NSF: Direct Imaging of Charge Distribution in Ceramic Materials

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If one knew the positions of all the electrons in a material, there would be no need to find where the nuclei are . This is a very strong statement, and whilst it may not true in all possible cases, for many materials it is. Whilst there have been developments in our ability to determine the local structure of materials at atomic resolution in projection almost all of these have focused on locating the atom positions. The more difficult problem of determining the positions of the electrons is much less well developed but, if possible would provide a new dimension of information in materials research. If successful, the potential application of this type of data is very wide ranging and includes studies of catalysis; as new dielectric, ferroelectric and in some cases magnetic devices and in oxygen transport membranes and fuel-cells; it is also critical to the understanding at the atomic level of many corrosion problems. These studies will also provide a rich seam of experimental data against which theoretical models can be compared and calibrated at far higher precision than is currently possible. Our proposed research therefore poses a Grand Challenge , namely the experimental determination of local charge distribution in ceramic materials at the nanoscale with particular reference to studies of individual defects. To understand the effects of charge distribution on material properties we intend to develop methods for directly imaging charge . In particular we wish to examine the redistribution of charge at surfaces and defects which are often crucial to materials properties and device performance. To achieve this we will develop experimental methods for imaging charge using both Scanning Tunneling Microscopy (STM) and aberration corrected High Resolution Transmission Electron Microscopy (HRTEM). We will also compare results from these two techniques which provide complementary information. This project will span two internationally leading institutions, one in the UK and one in the USA each of which has access to unique instrumentation and computation for this purpose. Each part of the proposal will deliver new general methodologies and we will utilize these in pioneering experiments involving a range of technologically important materials. Funding for this project will support two post doctoral research fellows working at each of the collaborating institutions together with travel costs to enable members of both research teams to work in the collaborating laboratories.