Remote Single-Molecule Switching: Identification and Nanoengineering of Hot Electron-Induced Tautomerization

Abstract

Molecular electronics where single molecules perform basic functionalities of digital circuits is a fascinating concept that one day may augment or even replace nowadays semiconductor technologies. The tautomerization of molecules, that is, the bistable functional position of hydrogen protons within an organic frame, has recently been intensively discussed as a potential avenue toward nanoscale switches. It has been shown that tautomerization can be triggered locally or nonlocally, that is, by a scanning tunneling microscope (STM) tip positioned directly above or in close vicinity to the molecule. Whereas consensus exists that local switching is caused by inelastic electrons that excite vibrational molecular modes, the detailed processes responsible for nonlocal tautomerization switching and, even more important in the context of this work, methods to control, engineer, and potentially utilize this process are largely unknown. Here, we demonstrate for dehydrogenated HPc molecules on Ag(111) how to controllably decrease or increase the probability of nonlocal, hot electron-induced tautomerization by atom-by-atom designed Ag nanostructures. We show that Ag atom walls act as potential barriers that exponentially damp the hot electron current between the injection point and the molecule, reducing the switching probability by up to 83% for a four-atom wide wall. By placing the molecule in one and the STM tip in the other focal point of an elliptical nanostructure, we could coherently focus hot electrons onto the molecule that led to an almost tripled switching probability. Furthermore, single and double slit experiment based on silver atom structures were used to characterize the spatial extension of hot electron packets. The absence of any detectable interference pattern suggests that the coherence length of the hot electrons that trigger tautomerization processes is rather short. Our results demonstrate that the tautomerization switching of single molecules can remotely be controlled by utilizing suitable nanostructures and may pave the way for designing new tautomerization-based switches.

Single-molecule tautomerization tracking through space- and time-resolved fluorescence spectroscopy

“…This conclusion is further supported by similar data acquired on single free-base naphthalocyanine molecules that have a lower optical gap and consequently revealed a tautomerization onset at a lower voltage (section S7 of the supplementary information). As fluorescence information was not available, this mechanism was not considered in previous tautomerization experiments induced by STM 3, 8,10,34,35 (see section S7 for a detailed discussion of the tautomerization mechanism). This mechanism may also be involved in other STM-activated phenomena such as diffusion, rotation, dissociation or switching of single molecules on surface.…”

Temperature dependence of the vibrational spectrum of porphycene: a qualitative failure of classical-nuclei molecular dynamics

“…2,3 The ability to enhance, deactivate or trigger hydrogen transfer events in this family of molecules has a potential impact on the fabrication of molecular machines and nanodevices. [4][5][6] Different strategies can be followed to achieve this control, for example modifying the electronic structure by addition of different substituents, altering the thermodynamic conditions, or using external stimuli. [7][8][9][10] Addressing this system using computer simulations requires a reliable description of the PES beyond the harmonic approximation, a full-dimensional representation of the system, and the inclusion of nuclear quantum effects (NQEs).…”

Reversible magnetic switching of high-spin molecules on a giant Rashba surface

“…Control and driving protocol for the switch To determine the control parameters and the driving mechanism of the induced state switching we developed a measurement protocol, 13,14 some elements of which are sketched in yellow color in Fig. 1b and which is based on the following six steps (i)-(vi): first, (i) the STM tip is moved by a distance d along the ½011-direction away from the center of the MnPc molecule [yellow cross in Fig.…”

“…2c] show that the activation probability is constant within the error bar, irrespective of the duration of the excitation pulse in the probed time interval from [0.1-4.0] s. We interpret these results as evidence that the time scale of the excitation pulses was much longer than the underlying switching processes. The driving mechanism of nonlocal excitations-with the tip being positioned away from the molecule-is usually based on either hot carriers 13,[15][16][17] or on a field effect. [18][19][20] In the first case, charge carriers are injected in surface or bulk bands, diffuse to the molecule and transfer energy to the molecule, which leads to the excitation, whereas in the second case the process is induced by the electric field between tip and sample.…”