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Patrick R. Whelan: Terahertz time-domain spectroscopy for electrical homogeneity mapping of graphene

posted 8 Aug 2019, 03:21 by info admin
Patrick R. Whelan, David Mackenzie, Dirch H. Petersen, Peter U. Jepsen, and Peter Bøggild DTU Physics, Technical University of Denmark, Denmark 

Terahertz-time domain spectroscopy (THz-TDS) is a rapid and non-destructive measurement technique for accurate scanning of the electrical properties of graphene [1]. By raster scanning samples in the focal plane of the THz beam it is possible to map the DC conductivity, scattering time, carrier density and mobility of graphene without physical contact to the sample [1]. Values obtained from THz-TDS measurements are benchmarked against micro four point probe (M4PP) and Hall measurements in order to compare and verify extracted values [1]. 
Here, we will highlight recent results on THz-TDS measurements of graphene on flexible polymeric substrates [2] and as-grown graphene on silicon carbide where a ~30x variation in conductivity across a 4 inch wafer is observed (see figure) [3].  

[1] P.Bøggild et al., 2D Materials, 4 (2017) 042003
[2] Whelan et al., Optics Exp., 26 (2018) 17748-17754
[3] Whelan et al., ACS App. Mater. Interfaces, 10
(2018), 31641-31647

Patrick Whelan is a postdoc at DTU Physics doing research in large-area characterization of graphene with a main focus on THz-TDS measurements.  He received his Master degree from Aalborg University in Nanophysics and -materials in 2013 and a PhD in 2016 from DTU Physics for his work on transfer and characterization of large-area CVD graphene for transparent electrode applications.