May 9, 2014
Nanostars for hot-spot engineering
With multiple sharp edges that produce electric field hot spots, the star shape is an appealing geometry in surface enhanced Raman spectroscopy (SERS). Now, reporting in Nanotechnology and using electron beam lithography, researchers can fabricate arrays of these versatile nanostructures and tune the plasmon resonance energy simply.
Giant electromagnetic (EM) field enhancement via specifically designed metal nanostructures plays a key role in SERS. The local EM field enhancement is strongly related to the collective oscillations of the conduction electrons in the nanostructures – or the localized surface plasmon resonances (LSPRs) – that can be excited by external light irradiation. The field enhancement is obtained by the sharp features of the metastructures through the "lightning rod" effect.
Advantageous properties include the possibility of resonance tuning with respect to the available laser sources, light polarization sensitivity and control on the spatial positions of the hot spots. The star shape is a very appealing geometry in this respect because it provides multiple sharp edges that produce electric field hot spots and it allows for the precise tuning of the resonance energy by varying the overall star size.
The research group at the Italian Institute of Technology (IIT) fabricates gold nanostar arrays using electron beam lithography and metal evaporation. They are used for chemical sensing of different organic and biomolecules via SERS. The detailed experimental and theoretical study of the optical properties of nanostar arrays with different size demonstrates good wavelength tunability to standard laser sources at 630 and 830 nm. There are also very high SERS enhancement factors that allow to clearly resolve the characteristic Raman bands of the analyte molecules.
More information about the research can be found in the journal Nanotechnology 25 235303.
About the author
Dr Roman Krahne is a senior researcher at the Italian Institute of Technology (IIT). With a background in the physics of low-dimensional systems, his research is focused on the optical and electrical properties of semiconductor and metallic nanostructures.