Nanoscale modification of silicon surfaces via Coulomb explosion
نویسندگان
چکیده
Coulomb explosions on silicon surfaces are studied using large-scale molecular-dynamics simulations. Processes under investigation begin by embedding a region consisting of 265–365 singly charged Si ions on a Si @111# surface. The repulsive electrostatic energy, initially stored in the charged region, leads to a local state with ultrahigh pressure and stress. During the relaxation process, part of the potential energy propagates into the surrounding region while the remainder is converted to kinetic energy, resulting in a Coulomb explosion. Within less than 1.0 ps, a nanometer-sized hole on the surface is formed. A full analysis of the density, temperature, pressure, and energy distribution as functions of time reveals the time evolution of physical properties of the systems related to the violent explosive event. A shock wave that propagates in the substrate is formed during the first stage of the explosion, 0,t,100 fs. The speed of the shock wave is twice the average speed of sound. After the initial shock the extreme nonequilibrium conditions leads to ultrarapid evaporation of Si atoms from the surface. Qualitatively similar features are observed on a smaller scale when the number of initial surface charges is reduced to 100. Our simulations demonstrate the details of a process that can lead to permanent structure on a semiconductor surface at the nanoscale level. The work reported here provides physical insights for experimental investigations of the effects of slow, highly charged ions (Q .40, e.g.! on semiconductor materials. @S0163-1829~97!02104-8#
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