Microwave to terahertz: Characterization of carbon-based nanomaterials

Microwave engineering has been an exciting forefront of modern technology and one of the major enablers of the fast-expanding information era. Since its formal establishment in the 19th century, this classic field has experienced many revolutions powered by discoveries of new materials and inventions of related devices. Rapid developments in nanotechnology in recent years have offered exciting possibilities for revolutionary discoveries in many branches of human endeavor. Nanomaterials and associated devices are being widely studied and developed for applications in electronics, optics, biology, energy, etc. Although it has been suggested that nanomaterials such as carbon nanotubes (CNTs) and graphene-based devices may work well in the microwave or even terahertz (THz) range [1], [2], most of the previous measurements were done at dc or lower frequency ( f < 300 MHz) [3]-[5]. The characterization techniques of nanomaterials at microwave and THz frequency are important for both fundamental research and practical applications before proposed components such as antennas, interconnections, and circuit building blocks [6]-[8] can be realized. In this article, a review of characterization methods and associated challenges for various CNT and graphene samples from microwave to THz frequencies is presented, and pros and cons of the approaches are highlighted.