Transcript No Slide Title

Application of molecular dynamics: HREM simulation of bonded interfaces
Kurt Scheerschmidt
MPI für Mikrostrukturphysik, 06120Halle,Germany, http://www.mpi-halle.de,[email protected]
Classical Molecular Dynamics (MD)
>10000 atoms
Bonding experiment
time-integration (fs-steps) up to relaxation (˜ 1ns)
simultaneously 3N Newtonian equations of motion
with V = empirical interaction potential
mjd2rj/dt2 = Fj = -V/rj
Initial conditions:
geometric start model, Boltzmann distributed momentums
Boundary conditions:
Fixed, Periodic, Thermo-Elastic
Constraints:
NVE, NVT, microcanonical ensembles
ab initio
˜ 100 atoms (parameter free all electron, pseudopotentials, LDA, CP, ...)
tight-binding ˜ 1000 atoms (wavefunction = atomic orbitals, TB-Hamilton ss, sp, pp, pp, .... )
Some of the most important properties of materials in high-technology applications are strongly influenced or even controlled by the presence
of solid interfaces. Especially for bonded interfaces are the structural characterization of their atomic arrangements and of the interface defects
of great importance in relation to the bonding process controlled by, for example, misfit, orientation relation, and adsorbates at the boundaries.
The interfaces are investigated by high resolution electron microscopy (HREM) providing local atomic information and using conventional
diffraction contrast techniques (DC) to analyze the defect structure. The relaxed atomic structures of the interfaces are modeled by molecular
dynamics (MD) using suitably fitted empirical potentials and thermo-elastic embedding. The HREM and DC images are simulated using the
multi-slice technique based on the MD relaxed structure models to reveal the interface structure resulting from the bonding process.
Bonding across surface steps
Twist rotation and screw dislocations:
cross section HREM and plan viewDC
Electronic interface structure
MD interface annealing: Potential energy
Variation of the rotation angle and the defect structure
a(degree) DE(eV/atom) atoms box(nm)
2.8 841
0.4
134500 22.3
4.6 313
0.5
40000 13.5
6.7 145
0.3
23000 9.2
12.7 41
0.2
6500 4.1
Simulated 400kV plan-view DC
bright-and dark-field images
demonstrating the visibility
of the two types of bonded
interface structures according
to differently dimerized surfaces.
Screw dissociation