Day 3 :
- 09:00-10:30 Workshop on Electronic structure of Carbon Nanomaterials by Dr. Jan Smotlacha
- Track 1: The States of Matter
Track 2: Phase Phenomena and Electronic Phenomena Track 7: Organic Electronics Track 8: Properties of Cellular Networks and Mesoscale Systems in Biology
Chair
Xiaoming Wen
University of New South Wales, Australia
Co-Chair
Fengyuan Yang
The Ohio State University, USA
Session Introduction
Xiaoming Wen
University of New South Wales, Australia
Title: Density Dependent Carrier Dynamics in Organic-inorganic Metal Halide Perovskite
Time : 10:50-11:10
Biography:
Xiaoming Wen has completed his PhD in 2007 from Swinburne University of Technology, Australia. He performed postdoctoral studies at University of Melbourne in Australia and Academia Sinica in Taiwan. He is currently a research fellow in Australian Centre for Advanced Photovoltaics, University of New South Wales. He has published more than 80 papers in refereed journals. His research includes ultrafast time-resolved spectroscopy and photophysics of nanomaterials, particularly focuses on photoexcited carrier dynamics in nanomaterials (metal nanoclusters and carbon nanodots and advanced photovoltaics.
Abstract:
Mixed organic-inorganic halide perovskite has emerged as very attractive high efficiency solar cells over the past few years. Significant progress has been achieved such as the most recent demonstration of independently certified efficiency of 20.1%, attribute not only the device structure, and superb light absorption, decent ambipolar charge mobility and less excitons binding energy compare with organic solar cells. The device design and performance improvement critically depend on the physical understanding, in particular, the carrier dynamics at various timescale. Despite the rapid progress in demonstrated efficiencies perovskite solar cells, there exists a gap in the fundamental understanding of the carrier dynamics such as generation; transport; and extraction. Here we systematically investigate the carrier dynamics in organic-inorganic halide perovskite CH3NH3PbI3 in the various timescale using steady state and time-resolved spectroscopy. Our investigation reveals both steady state PL and time-resolved PL is closely relevant to the excitation intensity. The carrier dynamics can be determined by the processes of carrier relaxations, such as free carrier recombination, exciton recombination, defect/surface trapping, relaxation of the trapped carriers, Auger recombination, charge migration and phase transition. An evident state filling is observed using ultrafast transient absorption. At low excitation density, defect/surface trapping and electron-hole recombination are the major processes. Therefore, an excitation density relevant carrier dynamics can be observed in photoluminescence (PL) decay by using time correlated single photon counting (TCSPC). A nonlinear relation between the excitation and emission intensity is also identified in the steady state PL by , withβ>1. Theoretical modelling reveals that the nonlinearity is determined by both the relaxation rate and density of the defect states; and thus relevant to the fabrication. Moreover, the variation of the carrier density with time, due to carrier migration and phase transition, is closely related to the carrier dynamics. Interestingly, charge detrapping, charge migration and accumulation result in a much slow process in milliseconds to seconds. In contract, at high density of excitation the saturation of the defect states and enhanced Auger nonradiative recombination becomes the dominant mechanism. The decreased PL efficiency and fastened carrier dynamics were observed in steady state and TRPL, respectively. It is confirmed that carrier dynamics is also closely correlated with the fabrication and morphology of the films.
Yuko Ichiyanagi
Yokohama National University, Japan
Title: Functional magnetic nanoparticles following Néel relaxation system for hyperthermia treatment
Time : 11:10-11:30
Biography:
Yuko Ichiyanagi is an Associate Prof. at Yokohama National University since 2009 (Applied Physics). Since 2007 she was concurrently a researcher of Precursor Research Embryonic Science and Technology of Japan Science and Technology Agency, and developed magnetic nanoparticles for biomedical applications. She chaired at several international conference. She got a prize of Industrial Times at 9th Annual Meeting of Society of Nano Science and Technology in 2011. Now she has published more than 50 papers and books. In recent year she focused on the magnetic nanoparticles for biomedical applications and was successful.
Abstract:
Recently, magnetic nanoparticles (MNPs) have attracted attention as they have potential medical applications, such as in MRI contrast agents, drug delivery systems (DDS), and in hyperthermia treatments. Magnetic ferrite nanoparticles encapsulated in amorphous SiO2 were prepared using our original wet chemical method. In these magnetic nanoparticles, Si ions are located on the surface, and because of this characteristic structure particles were functionalized by amino-silane coupling procedure. We tried to introduce these functional particles into the living cells, and these particles were localized by the external magnetic field. Then cancer cell selective particles were further developed by attaching folic acid. In order to estimate heating effect of magnetic nanoparticles, AC magnetic susceptibility was measured. The imaginary part of the AC magnetic susceptibilities, χ”, depending on the frequency, field, and particle size were analyzed. The most efficient heat dissipation can be predicted for the MnO.8ZnO.2Fe2O4 sample of particle size 18 nm. It was found that this sample followed Néel relaxation system. Then the temperature of samples was measured upon AC magnetic field of 151 Oe, 15 kHz at 310 K. The rise in temperature was found high enough to destroy the cancer cells. In vitro experiment was carried out for the cultured cancer cells. An extensive hyperthermia effect was observed, and thereby concluding that this sample is an effective agent of hyperthermia treatment.
Ajay Kumar Mishra
University of South Africa, South Africa
Title: Recent advances in nanocomposites
Time : 11:30-11:50
Biography:
Prof. Ajay Kumar Mishra is currently working as Professor at Nanotechnology and Water Sustainability Unit, College of Science, Engineering and Technology, University of South Africa, Florida Science Campus, Johannesburg, South Africa. He is also working as “Adjunct Professor” at Jiangsu University, China. Prof. Mishra has pursued PhD in Chemistry from Department of Chemistry, University of Delhi, Delhi, India. In 2006, he moved to the University of Free State, South Africa for Postdoctoral studies in the area of composites/nanocomposites. Later in 2009 Prof. Mishra has joined Department of Applied Chemistry as Senior Lecturer where he was promoted to Associate Professor in 2011. Prof. Mishra is currently group leader of the research area for the composites/nanocomposites, water research and bio-inorganic chemistry. He has hosted several visiting researchers/scientists/postdocs in his group. Prof. Mishra has also developed a number of collaborations worldwide. His research contribution includes many publications in international journals. He has delivered a number of including Plenary/Keynote/Invited Lectures. For his outstanding research profile, he was awarded a number of awards. Prof. Mishra also served as Associate Editor as well as member of the editorial board of many international journals. He has edited several books by the renowned publishers. He has been reviewing a number of international journals and member of a number of scientific societies.
Abstract:
Presently clean and safe drinking water is a prior requirement of the society. Water pollution due to toxic metals and organic compounds remains a serious problem to the environment and public health. Heavy metal ions, and dyes are often found in the environment as a result of industrialization. They are known to be common contaminants in wastewater and many of them are highly toxic. Thus, there is a need to develop technologies that can remove toxic pollutants found in wastewaters. Several methods are available; including membrane technology, but adsorption is one of the more popular methods for the removal of pollutants from the wastewater. Biopolymers represent an interesting and attractive alternative as adsorbents because of their particular structure, physico-chemical characteristics, chemical stability, high reactivity and excellent selectivity towards aromatic compounds and metals. Adsorption on biopolymers and their derivatives are known to remove pollutants from water. The current focus of the talk will be the recent advancement in nanocomposites with the synthesis of adsorbents containing polysaccharides, in particular modified biopolymers and also the advantages of the removal of pollutants from the wastewater.
Agnieszka Wolos
University of Warsaw, Poland
Title: Three-dimensional topological insulators - a new phase of quantum matter; growth issues and the properties of bismuth chalcogenides
Time : 11:50-12:10
Biography:
Agnieszka Wolos has completed her PhD in 2005 from the University of Warsaw, Faculty of Physics. In 2005-2006 she was a Post-Doc at the Johannes Kepler Universität Linz, Institut für Halbleiter- und Festkörperphysik. She is now an Assistant Professor at the Institute of Physics Polish Academy of Sciences and at the University of Warsaw. She is interested in electron paramagnetic resonance, in particular in the application to studies of the electron transport phenomena. She currently works on topological insulators
Abstract:
It has been recently discovered that bismuth chalcogenides, previously recognized for its thermoelectric properties, hide a surprise in the band structure - topologically protected surface states. They are so-called three-dimensional topological insulators constituting a new state of quantum matter. They possess a band gap in the bulk and metallic surface states resulting from the change of the topological invariant at the interface with other material (could be the vacuum). The crystal structure of bismuth chalcogenides hosts considerable amounts of lattice defects, which results in highly conducting bulk covering the surface electric transport. In order to investigate properties of both the bulk and the surface states, Bi2Te3, Bi2Se3, and Bi2Te2Se were grown by the vertical Bridgman method at the Institute of Electronic Materials Technology, Warsaw. Undoped Bi2Te3 is p-type due to bismuth anti-sites while Bi2Se3 is n-type due to selenium vacancies. The structure of Bi2Te2Se prevents formation of both types of defects, resulting in the lowest conductivity of all the three materials. The conductivity of Bi2Se3 was reduced by varying the stoichiometry and applying calcium acceptor doping. The limits for the reduction of the bulk concentration will be discussed. Bulk and surface states were investigated using the contactless microwave spectroscopy (with the use of a standard electron paramagnetic resonance spectrometer). Properties of the bulk conduction electron spin resonance will be presented, while the presence of the surface states is manifested in the cyclotron resonance and weak anti-localization phenomena.
Hong-Chen Jiang
SLAC National Accelerator Laboratory and Stanford University, USA
Title: Quantum spin liquid, topological order and entanglement entropy
Time : 12:10-12:30
Biography:
Hong-Chen Jiang has completed his PhD from Tsinghua University in China, and Postdoctoral studies from Microsoft Research Station Q and Kavli Institute for Theoretical Physics in University of California at Santa Barbara. After that, he spent half a year in University of California at Berkeley. Now, he is a Staff Scientist of Stanford Institute for Materials and Energy Science of SLAC National Accelerator Laboratory and Stanford University.
Abstract:
Quantum spin liquids (QSLs) are elusive magnets without magnetism, resisting symmetry breaking even at zero temperature due to strong quantum fluctuations and geometric frustration. The simplest QSLs known theoretically are characterized by topological order, i.e., topological QSL, and support fractionalized excitations. However, there is no practical way to directly determine the topological nature of the states. In my talk, I will introduce a simple and practical approach, i.e., cylinder construction, to identify topological order by entanglement entropy. As an example, by extracting accurate topological entanglement entropy (TEE), we identify the quantum spin liquid ground states with topological order in the antiferromagnetic spin-1/2 Heisenberg model on the Kagome lattice. Finally, I will also try to talk about the finite-size corrections to TEE, and its relevance to QSLs, as well as future searches for topological ordered phases.
Mengyan Shen
University of Massachusetts Lowell, USA
Title: Synthesizing hydrocarbons from carbon dioxide and water with metal nanostructures and solar energy
Time : 12:30-12:50
Biography:
Mengyan Shen is an Associate Professor of Physics at University of Massachusetts Lowell. He obtained his PhD from University of Science and Technology of China in 1990, and his MS and BS from Inner Mongolia University in 1987 and 1984, respectively. He has published about 100 research papers. He has served as reviewers for different journals and foundations. In September 2006, he resigned his faculty position at Tohoku University and joined University of Massachusetts Lowell to further develop nano manufacturing techniques using intense femtosecond laser pulses together with students and fellow researchers. In addition to research work, he has experience teaching and leading experiments for undergraduate and graduate students in China, Japan and United States.
Abstract:
For many years, researchers had endeavored to replicate natural photosynthesis converting carbon dioxide and water to hydrocarbons and carbohydrates. In their approaches, the efficiency of solar energy storage was very low and there had been no significant progress towards large-scale and highly efficient artificial photosynthesis. Pulsed laser-assisted etching is a simple but effective method for making small regular structures directly onto a solid surface. We have successfully fabricated sub micro- or nano-meter sized structures on different solid surfaces immersed in liquids with femtosecond laser pulse irradiations. We can control the experimental conditions to design and make nanostructures in different materials and on the surfaces with different morphologies. We have combined the plasmonic and the catalytic properties of metal nanostructures to obtain an efficient artificial photosynthesis, converting carbon dioxide and water into hydrocarbons for solar energy storage. In our experiments, we have discovered a highly efficient artificial photosynthetic process that utilizes cobalt (Co) or iron (Fe) nanostructures formed by the femtosecond laser pulse irradiation. The details of this discovery will be introduced and discussed in the talk.