Singapore Group: ALD is Merged with Joule Heating to Produce Modern Noble Alloys
On 15 February this year in Singapore, an interesting scientific report was published in Nature by researchers from the School of Materials Science and Engineering (Nanyang Technological University) and the Institute of Materials Research and Engineering (Agency for Science Technology and Research).
The work, in which Yuanyuan Guo, Yiming Zou, Chunyu Cheng, Leyan Wang, Riko I Made, Ronn Goei, Kwan Wee Tan, Shuzhou Li & Alfred Iing Yoong Tok were authors, details a new method of fabricating Rhodium–Iridium (Rh–Ir) metal alloy films using atomic layer deposition (ALD) and rapid Joule heating induced alloying. The associated techniques (ALD and Joule heating) makes it possible to produce functional thin film alloys while enabling conformal thin films with high aspect ratios on a 3D nanostructured substrate.
The advantage of reaching out to such noble metal alloys resides in their application. Modern alloys can be applied in industries like biomedical, aerospace industries, and energy conversion and storage applications, whereas the methods to produce such alloys only result in bulk materials, losing possible exciting properties that could only be achieved in mono or multi-layer alloy structures.
In the study, Yuanyuan et al. demonstrated for the first time a novel strategy with ALD to fabricate alternating layers of nanometer-thin constituent Ir and Rh films on the basis of crystallographic similarity and subsequent rapid EJH treatment to sinter these Rh–Ir films into an alloy.
The alloy was produced by ALD in three stages. The first is based on ALD of Rh on sapphire; the second is based on ALD of Ir on Rh; the third and last is toward a rapid Joule heating of the acquired Rh-Ir thin film. To achieve such, a custom-built ALD reactor was used. Uniformity was confirmed by techniques as SEM and TEM (scanning and transmission electron microscopy), with no signs of macroscopic phase segregation on sapphire (Al2O3)
The Singapore group concluded that the ALD technique was capable of fabricating relatively uniform thin films when compared to other alloy synthesis methods. Their proof-of-concept experiments suggested that coupling ALD with EJH enables a viable approach to preparing homogeneous single-phase solid-solution metal alloy thin films that could potentially be applied in microelectronics, catalysis, and other industries.
About the group leader:
Professor Alfred Tok has a bachelor's in Mechanical Engineering at the Queensland University of Technology, Australia, and graduated with a first-class honor in 1995. He was also conferred the Dean's Award for Excellence for being the top graduate on the course. After graduation, he worked as a mechanical engineer at ST Aerospace Engineering. In 1997, he was awarded two scholarships at Nanyang Technological University (NTU) to pursue his Ph.D. in Mechanical Engineering.
Professor Alfred Tok
After graduation, he joined the Materials Engineering school as a Research Fellow in 2000 and took up the position of Assistant Professor in 2003. In 2009, he bestowed the National Day Commendation Medal (PK) from the Singapore Prime Minister's Office. In the same year, he obtained his Nanyang MBA on the Dean's Honors List. He was then appointed Division Head of Materials Technology in MSE in 2009, and presently, he is the Deputy Director of the Institute for Sports Research. He also consults extensively for companies in various industries.
According to Professor Alfred Tok, his group's research interests are divided into five main areas:
1) Carbon-based Field-Effect Transistor Sensors
2) Synthesis of Nanostructured Materials using Atomic Layer Deposition
3) Hard & Tough Materials for Ballistic Protection Application
4) Institute for Sports Research
Specifically, on the synthesis of Nanostructured Materials using Atomic Layer Deposition (ALD), Professor Alfred affirms that ALD has evolved to be a unique tool for nanotechnology with atomic level control of the depositions, 3D conformity, and homogeneity. Film depositions can be realized for complex non-planar topographies for a wide range of applications such as energy conversion and storage, nanoparticle catalysts, nanostructures for drug delivery, gas separations, sensing, and photonic applications. His group also focuses on ALD materials for solar cells, hydrogen generation, and intelligent window applications.
Exciting applications of ALD in other fields by his group is also exemplified in solar cells and hydrogen generation from water.
In solar cell applications, they muse a transition metal with a structure analogous to graphene, and that has been extensively researched and applied in various areas: MoS2-based NaYF4. The compound can extend the absorption spectrum to the NIR range for efficient solar harvesting. They are also exploring ways to obtain 3D-structured MoS2 using environmentally friendly and non-toxic ALD suitable for industries.
On hydrogen generation from water, a promising approach to address energy security issues, ALD is used to produce 3D inverse opal photonic crystals with various reflection peaks, which in turn are capable of enhancing the efficacy of photoanodes.
You can find more information on:
Guo, Y., Zou, Y., Cheng, C. et al. Noble metal alloy thin films by atomic layer deposition and rapid Joule heating. Sci Rep 12, 2522 (2022). https://doi.org/10.1038/s41598-022-06595-9
Professor Alfred Tok webpage: https://personal.ntu.edu.sg/miytok