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doping inhomogeneity and staging of ultra-thin graphite intercalation compound flakes probed by visible and near-infrared Raman spectroscopy

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Chinese Physics B 2015年第7期24卷 524-528页

作者：鲁妍张昕吴江滨李晓莉厉巧巧谭平恒 State Key Laboratory for Superlattices and Microstructures Institute of SemiconductorsChinese Academy of Sciences

When ultra-thin graphite intercalation compounds（GICs） are deposited on the SiO2/Si substrate, it is found that their colors are dependent on the thickness of GIC flakes. The sample colors of ultrathin GIC flakes can no longer provide qualitative information on the stage index. Here, multi-wavelength Raman spectroscopy is thus applied to study the doping inhomogeneity and staging of ultra-thin GICs by FeCl3 intercalation. The G band intensity of stage-1 GIC flakes is strongly enhanced by 532-nm laser excitation, while that of stage-2 and stage-3 flakes exhibits strong intensity enhancement for 785-nm laser excitation. The near-infrared lasers are suggested to probe the doping inhomogeneity and staging of ultra-thin GIC flakes.

关键词： ultra-thin graphite intercalation compounds Raman spectroscopy intensity enhancement doping inhomogeneity

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Quality assessment of graphene： Continuity, uniformity, and accuracy of mobility measurements

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Nano Research 2017年第10期10卷 3596-3605页

作者： David M. A. Mackenzie Jonas D. Buron Patrick R. Whelan José M. Carida Martin Bjergfelt Bironq Luo Abhay Shivayogimath Anne L. Smitshuysen Joachim D. Thomsen Timothy J. Booth Lene Gammelgaard Johanna Zultak Bjarke S. Jessen Peter Boggild Dirch H. Petersen Department of Micro- and Nanotechnology Technical University of Denmark Orsteds Plads 345 B Kongens Lyngby 2800 Denmark Center for Nanostructured Graphene (CNG) Technical University of Denmark Kongens Lyngby 2800 Denmark

With the increasing availability of large-area graphene, the ability to rapidly and accurately assess the quality of the electrical properties has become critically important. For practical applications, spatial variability in carrier density and carrier mobility must be controlled and minimized. We present a simple framework for assessing the quality and homogeneity of large-area graphene devices. The field effect in both exfoliated graphene devices encapsulated in hexagonal boron nitride and chemical vapor-deposited （CVD） devices was measured in dual current-voltage configurations and used to derive a single, gate-dependent effective shape factor, t, for each device, β is a sensitive indicator of spatial homogeneity that can be obtained from samples of arbitrary shape. All 50 devices investigated in this study show a variation （up to tenfold） in β as a function of the gate bias. Finite element simulations suggest that spatial doping inhomogeneity, rather than mobility inhomogeneity, is the primary cause of the gate dependence of β, and that measurable variations of β can be caused by doping variations as small as 10^10 cm^-2. Our results suggest that local variations in the position of the Dirac point alter the current flow and thus the effective sample shape as a function of the gate bias. We also found that such variations lead to systematic errors in carrier mobility calculations, which can be revealed by inspecting the corresponding β factor.

关键词： chemical vapor-deposited (CVD) graphene doping inhomogeneity electrical measurements van der Pauw hBN-encapsulated graphene finite element simulations Raman mapping

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