Latest News

“Controlling many­body states by the electric­field effect in a two dimensional material” published in Nature and Straits Times!

Our research group has published a letter in Nature that provides the key to unlocking the secret of superconductivity in 2D thin films of TiSe2. Working in collaboration with the theoretical group of Prof. Antonio Castro­Neto and the experimental group of Prof. Kian Ping Loh, we used extremely sensitive control of huge electric fields at ultra­low temperatures to drive TiSe2 from a metallic state to superconductivity.

In a usual metal, such as copper or gold, individual electrons repel one another, but in a superconductor electrons prefer to pair together. This exotic state allows superconductors to carry electricity with zero resistance so that just a thin strand of superconducting wire can carry a huge electrical current that can be used, for example, to create the large magnetic field needed for magnetic resonance imaging in hospitals.

Creating the conditions under which electrons pair together is challenging, especially at temperatures that are not extremely cold. For this reason modern research has focussed on how to use electronic states such as the charge density wave, where electrons prefer to crowd together in certain positions in a crystal, to help superconductivity. Our study showed that rapid fluctuations in a charge density in TiSe2 nucleate superconductivity, analogous to how conditions on earth provided just the right conditions for life.

The result is a breakthrough in clearly demonstrating how superconductivity appears at the microscopic scale and adds weight to theories that have suggested that superconductivity in high temperature copper oxide superconductors proceeds by a similar mechanism. Our work may therefore act as a guide to how scientists can build a material that will superconduct at room temperature, supporting technologies such as clean energy distribution and quantum information.

Click here to read the Straits Times article on the above work.

Superconductivity Explained

The electric field drives electrons to dance together in TiSe2: On the left hand state the people representing electrons repel one another. By applying electric field, represented here by music, the electrons dance together in certain regions of the crystal where the charge density varies rapidly.

RESEARCH IN THE GRAPHENE LAB


In our lab, we focus on diverse research topics, pertaining to graphene and other promising 2D materials like metal dichalcogenides and black phosphorus, ranging from fundamental research including spintronics, chemical reactivity studies, etc. to applied research such as in the fields of flexible electronics (in conjunction with functional polymers), energy storage and conversion, nanoengines and transparent conducting electrodes.

We are currently looking for highly motivated PhD students and post doctoral fellows to join our efforts. Please see our openings.

Check out these useful links to learn more about Graphene.

The following YouTube Logo videos by our group shows how to make graphene and how to transfer CVD graphene:

Gen 1

Making Graphene

Gen 3

Flexible Touchpanel

Gen 2

Transfer of CVD Graphene

Graphene/Functional Polymer Laminates and Blends


Graphene has attracted a lot of interest from a wide range of industries. Graphene's high mechanical strength & flexibility, optical transparency and exceptional heat & charge transport properties make it appealing for a wide range of novel device concepts. These range from flexible smart phones, roll-able AM-OLED, anti-bacterial coatings, water filtration membranes, photovoltaics, energy storage, etc. While proof-of-concepts, for most of these ideas, has already been realized at the lab scale, many challenges still lie ahead in terms of large scale synthesis, transfer and incorporation in existing industrial production processes. Our group is working on overcoming some these challenges by combining graphene with functional polymers. This approach not only provides mechanical support to an atomically thin membrane but also enhances graphene's unique intrinsic properties.

One of the polymers which can potentially boost tremendously the robustness of graphene films and simultaneously offer chemical resistance is PVDF. In addition, the multi-functionality of PVDF (ferro-electric, pyro-electric, piezo-electric) adds new possibilities for graphene's use in novel applications including nanogenerators, temperature sensors, etc.

Some of the recent results from our lab are:

Energy Storage


A phone battery typically takes at least 30 min to 1 hour to charge completely. Imagine being able to charge the same within a few minutes. Supercapacitors are one of the key devices for energy-storage applications which possess much better power handling capabilities than batteries, i.e. they can be charged much faster than batteries, and can store much higher amounts of energy than conventional capacitors. To achieve a high performance supercapacitor, we need materials with high surface area, along with high material density and superior conductivity. But unfortunately, as surface area and material density are inversely proportional characteristics of a material. In particular, porous materials have high surface area, but lack a large material density and hence exhibit a poor electrical conductivity. We have recently been awarded S$ 10 million from the Singapore National Research Foundation (NRF) to produce self-standing supercapacitor electrodes, in the form of a highly dense porous graphene foams, which have excellent conductivity (comparable to graphene) combined with high surface area as part of this project. A new lab is under construction for this operation and is expected to become operational in October, 2014. (List of awarded NRF CRP projects)

Phosphorene


Just six months ago, our group was among the first to explore, that this ultra-thin version of black phosphorus could provide complementary properties to graphene and could also surpass some unique properties of the latter. For example, in the short term, graphene might not be useful for semi-conducting transistor applications for computer circuits since it lacks a natural band gap. Phosphorene on the other hand has a direct band gap in a suitable energy range, making it a very promising material in areas such as transistor applications, photodetectors, heat-dessipating layers, etc.

One of the first papers in this area is:

2D van der Waals Heterostructures


There are a wide range of 2D crystals with distinct properties. For example, graphene is a semi-metal, boron nitride (BN) is an insulator, molybdenum disulfide (MoS2) is a semiconductor. By combining atomically thin layers of these materials in a layer-by-layer fashionn, one creates a new three dimensional crystal with completely new properties. These new crystals are generally referred to as van der Waals heterostructures. Our group is in particular interested in enhancing graphene's spin transport properties by combining it with metal dichalcogenides such as tungsten disulfide. We have recently demonstrated that the spin orbit coupling of graphene can be enhanced by a factor of thousand, utilizing the proximity effect. These efforts are the first steps towards spin-based electronics: