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Oxygen-concentration dependence of secondary ion yield enhancement
A428 168
Surface Science 112 (1981) 168 180 North-Holland Publishing C o m p a n y
O X Y G E N - C O N C E N T R A T I O N D E P E N D E N C E OF S E C O N D A R Y ION YIELD E N H A N C E M E N T * K. WITTMAACK
Gesellschaft fiir Stmhlen- und Umweltforschung mbH, Physikalisch- Technische A bteilung, D-8042 Neuherberg, Fed. Rep. Germany Received 6 April 1981; accepted for publication 27 July 1981 The effect of implanted oxygen on secondary ion intensities has been investigated quantitatively for the first time. Depth profiles of the intensity of Si-+, SiO +, S i r , Si20 + and O ± were recorded under 3 keV Ar bombardment. The average oxygen concentration was derived from the oxygen range profile (6 keV) and the implantation fluence, it was found that at low oxygen concentrations, C o ~ 3 at%, the oxygen-induced signals are directly proportional to c o, whereas above that limit a power law is observed (power up to 3.7). The intensities of Si + (corrected for intrinsic emission) as well as of O - are proportional to each other throughout the concentration regime investigated (l~Z c o ~<35 at%), contrary to the behaviour of S i - and O +. Moreover, Si + emission is found to be much more sensitive to the presence of oxygen than Si - emission. Efficient production of Si + and Si - apparently requires (local) growth of SiO 2 (more so in the case of Si ). The results for Si + and O - suggest an interpretation in terms of the bond-breaking model or, more generally, in terms of a model involving localized electron transfer. Dissociation of SiO into Si + and O - could also be responsible for the observed phenomena.
Surface Science 112 (1981) 181-196 North-Holland Publishing Company THE
SURFACE
STRUCTURE
181 OF THE
(110)
ZONE
OF TUNGSTEN:
A LEED A N D WORK F U N C T I O N S T U D Y T.M.
GARDINER,
H.M.
KRAMER
a n d E. B A U E R
Physikalisches Institut, Technische UniversitiJt Clausthal, Leibnizstrasse4, D-3392 ClausthalZellerfeld, and Sonderforschungsbereich 126 G6ttingen-Clausthal, D-3392 Clausthal-Zellerfeld, Fed. Rep. Germany Received 26 June 1981; accepted for publication 2 September 1981 The surface structure of a cylindrical tungsten single crystal with its axis parallel to a (110) direction is examined by LEED and for work function change. Three kinds of surfaces are distinguished: the atomically smooth low index planes, their stepped vicinal regions and what are termed the atomically rough planes, far from any low index orientation. For low index planes, LEED patterns and work function values in agreement with those from plane crystals are observed. For all surface orientations, a good correlation between calculated and measured LEED reflection s p i t t i n g is found. Dipole moments per step edge atom are given and compared with values found in the literature. The atomically rough surfaces are found to be stable with respect to facetting into low index planes and dipole interactions between the outermost surface atoms appear to govern the work function. It is shown that any surface orientation can be unambiguously determined by LEED measurements alone.
Surface Science 112 (1981) 168 180 North-Holland Publishing C o m p a n y
O X Y G E N - C O N C E N T R A T I O N D E P E N D E N C E OF S E C O N D A R Y ION YIELD E N H A N C E M E N T * K. WITTMAACK
Gesellschaft fiir Stmhlen- und Umweltforschung mbH, Physikalisch- Technische A bteilung, D-8042 Neuherberg, Fed. Rep. Germany Received 6 April 1981; accepted for publication 27 July 1981 The effect of implanted oxygen on secondary ion intensities has been investigated quantitatively for the first time. Depth profiles of the intensity of Si-+, SiO +, S i r , Si20 + and O ± were recorded under 3 keV Ar bombardment. The average oxygen concentration was derived from the oxygen range profile (6 keV) and the implantation fluence, it was found that at low oxygen concentrations, C o ~ 3 at%, the oxygen-induced signals are directly proportional to c o, whereas above that limit a power law is observed (power up to 3.7). The intensities of Si + (corrected for intrinsic emission) as well as of O - are proportional to each other throughout the concentration regime investigated (l~Z c o ~<35 at%), contrary to the behaviour of S i - and O +. Moreover, Si + emission is found to be much more sensitive to the presence of oxygen than Si - emission. Efficient production of Si + and Si - apparently requires (local) growth of SiO 2 (more so in the case of Si ). The results for Si + and O - suggest an interpretation in terms of the bond-breaking model or, more generally, in terms of a model involving localized electron transfer. Dissociation of SiO into Si + and O - could also be responsible for the observed phenomena.
Surface Science 112 (1981) 181-196 North-Holland Publishing Company THE
SURFACE
STRUCTURE
181 OF THE
(110)
ZONE
OF TUNGSTEN:
A LEED A N D WORK F U N C T I O N S T U D Y T.M.
GARDINER,
H.M.
KRAMER
a n d E. B A U E R
Physikalisches Institut, Technische UniversitiJt Clausthal, Leibnizstrasse4, D-3392 ClausthalZellerfeld, and Sonderforschungsbereich 126 G6ttingen-Clausthal, D-3392 Clausthal-Zellerfeld, Fed. Rep. Germany Received 26 June 1981; accepted for publication 2 September 1981 The surface structure of a cylindrical tungsten single crystal with its axis parallel to a (110) direction is examined by LEED and for work function change. Three kinds of surfaces are distinguished: the atomically smooth low index planes, their stepped vicinal regions and what are termed the atomically rough planes, far from any low index orientation. For low index planes, LEED patterns and work function values in agreement with those from plane crystals are observed. For all surface orientations, a good correlation between calculated and measured LEED reflection s p i t t i n g is found. Dipole moments per step edge atom are given and compared with values found in the literature. The atomically rough surfaces are found to be stable with respect to facetting into low index planes and dipole interactions between the outermost surface atoms appear to govern the work function. It is shown that any surface orientation can be unambiguously determined by LEED measurements alone.