Author Archives: Matthew Wolf

Engineering Polarons at a Metal Oxide Surface

Authors: C. M. Yim, M. B. Watkins, M. J. Wolf, C. L. Pang, K. Hermansson, and G. Thornton

Engineering Polarons Figure 1Polarons in metal oxides are important in processes such as catalysis, high temperature superconductivity, and dielectric breakdown in nanoscale electronics. Here, we study the behavior of electron small polarons associated with oxygen vacancies at rutile TiO2(110), using a combination of low temperature scanning tunneling microscopy (STM), density functional theory, and classical molecular dynamics calculations. We find that the electrons are symmetrically distributed around isolated vacancies at 78 K, but as the temperature is reduced, their distributions become increasingly asymmetric, confirming their polaronic nature. By manipulating isolated vacancies with the STM tip, we show that particular configurations of polarons are preferred for given locations of the vacancies, which we ascribe to small residual electric fields in the surface. We also form a series of vacancy complexes and manipulate the Ti ions surrounding them, both of which change the associated electronic distributions. Thus, we demonstrate that the configurations of polarons can be engineered, paving the way for the construction of conductive pathways relevant to resistive switching devices.

Phys. Rev. Lett. 117, 116402, (2016)
DOI: http://dx.doi.org/10.1103/PhysRevLett.117.116402

The Structure and Properties of Clean Steps at Oxide Surfaces

Authors: Matthew J. Wolf, Alexander L. Shluger

We present an overview of the structure and properties of clean steps at the surfaces of binary oxides, utilising recent data from scanning probe and spectroscopic experiments, and theoretical calculations. We review and discuss their atomic structure, electronic structure, and interactions with prototypical point defects, using examples from studies on technologically important oxides such as MgO, CeO2, TiO2 and ZrO2. We also review methods of calculating the step formation energy, and discuss reasons for their limited success in explaining the step structures observed in experiments.

Defects at Oxide Surfaces , Springer Series in Surface Sciences Volume 58 , 2015, pp 191-214.

DOI: 10.1007/978-3-319-14367-5_6