Abstract:A structural phase transition, conductivity and dielectric permittivity anomalies, together with a polarization hysteresis loop which collapses above the Curie temperature ( ∼ 105°C) provide converging lines of evidence for ferroelectricity in the single and polycrystalline natural samples of chalcocite, Cu2S, investigated. Chalcocite is an important ore of copper, and its electrical properties are a factor both in exploration for the mineral and processing the ore.
“…The long range 1D and 3D ordering observed in these formations appears to result from attraction other than just asymmetric van der Waals attraction. One possibility is that the nanocrystals are ferroelectric as observed in bulk hexagonal Cu 2 S with the individual nanocrystal dipole−dipole moments aligning with respect to one another. , 3 SEM images of self-assembled three-dimensional colloidal crystals of Cu 2 S nanodisks formed via deposition of monodisperse (A) and more polydisperse (B) and (C) nanodisks from concentrated dispersions.…”
Cu2S nanocrystals with disklike morphologies were synthesized by the solventless thermolysis of a copper alkylthiolate molecular precursor. The nanodisks ranged from circular to hexagonal prisms from 3 to 150 nm in diameter and 3 to 12 nm in thickness depending on the growth conditions. High resolution transmission electron microscopy (HRTEM) revealed the high chalcocite (hexagonal) crystal structure oriented with the c-axis ([001] direction) orthogonal to the favored growth direction. This disk morphology is thermodynamically favored as it allows the extension of the higher energy {100} and {110} surfaces with respect to the {001} planes. The hexagonal prism morphology also appears to relate to increased C-S bond cleavage of adsorbed dodecanethiol along the more energetic {100} facets relative to {001} facets. Monodisperse Cu2S nanodisks self-assemble into ribbons of stacked platelets. This solventless approach provides a new technique to synthesize anisotropic metal chalcogenide nanostructures with shapes that depend on both the face-sensitive thermodynamic surface energy and the surface reactivity.
“…The long range 1D and 3D ordering observed in these formations appears to result from attraction other than just asymmetric van der Waals attraction. One possibility is that the nanocrystals are ferroelectric as observed in bulk hexagonal Cu 2 S with the individual nanocrystal dipole−dipole moments aligning with respect to one another. , 3 SEM images of self-assembled three-dimensional colloidal crystals of Cu 2 S nanodisks formed via deposition of monodisperse (A) and more polydisperse (B) and (C) nanodisks from concentrated dispersions.…”
Cu2S nanocrystals with disklike morphologies were synthesized by the solventless thermolysis of a copper alkylthiolate molecular precursor. The nanodisks ranged from circular to hexagonal prisms from 3 to 150 nm in diameter and 3 to 12 nm in thickness depending on the growth conditions. High resolution transmission electron microscopy (HRTEM) revealed the high chalcocite (hexagonal) crystal structure oriented with the c-axis ([001] direction) orthogonal to the favored growth direction. This disk morphology is thermodynamically favored as it allows the extension of the higher energy {100} and {110} surfaces with respect to the {001} planes. The hexagonal prism morphology also appears to relate to increased C-S bond cleavage of adsorbed dodecanethiol along the more energetic {100} facets relative to {001} facets. Monodisperse Cu2S nanodisks self-assemble into ribbons of stacked platelets. This solventless approach provides a new technique to synthesize anisotropic metal chalcogenide nanostructures with shapes that depend on both the face-sensitive thermodynamic surface energy and the surface reactivity.
“…Although one would expect one-dimensional ordering of this type for magnetic particles with strong magnetic dipole−dipole interactions, asymmetric van der Waals forcesalthough directionalare not expected to give rise to these structures. Both hexagonal and monoclinic forms of Cu 2 S are ferroelectric, and apparently dipole−dipole interactions are responsible for these long strands of nanorods. The potential ferroelectric properties of these nanorods are currently under investigation.…”
Organic monolayer protected Cu2S nanorods, 4 nm in diameter and 12 nm long, were synthesized using a novel solventless synthetic approach. Thermolytic degradation of a copper thiolate precursor at temperatures ranging from 140 to 200 degrees C produces Cu2S nanorods. Higher temperatures promote isotropic growth of spherical nanocrystals. X-ray diffraction and high-resolution TEM reveal that the nanorods exhibit a hexagonal Cu2S crystal structure, which in the bulk is ferroelectric. The appropriate reaction conditions produce nanorods that are size and shape monodisperse and organize into smectic superlattices. The extent of superlattice ordering and the appearance of extended strands of nanorods provide evidence for strong dipole-dipole coupling between Cu2S nanorods.
“…The orientation of deposited Cu 2 S did not appear to be influenced by the substrate and always assembled edge-down on both TEM substrates and oxide-coated Si. Although more data are needed to be certain, it appears that nanodisks of Cu 2 S have stronger attractive forces between disk faces than CuS, perhaps as a result of stronger electric dipole coupling, as hexagonal Cu 2 S has been reported to be ferroelectric. , …”
mentioning
confidence: 99%
“…Although more data are needed to be certain, it appears that nanodisks of Cu 2 S have stronger attractive forces between disk faces than CuS, perhaps as a result of stronger electric dipole coupling, as hexagonal Cu 2 S has been reported to be ferroelectric. 50,51 TEM and SEM images provide excellent snapshots of nanodisk order, but only on very small local length scales (micrometers). Scattering techniques, such as SAXS, supplement TEM and SEM imaging techniques by probing very large sample volumes (∼mm 3 ) to give an average description of average structural organization in the material.…”
The self-assembly of sterically stabilized colloidal copper sulfide nanodisks, 14-20 nm in diameter and 5-7 nm thick, was studied. The nanodisks were observed by electron microscopy and small-angle X-ray scattering to form columnar arrays when evaporated as thin films from concentrated dispersions. These superstructured nanomaterials might give rise to technologically useful properties, such as anisotropic electrical transport and electrorheological and optical properties.
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