Name: Projesh Kumar Roy
Diploma / M.Sc degree: IIT Kanpur, India
(May 2013)

PhD Project: Structure formation of glass on surfaces after vapor deposition: a computational study

Abstract of Research Project

Glassy materials are normally prepared by slow cooling of the metastable liquid phase up to its glass transition temperature (Tg). It is known that the 'stability' (low enthalpy) of the glass increases as the cooling rate is lowered. In recent experiments, it was found that if glass was prepared by depositing vaporised molecules of a glass-forming system on a metal surface of constant temperature the stability of the resulting glass can be much more higher than that of ordinary glasses. This stability depends on the flux of depositing molecules, type of the surface used, and temperature of the surface. The origin of this extraordinary stability is still a mystery. The goal of this project is to understand the structural differences of the vapor-deposited glass with ordinary glass and the relation of the stability to various factors by using molecular dynamics simulations. We are also intending to simulate a flux experiment similar to the actual vapor deposition experiment using MD simulation to understand this phenomenon on the molecular level.

In recent experiments a two dimensional silica bilayer was grown on a metal surface[Ru(0001)] and studied with Scanning Probe Microscopy(SPM). Interestingly, depending on the flux and the chosen silica and oxygen concentration amorphous as well as crystalline bilayers could be grown. Under specific conditions even both structures could be generated in the same layer, allowing one to study the transition from the amorphous to the crystalline region. Via simulations, we want to computationally reproduce these local structural diversities of silica and try to improve the understanding under which conditions amorphous or crystalline structures are preferred, respectively.