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Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 76: Graphene: Applications, Luminescence, and Spin Relaxation (jointly with HL, O)

TT 76.4: Talk

Wednesday, March 18, 2015, 17:30–17:45, ER 270

Correlation of the crystallite sizes and D band frequency of non-graphitic carbons — •Dominique B. Schuepfer1, Kristin Faber2, Bernd M. Smarsly2, Roman V. Yusupov3, and Peter J. Klar11Institute of Experimental Physics I, Justus-Liebig-University Giessen, Germany — 2Institute of Physical Chemistry, Justus-Liebig-University Giessen, Germany — 3Institute of Physics, Kazan Federal University, Russia

Raman spectroscopy is often used to determine the crystallite size La of non-graphitic carbons by taking into account the intensity ratio of the defect-induced D band and the G band. We present an analysis of soft pitches via Raman spectroscopy in comparison to wide-angle X-ray spectra revealing discrepancies for La. Significant errors can be caused by known issues, for example the superposition of certain bands while estimating the intensities. Therefore, we introduce an alternative approach: An analysis of the D band revealed a correlation between its position and the crystallite size in the range of crystallite sizes less than 2 nm. The Raman shift significantly increases for smaller La using an excitation wavelength in the visible range. UV light yields the opposite behavior of the D band position, probably because of resonant absorption processes. To further characterize the samples in different La-ranges (La < 2 nm and La > 2 nm) electron paramagnetic resonance spectroscopy (EPR) has been carried out. Isotropic shaped EPR spectra are observed up to a crystallite size of 2 nm and samples containing crystallite sizes larger 2 nm show anisotropic signals. This behavior correlates with the detected Raman shift.

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