Nanoscale molecular device fabrication via solution and vapor phase deposition

This work describes the fabrication of molecular electronic devices using solution phase and vapor phase assembly methods. The project was motivated by the existing limits of molecular electronics including: a lack of reproducible nanoscale molecular test devices, limited device fabrication techniques that resulted in low yields, and molecular devices that lacked potential for integration with traditional CMOS components. To address these issues, I first designed and fabricated a nanoscale molecular test device using traditional solution phase assembly methods. This test device was shown to be effective and reproducible by characterizing molecules with well-established electrical behaviors. I then used this test device to investigate the electrical behavior of an oligo(phenylene ethynylene) molecule with a nitro sidegroup, known as the nitro molecule. This molecule exhibited interesting electrical behavior with the potential for use in memory and logic devices. In order to better understand the behavioral variations observed from the nitro molecule, I investigated the effect that different molecular environments had on its electrical behavior.; Next, molecular device fabrication procedures were improved by developing a method of vapor phase assembly. For this vapor phase deposition, I modified an existing ultra-high vacuum molecular beam epitaxy chamber and developed procedures for purifying the organic molecules prior to assembly. Vapor phase deposition was used to assemble single monolayers of various conducting molecules on gold substrates and the monolayers were characterized to confirm that they were chemisorbed, dense, uncontaminated, and ordered. Nanowell test devices that were fabricated via vapor phase deposition showed the expected electrical characteristics - verifying the effectiveness of vapor phase assembly for molecular electronic device fabrication. I also used vapor phase deposition to assemble conducting molecules on silicon substrates. This switch from gold to silicon substrates helped to increase the potential for molecular devices to be integrated with traditional CMOS devices for hybrid circuits. Overall, vapor phase deposition was established as an effective reproducible molecular assembly method for fabricating molecular electronic devices with the potential for integration with traditional CMOS technology.