研究目的
To unravel the origin of the G* band in the Raman spectrum of graphene by performing detailed Raman studies using multiple laser excitations.
研究成果
The G* band in graphene arises from time-ordered combination of iTO and LA phonons along the K-Γ direction, with asymmetry due to LA-first and iTO-first processes. This is supported by evidence from laser energy, defect, and temperature dependencies. The findings have implications for graphene-enhanced Raman scattering and sensing applications.
研究不足
The study is limited to graphene samples and may not generalize to other materials. Theoretical calculations of matrix elements in the presence of defects were not performed and are noted as a topic for future work. The resolution of the Raman spectrometer may limit the ability to deconvolute all sub-peaks in multi-layer graphene.
1：Experimental Design and Method Selection:
The study involved Raman spectroscopy to investigate the G* band in graphene, utilizing the Double Resonance (DR) mechanism. Detailed procedures included fitting spectra with Voigt lineshapes and analyzing phonon dispersions.
2：Sample Selection and Data Sources:
Graphene samples (single-layer, bi-layer, and few-layer) were prepared via mechanical exfoliation from HOPG on SiO2/Si substrates and chemical vapor deposition (CVD) on Cu or Ni foils, followed by transfer to substrates. Samples were characterized using Atomic Force Microscopy (AFM) and micro-Raman spectroscopy.
3：List of Experimental Equipment and Materials:
Equipment included a Renishaw InVia Raman microscope, a Dilor XY micro-Raman setup, a thermal stage (Linkam Scientific Instruments Ltd), and lasers with energies from
4：96 to 81 eV. Materials included HOPG, SiO2/Si substrates, Cu and Ni foils, methane, hydrogen, argon, ferric nitrate, and HCl. Experimental Procedures and Operational Workflow:
Raman spectra were acquired with laser power kept below 1 mW to avoid heating. Spectra were normalized to G band intensity and baseline corrected. Temperature-dependent measurements were conducted from 25 to 250°C using a thermal stage under controlled atmosphere.
5：Data Analysis Methods:
Data were analyzed using Voigt lineshape fitting for peak deconvolution, comparison with phonon dispersion relations, and statistical analysis of intensity ratios and frequency shifts with respect to laser energy, defect density, and temperature.
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