Plasmonic Resonances in Carbon Microfibres for Engineerable Terahertz Absorption

Irina Khromova Department of Electronic and Electrical Engineering, University College London, London, UK The International Research Centre for Nanophotonics and Metamaterials, ITMO University, St. Petersburg, Russia Department of Electrical and Electronic Engineering, Public University of Navarra, Pamplona, Spain Oleg Mitrofanov Department of Electronic and Electrical Engineering, University College London, London, UK Miguel Navarro-Cia Department of Electronic and Electrical Engineering, University College London, London, UK Inigo Liberal Department of Electrical and Electronic Engineering, Public University of Navarra, Pamplona, Spain Igal Brener Center for Integrated Technologies, Sandia National Laboratory, Albuquerque, USA John Reno Center for Integrated Technologies, Sandia National Laboratory, Albuquerque, USA Leonid Melnikov Chair of Instrumentation Engineering, Saratov State Technical University, Saratov, Russia Andrey Ponomarev -, Scientific Technical Centre of Applied Nanotechnologies, St. Petersburg, Russia

We performed near-field time-domain spectroscopy on individual milled carbon microfibres (CMFs) to verify the presence of strong plasmonic resonances at terahertz frequencies. These plasma-chemically treated microfibres are 7 μm in diametre and their lengths vary from 10 μm to 150 μm. Fig.1 shows: (a) a SEM image of the CMFs, and (b) a space-time THz near-field map and (c) an image of a of a 133μm-long CMF. The terahertz conductivity of CMFs was extracted from the shift between the frequencies of an individual CMF absorption peak and the resonance frequency of the corresponding perfectly conducting dipole. Its value lies very close to the condition of maximum absorption to scattering relation.

We used semi-analytical models to predict the usability of CMFs for efficient terahertz absorbers with engineerable response. Combining the effective medium approximation with a simple dipole antenna model, we numerically obtained scattering and absorption characteristics of composites containing CMFs with given lengths distributions.

We experimentally studied the terahertz response of thin pellets of high density polyethylene (HDPE) with arbitrarily oriented and differently sized CMF inclusions. These samples demonstrated a clearly resonant behaviour: broad absorption peaks at around 1.5 THz indicate the presence of size effects distributed over lengths of CMFs in each sample.

With artificialy created distribution of lengths, CMF-based composites may be designed according to desirable absorption profiles. This simlpe and inexpensive technique may, in particular, be used to achieve flat absorption at terahertz frequencies.

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