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Surface- and tip-enhanced resonant Raman scattering (resonant SERS and TERS) by optical phonons in a monolayer of CdSe quantum dots (QDs) is demonstrated. The SERS enhancement was achieved by employing plasmonically active substrates consisting of gold arrays with varying nanocluster diameters prepared by electron-beam lithography. The magnitude of the SERS enhancement depends on the localized surface plasmon resonance (LSPR) energy, which is determined by the structural parameters. The LSPR positions as a function of nanocluster diameter were experimentally determined from spectroscopic micro-ellipsometry, and compared to numerical simulations showing good qualitative agreement. The monolayer of CdSe QDs was deposited by the Langmuir-Blodgett-based technique on the SERS substrates. By tuning the excitation energy close to the band gap of the CdSe QDs and to the LSPR energy, resonant SERS by longitudinal optical (LO) phonons of CdSe QDs was realized. A SERS enhancement factor of 2 × 10(3) was achieved. This allowed the detection of higher order LO modes of CdSe QDs, evidencing the high crystalline quality of QDs. The dependence of LO phonon mode intensity on the size of Au nanoclusters reveals a resonant character, suggesting that the electromagnetic mechanism of the SERS enhancement is dominant. Finally, the resonant TERS spectrum from CdSe QDs was obtained using electrochemically etched gold tips providing an enhancement on the order of 10(4). This is an important step towards the detection of the phonon spectrum from a single QD.

Here, we present the results on the investigation of structural and vibrational properties of Cu x S (x = 1−2) nanocrystals formed using the Langmuir−Blodgett technique. The synthesis requires deposition of high quality Langmuir− Blodgett films of copper behenates on a solid substrate (Si, Au, and Pt). The Langmuir−Blodgett film is then sulfidized, what results in the formation of the copper sulfide nanocrystals embedded in behenic acid matrix. Finally, free-standing Cu x S nanocrystals are obtained after temperature annealing at 120−400 °C in an Ar atmosphere. Morphology (size, shape, and areal density) and the crystal structure of nanocrystals were determined by direct structural methods including scanning and transmission electron microscopies and high-energy electron diffraction. Surface-enhanced Raman scattering (SERS) by optical phonons in Cu x S nanocrystals in the vicinity of metal nanoclusters provided a significant enhancement factor (about 25) and allowed the fine structure of their phonon spectrum to be observed. SERS spectra of Cu x S nanocrystals under annealing reveal the high frequency shift of optical phonon modes from 475 to 492 cm −1 , which is explained by the existence of minor copperdeficient crystal phases. The combination of surface-enhanced Raman scattering spectroscopy, electron diffraction, and electron transmission microscopy allowed us to establish at least three stable phases: CuS, Cu 1.8 S, and Cu 2 S.

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