Time-resolved EPR of spin-polarized mobile H atoms in amorphous silica: The involvement of small polarons

Journal Article · Sun Dec 01 04:00:00 EST 1996 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.54.15073· OSTI ID:397605

Shkrob, I A; Trifunac, A D ^[1]

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1. Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

Time-resolved pulsed electron paramagnetic resonance (EPR) was used to study the formation and decay kinetics of spin-polarized mobile H atoms in {open_quote}{open_quote}wet{close_quote}{close_quote} fused silica containing {approximately}1200 ppm of SiOH groups. The H atoms were produced using 5{endash}100 ns pulses of 3 MeV electrons. The EPR polarization pattern of these H atoms indicates the occurrence of chemically induced dynamic electron polarization in spin-selective reactions of H atoms with other paramagnetic species. The EPR kinetics observed from 180 to 530 K are independent of the dose absorbed per pulse and exhibit fast exponential growth and slow exponential decay. The slow component with activation energy of 15{endash}18 kJ/mol corresponds to diffusion-controlled scavenging of H atoms by metastable paramagnetic centers ({approximately}3{times}10{sup 17} cm{sup {minus}3}) generated by electron irradiation. At room temperature, the diffusion coefficient is 10{sup {minus}7}{endash}10{sup {minus}6} cm{sup 2}/s. The fast component with activation energy of 6{endash}8 kJ/mol corresponds to the decay of a mobile radical (ion) partner of the H atom. It is argued that this partner is a small polaron (intrinsic hole) in amorphous silica. {copyright} {ital 1996 The American Physical Society.}

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 397605
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 21 Vol. 54; ISSN PRBMDO; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AMORPHOUS STATE
DIFFUSION
EPR SPECTRA
HYDROGEN
HYDROXYL RADICALS
SILICON OXIDES
SPIN ORIENTATION
SURFACE STATES
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TIME RESOLUTION