In the colloidal synthesis of iron sulfides, a series of dialkyl disulfides, alkyl thiols, and dialkyl disulfides (allyl, benzyl, tert-butyl, and phenyl) were employed as sulfur sources. Their reactivity was found to tune the phase between pyrite (FeS2), greigite (Fe3S4), and pyrrhotite (Fe7S8). DFT was used to show that sulfur-rich phases were favored when the C–S bond strength was low in the organosulfurs, yet temperature dependent studies and other observations indicated the reasons for phase selectivity were more nuanced; the different precursors decomposed through different reaction mechanisms, some involving the oleylamine solvent. The formation of pyrite from diallyl disulfide was carefully studied as it was the only precursor to yield FeS2. Raman spectroscopy indicated that FeS2 forms directly without an FeS intermediate, unlike most synthetic procedures to pyrite. Diallyl disulfide releases persulfide (S–S)2– due to the lower C–S bond strength relative to the S–S bond strength, as well as facile decomposition in the presence of amines through SN2′ mechanisms at elevated temperatures.

Cation exchange is a versatile postsynthetic technique that has been exploited in the synthesis of metastable nanocrystals through preservation of the anion sublattice. Here, we report on the mechanistic details of the synthesis of metastable Au 2 S via cation exchange with Cu 2−x S nanocrystals. This conversion requires a transformation of the anion sublattice, from hexagonal close-packed in Cu 2−x S to body-centered cubic in Au 2 S, accompanied by an expansion of the unit cell. The ligand environment plays a key role in the driving force of the reaction as the presence of oleylamine allows the conversion to proceed at room temperature, whereas the addition of trioctylphosphine hinders the reaction. By employing transmission electron microscopy (TEM) on faceted nanocrystals and partial cation exchange of nanocrystals, it was demonstrated that the reaction proceeds in a highly directional manner through the pyramidal facets. Since cation exchange produces high-quality nanocrystals as seen through Xray diffraction and TEM, UV−vis and Raman spectroscopy were used to characterize the optoelectronic properties of the metastable Au 2 S nanocrsytals. A Tauc plot analysis revealed a band gap of 2.6 eV, whereas two intrinsic Raman modes were identified at 265 and 329 cm −1 . Density functional theory calculations of structures, energy bands, optical spectra, and phonon spectra were performed and combined with the experimental data to provide additional insights into the characterization of Au 2 S nanocrystals.

The ternary copper chalcogenide semiconductor nanoparticles have gained much attention as their optical properties make them ideal candidates for many applications ranging from photovoltaics to bioimaging. While their synthesis is well documented, there have been few reports on the synthesis of ternary copper chalcogenide−metal hybrid nanoparticles, which can further expand the list of potential applications through synergistic properties. To this end, Pt− CuInS 2 hybrids have been synthesized by a two-step approach in high boiling organic solvents. The hybrid nanostructures were characterized employing transmission electron microscopy, X-ray diffraction, UV−Vis spectroscopy, and energydispersive X-ray spectroscopy mapping. We find that during hybrid nanoparticle synthesis under conditions modified from typical Pt nanoparticle reaction schemes, a near-complete shell of Pt forms on the semiconductor nanoparticles. Careful control of the reactivity of the Pt precursor, through choice of organic reducing agent and Pt coordinating ligands, was successfully used to obtain controlled and isolated domains on the semiconductor nanoparticles. This strategy was further extended for the synthesis of Pd−CuInS 2 hybrids.

Magnetic stability of iron mineral phases is a key for their use as paleomagnetic information carrier and their applications in nanotechnology, and it critically depends on the size of the particles and their texture. Ferrimagnetic greigite (Fe3S4) in nature and synthesized in the laboratory forms almost exclusively polycrystalline particles. Textural effects of inter-grown, nano-sized crystallites on the macroscopic magnetization remain unresolved because their experimental detection is challenging. Here, we use ferromagnetic resonance (FMR) spectroscopy and static magnetization measurements in concert with micromagnetic simulations to detect and explain textural effects on the magnetic stability in synthetic, polycrystalline greigite flakes. We demonstrate that these effects stem from inter-grown crystallites with mean coherence length (MCL) of about 20 nm in single-domain magnetic state, which generate modifiable coherent magnetization volume (CMV) configurations in the flakes. At room temperature, the instability of the CVM configuration is exhibited by the angular dependence of the FMR spectra in fields of less than 100 mT and its reset by stronger fields. This finding highlights the magnetic manipulation of polycrystalline greigite, which is a novel trait to detect this mineral phase in Earth systems and to assess its fidelity as paleomagnetic information carrier. Additionally, our magneto-spectroscopic approach to analyse instable CMV opens the door for a new more rigorous magnetic assessment and interpretation of polycrystalline nano-materials.