Sulfur Precursor Conversion Pathways in Phase Control of Cu_2-xS Nanocrystals

Area of Science:

• Materials Science
• Nanotechnology
• Inorganic Chemistry

Background:

• Phase control of copper sulfide (Cu2-xS) nanocrystals (NCs) is vital for applications.
• Colloidal synthesis has explored various sulfur precursors, but conversion pathways remain unclear.
• Understanding precursor conversion is key to tailoring NC properties.

Purpose of the Study:

• To investigate the conversion pathways of thiourea (TU) in oleylamine (OAm).
• To identify reactive sulfur species generated during TU pyrolysis.
• To establish the link between these species and the resulting Cu2-xS NC phases.

Main Methods:

• Colloidal synthesis of Cu2-xS NCs using TU as a sulfur precursor in OAm.
• Analysis of pyrolysis intermediates and reactive sulfur species.
• Phase characterization of synthesized Cu2-xS NCs.

Main Results:

• Thiourea pyrolysis in OAm yields CS2, H2S, and N,N'-disubstituted TU.
• H2S is linked to cubic-phase digenite (Cu1.8S) NCs.
• N,N'-disubstituted TU is linked to hexagonal-phase djurleite (Cu1.94S) NCs.
• These pathways were extended to synthesize Cu-In-S and Cu-Sn-S NCs with desired phases.

Conclusions:

• The conversion pathways of sulfur precursors directly influence the phase of metal sulfide NCs.
• Identifying reactive sulfur species provides control over NC polymorphism.
• This approach offers a promising route for synthesizing phase-controlled metal sulfides.