NSF: Direct Imaging of Charge Distribution in Ceramic Materials

如果人们知道一种物质中所有电子的位置，就不需要找出原子核的位置了。这是一个非常强烈的说法，虽然它可能不是在所有可能的情况下都是正确的，但对于许多材料来说是正确的。虽然在我们在投影中以原子分辨率确定材料的局部结构的能力方面有了进展，但几乎所有这些都集中在定位原子位置上。更困难的确定电子位置的问题还没有得到很好的开发，但如果可能的话，它将为材料研究提供一个新的信息维度。如果成功，这类数据的潜在应用范围非常广泛，包括催化研究；作为新的介电、铁电和某些情况下的磁性装置，以及在氧传输膜和燃料电池中；它对于在原子水平上理解许多腐蚀问题也是至关重要的。这些研究还将提供丰富的实验数据，可以对理论模型进行比较和校准，其精度远远高于目前可能的水平。因此，我们提出的研究提出了一个巨大的挑战，即在纳米尺度上实验确定陶瓷材料中的局部电荷分布，特别是参考单个缺陷的研究。为了了解电荷分布对材料性质的影响，我们打算开发直接成像电荷的方法。特别是，我们希望研究电荷在表面和缺陷上的重新分布，这通常是材料性能和器件性能的关键。为了实现这一点，我们将开发使用扫描隧道显微镜(STM)和像差校正高分辨率电子显微镜(HRTEM)来成像电荷的实验方法。我们还将比较这两种提供互补信息的技术的结果。该项目将跨越两个国际领先的机构，一个在英国，一个在美国，每个机构都可以获得用于这一目的的独特仪器和计算。提案的每一部分都将提供新的一般方法，我们将在涉及一系列重要技术材料的开创性实验中利用这些方法。该项目的资金将支持在每个合作机构工作的两名博士后研究员，以及使两个研究小组的成员能够在合作实验室工作的旅费。

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.