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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The morphology and structure of CuS crystals formed during sulfidation of copper behenate films obtained by the Langmuir-Blodgett (LB) method have been studied using high resolution electron microscopy. The average size of these crystals is about 3 nm and increases by a factor of approximately 2.2 after annealing at a temperature of 150 • C or above. Analysis of interplanar distances has shown that in the range of annealing temperatures of 150-200 • C, CuS nanocrystals have a P6 3/mmc hexagonal crystal lattice with parameters a = 0.38 nm and c = 1.64 nm. At annealing temperatures of 250 • C or above, the Cu2S crystalline phase begins to form, in addition to CuS nanocrystals. The proportion of this phase increases with increasing annealing temperature. Cu2S nanocrystals have a hexagonal crystal lattice type with the P6 3/mmc spatial group and unit cell parameters a = 0.39 nm and c = 0.68 nm. Quantitative evaluation of copper and sulfur in individual CuS and Cu2S nanocrystals was performed by local analysis of characteristic X-ray spectra.