| AVS 54th International Symposium | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuM |
| Session: | Molecular Electronics |
| Presenter: | A. Scott, Purdue University |
| Authors: | A. Scott, Purdue University D.B. Janes, Purdue University |
| Correspondent: | Click to Email |
Recently there has been a significant amount of interest in developing molecular electronics to miniaturize and enhance functionality of integrated circuits. Molecular electronic devices with silicon contacts are of particular interest due to the relevance of silicon as an electronic material and the ability to engineer the substrate properties through doping. Molecular layers have been grafted to <111> silicon by electrochemical reduction of para-substituted aryl-diazonium salts for use in silicon-based molecular electronics. These molecular layers were characterized using atomic force microscopy, ellipsometry, x-ray photoemission spectroscopy, infrared spectroscopy, and contact angle measurements. It was found that the surface characteristics were dependent both on monolayer headgroup chemistry and substrate doping. Consequences for the application of these molecular layers to electronic devices on silicon were examined. Hydrogen-terminated silicon samples were prepared by etching cleaned silicon in deoxygenated ammonium fluoride. Various doping densities of silicon were used and it was determined that oxide-free surfaces could be realized on all of them using this method, however the doping affected the surface topology. Lightly doped samples exhibited atomically flat surfaces with well-defined step edges corresponding to individual planes of silicon atoms, whereas heavily doped samples maintained a low surface roughness, but had no defined structure. Molecular layers were prepared on hydrogen-terminated silicon by electrochemical reduction of various commercially available para-substituted aryl-diazonium salts in acidic aqueous solution.1 Chemical characterization of the surfaces indicates that the substituent plays an important role in monolayer quality. Nitro-substituted species exhibited chemical instability and significant oxidation of the silicon substrate. Other molecular layers showed more ideal monolayer characteristics. These findings can be correlated with observations about electronic transport in gold-molecule-silicon devices.2
1 P. Allongue, C. H. de Villenueve, J. Pinson, F. Ozanam, J. N. Chazalviel, and X. Wallart, Electrochim. Acta 43, 2791 (1998).
2 A. Scott, C. Risko, M. A. Ratner, D. B. Janes, Appl. Phys. Let., to be published.