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Chemical Resolution at Ionic Crystal Surfaces Using Dynamic Atomic Force Microscopy with Metallic Tips

This work demonstrated how tips coated with chromium can be characterised in-situ and used to image an ionic surface with atomic resolution, at a tip-sample separation significantly larger than is usually the case. Extensive calculations determined that atomic-scale contrast is due to a known quantum mechanical effect where an intrinsic dipole develops at metallic nano-asperities – a finding which enables the polarity and chemical identity of image features to be determined directly from an image. This approach to imaging surfaces with coated tips leads to a general method for the chemical identification of features in atomic resolution AFM images.