Research Group Website
Near-field scanning Raman microscopy (NSRM)
Our group has very recently achieved the first demonstration of near-field Raman signal that is comparable or stronger than the far-field signal, which is 104 times stronger than the traditional near-field Raman signal. We are currently currying out near-field Raman imaging experiment using the new technique. This achievement is a very significant milestone in the near-field Raman development as it allows, for the first time, structural imaging with spatial resolution of 100 nm or batter in reasonable time, i.e. minutes to a couple of hours, rather than days. This system could provide the first non-destructive nano-characterization tool for structural analysis of any samples. Our paper, "Preparation of cantilevered W tips for atomic force microscopy and apertureless near-field scanning optical microscopy", published in Review of Scientific Instruments 73, 2942 (2002), has been selected for the August 5, 2002 issue of the VIRTUAL JOURNAL OF NANOSCALE SCIENCE & TECHNOLOGY. A US patent has been approved (US patent No. 6,643,012). A Raman manufacturer, Renishaw plc, has provided cash contribution ($45K and other materials support) to work with our group to commercialize our invention.
Titanium silicide formation by laser annealing
Titanium disilicide exhibits many excellent characteristics such as low electric resistivity, high adherence to Si, good thermal stability, and compatibility with the self-aligned silicidation. TiSi2 has been extensively used in VLSI and ULSI. However, the traditional processing method using RTA is not suitable for their use in the 0.25 micron technology as the grain size (100-200 nm) is too big and the formation of the preferred C54 phase is more difficult for narrower lines. (1) In collaboration with Chartered Semiconductor Manufacturing (CSM) and Gintic Institute of Manufacturing Technology, we are the first lab to have formed C54 successfully using laser annealing. Moreover, the grain size is extremely small (~20 nm) demonstrating distinct advantages of this technique. Laser annealing will be expanded to processing other materials, such as Co silicide, activation of dopants in semiconductors, selective heating of buried layers. (2) We have also achieved the pure TiSi2 C40 phase, a new phase which can be used as a template to grow C54 TiSi2, without doping using laser annealing of Ti/Si samples for the first time. We have demonstrated that C54 can easily grow on C54 at much lower temperatures. A US patent has been granted. Our work on laser-induced formation of metal silicides has been reported in the electronic newsletter ADVANCED COATINGS & SURFACE TECHNOLOGY ALERT published by Wiley.
Metal or semiconductor/Si interface roughness evaluation using Raman imaging
We have devised a convenient and non-destructive technique to use micro Raman imaging to evaluate the metal or semiconductor film/Si interface roughness which is critically important for the fabrication of Si based IC devices. A US patent is under preparation for this invention.
Effects of strain/stress on semiconductor quantum dots and nano-systems
Many interesting and unique properties of nanomaterials arise because of its sizes, shapes and different surfaces/interfaces. The nano-sized materials can also be used as building blocks to assemble new generations of nanoscale electronic circuits and photonic devices. In particular, the rapid evolution of QD studies has opened up the possibility of building devices that reveal both classical and quantum features, for example the promising application of quantum communications and quantum computation using semiconductor QDs. However, there are still many challenging questions to be answered in terms of both fundamental understanding and potential applications. In this proposal, we deal with one of such critical problems – interface strain/stress in semiconductor QD and nano-devices, using a combination of theoretical and experimental approaches.
Raman study of pressure-induced amorphization and phase transitions in ferroelectric nonlinear optical crystals
The barium titanate family ferroelectric materials have outstanding electro-optical, non-linear optical and photorefractive properties, and have found widespread applications in nonlinear optics and electro-optics. They are also the prototype perovskite ferroelectrics and their successive phase transitions provide the typical examples for the study of paraelectric and ferroelectric transitions. The phase transitions and phase stability of these materials with temperature and pressure are investigated. The samples studied include, KNbO3, NaNbO3, KIO3, KTiOAsO4, a-NaVO3, b-NaVO3, and LiVO3.