PrimarySi29hyperfine structure ofE′centers in nm-sized silica: Probing the microscopic network structure

Abstract

Point defects in fumed ϳ7-nm-sized fumed silica nanoparticles have been studied by X-, K-, and Q-band electron spin resonance ͑ESR͒ following 10-eV irradiation. The EЈ defects are monitored as a function of post manufacture heat treatment with the sample brought into contact with "bulk" Si/ SiO 2 entities at elevated temperatures in vacuum ͑T an = 1005-1205°C͒, i.e., the presence of an Si/ SiO 2 interface. This results in a drastic increase in EЈ defect density with increasing T an , enabling us to resolve the primary 29 Si hyperfine ͑hf͒ structure of the EЈ centers located in the core region of the nanoparticles. Detailed analysis of the observed hf spectra reveals several items pointing to a modification of the specific network structure of the core region of the nanoparticles. An increased hf splitting of 438Ϯ 2 G is observed compared to bulk silica ͑418Ϯ 2 G͒ indicating that the core part EЈ centers exhibit a more pyramidal defect structure. Moreover, the increased primary hf splitting indicates that the core of the fumed silica particles is densified, possibly associated with the presence of more low-membered rings in the nm-sized silica network.

Electron spin resonance spectroscopy investigation of ion beam sputtered HfO 2 and SiO 2 thin films

“…The chemical shift to higher g values in the DIBS deposited HfO 2 film suggests that the unpaired electrons are associated with oxygen rather than with the heavier hafnium atom. This ESR signal has a similar shape to the E' signal previously identified in bulk irradiated SiO 2 [10,11] and characterized by g-tensor of [2.0116, 2.0138, 2.0614]. In order to assure that the signal assigned to the deposited HfO 2 film was not from the SiO 2 substrate, HfO 2 was deposited on a sapphire substrate.…”