It’s been a busy year for the Australian National Fabrication Facility’s Victorian Node (ANFF-VIC). The open-access network of nano- and micro-fabrication capabilities has seen the appointment of a new Director, a new General Manager, and the addition of some exciting new tools across the state. The node has also continued to enable research, with highlights including diamond coating of carbon fibre, creating nanometre-thick holograms, and increasing the efficiency of photovoltaic cells.
The Victorian Node is one of eight nodes in the national ANFF network. ANFF-VIC has tools and experts available for training or advice at the CSIRO, Deakin University, La Trobe University, the Melbourne Centre for Nanofabrication (MCN), Monash University, RMIT, Swinburne University of Technology, and the University of Melbourne. Both ANFF-VIC and ANFF national are headquartered at MCN, home to one of the largest open-access cleanrooms in the world.
In February, Professor Nicolas Voelcker was appointed as Director of ANFF-VIC and Scientific Director of the MCN. With more than 300 peer-reviewed articles and book chapters to his name, he is a leader in his field of biomaterials engineering. Professor Voelcker’s aim is to increase the interaction between academics and industry drivers within the region, given Victoria’s pedigree for research in this area. With MCN located within a stone’s throw of Monash University, the Australian Synchrotron and the array of tech businesses spread across the Clayton area, it’s ideally positioned to act as a melting pot for commercialisation of ground-breaking technologies.
ANFF-VIC and MCN also have a new General Manager, Dr Sean Langelier, who had been a senior process engineer at MCN for a number of years. In addition to the general handling of the Centre’s activities, Dr Langelier’s role is to help Professor Voelcker to drive industry engagement.
ANFF-VIC has been adding to its facilities’ collection of capabilities. Notably, MCN recently became the first owner of SwissLitho’s NanoFrazor in Australia. The system uses Thermal Scanning Probe Lithography to produce micro- or nano-scale structures and patterns with nanometre accuracy. The process involves heating a scanning probe to around 1,000 degrees Celsius to rapidly evaporate a specialised polymer material. By varying the force applied by the scanning the probe as it writes, intricate 3D structures can be created.
This allows for the fabrication of optical devices, such as aspherical microlenses and tapered waveguides, which can be harnessed for a host of potential end applications including plasmonics, nanoelectronics, biochemical patterning and storage devices.
La Trobe’s Centre for Materials and Surface Science (CMSS) is also part of the ANFF-VIC Node and has recently installed a new sample mounting system for its XPS and ToF-SIMS surface analysis instruments. The new system allows for far more efficient and flexible analyses, batched submission of samples, and transfer of samples between XPS and ToF-SIMS without remounting.
Tools like these, combined with experienced staff, continue to allow ANFF-VIC users to conduct their ground-breaking research in a state-of-the-art collaborative environment. Here’s a collection of a few of the recent highlights.
Diamond coating carbon fibre
Carbon fibre is now wearing some flashy new jewellery, thanks to a team of Victorian scientists. They’ve coated carbon fibre with diamond, enhancing the material’s usability in medical and sensor applications where the composite material offers huge potential advantages.
Microelectrodes are important in bioelectronic medicine for the treatment of a variety of debilitating conditions. They can often eliminate the need for drugs and spare patients unwanted side effects. Treatable conditions include epilepsy, auto-immune and Parkinson’s disease and migraines.
Unfortunately, the materials currently used for fabrication of microelectrodes, often noble metals or silicon, have a much higher density than human tissue and are thought to produce scarring which reduces their long-term efficiency.
A team of researchers from CSIRO Manufacturing, Deakin University, Melbourne University and the MCN, hope to solve this problem by combining two exceptional materials – carbon fibre and diamond – that, used together, may possess the desired properties.
Carbon fibre has been exciting medical circles due to its small diameter (less than 10 microns) and ability to act as a light-weight, conductive filament. However, in practice it typically has to be insulated in bulky glass capillaries in order to be useful.
The team began attempting to coat the fibres with microcrystalline diamond to form a thin, insulating and biocompatible sheath.
The difficulty is that growing diamond requires harsh conditions that can easily damage the carbon fibres. Through careful tuning of the diamond seeding – an early-stage process in which nanodiamond “seeds” are ultrasonically embedded in the fibre surface – and deposition conditions while working with MCN, the team has managed to achieve uniform diamond coatings that leave the carbon fibre intact.
“This has been an extremely rewarding project and these new micro-electrodes have real potential to improve neuroscience research and people’s lives with debilitating neurological conditions,” says Dr Kallista Sears, who led the team.
The next step is to further optimise the process and benchmark the diamond-coated carbon fibres for their performance as microelectrodes.
“This will require further involvement with ANFF-VIC staff and use of their world-class diamond coating facilities,” adds Dr Julius Orwa, a Deakin University researcher on the project.
Creating back-contacted solar cells
Solar cells are one of the most promising and accessible mechanisms by which Australia can reduce its carbon footprint. However, inefficiencies remain a barrier to widespread usage. By combining the benefits of back-contacted solar cells with perovskite materials, researchers have achieved a much sought-after pathway to more efficient photovoltaic devices.
Solar cells work by using a photovoltaic material to produce an electric current between an anode and cathode when illuminated by the sun. The way a cell is structured and the materials it’s built from have a dramatic effect on its ultimate performance.
Currently two leading methods are back-contacted silicon cells and perovskite-based devices. While each have their own efficiency advantages, but also limitations. Perovskite is a material that is incredibly good at taking in light and converting it to electrical energy. However, perovskite solar cells (PSCs) are currently built using a “sandwich structure”, which requires a conductive and opaque electrode above and below the photosensitive perovskite material, limiting the directions in which they can receive light, which reduces the overall device efficiency.
Back-contacted solar cells are the widely preferred method for collecting the electricity created by photovoltaic material. Building the electrodes into an underlying structure of the light-sensitive material reduces transmission losses associated with top-side electrodes and allows it to be illuminated from all sides. Back-contacted silicon photovoltaic cells have already been manufactured and are commercially available, but silicon isn’t as good as perovskite at converting light to electricity.
Adaptation of a back-contacted design to the perovskite solar cell is incredibly difficult as the interdigitated array of electrodes must be delicately structured, which provides a number of major fabrication challenges.
However, the latest research from a team of CSIRO and Monash University researchers, working out of the MCN, has combined the benefits of both device types using a series of photolithography and vacuum deposition processes. The technique enabled an alternative design in which the interlocking array of anodes and cathodes were no longer on the same plane, but remained on only one side of the perovskite absorber layer. This has, for the first time, demonstrated the possibility of constructing a back-contacted PSC.
Now, the team are working to develop the processes used to make these cells in order to make them suitable for mass production. Once found, scalable, affordable fabrication techniques will bring back-contacted perovskite solar cells into the light, along with all the advantages they offer.
Ultrathin holograms open doors to 3D displays
A team led by Professor Min Gu from RMIT University and Beijing Institute of Technology have fabricated the world’s thinnest hologram – and it could revolutionise the way we interact with everyday technologies. The team’s research, published in Nature Communications, takes a step closer to three-dimensional (3D) displays for smart devices by reducing physical dimensions of a hologram to the nanometer scale.
Holograms are the result of shining light on an interference pattern to recreate a seemingly 3D object within a film. Even the parallax effect is captured, meaning when the viewer moves, the image appears to move too.
An interference pattern is produced by splitting a light beam into two with each beam travelling different paths of varying length. The additional time causes a phase difference in the light, resulting in peaks and troughs of intensity when the beams are recombined. Holograms have to be thick enough to allow enough time for the phase difference to become noticeable.
Since the 1960s it’s been common practice to use computer-generated patterns – a process called computer-generated holography (CGH). CGH can in principle be applied to smart technologies, but the physical size of holograms – currently ranging between micrometres to millimetres – makes this currently impractical.
The paper’s lead author, Dr Zengji Yue, explained that to reduce the depth, the team began working with antimony telluride (Sb2Te3) that had been laser etched to feature the desired interference pattern. The new film acts as a resonance cavity – light is bounced between the surfaces, amplifying the phase difference. Sb2Te3 is rare in the respect that its refractive index at the surface is far lower than within the body of the material which helps to retain the light.
The team used MCN’s atomic layer deposition (ALD) capabilities as the basis to fabricate the Sb2Te3 hologram film. The Centre’s ellipsometry equipment was used to compare the sample’s refractive index to theoretical models. The result is a 60nm thick film that produces the holographic images. Considering most of the processes are scalable, the new holograms could be produced on a large scale.
The team now aims to create smaller pixels to increase the resolution of the images, and to investigate dynamic displays.