Functional Materials and Microsystems – Publications

Full publication list of the research group can be found in the RMIT Research Repository.

Selected recent publications

Plasmonic resonance toward terahertz perfect absorbers

W. Withayachumnankul, C. M. Shah, C. Fumeaux, B. S.-Y. Ung, W. J. Padilla, M. Bhaskaran, D. Abbott, and S. Sriram

ACS Photonics 1 625 (2014). [doi: 10.1021/ph500110t]

Abstract: Metamaterial perfect absorbers have garnered significant interest with applications in sensing, imaging, and energy harnessing. Of particular interest are terahertz absorbers to overcome the weak terahertz response of natural materials. Here, we propose lossy plasmonic resonance in silicon-based annular microcavities for perfect terahertz absorption. This mechanism is in stark contrast to earlier demonstrations of conventional terahertz perfect absorbers that invoke Lorentzian electric and magnetic resonances. A fundamental cavity mode coupled to coaxial surface plasmon polaritons is responsible for the predicted exceptional absorption of −58 dB with a 90% absorption bandwidth of 30%. The performance is in agreement with experimental validation and consistent with critical coupling and resonance conditions. This specific cavity design possesses great thermal isolation and minimal electromagnetic coupling between unit cells. These unique features exclusive to the plasmonic cavity introduce a promising avenue for terahertz imaging with enhanced contrast, resolution, and sensitivity.

Terahertz reflectarray as a polarizing beam splitter

T. Niu, W. Withayachumnankul, A. Upadhyay, P. Gutruf, D. Abbott, M. Bhaskaran, S. Sriram, and C. Fumeaux

Optics Express 22 16148 (2014). [doi:  10.1364/OE.22.016148]

Abstract: A reflectarray is designed and demonstrated experimentally for polarization-dependent beam splitting at 1 THz. This reflective component is composed of two sets of orthogonal strip dipoles arranged into interlaced triangular lattices over a ground plane. By varying the length and width of the dipoles a polarization-dependent localized phase change is achieved on reflection, allowing periodic subarrays with a desired progressive phase distribution. Both the simulated field distributions and the measurement results from a fabricated sample verify the validity of the proposed concept. The designed terahertz reflectarray can efficiently separate the two polarization components of a normally incident wave towards different predesigned directions of ±30°. Furthermore, the measured radiation patterns show excellent polarization purity, with a cross-polarization level below −27 dB. The designed reflectarray could be applied as a polarizing beam splitter for polarization-sensitive terahertz imaging or for emerging terahertz communications.

Field effect biosensing platform based on 2D α‑MoO3

S. Balendhran, S. Walia, M. Alsaif, E. P. Nguyen, J. Z. Ou, S. Zhuiykov, S. Sriram, M. Bhaskaran, and K. Kalantar-zadeh

ACS Nano 7 9753 (2013). [doi: 10.1021/nn403241f]

Abstract: Electrical-based biosensing platforms offer ease of fabrication and simple sensing solutions. Recently, two-dimensional (2D) semiconductors have been proven to be excellent for the fabrication of field effect transistors (FETs) due to their large transconductance, which can be efficiently used for developing sensitive bioplatforms. We present a 2D molybdenum trioxide (MoO3) FET based biosensing platform, using bovine serum albumin as a model protein. The conduction channel is a nanostructured film made of 2D α-MoO3 nanoflakes, with the majority of nanoflake thicknesses being equal to or less than 2.8 nm. The response time is impressively low (less than 10 s), which is due to the high permittivity of the 2D α-MoO3 nanoflakes. The system offers a competitive solution for future biosensing applications.

Transparent functional oxide stretchable electronics: Micro-tectonics enabled high strain electrodes

P. Gutruf, C. M. Shah, S. Walia, H. Nili, A. S. Zoolfakar, C. Karnutsch, K. Kalantar-zadeh, S. Sriram, and M. Bhaskaran

NPG Asia Materials 5 e62 (2013). [doi: 10.1038/am.2013.41]

Abstract: Fully transparent and flexible electronic substrates that incorporate functional materials are the precursors to realising next-generation devices with sensing, self-powering and portable functionalities. Here, we demonstrate a universal process for transferring planar, transparent functional oxide thin films on to elastomeric polydimethylsiloxane (PDMS) substrates. This process overcomes the challenge of incorporating high-temperature-processed crystalline oxide materials with low-temperature organic substrates. The functionality of the process is demonstrated using indium tin oxide (ITO) thin films to realise fully transparent and flexible resistors. The ITO thin films on PDMS are shown to withstand uniaxial strains of 15%, enabled by microstructure tectonics. Furthermore, zinc oxide was transferred to display the versatility of this transfer process. Such a ubiquitous process for the transfer of functional thin films to elastomeric substrates will pave the way for touch sensing and energy harvesting for displays and electronics with flexible and transparent characteristics.

Transition metal oxides - thermoelectric properties

S. Walia, S. Balendhran, H. Nili, S. Zhuiykov, G. Rosengarten, Q. H. Wang, M. Bhaskaran, S. Sriram, M. S. Strano, and K. Kalantar-zadeh

Progress in Materials Science 58 1443 (2013). [doi: 10.1016/j.pmatsci.2013.06.003]

Abstract: Transition metal oxides (TMOs) are a fascinating class of materials due to their wide ranging electronic, chemical and mechanical properties. Additionally, they are gaining increasing attention for their thermoelectric (TE) properties due to their high temperature stability, tunable electronic and phonon transport properties and well established synthesis techniques. In this article, we review TE TMOs at cryogenic, ambient and high temperatures. An overview of strategies used for morphological, composting and stoichiometric tuning of their key TE parameters is presented. This article also provides an outlook on the current and future prospects of implementing TMOs for a wide range of TE applications.

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