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 three highly motivated PhD students and two post doctoral fellows to join our efforts. Please see our openings.
Check out these useful links to learn more about Graphene.
The following videos by our group shows how to make graphene and how to transfer CVD graphene:
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:
- Graphene–Ferroelectric Hybrid Structure for Flexible Transparent Electrodes;
G.-X. Ni, Y. Zheng, S. Bae, C.Y. Tan, O. Kahya, J. Wu, B.H. Hong, K. Yao, B. Özyilmaz
ACS Nano, 6 (5), pp 3935–3942 (2012).
- Gate-controlled nonvolatile graphene-ferroelectric memory;
Yi Zheng, Guang-Xin Ni, Chee-Tat Toh, Ming-Gang Zeng, Shu-Ting Chen, Kui Yao, Barbaros Özyilmaz.
Applied Physics Letters 94, 163505-163503 (2009).
- Graphene-P(VDF-TrFE) multilayer film for flexible applications;
Bae, S.-H., Kahya, O., Sharma, B. K., Kwon, J. G., Cho, H. J., Özyilmaz, B., Ahn, J.-H.
ACS Nano, Volume 7, Issue 4, pp 3130–3138 (Feb 2013).
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)
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:
- Electric field effect in ultrathin black phosphorus;
Koenig, S. P., Doganov, R. A., Schmidt, H., Castro Neto, A. H., and Özyilmaz, B.
Appl. Phys. Lett. 104, 103106 (Mar 2014).
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:
- Spin-Orbit Proximity Effect in Graphene;
Avsar, A., Tan, J. Y., Balakrishnan, J., Koon, G. K. W., Lahiri, J., Carvalho, A., Rodin, A. S., Taychatanapat, T., O'Farrell, E. C. T., Eda, G., Castro Neto, A. H., and Özyilmaz, B.
Nature Comms. (Aug 2014), Accepted
- Giant Spin Hall Effect in Graphene Grown by Chemical Vapor Deposition;
Balakrishnan, J., Koon, G. K. W., Avsar, A., Ho, Y., Lee, J. H., Jaiswal, M., Baeck, S-J., Ahn, J-H., Ferreira, A., Cazalilla, M. A., Castro Neto, A. H., and Özyilmaz, B.
Nature Comms. (Aug 2014), Accepted
- Electronic transport in graphene-based heterostructures;
Tan, J. Y., Avsar, A., Balakrishnan, J., Koon, G. K. W., Taychatanapat, T., O'Farrell, E. C. T., Watanabe, K., Taniguchi, T., Eda, G., Neto, A. H. C., and Özyilmaz, B.
Appl. Phys. Lett. 104, 183504 (May 2014)
- Colossal Enhancement of Spin-Orbit Coupling in Weakly Hydrogenated Graphene;
Balakrishnan, J., Koon, G. K. W., Jaiswal, M., Castro Neto, A. H., Özyilmaz, B.
Nature Physics 9, pp 284–287 (May 2013).