Undergraduate project opportunities

Supervisor: Dr Xiaoming Wen, Contact: xwen@swin.edu.au, 9214 8625

Organic-inorganic hybrid perovskites have attracted considerable research interest due to the enormous potential for highly efficient optoelectronic applications such as solar cells, light-emitting diodes (LEDs) and photodetectors. Mixed-halide perovskites are very promising materials for optoelectronics due to their tunable band gap in the entire visible region. A challenge remains, however, in the photoinduced phase segregation, narrowing the band gap of mixed-halide perovskites under illumination thus restricting applications. In this project, combining time-resolved photoluminescence (PL), fluorescence lifetime imaging microscopy (FLIM) and micro-PL spectroscopy and other optical techniques, you will investigate the light illumination induced phase segregation. This study will reveal the physical mechanism of phase segregation in mixed perovskites, providing the details of correlation between the conditions of illumination and sample fabrication with the phase segregation and recovery.

Further Reading
1. Illumination‐Induced Halide Segregation in Gradient Bandgap Mixed‐Halide Perovskite Nanoplatelets, Advanced Optical Materials, 1801107 (2018) (IF 7.43)
2. Dynamic study of the light soaking effect on perovskite solar cells by in-situ photoluminescence microscopy, Nano Energy 46, 356-364 (2018) (IF 15.548)
3. Tracking Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals under Two‐Photon Scanning Laser Illumination, Small Methods, 2019, 1900273

Supervisor: Dr Xiaoming Wen, Dr. Weijian Chen, Contact: xwen@swin.edu.au, 9214 8625

Time-resolved photoluminescence (PL) has been widely applied for investigating the photogenerated carrier dynamics, providing invaluable information of charge carrier recombination, photon-phonon scattering, carrier transfer and extraction; and intimately correlated with their applications of photovoltaics, photocatalysis, PED and lasing etc. photonics, therefore critically important for renewable energy and LED/display industries. Basically, time-resolved PL can be performed in the time domain and in the frequency domain. In this project, the carrier dynamics of hybrid perovskite will be investigated using both time domain and in the frequency domain techniques. Each will provide useful information for the physical understanding of photogenerated charge carriers in perovskites.

Further Reading:

  1. Zheng et al. Triggering the Passivation Effect of Potassium Doping in Mixed‐Cation Mixed‐Halide Perovskite by Light Illumination, Advanced Energy Materials, 1901016 (2019) (IF 24.884)
  2. Hole Transport Layer Free Inorganic CsPbIBr2Perovskite Solar Cell by Dual Source Thermal Evaporation, Advanced Energy Materials 6 (7), 1502202 (2017) (IF 24.884)
  3. Acoustic-optical phonon up-conversion and hot-phonon bottleneck in lead-halide perovskites, Nature communications 8, 14120 (2017) (IF 11.88)

Supervisor: Dr Xiaoming Wen, Prof. Baohua Jia, Contact: xwen@swin.edu.au, 9214 8625

Lead halide perovskites are widely applied in not only photovoltaics but also on-chip light sources and photon detection. Femtosecond (fs) laser fabrication is used to be demonstrated significant advantages of high spatial resolution, low surround damage and high processing efficiency. In this project, fs laser is used for directly fabricate 3-dimension high resolution, multiple color pattern in mixed-halide perovskite single crystal. The mechanism of the fs laser writing and controlling will be investigated for various perovskite material and their nanostructures. 

Further Reading:

  1. Spatially Modulating the Fluorescence Color of Mixed-Halide Perovskite Nanoplatelets through Direct Femtosecond Laser Writing, ACS Appl. Mater. Interfaces (2019) (IF8.456)
  2. Chemical dopant engineering in hole transport layers for efficient perovskite solar cells: insight into the interfacial recombination, ACS Nano 12 (2018), 10452 (IF903)

PhD project opportunities

The flexibility of printable circuits has had a major impact on established technologies, from solar cells to thin film transistors, and ushered in new developments, such as the use of radio frequency tags in contactless credit cards. But current printing methods are proving to be inefficient. Recent development in laser photo-reduction of graphene oxide materials in our group allows conversion of the insulating graphene oxide to conductive graphene material, thus one-step fabrication of electronic devices on thin film. The project will focus on the fabrication of high performance functional circuits, such as Radio-frequency identification (RFID) chips, on thin film graphene oxide material using laser photo-reduction of graphene oxide technique. The project will include both the design and the fabrication of the circuit.

Energy storage is the key component for creating sustainable energy systems. Electronic devices, which have become ubiquitous in modern society, are also heavily reliant on energy storage technologies. Currently, the dominating energy storage device remains the battery, which charge and discharge extremely slow, have limited lifetime and are harmful to environment. In comparison, supercapacitors can charge/discharge millions of cycles with high speed and without losing energy storage capability. This project will focus on the design and fabrication of novel energy storage system based on the graphene oxide supercapacitors for target applications.

Smart materials are the materials that can significantly change their mechanical, thermal, optical, or electromagnetic properties, in a predictable or controllable manner in response to their environment. One way to achieve smart micro/nano material is through structure design. This project will focus the design of micro/nanostructures which show outstanding optical, electrical or mechanical properties that can be controlled by the environment such as light illumination, sound wave or thermal process. The design structures will be fabricated by using the 3D laser printing system.

Three-dimensional fabrication techniques, especially the additive manufacturing or 3D printing have revolutionized the entire field of manufacturing. By using a focusing laser beam it is possible to fabricate 3D structures at micro/nanoscale, which have found broad applications in medical, biology, electronics and photonics. This project will focus on the development of 3D micro/nanofabrication platform based on the laser writing technique. It is aimed to develop a fully automatic platform with the capability of sample preparation and fast fabrication by implement the dynamic laser printing technique.

Graphene material has found broad applications in biology. By using simultaneously laser photo cross-linking and photo-reduction of the graphene oxide material, it is possible to directly print 3D network with graphene material. The project will focus on the development of techniques to 3D printing complex networks made of graphene materials by using focused laser beam and find the application in biology especially the use as the backbones to guide the cell growth.

Metamaterials process the properties that do not exist in natural materials, which have found broad applications in photonics, mechanics and communications. In the meantime, graphene has exceptional optical, mechanical and electrical properties. The project will focus on the development of novel metameterials made of graphene based on its unique properties. Further, the designed structures will be fabricated by the fast and low cost laser nanofabrication techniques, which will find broad applications.

Heterostructures of layered 2D materials have shown outstanding optical, electrical and mechanical properties. However, the 2D heterostructures can only be fabricated by the slow, expensive epitaxial deposition methods. This project aims to develop a new fabrication method based on the inexpensive chemical synthesis techniques and laser nanofabrication method to large scale produce 2D heterostructures with outstanding properties.

Currently, no techniques are able to directly 3D printing of precious metals, including silver, gold and platinum. The project aim to develop a technique that is able directly print the precious metal in the solution based on the photo-chemical process. In this way, it is possible to low-cost and large-scale 3D printing of precious metals, which will find broad applications in optics, electronics and mechanics.

Ion transportation process holds the key to decide the performance of supercapacitors. Although supercapacitors based on graphene and graphene oxide materials have shown superior performance, the ion transportation process inside of the porous layered graphene electrodes hasn’t been shown. The project will study the ion transportation process in the supercapacitors with porous graphene electrode in the charge/discharge process. Different types of ions will be studied, and the best pore size for each type of ions will be understood and predicted. In this way, the performance of graphene supercapacitors can be further improved.

Rechargeable aluminium-based batteries offer the possibilities of low cost and low flammability, together with three-electron-redox properties leading to high capacity. It has been shown recently the performance of the aluminium batteries can be significantly improved, especially the speed of charge and discharge, by using graphitic-foam cathode with pore size of hundreds of microns. It is expected the performance can be further improved by controlling the pore size down to nanometre scale. This project will focus on the design and fabrication of graphene electrodes with nanometre size pores and the applications in aluminium battery. Considering the layered structure of graphene electrodes, the best design should be interdigital design which is challenging to be fabricated for batteries and never demonstrated before as the materials of two electrodes are different. This project will also develop novel fabrication technique for interdigital batteries.

Capacitance can be increased by a phenomenon called lateral fringing. The increase is proportional to the length of the boundary of the conductor. Because fractal curves can enclose a modest area with a very long boundary, these designs can give substantial capacitance increases, for instance, a factor of 6 over Euclidean designs. The aims of the project including: 1) design novel graphene electrodes with fractal properties that is able to maximize the area of the electrodes in order to provide an exponential increase in capacitance of supercapacitors. 2) Fabrication of fractal graphene structures in 2D and 3D, in order to experimentally demonstrate the effects of the parameter of the fractal structure of the performance of the graphene supercapacitors.

The optical elements based on the graphene materials have the advantages of ultra-high performance, ultra-thin and ultra-light-weight, and can be easily integrated with any devices. A major application of microfluidics is biological automation, as this involves scaling fluid manipulations from millilitres and microlitres to the nanolitre scale. The project will integrate the graphene optical elements, such as lens, gratings, with microfluidic chips create a lab-on-a-chip device. The uniqueness of the device will be 1) to faster analyse and better control a biological process; 2) Compact system; 3) massive parallelization, high-throughput analysis; 4) lower fabrication costs; 5) safer platform for chemical, radioactive or biological studies.

We recently achieved the design and fabrication of graphene oxide (GO) ultrathin flat lens based on the mechanism of photo-reduction of GO material. The GO lens is ultrathin, ultra-lightweight, high performance and able to integrate with photo-electronic devices. This project will explore the application of the GO lens in the virtue reality (VR) devices, especially the VR headset and camera. Currently, the lenses in the headset is bulky and heavy, therefore, it is expected that by replacing the current lenses with GO ultrathin flat lenses the headset will be more comfortable and able to provide outstanding visual experience due to the light weight properties and the high performance. The challenge lies in the design and fabrication the GO lens suitable for VR headset, which will be targeted in this project. On the other hand, the resolution of current VR camera is limited by the large size of the microlenses which is on each pixel of the CMOS or CCD to improve to the light collection efficiency of the camera. As a solution, the GO lenses can be made ultra-small size down to a few microns with high focusing efficiency which is able to significantly increase the resolution and signal to noise ratio of the camera. The project will also study the design, fabrication of the GO lens which can be integrated with CMOS and CCD, and characterize the performance of the final devices.

Recent development of micro-endoscope is able to look inside human body and do surgery with minimal wound, which significantly reduce the risk of bleeding, the incision size and the exposure of the internal organs. In this way, the surgery become much safer and the patient is able to heal much faster. However, current endoscope is still too big to be directly insert into human’s artery due to the bulky lens. As the graphene oxide (GO) ultrathin flat lens can be designed and fabricated in an ultra-small size, comparable to a core of an optical fibre, without compromising the performance. In addition, by using the self-assembly film synthesis technique, the GO film can be attached any surface with ease. In this way, it is possible to integrate the high performance GO lens with the optical fibre, which allows the fabrication of endoscope as thin as an optical fibre. As a result, such an ultracompact micro-endoscope can be directly inserted into human artery to study the spectral information of blood and monitor or detect diseases even at early stage. This project will explore the design and fabrication optical micro-endoscope with GO lens, and the application in acquire spectral information in microfluidic devices that simulate human blood vessels. In addition, a proof-of-principle prototype will be developed.

Graphene oxide (GO) filters have demonstrated superior properties, such as ultrahigh flow rate and high precision molecular sieving, in water filtration. However, the mechanism of the filtration process inside the GO filters is unrevealed. The mechanism of the graphene filters have been studied by using the molecular dynamic simulation. Compared to the case of graphene, the case of the GO filter is much more complex and challenge, due to the following points: 1) different from the water going through the graphene filter with a flow perpendicular to the surface of the filter, the water flows parallel to the GO filter between GO layers. Therefore, it is necessary to consider multilayer structure of GO filter while only graphene layer is considered as a filter. In addition, the friction between the GO layer and water molecules have to be taken into account, which create a gradient flow rate. 2) two factors decide the performance of GO filters, namely pore size and layer spacing, in comparison only one mechanism, the pore size, decides the results of graphene filter. 3) the variety of oxygen functional groups which control the hydrophilicity of the GO filter and the interaction between the GO filter and the ions due to surface charge properties, which don’t exist in the graphene filter. This project will build molecular dynamic simulation models by taking those factors into account in order to completely understand the filtration mechanisms of GO filters and the effects of each parameters, including the pore size and layer spacing, the type and coverage of oxygen functional groups and the pressure and flow rate inside the GO filter.

As the energy density of supercapacitors (SC) is linearly proportional to the square of voltage window of the SCs, it is essential to enlarge the voltage window. However, it is the most challenge work in the development of SCs. Current voltage window is limited by the breakdown voltage of the electrolyte, which can only be up to 3.5 V when ionic liquid is used. As the electrolyte is stored in the porous electrodes and the break down is due to the high electric field inside the electrode, it is necessary to study the effect of the geometrical design of the electrodes on electric field distribution and design the electrodes with uniform field distribution to minimise high field strength points. The designed electrodes will be fabricated by the flexible laser photo-reduction technique. In this way, it is expected enlarge the working voltage of the SCs and eventually boost the energy density. Further, the asymmetric configuration can extend the operating voltage window of electrolytes beyond the breakdown limit of the electrolyte, leading to significantly higher working voltage. The asymmetric electrodes can be achieved by doping one electrode with other materials. The effects of different doping material and the doping methods will also studied in this project.

 

The two-dimensional structure and tunable physicochemical properties of graphene oxide (GO) offer an exciting opportunity to make a fundamentally new class of sieving membranes by stacking GO nanosheets. The filtration performance is mainly controlled by the layer spacing of the GO filters as the ions and molecules permeate through the interconnected nanochannels formed between GO nanosheets. Therefore, it is of great importance to control the interlayer spacing of the GO nanosheets. The interlayer spacing between 0.3~0.8 nm can be comfortably controlled by the reduction extend of the GO filter. In comparison, the larger size range is more challenging as spacers to be inserted between GO sheets is necessary. The applications in water purification, wastewater reuse, and pharmaceutical and fuel separation require layer spacing between 1 nm and 2 nm, while biomedical applications (e.g., artificial kidneys and dialysis) that require precise separation of large biomolecules and small waste molecules need layer spacing larger than 2 nm. This project will explore the optimal spacer for different requirements of different applications, as well as the synthesis of GO filters with spacers and the applications.  

Broadband strong light absorption of unpolarized light over a wide range of angles in a large-area device is critical for applications such as photovoltaics, photodetectors, thermal emitters and optical modulators. Despite long-standing efforts in design and fabrication, however, it has been challenging to achieve all these desired properties simultaneously.

In this project, combining numerical simulations, nanofabrication and characterization techniques, we will study the light-matter interactions at nanoscale. This study will investigate the physical mechanism of photon-phonon-electron interactions at nanoscale, providing the details of photothermal manipulation by dielectric/plasmonic nanostructures. Also, we will study the photothermal performance of these developed nanostructures and directly integrate them into many practical applications, such as solar thermal harvesting, photodetection, and sensing.  

Further Reading:

  1. Han Lin, Björn C. P. Sturmberg, Keng-Te Lin, Yunyi Yang, Xiaorui Zheng, Teck K. Chong, C. Martijn de Sterke, and Baohua Jia “A 90-nm-thick graphene metamaterial for strong, extremely broadband absorption of unpolarized light” Nature Photonics 2019, 3, 270−276. [SCI Q1, IF:583]
  2. Keng-Te Lin, Hsuen-Li Chen, Yu-Sheng Lai, Chen-Chieh Yu, Yang-Chun Lee, Pao-Yun Su, Yu-Ting Yen, and Bo-Yi Chen “Loading effect–induced broadband perfect absorber based on single-layer structured metal film” Nano Energy 2017, 37, 61–73. [SCI Q1, IF:548]