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The advancement in two-dimensional (2D) materials has led to the development of new charging methods in portable and wearable electronic devices. However, their charging methods are still confined to contact/wired mode. Radio Frequency (RF) energy harvesting exhibits potential for extracting electrical power from the environment, benefiting from its limitless ambient availability and extended power transfer capabilities. This paper demonstrates the fabrication of an RF energy harvesting device using liquid phase exfoliated atomically thin earth-abundant pyrite ore (iron sulfide (FeS2)). Owing to pyrite's unique semiconductor properties such as a very small narrow band gap (0.8 eV) and high carrier mobility (360 cm2 V−1 s−1), it is possible to make a Schottky junction with a metal electrode. Hence, we fabricated a Schottky device employing a Ti/2D-FeS2/ITO configuration using drop casting methods. Electrical measurements reveal that the device has a low turn-on voltage of 0.18 V and a low Schottky barrier height of 0.14 eV. To substantiate the role of 2D-FeS2, density functional theory (DFT) studies were performed revealing the impact of the Giant Stark Effect (GSE) in lowering the bandgap of 2D FeS2. This insidious phenomenon of GSE in 2D-FeS2 makes it an ideal material of choice for RF energy harvesting applications. The device we fabricated functions within the commercial frequency modulation broadband range and extends seamlessly into the very high-frequency radio spectrum. It generated a 1.5 V output voltage using commercial FM broadband frequencies, sufficient for charging a 1.5 F supercapacitor. Subsequent experimentation with a handheld walkie-talkie demonstrated that the device could achieve a maximum voltage of 3.5 V within the one-meter range, exhibiting an efficiency of 30%. The implications of this discovery suggest that 2D-FeS2-based wireless energy-powered portable devices hold promise for healthcare/biomedical device applications, energy harvesting in remote areas, and regions affected by floods or natural disasters. [ABSTRACT FROM AUTHOR]

A machine learning (ML) guided approach is presented for the accelerated optimization of chemical vapor deposition (CVD) synthesis of 2D materials toward the highest quality, starting from low‐quality or unsuccessful synthesis conditions. Using 26 sets of these synthesis conditions as the initial training dataset, our method systematically guides experimental synthesis towards optoelectronic‐grade monolayer MoS2 flakes. A‐exciton linewidth (σA) as narrow as 38 meV could be achieved in 2D MoS2 flakes after only an additional 35 trials (reflecting 15% of the full factorial design dataset for training purposes). In practical terms, this reflects a decrease of the possible experimental time to optimize the parameters from up to one year to about two months. This remarkable efficiency was achieved by formulating a constrained sequencing optimization problem solved via a combination of constraint learning and Bayesian Optimization with the narrowness of σA as the single target metric. By employing graph‐based semi‐supervised learning with data acquired through a multi‐criteria sampling method, the constraint model effectively delineates and refines the feasible design space for monolayer flake production. Additionally, the Gaussian Process regression effectively captures the relationships between synthesis parameters and outcomes, offering high predictive capability along with a measure of prediction uncertainty. This method is scalable to a higher number of synthesis parameters and target metrics and is transferrable to other materials and types of reactors. This study envisions that this method will be fundamental for CVD and similar techniques in the future. [ABSTRACT FROM AUTHOR]

In this short review, an overview of recent progress in deploying advanced characterization techniques is provided to understand the effects of spatial variation and inhomogeneities in moiré heterostructures over multiple length scales. Particular emphasis is placed on correlating the impact of twist angle misalignment, nano-scale disorder, and atomic relaxation on the moiré potential and its collective excitations, particularly moiré excitons. Finally, future technological applications leveraging moiré excitons are discussed., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)