Raman spectroscopic investigation of the single-monolayer Langmuir–Blodgett film of C 16NaphOH and C 10AzoNaphC 4N-SDS

Abstract

Raman spectra were measured for Langmuir–Blodgett (LB) films of C 16NaphOH and C 10AzoNaphC 4N-SDS on Calcium Fluorite substrate for the first time. In order to find out favorable excitation condition, Raman spectra of the single and multi-monolayer LB films excited at different lines at 244, 514, 633 and 778 nm are recorded and compared in the present study. Raman spectrum of the monolayer LB film of C 16NaphOH excited by 244 nm demonstrate that excellent signal to noise is achieved even for one monolayer LB film with an extremely short integrating time as 60 s because of being resonantly enhanced, while no meaningful spectra were recorded under the same condition for the monolayer LB film of C 10AzoNaphC 4N-SDS because of burning. Using a HeNe 633 nm excitation the problem with strong substrate fluorescence was partially solved, since under these conditions this fluorescence is mainly outside the fingerprint region of the LB film molecules (1000–2000 cm −1). Therefore by using the HeNe laser excitation, Raman spectra with high signal to noise ratio of LB films of C 16NaphOH were collected and shown in this paper. These findings stress again the necessity to define an appropriate Raman system for this special application of LB film diagnosis.