Computer Simulation of Marker Evolution upon Ion Irradiation
- PDF / 596,090 Bytes
- 4 Pages / 417.6 x 639 pts Page_size
- 44 Downloads / 185 Views
Qinghua University,
Beijing, China ABSTRACT In ion beam mixing, the subject on the marker evolution of Si/Pt/Si target during 300 keV Xe ion irradiation has been an interesting topic of recent years. A computer simulation for this system by using the Monte Carlo code TCIS-4 is reported here. Dynamic target model was employed. Some radiation-enhanced diffusion and relaxation of the displacement cascades were also considered. Results of this simulation study reveal the evolution of Pt marker profile with fluences during bombardment. The shifts of Pt marker and the dispersions evaluated from the profiles agree fairly well with experimental date, demonstrating a reslistic model of the target being irradiated is important. 1.
Introdution
Marker experiment is a fundamental method for quantitative study on the mechanism of ion beam mixing of layered solids. The evolution of Pt marker in the Si/Pt/Si target upon 300 keV Xe ion irradiation has been an interesting subject and investigated extensively in recent years, e.g., by experimental measurements [i], by transport theory analyses [2,3] and by Monte Carlo simulations (4,5]. This paper reports some of our results on the mixing of this system by means of Monte Carlo simulations with the TCIS-4 code which incorporates a dynamic target, relaxation and sane simple consideration of radiation-enhanced diffusion. 2.
A Description of The Computer Mode
TCIS-4 code considers a dynamic target instead of a static one as described previously [6]. This code employs the procedure proposed by Roush et al [4,7] to simulate the evolution of the three-element targets under ion bombardment. The target is treated as a nutber of parallel layers containing randomly located atoms, with the composition of each layer specified by the appropriate pseudo-particles. The width of a thin layer is about 10 A, and non-equidistant depth grid is maintained in the eascade simulations. Atomic pair collision is governed by the Moliere potential with Firsov screen Length [8). According to a generally accepted idea in metallurgy, the static atcmic volume of an element in various alloys maintains approximately a constant [9]. This principle is adopted when relaxation of target after each collision cascade is considered. Because of the strong chemical affinity between Pt and Si stares [10], the short range radiation-enhanced diffusion may be an important mechanism at low temperature as 90 K. A simple mode to incorporate this diffusion is hence considered. It is assuned that, other than ballistic mixing, a recoil can make a diffusion jump toward its closer neighbour layer, if the atomic concentration of this recoil species in its original layer is larger than that of the neighbour one. The jtmp length is taken as o-i/3 times the concentration difference of this recoil species between the two layers,
Mat. Res. Soc. Symp. Proc. Vol. 54. 1986 Materials Research Society
228
where 10 denotes the average atomic density in the original layer. TCIS-4 code has the capability to show the atomic trojectories of a ca
Data Loading...
