Desorption of metal atoms and large molecules by laser induced surface plasmons

Surface plasmons excited by a Nd:YAG laser in an attenuated-total-reflection (ATR) geometry were used to desorb Al, Au, Ag atoms, and rhodamine B molecules. The metal films were vacuum-evaporated on glass prisms while the rhodamine B film was deposited on an Al film. The desorbed neutrals were ionized by a XeCI excimer laser and measured by a time-of-flight mass spectrometer. The desorption yield exhibits a sharp maximum at the surface-plasmon resonance angle. The kinetic energy (KE) distributions of the desorbed particles were obtained by varying the delay time between the two lasers. For all the metals, there were one low energy peak and one high energy peak in the KE distribution. The low energy peak was identified as a thermal peak. The high energy peak was identified by further experiments and calculations as electronic-excited desorption. Rhodamine B molecules were desorbed by this method without fragmentation. Finally, we discussed the possible desorption mechanisms and gave reasons for our conclusion.