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EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon

Barklie, RC, Collins, M and Silva, SRP (2000) EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon Physical Review B - Condensed Matter and Materials Physics, 61 (5). pp. 3546-3554.

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Electron paramagnetic resonance (EPR) measurements have been made of amorphous hydrogenated carbon (a-C:H) films grown by plasma enhanced chemical vapor deposition (PECVD) with negative self-bias voltages Vb in the approximate range 10-540 V. For Vb<100 V, as the film changes from polymerlike to diamondlike, the changes in linewidth and shape are interpreted in terms of changes to two contributions - one due to dipolar interactions between the unpaired spins and one due to unresolved lines arising from hyperfine interactions with H1. The former yields a Lorentzian line, the latter a Gaussian, and the resultant spectrum has the Voigt shape. The empirical relation ΔBppG (in Gauss)=(0.18±0.05)×(at. % H) between the peak-to-peak Gaussian contribution (in Gauss) ΔBppG and the hydrogen content in atomic percentage is obtained. For Vb>100 V the linewidth is shown to be dominated by the dipolar interactions and exchange and it decreases as Vb increases; the change is shown to arise primarily from a change in the exchange interaction. Evidence for this comes from measurements which show that the spin-lattice relaxation time appreciably shortens and the spin-spin relaxation time lengthens as the bias voltage is increased. The magnitude and variation with bias of the linewidth are consistent with the EPR signal originating from the π-type radicals. ©2000 The American Physical Society.

Item Type: Article
Divisions : Surrey research (other units)
Authors :
Barklie, RC
Collins, M
Date : 1 December 2000
Depositing User : Symplectic Elements
Date Deposited : 17 May 2017 12:22
Last Modified : 24 Jan 2020 22:08

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