Predicting the impact of the environment on the structure,
chemistry, and electronic properties of metal oxide surfaces
Anne M. Chaka, Physical and Chemical Properties Division
Metal oxide surfaces are important in a wide range of technological
applications such as catalysis, microelectronics, gas sensors,
and corrosion protection. The growth, structure, and subsequent
performance of these surfaces are very sensitive to the amount and
type of chemical species present in the environment, such as oxygen
and water. Hence understanding how dissociation of oxygen and water
at surfaces depends upon the type of metal oxide and concentration
of reactants is key for predicting and controlling performance of
these materials. Unfortunately the gap between conditions accessible
to UHV surface science and what is observed in nature or in industry
has made it difficult to understand why, for example, the hematite
(0001) surface reacts with water vapor at a far lower threshold
pressure than corundum, α-Al2O3, but
yet is much more stable with respect to weathering and solubility.
Theoretical predictions and modeling can provide a powerful means
to evaluate fundamental chemical processes with atomic
resolution, but also face the challenge of including the effects of
a complex environment. We employ a method of ab initio thermodynamics
that enables us to link 0K density functional theory electronic
structure and vibrational calculations to finite temperatures and
pressures. We are thus able to calculate the free energy of a
surface in equilibrium with multiple species in heterogeneous
systems and predict how surface structure, reactivity, electronic,
and magnetic properties change in response to the environment.
Integrating theory and modeling with experimental techniques has
led to improved understanding of aqueous interfaces, how
SnO2 gas sensors function, and how stainless steel
becomes passivated.
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