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

EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon
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无定形氢化碳中的 EPR 线宽变化、自旋弛豫时间和交换

DOI：
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发表时间：
2000
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影响因子：
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通讯作者：
S. Silva
S. Silva
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文献类型：
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作者：
R. Barklie;M. Collins;S. Silva

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电子顺磁共振！对无定形氢化碳~a-C：H！等离子体增强化学气相沉积（PECVD）生长的薄膜！对于Vb，100 V，当膜从类聚合物改变为类金刚石时，线宽和形状的变化被解释为两个贡献的变化-一个是由于未成对自旋之间的偶极相互作用，另一个是由于与H1的超精细相互作用产生的未解析线。前者产生洛伦兹线，后者产生高斯线，所得光谱具有福格特形状。经验关系DBPP 高斯！5~0.1860.05！3~at.% H）峰-峰高斯贡献~以高斯！DBpp G和以原子百分比计的氢含量。对于Vb.100 V， 线宽主要受偶极相互作用和交换作用的影响，随着Vb的增加而减小; 所示的变化主要是由交换相互作用的变化引起的。这一点的证据来自测量，测量表明自旋-晶格弛豫时间明显缩短，自旋-自旋弛豫 时间随着偏置电压的增加而延长。线宽的大小和随偏置的变化是 与源自p型自由基的EPR信号一致。
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 DBpp G ~in Gauss!5~0.1860.05!3~at.%H) between the peak-to-peak Gaussian contribution ~in Gauss! DBpp G 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 p-type radicals.