Abstract
We present a theory for Raman scattering by current-carrying molecular junctions. The approach combines a nonequilibrium Green's function (NEGF) description of the nonequilibrium junction with a generalized scattering theory formulation for evaluating the light scattering signal. This generalizes our previous study [M. Galperin and A. Nitzan, Phys. Rev. Lett. 95, 206802 (2005); J. Chem. Phys. 124, 234709 (2006)] of junction spectroscopy by including molecular vibrations and developing machinery for calculation of state-to-state (Raman scattering) fluxes within the NEGF formalism. For large enough voltage bias, we find that the light scattering signal contains, in addition to the normal signal associated with the molecular ground electronic state, also a contribution from the inverse process originated from the excited molecular state as well as an interference component. The effects of coupling to the electrodes and of the imposed bias on the total Raman scattering as well as its components are discussed. Our result reduces to the standard expression for Raman scattering in the isolated molecule case, i.e., in the absence of coupling to the electrodes. The theory is used to discuss the charge-transfer contribution to surface enhanced Raman scattering for molecules adsorbed on metal surfaces and its manifestation in the biased junction.
| Original language | English (US) |
|---|---|
| Article number | 144109 |
| Journal | Journal of Chemical Physics |
| Volume | 130 |
| Issue number | 14 |
| DOIs | |
| State | Published - 2009 |
Funding
The research of A.N. is supported by the Israel Science Foundation (Grant No. 1646/08), the U.S.-Israel Binational Science Foundation, the Germany-Israel Foundation, and the European Research Commission. M.G. gratefully acknowledges the support of UCSD startup funds, UC Academic Senate research grant, and a LANL Director\u2019s Postdoctoral Fellowship. M.R. thanks the Chemistry Division of the NSF, and the MRSEC program of the NSF, through the Northwestern MRSEC (Grant No. DMR 0520513), for support. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. Department of Energy, Office of Basic Energy Sciences user facility. Los Alamos National Laboratory, an affirmative action equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under Contract No. DE-AC52-06NA25396.
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry