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首页> 外文期刊>Journal of Physics. Condensed Matter >Raman spectra of multilayer graphene under high temperatures
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Raman spectra of multilayer graphene under high temperatures

机译:高温下多层石墨烯的拉曼光谱

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摘要

For graphitic materials, Raman technique is a common method for temperature measurements through analysis of phonon frequencies. Temperature (T) induced downshift of the bond-stretching G mode (Delta G) is well known, but experimentally obtained thermal coefficients Delta G/Delta Tvary considerably between diverse works. Further, Delta G/Delta T coefficients usually were evaluated for relatively low temperatures and found to differ strongly for mono, a few and multilayer graphene. We studied G band behavior in freely suspended multilayer graphene flakes (or graphite nanoflakes) under localized heating by a laser beam. Analysis of Stokes and anti-Stokes signals showed that G band has a complex structure and can be deconvoluted into several peaks that demonstrate distinctly different behavior under heating. A plausible assumption is that these peaks correspond to several groups of graphitic layers (surface, near-surface and bulk) and then different thermal coefficients were determined for these groups. This behavior can be explained by decreasing interaction between surface layers and underlying material at high temperatures that affects especially vibrational properties of a few outermost layers. Estimates of temperatures using anti-Stokes/Stokes intensity ratio (I-aS/I-S) were also done to give results comparable with those obtained from G band downshift,T-Delta G approximate to T-aS/S, supporting the proposed model. The range of temperatures obtained by laser heating, as evaluated by both methods, was from 450 to 1200 K.
机译:对于石墨材料,拉曼技术是通过分析声子频率的温度测量的常用方法。温度(T)诱导键拉伸G模式(Delta G)的降档是众所周知的,但是通过实验获得的热量系数Delta G / Delta在多样化的作品之间显着实现。此外,通常评估ΔG/ΔTT系数对于相对低的温度,发现单次,少数和多层石墨烯强烈地不同。在通过激光束下,我们在自由悬挂的多层石墨烯片(或石墨纳米薄片)中研究了G频段行为。斯托克斯和抗斯托克斯信号的分析表明,G频段具有复杂的结构,可以被解碳成几个峰,其在加热下表现出明显不同的行为。合理的假设是这些峰值对应于几组石墨层(表面,近表面和散装),然后针对这些组测定不同的热系数。这种行为可以通过在影响少数最外层的尤其振动性质的高温下降低表面层和底层材料之间的相互作用来解释。还进行了使用抗Stokes / Stokes强度比(I-AS / I-S)的温度估计,得到结果与从G频段下降,T-Delta G近似到T-AS / s的结果相当,支持所提出的模型。通过两种方法评估的激光加热所获得的温度范围为450至1200k。

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