Elucidating Piezoelectricity and Strain in Monolayer MoS₂ at the Nanoscale Using Kelvin Probe Force Microscopy

Strain engineering modifies the optical and electronic properties of atomically thin transition metal dichalcogenides. Highly inhomogeneous strain distributions in two-dimensional materials can be easily realized, enabling control of properties on the nanoscale; however, methods for probing strain on the nanoscale remain challenging. In this work, we characterize inhomogeneously strained monolayer MoS2 via Kelvin probe force microscopy and electrostatic gating, isolating the contributions of strain from other electrostatic effects and enabling the measurement of all components of the two-dimensional strain tensor on length scales less than 100 nm. The combination of these methods is used to calculate the spatial distribution of the electrostatic potential resulting from piezoelectricity, presenting a powerful way to characterize inhomogeneous strain and piezoelectricity that can be extended toward a variety of 2D materials

Electrically Activated UV‑A Filters Based on Electrochromic MoO_3–<i>x</i>

Chromism-based optical filters is a niche field of research, due to there being only a handful of electrochromic materials. Typically, electrochromic transition metal oxides such as MoO3 and WO3 are utilized in applications such as smart windows and electrochromic devices (ECD). Herein, we report MoO3–x-based electrically activated ultraviolet (UV) filters. The MoO3–x grown on indium tin oxide (ITO) substrate is mechanically assembled onto an electrically activated proton exchange membrane. Reversible H+ injection/extraction in MoO3–x is employed to switch the optical transmittance, enabling an electrically activated optical filter. The devices exhibit broadband transmission modulation (325–800 nm), with a peak of ∼60% in the UV-A range (350–392 nm). Comparable switching times of 8 s and a coloration efficiency of up to 116 cm2 C–1 are achieved