Strong Polarity Asymmetry and Abnormal Mechanical Electroresistance Effect in the Organic Monolayer Tunnel Junction

Abstract

The performance of organic polar tunnel junctions under external electrical/mechanical stimuli is crucial for their great promise in developing flexible and high-performance sensor and memristive devices. Here, we prepared a single P­(VDF-TrFE) monolayer on an Au(111) atomic-level surface by using a Langmuir–Blodgett (LB) technique. The polarity stability and electronic transport behavior of the monolayer were investigated via piezoresponse force microscopy (PFM) and conductive atomic force microscopy (c-AFM) measurements. We observed a strong polarity asymmetry in the P­(VDF-TrFE) monolayer tunnel junction. Electrical bias and mechanical force exerted by the tip both can switch the monolayer from the metastable state (“H–Au” state, down polarity) to the stable state (“F–Au” state, up polarity). Moreover, the conductance of the monolayer tunnel junction can be controlled not only by the electrical bias but also by the tip force. Interestingly, a decrease of conductance from the ON state to OFF state is caused by the tip force, which is against our common sense that the larger the tip force, the larger the tunnel conductance. This abnormal mechanical electroresistance effect is attributed to the strong asymmetric interfacial barriers and is useful for the design of novel mechanical sensor and memristive devices.

A Roadmap for Mechanically Interlocked Molecular Junctions at Nanoscale

“…When a MIM exists as two states at equilibrium, namely, the ground-state co-conformation (GSCC) and the metastable state co-conformation (MSCC), the MIM may show a bistable switching and memory effect. 61 Different from the switching mechanism existing in other monolayer junctions based on ferroelectric polymers 62 or molecular rotors, 63 the design of switching MIMs depends on the incorporation of many different recognition sites (Figure 4a). As illustrated in Figure 4, degenerate (Figure 4b, left) and nondegenerate (Figure 4c, left) MIMs are used to explain the phenomenon of translational isomerism.…”