Control of the Spatial Resolution in Ultimately High Resolution STM Experiments with [001]-Oriented Single Crystalline Tungsten Probes

We report high resolution scanning tunneling microscopy (STM) studies performed with [001]-oriented single crystalline tungsten tips. The sharpness of the W[001] tips cleaned by electron beam heating and ion sputtering is confirmed by electron microscopy data. Distance dependent STM experiments with the W[001] tips on a graphite surface demonstrate possibility to select the tip electron orbitals responsible for high resolution imaging using single crystalline probes. This is confirmed by imaging two-fold and four-fold split subatomic features reproducing the shapes of tungsten d(xz) and d(xy) atomic orbitals at specific tunneling conditions. (C) 2012 Published by Elsevier B. V. Selection and/or peer review under responsibility of Chinese Vacuum Society (CVS).