Structure and Thermodynamics of Model Catalytic Oxide Surfaces
Ann Chiaramonti Debay | Download entire thesis

The atomic scale structure of crystalline surfaces plays an important role in the
overall properties of materials systems, especially those relating to heterogeneous
catalysis, thin film growth, and the increasingly miniaturized world of micro elec-
trical mechanical systems (MEMS). Nanoscale engineering of materials has become
commonplace and as technologies begin to emerge on smaller and smaller length
scales, surface properties become increasingly more important relative to those
of the bulk. Only through knowledge of the surface structure of materials can
one truly understand the nature of the processes that play out on them. The
research described in this manuscript involves a combination of computational
(Direct Methods) and experimental (TEM) methods for the investigation of the
surface structure and thermodynamics of two model heterogeneous catalytic ox-
ides, alpha-Fe2 O3 (the mineral hematite) and SrTiO3 .

A new flux system has been developed for the growth of single crystal alpha-Fe2 O3 .
The effect of ion bombardment and annealing on the (0001) surface of hematite was
investigated, and the differences between pure and impure samples are presented.
Finally, methodologies are discussed for obtaining the “biphase” surface structure
on a TEM-ready sample.
Several new reconstructions were observed on the (111) surface of SrTiO3 , in-
cluding (3x3), ( 9/5 x 9/5 ), (6x6), and (4x4) unit cells. The structure of the (3x3) surface
has been solved and it is proposed that all of the herein observed reconstructions
will be scaleable structures from a general motif, with the different unit cell sizes
being accommodated by differences in the occupancy of surface sites. The regions
of phase stability have been accurately determined for the reconstructions in time,
temperature and oxygen partial pressure, and a metastable surface phase diagram
has been constructed. A region of metastable three-phase coexistence has been
observed over a wide range of temperatures and oxygen partial pressures.