Long-Range Coherent Tunneling in Physisorbed Molecular Ensembles

5 years ago

Long-Range Coherent Tunneling in Physisorbed Molecular Ensembles

Leandro Merces, Carlos César Bof Bufon, Davi Henrique Starnini de Camargo, Rafael Furlan de Oliveira

The charge transport in molecular systems is governed by a series of carrier-molecule quantum interactions, which result in a broad set of chemical and physical phenomena. The precise control of such phenomena is one of the main challenges toward the development of novel device concepts. In molecular systems, direct tunneling across 1–10 nm barriers and activated hopping over longer distances have been described as the main charge transport mechanisms. The continuous transition from one mechanism to the other, by increasing the transport distance, has mainly been reported for molecular chains covalently bonded to the electrodes. In elementary molecular junctions, like those formed by physisorbed organic semiconductor thin films, such transition remains unclear. Here, we report the first experimental evidence for sequential, long-range coherent tunneling across physisorbed ensembles by investigating the charge transport in copper phthalocyanine layers (5–60 nm thick films). Like observed for chemisorbed molecules, our junction exhibits a gradual transition from coherent tunneling to activated transport in the 10–22 nm thickness range. The present work contributes to connect the quantum transport to diffusive-related phenomena in such an elementary organic system.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b02528

DOI: 10.1021/acs.jpcc.7b02528