Ag ion formation mechanisms in molten glass ion emitters

Abstract

Experimental and computational studies were conducted on silver/molten borosilicate glass (silica gel) ion emitters to better understand the physical and chemical processes associated with them, and in particular the chemistry of the molten glass solution that enhances ion emission. Based on the results of these studies and previous work, a model is proposed that explains the major features of the observed phenomena. It is believed that the molten glass dissolves both the analyte element and some Re from the filament. Rhenium is oxidized by the B2O3 of the borosilicate glass producing a rhenium oxide that migrates to the surface of the glass, providing a high work function surface that enhances cation emission. Last, we believe the analyte element (in this case Ag) resides in the glass primarily in the zero oxidation state (reduced by thermal decomposition of the oxide or nitrate) and volatilizes from the surface with a percentage of Ag atoms volatilizing as cations determined by the difference between the work function of the surface and the ionization potential of the analyte atom. This explanation may be applicable to other elements analyzed by silica gel technology that are readily reduced to the elemental form (by thermal decomposition or by reduction by the Re filament). Selected features of this explanation, such as analyte solubility and a high work function surface, may be applicable to analyte elements that are not readily reduced to elemental form.