Probing the Edges between Stability and Degradation of a Series of ZnSe‐Based Layered Hybrid Semiconductors

Abstract

The discovery of layered materials with potentially unique electrical and chemical properties has become a major focus of materials research in the past decade. 2D II–VI layered hybrids (LHs) are a family of ligand‐protected layered materials capable of isolation in few‐layer form and possess emissive and electronic properties of potential relevance to semiconductor device technologies. The authors showed previously that, akin to black phosphorus and transition metal dichalcogenides, 2D II–VI LHs are sensitive to ambient atmospheric conditions. However, the causes for degradation of these ligand‐protected materials remain unclear. Using ZnSe‐based LHs, it is shown herein that the stability of these materials is related to the length and chemistry of the organic ligands coordinated to the LH surfaces. Furthermore, exposure to isotopically enriched H218O and 18O2 reveals that H2O and O2 are both reactants contributing to ZnSe‐LH degradation. An H2O‐initiated degradation pathway is proposed and is supported by density functional theory calculations. The findings contribute to the discovery of protection strategies for layered materials and elucidate a degradation pathway that may also be applicable to other layered materials.

Degradation Kinetics of Organic–Inorganic Hybrid Materials from Micro‐Raman Spectroscopy and Density‐Functional Theory: The Case of β‐ZnTe(en)0.5

“…[29] However, in the low temperature orthorhombic phase, the molecules are locked spatially and somewhat distorted, and the structure becomes slightly more stable. [8] Similarly, the layered versions of the II-VI hybrids are also less stable, [13,25] because the molecules are unconstrained on one end, thus, less distorted. This understanding reveals an important mechanism that may simultaneously enhance both the formation energy and kinetic barrier of a superstructure-the substructure distortion enhanced stability.…”

“…It has been found that for the II-VI hybrids, degradation often starts at the edge of the samples. [17,25] To minimize the potential extrinsic sample inhomogeneity on the thermal degradation, we apply a localized probing technique that monitors the degradation of an interior region sufficiently away from any edge and free of obvious surface defect, which is more reliable than a technique probing the whole sample, as done in the past for the perovskites. [9,10] It is also desirable to use a technique that only causes minimal perturbation to the sample, for instance, Raman spectroscopy using excitation energy below the bandgap, since above-bandgap excitation often leads to photodegradation of the hybrid materials.…”