Mechanism of high-resolution STM, AFM and IETS-STM imaging with functionalized tips

High-resolution AFM and STM with functionalized tips is well established [1,2], but a detailed understanding of the image mechanism is still missing. Moreover, recently this family of imaging techniques has been complemented by a method based on inelastic electron tunneling spectroscopy [3]. Here we present a comprehensive mechanical and transport simulation model [4,5] that explains essentially all image features in functionalized tip STM, AFM and IETS-STM. Important aspects of the mechanism are: (i) Images are dominantly determined by Pauli repulsion [6], (ii) in STM and IETS STM this force signal is transduced into an elastic [6,7] or inelastic [5] conductance signal, (iii) probe particle relaxation leads to image sharpening [4], (iv) the apparent imaging of hydrogen bonds can be explained by a relaxation effect [4], and (v) electrostatic forces may also influence the image contrast [5]. [1] Temirov et al., New J Phys 10, 053012 (2008) [2] Gross et al., Science 325, 1110 (2009) [3] Chiang, et al., Science 344, 885 (2014) [4] Hapala et al. Phys. Rev. B 90, 085421 (2014) [5] Hapala et al. Phys. Rev. Lett. 2014 in press [6] Weiss, et al. Phys. Rev. Lett. 105, 086103 (2010) [7] Kichin et al. Phys. Rev. B 87, 081408(R) (2013)