Tingyu’s Paper has been accepted and published on Physical Review Research!

Breakthrough in Magnetoresistance Properties of MoS2 Unveiled by Barbaros Group

In a landmark study, we have made significant strides in understanding the magnetoresistance properties of bilayer molybdenum disulfide (MoS2), a material poised to revolutionize electronic devices and sensors. The team, led by prominent scientists in the field of material science, explored the properties of MoS2 encapsulated by hexagonal boron nitride, using a sophisticated dual-gated setup.

The research reveals an unexpected negative magnetoresistance at low magnetic fields (less than 0.5 Tesla), primarily attributed to the weak localization effect—a quantum phenomenon that enhances the electron’s ability to resist changes in its path due to disorder. This insight opens up new avenues for the development of high-performance electronic components that could operate efficiently in varying magnetic environments.

Further investigations by our team have demonstrated a consistent increase in the phase coherence length and mean free path with electron density, suggesting enhanced performance characteristics at higher electron densities. Interestingly, the displacement field showed no significant impact on these parameters, highlighting the unique properties of MoS2 as influenced by electron interactions rather than external tuning.

Additionally, temperature-dependent studies identified Coulomb scattering as the primary dephasing mechanism when lower spin-orbit split bands are involved in transport. This finding supports the concept of spin-polarized valleys, or ‘spin-valley locking’, where intrinsic spin-orbit coupling helps maintain spin states, offering a protective mechanism absent in conventional materials.

Barbaros group is excited to share these findings, which not only advance the understanding of two-dimensional materials but also suggest potential applications in next-generation electronic and quantum devices. The lab is currently seeking new students, researchers, and potential industrial partners to join in exploring the vast potential of these materials. This research promises to open doors to innovative technologies and foster collaborations that could shape the future of materials science. For those interested in joining or collaborating with our team, please contact us through our website or directly at barbaros@nus.edu.sg. Let’s innovate together!

We are thrilled to share that we’ve achieved a breakthrough in battery technology!

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Graphene and positively polarized P(VDF-TrFE) assist in controlling Zn nucleation and growth on Cu substrate, enabling a high-performance zinc metal-free zinc-ion batteries.

Aqueous zinc-ion batteries have attracted extensive attention due to its use of aqueous electrolyte, high theoretical Zn capacity, high energy density, abundant resources, and easy material handling. And zinc metal-free zinc-ion batteries hold promise for achieving higher energy densities by eliminating the need for dense zinc foil as the anode. However, the direct use of substrates like copper foil in these batteries results in poor cyclic stability due to dendrite growth. In order to prevent dendrite formation, delving into the nucleation sites and growth dynamics of Zn can yield valuable insights. The initial nucleation of Zn can be controlled through substrates that offer a minimal lattice mismatch with Zn. Furthermore, the growth process influenced by the flux of Zn²⁺ and its deposition can be influenced by the electric field originating from the surface. Thus, tailoring the surface characteristics of the substrate for zinc metal-free Zn-ion batteries should address the challenges posed by dendrite growth.

Herein, we proposed a strategy to guide the nucleation sites and growth dynamics of Zn by introducing Graphene and positively polarized (poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))) on the copper substrate. The graphene coating guides the initial nucleation of Zn to form hexagonal plate. Then, the positively polarized P(VDF-TrFE) enable the growth along the hexagonal plate to regular crystalline plate. As expected, for the half-cell, a significant improvement in the cell cycle life up to 3000 cycles at a high current density of 10 mA cm-2 with a capacity of 1 mAh cm-2 was achieved, which is to our knowledge one of the longest lifespan ever reported for Zinc ion battery.

Combined with the Zn-inserted MnO2 cathode, the full cell is constructed, which showed good cycling stability (83% after 500 cycles) and high energy density of 378 Wh Kg-1 at 0.5 mA cm-2, higher than the traditional Zn ion battery using Zn anode (136 Wh Kg-1). As a demonstration, the pouch cell was prepared, which can successfully power the electric fan and LED lights, demonstrating its promising applications as high-performance zinc metal-free Zn ion battery.

CDE Awards and Recognition 2023

Professor Barbaros Özyilmaz is recognised at the ceremony having been named in the 2022 Highly Cited Researchers list and among the World’s Most Influential Scientific Minds – an annual list compiled by Clarivate.

We are proud to share that as NUS Centre for Advanced 2D Materials (CA2DM)’s leadership, Professor Barbaros Oezyilmaz is amongst the recent Stanford University’s World Top 2% of Scientists. Congratulations Professor Barbaros Oezyilmaz.

Researchers at NUS Physics, CA2DM and Materials Science and Engineering have created the world’s first atomically thin amorphous carbon film. The amorphous structure has widely varying atom-to-atom distance unlike crystals. This is because of the random arrangement of five-, six-, seven- and eight-carbon rings in a planar carbon network, leading to a wide distribution of bond lengths (in Å) and bond anglesResearchers from NUS have synthesised the world’s first one-atom-thick amorphous material. Previously thought to be impossible, the discovery of monolayer amorphous carbon (MAC) could finally settle a decades-old debate of exactly how atoms are arranged in amorphous solids, and open up potential applications.

This major research breakthrough was led by Professor Barbaros Özyilmaz, Head of the NUS Materials Science and Engineering. The results were published in the prestigious scientific journal Nature on 8 January 2020.

The NUS team grew the material and studied its properties and potential areas of application. In addition, atomic resolution imaging was performed by the group of Professor Kazu Suenaga from the National Institute of Advanced Industrial Science and Technology (AIST), Japan, and Professor Junhao Lin from Southern University of Science and Technology (SUSTECH), China. Furthermore, theoretical simulations were carried out by the group of Professor Sokrates Pantelides from Vanderbilt University, USA.

“With MAC, we have shown for the first time that fully amorphous materials can be stable and free-standing in single atomic layers. Amorphous materials are of great technological importance, but surprisingly, they remain poorly understood from a basic science point of view. This breakthrough allows for direct imaging to reveal how atoms are arranged in amorphous materials, and could be of commercial value for batteries, semiconductors, membranes and many more applications,” said Prof Özyilmaz, who is also from NUS Physics and the NUS Centre for Advanced 2D Materials.

The structure and synthesis of monolayer amorphous carbon

In the study of amorphous materials, there are two opposing groups. One says that it is possible for materials to have a fully-disordered, completely random structure. The other, says there is always nanometre-sized order, of tiny crystallites, that is surrounded by random disorder.

The newly synthesised MAC films show the latter arrangement. The researchers see nanometre-sized patches of strained and distorted hexagonal carbon rings, but there is random disorder between these patches. Hence, the MAC films also contain 5-, 7-, and 8-membered rings too.

These atomically-thin sheets of amorphous carbon are synthesised by using a laser vaporising a carbon-containing pre-cursor gas into an atomically fine mist. This turns the carbon precursors into highly reactive, energetic species which immediately form a MAC film when they hit the surface of almost any substrate.

The revolutionary properties of monolayer amorphous carbon

Despite having a disordered atomic structure, MAC is capable of some truly incredible behaviour. Dr Toh Chee Tat, the first author of the paper, said, “What is amazing about MAC is that it exhibits some properties that are totally different from traditional monolayer materials.”

One such exceptional property is that MAC films can be ‘plastically deformed’. This means that they can be stretched into irregular shapes, and stay conformed to that position. There is no other single-layer material in existence that displays significant plastic deformation.

The fact that MAC behaves this way, compared to nanometre-thick crystalline materials which would easily snap when stretched, significantly expands the number of industrial applications it could be suitable for.

Holes can even be punched into the material, or it can be torn, and yet the film will retain its key properties. Also, MAC can be grown on many different substrates including copper, gold and stainless steel. “Everything that is understood from atomically thin crystals — in terms of their properties and how they are analysed — does not apply here. It is a completely new material that we are studying,” shared Dr Toh.

Industrial applications of monolayer amorphous carbon

“MAC is much more hardy and cheaper to make than conventional crystalline two-dimensional films. The laser-assisted deposition process through which MAC is synthesised is already commonly used in industry. Hence, we can grow a large-area, defect-free, monolayer film on a wide variety of substrates with high throughput and at low temperature,” explained Prof Özyilmaz. This makes MAC a potential low-cost material to address industry needs, and for some applications, it may be an alternative to two-dimensional crystals such as graphene.

For example, ultrathin barrier films are sorely needed in many industries — for next-generation magnetic recording devices, copper interconnects, flexible displays, fuel cells, batteries and other electronic devices. However, the performance of conventional amorphous thin films is poor when made very thin, and other atomically-thin films cannot be produced according to stringent industry standards without compromising their qualities.

“Our monolayer amorphous films not only achieve the ultimate thickness limit, but also do not compromise on uniformity and reliability, and are generally considered viable for industry,” said Prof Özyilmaz.

Next steps

Prof Özyilmaz is the lead Principal Investigator of a multidisciplinary team that was recently awarded a grant under the National Research Foundation Singapore’s Competitive Research Programme to investigate the properties of monolayer amorphous materials. The research team will be studying the many possible applications of this material and will be collaborating with industrial partners to accelerate the commercialisation of monolayer amorphous materials such as MAC.