|Asst Prof Sum Tze Chien|
Division of Physics & Applied Physics
School of Physical & Mathematical Sciences
College of Science
- PhD National University of Singapore 2005
- MSc National University of Singapore 2001
- BSc(Hons) National University of Singapore 1999
- BSc National University of Singapore 1998
|Tze Chien graduated with a B.Sc. (1st Class Hon), a M.Sc. and a Ph.D. degree in Physics from the National University of Singapore, Singapore in 1999, 2001 and 2005, respectively, where he had worked on the development of a novel direct-write lithographic technique (proton beam writing) for photonic applications. In 2005, he joined the Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University as a Lecturer where he switched his research field from applied nuclear physics (proton beam writing and accelerator-based nuclear spectroscopy) to Femtosecond Laser Spectroscopy and its applications. Subsequently, he established the Femtosecond Dynamics Laboratory (xC-Lab) and a new research group at the Division of Physics & Applied Physics. He is presently an Assistant Professor and is interested in the development and application of time-resolved and time-integrated optical spectroscopic techniques to interrogate the fundamental and applied properties of materials – i.e. probing the energy and charge transfer mechanisms in semiconducting nano-heterostructures & light harvesting systems; as well as investigating the nonlinear optical properties of nano-scale systems. A brief description of the various ongoing projects can be found below. |
Tze Chien has received a total of 10 teaching awards from both the National University of Singapore (while he was a TA at the Department of Physics then) and the Nanyang Technological University, including the Nanyang Award for Excellence in Teaching in 2006 and the SPMS Teaching Excellence Award – Honour Roll 2010. He was also credited with the establishment of the 1st Year Physics Teaching Laboratory, the 3rd Year Physics Teaching Laboratory and the NTU H3 Physics Teaching Labs for the MOE H3 program.
|1. Energy Transfer and Charge Transfer Mechanisms in Semi-conducting Nano-heterostructures|
In this work, we seek to understand the dynamics of the energy transfer processes in semi-conducting nanostructure systems such as quantum dots, nanorods and nano-belts. Using femtosecond time-resolved spectroscopy, we probe these energy transfer processes in these systems that comprises of the interplay of carrier dynamics between the host energy levels, defect energy levels and the dopant energy levels. The systems we have investigated include: ZnS quantum dots, ZnO nanowires; CdSe nanodot/CdS nanorod heterostructures; ZnCdO/ZnO multiple quantum well nanowire heterostructures; CdS nano-belts. Highlights of these studies include: (a) uncovering an ultrafast electron transfer process from the ZnO host to the Cu subsystem in Cu-doped ZnO nanowires and (b) shedding new light on the photoinduced charge transfer processes in surface treated ZnO nanowires.
2. Nonlinear Optical Properties of Nano-scale systems
In this work, we seek to characterize the non-linear optical properties (e.g. nonlinear absorption coefficients and absorption cross-sections) of novel nanoscale systems that include atomic layer graphene; CdSe dot/ CdS nanorod heterostructures. Through Femtosecond time-resolved spectroscopy, we seek to understand the photophysics in these systems which give rise to these unique properties. Recent highlights include:
a. In the CdSe dot/ CdS nanorod heterostructures, we have demonstrated that CdS shell can be utilized as tunable antenna to enhance the two-photon absorption cross-section by 2-3 orders (compared to CdSe quantum dots) without affecting its emission wavelengths. We have also recently leveraged on this property to achieve two-photon pumped ASE in these heterostructures with a threshold fluence of 1-2 orders lower than CdSe quantum dots.
b. We uncovered evidence of an ultrafast carrier-carrier scattering process of ~ 8fs in atomic layer graphene and provided an insight into the physics of ultrafast saturable absorption of graphene that allows it to function as passive mode-lockers and pulse shapers.
3. Energy Transfer Mechanisms in Photovoltaic Devices
In this work, we seek to understand energy transfer mechanisms in hybrid organic photovoltaic devices, in particular that of the exciton and polaron dynamics resulting from interchain effects under device conditions (field-induced changes in the optical behaviour). Systems include hybrid Au nanowire/P3HT-PCBM photovoltaic devices and fiber-P3HT-PCBM systems. The recombination pathways will be investigated using both time-resolved photoluminescence and transient absorption spectroscopy. The knowledge gained would serve to guide the design of such organic materials in improving the PCE through chemical and structural modifications.
|Research Grant |
- Academic Research Fund Tier 1 (2009-)
- Academic Research Fund Tier 2 (2012-)
- NRF CREATE (2012-)
- NRF Competitive Research Program (2010-)
- SPMS Collaborative Research Award (2011-)
- Start Up Grant (2009-)
|Current Projects |
- Coupling between Surface Plasmons and Excitons: Towards Sub-wavelength Photonics
- Energy Transfer Mechanisms in Doped Nanoparticle Systems
- Investigating Energy & Charge Transfer Mechanisms in Hybrid Metal-Semiconductor Nano-Heterostructures
- Magneto-Optical Spectroscopy of Tunable Highly Spin Polarized Ferromagnetic Systems
- Organic Solid Solar Cell Fabricated via Water-based Processing Routes ? Studies on Materials Selection and Characterization, Fundamental Photo-physics and Device Physics
- SinBeRISE Subproject 5 - Characterization
- Toward Efficient Sunlight Harvesting
- Towards Efficient Sunlight Harvesting
- M. Kurniawan, T. Salim, K. F. Tai, S. Sun, E. J. Sie, X. Wu, E. K. L. Yeow, C. H. A. Huan, Y. M. Lam and T. C. Sum*. (2012). Carrier Dynamics in Polymer-Nanofiber:Fullerene Solar Cells. Journal of Physical Chemistry C, 116, 18015 - 18022.
- B. Wu, T. Z. Oo, X. Li, X. Liu, X. Wu, E. K. L. Yeow, H Fan, N. Mathews and T. C. Sum*. (2012). Efficiency enhancement in Bulk-Heterojunction Solar Cells integrated with large area Ag nano-triangle arrays. Journal of Physical Chemistry C, .
- Mingjie Li, Guichuan Xing, Lloyd Foong Nien Ah Qune, Guozhong Xing, Tom Wu, Cheng Hon Alfred Huan, Xinhai Zhang, and Tze Chien Sum*. (2012). Tailoring the charge carrier dynamics in ZnO nanowires: the role of surface hole/electron traps. Physical Chemistry Chemical Physics, 14, 3075 - 3082.
- Guozhong Xing, Guichuan Xing, Mingjie Li, Edbert Jarvis Sie, Dandan Wang, Arief Sulistio, Quan-lin Ye, Cheng Hon Alfred Huan, Tom Wu, and Tze Chien Sum*. (2011). Charge transfer dynamics in Cu-doped ZnO nanowires. Applied Physics Letters, 98(10), 102105.
- G. C. Xing, H. C Guo, X. H. Zhang, T. C. Sum* and C. H. A. Huan. (2010). The Physics of Ultrafast Saturable Absorption in Graphene. Optics Express, 18, 4564.