The advent of graphene, and more recently of two-dimensional (2D) layered materials, has opened new perspectives in electronics, optoelectronics, energy generation and sensing applications. 2D materials can be fabricated with relatively inexpensive production methods, integrated into existing semiconductor technologies, and offer new physical and chemical properties. Electrically, they can behave as insulators, semiconductors, metals or even superconductors. Layered materials consist of covalently bonded and dangling-bond-free layers that can be stuck on top of each other by van der Waals forces to form bulk structures. In general, the number of layers can be controlled to tailor specific properties. The possibility to accurately predict the physical properties of layered materials with the exact number of layers is a unique opportunity for directing the design and fabrication of new electronic and optoelectronic devices. Different types of 2D materials can form heterojunctions with each other or with bulk materials, without the need of a close lattice matching. In these heterojunctions, the weak van der Waals forces between the participant materials do not introduce significant changes at the atomic scale and usually maintain the original electronic structure of the materials. Hence, van der Waals heterojunctions offer the opportunity to combine layers with different properties as the building blocks to engineer new functional materials for high-performance electronic devices, chemical sensors or water-splitting photocatalysts. A great advantage is that the easy stacking of a variety of 2D materials allows a far greater number of combinations than any traditional growth method. A tremendous amount of work has been done thus far on the physical and chemical properties as well as on the synthesis and the characterization of 2D materials such as graphene, transition metal chalcogenides and dichalcogenides, hexagonal boron nitride, black phosphorus, organic perovskites, etc. Many of these materials have been used to fabricate stacked 2D-2D heterostructures, 2D/3D heterojunctions with common bulk semiconductors or even 0D-2D and 1D-2D hybrids. The underlying physics and the possible applications in photodetection, biochemical sensing, strain gauges, photovoltaic energy generation and photocatalytic water splitting have attracted the attention of both theorists and experimentalists. This article collection, reprint of the Special Issue “2D Materials and Van der Waals Heterostructures: Physics and Applications” published by Nanomaterials – MDPI, covers state-of-the-art experimental, simulation and theoretical research on 2D materials and on their van der Waals heterojunctions for applications in electronics, optoelectronics, energy generation and photocatalysis.
Di Bartolomeo, Antonio
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