Probing the future of advanced materials
By : Michael Gibb
There are only four APT laboratories in China but not a single one south of the Yangtze River. That means CityU’s APT Lab is pretty special for the study of nanostructures in advanced materials.
And it is even more special because CityU’s APT technology produces data faster, cheaper and more efficiently than any other models.
“What used to take two and half days now takes less than half a day with the new APT facility that CityU acquired last year,” explains Professor Liu Chain-tsuan, University Distinguished Professor at CityU and an expert in new materials.
High-res, 3D imaging
Atom probe tomography (APT) is one of the most exciting analytical techniques for studying materials at the atomic scale. APT allows researchers to examine the 3D morphology, and composition of nanostructures in the highest spatial resolution.
Professor Liu Chain-tsuan “What we can do now at CityU’s APT Lab is, quickly and more effectively than ever before, look at the shape, size, and composition of nanoscale morphologies,” says Professor Liu, who is responsible for the facility established at CityU last year with a grant from the Collaborative Research Fund (CRF) of the Research Grants Council (RGC) in 2015.
CityU’s new facility for producing highly detailed 3D nanoscale characterisations of materials is important on several levels. The visual data produced allows analysts to manipulate and control nanostructures for the design of both structural and functional materials. For example, the APT technology can help to strengthen steels by identifying and characterising the size, morphology and composition of nanoparticles formed in these high-strength materials.
“As material scientists, we aspire to accurately locate and identify individual and groups of nanostructures with the fundamental physical and mechanical properties of new materials,” says Professor Liu, a Member of the National Academy of Engineering (USA) and a Foreign Member of the Chinese Academy of Engineering.
Maintaining the nano edge
The challenge researchers have faced for years in Hong Kong is the lack of equipment for conducting this level of analysis for advanced nanostructured materials. Over 90 APT instruments can be found all over the world, mainly in America and Europe, but Hong Kong, and the whole of southern China in fact, had no such facility. Researchers in this part of the world had to rely on APT centres overseas, a process that incurred scheduling difficulties as well as high costs.
“The visual data produced allows analysts to manipulate and control nanostructures for the design of both structural and functional materials.” In order to maintain a competitive position in researching advanced materials and nanoscience related areas, CityU teamed up with the University of Hong Kong, Hong Kong University of Science and Technology, Chinese University of Hong Kong and Hong Kong Polytechnic University to establish the APT Lab at CityU.
“In the past we could determine what materials were strong, but we didn’t really know why. With APT, we can better understand the form and structure of nanoscale particles, how they are distributed and their composition, allowing us to work out ways to add performance to create new and more advanced materials,” he says. The most compelling example would be the development of new forms of ultra-high strength steels for building safer, stronger buildings, vehicles, ships and energy conversion systems.
The technique used in the APT facility works like this. A charge of about 7 kilovolts is applied to a needle specimen, a piece of nanostructured steel for instance. The excited atoms pass through a local electrode to a detector, and an algorithm re-constructs the nanoscale structures based on data such as time of flight, position of the ion impact on the detector, and other factors revealed by the excited ions. The result is a 3D visualisation of the nanostructural features and a quantitative analysis of its chemical composition and morphology.
“What is so great about our APT technology at CityU is that previously we could only get about 37% of the atoms through the detector to form the 3D image but the new APT version we have at CityU, the LEAP 5000R, manages to capture 52%, adding greatly to the degree of accuracy in nanostructural analyses,” Professor Liu says.
Investing in the future
There is no doubt that the APT is an expensive facility. The cost of the technique amounts to around HK$30 million, but the plus side is that using the APT (LEAP 5000R) is dramatically cheaper than having to use APT facilities in other parts of the world, which was the practice in Hong Kong prior to CityU’s APT Lab.
“Our 3D atom probe facility jointly set up with sister institutions in Hong Kong offers scientists tremendous opportunities for innovation and discovery in advanced materials. We need sophisticated facilities if we are to conduct first-class research for publications. So the investment is well worth it,” says Professor Liu.
40-year-old mystery solved
Scientists who study advanced materials made a noteworthy discovery at CityU recently when they solved a 40-year-old mystery about metallic glass alloys. In essence, their findings explained a puzzle about a thermodynamic anomaly seen when scanning a certain kind of metallic glass alloy, says Professor Wang Xunli (2nd from right, below photo), Chair Professor of Physics and Head of the Department of Physics and Materials Science.
“We discovered a hidden amorphous phase in the formation of metallic glass. As a result, we can manipulate the nanoscale structure of metallic glass and produce better materials,” he says.
Molecules in a glass are arranged much like those in liquids but are more tightly packed. So what scientists want to understand is where and why liquid ends and glass begins. This area of scientific enquiry was included in a list of 100 questions in the July 2005 edition of Science Magazine. Other questions on the list include: Is ours the only universe? What drove cosmic inflation? When and how did the first stars and galaxies form?
The CityU scholars used high-entry synchrotron x-ray and neutron diffraction to provide evidence of a polyamorphous phase transition during the creation of metallic glass. Knowing about this hidden phase in the creation process means that researchers can understand more about how to manipulate the material and thus how to make new, advanced variations.
“The discovery is an important observation in glass physics. We can explore how to produce or induce this amorphous phase in metallic glass so that we can tune the properties of the material for larger size and better application,” Professor Wang says.