Beneficial Impurities and Phase Control in Colloidal Synthesis of Tin Monoselenide

Real-time monitoring of phase transitions in π-SnS nanoparticles

While the new cubic phase of tin monosulfide, π-SnS, shows potential for various applications, not much work was focused on the phase transitions, thermal stability, and thermal properties of π-SnS. In this work, we addressed these issues using temperature-resolved in situ X-ray diffraction combined with thermo-gravimetric differential scanning calorimetry and thermo-gravimetric infrared spectroscopy. The cubic π-SnS phase nanoparticles capped with polyvinylpyrrolidone were proven stable for 12 hours at 400 °C, pointing out the possible utilization of this new cubic phase at elevated temperatures. At the same time, heating above this temperature resulted in a phase transition to the high-temperature orthorhombic β-SnS phase. Subsequent cooling to room temperature led to an additional phase transition to the stable orthorhombic α-SnS phase. Interestingly, heating-induced phase transformation of π-SnS nanoparticles always resulted in β-SnS, even at temperatures below the α- to β-SnS equilibrium transition temperature. It was shown that surfactant decomposition and evaporation triggers the phase transition. Several thermal parameters were calculated, including the phase transition activation energy and the thermal expansion of the unit cell parameter of π-SnS.

Cow-to-cow variation in nanocrystal synthesis: learning from technical-grade oleylamine

Many technical-grade reagents, including oleylamine, are broadly used as ligands in nanocrystal synthesis, allowing for cost-effective, and more environmentally friendly, preparation of materials in useful quantities. Impurities can represent 30% or more of these reagent blends, and have frequently emerged as substantial drivers of nanocrystal morphology, assembly, or other physical properties, making it important to understand their composition. Some functional alkyl reagents are derived from natural sources (e.g. often beef tallow, in the case of oleylamine), introducing alkyl chain structures very different than those that might be expected as side products of synthesis from pure feedstocks. Additionally, impurities can exhibit variations based on biological factors (e.g. species, diet, season). In biology, blends of alkyl chains allow for surprisingly sophisticated function of amphiphiles in the cell membrane, pointing to the possibility of similar control in synthetic materials if reagent composition were either better controlled or better understood. Here, we provide brief context on the breadth of roles technical-grade impurities have played in nanocrystal materials, followed by a perspective on oleylamine impurities, their physical properties, and their potential contributions to nanomaterial function.

'Beneficial impurities' in colloidal synthesis of surfactant coated inorganic nanoparticles

Colloidal synthesis of nanoparticles (NP) has advanced tremendously over the past 25 years, with an increasing number of research papers introducing nanomaterials with a variety of compositions, shapes, sizes, and phases. Although much progress has been achieved, commonly used synthetic procedures often fail to reproduce results, and the fine details of the syntheses are often disregarded. Reproducibility issues in synthesis can be ascribed to the effects of impurities, trace amounts of chemical moieties which significantly affect the reaction products. Impurities in NP synthesis are rarely reported or regularly studied, despite their impact, deleterious, or beneficial. This topical review discusses several case studies of colloidal NP synthesis where the sources and the chemistry of impurities are highlighted, and their role is examined.

Chemical epitaxy of π-phase cubic tin monosulphide

Epitaxial thin films of cubic tin monosulfide (π-SnS), a recently discovered new binary phase, were deposited from solution on GaAs substrates and on GaAs with intermediate PbS layers.