Photoatomic effect: Light-induced ejection of Na andNa2from polydimethylsiloxane surfaces

Abstract

The photoejection of Na and Na 2 from surfaces prepared by adsorption of sodium vapor on solid films of polydimethylsiloxane ͑PDMS͒ of various molecular weights and structures is found to be dependent on light intensity and frequency. At low power levels the desorption yields of Na and Na 2 are linear functions of desorbing light power and exhibit frequency thresholds for photoejection analogous to the photoelectric effect. The frequency thresholds are 9500 cm Ϫ1 for Na and 11 500 cm Ϫ1 for Na 2 , and the 2000-cm Ϫ1 difference can be accounted for with a model in which the alkali-metal species form charge-transfer complexes Na ϩ PDMS Ϫ and Na 2 ϩ PDMS Ϫ , with the cations stabilized by interaction with the oxygen atoms of the PDMS polymer backbone. The ejection mechanism takes place by a reverse charge transfer to form a less polar complex with enough energy to eject Na or Na 2 from the surface.

Relaxation of atomic polarization in paraffin-coated cesium vapor cells

“…When these cells are then exposed to light of sufficiently short wavelength, alkali atoms are desorbed from the paraffin coating into the volume of the cell [24]. This phenomenon, known as light-induced atomic desorption (LIAD), has been observed using a wide range of surfaces: sapphire [40,41,42], silane-coated glass (in particular polydimethylsiloxane) [43,44,45,46,47], superfluid 4 He films [48,49], quartz [50], and porous silica [51]. LIAD is useful as a method for the rapid control of atomic density, and is of particular interest in the development of miniaturized atomic clocks and magnetometers [16].…”

Classification of Light-Induced Desorption of Alkali Atoms in Glass Cells Used in Atomic Physics Experiments

“…It is noted that LIAD in vapor cells was first observed for silane coatings (in particular, polydimethylsiloxane) on cell walls in the early 90s [19], and since then there have been many investigations [20][21][22][23] including desorption from a paraffin coating [24]. In this paper we do not discuss LIAD from polymer coatings, because its mechanism is probably different from the desorption from bare glass surfaces.…”

Low Energy Atomic Photodesorption from Organic Coatings

“…In particular, Xu et al [5] consider the adsorption process of Na from PDMS. They claim that the oxygen atoms in the PDMS backbone can serve to stabilize the Na + by complexation.…”

“…A theory takes into account a chemical process (chemisorption) in order to explain the LIAD, at least for the silanes coatings [5,41]. In particular, Xu et al [5] consider the adsorption process of Na from PDMS.…”

“…In this experiment, photodesorption of Rb atoms from PDMS was measured as a function of the desorbing light intensity and frequency, and the acronym LIAD (Light Induced Atomic Desorption) was introduced [4]. In 1996, the photodesorption of Na and Na 2 from PDMS was demonstrated and suggested a tentative interpretation of LIAD at microscopic scale along with a first theoretical model [5]. After these pioneer works, LIAD has been extensively investigated with a growing interest both as a tool to obtain a deeper insight into surface/atom interaction and as a technique for numerous applications.…”