Chemical and Nanoengineering Regulation of Inter-molecular Electron Transport in Organic Semiconductor Thin Films

University Of California-Davis, Davis CA

Investigators

Abstract

TECHNICAL SUMMARY: This research program, supported by the Solid State and Materials Chemistry Program, aims at a molecular level understanding of chemical modulation of intermolecular electron transport using a specially designed model device containing pi-conjugated molecules such as oligothiophene based organic thin films. To circumvent contribution from surface roughness, Ultraflat NanoElectrodes (UNEs) with sub-nanometer roughness will be fabricated, onto which designed molecules will be placed using atomic force microscopy (AFM) based nanografting method. The multifunctional AFM enables in situ nanolithography, high-resolution structural characterization, and measurements of electron transport. The chemical and electronic properties of organic films will be controlled by varying their head group, intermolecular interactions and terminal group. The response of the electronic properties during and after exposure to chemical species will be studied, in correlation to structure in situ. The project combines the technical strength of nanolithography and imaging (PI), UNE fabrication and electron transport (co-PI), and organic synthesis (collaborator). With molecular level structure and packing engineered precisely on UNEs, the systematic investigation of intermolecular electron transport becomes feasible and reliable. This systematic investigation will review the correlation of intermolecular transport with the film morphology, reveal the role of structure, especially domain boundaries and molecular level packing, and examine the influence of analytes binding to the film termini. NON-TECHNICAL SUMMARY: The research aims at accurate measurements of electron transport along and in between molecules within model junctions of electronic devices. These measurements are technically very challenging, yet critical in order to realize the great potential of modern molecular electronic devices, which are smaller than state-of-the-art transistors, with properties tunable by varying the structure and packing of the molecules. The research team plans to take best advantage of today's technology, fabrication of ultraflat microelectrodes with sub-nanometer roughness, the ability to position molecules with high precision, and measurements of electron transport over these well-engineered junctions. This investigation should yield reliable and fundamental information in understanding organic semiconductor based devices, and guiding design of a next generation of molecular devices. The investigation is highly interdisciplinary, and requires close collaboration among Liu (AFM nanofabrication and high resolution imaging), Salmeron (UNE fabrication and device characterization), and Schore (synthesis of organic semiconductor materials), whose team members will attain advanced training in micro/nanofabrication, molecular resolution imaging, electron movement in confined space, and device making. The team has been working closely with local community college faculty (Miller, SacCity College) and students to expose them to the concept and experiments of these model devices. Being extremely proficient in both Spanish and English languages, Salmeron has participated and will continue to participate in Hispanic Radio Shows to attract Hispanic students to the forefront of modern devices and materials science.