Desorption Of Sodium Atoms Research Articles

Electron-stimulated desorption of sodium atoms initiated by their reverse motion

This paper reports on the first measurement of the yield and energy distributions of sodium atoms in electron-stimulated desorption at T = 160 K from sodium layers adsorbed on tungsten with a gold film atop. The Na atom yield has a resonant pattern with an appearance threshold of 30 eV, which can be attributed to exciton excitation in the Na 2p level. The Na yield is associated with the formation of a semiconducting NaxAuy film at T ∼ 300 K and sodium and gold coverages in excess of one monolayer. Sodium atoms are desorbed through Auger neutralization of Na2+ ions in their reverse motion toward the surface and is limited by the resonant ionization of Na atoms as they pass through the adsorbed layer of Na+ ions. The energy distributions of Na atoms are bell shaped with a maximum at about 0.56 eV.

Temperature and concentration effects in electron-stimulated desorption of sodium atoms from sodium layers adsorbed on tungsten coated with a gold film

The yield and energy distributions of sodium atoms upon electron-stimulated desorption from sodium layers adsorbed on tungsten coated with a gold film are investigated for the first time as functions of the thickness of the gold film, the concentration of deposited sodium, and the surface temperature. It is found that the energy distributions exhibit two peaks, namely, a narrow peak with a maximum at about 0.15 eV, whose intensity continuously increases with increasing temperature, and a broad peak with a maximum at about 0.35 eV, whose intensity either decreases or remains constant with increasing temperature. It is shown that both peaks arise as a result of the same excitation, which gives rise to different channels of electron-stimulated desorption of sodium atoms. Possible mechanisms of electron-stimulated desorption and the kinetics of destruction of the surface coating are discussed.

Electron-stimulated desorption of sodium atoms from germanium-coated tungsten

The yield of sodium atoms and energy distribution upon electron-stimulated desorption from sodium layers adsorbed on tungsten coated with a germanium thin film are measured under variations in the electron energy, the sodium coverage, and the surface temperature by the time-of-flight method with the use of a surface ionization detector. It is revealed that the electron-stimulated desorption of sodium atoms occurs via three channels, namely, a channel involving ionization of adsorbed sodium; the most efficient channel, which is produced by the germanium ionization; and a channel associated with the formation of tungsten excitons, which brings about desorption of NaGe molecules.

Heliocentric Dependence of Sodium Emission of Comet Hale‐Bopp (C/1995O1)

A sequential spectroscopic observation of comet C/1995 O1 (Hale-Bopp) was performed from 1996 September to 1997 May. After the first positive detection in early 1997 February, the development of the neutral sodium emission was monitored during about 4 months around the perihelion passage. The ratio of the sodium D-line emission relative to the continuum emission strength varied with the days from perihelion. The sodium D-line emission was weak relative to the continuum near the perihelion because of the Swings effect. We corrected the Swings effect, the phase angle dependence of continuum emission, and the differences in geocentric distance. We found that the corrected sodium-to-continuum ratio varied with the dependence of r-k; k = 5-6, r denotes a heliocentric distance of the comet. Our result supports the hypothesis of thermal desorption of sodium atoms from dust grains.

Time response and temperature dependence of photo-stimulated desorption of sodium atoms from sodium halides

Abstract Photo-stimulated desorption (PSD) of sodium atoms from sodium halide crystals has been investigated using intense synchrotron radiation from a planar-type undulator. The PSD intensities of ground-state and excited-state Na atoms showed different temperature dependence, indicating different desorption processes. The temperature dependence of the PSD intensities was also different from that of thermally stimulated desorption. Moreover, time response of the excited-state Na desorption was found to consist of a nanosecond component and a slower one. The temperature dependence of the nanosecond component was also different from that of the slow PSD. These present results are consistent with the idea that the excited-state alkali desorption can be interpreted with two models, a fast desorption induced by electronic transition in the surface layer and a slow one due to thermal process of surface defects.

Electron-stimulated desorption of sodium atoms from oxidized molybdenum

The time-of-flight technique combined with a surface-ionization-based detector has been used to investigate the yield and energy distribution of sodium atoms escaping in electron-stimulated desorption (ESD) from adlayers on the surface of molybdenum oxidized to various degrees and maintained at T=300 K as functions of incident electron energy and surface coverage by sodium. The sodium-atom ESD threshold is about 25 eV, irrespective of sodium coverage and extent of molybdenum oxidation. Molybdenum covered by an oxygen monolayer exhibits secondary thresholds at ∼40 eV and ∼70 eV, as well as low-energy tailing of the energy distributions, its extent increasing with surface coverage by sodium Θ. The most probable kinetic energies of sodium atoms are about 0.23 eV, irrespective of the degree of molybdenum oxidation and incident electron energy at Θ=0.125, and decrease to 0.17 eV as the coverage grows to Θ=0.75. The results obtained are interpreted within a model of Augerstimulated desorption, in which adsorbed sodium ions are neutralized by Auger electrons appearing as the core holes in the 2sO, 4sMo, and 4pMo levels are filled. It has been found that the appearance of secondary thresholds in ESD of neutrals, as well as the extent of their energy distributions, depend on surface coverage by the adsorbate.