Interaction of wide-band-gap single crystals with 248-nm excimer laser irradiation. IX. Photoinduced atomic desorption from cleaved NaCl„100... surfaces

Neutral atomic sodium and chlorine emissions from cleaved, single-crystal NaCl 100 surfaces due to pulsed, 248-nm excimer laser irradiation have been characterized by time-resolved, quadrupole mass spectroscopy. At laser fluences below the threshold for optical breakdown, the resulting time-of-flight signals are consistent with particles emitted in thermal equilibrium with a laser-heated surface. Activation energy measurements made by varying the substrate temperature are consistent with F-H pair formation under UV excitation. By varying the laser fluence and estimating the effective surface temperature from the time-of-flight signals, additional activation energy measurements were made. The corresponding rate-limiting step is attributed to a thermally assisted, photoelectronic process involving atomic steps. Atomic force microscope images of surfaces irradiated at low fluences show monolayer islands that are created by the aggregation of material desorbed from steps. At somewhat higher fluences, monolayer pits due to F-center aggregation are also observed. © 2005 American Institute of Physics. DOI: 10.1063/1.1927701