Electron‐Induced Dynamics of Heptathioether β‐Cyclodextrin Molecules

Abstract

Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are performed on heptathioether β-cyclodextrin (β-CD) self-assembled monolayers (SAMs) on Au. The β-CD molecules exhibit very rich dynamical behavior, which is not apparent in ensemble-averaged studies. The dynamics are reflected in the tunneling current-time traces, which are recorded with the STM feedback loop disabled. The dynamics are temperature independent, but increase with increasing tunneling current and sample bias, thus indicating that the conformational changes of the β-CD molecules are induced by electrons that tunnel inelastically. Even for sample biases as low as 10 mV, well-defined levels are observed in the tunneling current-time traces. These jumps are attributed to the excitations of the molecular vibration of the macrocyclic β-CD molecule. The results are of great importance for a proper understanding of transport measurements in SAMs.

Dynamics of Decanethiol Self-Assembled Monolayers on Au(111) Studied by Time-Resolved Scanning Tunneling Microscopy

“…In this paper, the bandwidth of the current−voltage converter (≈50 kHz) limits our temporal resolution to 20 μs. 38 This motivated us to conduct the present study, in which the dynamics on various phases were studied by recording the current−time spectroscopy with a temporal resolution of 20 μs. (11 × 11 mm 2 , 250 nm Au on 2 nm Cr on borosilicate glass) for STM measurements were purchased from Arrandee (Werther, Germany).…”

“…Due to this limitation in temporal resolution, dynamic events are often averaged out. Only a limited number of studies have been performed with a substantially higher time resolution; see, for instance, refs and . The time resolution of a standard STM instrument can be improved by 6–7 orders of magnitude by recording tunnel current–time traces at a preselected position with the feedback loop disabled.…”

“…The time resolution of a standard STM instrument can be improved by 6–7 orders of magnitude by recording tunnel current–time traces at a preselected position with the feedback loop disabled. In this paper, the bandwidth of the current–voltage converter (≈50 kHz) limits our temporal resolution to 20 μs . This motivated us to conduct the present study, in which the dynamics on various phases were studied by recording the current–time spectroscopy with a temporal resolution of 20 μs.…”