiCo.Tm, is heated at high temperatures in vacuum better than 10 -7 Pa. The topmost (110) layer consists of both Ti and C atoms. The instability in the electron emission current of titanium carbide is conSidered to be due to the local work function change caused by an interaction between vacuum residual gases and chemically active titanium atoms on the emitter surface.