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Two-dimensional (2D) transition metal dichalcogenide (TMD) layers have gained increasing attention for a variety of emerging electrical, thermal, and optical applications. Recently developed metallic 2D TMD layers have been projected to exhibit unique attributes unattainable in their semiconducting counterparts; e.g. , much higher electrical and thermal conductivities coupled with mechanical flexibility. In this work, we explored 2D platinum ditelluride (2D PtTe 2 ) layers – a relatively new class of metallic 2D TMDs – by studying their previously unexplored electro-thermal properties for unconventional window applications. We prepared wafer-scale 2D PtTe 2 layer-coated optically transparent and mechanically flexible willow glasses via a thermally-assisted tellurization of Pt films at a low temperature of 400 °C. The 2D PtTe 2 layer-coated windows exhibited a thickness-dependent optical transparency and electrical conductivity of >10 6 S m −1 – higher than most of the previously explored 2D TMDs. Upon the application of electrical bias, these windows displayed a significant increase in temperature driven by Joule heating as confirmed by the infrared (IR) imaging characterization. Such superior electro-thermal conversion efficiencies inherent to 2D PtTe 2 layers were utilized to demonstrate various applications, including thermochromic displays and electrically-driven defogging windows accompanying mechanical flexibility. Comparisons of these performances confirm the superiority of the wafer-scale 2D PtTe 2 layers over other nanomaterials explored for such applications. 

Modern electronics have been geared toward exploring novel electronic materials that can encompass a broad set of unusual functionalities absent in conventional platforms. In this regard, two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductors are highly promising, owing to their large mechanical resilience coupled with superior transport properties and van der Waals (vdW) attraction-enabled relaxed assembly. Moreover, 2D TMD heterolayers based on chemically distinct constituent layers exhibit even more intriguing properties beyond their mono-component counterparts, which can materialize only when they are manufactured on a technologically practical wafer-scale. This mini-review provides a comprehensive overview of recent progress in exploring wafer-scale 2D TMD heterolayers of various kinds. It extensively surveys a variety of manufacturing strategies and discusses their scientific working principles, resulting 2D TMD heterolayers, their material properties, and device applications. Moreover, it offers extended discussion on remaining challenges and future outlooks toward further improving the material quality of 2D TMD heterolayers in both material and manufacturing aspects. 

A new type of soft actuators based on a vertical stack of nanoporous 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐oxidized cellulose nanofibers (TOCNs) and atomically thin 2D platinum ditelluride (PtTe₂) layers is reported. The actuation of TOCNs is driven by the interfacing 2D PtTe₂layers whose electrothermal proficiency precisely controls their hydration/dehydration states sensitive to mechanical deformation. These vertically stacked TOCN/2D PtTe₂actuators present excellent actuation characteristics such as high linearity of bending curvature versus applied voltage and well‐preserved reversibility during cyclic operations. Most notably, they exhibit an extremely large weight‐lifting ratio, i.e., ≈1000 times the mass of the TOCN layers, confirming superior mechanical robustness. Furthermore, complicated actuations such as twisting in a 3D manner are demonstrated by judiciously controlling the surface wettability of TOCN layers. This study unveils opportunities for CNFs and 2D materials for actuator applications, as well as suggests new design strategies broadly applicable to soft robotics and biomimetic devices.

 

Biomorph actuators composed of two layers with asymmetric thermal expansion properties are widely explored owing to their high mechanical adaptability. Electrothermal nanomaterials are employed as the Joule heating components in them for controlled thermal expansion, while their large integration thickness often limits resulting actuation performances. This study reports high‐performance ultrathin soft biomorph actuators enabled by near atom‐thickness 2D platinum ditelluride (PtTe₂) layers—a new class of emergent metallic 2D transition metal dichalcogenides. The actuators employ wafer‐scale 2D PtTe₂layers sandwiched in between two polymer films of largely mismatched thermal expansion coefficients, which are electrically biased to generate Joule heating. This electrical‐to‐thermal conversion causes the asymmetric expansion of the polymers achieving outstanding actuation motions; i.e., large bending curvature, fast responsiveness, as well as high reversibility and endurance, which surpass the performances of previously explored graphene‐based actuators with much smaller dimensions. Furthermore, the 2D PtTe₂layers‐enabled actuators are demonstrated to function as soft grippers in lifting and relocating heavier objects, implying the great potential of near atom‐thickness materials in biomimetic devices.