Nanowires / Nanoobjects

MD-simulations of silica, glasses and small particles

Abstract People Publications Cooperations Alumni

Starting from crystalline structures amorphous silica and silicate glass models are generated using melting and annealing procedures in the classical molecular dynamics simulation. Optical and mechanical properties of glasses are strongly influenced by the formation of metallic inclusions. Structural models of sodium silicate glasses and embedded silver particles generated by means of molecular-dynamics and molecular-static calculations prove the effects, in particular the influence of the matrix on the particle relaxation (cf. [1]). Furthermore, image simulations carried out on the basis of relaxed structure models confirm the possibilities of HREM of imaging small Ag-particles in glass as a function of the imaging process in the HREM micrographs. The atomic potentials applied to the MD simulations are improved by considering the processes of particle migration and nucleation. Structural models of silica enable to simulate hodrophilic wafer bonding and to understand the hydrogenizations of silica surface (cf. [2]).

The Figure shows a cuboctahedral crystalline Ag-particle (1290 atoms) in a 10x14x12 supercell (6.4x6.2x5.8 nm3) of sodium silicate glass matrix at start (a)  and in the equilibrium state after molecular dynamics annealing and relaxation (b). The 400kV (111) lattice fringes of an Ag particle within commercial glass after ion exchange and annealing (c; HREM: H. Hofmeister, MPI-Halle, Ion exchange: M. Dubiel, University Halle) is compared with calculated HREM micrographs of a spherical (011) oriented Ag particle (1722) atoms in glass before and after relaxation (sample rotation 0°-10°;  voltage 400kV, defocus 37nm, spherical aberration 1mm, defocus spread 10nm, divergence 0.5mrad, aperture 16nm^-1). While particle rotation solely causes minor changes of the lattice fringe distances, the relaxation behaviour is clearly revealed by HREM.