Fig. 4: Ångström-scale resolution in laser-induced molecular orbital imaging.
From: Real-space subfemtosecond imaging of quantum electronic coherences in molecules
a, Differential conductance (dI/dV) measurements on an individual PTCDA molecule constituting a four-monolayer-thick multilayer assembly on a Au(111) surface. The two curves are measured on PTCDA molecules in adjacent rows. The spatial positions of the nanotip during the measurement are indicated by coloured crosses in f. The d.c. bias and set-current before the start of the measurement are –2 V and 50 pA, respectively. b,c, Simulated constant-current (50 pA) STM images of the HOMO and LUMO of PTCDA molecules constituting a four-monolyer thick multilayer on top of Au(111), respectively, by utilizing the Tersoff–Hamann approximation (Supplementary Section 8). d,e, Simulated STM images obtained by convoluting the images given in b and c with an s-type wavefunction of the nanotip of the STM with a decay length of 1.8 Å along the vertical direction and 0.8 Å along the horizontal direction. f,g, Experimentally measured spatial distribution of the laser-induced tunnelling current for the HOMO (–1.8 V; g) and LUMO (1.4 V; h) orbitals. Scale bars in all the panels denote a spatial distance of 1 nm. White dashed circles in d–g are guides to the eye. Steady-state STM imaging was performed in the constant-current mode at a set-point current of Id.c. = 50 pA. The reproducibility of the data in f and g was confirmed in five individual measurements.
