Surface enhanced Raman spectroscopy of the liquid crystal 8CB using chip structures

• Published in: Physica Status Solidi (b) Vol. 245; no. 10; pp. 2193 - 2196
• Main Authors: Plank, W., Hulman, M., Kuzmany, H., Köck, A., Roppert, K., Kukovecz, A., Krenn, J., Bischof, R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Berlin WILEY-VCH Verlag 01-10-2008; WILEY‐VCH Verlag; Wiley
• Subjects: 33.20.Fb; 63.22.Np; 71.45.Gm; 78.30.Jw; 78.66.Qn; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Infrared and raman spectra and scattering; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Physics; Nanoparticles; Raman spectra; Investigation method; SERS; Colloids; Benzenic compound; Liquid crystals; Optimization
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.200879653

Molecular nanostructures are excellent systems to study surface enhanced Raman scattering (SERS), since monolayers or sub‐monolayers are expected to provide maximum scattering enhancement. The SERS enhancement is due to a plasma induced field enhancement by metallic nanoparticles. By this effect the Raman response of molecules in the immediate neighborhood of the particles can be dramatically increased. We investigated the SERS effect of Ag colloids on glass substrates and on lithographically produced nanostructures of gold and aluminum on silicon and ITO‐glass.
For testing extremely thin layers (monolayers and submonolayers) of 4‐octyl‐4′‐cyanobiphenyl (liquid crystal 8CB) were prepared. The observed enhancement for 8CB on Ag colloids was about 103. Enhancement factors for the lithographic structures were initially below 100. To increase the enhancement the Au nanostructures were coated with a 20 nm thick Ag‐layer. Optimisation of the Ag nanoparticle geometry was investigated as an alternative SERS improvement routine. The viability of the chip structures for multiple usage was tested. The experimental analysis was supported by calculations of the SERS cross‐section for different structure geometries. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)