A nanogap–array platform for testing the optically modulated conduction of gold–octithiophene–gold junctions for molecular optoelectronics

Abstract

We studied the light dependent conduction of gold–oligothiophene–gold molecular junctions as a fully–customized platform. The flexibility and novelty of the platform relies on its plug-and-play connection to an external electronic board to perform eight parallel nanogap fabrications by Electromigration Induced Break Junction (EIBJ) and molecular electrical characterization. In addition, the octithiophene molecules are synthesized ad-hoc to efficiently self-assembly and selectively bridge the nanogap electrodes upon deposition, which can be carried out directly and in parallel on the 8 nanogap array platforms. The high portability of the platform is well suited for in–situ microscopic and spectroscopic analyses. In particular, we tested the electrical functionality of the octithiophene molecular junctions by coupling electrical current–voltage (I–V) characterization with fluorescence and Raman spectroscopies. In addition, surface-enhanced Raman spectroscopy (SERS) was used for the first time to precisely correlate the position of the molecule with the conductance of the junction. Modulation of the electrical conductance can also be achieved by varying the light excitation wavelength. Such electrical transduction of the junction revealed a peak in molecule conduction around the light excitation wavelength of 450 nm, with a photoresponsive modulation of the current at low bias voltage up to 120% with respect to the initial value at 300 nm. The proposed ad-hoc platform design makes molecular junctions real working blocks, which can be interfaced with external circuitries to serve the function of electronic components or sensors and overcome the limitations of usability, cost and portability of traditional molecular contacting methods, such as Mechanically Controlled Break Junction (MCBJ) or scanning probe microscopy. We thus demonstrate that the optoelectronic properties of oligothiophenes can be exploited in the form of molecular junctions to fabricate optoelectronic devices for molecular electronics.