Principles and simulations of high-resolution STM imaging with flexible tip apex

We present a robust but still efficient simulation approach for high-resolution scanning tunneling microscopy with a flexible tip apex showing sharp submolecular features. The approach takes into account the electronic structure of sample and tip and relaxation of the tip apex. We validate our model by achieving good agreement with various experimental images which allows us to explain the origin of several observed features. Namely, we have found that high-resolution STM mechanism consists of the standard STM imaging, convolving electronic states of the sample and the tip apex orbital structure, with the contrast heavily distorted by the relaxation of the flexible apex caused by interaction with the substrate.