AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS3-WeM

Paper SS3-WeM7
Trapping Dynamics of Ethane on Si(100)-(2x1) Studied by Molecular Beam Experiments and Classical Molecular Dynamics Simulations

Wednesday, October 4, 2000, 10:20 am, Room 210

Session: Gas/Surface Dynamics
Presenter: C.T. Reeves, University of Texas at Austin
Authors: C.T. Reeves, University of Texas at Austin
C.B. Mullins, University of Texas at Austin
Correspondent: Click to Email
In order to gain insight into the dynamics of trapping, or physical adsorption, we have experimentally measured the trapping probability of ethane on a clean Si(100) surface as a function of the incident translational energy and incident polar angle of the molecule at a surface temperature of 65 K using UHV molecular beam techniques. At all incident angles the trapping probability decreases as the translational energy of the incoming ethane molecule is increased from 0.05 to 1.3 eV. As the incident polar angle, with respect to the surface normal, is increased, the trapping probability decreases. This decrease in trapping probability with increasing polar angle contradicts the idea of normal energy scaling and has been seen in very few cases. Classical molecular dynamics calculations have been employed to study the cause of this unusual angular dependence. This simulation predicts trapping probabilities in good agreement with the experimental data. Analysis of the computed trajectories indicates that the initial site of impact within the unit cell, as well as the details of energy exchange during the initial impact with the surface, is important in determining the fate of an incident molecule. Although it is difficult to experimentally measure the effect of rotational energy and surface temperature on trapping, molecular dynamics simulations offer a means to study the details of these effects. Recent experimental studies by Vattuone et al. have indicated that for trapping of ethylene on Ag(001), increasing the average rotational energy from J = 2 to J = 8 can greatly decrease the trapping probability. Our simulations of ethane trapping on Si(100) have indicated that the trapping probability does decrease with increasing J, although the effect is only significant at very high values of J (>20). We have also computationally investigated the effect of surface temperature on trapping and these results will be reported.