Molecular Electronics

As silicon-based electronics component are achieving inherent performance limits, devices using small molecular ensembles as the active elements are seen as a viable, next-generation technology. Measurement methods, standards, and data are critical to the realization of molecular electronic components. NIST is developing measurement tools to characterize the structure, composition, and electrical performance molecules in prototypical environments, as well as modeling charge transport phenomena in these structures. (This project is carried out as part of a competence-building project with EEEL).

• Theoretical Studies of Electron Transport in Molecular Wires : Algorithms have been developed to study trends in conductance in molecules connected to metal junctions. This methodology couples high-level, first-principles electronic structure calculations of the molecule in capacitor-like electric fields with simplified theories for electronic conductance in metal/molecule systems. The value of this simplified approach is the comparative computational efficiency and the ability to interpret the results using familiar and accepted concepts of molecular orbitals. The method has been applied to organic thiolates.
• SPM Directed Device Fabrication: To enable comparison between device prototype measurements and molecule-level measurements made using scanned-probe instruments, a method has been developed to embed “pads” of conductive molecules into an insulating molecular matrix. These “pads” have been shown to be stable. Current-voltage measurements on these pads are being compared to device-prototype measurements.
• Orientational Effects on Electron Tunneling in Dodecanethiol: Detailed understanding of electronic transport properties in molecules requires the ability to correlate molecular structure with electron transport mechanisms. Extensive data on dodecanethiol has been developed that allows its use as a “standard” test molecule to provide reference I-V measurements. This molecule affords a means of probing the impact of molecular orientation on tunneling behavior. Measured I-V curves have been compared to compared to the theoretical predictions, validating the predictive capabilities of those models.
• Spectroscopic Measurements : Molecular configuration of the electronic structure of electrically-active molecules are governing factors in the electrical conductance of molecules. To investigate whether and how such molecular properties are related to test-structure measurements, ultra-fast laser spectroscopies have been developed and used to study the geometry and electronic structure of moletronic films. The electronic structure of these films was studied using one- and two-photon photoemission. From these spectroscopic measurement reference data, including energy-level alignments and charge-injection barriers have been obtained. These numbers are being compared to scanned-probe, device prototype measurements, and theoretical predictions.