Annual Meeting of the American Physical Society, March 1999, Atlanta, GA

Session BC18 - Surfaces (General).
ORAL session, Sunday afternoon, March 21
Room 258W, GWCC


[BC18.06] The desorption yield dependence on wavelength of femtosecond laser from CO/Cu(111)

Jingyan Guo, Hidong Kwak, Harry W. K. Tom (Department of Physics, University of California, Riverside)

The femtosecond laser desorption yield of molecular CO from Cu(111) is measured with 800 and 400 nm wavelength radiation and compared to previous studies using 620 nm radiation(J. A. Prybyla, H. W. K. Tom and G. D. Aumiller, Phys. Rev. Lett. \textbf68), 503(1992). The desorption yield is less nonlinear with absorbed fluence and more efficient for shorter wavelength radiation. Surprisingly, for 400 nm (3 eV) radiation 100% of the CO molecules may be desorbed. This observation indicates the

importance of the copper d-band states in femtosecond laser- induced desorption. First, the d-bands provide the initial states for photoexcited electronic populations at \sim 1 and 4 eV above E_F. Secondly, the d-band holes become a secondary source of hot electrons through Auger recombination and other scattering processes. The density of 3-4 eV electrons can thus be high and have a surface residence time of 20-30 fs(S. Ogawa, H. Nagano and T. Petek, Phys. Rev. B \textbf55), 10869(1997). Both are necessary components to proposed desorption mechanisms involving multiple electronic excitation-deexcitation cycles on a timescale short compared to the molecule-substrate stretch mode period.