Abstract-Conductivity mapping of graphene on polymeric films by terahertz time-domain spectroscopy

Patrick R. Whelan, Deping Huang, David Mackenzie, Sara A. Messina, Zhancheng Li, Xin Li, Yunqing Li, Timothy J. Booth, Peter U. Jepsen, Haofei Shi, Peter Bøggild,

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-26-14-17748

Fast inline characterization of the electrical properties of graphene on polymeric substrates is an essential requirement for quality control in industrial graphene production. Here we show that it is possible to measure the sheet conductivity of graphene on polymer films by terahertz time-domain spectroscopy (THz-TDS) when all internally reflected echoes in the substrate are taken into consideration. The conductivity measured by THz-TDS is comparable to values obtained from four point probe measurements. THz-TDS maps of 25x30 cm2 area graphene films were recorded and the DC conductivity and carrier scattering time were extracted from the measurements. Additionally, the THz-TDS conductivity maps highlight tears and holes in the graphene film, which are not easily visible by optical inspection.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping

David M. A. Mackenzie, Patrick R. Whelan, Peter Bøggild, Peter Uhd Jepsen, Albert Redo-Sanchez, David Etayo, Norbert Fabricius, and Dirch Hjorth Petersen

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-7-9220

We present a comparative study of electrical measurements of graphene using terahertz time-domain spectroscopy in transmission and reflection mode, and compare the measured sheet conductivity values to electrical van der Pauw measurements made independently in three different laboratories. Overall median conductivity variations of up to 15% were observed between laboratories, which are attributed mainly to the well-known temperature and humidity dependence of non-encapsulated graphene devices. We conclude that terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties. The conductivity obtained via terahertz time-domain spectroscopy were consistently in agreement with electrical van der Pauw measurements, while offering the additional advantages associated with contactless mapping, such as high throughput, no lithography requirement, and with the spatial mapping directly revealing the presence of any inhomogeneities or isolating defects. The confirmation of the accuracy of reflection-mode removes the requirement of a specialized THz-transparent substrate to accurately measure the conductivity.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Robust mapping of electrical properties of graphene from terahertz time-domain spectroscopy with timing jitter correction

Patrick R. Whelan, Krzysztof Iwaszczuk, Ruizhi Wang, Stephan Hofmann, Peter Bøggild, and Peter Uhd Jepsen
obust mapping of electrical properties of graphene from terahertz time-domain spectroscopy with timing jitter correction

We demonstrate a method for reliably determining the electrical properties of graphene including the carrier scattering time and carrier drift mobility from terahertz time- domain spectroscopy measurements (THz-TDS). By comparing transients originating from directly transmitted pulses and the echoes from internal reflections in a substrate, we are able to extract electrical properties irrespective of random time delays between pulses emitted in a THz-TDS setup. If such time delays are not accounted for they can significantly influence the extracted properties of the material. The technique is useful for a robust determination of electrical properties from THz-TDS measurements and is compatible with substrate materials where transients from internal reflections are well-separated in time.

© 2017 Optical Society of America

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