Spatially resolved electrical characterisation of graphene layers by an evanescent field microwave microscope

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• 作者：Andrew Gregory ; Ling Hao ; Norbert Klein ; John Gallop ; Cecilia Mattevi ; Olena Shaforost ; Kevin Lees ; Bob Clarke
• 刊名：Physica E
• 出版年：February, 2014
• 年：2014
• 卷：56
• 期：Complete
• 页码：431-434
• 全文大小：1024 K

文摘

An evanescent field microwave microscope has been developed at the National Physical Laboratory. This instrument has multiple applications and has been developed to allow traceable measurements of local complex permittivity, unlike most other microwave scanning microscopes. In this paper we describe basic operation of the microscope and show measurements on graphene samples produced at Imperial College. The microscope obtains images by raster scanning of a wire probe in 鈥榗ontact mode鈥? Of particular interest to the graphene community is the possibility of being able to scan over large areas (up to 4脳4 mm²), and to be able to measure actual values of surface resistance without a requirement for metal contacts. As an ultrathin semimetal, a graphene layer being placed in the evanescent field of the probe is expected to behave like a lossy dielectric material, its microwave loss tangent is proportional to its conductivity. Employing a high Q dual mode re-entrant cavity as host resonator and a spherical metal probe of 180 渭m diameter, we found that spatial variations of the conductivity of graphene can be clearly resolved.