| AVS 56th International Symposium & Exhibition | |
| Surface Science | Friday Sessions |
| Session SS2-FrM |
| Session: | Semiconductor Surfaces and Interfaces II: Si |
| Presenter: | M. Dubey, University of Washington |
| Authors: | M. Dubey, University of Washington T. Weidner, University of Washington L.J. Gamble, University of Washington D. Ratner, University of Washington D.G. Castner, University of Washington |
| Correspondent: | Click to Email |
Organophosphonic acid self-assembled monolayers on oxide surfaces have seen growing use in electrical and biological sensor applications [1-2]. Molecular order in organophosphonic acid SAMs is highly desirable for reproducible electronic properties of these modified surfaces. In this regard, packing and order of the SAMs is important, as it influences the electron transport measurements. In this study, we examined the order of the phosphonate films deposited on silicon oxide surface by the Tethering By Aggregation and Growth (T-BAG) method [3] using various state-of-art surface characterization tools. Near edge x-ray absorption fine structure (NEXAFS) spectroscopy is used to study the order of a methyl- and hydroxyl- terminated phosphonate SAMs in vacuum and sum frequency generation (SFG) spectroscopy is used to study their order in aqueous condition. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) on these samples confirm the presence of chemically intact monolayer phosphonate films. NEXAFS spectroscopy confirmed a considerable degree of molecular order in the octadecylphosphonic acid (ODPA) and 11‑hydroxyundecylphosphonic acid (PUL) films with a tilt angle of 37° and 47° respectively. In situ SFG studies in deuterated water were conducted to determine the order of these films under biologically relevant conditions. The ODPA film showed the peaks for terminal methyl units, which are expected for ordered films. PUL films also showed a considerable degree of alignment indicated by resonances of the methylene unit next to the terminal hydroxyl group. These studies indicate that well ordered SAMs with methyl or hydroxyl termination can be prepared on oxide surfaces using phosphonate headgroups. These surfaces can be subsequently used to anchor biomolecules for biomaterial and biosensor applications.
[1] A. Cattani-Scholz, D. Pedone, M. Dubey, S. Neppl, B. Nickel, P. Feulner, J. Schwartz, G. Abstreiter, M. Tornow, Acs Nano 2008, 2, 1653.
[2] H. Klauk, U. Zschieschang, J. Pflaum, M. Halik, Nature 2007, 445, 745.
[3] E. L. Hanson, J. Guo, N. Koch, J. Schwartz, S. L. Bernasek, Journal of the
American Chemical Society 2005, 127, 10058