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Computer simulation of sputtering and oxygen desorption processes at grazing ion bombardment of Ag(110 ) surface
Computational Materials Science 27 (2003) 117–122 www.elsevier.com/locate/commatsci
Computer simulation of sputtering and oxygen desorption processes at grazing ion bombardment of Ag(1 1 0) surface A.A. Dzhurakhalov a
a,*
, S.E. Rahmatov a, N.A. Teshabaeva a, H. Dreysse
b
Arifov Institute of Electronics, F. Khodjaev Str. 33, 700187 Tashkent, Uzbekistan b IPCMS-GEMME, 23 rue du Loess, F-67037 Strasbourg Cedex, France
Abstract The ion sputtering and oxygen desorption processes at 5 keV Ne ion bombardment of clean and O2 covered Ag(1 1 0) surface have been investigated by computer simulation. The trajectories of the colliding particles were constructed as a sequence of binary collisions. The influence of surface potential barrier on the non-dissociative desorption yield has been studied and it was observed that the basic part of ion-impact desorbed particles overcomes a potential barrier. The sputtering yield of Ag atoms and the non-dissociative O2 desorption yield versus the azimuth angle of incidence at grazing ion bombardment have been presented. It was shown that these dependencies correlate the orientation of crystal. At grazing ion bombardment the particles are ejected on azimuth angle mainly along the normal of plane of incidence. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Computer simulation; Sputtering; Ion-impact desorption; Grazing ion bombardment
1. Introduction Ion sputtering processes on the surface of single crystals have been investigated very well when angle of ion bombardment is large [1,2]. In the case of grazing angles of incidence the information about ion sputtering processes is not enough [3,4]. Many researchers exhibit concern about so-called
* Corresponding author. Tel.: +998-71-162-7331; fax: +99871-162-8767. E-mail address: [email protected] (A.A. Dzhurakhalov).
ion-impact desorption processes of the adsorbed particles, i.e. to an immediate knocking-out of adsorbed particles caused by incident ions [5–11]. In Onsgaard et al. [5] and Taglauer et al. [6,7] the ion-impact desorption processes of the adsorbed particles on metal surfaces has been studied by low-energy ion scattering. In Kapur and Garrison [8], OÕConnor et al. [9] and Dzhurakhalov et al. [10], the process of ion-impact desorption has been investigated immediate detection of the desorbed particles (basically, an atomic adsorption of these particles). The results of investigation of the ionimpact desorption are valuable not only for study of desorption process as effective method of
0927-0256/03/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0927-0256(02)00434-2
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clearing of a surface from contamination by ion bombardment, but also for determination of some characters of adsorption states. In this report the sputtering of Ag atoms from the Ag(1 1 0) and the processes of an ion-impact desorption of O2 molecules adsorbed on the Ag(1 1 0) surface under low-energy grazing ion bombardment have been studied by computer simulation using a consequence binary collision approximation.
2. Computational methods The trajectories of the colliding particles were constructed as a sequence of binary collisions. The particle interactions were described by the screened Coulomb potential with the Ziegler– Biersack–Littmark approximation [12] to the Thomas–Fermi screening function. The inelastic energy losses were considered as local and calculated by modified Firsov model [13] with their including into the scattering kinematics. The simulations were run with the crystal atoms initially stationary at equilibrium lattice sites because in the conditions of grazing incidence the influence of the thermal vibrations of lattice atoms at room temperature on ion sputtering results is insignificant. The sputtering has been simulated in the primary knock-on regime. Only the primary knockon recoil (PKR) atoms ejected from first, second and third layers have been considered. The presence of a planar potential energy barrier with the height Us ¼ 3:05 eV for Ag atoms on the surface was taken into account. The number of incident ions is 2 104 . The incident ions and the recoil atoms were followed throughout their slowing-down process until their energy falls below a predetermined energy: 25 eV was used for the incident ions, and the surface binding energy was used for the knock-on atoms. The possibilities of this code are following: (1) to carry out the calculations without inelastic energy losses or with their inclusions on one of three models: Kishinevsky (modified Firsov model) [13], Firsov [14], Oen–Robinson (for light particles)
[15]; (2) to vary the interaction potentials: Born– Mayer, Moliere, BZL; (3) to compute the time integral or to use the hard sphere model; (4) to calculate the parameters of the scattering ions and recoil atoms for different values of mass ratio of colliding particles; (5) to determine the contributions of PKR formed from the first three layers to the sputtering yields; (6) to calculate the parameters of the ion-impact desorption (as well as nondissociative) of two atomic molecules adsorbed on the surface. These calculations do not require the change of code structure and may be performed by choice input parameters. In our calculation an adsorption site of O2 molecules corresponds to the atop second layer site with the O–O axis parallel to the Ag(1 1 0) surface along a h1 1 0i direction at the C(2 2) adsorption structure (Fig. 1(a)). The height of its center of mass above the surface plane is 0.094 nm, O–O bond length is 0.155 nm, binding energy Eb of O2 with a surface is 0.53 eV and molecular binding (dissociation) energy e of O2 is 5 eV. The angle of incidence of the ion beam relative to the surface was changed in the range w ¼ 5–20°, the azimuth angle of incidence changed in the range n ¼ 0–90° by rotation of a target around its normal was counted from h0 0 1i direction, the polar and azimuth angle of ejection of desorbed particles are marked in d and u, respectively (see Fig. 1(a)). Dissociative (at the gap of intramolecular bond) and non-dissociative desorption of adsorbed molecules were simulated. In the case of a dissociative desorption the possible collisions of ejected atom of a molecule with neighbour molecules and with surface atoms have been taken account. The atom or molecule was considered as desorbed, if its impulse after all possible collisions was directed to a vacuum and its energy was sufficient for overcoming a surface barrier. For calculations of non-dissociative desorption of molecules from a surface of single crystals the approach similar in ‘‘cut-off’’ model [16] used for description of the sputtered particles as dimers. Accordingly to [16], the ion as a result of the series correlated collisions can eject a molecule without gap of bond between its atoms, if the
A.A. Dzhurakhalov et al. / Computational Materials Science 27 (2003) 117–122
119
Fig. 1. Projections of the adsorbed molecules O2 and atoms of a matrix on the Ag(1 1 0) surface plane and angles used in calculations (a); the scheme of non-dissociative desorption of O2 molecules and distances between atoms (b).
relative kinetic energy of atoms does not exceed a binding (dissociation) energy e of molecule (Fig. 1(b)): Ermol ¼
m2 ð~ v1 ~ v2 Þ2 6 e; 4
ð1Þ
and the energy of a center of mass is sufficient for overcoming a binding energy of molecule with a surface Eb : Ec ¼
m2 2 ð~ v1 þ~ v2 Þ P E b ; 4
tions. For such molecules their polar d and azimuth u angular distributions, as well as the yield of a non-dissociative desorption have been calculated.
ð2Þ
here m2 is the mass of atom of a molecule, v1;2 is the velocities of atoms of molecule. The molecule was considered as non-dissociative desorbed, if an impulse of its center of mass is directed to a vacuum at a fulfilment of (1) and (2) condi-
3. Results and discussion In Fig. 2 the number of particles ejected as Ag atoms ðrÞ sputtered from clean Ag(1 1 0) surface and as oxygen molecules non-dissociatively desorbed (nd0––total, nd––overcome a potential barrier) from oxygen covered Ag(1 1 0)–O2 – c(2 2) surface versus the azimuth angle of incidence at 5 keV Neþ ion bombardment for w ¼ 10° has been presented. It is seen that all curves change significantly versus the azimuth angle of incidence. Comparison of curves nd0 and nd shows that
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Fig. 2. The number of sputtered Ag atoms ðrÞ, total ðnd0Þ and as overcome a potential barrier ðndÞ non-dissociative desorbed oxygen molecules versus the angle n at 5 keV Neþ ion bombardment of Ag(1 1 0) and O2 /Ag(1 1 0) surface for w ¼ 10°. Number of incident particles is 2 104 .
surface potential barrier does not change the shape of curves, it reduce the value of desorption yields. The basic part of desorbed particles overcomes a potential barrier. Sputtering yield of Ag atoms is 2–5 times more than non-dissociative desorption yield in the region of n ¼ 0–75° (compare the curves r and nd). The curve r has the minima at n ¼ 0°; 35° and 90° which correspond to the directions h0 0 1i, h2 2 1i and h1 1 0i respectively. There are surface semichannels and channels along these directions that lead to the reflection of main part of incident ions from the surface at w ¼ 10° and thus to decreasing the sputtering yields in these directions. The curve nd has a maximum at n ¼ 20, broad maximum at n ¼ 50° and increases monotonic in the region of azimuth angle of incidence 65° < n 6 90°. The formation of these maxima testifies to favorable realization of conditions (1) and (2) for non-dissociative desorption of adsorbed molecules. Present code allows to differ three compound parts of non-dissociative desorbed molecules: in first case during the collision processes the both atoms of molecule receive the impulses directed to the vacuum; and two other cases one of atoms of molecule receives an impulse directed to the vacuum, the second of them receives an impulse
Fig. 3. The dependencies nd1, nd2, nd3 versus the azimuth angle of incidence n at w ¼ 10° and 5 keV Neþ ion bombardment of O2 /Ag(1 1 0) surface. Number of incident particles is 2 104 .
directed to the crystal. Fig. 3 shows these components versus the azimuth angle of incidence, where nd1 corresponds to the first case; nd2 corresponds to the case when atom number 1 of molecule has an impulse directed to the vacuum (and atom number 2 can have an impulse directed to the crystal); nd3 corresponds to the case when atom number 2 of molecule has an impulse directed to the vacuum. Thus, the number of non-dissociative desorbed molecules consists of three components: nd ¼ nd1 þ nd2 þ nd3 (see curve nd in Fig. 2). In Fig. 3 it is possible to observe the local maximum at n ¼ 0 and main maxima at n ¼ 15; 55; 90° in curve nd1. The most broad intensive maximum near n ¼ 90° was conditioned by the presence of favorable conditions for non-dissociative desorption of adsorbed molecules due to the possibility of a channeling of incident particles under an adsorption layer in this direction, as long as an axis of molecules is parallel to the h1 1 0i direction. In curve nd2 the basic maxima are observed at n ¼ 45°; 70° and calculation results show that in this case the significant part of ion energy loses at collisions by the atom number 1 of molecule. In dependence nd3 there is one intensive peak, and this peak gives the basic contribution on quantity of non-dissociative desorbed molecules of oxygen at n ¼ 20°. In Fig. 4 the spatial angular distribution of the sputtered Ag atoms on polar d and azimuth u angles of ejection has been presented at 5 keV Neþ
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121
Fig. 4. The angular (polar d and azimuth u) distribution of the sputtering Ag atoms at 5 keV Neþ ion bombardment of Ag(1 1 0) surface for w ¼ 10° and n ¼ 55°. Number of incident particles is 2 104 .
ion bombardment of Ag(1 1 0) surface for w ¼ 10° and n ¼ 55°. Distribution shows that the sputtered atoms are ejected mainly under polar angles d ¼ 40–75° and azimuth angles near u ¼ 90°, 270°. Such distribution on azimuth angles corresponds to the ejection of matrix atoms along the normal of plane of incidence.
4. Conclusions The ion sputtering of Ag atoms and ion-impact desorption (in particular non-dissociative desorption) of O2 molecules in the case of low energy grazing Ne ion bombardment of clean and O2 covered Ag(1 1 0) surface have been simulated in the consequence binary collision approximation. The azimuth angular dependencies of Ag sputtering yield and non-dissociative O2 desorption yield for the case of 5 keV Neþ ion bombardment at w ¼ 10° have been calculated. It was shown that these dependencies correlate the crystal orientation. The influence of surface potential barrier on
the non-dissociative desorption yield has been studied and it was observed that the basic part of ion-impact desorbed particles overcomes a potential barrier. The calculated results show that in the certain directions of incidence owing to channeling of ions between adsorption layer and surface the effective desorption of adsorbed particles occurs and the character of desorption strongly depends on orientation of a crystal. Spatial distribution of sputtered particles shows that in the case of grazing ion bombardment the particles are mainly ejected in the direction near the normal of plane of incidence.
Acknowledgements Authors thank the Fundamental Research Foundations of Uzbek Academy of Sciences and CNRS (National Center of Scientific Investigations of France) for their support.
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References [1] R. Behrisch (Ed.), Sputtering by Particle Bombardment I, Springer, New York, 1981. [2] R. Behrisch (Ed.), Sputtering by Particle Bombardment II, Springer, New York, 1984. [3] E.S. Mashkova, V.A. Molchanov, Rad. Eff. 102 (1987) 125. [4] A.A. Dzhurakhalov, I.I. Khafizov, Nucl. Instrum. Meth. Phys. Res. B 153 (1999) 326. [5] J. Onsgaard, W. Heiland, E. Taglauer, Surf. Sci. 99 (1980) 112. [6] E. Taglauer, G. Marin, W. Heiland, U. Beitat, Surf. Sci. 63 (1977) 507. [7] E. Taglauer, U. Beitat, W. Heiland, Nucl. Instrum. Meth. 149 (1978) 605. [8] Sh. Kapur, B.J. Garrison, Chem. Phys. 75 (1981) 445.
[9] D.J. OÕConnor, R.J. MacDonald, W. Eckstein, P.R. Higginbottom, Nucl. Instrum. Meth. Phys. Res. B 13 (1986) 235. [10] A.A. Dzhurakhalov, N.A. Teshabaeva, V.Kh. Ferleger, Uzb. Fiz. Zhurn. 4 (1993) 65. [11] A.A. Dzhurakhalov, S. Rahmatov, Surface and Coatings Technology 158–159 (2002) 277–280. [12] D.J. OÕConnor, J.P. Biersack, Nucl. Instrum. Meth. Phys. Res. B 15 (1986) 14. [13] E.S. Parilis, L.M. Kishinevsky, N. Yu. Turaev, B.E. Baklitzky, F.F. Umarov, V.Kh. Verleger, S. Niznaya, I.S. Bitensky, Atomic Collisions on Solid Surfaces, NorthHolland, 1993. [14] O.B. Firsov, Zhurn. Eksper. Teor. Fiz. 36 (1958) 1517. [15] O.S. Oen, M.T. Robinson, Nucl. Instrum. Meth. 132 (1976) 647. [16] I.S. Bitenskiy, E.S. Parilis, Zhur. Tekh. Fiz. 51 (1981) 2134.
Computer simulation of sputtering and oxygen desorption processes at grazing ion bombardment of Ag(1 1 0) surface A.A. Dzhurakhalov a
a,*
, S.E. Rahmatov a, N.A. Teshabaeva a, H. Dreysse
b
Arifov Institute of Electronics, F. Khodjaev Str. 33, 700187 Tashkent, Uzbekistan b IPCMS-GEMME, 23 rue du Loess, F-67037 Strasbourg Cedex, France
Abstract The ion sputtering and oxygen desorption processes at 5 keV Ne ion bombardment of clean and O2 covered Ag(1 1 0) surface have been investigated by computer simulation. The trajectories of the colliding particles were constructed as a sequence of binary collisions. The influence of surface potential barrier on the non-dissociative desorption yield has been studied and it was observed that the basic part of ion-impact desorbed particles overcomes a potential barrier. The sputtering yield of Ag atoms and the non-dissociative O2 desorption yield versus the azimuth angle of incidence at grazing ion bombardment have been presented. It was shown that these dependencies correlate the orientation of crystal. At grazing ion bombardment the particles are ejected on azimuth angle mainly along the normal of plane of incidence. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Computer simulation; Sputtering; Ion-impact desorption; Grazing ion bombardment
1. Introduction Ion sputtering processes on the surface of single crystals have been investigated very well when angle of ion bombardment is large [1,2]. In the case of grazing angles of incidence the information about ion sputtering processes is not enough [3,4]. Many researchers exhibit concern about so-called
* Corresponding author. Tel.: +998-71-162-7331; fax: +99871-162-8767. E-mail address: [email protected] (A.A. Dzhurakhalov).
ion-impact desorption processes of the adsorbed particles, i.e. to an immediate knocking-out of adsorbed particles caused by incident ions [5–11]. In Onsgaard et al. [5] and Taglauer et al. [6,7] the ion-impact desorption processes of the adsorbed particles on metal surfaces has been studied by low-energy ion scattering. In Kapur and Garrison [8], OÕConnor et al. [9] and Dzhurakhalov et al. [10], the process of ion-impact desorption has been investigated immediate detection of the desorbed particles (basically, an atomic adsorption of these particles). The results of investigation of the ionimpact desorption are valuable not only for study of desorption process as effective method of
0927-0256/03/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0927-0256(02)00434-2
118
A.A. Dzhurakhalov et al. / Computational Materials Science 27 (2003) 117–122
clearing of a surface from contamination by ion bombardment, but also for determination of some characters of adsorption states. In this report the sputtering of Ag atoms from the Ag(1 1 0) and the processes of an ion-impact desorption of O2 molecules adsorbed on the Ag(1 1 0) surface under low-energy grazing ion bombardment have been studied by computer simulation using a consequence binary collision approximation.
2. Computational methods The trajectories of the colliding particles were constructed as a sequence of binary collisions. The particle interactions were described by the screened Coulomb potential with the Ziegler– Biersack–Littmark approximation [12] to the Thomas–Fermi screening function. The inelastic energy losses were considered as local and calculated by modified Firsov model [13] with their including into the scattering kinematics. The simulations were run with the crystal atoms initially stationary at equilibrium lattice sites because in the conditions of grazing incidence the influence of the thermal vibrations of lattice atoms at room temperature on ion sputtering results is insignificant. The sputtering has been simulated in the primary knock-on regime. Only the primary knockon recoil (PKR) atoms ejected from first, second and third layers have been considered. The presence of a planar potential energy barrier with the height Us ¼ 3:05 eV for Ag atoms on the surface was taken into account. The number of incident ions is 2 104 . The incident ions and the recoil atoms were followed throughout their slowing-down process until their energy falls below a predetermined energy: 25 eV was used for the incident ions, and the surface binding energy was used for the knock-on atoms. The possibilities of this code are following: (1) to carry out the calculations without inelastic energy losses or with their inclusions on one of three models: Kishinevsky (modified Firsov model) [13], Firsov [14], Oen–Robinson (for light particles)
[15]; (2) to vary the interaction potentials: Born– Mayer, Moliere, BZL; (3) to compute the time integral or to use the hard sphere model; (4) to calculate the parameters of the scattering ions and recoil atoms for different values of mass ratio of colliding particles; (5) to determine the contributions of PKR formed from the first three layers to the sputtering yields; (6) to calculate the parameters of the ion-impact desorption (as well as nondissociative) of two atomic molecules adsorbed on the surface. These calculations do not require the change of code structure and may be performed by choice input parameters. In our calculation an adsorption site of O2 molecules corresponds to the atop second layer site with the O–O axis parallel to the Ag(1 1 0) surface along a h1 1 0i direction at the C(2 2) adsorption structure (Fig. 1(a)). The height of its center of mass above the surface plane is 0.094 nm, O–O bond length is 0.155 nm, binding energy Eb of O2 with a surface is 0.53 eV and molecular binding (dissociation) energy e of O2 is 5 eV. The angle of incidence of the ion beam relative to the surface was changed in the range w ¼ 5–20°, the azimuth angle of incidence changed in the range n ¼ 0–90° by rotation of a target around its normal was counted from h0 0 1i direction, the polar and azimuth angle of ejection of desorbed particles are marked in d and u, respectively (see Fig. 1(a)). Dissociative (at the gap of intramolecular bond) and non-dissociative desorption of adsorbed molecules were simulated. In the case of a dissociative desorption the possible collisions of ejected atom of a molecule with neighbour molecules and with surface atoms have been taken account. The atom or molecule was considered as desorbed, if its impulse after all possible collisions was directed to a vacuum and its energy was sufficient for overcoming a surface barrier. For calculations of non-dissociative desorption of molecules from a surface of single crystals the approach similar in ‘‘cut-off’’ model [16] used for description of the sputtered particles as dimers. Accordingly to [16], the ion as a result of the series correlated collisions can eject a molecule without gap of bond between its atoms, if the
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119
Fig. 1. Projections of the adsorbed molecules O2 and atoms of a matrix on the Ag(1 1 0) surface plane and angles used in calculations (a); the scheme of non-dissociative desorption of O2 molecules and distances between atoms (b).
relative kinetic energy of atoms does not exceed a binding (dissociation) energy e of molecule (Fig. 1(b)): Ermol ¼
m2 ð~ v1 ~ v2 Þ2 6 e; 4
ð1Þ
and the energy of a center of mass is sufficient for overcoming a binding energy of molecule with a surface Eb : Ec ¼
m2 2 ð~ v1 þ~ v2 Þ P E b ; 4
tions. For such molecules their polar d and azimuth u angular distributions, as well as the yield of a non-dissociative desorption have been calculated.
ð2Þ
here m2 is the mass of atom of a molecule, v1;2 is the velocities of atoms of molecule. The molecule was considered as non-dissociative desorbed, if an impulse of its center of mass is directed to a vacuum at a fulfilment of (1) and (2) condi-
3. Results and discussion In Fig. 2 the number of particles ejected as Ag atoms ðrÞ sputtered from clean Ag(1 1 0) surface and as oxygen molecules non-dissociatively desorbed (nd0––total, nd––overcome a potential barrier) from oxygen covered Ag(1 1 0)–O2 – c(2 2) surface versus the azimuth angle of incidence at 5 keV Neþ ion bombardment for w ¼ 10° has been presented. It is seen that all curves change significantly versus the azimuth angle of incidence. Comparison of curves nd0 and nd shows that
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Fig. 2. The number of sputtered Ag atoms ðrÞ, total ðnd0Þ and as overcome a potential barrier ðndÞ non-dissociative desorbed oxygen molecules versus the angle n at 5 keV Neþ ion bombardment of Ag(1 1 0) and O2 /Ag(1 1 0) surface for w ¼ 10°. Number of incident particles is 2 104 .
surface potential barrier does not change the shape of curves, it reduce the value of desorption yields. The basic part of desorbed particles overcomes a potential barrier. Sputtering yield of Ag atoms is 2–5 times more than non-dissociative desorption yield in the region of n ¼ 0–75° (compare the curves r and nd). The curve r has the minima at n ¼ 0°; 35° and 90° which correspond to the directions h0 0 1i, h2 2 1i and h1 1 0i respectively. There are surface semichannels and channels along these directions that lead to the reflection of main part of incident ions from the surface at w ¼ 10° and thus to decreasing the sputtering yields in these directions. The curve nd has a maximum at n ¼ 20, broad maximum at n ¼ 50° and increases monotonic in the region of azimuth angle of incidence 65° < n 6 90°. The formation of these maxima testifies to favorable realization of conditions (1) and (2) for non-dissociative desorption of adsorbed molecules. Present code allows to differ three compound parts of non-dissociative desorbed molecules: in first case during the collision processes the both atoms of molecule receive the impulses directed to the vacuum; and two other cases one of atoms of molecule receives an impulse directed to the vacuum, the second of them receives an impulse
Fig. 3. The dependencies nd1, nd2, nd3 versus the azimuth angle of incidence n at w ¼ 10° and 5 keV Neþ ion bombardment of O2 /Ag(1 1 0) surface. Number of incident particles is 2 104 .
directed to the crystal. Fig. 3 shows these components versus the azimuth angle of incidence, where nd1 corresponds to the first case; nd2 corresponds to the case when atom number 1 of molecule has an impulse directed to the vacuum (and atom number 2 can have an impulse directed to the crystal); nd3 corresponds to the case when atom number 2 of molecule has an impulse directed to the vacuum. Thus, the number of non-dissociative desorbed molecules consists of three components: nd ¼ nd1 þ nd2 þ nd3 (see curve nd in Fig. 2). In Fig. 3 it is possible to observe the local maximum at n ¼ 0 and main maxima at n ¼ 15; 55; 90° in curve nd1. The most broad intensive maximum near n ¼ 90° was conditioned by the presence of favorable conditions for non-dissociative desorption of adsorbed molecules due to the possibility of a channeling of incident particles under an adsorption layer in this direction, as long as an axis of molecules is parallel to the h1 1 0i direction. In curve nd2 the basic maxima are observed at n ¼ 45°; 70° and calculation results show that in this case the significant part of ion energy loses at collisions by the atom number 1 of molecule. In dependence nd3 there is one intensive peak, and this peak gives the basic contribution on quantity of non-dissociative desorbed molecules of oxygen at n ¼ 20°. In Fig. 4 the spatial angular distribution of the sputtered Ag atoms on polar d and azimuth u angles of ejection has been presented at 5 keV Neþ
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121
Fig. 4. The angular (polar d and azimuth u) distribution of the sputtering Ag atoms at 5 keV Neþ ion bombardment of Ag(1 1 0) surface for w ¼ 10° and n ¼ 55°. Number of incident particles is 2 104 .
ion bombardment of Ag(1 1 0) surface for w ¼ 10° and n ¼ 55°. Distribution shows that the sputtered atoms are ejected mainly under polar angles d ¼ 40–75° and azimuth angles near u ¼ 90°, 270°. Such distribution on azimuth angles corresponds to the ejection of matrix atoms along the normal of plane of incidence.
4. Conclusions The ion sputtering of Ag atoms and ion-impact desorption (in particular non-dissociative desorption) of O2 molecules in the case of low energy grazing Ne ion bombardment of clean and O2 covered Ag(1 1 0) surface have been simulated in the consequence binary collision approximation. The azimuth angular dependencies of Ag sputtering yield and non-dissociative O2 desorption yield for the case of 5 keV Neþ ion bombardment at w ¼ 10° have been calculated. It was shown that these dependencies correlate the crystal orientation. The influence of surface potential barrier on
the non-dissociative desorption yield has been studied and it was observed that the basic part of ion-impact desorbed particles overcomes a potential barrier. The calculated results show that in the certain directions of incidence owing to channeling of ions between adsorption layer and surface the effective desorption of adsorbed particles occurs and the character of desorption strongly depends on orientation of a crystal. Spatial distribution of sputtered particles shows that in the case of grazing ion bombardment the particles are mainly ejected in the direction near the normal of plane of incidence.
Acknowledgements Authors thank the Fundamental Research Foundations of Uzbek Academy of Sciences and CNRS (National Center of Scientific Investigations of France) for their support.
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References [1] R. Behrisch (Ed.), Sputtering by Particle Bombardment I, Springer, New York, 1981. [2] R. Behrisch (Ed.), Sputtering by Particle Bombardment II, Springer, New York, 1984. [3] E.S. Mashkova, V.A. Molchanov, Rad. Eff. 102 (1987) 125. [4] A.A. Dzhurakhalov, I.I. Khafizov, Nucl. Instrum. Meth. Phys. Res. B 153 (1999) 326. [5] J. Onsgaard, W. Heiland, E. Taglauer, Surf. Sci. 99 (1980) 112. [6] E. Taglauer, G. Marin, W. Heiland, U. Beitat, Surf. Sci. 63 (1977) 507. [7] E. Taglauer, U. Beitat, W. Heiland, Nucl. Instrum. Meth. 149 (1978) 605. [8] Sh. Kapur, B.J. Garrison, Chem. Phys. 75 (1981) 445.
[9] D.J. OÕConnor, R.J. MacDonald, W. Eckstein, P.R. Higginbottom, Nucl. Instrum. Meth. Phys. Res. B 13 (1986) 235. [10] A.A. Dzhurakhalov, N.A. Teshabaeva, V.Kh. Ferleger, Uzb. Fiz. Zhurn. 4 (1993) 65. [11] A.A. Dzhurakhalov, S. Rahmatov, Surface and Coatings Technology 158–159 (2002) 277–280. [12] D.J. OÕConnor, J.P. Biersack, Nucl. Instrum. Meth. Phys. Res. B 15 (1986) 14. [13] E.S. Parilis, L.M. Kishinevsky, N. Yu. Turaev, B.E. Baklitzky, F.F. Umarov, V.Kh. Verleger, S. Niznaya, I.S. Bitensky, Atomic Collisions on Solid Surfaces, NorthHolland, 1993. [14] O.B. Firsov, Zhurn. Eksper. Teor. Fiz. 36 (1958) 1517. [15] O.S. Oen, M.T. Robinson, Nucl. Instrum. Meth. 132 (1976) 647. [16] I.S. Bitenskiy, E.S. Parilis, Zhur. Tekh. Fiz. 51 (1981) 2134.