1:30pm - 2:00pmInvited
Reactions between Nanoparticles
Indian Institute of Technology Madras, India
Atom and structure conserving chemical reactions between nanoparticles is presented. Two atomically precise archetypal nanoparticles[1,2], Ag25(SR)18 and Au25(SR)18, are used for this purpose. Despite their geometric robustness and electronic stability, reactions between them in solution produce alloys, AgmAun(SR)18(m+n=25), keeping their M25(SR)18 composition, structure and topology intact. We demonstrate that a mixture of Ag25(SR)18 and Au25(SR)18 can be transformed to any arbitrary alloy composition, AgmAun(SR)18 (n=1–24), merely by controlling the reactant compositions. We capture one of the earliest events of the process, namely the formation of the dianionic adduct, [Ag25Au25(SR)36]2-, by electrospray ionization mass spectrometry. Molecular docking simulations and density functional theory (DFT) calculations also suggest that metal atom exchanges occur through the formation of an adduct between the two clusters. DFT calculations further confirm that metal atom exchanges are thermodynamically feasible. Such isomorphous transformations between nanoparticles imply that microscopic pieces of matter can be transformed completely to chemically different entities, preserving their structures, at least in the nanometric regime. The capability envisioned here is important for sustainable development.
 M. W. Heaven, A.Dass, P. S. White, K. M. Holt, and R. W. Murray J. Am. Chem. Soc. 2008, 130, 3754-3755.
 C. P. Joshi, M. S. Bootharaju, M. J. Alhilaly, and O. M. Bakr J. Am. Chem. Soc. 2015, 137, 11578−11581.
 K.R. Krishnadas, AnanyaBaksi, Atanu Ghosh, Ganapati Natarajan andThalappil Pradeep Nat. Commun. 2016 DOI: 10.1038/ncomms13447 (In press).
2:00pm - 2:30pmInvited
Solution-Processed Plasmonic Semiconductor Nanocrystals for Nonlinear Optics and Ultrafast Optical Switch
Zhejiang University, China
Plasmonic nanomaterials have evoked growing interest in recent years due to their diverse applications from photonics to biomedicine. The active spectral range of most noble metal based plasmonic materials is however limited to the visible range due to the relative high free electron density. Degenerate semiconductors therefore appear as alternative plasmonic materials which offer a tunable plasmon frequency covering the entire near infrared (NIR) and mid-IR spectral range. We investigated the nonlinear optical properties of typical degenerate semiconductors, including Cu2-xS, Cu-In-S and indium tin oxides. Our results show that these semiconductor-based plasmonic nanocrystals accessed by wet-chemistry route exhibit strong nonlinear optical response, characterized by prominent saturable absorption and high modulation depth. The hot carrier relaxation process as reveal by ultrafast spectroscopy consists of typical sub-picosecond (ps) electron-electron and 10-ps scale electron-phonon scattering. The high nonlinear optical modulation depth combined with the ultrafast relaxation enabled the fabrication of high efficient saturable absorbers for optical modulation in ultrafast lasers. We have successfully demonstrated both Q-switched and mode-locked laser pulse generation with pulse duration down to the femtosecond region in different fiber and solid state lasers, which operate at wavelength region from 1000 nm to near 3000 nm. Our results therefore provide a simple but highly efficient material solution to the development of compact ultrafast lasers operating the IR range.
2:30pm - 2:45pmOral
Dual Functional Light Emitting Diode for Fast White Light Communications
1Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore; 2Department of Physics, National University of Singapore, Singapore
In recent years, there has been a growing interest in using light emitting diodes for visible light communications (VLC), besides illumination. VLC can provide fast and secure communications to help relieve the congested Wi-Fi and provide accessibility to RF restricted areas. GaN based light emitting diodes (LEDs) are the preferred transmitters for this application due to their high brightness, fast modulation speed and low power consumption. By operating LEDs in reverse bias, visible light detection is possible. This dual functionality enables LED-to-LED communications, without the need for additional photo-detectors.
In this paper, we present the use of textured V-pit InGaN LED for enhanced emission and detection. We show a 180% increase in electroluminescence and a 84% increase in peak responsivity through higher light extraction efficiency and absorption efficiency respectively. 3D FDTD simulations show larger angular scattering and increased optical path length for light absorption and extraction. Spectral and temporal studies of the detector characteristics are carried out to help us understand its responsivity in the visible range and the ultimate speed limit of the detector, which are important for fast white light communications. Finally, we demonstrate the ability to increase the speed of white light modulation from 5MHz to 20 MHz using this detector. Such a device is suitable not only as a transmitter, but also a highly responsive detector for high speed LED-to-LED communications.
2:45pm - 3:00pmOral
Effective Hyper-Raman Scattering via Inhibiting Electromagnetically Induced Transparency in Monolayer Graphene under an External Magnetic Field
1Department of Physics, Southeast University, Nanjing, China; 2Institute of Photonics Technologies, National Tsing-Hua University, Taiwan
Monolayer graphene under a strong magnetic field has fascinating electronic and optical properties, such as linear dispersion relation, massless Dirac low-energy electrons, chiral character of electron states and special selection rules between Landau levels. These properties involving the fields of quantum optics and solid material science provide great opportunities for the applications of coherent optics and nonlinear optics. Here, we propose and analyze an effective scheme to generate hyper-Raman scattering via inhibiting electromagnetically induced transparency (EIT) in a monolayer graphene under a magnetic field. By solving the Schrödinger-Maxwell formalism, we derive explicitly analytical expressions for linear susceptibility, nonlinear susceptibility, and generated Raman electric field under the steady-state condition. Based on dressed-state theory, our results show a competition between EIT and hyper-Raman scattering, in which the different competition situations depend on whether multiphoton destructive interference is quenched or well-developed. Furthermore, we reveal that the hyper-Raman process is totally dominant when multiphoton destructive interference is completely suppressed. This interesting scheme may be used to produce coherent terahertz radiation in nonlinear spectroscopy and quantum nonlinear optics.
3:00pm - 3:15pmOral
Medical Diagnostics with Functionalized Fluorescent Magnetic Nanobeads and Planar Micro-coils
1Graduate School of Information and Engineering, University of Electro-Communications, Japan; 2Electronics Inspired Interdisciplinary Research Institute, Toyohashi University of Technology, Japan
Functionalized superparamagnetic magnetic nanoparticles (MNPs) are important materials as ‘magnetic labels’ for biomolecular recognition protocols in medical diagnostics [1,2]. However, non-specific biomolecular interactions between MNPs and sensor surfaces induce noise that limits sensitivity and applications of diagnostics platforms. Furthermore, diagnostics methods currently used require sophisticated and expensive devices and equipment, which reduces their accessibility in regions without financial resources and medical care infrastructure. Here, were describe an innovative biosensing platform incorporating fluorescent MNPs, micro-coils and detection with CCD-based digital image processing.
In our approach, we designed micrometer current coils to exert precise three-dimensional magnetic forces on MNPs floating in a liquid over the sensing area of biosensing devices to enable ‘magnetic washing’ of non-specific, loosely attached MNPs. The detection process consists of imaging the precise location of functionalized fluorescent MNPs with a fluorescent microscope, and processing the digital image to determine the number of specific interactions of these ‘magnetic nanolabels’.
We demonstrated the effectiveness of this method using a streptavidin coated substrate surface and biotin coated nanobeads, which fluoresce red under UV excitation. The results yielded show a wide dynamic range of over four orders of magnitude with the minimum concentration of biomolecules detected being of a few nano-moles per liter.
This biosensing platform is rapid and sensitive. Quantitative detection of biomolecules does not require a reference light source and the micro-coils can be fabricated using conventional photolithography. CCD camera imaging ensures that the approach is not affected by magnetic noise due to fluctuations in the flow of electrical currents and opens up the possibility of integrating the biosensing platform with smartphones, thereby potentially improving healthcare for millions of people worldwide.
 A. Sandhu, H. Handa, and M. Abe, Nanotechnology, 21, 442001, (2010).
 A. Sandhu, Nature nanotechnology 2,746, (2007).