Role of Excitons in Electron- and Photon-Stimulated Desorption of Neutrals from Alkali Halides

Abstract

Low-energy (5-15 eV) electron- and photon-stimulated desorption of KI(100) yields I2P3/2 and 2P1/2 with hyperthermal (0.3 eV) and thermal velocity components. The desorption threshold for both components is 5.3 eV and is correlated with the gamma3/2-exciton long-wavelength edge. Exciton decay at the surface directly produces I2P3/2 and 2P1/2 with hyperthermal velocity and is in competition with self-trapping. Spin memory of the gamma-exciton hole-component is also evident in the hyperthermal channel. An exciton mediated desorption mechanism is presented which is general in alkali halides.

Control of laser desorption using tunable single pulses and pulse pairs

“…However, surface excitons are very elusive species that have not been directly observed in alkali halides. Their existence has been inferred in recent studies of photoinduced desorption from KI 14,20 and KBr, 15,21 energy loss of low energy protons on the LiF ͑001͒ surface, 28 and photochemistry of ethene on NaCl crystallites 13 ͑see also the discussion in Ref. 29͒.…”

Low-energy electron-stimulated desorption of cations and neutrals from Si(111)-(7×7):C2D2

“…40,41 In this study, the ESD of D͑ 2 S͒ from acetylene-d 2 adsorbed on Si͑111͒-͑7 ϫ 7͒ is also likely the result of decay of a localized single-centered exciton. 40,41 In this study, the ESD of D͑ 2 S͒ from acetylene-d 2 adsorbed on Si͑111͒-͑7 ϫ 7͒ is also likely the result of decay of a localized single-centered exciton.…”

Ionic displacement caused by electronic excitations

“…In all cases the iodine atom leaves the surface as a neutral atom at a velocity of several 100 m/s, corresponding to a kinetic energy of several 100 meV. This picture is confirmed by experiments which combine pulsed laser excitation with time-of-flight detection of the expelled halogen atoms [19].…”

“…Typical examples are the photo-induced desorption of molecules from surfaces and the photodissociation of molecules and other systems. One well-studied class of systems is given by alkali-halide surfaces, like the potassium iodide (001) surface [18][19][20][21]. Such dynamics may even be described by classical molecular dynamics, which is conceptually simpler than the quantum-dynamics effects discussed above.…”