Electron Beam Induced Damage of NaNO3 Single Crystals: An Energy, Temperature, and Quantum State Resolved Study

Abstract

Electron beam induced damage of NaNO{sub 3} single crystals is examined using laser resonance enhanced multiphoton ionization detection of the neutral desorption products, post-irradiation temperature-programmed desorption (TPD), secondary electron emission microscopy (SEEM), and Auger electron spectroscopy (AES). The damage initially involves destruction of the nitrate group and production of O ({sup 3}P{sub J}) and NO ({sup 2}II) fragments with nonthermal energy distributions. Specifically, the O ({sup 3}P{sub J}) J state distribution measured at 100 eV incident electron energy is 5:1.5:0.25 for J = 2:1:0, the NO ({sup 2}II) vibrational state distribution is 1:0.56:0.35:0.40:0.23 for {nu} = 0:1:2:3:4, and the NO ({sup 2}II{sub 1/2,3/2}) rotational distribution has a high population of the upper ({sup 2}II{sub 3/2}) spin-orbit component. Production and desorption of these nonthermal fragments are dominated by the decay of {l{underscore}brace}NO{sub 3}{sup {minus}}{r{underscore}brace}*. At higher electron fluences, thermalized NO, O{sub 2}, and NO{sub 2} are also produced and released, through the NO{sub 2} is a minor product. The authors suggest that the formation and desorption of thermalized NO and O{sub 2} both involve NO{sub 2}{sup {minus}} defect states and unimolecular dissociation of NO{sub 3}{asterisk}. This is supported by the observation that the NO and O{sub 2} yields have the samemore » temperature dependence which is well described by the sum of two Maxwell-Boltzmann type equations with activation energies of 0.16 {+-} 0.03 and 0.010 {+-} 0.004 eV. O{sub 2} gas is also released in post-irradiation thermal cycling from 110 to 440 K with peaks at {approximately}260 and {approximately}340 K. The authors associate the post-irradiation TPD of O{sub 2} with reactions involving O atoms released during thermal decomposition of {l{underscore}brace}NO{sub 2}{sup {minus}}{hor{underscore}ellipsis}O{r{underscore}brace} and ONOO{sup {minus}}. The SEEM image shows damage features, and the AES spectra indicate that the irradiated region is depleted in both nitrogen and oxygen relative to Na. The elemental composition shows Na{sub 2}O as a final product of the NaNO{sub 3} radiation decomposition. The 100 eV electron beam damage cross section is at least {approximately}10{sup {minus}16} cm{sup 2}.« less