Functional Materials and Microsystems – Publications

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

Selected recent publications

Mechanically tunable terahertz metamaterials

J. Li, C. M. Shah, W. Withayachumnankul, B. S.-Y. Ung, A. Mitchell, S. Sriram, M. Bhaskaran, S. Chang, and D. Abbott

Applied Physics Letters 102 121101 (2013) [doi 10.1063/1.4773238]

Abstract: Electromagnetic device design and flexible electronics fabrication are combined to demonstrate mechanically tunable metamaterials operating at terahertz frequencies. Each metamaterial comprises a planar array of resonators on a highly elastic polydimethylsiloxane substrate. The resonance of the metamaterials is controllable through substrate deformation. Applying a stretching force to the substrate changes the inter-cell capacitance and hence the resonance frequency of the resonators. In the experiment, greater than 8% of the tuning range is achieved with a good repeatability over several stretching-relaxing cycles. This study promises applications in remote strain sensing and other controllable metamaterial-based devices.


Enhanced charge carrier mobility in two-dimensional high dielectric molybdenum oxide

S. Balendhran, J. Deng, J. Z. Ou, S. Walia, J. Scott, J. Tang, K. L. Wang, M. R. Field, S. P. Russo, S. Zhuiykov, M. S. Strano, N. Medhekar, S. Sriram, M. Bhaskaran, and K. Kalantar-zadeh

Advanced Materials 25 109 (2013) [doi 10.1002/adma.201203346]

Abstract: We demonstrate that the energy bandgap of layered, high-dielectric α-MoO3 can be reduced to values viable for the fabrication of 2D electronic devices. This is achieved through embedding Coulomb charges within the high dielectric media, advantageously limiting charge scattering. As a result, devices with α-MoO3 of ∼11 nm thickness and carrier mobilities larger than 1100 cm2 V−1 s−1 are obtained.


Dielectric resonator nanoantennas at visible frequencies

L. Zou, W. Withayachumnankul, C. M. Shah, A. Mitchell, M. Bhaskaran, S. Sriram, and C. Fumeaux

Optics Express 21 1344 (2013) [doi 10.1364/OE.21.001344]

Abstract: Drawing inspiration from radio-frequency technologies, we propose a realization of nano-scale optical dielectric resonator antennas (DRAs) functioning in their fundamental mode. These DRAs operate via displacement current in a low-loss high-permittivity dielectric, resulting in reduced energy dissipation in the resonators. The designed nonuniform planar DRA array on a metallic plane imparts a sequence of phase shifts across the wavefront to create beam deflection off the direction of specular reflection. The realized array clearly demonstrates beam deflection at 633 nm. Despite the loss introduced by field interaction with the metal substrate, the proposed low-loss resonator concept is a first step towards nanoantennas with enhanced efficiency. The compact planar structure and technologically relevant materials promise monolithic circuit integration of DRAs.


In situ nanoindentation: Probing nanoscale multifunctionality

H. Nili, K. Kalantar-zadeh, M. Bhaskaran, and S. Sriram

Progress in Materials Science 58 1 (2013). [doi: 10.1016/j.pmatsci.2012.08.001]

Abstract: Nanoindentation is the leading technique for evaluating nanoscale mechanical properties of materials. Consistent developments in instrumentation and their capabilities are transforming nanoindentation into a powerful tool for characterization of multifunctionality at the nanoscale. This review outlines the integration of nanoindentation with real-time electron imaging, high temperature measurements, electrical characterization, and a combination of these. In situ nanoindentation measurements have enabled the real-time study of the interplay between mechanical, thermal, and electrical effects at the nanoscale. This review identifies previous reviews in this area, traces developments and pinpoints significant recent advances (post-2007), with emphasis on the applications of in situ nanoindentation techniques to materials systems, and highlighting the new insights gained from these in situ techniques. Based on this review, future directions and applications of in situ nanoindentation are identified, which highlight the potential of this suite of techniques for materials scientists from all disciplines.


Elevated temperature anodized Nb2O5: A photoanode material with exceptionally large photoconversion efficiencies

J. Z. Ou, R. A. Rani, M. H. Ham, M. R. Field, Y. Zhang, H. Zheng, P. Reece, S. Zhuiykov, S. Sriram, M. Bhaskaran, R. B. Kaner, and K. Kalantar-zadeh

ACS Nano 6 4045 (2012). [doi: 10.1021/nn300408p]

Abstract: Here, we demonstrate that niobium pentoxide (Nb2O5) is an ideal candidate for increasing the efficiencies of dye-sensitized solar cells (DSSCs). The key lies in developing a Nb2O5 crisscross nanoporous network, using our unique elevated temperature anodization process. For the same thicknesses of ~4 μm, the DSSC based on the Nb2O5 layer has a significantly higher efficiency (~4.1%) when compared to that which incorporates a titanium dioxide nanotubular layer (~2.7%). This is the highest efficiency among all of the reported photoanodes for such a thickness when utilizing back-side illumination. We ascribe this to a combination of reduced electron scattering, greater surface area, wider band gap, and higher conduction band edge, as well as longer effective electron lifetimes.


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