An experimental study of molecular electronic devices
Abstract
Reversible conductivity modulation through single/few molecules in a metal-molecule-metal device has been demonstrated by changing the chemical nature of the active molecular components through a molecular doping stimulus. Lateral nanogaps were fabricated using electromigration and shadow evaporation. Self-assembly of charge-transfer complexes in the nanogaps using a donor-acceptor pair leads to increased conductivity as compared to a metal-donor-metal device, which can be reversed by removing the acceptor molecule. Besides chemically tuning the molecules, engineering the contacts can also enhance device functionality. Molecular devices in a metal/molecule/GaAs configuration have been fabricated, electrically characterized and analyzed using an electrostatic model. Various alkane and aromatic thiols were self-assembled on GaAs substrates and the top metal contact was formed by a low energy, indirect path technique. AFM, FTIR, ellipsometry and ToF-SIMS measurements indicate the formation of a robust metal contact on smooth, uniform and crystalline monolayers. I-V measurements show an increase in conductivity due to the presence of a molecular layer. The results indicate strong molecular coupling to the contacts with a significant density of molecular states near the Fermi level. An electrostatic model which considers the molecular dipole moments has been developed to explain the observed characteristics. Temperature independent I-V data is consistent with tunneling-based transport through the molecular layer. Different metal evaporation techniques and metals for evaluating the performance of the top metal contact, and control of molecular conduction by unpinning the GaAs surface using low-temperature-grown surface layers, have also been studied. A possible device application as an electronic switch has been demonstrated.
Degree
Ph.D.
Advisors
Janes, Purdue University.
Subject Area
Electrical engineering|Materials science
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