Tomasz Zientarski

Molecular dynamics study of roughness and stress evolution using a Lennard--Jones potential

A three-dimensional molecular dynamics (MD) simulation is proposed to study the film growth, roughness and stress evolution during atom deposition on the (100) plane of a fcc regular crystal. We use the cubic system with an x–y periodic boundary condition. At the bottom we have an atomic surface and at the top a reflecting wall. The model uses the Lennard-Jones potential to describe the interatomic forces. The simulation results show that the film grows with the Volmer–Weber mode and exhibits specific curve shape of the stress evolution. The mean biaxial stress obtained during the simulation attains a local tension maximum at a coverage of two monolayers. The stress in the normal direction is smaller than the biaxial stress. The main contribution to the stress in the film arises from the first monolayer. The curves describing roughness possess maximum values at the same substrate coverage. The dependence of the roughness on the temperature is examined.

Stress evolution during deposition of heteroepitaxial systems

Stress evolution during deposition of heteroepitaxial systems on flat and line-patterned substrates was studied by three-dimensional (3D) molecular dynamics simulation. The simulation of deposition process was carried out in a system consisting of the (001) substrate of a face-centred cubic crystal and pre-deposited atoms forming flat layers or patterned lines. Interactions between the atoms were described by the Lennard-Jones potentials. Kinematic theory of scattering was used to analyse the structures obtained from simulations. Stress evolution during the growth of thin films at different temperatures of the systems was also studied. It was found that in-plane stress is an anisotropic in heteroepitaxial systems. In the case of flat pre-deposited layers, the distribution of stress does not depend on temperature and the distribution of stress is determined by orientation of linear structures in patterned systems.

Study of Structure and Strain in Au/Cu Systems Using Molecular Dynamics Simulation: X-Ray Scattering Analysis

The aim of this work is to investigate structure and stress evolution in Au/Cu bilayer systems during deposition. The approach used here is based on an embedded atom method (EAM). interatomic potential database for different metal elements, their alloys and multilayers. We applied the kinematical scattering theory to calculate the X-ray scattering profiles. In this case the X-ray scattering techniques are used for the structural characterization of crystal structures obtained from simulation data. This method was applied to determine the lattice parameters in any directions. The lattice parameters in deposited layers were directly determined by the analysis of X-ray diffraction profiles. Results shows that on the interface of Au/Cu system, the crystalline lattice of Au layer is fitted to crystalline lattice of Cu layer. We found that deformation of the crystal lattice near the interface has a major influence on the stress.

Molecular Dynamics Study of Adatom Size Effect on Stress Evolution in Lennard-Jones Thin Films: X-Ray Scattering Analysis

Molecular dynamic simulations are used to study the structure and the evolution of stress during the deposition of atoms with different size on the (001) FCC plane. The relative size of deposited atoms is changed in the range from 0.75 to 1.0. To calculate the X-ray scattering profiles we applied the model that is based on the kinematical scattering theory. Deformation of the lattice parameters in deposited layers were directly determined by the analysis of X-ray diffraction profiles. It was found that the crystal lattice near the surface exhibits a major influence on the stress evolution. The deposited atoms form the same structure in entire systems, regardless of the their relative size.

Molecular dynamics simulation of stress and grain evolution

A three-dimensional molecular dynamics simulation is carried out to study the evolution of grains and stresses during the deposition of atoms on the (100) plane of a fcc regular crystal, using the cubic system with x–y periodic boundary conditions. At the bottom an atomic surface and at the top a reflecting wall are assumed. Atoms in the system interact via the Lennard–Jones potential. During simulation the films grow according to the Volmer–Weber mode and exhibit specific shape of the stress curves. When the film becomes continuous, the stress during the growth possesses a maximum value, but later new grain boundaries are formed. Individual atoms in the grain boundaries generate compressive stress in the films.