Divergent Vibrational Property Induced by an Anomalous Layer Sequence in Two-Dimensional GaPS4.

Recently, various fundamental properties of GaPS4 such as anisotropy and strain-induced properties have been reported, but the impacts of the stacking sequence in layered materials remain ambiguous. This ambiguity is evident in the inconsistent Raman scattering data reported for GaPS4, suggesting a significant influence of stacking order on its physical properties. To demonstrate the discrepancies, this study investigates the vibrational characteristics of 2D GaPS4 under different stacking sequences using both experimental observations and theoretical models (AA and AB sequences) through density functional theory calculations. The results of our theoretical calculations revealed that the identical stacking sequence structure significantly influences the vibrational configurations of GaPS4, which results in divergent configurations of Raman scattering spectra including unidentified Raman peaks. Our study addresses not only the clarification of the ambiguity of experimental observations but also qualitative criteria to evaluate the degree of each stacking sequence.

Mitigating substrate effects of van der Waals semiconductors using perfluoropolyether self-assembled monolayers.

The properties of transition metal dichalcogenides (TMDCs) are critically dependent on the dielectric constant of substrates, which significantly limits their application. To address this issue, we used a perfluorinated polyether (PFPE) self-assembled monolayer (SAM) with low surface energy to increase the van der Waals (vdW) gap between TMDCs and the substrate, thereby reducing the interaction between them. This resulted in a reduction in the subthreshold swing value, an increase in the photoluminescence intensity of excitons, and a decrease in the doping effect by the substrate. This work will provide a new way to control the TMDC/dielectric interface and contribute to expanding the applicability of TMDCs.

Uncertainty evaluation of photoluminescence quantum yield measurement in an integrating hemisphere-based instrument.

We present an integrating hemisphere-based (i.e., a variant of integrating spheres) implementation of the indirect illumination method for absolute photoluminescence quantum yield measurements, which is a recommended method in the international standard IEC 62607-3-1:2014. We rigorously formulated a mathematical model and a measurement procedure for the absolute photoluminescence quantum yield measurement in the integrating hemisphere-based system. The measurement system was calibrated using an Hg-Ar discharge lamp and spectral irradiance standard lamps for wavelength and relative spectral radiant flux scales, respectively. Furthermore, we identified and evaluated uncertainty components involved in the photoluminescence quantum yield (PLQY) measurement. To validate our measurement system, we applied it to the two de facto standard dyes: quinine bisulfate (QBS) and fluorescein (FLS). Consequently, their PLQY values were determined to be 0.563±0.024 (k=2) and 0.876±0.032 (k=2) for, respectively, QBS and FLS, which are consistent with previous reports.