SRFDP&RGC ERG Joint Research Scheme - Layman Summaries of Projects Funded in 2012/13 Exercise

Surface Plasmon Enhancement of Quantum Dot Based Intermediate Band Solar Cells

Hong Kong Principal Investigator: Prof Andrey Rogach (City University of Hong Kong)
Mainland Principal Investigator: Prof Zhiming Wang (University of Electronic Science and Technology of China (UESTC)

This project aims to study the surface plasmon enhanced quantum dot based intermediate band solar cell concept. Nanometer-sized semiconductor crystals, or quantum dots, will be grown as the sunlight absorber materials. The discrete energy levels in quantum dots form an energy band which potentially can be used as a middle band assisting absorption of photons at different wavelength and thus lead to solar cell efficiency over 60%. An intermediate band solar cell can be equivalently considered as one solar cell absorbing high energy photons in parallel with two solar cells in series absorbing low energy photons. Due to low absorption volume and cross-section of quantum dots, it is challenging to obtain practical quantum dot based intermediate band solar cells.

A promising solution to enhance the sunlight absorption in quantum dots is the use of a strong near-field generated by metallic nanoparticles. Such a strong near-field can amplify the sunlight absorption in quantum dots to a few orders in magnitude. Besides engineering and design of optimized semiconductor and metallic nanomaterials and solar cell devices, the main research challenge is to integrate epitaxial semiconductor nanocrystals and colloidal metallic nanoparticles, which are belonging to different material systems and prepared by very different methods.

Based on the expertise of the principle investigators from participating research groups, strategies will be developed for integrating metallic nanoparticles with quantum dot solar cells. The success in surface plasmon enhanced quantum dot solar cells may open opportunities for full utilization of solar energy spectrum.

Fiber-shaped Photovoltaic Cells

Hong Kong Principal Investigator: Prof Furong Zhu (Hong Kong Baptist University)
Mainland Principal Investigator: Prof Dechun Zou (Peking University)

There has been a great deal of activity in the development of fibrous photovoltaic cells. Development of new organic photoactive materials with tailored energy levels, virtue of optimization of materials processing parameters and new fabrication methodologies are the main challenges. In this work, modified fine metal wires and fibers will be used for application in fibrous photovoltaic cells. Solution-processable functional materials incorporating semiconducting nanoparticles for absorption enhancement in fiber-shaped photovoltaic cells will be studied. Optical modelling will be utilized to study the light trapping and its effect on power conversion efficiency of fiber-shaped photovoltaic cells. Primary emphasis of the project will focus on cell design, device physics, interfacial engineering, and process integration and performance optimization of fibrous photovoltaic cells.

A Gold Nanoplate-Based Plasmonic Platform for Sensing and Photoswitching Applications

Hong Kong Principal Investigator: Prof Jianfang Wang (The Chinese University of Hong Kong)
Mainland Principal Investigator: Prof Chun-Hua Yan (Peking University)

The aim of this proposal is to develop a new gold nanoplate-based plasmonic platform for sensing and photoswitching applications.

Noble metal nanocrystals can support localized surface plasmon resonances, giving rich and attractive light absorption and scattering properties. The interactions between localized plasmon resonances, that is, plasmon coupling, which can bring about improved plasmonic properties, such as larger electric field enhancements, magnetic plasmon modes, controllable light polarization and propagation, are strongly dependent on the geometrical configurations of the oligomers of metal nanocrystals. Therefore, the oligomers made of plasmonic metal nanocrystals present great potential for the fabrication of optical devices and the development of high-performance sensing methods for biotechnology, chemistry, food safety, and environmental monitoring. However, the full realization of this potential has encountered difficulties. Chemically grown colloidal metal nanocrystals are generally much better than lithographically fabricated ones in terms of their plasmonic properties and surface chemistry because the former are usually single-crystalline with smooth surfaces while the latter are polycrystalline with rough surfaces and contain plasmon-damping metals. Commonly encountered difficulties for colloidal metal nanocrystals include inability to assemble them reproducibly in a uniform geometry, easy aggregation, poor uniformity and controllability in their large-area deposition on substrates, inability to bond functional molecules to the desired positions on metal nanocrystals, and lack of full understanding of the plasmon coupling behaviors among irregularly shaped metal nanocrystals.

Here we propose to develop a Au nanoplate-based plasmonic platform to address the aforementioned difficulties. Single-crystalline Au nanoplates with large smooth surfaces will be prepared chemically. Due to the plate geometry, Au nanoplates are easy to be deposited on substrates over large areas and can be readily purified. The atomically flat surfaces of Au nanoplates allow for easy molecular functionalization, which will be beneficial for sensing and photoswitching applications. We will study the configuration-dependent plasmon coupling between Au nanoplates and Au nanospheres (or nanorods). On the basis of the achieved understanding, we will demonstrate biological sensing and fabricate photoswitching devices by including photoswitchable molecules. The success of this project will lead to cost-effective and large-area deposition of plasmonic metal nanostructures and the development of robust and ultrasensitive sensing devices. Moreover, photoswitchable materials feature reversible changes in properties such as absorption, emission, scattering, chemical reactivity, and interface tension. The integration of strongly light-responsive plasmonic metal nanostructures with photoswitchable entities can largely enhance the photoresponses, which will find applications in fields including display, optical data storage, non-contact manipulation, and anti-counterfeit marking.

Enhancement of polarizabilities of small particles through particle-substrate resonances

Hong Kong Principal Investigator : Prof Che Ting Chan (Hong Kong University of Science and Technology)
Mainland Principal Investigator : Prof Hui Liu (Nanjing University)

As light sources such as lasers are easily available and quite affordable, it would be highly desirable if light could be used as an effective tool to detect and to manipulate very small particles. However, if an object is very small in size compared with the wavelength of light, it does not scatter light efficiently. The interaction of light with a small particle is usually very weak. It is hence difficult to detect a very small particle with light and it is not practical to manipulate a sub-wavelength particle with light. In technical terms, we say that coupling of light with a particle is characterized by a quantity called the "polarizability" of the particle and the polarizability of a small particle is small. It would be highly desirable if we can increase the polarizability of a small object. What we intend to accomplish in this project is to find ways to boost the polarizability of a small particle by coupling it with a substrate. The enhancement due to the proximity effect can be explained qualitatively as follows. The interaction of a small particle with light is weak because there are not enough atoms/molecules in the small particle to interact with the external light source. If we put the particle near a substrate and we tune system parameters such that the particle and the substrate are coupled through a particle-substrate resonance, the atoms/molecules in the substrate will be excited together with those in the particle by the external source. The particle hence becomes effectively larger in size, leading to an enhancement in polarizability. This in turn means that the particle can respond more strongly to the external light field, possibly allowing us to use light to detect and manipulate a small object more effectively.

Crowdsourcing via Social Medical Media Platforms

Hong Kong Principal Investigator: Prof Lei Chen (Hong Kong University of Science and Technology)
Mainland Principal Investigator: Prof Yunhao Liu (Tsinghua University)

The Concept of the wisdom of crowds is attracting tremendous interests from both academic and industrial communities. Crowds perform better at a variety of human-intrinsic tasks, like text interpretation, speech recognition, etc. than sophisticated computer systems. The cost of hiring a group of common online users is also much lower than that of hiring individual human experts. The rapid development of Internet technologies and Web2.0 applications facilitates this computational paradigm which is known as "crowdsourcing", "human computation" and "social computing" depending on your perspective. Generally, crowdsourcing applications connect two group of people, "requesters" who publish problems to be solved and "workers" who participate in the tasks for different reasons. In most cases, the "workers" get to choose which tasks to get involved in, and the solutions they offer are aggregated and validated.

However, current general micro-task marketplaces, such as Amazon Mechanical Turk, Crowd Flower, Odesk, etc., suffer from three major drawbacks: 1) "wisdom"(solutions offered by workers) is harvested from a relatively small portion of a crowd which inevitably leads to biased results; 2) payments to workers are weakly associated with the quality of their work due to the nature of these marketplaces: and 3) requesters do not get to choose the workers.

In this project, we will design a framework for making use of social media platforms for crowdsourcing. Social media platforms have the following advantages over general micro-task platform: 1) the demographics of users of social media are much broader, and of course, there is a larger population of them: 2) it is easier and more practical to identify user profiles from social media in order to evaluate their abilities: and 3) requesters can easily identify/hire desired workers using built-in functions like "@" in most social media such as Twitter and Facebook. As part of this framework, we will design solutions for 1) automatic profiling of social media users; 2) aggregating crowd intelligence: and 3) controlling the quality of aggregated crowdsourcing results.

This project will make important technical contributions to a broad range of research areas, including but not limited to the mining of social media data, the assignment of tasks in an optimal (in terms of monetary cost and time delay) manner, and the quality control of collected intelligence. The key deliverables of this project will include top conference and journal publications, and a prototype system for demonstrating the research output with example applications.

Hierarchical Radio Resource Management for 5G Heterogeneous Networks

Hong Kong Principal Investigator: Prof Vincent Lau (Hong Kong University of Science and Technology)
Mainland Principal Investigator: Prof Mugen Peng (Beijing University of Posts & Telecommunication)

Future 5G wireless networks have to achieve challenging goals of 1000X capacity increase and 1000X improvement in energy efficiency by 2020. To support such aggressive goals, breakthroughs in network architecture is needed. The heterogeneous network (HetNet) is a new paradigm in wireless network architecture and it is receiving intense interests from both the academia and the industry. While the HetNet architecture has a lot of advantages, such an overlaid structure may lead to a severe interference problem. Hence, it is extremely critical to control interference via advanced Radio Resource Management (RRM) algorithms to fully unleash the potential gains from HetNet. In this project, we shall tackle the challenges by proposing a hierarchical RRM design for HetNet. We shall model the RRM design as a large-scale stochastic optimization problem, which embraces both information theory (characterizing the dynamics of the physical layer) and queueing theory (characterizing the network delay dynamics). Instead of targeting for a brute-force solution, we shall utilize time-scale separation to derive low complexity and scalable solutions with potential applications for LTE+ systems.

Development of New Environmentally Friendly Green Catalytic Processes for Chiral Drug Discovery

HK Principal Investigator: Prof Jianwei Sun (Hong Kong University of Science and Technology)
French Principal Investigator: Prof Jing Zhao (Nanjing University)

Despite the significant improvements in medical treatments in the past decades, there remain many incurable diseases that affect human health all over the world. The development of new drugs provides new solutions to help fight these diseases. Chiral drugs, whose stereoisomers have different biological activities, account for over two thirds of all the drugs that are currently being developed. Thus, the efficient and cost-effective synthesis of chiral drugs is an important area of current drug development.

Asymmetric catalysis represents one of the most efficient strategies to install chiral centers that are present in most drug molecules. Although the use of metal-based chiral catalysts has been the focus of asymmetric synthesis in the past, the development of asymmetric catalytic processes without the involvement of metal catalysts is becoming more and more important owing to their environmentally friendly nature and the avoidance of additional metal residual removal processes that are sometimes tedious during pharmaceutical manufacturing.

In this proposed project, we aim to develop several such organocatalytic asymmetric processes based on oxetane desymmetrization. These catalytic processes are environmentally benign. We will also apply these processes to the synthesis of a range of potential drug candidates containing important structure units such as 1,2,3,4-tetrahydroisoquinoline, and further evaluate their biological activities (e.g. anticancer activity). This research project combines expertise in organocatalytic process development and chemical biology. We believe that the successful execution of the proposed project will benefit many aspects of our society, such as drug development, environmental protection, materials science, the agrochemical industry, etc.

Chemical Speciation and Source Identification of Water-soluble Organic Aerosols in Urban Environments for a Mechanistic Understanding of Haze Pollution

HK Principal Investigator: Prof Jianzhen Yu (Hong Kong University of Science and Technology)
French Principal Investigator: Prof Guangli Xiu (East China University of Science & Technology)

Haze pollution, characterized by high ozone and particulate matter (PM), is becoming increasingly serious in Hong Kong and many urban areas in China. The primary cause for poor visibility is the small particles suspended in the atmosphere, also called PM2.5. The water-soluble components in PM2.5 include inorganic ions and water-soluble organic carbon (WSOC) species. They play an active role in haze pollution through their interactions with water vapor, which is abundant in the ambient atmosphere. We have a reasonable understanding of the contribution of inorganic ions to visibility degradation, but we know little about the link between WSOC and visibility. WSOC could either suppress or enhance water uptake by inorganics in atmospheric PM, presumably depending on the chemical make-up of the WSOC fraction. In this project, we propose to separate WSOC aerosols into hydrophilic and hydrophobic fractions as the two fractions are anticipated to have different affinities for water. We will quantify these two WSOC fractions and inorganic ions, as well as elemental and organic carbon and select aerosol source markers in PM2.5 samples and in samples of different particle sizes. Aerosol samples will be collected in Hong Kong and Shanghai over a period of a year. The detailed PM2.5 chemical data will be used to identify pollution sources through advanced receptor modeling analysis. We will establish empirical relationships between light extinction and water-soluble inorganics, two fractions of WSOC and other aerosol constituents through multi-linear regressions. The proposed study will generate data useful to understand the haze pollution problems in Hong Kong and Shanghai and bring us closer to quantifying the contributions of water-soluble organic aerosols to haze pollution.

The two collaborating teams have more than ten years of experience in studying air pollution issues. The two teams will collaborate on method development in chemical analysis and data interpretation. As atmospheric conditions such as humidity, temperature, and other pollutant levels are important factors in haze pollution, contrasts and commonalities communalities between Hong Kong and Shanghai provide another dimension of information in gaining an improved mechanistic understanding of haze pollution.

Phosphorescent Metal Complexes for Solar Energy Conversion Reactions

HK Principal Investigator: Prof Chi Ming Che (The University of Hong Kong)
French Principal Investigator: Prof Zhong Min Su (Northeast Normal University)

The realization of highly robust, photochemically active molecular materials/catalysts capable of capturing solar energy for converting naturally abundant materials into useful feed stocks with practical interests is a step forward to use sunlight as a source of clean renewable energy. To achieve this goal, we have to develop new chemistry whereby solar energy can be efficiently and practically used for chemical synthesis with high efficiency. Specifically, we target to develop highly robust and reusable metal-based photo-catalysts. By ultrafast laser spectroscopy and high level theoretical calculations, we probe the nature of the electronic excited states and its reaction dynamics. With the combined efforts of a complementary team with expertise composed of synthetic chemistry (led by Che of HKU), ultrafast laser spectroscopy (led by Phillips of HKU) and computation chemistry (led by Su of NENU), we anticipate to discover new knowledge on the photo-physics of transition metal complexes. The knowledge thus obtained is instrumental to the design of new molecular catalysts. Complexes of inexpensive 1st row transition metals will be developed as new photo-catalysts. We also target to develop new practical photo-catalysis which can be used for the synthesis of organic compounds without the use of hazardous reagents and/or reaction conditions. This MOE-RGC project can strengthen the inter-institutional collaborations between Hong Kong and Mainland China. Young scientists with skills and knowledge in Synthetic Chemistry, Photochemistry and Computational Chemistry will be trained. These young scientists will develop research in the frontier interdisciplinary areas of Solar Energy Conversion Reactions. An ultimate goal is to make contributions that render Hong Kong and Mainland as world centers of Excellence in the area of Transition Metal Photo-physics and Photochemistry in the forthcoming decades.

Achieving high-efficiency polymer solar cells through newly solution-processed polymers, carrier transport layer materials and novel device structures

HK Principal Investigator: Dr. Wallace Chik Ho Choy (The University of Hong Kong)
Mainland Principal Investigator: Prof Fei Huang (South China University of Technology)

Polymer solar cells (PSCs) have been considered as one of the potentially practical photovoltaic candidates. The efficiency of tandem PSCs has remarkably increased to over 10% and PSC lifetime has reached 7-10 years recently. However, due to the low carrier mobilities and short exciton diffusion length of organic materials, PSCs typically have thin active layer which limits light absorption. Meanwhile, it is desirable that the open-circuit voltage and short-circuit current of PSCs can be further increased. After the generation of electrons and holes in active layer, it is important to efficiently transfer carriers to electrodes. Metal oxides have been considered as the potential candidates for functioning as effective carrier transport layers. The prospects of metal oxides for low-cost and scalable PSCs are laid on low-temperature, simple and solution-based process. We will investigate a general method with the process features for forming carrier transport layers is attractive for their practical applications.

Meanwhile, PSCs are thin film solar cells due to low mobilities and short diffusion length of excitons. Light trapping schemes of localized and surface plasmonic resonances (PRs) using metal nanoparticles and large area metal nanostructures respectively have been introduced into different regions of PSCs such as buffer layers, active layer and interface layers. We will investigate new PR structures in PSCs to realize polarization independent and wide band absorption enhancement.

Strained topological insulator thin films

HK Principal Investigator: Prof Mao Hai Xie (The University of Hong Kong)
Mainland Principal Investigator: Prof Jinfeng Jia (Shanghai Jiao Tong University)

Topological insulators (TIs) refer to a family of materials that are insulators in the bulk but metallic on surface. It has drawn extensive research attention recently due to the unique and potentially useful properties. Most of the known three-dimensional TIs are layered crystals bonded by the weak van der Waals (vdW) forces along a particular direction of the crystal (i.e., the c-axis). Because of such weak vdW bonds, growth of such crystals on foreign substrates gives rise to films that are strain-free, the same as a free-standing crystal. On the other hand, it is known that when a crystal is deformed by the lattice of the substrate, thereby creating a strained film, the properties of the latter can be greatly modified. How strain will affect the properties of the TIs remains an under explored subject today. This is partly because of the difficulty to obtain strained TI films experimentally where its growth has been exclusively along the c-axis and so the vdW gaps readily relieve the lattice misfit strain. Here in this research, we set out to grow strained TI layers by molecular-beam epitaxy (MBE) and investigate their electronic properties, aiming at revealing some of the strain effects in the TIs. To overcome the difficulty of strain relaxation at vdW gaps, we plan to grow Bi2Se3 or other TI films along directions other than the c-axis on non-hexagonal substrates. For such films, the vdW planes are inclined to the interface, so they may be adjusted by the lattices of the substrates. Then by adopting different substrates, the TI films with varying strains may be obtained.