Electron microscopic studies of CuS nanocrystals formed in Langmuir-Blodgett films

Abstract

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.

Synthesis and Characterization of CuxS (x = 1–2) Nanocrystals Formed by the Langmuir–Blodgett Technique

“…Typical diffraction patterns of the samples with Cu x S NCs annealed at (a) 150, (b) 250, and (c) 400 °C. The indexing is taken from ref …”

“…At the second stage, the nucleation of Cu x S nanoclusters in the organic matrix took place by sulfidizing the structure. The existence of Cu x S nanoclusters with an average size of 3 nm and areal density of 10 11 cm –2 formed in the organic matrix was confirmed by high-resolution transmission electron microscopy (HRTEM) . Because of the small size of Cu x S nanoclusters, establishing their crystallinity is hardly possible by HRTEM.…”

“…The existence of Cu x S nanoclusters with an average size of 3 nm and areal density of 10 11 cm −2 formed in the organic matrix was confirmed by highresolution transmission electron microscopy (HRTEM). 32 Because of the small size of Cu x S nanoclusters, establishing their crystallinity is hardly possible by HRTEM. At the last stage, 4 h annealing in a temperature range of 120−400 °C in an Ar atmosphere resulted in the removal of the matrix and the formation of free-standing Cu x S NCs on a solid substrate (bare Si, Au, and Pt).…”

“…Upon temperature annealing in the range of 120−400 °C, the crystals reveal a hexagonal symmetry. A more detailed HRTEM analysis of Cu x S NCs was performed by Gutakovskii et al32…”