Research Collaborations

Ecology is being recognized globally as an increasingly important discipline, as human pressure on the environment continues to grow and as the consequences of human-induced global change phenomena become increasingly apparent. This is of direct relevance to Singapore. For example, large fires caused by burning of peat ecosystems in the region impact significantly on air quality and human wellbeing in Singapore. Further, human activity influences food security, and environmental change caused by humans has various geopolitical consequences. In addition, Singapore is part of a biodiversity hotspot characterized by a unique and rich community of plants, animals and microbes, but which is under continual threat.

The linkage between the Asian School of the Environment (ASE) and the Smithsonian Tropical research Institute was recently formalized by a MoU signed between the two organizations. It is aimed at developing a world-class capacity in forest and ecosystem ecology in the Southeast Asian region in order to address environmental issues that are expected to become increasingly pressing in the region over the 21 ^st Century. As an initial step, in January 2017 Professor David Wardle started a new position at the ASE as the Smithsonian Professor of Forest Ecology.

He is, together with other researchers at the ASE and at the Smithsonian Institute, planning new projects to understand the drivers of biodiversity and ecosystem processes in forests in Southeast Asia (including in Singapore), ecology of managed and natural peat ecosystems in the region whose burning impairs air quality in Singapore, and the functioning of urban green areas in Singapore. The expectation is that as these projects develop, the team will have an enhanced mechanistic understanding of the environmental problems that confront the ecosystems in and around Singapore, which will in turn contribute to attempts at their remediation.

Water, the most abundant volatile in Earth’s interior, preserves the young surface of our planet by catalysing mantle convection, lubricating plate tectonics and feeding arc volcanism. Since planetary accretion, water has been exchanged between the hydrosphere and the geosphere, but its depth distribution in the mantle remains elusive.

In collaboration with Professor Shun Karato from Yale University, Nanyang Assistant Professor Sylvain Barbot from Asian School of the Environment and his team have derived a new way to constrain water contant in the upper mantle. Water drastically reduces the strength of olivine, the weakest and most abundant mineral in the Earth's upper mantle, and this effect can be exploited to estimate the water content of olivine from the mechanical response of the asthenosphere to stress perturbations such as the ones following large earthquakes. They exploited the sensitivity to water of the strength of olivine and observations of the exceptionally large (moment magnitude 8.6) 2012 Indian Ocean earthquake3 to constrain the stratification of water content in the upper mantle. Taking into account a wide range of temperature conditions and the transient creep of olivine, they explained the transient deformation in the aftermath of the earthquake that was recorded by continuous geodetic stations along Sumatra as the result of water- and stress-activated creep of olivine.

This implies a minimum water content of about 0.01 per cent by weight—or 1,600 H atoms per million Si atoms—in the asthenosphere (the part of the upper mantle below the lithosphere). The earthquake ruptured conjugate faults down to great depths, compatible with dry olivine in the oceanic lithosphere. They attributed the steep rheological contrast to dehydration across the lithosphere–asthenosphere boundary, presumably by buoyant melt migration to form the oceanic crust.

Figure 1 – The team exploits GPS measurements of rapid deformation following the 2012 Indian Ocean earthquake to infer the water content in the oceanic asthenosphere. The oceanic brittle lithosphere is dry (0.001–0.005 wt%) and the oceanic asthenosphere is wet (about 0.013 wt%), with a water content given by the probability density (inset) assuming the mantle temperature Tm = 1,380 °C.

3D plasmonic colloidosomes are superior SERS sensors due to their high sensitivity and excellent laser misalignment tolerance. However, the current sensing applications of plasmonic colloidosomes are performed with static state measurements that under-utilize their advantages as a dynamic substrate-less sensing platform, and limiting the detection throughput while generally require accurate laser alignment prior to every measurement. This project incorporates plasmonic colloidosomes in a microfluidic channel for on-line SERS detection (Figure 1).¹

The original idea of using plasmonic colloidosomes in a flow system was conceived and developed by Professor Ramón A. Alvarez-Puebla from Universitat  Rovira i Virgili, Tarragona, Spain and Associate Professor Ling Xing Yi’s research lab from School of Physical and Mathematical Sciences. This method resolves the poor signal reproducibility and inter-sample contamination in the existing on-line SERS platforms. The flow system offers rapid and continuous on-line detection of 20 samples in < 5 minutes with excellent signal reproducibility, while preventing cross-sample and channel contamination and allowing accurate quantification of samples with six orders of magnitude concentration range. The system demonstrates high resolution multiplex detection with fully preserved signal and Raman features of individual analytes in a mixture. 

Figure 1. (A) 3D scheme of the sequential on-line SERS detection of analyte samples encapsulated within plasmonic colloidosomes. (B) Time-lapsed SERS spectra obtained within 2 minutes exhibiting specific SERS fingerprints of each analyte, with respective concentrations obtained from tallying the peak intensities with calibration curves.

Reference
Gia Chuong Phan-Quang, Elizabeth Hui Zi Wee, Fengling Yang, Hiang Kwee Lee, In Yee Phang, Xiaotong Feng, Ramón A. Alvarez-Puebla, Xing Yi Ling, Angew. Chem. Int. Ed., 2017, 56, 5565 – 5569.

Rising levels of carbon dioxide (CO₂) are of significant concern in modern society, as they lead to global warming and consequential environmental and societal changes. It is of importance to develop industries with a zero or negative CO₂ footprint. Electrochemistry, where one of the reagents is electrons, is an environmentally clean technology that is capable of addressing the conversion of CO₂ to value-added products. The key factor in the process is the use of catalytic electrode materials that lead to the desired reaction and product. Significant progress in this field has been achieved in past few years by collaborative efforts of leading electrochemistry and materials science & engineering groups, Associate Professor Martin Pumera from School of Physical and Mathematical Sciences and Prof. Adrian Fisher from Cambridge University.

Intensive CO2 emission results in serious enviromental issues globally. Adsorptive separation of CO2 from gas mixtures utilizing porous materials provides an alternative, energy-efficient, and low-cost separation technique. In order to address the CO2 issue from fundamental and practical perspectives, a research team led by Associate Professor Zhao Yanli from School of Physical and Mathematical Sciences in collaboration with Professor Zou Ruqiang from Peking University China has developed novel porous materials to achieve selective capture and conversion of CO2.

Specifically, they have innovatively prepared nitrogen-rich porous materials for selective CO2 capture, since the incorporation of accessible nitrogen-donor groups onto the internal walls of porous materials can dramatically improve CO2 uptake capacity and selectivity (J. Am. Chem. Soc. 2016, 138, 2142–2145; Adv. Mater. 2016, 28, 2855–2873; Angew. Chem. Int. Ed. 2015, 54, 12748–12752; J. Am. Chem. Soc. 2015, 137, 1020–1023). One of the nitrogen-rich porous materials shows a significant enhancement in the CO2 adsorption (over 37 wt% at 1 atm), along with a high selectivity of CO2 over N2. Some developed porous materials could also be employed as highly effective and substrate size-dependent catalysts for the CO2 conversion into value-added chemicals and materials. A laboratory-scale prototype facility using the developed nitrogen-rich porous materials has been set up by them for high-performance CO2 capture and conversion.

Block ciphers are among the most important primitives in cryptography, backbones of the security applications in various industries. Block ciphers are used in places where privacy of the data is required, for example in satellite or military communications, Internet and networks data flow, banking and money transfers, etc. Whenever one needs to hide the contents of the communication with another user, block ciphers are very likely to be used. They can also be utilized to cipher data at rest, such as sensitive databases or computer hard-drives, in order to protect its privacy in case physical compromise. Even though very efficient and strong block ciphers are already available (such as the worldwide standard AES), these primitives might be unusable when placed in a very constrained environments, such as passive RFID tags, or many tiny devices that will soon become the backbone of the Internet of Things (IoT). Securing these devices is of utmost importance as they might mange sensitive data and moreover the security chain of an information system is only as strong as its weakest link.

Nanyang Asistant Professor Thomas Peyrin from School of Physical and Mathematical Sciences and his student Siang Meng Sim and postdoc Jeremy Jean, in collaboration with researchers from NTT (Japan), Ruhr-Universität Bochum (Germany) and Technical University of Denmark (Denmark), have designed a new block cipher, named Skinny, specially crafted to fit in the most constrained environments. Skinny is currently the most efficient block cipher primitive for so-called lightweight cryptography applications (it even compares favourably with NSA cipher SIMON, see Table below). Not only our cipher is very efficient, but it also provides strong security guarantees with regards to all state-of-the-art attacks.

The main novelty of Skinny is a new method to build the internal round function that performs the encryption. Very specific cryptopgrahic components have been carefully chosen, but also placed, to ensure a maximisation of the security while keeping the cost as low as possible. 

As Moore’s law push the size of memory devices to their physical limits, Spintronic devices allow additional utilities such as enhancing endurance, lowering energy consumption and non-volatility. These magnetic devices use the spin of the electron to read, write and store memory. As current driving methods such as spin transfer torque requires higher power consumption which in turn causes joule heating, voltage controlled magnetic anisotropy (VCMA) can improve energy dissipation by 100 times. In recent years, VCMA has gathered interest and has shown its capabilities to either write or drive spintronic devices such as magnetic tunnel junction, domain wall memory and magnetic Skyrmion. This project is led by Associate Professor Lew Wen Siang from School of Physical and Mathematical Sciences with collaboration from GLOBALFOUNDRIES Singapore is to achieve high speed spintronic devices by utilizing the VCMA effect. 

Figure 1. Magnetic tunnel junction under opposite applied voltage, the white arrows show the magnetic easy axis of the material

Key Features and Innovation	·         New generation of ultra low-power non-volatile spintronic devices ·         High energy efficiency of spintronic devices and enhanced performance of magnetic memories
Potential Application	·         Dynamic random access memory (DRAM) replacement ·         STT- magnetoresistive random access memory (MRAM) replacement
Relevance to which Industry	·         Semiconductor ·         Micro- and Nano-electronics ·         Spintronics
	Voltage Controlled Magnetic Anisotropy measurement on a Hall cross device

In order to keep up with the trend set by Moore’s law, the rapid advancement and reliance on smaller and faster electronics have led to the development of new technologies such as magnetoresistive random access memory (MRAM). The core element to enable fast switching and non-volatility seen in MRAM is a magnetic tunnel junction (MTJ), which in its rudimentary form consists of two ferromagnetic elements sandwiching a dielectric barrier. Amongst various other physical, magnetic and electrical requirements, the MTJ must also be able to withstand 400°C annealing temperature found in matured CMOS back-end-of-line (BEOL) technology, as well as a minimum thermal stability for 10 year data retention capability.

At NTU Spintronics lab, Associate Professor Lew Wen Siang from School of Physical and Mathematical Sciences and his team work closely with GLOBALFOUNDRIES through various project initiatives to improve on the various aspects of the MRAM fabrication processes, such as etch method evaluation, micromagnetics simulation and novel switching mechanism. In this project, they focus on evaluating novel materials that can be implemented in the current stack design to solve the above challenges, as well as the characterization of the core element of the MRAM device by probing the magnetization dynamics of the system.

Figure 1. Ferromagnetic resonance spectrometer (FMR) contrast plot profile used to individually identify the anisotropy strengths of the free layer and reference layer in the MTJ.

Key Features and Innovation	·         Magnetization dynamics study of magnetic tunnel junction (MTJ) ·         Thermally robust MTJ for back-end-of-line (BEOL) integration
Potential Application	·         STT- magnetoresistive random access memory (MRAM) ·         Spin diode
Relevance to which Industry	·         Semiconductor ·         Micro- and Nano-electronics ·         Spintronics
	High stability, integrated and automated ferromagnetic resonance spectrometer (FMR) syste