In this thesis a new top-down nanofabrication technology was developed, to realize gold nanowire arrays with tunable separation nanogaps. ‘Reaching nanogaps down to 5 nm enabled huge surface-enhanced Raman Scattering factors, which was a great achievement,’ Le Thi Ngoc Loan says. ‘On top of that, the gaps could precisely be tuned, to match the wavelengths of common laser sources.’
In the top-down fabrication technology developed here, Loan achieved the realization of high-density gold nanowire arrays, without chemical etching or milling the metal layers. The huge and highly reproducible surface-enhanced Raman scattering (SERS) enhancements over large electromagnetic field areas, led to several types of measurements in this thesis work.
‘These findings resulted in four publications, in ACS Nano, the Journal of Physical Chemistry C, Optics Express, and Analytical Chemistry.’ Loan is proud to say.
Efforts to measure non-resonant vibrational spectra from single molecules was not conclusive yet. ‘However, we observed certain trends in the well known background continuum in the SERS spectra, which turned out to be very fruitful,’ Loan says. ‘We were able to resolve two different plasmon-enhanced photoluminescence processes that are dependant on the wavelength of the laser source, and we were able to convincingly explain the SERS background signal. This work led to a publication in Optics Express.’
In the last year of her PhD project, Loan and her MESA+ colleagues from the BIOS Lab-on-a-Chip Group, collaborated with the Analytical and Organic Chemistry Group at the University of Groningen (RUG).
Loan: ‘We succeeded in implementing a SERS spectroelectrochemical analysis system, by combining our SERS substrate with a small volume microfluidic sample chamber. The system is not yet optimized. More research is required before this will be a routine analytical technique.’
After her PhD-defence Loan plans to return to her hometown, and work at the University of Quy Nhon. ‘By teaching talented students I hope to stimulate interest in the research topics that I encountered during my PhD and master degree projects. Furthermore, I plan to start my research group on developing SERS analytical systems. But first I have to build up the required facilities and expertise.’