Silicon based nanogap device for investigating electronic transport through 12 nm long oligomers

We have fabricated vertical nanogap electrode devices based on Silicon-on-Insulator (SOI) substrates for investigating the electronic transport properties of long, conjugated molecular wires. Our nanogap electrode devices comprise smooth metallic contact pairs situated at the sidewall of an SOI structure, obtained by selective recess-etching a few nanometers thin buried oxide layer and subsequent thin film metallization. The electrodes are separated by a predetermined distance down to about 5 nm and feature a well-tailored material layer structure, as characterized by SEM and scanning TEM analysis. We studied the electronic transport properties of 12 nm long, specifically synthesized dithiolated oligo-phenylene-vinylene derivatives assembled onto the electrode gap from solution. In particular, we observed a pronounced, non-linear current-voltage characteristic featuring a large conductance gap up to approx. ±1.5 V. The occurrence of this gap can be assigned to energetic barriers originating from short conjugation-breaking linker groups at the termini of the molecule. Model calculations that involve Density Functional Theory (DFT) and Non Equilibrium Green's Function (NEGF) methods agree qualitatively well with the data.