Tunneling electron induced rotation of a copper phthalocyanine molecule on Cu(111)

Abstract

The rates of a hindered molecular rotation induced by tunneling electrons are evaluated using scattering theory within the sudden approximation. Our approach explains the excitation of copper phthalocyanine molecules (CuPc) on Cu(111) as revealed in a recent measurement of telegraph noise in a scanning tunneling microscopy experiment [Schaffert et al., Nat. Mater. 12, 223 (2013)]. A complete explanation of the experimental data is performed by computing the geometry of the adsorbed system, its electronic structure, and the energy transfer between tunneling electrons and the molecule's rotational degree of freedom. The results unambiguously show that tunneling electrons induce a frustrated rotation of the molecule. In addition, the theory determines the spatial distribution of the frustrated rotation excitation, confirming the striking dominance of two out of four molecular lobes in the observed excitation process. This lobe selectivity is attributed to the different hybridizations with the underlying substrate.

Controlled switching of a single CuPc molecule on Cu(111) at low temperature

“…3(c) and (d) these rings are relaxed more strongly towards the substrate. This also is consistent with the predicted larger local density of states of the split LUMO level aligned with the H-axis 49.…”

“…Subsequently, the same group identified the high-current state with the lowest energy configuration of the molecule, in which the opposite lobes in question are aligned perpendicular to a 110 direction of the Cu(111) substrate, and the low-current state with two metastable configurations in which the same lobes are rotated by ±7 • . 48,49 However, we show that this assignment has to be partly revised in the light of additional details revealed by our experiments.…”

“…Such random signals are assigned to a random jump between two distinct conformations of the molecule. The position sensitive telegraph noise of CuPc on Cu(111) was explained by an athermal activation of frustrated rotations of the molecules by ±7 • around their center driven by inelastic tunneling 48,49. Since the ±7 • rotations lead to two equivalent conformations, we assign the telegraph noise to random jumps between the two ±7 • rotated conformations passing in every jump the 0 • position, corresponding to the excited and ground states of the molecule, respectively.…”

Mechanical and Electrical Properties of Single Molecules

“…For metal phthalocyanine molecules, it is assumed that an electron transfer from the metal surface to the molecule takes place [64,65]. For CuPc on Cu(111), the overall charge transfer is assumed to be two electrons [66,67]. However, in the presence of a NaCl bilayer, this charge transfer is affected and the electronic structure of the molecule remains nearly as in its gas phase [7].…”

Hindered surface diffusion of bonded molecular clusters mediated by surface defects

“…Such systems form a variety of 2D structures [11,12] and have applications ranging from catalysis [13], molecular spintronics [14,15], and organic electronic devices [16,17]. Specifically, the CuPc/Cu(111) system has been extensively characterized across many techniques from sub-ML to multi-layer coverage across a large temperature range [18][19][20][21][22][23][24][25][26][27][28][29][30]. Room temperature (RT) STM experiments show that CuPc is highly mobile on noble metal (111) surfaces under 1 ML [21,28,29,31].…”