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 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:
- A wafer-scale graphene and ferroelectric multilayer for flexible and fast-switched modulation applications;
Zhu, M., Wu, J., Du, Z., Tay, R. Y., Li, H., Özyilmaz, B., and Teo, E. H. T.
Nanoscale, 7 14730-14737 (Aug 2015)
- Ultrathin Organic Solar Cells with Graphene Doped by Ferroelectric Polarization;
Kim, K., Bae, S.-H., Toh, C. T., Kim, H., Cho, J. H., Whang, D., Lee, T.-W., Özyilmaz, B., and Ahn, J.-H.
ACS Appl. Mat. & Inter. 6(5), 3299-3304 (Mar 2014)
- 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).
- 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).
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, 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.
In our lab, we have developed a bottom-up approach to synthesise novel nano-structures, leading us to a unique, controlled spatial arrangement of nano-particles, which in turn has provided us the key to achieving the highest volumetric surface area reported so far for carbon. This approach enabled us to create carbon foams to target very specific applications and tailor material properties accordingly. For example, these carbon foams as ultra-thick electrodes for supercapacitor applications resulted in very high energy density and high power devices, thanks to the hierarchical structure of the pores made by nano-particles of specific aspect-ratios. Also, in the electrode developed for Si-based battery anodes, by introducing a novel elastic material, we have obtained excellent structural stability under high lithiation rate.
We have been awarded S$ 10 million from the Singapore National Research Foundation (NRF) for the above projects (List of awarded NRF CRP projects). A new lab is under operation for this at S12-01-08, Department of Physics, National University of Singapore. Simultaneously, we are in collaboration with a key industry player in supercapacitors, muRata Manufacturing Co. Ltd.
In 2014, our group was among the first to explore, that this ultra-thin version of black phosphorus could provide complementary properties to graphene and MoS2 and could also surpass some unique properties of the latter. For example, in the short term, graphene might not be useful for semiconducting transistor applications for computer circuits since it lacks a natural band gap. MoS2 has a sizable bandgap but the carrier mobility is very low, limiting its applications in electronics. Phosphorene on the other hand has a direct band gap in a suitable energy range and high carrier mobility, making it a very promising material in areas such as transistor applications, photodetectors, heat-dessipating layers, etc.
Our recent publications in this area are:
- Electron Doping of Ultrathin Black Phosphorus with Cu Adatoms;
Koenig, S. P., Doganov, R. A., Seixas, L., Carvalho, A., Tan, J. Y., Watanabe, K., Taniguchi, T., Yakovlev, N., Castro Neto, A. H., and Özyilmaz, B.
Nano Letters 16 (4), pp 2145–2151 (Mar 2016)
- Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus;
Wu, J., Koon, G. K. W., Xiang, D., Han, C., Toh, C. T., Kulkarni, E. S., Verzhbitskiy, I., Carvalho, A., Rodin, A. S., Koenig, S. P., Eda, G., Chen, W., Castro Neto, A. H., and Özyilmaz, B.
ACS Nano, 9 (8) 8070-8077 (Jul 2015)
- Transport properties of ultrathin black phosphorus on hexagonal boron nitride;
Doganov, R. A., Koenig, Yeo, Y., S. P., Watanabe, K., Taniguchi, T., and Özyilmaz, B.
Applied Phys. Lett. 106, 083505 (Jun 2015)
- Transport properties of pristine few-layer black phosphorus by van der Waals passivation in inert atmosphere;
Doganov, R. A., O’Farrell, E. C. T., Koenig, S. P., Yeo, Y., Ziletti, A., Carvalho, A., Campbell, D. K., Coker, D. F., Watanabe, K., Taniguchi, T., Castro Neto, A. H., and Özyilmaz, B.
Nature Comms., 6:6647 (Apr 2015)
- Air-Stable Transport in Graphene-Contacted, Fully Encapsulated Ultrathin Black Phosphorus-Based Field-Effect Transistors;
Avsar, A., Vera-Marun, I. J., Tan, J. Y., Watanabe, K., Taniguchi, T., Castro Neto, A. H., and Özyilmaz, B.
ACS Nano, 9 (4) 4138-4145 (Mar 2015)
- 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:
- Optospintronics in graphene via proximity coupling;
Avsar, A., Unuchek, D., Liu, J., Sanchez, O.L., Watanabe, K., Taniguchi, T,. Özyilmaz, B., and Kis, A.
- Gate-tunable black phosphorus spin valve with nanosecond spin lifetimes;
Avsar, A., Tan, J.Y., Kurpas, M., Gmitra, M., Watanabe, K., Taniguchi, T., Fabian, J., and Özyilmaz, B.
Nature Physics (May 2017)
- Rashba Interaction and Local Magnetic Moments in a Graphene-BN Heterostructure Intercalated with Au;
O'Farrell, E. C. T., Tan, J. Y., Yeo, Y., Koon, G. K. W., Özyilmaz, B., Watanabe, K. and Taniguchi, T.
Phys. Rev. Lett. 117, 076603 (Aug 2016)
- Electronic Spin Transport in dual-gated bilayer graphene; OPEN ARTICLE
Avsar, A. ,Vera-Marun, I. J., Tan, J. Y., Koon, G. K. W., Watanabe, K., Taniguchi, T., Adam, S., and Özyilmaz, B.
Nature Asia Materials 8, e274 (Mar 2016)
- Quantum Transport Detected by Strong Proximity Interaction at a Graphene–WS2 van der Waals Interface;
O'Farrell, E. C. T., Avsar, A., Tan, J. Y., Eda, G., and Özyilmaz, B.
Nano Letters, 15 (9) 5682-5688 (Aug 2015)
- Conductance oscillations induced by ballistic snake states in a graphene heterojunction;
Taychatanapat, T., Tan, J., Y., Yeo, Y., Watanabe, K., Taniguchi, T., and Özyilmaz, B.
Nature Comms., 6:6093 (Feb 2015)
- 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)
- 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)