Department of Materials Science and Engineering, Monash University, Australia
Our research interests are mainly focused on the light-matter interactions in 2D materials in the forms of nonlinear light absorption, light modulation (amplitude, phase and polarisation), photo-electrical conversion, wave-guiding and polaritonic behaviours. This talk will give an overview of photonic and optoelectronic device applications based on these optical phenomena in 2D materials. Firstly, to overcome the limit light absorption in graphene and obtain large nonlinear optical modulation depth, we developed a serial of new saturable absorbers based on graphene heterostructures and other 2D materials, including graphene/Bi2Te3, black phosphorus and self-doped plasmonic 2D Cu3-xP nanosheets as well as 2D halide perovskite. Depending on their nonlinear optical properties, either high energy Q-switched laser or ultrafast mode-locked pulse generation were demonstrated. Secondly, in order to fabricate improved graphene photodetectors working in different spectral ranges, we integrated graphene with other 2D materials with variant electronic structures, for example, graphene/perovskite for visible light detection, graphene/MoTe2 and graphene/Cu3-xP for near infrared light detection, and graphene-Bi2Te3 for broadband infrared light detection. We show how photo-gating effect plays a significant role to amplify the photocurrent in the photodetectors as well solar cell device. By fine tuning or aligning the electronic structure, we are able to engineer the depletion width in 2D material heterostructures, such as graphene/WS2, MoS2/WS2 and WSe2/WS2heterojunction, monolayer-bilayer WSe2 heterojunction and 2D perovskite p-n junction, so as to achieve higher photo-responsivity and large photo-active area. Lastly, the THz light modulation associated with plasmonic excitation in graphene/Bi2Te3, topological insulator Bi2Te3, graphene nanoribbon and 3D graphene was investigated using either spectroscopic or real space imaging techniques. We show how the plasmonic coupling happens in two Dirac materials, how high-order plasmonic modes are observed in 3D graphene structure, how multiple plasmonic polariton modes at sub-wavelength are achieved in graphene nanoribbon and how edge chirality controls the polaritonic shift. In particular, we update our recent progress on the observation of anisotropic and ultra-low-loss polariton propagation along the surface of natural vdW material α-MoO3. We visualized and verified phonon polaritons with elliptic and hyperbolic in-plane dispersion, which have been theoretically predicted but never experimentally observed in natural materials before. We measured polariton amplitude lifetimes of 8 picoseconds, which is more than ten times larger than that of graphene plasmon polaritons at room temperature. In-plane anisotropic and ultra-low-loss polaritons in 2D materials could enable directional and strong light–matter interactions, nanoscale directional energy transfer and integrated flat optics in applications ranging from bio-sensing to quantum nanophotonics. In summary, the advances of 2D materials research may pave the way for the next generation photonic and optoelectronic device applications.
Brief bio: Dr. Qiaoliang Bao received his Bachelor (2000) and Master (2003) degree from School of Materials Science and Engineering, Wuhan University of Technology, and Ph. D degree from Department of Physics, Wuhan University (2007). From 2006 to 2008, he studied at Nanyang Technological University as a visiting student and research associate. From 2008 to 2012, he worked as a postdoctoral fellow in Graphene Research Centre, National University of Singapore (NUS). He was enrolled into China Thousand Youth Talent Program in 2012. He obtained ARC Future Fellowship in 2016 and is now an Associate Professor at Department of Materials Science and Engineering, Monash University, Australia. He is one of the 20 lead CIs of the Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technology (ARC COE FLEET). He has authored or co-authored more than 170 refereed journal articles with around 20,000 total citations and an H-index of 58 (谷歌 Scholar). His research involves the investigation of waveguide-coupled 2D semiconductors and polariton-coupled 2D materials and devices, focusing on the effect of confined-space light-matter interactions on the transport of electrons or other quasi-particles such as plasmon polariton, exciton polarition and phonon polariton.