Using multi-scale modelling techniques developed in the group we aim to assist experimentalists in the interpretation and understanding of collected images, but also to suggest new experimental procedures protocols. the modelling requires a balance of high level ab initio modelling with the use, and development of empirical force fields.
Most NC-AFM imaging is carried out on insulating surfaces, frequently metal-oxides. Atomic resolution has been achieved on several metal oxides e.g. MgO, NiO, CeO2, TiO2, as well as alkali halides and some fluorides. Understanding the images produced experimentally requires close cooperation between experiment and theory and has led to the unambiguous interpretation of images on CaF2. One surface under examination at present is CeO2, which presents a number of challenges â€“ particularly modeling the rare earth metal Ce require the use of advanced techniques, going beyond conventional density functional theory, such as DFT+U. We are currently trying to understand the nature of stable defects imaged on the ceria surface, which we hope will enable us to understand in more detail the nature of the tip used in these experiments.
As well as conventional imaging we are interested in the use of NC-AFM to carry out manipulation chemistry in a controlled way on insulating surfaces. To this end we have examined the conditions for simultaneous imaging of adsorbed molecules and the ideal surface and also the conditions required for the manipulation of surface defects. Of particular interest, as both a pedagogical tool and also a realistic scenario, has been an oxygen vacancy on a MgO surface, where we find the AFM tip has the potential to strongly influence surface diffusion barriers and where we believe controlled manipulation in dynamic operating mode is feasible.
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