Character of the Reaction between Molecular Hydrogen and a Silicon Dangling Bond in Amorphous SiO₂

Abstract

The passivation by diffusing H 2 of silicon dangling bond defects (E' centers, O 3 ≡Si•)induced by laser irradiation in amorphous SiO 2 (silica), is investigated in situ at several temperatures. It is found that the reaction between E' center and H 2 requires an activation energy of 0.38eV, and that its kinetics is not diffusion-limited. The results are compared with previous findings on the other fundamental paramagnetic point defect in silica, the non bridging oxygen hole center, which features completely different reaction properties with H 2 . Besides, a comparison is proposed with literature data on the reaction properties of surface E' centers, of E' centers embedded in silica films, and with theoretical calculations. In particular, the close agreement with the reaction properties of surface E' centers with H 2 leads to conclude that the bulk and surface E' varieties are indistinguishable from their reaction properties with molecular hydrogen.

Hydrogen Passivation Induced Dispersion of Multi‐Walled Carbon Nanotubes

“…Hydrogen atoms absorbed by CNTs can be either in the physisorption state, where the hydrogen molecules are bonded with the exterior CNTs surface via weak van der Waals interaction, or in the chemisorption state, where a hydrogen atom is chemically bonded with a carbon atom of the CNTs. [23,36] However, to the best of our knowledge, there are no reports on dispersion of CNTs using hydrogen passivation (HP).…”

Temperature dependence of the generation and decay of E′ centers induced in silica by 4.7eV laser radiation

“…Previous experiments allowed to propose the following model for the generation of E 0 centers in fused silica at room temperature [18][19][20]: the main generation process of defects is the laser-induced breaking of Si-H precursors:…”

“…Aside from E 0 center, this process generates H atoms which dimerize in H 2 and react with E 0 centers in the post-irradiation stage causing their partial decay in a time scale of a few hours [18][19][20]:…”

“…An important feature of the E 0 center, shared by other paramagnetic defects, is that it can be annealed by reaction with diffusing H 2 [10,12,[14][15][16][17][18][19][20]. This process is widely exploited in optical fibers technology where H 2 loading of the SiO 2 core material is used to prevent it from being damaged by UV light.…”

“…Since passivation of E 0 by H 2 is thermally activated as well, the presence of hydrogen may be expected to influence the temperature dependence of the formation efficiency of the defects, due to the interplay between generation and passivation. To thoroughly investigate this issue it is needed to measure in situ the kinetics of the defects in temperature-controlled experiments [16,[18][19][20], in contrast with previous works that measured only the stationary concentration of E 0 centers [4,5,[8][9][10][11] …”