Light-induced atom desorption from glass surfaces characterized by X-ray photoelectron spectroscopy

Abstract

the first approximation, but they actually have some interactions with each other and also with the inner surface of the cell walls, which are often made of glass. Specifically, the atom-surface interactions cause undesired effects that cannot be easily understood and controlled, such as broadening and frequency shifts of resonance lines [3,4]. There have been many studies to understand surface-related phenomena in alkali metal vapor cells, such as anti-spinrelaxation coatings [5], surface modification to cause conductivity of cells [6] and stray electric fields [7], testing of several different surface materials for laser traps [8], direct measurements of adsorption/desorption dynamics [9], and measurement of passivation of a surface with alkali metal atoms, called "curing" [10]. However, there have mostly been only indirect studies of surfaces via atoms in the gas phase. Direct characterization of surfaces using standard surface science techniques has been very limited for atomic physics purposes [11].The same is true for studies of light-induced atom desorption [12]. This phenomenon has attracted particular attention in laser cooling and trapping experiments using ultrahigh vacuum cells, into which atoms can be loaded quickly on demand from the surface by LIAD techniques [13,14]. However, most LIAD studies [13,[15][16][17][18][19] focused only on desorbed atoms, and lack of basic knowledge of the surface itself leads to a poor understanding of desorption mechanisms and also some contradictory practical information. For example, one group reported that LIAD from quartz glass is not effective [20], but another loaded a magneto-optical trap in a quartz cell by LIAD [16].Following our previous study [21], we introduce surface analysis for glass surfaces, for which LIAD measurements were then carried out by focusing on differences between vitreous silica (synthetic quartz) and commercial borosilicate glass (Pyrex), which are the most commonly used Abstract We analyzed the surfaces of vitreous silica (quartz) and borosilicate glass (Pyrex) substrates exposed to rubidium (Rb) vapor by X-ray photoelectron spectroscopy (XPS) to understand the surface conditions of alkali metal vapor cells. XPS spectra indicated that Rb atoms adopted different bonding states in quartz and Pyrex. Furthermore, Rb atoms in quartz remained in the near-surface region, while they diffused into the bulk in Pyrex. For these characterized surfaces, we measured light-induced atom desorption (LIAD) of Rb atoms. Clear differences in time evolution, photon energy dependence, and substrate temperature dependence were found; the decay of LIAD by continuous ultraviolet irradiation for quartz was faster than that for Pyrex, a monotonic increase in LIAD with increasing photon energy from 1.8 to 4.3 eV was more prominent for quartz, and LIAD from quartz was more efficient at higher temperatures in the range from 300 to 580 K, while that from Pyrex was almost independent of temperature.

Systematic studies of rubidium-exposed surfaces by X-ray photoelectron spectroscopy and light-induced atom desorption

“…4 of Ref. [17]. Further elevation of the temperature above room temperature led to additional enhancement of thermal desorption.…”

“…4 of Ref. [17]. Rb atoms began desorbing thermally at 1.5 h (210 K) and a large peak in thermal desorption was observed at 3.5 h (260 K).…”

“…The amount of Rb atoms deposited on a surface after exposure to Rb vapor depends on the substrate material. Among the materials that we have studied, glass (synthetic quartz and Pyrex) and metal (yttrium) adsorbed Rb atoms, which were detected by our XPS system (on the order of 10 12 -10 13 cm −2 surface density or 10 −1 -10 −2 surface concentration [17]) after exposure to Rb vapor at room temperature, whereas no Rb was observed on the polymer (paraffin and PDMS) surfaces. Rb aggregates or films that form on a substrate are unstable and tend to desorb at room temperature under ultrahigh vacuum conditions, due to the high vapor pressure of Rb (10 −5 Pa).…”

“…A detailed description of the apparatus was provided in Ref. [17]. Here, we provide a brief explanation of the set-up.…”

“…Detailed microscopic LIAD mechanisms should depend on surface materials and conditions. Our past X-ray photoelectron spectroscopy (XPS) study [17] involving two types of glass, synthetic quartz and Pyrex (a commercial borosilicate glass), revealed different states and LIAD properties of the two Rb-deposited surfaces. As another example of material dependence, time-offlight measurements for desorbed atoms from PDMS films have indicated that the desorption process includes a diffusion component [14,18].…”