Day 3 :
- Optical Materials and Plasmonics | Energy and Harvesting Materials | Optical Materials and Plasmonics
Université Paris-Sud, France
Time : 09:30-09:50
Gérald Dujardin is « Directeur de Recherche at CNRS ». He started working on « Manipulation of single molecules with the STM » at IBM (Yorktown, USA) in 1991 with Phaedon Avouris. . Over the past years, he developed a team in Orsay which acquired experience in the electrical and optical control of atomic-scale devices. His current research interests are focused on the electrical excitation of hybrid plasmon-exciton optical nanodevices.
To optimize the optoelectronic properties of plasmon based nanostructures and their integration in functionalized nanodevices, it is crucial to design dedicated electrical nanosources of surface plasmons whose size is compatible with that of the studied nanostructures. Here, we report an electrical surface plasmon nanosource using inelastic electron tunneling from the tip of a scanning tunneling microscope (STM). The main advantages of STM induced surface plasmon excitation are (i) the very local excitation (10 nm) which enables precise localization of the excitation inside the nanometer size plasmonic devices, (ii) the nature of the excitation which is equivalent to a point-like vertical dipole, (iii) the low energy electrical character (» 3 eV) of the excitation which makes nanoplasmonics compatible with nanoelectronics, and (iv) the ability to excite both localized and propagating surface plasmons with a broadband energy distribution. As an example of the integration of this electrically driven plasmon nanosource into elementary plasmonic devices we show the production of cylindrical vector beams of light from an electrically excited plasmonic lens. The plasmonic lens consists of concentric circular subwavelength slits that are etched in a thick gold film. Due to the very local electrical excitation of the plasmonic lens, a highly collimated beam with an angular divergence of less than 4° and a polarization with a cylindrical symmetry are demonstrated. The variable direction of emission is controlled by the precise positioning of the STM tip.
Chinese Academy of Sciences, China
Dr. Yuyan Jiang is a professor in the Institute of Engineering Thermophysics (IET), Chinese Academy of Sciences (CAS). He received a B.E. degree from Xi'an Jiaotong University (1996), a M.E. degree from Tsinghua University (1999) and a PhD from the University of Tokyo (2002). He has been a post-doctoral researcher in IIS, the University of Tokyo (2002-2005), a senior research fellow in AdvanceSoft Inc.(2005-2008) and a visiting researcher in Toyota Central R&D Labs Inc. (2008-2011). He has also been working with CD-Adapco as a senior software engineer. Dr. Jiang's research interests include the boiling heat transfer, computations of two-phase flows with phase change. He is one of the major developers of the general-purpose CFD code, FrontFlow/Red. He has published more than 70 peer reviewed journal papers and has 30 disclosed patents. In their latest study, they invented surfaces with deformable micro structures made of shape memory alloys for the enhancement and smart control of boiling.
Smart materials, that can change structures and/or physical-chemical properties by active or passive control, has potential applications in energy engineering. They can be used to design cute and efficient energy converting systems, e.g. waste heat generation systems made of shape-memory-alloys (SMA). The advances of electronic and aerospace engineering calls for more robust thermal management technologies that can help the devices to discharge intensive heat release and mitigate the temperature fluctuation. To this end, smart materials can take their inherent advantages in heat transfer enhancing and in providing extra measures for driving coolant flow.
In our latest studies, a novel deformable structured surface was fabricated by SMA for the enhancement of boiling heat transfer. Pool boiling heat transfer on deformable structures were performed in three fluids (ethanol, FC-72, water) with different thermal properties was explored. Comparing heat flux versus wall superheat and HTC at different fluxes with fixed geometry, it is found that deformable structure combines the merits of closed-tunnel and open-tunnel. At low heat fluxes, it can increase the numbers of nucleation sites inside the closed tunnels with bent fins and after recovering with open tunnels, the nucleation sites are activated and the bubble growth and departure is accelerated to enhance the HTC significantly. On the other hand, by choosing the appropriate time and opportunity for different fluid to open the tunnels, the deformable structures can be used to achieve adaptive-control of boiling heat transfer. In another study, researchers from POSTECH proposed a smart TiO2-coated surface (TCS) for boiling heat transfer. The surface changes its wettability with temperature. Measurement of the contact angle of a water droplet on the tested surfaces after heat treatment showed a wettability increase of TCS, a contact angle reduction from 83.1_ to 32.7_ when the heat treatment temperature changed from 100 _C to 200 _C, in other words, TCS is hydrophobic at a low wall temperature and becomes hydrophilic as the wall temperature increases. Hydrophobicity of TCS at low wall temperatures. The TCS improved both the heat transfer coefficient near the boiling inception point at low heat flux regime, and critical heat flux at high wall temperatures. People are also developing heat transfer devices that have SMA self-driven unit for flow circulations that working with temperature differences.
The study on energy harvesting and thermal management by use of smart materials is a quite young interdiscipline research field, which is still in the initial stage. This presentation gives a critical review to the latest pioneering work. By summarizing the advancements, we propose some comments on the principles and prospect for the future development.
The Hong Kong Polytechnic University, Hong Kong
Dr. Yuen Hong Tsang has completed BSc and PhD study in the School of Physics and Astronomy, The University of Manchester, UK in 2004. He is now Assistant Professor in Applied Physics Department, The Hong Kong Polytechnic University. He has published >100 SCI international journals with H-index >20 and total citation >1400. His current research interests include development of novel 2D materials, e.g. MoS2, WS2, etc. for laser photonics, photo-catalysis, solar energy conversion applications, e.g. photo-catalyst, solar heat absorber, saturable absorber, optical limiter, photodetection, Q-switched and mode locked lasers, etc
To understand and modify the nonlinear optical properties of transition metal dichalcogenides, TMDs, two-dimensional layered materials are very important research topics nowadays as they can serve as building block for developing next generation high performance micro optics and photonic devices. These materials are very compact with atomic thick layer and have natural bandgap so they can provides strong interaction with light and other favorable features e.g. broadband absorption, transparent and high carrier mobility etc. WS2, which is a typical TMDs material, has layer number depending bandgap energy. The WS2 bandgap energy and optical properties can be modified by varying their size, layer number and structures. The WS2 nano materials and film in various size, layer number or film thickness are fabricated by two methods – ultrasound and sputtering. The nonlinear optical properties of different samples are then studied by using z-scan technique. We have successfully demonstrated some viable methods to tune the nonlinear absorption properties of WS2. We also use the fabricated WS2 film within the diode pumped solid state Nd:YVO4 crystal laser to generate pulsed laser output. A stable pulsed laser operation is achieved by using the fabricated WS2 saturable absorber. The average output power obtained is 19.6 mW (135 kHz). These research findings indicate strong nonlinear optical proporties of WS2 and high potential for nonlinear optical devices.
The Hong Kong Polytechnic University, Hong Kong
Jianhua Hao is a Full Professor and Associate Head of Department of Applied Physics in the Hong Kong Polytechnic University (PolyU). He received his BSc, MSc and PhD at Huazhong University of Science and Technology. After working at Penn State University, University of Guelph and University of Hong Kong, Jianhua Hao joined the faculty in PolyU in 2006. He has published more than 200 SCI papers. He is the first inventor of several US patents. He serves as Editorial Board Member/Senior Editor for several international journals, such as Scientific Reports（NPG）and Advanced Optical Materials
The ability of lanthanide ions to generate fascinating near-infrared (NIR) emissions has played important roles in optical fibre communication, semiconductor optoelectronic devices, biomedical imaging and bioanalyses. Two aspects of my group’s recent works on the lanthanide activated advanced materials and nanotechnology will be introduced. Firstly, we have developed various lanthanide doped nanocrystals for photonic and biological applications. For instance, biosensors with both high sensitivity and rapid response are greatly desired for enabling rapid and sensitive detection of various virus gene in a cost-effective way. We have developed lanthanide doped upconversion nanoprobe/nanoporous membrane to form a heterogeneous assay. Compared to the homogeneous assay, the limit of detection in the heterogeneous assay is significantly improved. Secondly, the ultimate goal of making nanoscale electronic and optoelectronic devices greatly stimulates atomically thin material and heterostructure research. We have introduced lanthanide dopants into two-dimensional (2D) layered semiconductor nanosheet hosts and realize NIR-to-NIR down- and up-conversion photoluminescence. Importantly, the luminescence of 2D materials simply pumped by a single NIR laser diode can be extended to a wide range of NIR spectrum, including telecommunication range at 1.55 μm. By considering the abundant energy levels arisen from lanthanide ions, our works open a door to greatly extend and modulate the luminescence wavelengths of 2D semiconductors, which will benefit for not only investigating many appealing fundamental issues, but also developing novel nanophotonic devices.