Theoretical Research On The Interactions Between Ion Cluster And Metal Oxides

The Coulomb explosion process for energetic ion clusters penetrating through several metal oxides (Al₂O₃,SiO₂) with different incident velocity have been studied in the present work. While penetrating through the solid target, the cluster's motion is governed by two basic effects. Coulomb repulsion potential leads to a separation among the ions, meanwhile the potential induced by excitation of the electron gas slows down the explosion pace. In our present work, this induced potential is described by the dielectric response formalism in joint with a dielectric function which was introduced by Abril and Arista. The dielectric function is a linear combination of series of Mermin-type functions, with coefficents fitted from experiment data at optical limit (k=0). The advantage of this dielectric function is that it can be capable for different compounds and the ions with small incident velocity. Different from the Coulomb potential, the induced potential is unsymmetrical, which leads to the vicinage effect. The individual ion's charge distribution is derived by using Brandt-Kitagawa effective charge model in conjunction with the spacial potential. Coulomb explosion's pattern is simulated by solving equations of motion for individual ions. The multiple scattering effect is also considered. We consider the multiple scattering only affect on the ion's velocity. A multiple scattering model is built up with three random parameters (free path, axial and radial deflective angle). The influence of multiple scattering was simulated by Monte Carlo method while applying this model to the Coulomb explosion process with random free path.With this Mermin-type dielectric function, our research object can be enlarged to the cases for metal oxides or with small incident velocity. Our work begins with the simple 2D structured B₃⁺, B₄⁺ clusters and then extend to the spherical C₂₀. We focus on the metaloxides medium and small incident velocity and the result is compared with high incident velocity.It is found that, with high incident velocity, the cluster's structure and ions' charge distribution shows an asymmetry. And following ions' charge oscillate obviously, the spherical C₂₀ transforms to a tube-like structure after a certain time. This vicinage effectdecays with the distance increase. As the incident velocity decreases, the vicinage effect gets diminished, leading to a more symmetric cluster structure and the ions' charge state close tothat of isolated ions.Thus, the multiple scattering becomes the main factor that affect thecluster's structure for the case of low ion velocities.