Singapore Synchrotron Light Source

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SSLS PhD projects

Statistical analysis of reconstruction algorithms in phase contrast tomographic imaging


Phase contrast tomographic imaging is commonly used to increase image contrast by highlighting small details of differing refractive index within structures that are otherwise uniform. It is widely used in biological, medical and geological science. Propagation-based phase contrast uses free-space propagation to give edge enhancement. This method however require more sophisticated source of X-rays such as synchrotron and more complicated data evaluation algorithms. In this project a procedure for quantitative quality control of tomographic reconstruction algorithms will be established. It is based on evaluation of correct reproduction of phase boundaries. Indirectly this monitors accurate reproduction of a variety of locally defined image features such as interface positions, microstructures, cracks and pores. Statistical analysis of tomographic results will provide the knowledge about quality of the reconstruction. The reconstruction algorithms will be also tested for computational speed and robustness in the presence of tomographic artifacts and errors of the local nature.


Evaluation of multivariate classification techniques in Fourier Transform Infra-red spectra of biological samples


Fourier Transform Infra-red (FTIR) spectroscopy is a method based on measurement of vibrations of molecules which are excited by IR radiation at a specific wavelength range. Complex (from the point of FTIR spectroscopy) samples such as biological material produce overlapping spectra, which may lead to misinterpretation of results. Thus careful data collection, proper pre-processing and application of the statistical analysis of spectra is required. A chemometric approach in the analysis and classification of spectral data sets using open source software (R platform) will be used in this project. Various supervised and unsupervised statistical techniques (like principal component analysis, hierarchical cluster analysis, soft independent modeling by class analogy and artificial neural network) will be tested for specificity and selectivity.


Assessment of traditional herbal medicines using synchrotron radiation


Herbal medicines have a history of documented use in healing over thousands of years, and are still used widely in many cultures around the world. According to World Health Organization, it is estimated that about 70–80% of the world's population relies on non-conventional medicine, mainly of herbal origin in their primary healthcare. The quality of pharmaceutical products is very important in order to ensure safety of consumers. However most of the herbal products are not regulated as they are considered as dietary supplements and not medicines. Taking into account the nature and sources of herbal medicines, they may be contaminated with some toxic elements, or in case of expensive herbs can be adulterated with cheaper substitutes; posing serious health risks to patients. In this work various herbal medicines will be analyzed by means of synchrotron radiation based methods; namely SRIXE (Synchrotron Radiation Induced X-ray Emission), XAFS (X-ray Absorption Fine Structure) and FTIR (Fourier Transform Infrared) spectroscopy to determine the local structure and concentration level of toxic elements within them, as well as to describe infrared fingerprint pattern of their various constituents. Chemometric techniques will be used to develop a rapid method of distinguishing the real products from fake ones.


Forensic investigation of human hair fibers using FTIR spectroscopy


Hair fibers are a common evidence type found at crime scenes, being the result of some form of physical contact between the perpetrator and the victim and/or the surrounding. Unless they are destroyed by fire or chemicals, the fibers maintain their structural integrity for a longer period of time than most other tissue types. Light microscopy is routinely used in forensics to determine if an unknown hair sample could have originated from a known source. Forensic scientists are trained to identify and correlate physical hair features and appearances to a particular ethnic group. This information may be useful in identifying potential suspects but more information is necessary in order to prove beyond a reasonable doubt that a suspect is guilty or innocent. Therefore, a reliable and flexible analytical technique is necessary to provide both visual and chemical information. Synchrotron radiation based Fourier Transform Infrared (SR-FTIR) micro-imaging has been developed as a rapid, direct and non-destructive technique. This method takes advantage of synchrotron light brightness and a small effective source size, and is capable of exploring the molecular chemistry within the microstructures without the destruction of inherent structures at high resolution. FTIR has become increasingly valuable forensic technique within last decades because of its detection sensitivity and versatility. FTIR micro-imaging can combine visual microscopic hair fiber analysis with valuable and discriminating infrared chemical information. Hair fiber chemical information can reveal residual hair styling products and protein structure changes due to chemical treatments. This additional information may prove essential in identifying a suspect.


Diffractometry Characterization of Strain in Nano-meter Scale


In the research and development of advanced processing technology for Integrated Circuit (IC) manufacturing, strain engineering plays an important role. The key point of strain engineering is that the carriers in the channel of the MOSFET can have a different mobility under different strain states, thus yielding large differences in the performance of the MOSFETs. Higher mobility induced by the strain in the channel area gives a larger on-state current, which is the expected for high switching speed.

Since the 65nm generation of ICs, the strained SiGe technique for the PMOS Source/Drain area has contributed to the scaling-down strategy. It is believed that the strained Source/Drain could transfer stress to the channel area between the source and drain, and thus help the PMOSFET to perform better. For NMOSFET, the strain could transfer stress to the channel as well to improve electron mobility. When the devices are scaled down to the sub-22nm generation, a directly strained channel is induced artificially by forming a Ge channel or III-V compound channel to improve device performance.

We propose to develop nano-meter X-ray topography (nm-XRT) in conjunction with transmission X-ray microscopy (TXM) in full-field mode for revealing defects and strain fields in crystalline materials. More quantitatively, the strain inside the channel area of strained Si, Ge or III-V compound epitaxial layers on Si substrate will be analyzed using a nano-meter focused X-ray beam, with a size of 10-30nm. The methods can be in-situ, non-invasive probing and non-destructive. The experimental work will be done in Singapore Synchrotron Light Source (SSLS) and other synchrotron radiation sources. Students from Electronic Engineering, Physics and Material Science are welcome to join the study.

Project supervisor:
Dr. Yang Ping, Singapore Synchrotron Light Source (SSLS), National University of Singapore,


For further enquiries please contact:

Professor Mark B H Breese (Director)
5 Research Link
Singapore 117603