|AVS 55th International Symposium & Exhibition|
|Nanometer-scale Science and Technology||Thursday Sessions|
|Presenter:||M.A. Walsh, Northwestern University|
|Authors:||M.A. Walsh, Northwestern University
J.-C. Lin, Northwestern University
J.-H. Kim, Northwestern University
K.H. Bevan, Purdue University
G.Y. Stokes, Northwestern University
F. Geiger, Northwestern University
S.T. Nguyen, Northwestern University
M.J. Bedzyk, Northwestern University
M.C. Hersam, Northwestern University
|Correspondent:||Click to Email|
Functionalized organic nanostructures on silicon present unique opportunities for integrating molecular electronic devices and sensors with conventional microelectronics. Of particular interest are 1-alkyne molecules since they have been shown to retain pi character following covalent attachment to the silicon surface, thus creating fully conjugated organosilicon nanostructures.1 In an effort to quantify the structure and chemistry of 1-alkyne molecules mounted on silicon surfaces with atomic-scale spatial resolution, this study probes phenylacetylene and 1-bromo-4-ethynylbenzene adlayers on the Si(100)-2x1:H surface with ultra-high vacuum (UHV) scanning tunneling microscopy (STM) and complementary synchrotron X-ray techniques. UHV STM images reveal well-ordered one-dimensional nanostructures consisting of 1-alkynes that are aligned with the underlying silicon dimer rows. This observed alignment is consistent with the radical mediated chain growth reaction mechanism that has been previously observed for 1-alkenes on silicon. In an effort to provide further evidence in support of this mechanism, a suite of additional surface science techniques and theoretical calculations have been applied to this system. Specifically, the bromine tag on 1-bromo-4-ethynylbenzene can be probed with synchrotron X-ray radiation.2 For example, X-ray photoelectron spectroscopy confirms that the bromine moiety remains intact following attachment to the silicon surface. Additional X-ray techniques, such as X-ray standing wave (XSW), X-ray fluorescence (XRF), and X-ray reflectivity (XRR), allow the bromine position to be triangulated with sub-angstrom precision. In particular, these X-ray measurements yield a bromine height of 8.85 angstroms above the bulk-like silicon, which agrees well with theoretical values determined by periodic density functional theory. The agreement between the theoretical and experimental results provides strong evidence for the expected sp2 hybridization of the terminal carbon-carbon bond. Overall, this study reveals 1-alkynes as a promising chemistry for forming conjugated organosilicon nanostructures on technologically relevant silicon surfaces.
1 Cicero, R.L., M.R. Linford, and C.E.D. Chidsey, Langmuir, 2000. 16(13): p. 5688-5695.
2 Basu, R., et al., Langmuir, 2007. 23(4): p. 1905-1911.