Formation stability and electronic structure of surfaces and interfaces from first principles
This thesis deals with two closely interwoven aspects of first-principle
(density functional theory) materials modeling:
(1)~prediction of atomic structure & chemical composition,
and (2)~prediction of electronic properties.
In the first part, we focus on atomic structure (AS) and chemical composition (CC) of surface and interface
These systems have a large range of technical applications,
building on both mechanical strength and electron behavior.
Surface and interface systems are often fabricated
in complex gas-phase deposition environments.
Characterizing and predicting AS and CC
is an important challenge and understanding of how these result in
a growth environment is
of particular interest.
We formulate a novel nonequilibrium thermodynamic method
to predict AS and CC as a function of the deposition environment.
The method combines first-principle calculations with
chemical reaction theory
and rate-equation modeling.
We implement this method and use it to illustrate its predictive power
for characterizing AS and CC
at industrially relevant interfaces between alumina and titanium carbide,
grown by chemical vapor deposition.
Our predictions of AS and CC result in adhesion properties that agree with
the wear-resistant nature of TiC/alumina multilayers;
equilibrium predictions do not.
This result suggests that our method is a useful theoretical tool
for characterizing materials whose AS and CC is determined
by the specific deposition conditions.
In the second part, we investigate the relevance of van der Waals (vdW)
interactions for electronic properties.
We focus on vdW binding in graphene overlayers at silicon carbide surfaces
and in multilayers of graphane (a fully hydrogenated derivative of graphene).
These materials are promising candidates for future electronic
Performing band-structure calculations and wave-function analysis,
we find that vdW binding to a neighboring layer or substrate
can significantly alter the electronic behavior and in particular the band struc
Our calculations predict strong
local band-gap modifications in insulating graphane multilayers
due to vdW interactions.
We also document
that vdW binding effectively amounts to a doping
of graphene overlayers at SiC surfaces.
van der Waals interaction
density functional theory