Surface-enhanced Raman scattering by colloidal CdSe nanocrystal submonolayers fabricated by the Langmuir–Blodgett technique

Abstract

SummaryWe present the results of an investigation of surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on both arrays of Au nanoclusters and Au dimers using the Langmuir–Blodgett technique. The coverage of the deposited NCs was less than one monolayer, as determined by transmission and scanning electron microscopy. SERS by optical phonons in CdSe nanocrystals showed a significant enhancement that depends resonantly on the Au nanocluster and dimer size, and thus on the localized surface plasmon resonance (LSPR) energy. The deposition of CdSe nanocrystals on the Au dimer nanocluster arrays enabled us to study the polarization dependence of SERS. The maximal SERS signal was observed for light polarization parallel to the dimer axis. The polarization ratio of the SERS signal parallel and perpendicular to the dimer axis was 20. The SERS signal intensity was also investigated as a function of the distance between nanoclusters in a dimer. Here the maximal SERS enhancement was observed for the minimal distance studied (about 10 nm), confirming the formation of SERS “hot spots”.

Vibrational spectroscopy of compound semiconductor nanocrystals

“…NCs of ZnO, for instance, can be formed through thermal oxidation of zinc behenate films in air at a temperature of 400 °C-600 °C [51]. The LB technique was also adapted for homogeneous deposition of NC arrays of colloidal NCs [57][58][59][60][61][62][63].…”

“…Anisotropy causes the splitting of the plasmonic mode polarized along and perpendicular to the long dimer axis. The splitting value increases with decreasing gap between Au nanoclusters in a dimer as shown in figure 29(b) [61,[390][391][392]. While the LSPR energy for Au nanoclusters and dimers varies gradually in the red spectral range, an array with optimal structural parameters can be chosen for SERS experiments.…”

Surface-Enhanced Infrared Absorption by Optical Phonons in Nanocrystal Monolayers on Au Nanoantenna Arrays

“…Monolayers of colloidal CdSe NCs with a size of (5.0 ± 0.3) nm purchased from Lumidot were homogeneously deposited on specially prepared plasmonic substrates by means of the modified LB technique as described in ref . LB is a well-proven technique for fabricating both highly ordered organic films and NCs with controlled areal density , on solid substrates.…”

“…Monolayers of colloidal CdSe NCs with a size of (5.0 ± 0.3) nm purchased from Lumidot were homogeneously deposited on specially prepared plasmonic substrates by means of the modified LB technique as described in ref 21. LB is a well-proven technique for fabricating both highly ordered organic films 29 and NCs with controlled areal density 20,21 on solid substrates. The size, shape, and areal density of CdSe NCs, as well as structural parameters of nanoantennas (length, width, period) were determined by SEM using the same Raith-150 system at 10 kV acceleration voltage, 30 μm aperture, and 6 mm working distance.…”

“…SERS by confined and surface optical phonons in semiconductor nanostructures including CdS, ,, CdSe, ,,− Cu x S, ,− and ZnO , NCs and GaN, AlN, and ZnO , nanorods was observed and investigated by different groups. A strong SERS enhancement by surface optical (SO) modes with the gain factor up to 10 4 was reported for ZnO nanostructures. , The vibrational response from localized optical phonons in CdSe NC arrays of a low areal density down to a few NCs per square micrometer was also probed by SERS. , …”