A class of wide bandgap van der Waals materials termed II-VI layered hybrids (II-VI LHs) are capable of broad-band white light-emission and possess potentially high charge carrier mobility. However, only the properties of the bulk (non-exfoliated) material have been studied; their few- or single-layer counterparts remain unexamined by experiment. We demonstrate the exfoliation of two of LHs, ZnSe(ba) (ba = n-butylamine) and ZnSe(oa) (oa = n-octylamine) by shear mixing for the first time, and the results show that shear exfoliation can produce II-VI LH dispersions having concentrations comparable to those achievable with shear-exfoliated graphene. Casting on substrates reveals shear-thinned sheets, the thinnest of which have thicknesses of just 4 nm, corresponding to bilayer ZnSe(alkylamine). However, structural rearrangement and chemical degradation occur during exfoliation, and our experimental results support that shear rate, exfoliation solvent, alkylamine identity, and environmental exposure all play important roles in the stability of these materials. To develop a better understanding of how ligand identity influences the degradation rate, a series of ZnSe(alkylamine) lamellar hybrids are successfully synthesized by ligand metathesis. Analysis by diffuse reflectance spectroscopy and contact angle measurements show that degradation rate is inversely related to ligand length. Metathesis with cyclic and heteroatom ligands show that hydrophilicity also plays a role in the stabilization of this class of materials. Exposure to isotopically enriched water and dioxygen and subsequent analysis by dynamic secondary ion mass spectrometry shows that both water and dioxygen are chemical reactants in the LH degradation process. A water-initiated degradation pathway is proposed and is supported by density functional theory (DFT) calculations.

Dimensional reduction and chemical stability of a series of ZnSe-based layered hybrid semiconductors

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.