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High mobility is a crucial requirement for a large variety of electronic device applications. The state of the art for high-quality graphene devices is based on heterostructures made with graphene encapsulated in >40 nm-thick flakes of hexagonal boron nitride (hBN). Unfortunately, scaling up multilayer hBN while precisely controlling the number of layers remains an outstanding challenge, resulting in a rough material unable to enhance the mobility of graphene. This leads to the pursuit of alternative, scalable materials, which can be used as substrates and encapsulants for graphene. Tungsten disulfide (WS2) is a transition metal dichalcogenide, which was grown in large (∼mm-size) multi-layers by chemical vapor deposition. However, the resistance vs gate voltage characteristics when gating graphene through WS2 exhibit largely hysteretic shifts of the charge neutrality point on the order of Δn∼ 3 × 1011 cm−2, hindering the use of WS2 as a reliable encapsulant. The hysteresis originates due to the charge traps from sulfur vacancies present in WS2. In this work, we report the use of WS2 as a substrate and overcome the hysteresis issues by chemically treating WS2 with a super-acid, which passivates these vacancies and strips the surface from contaminants. The hysteresis is significantly reduced by about two orders of magnitude, down to values as low as Δn∼ 2 × 109 cm−2, while the room-temperature mobility of WS2-encapsulated graphene is as high as ∼62 × 103 cm2 V−1 s−1 at a carrier density of n ∼ 1 ×1012 cm−2. Our results promote WS2 as a valid alternative to hBN as an encapsulant for high-performance graphene devices. 

Abstract The advent of 2D materials has revolutionized condensed matter physics and materials science, offering unprecedented opportunities to explore exotic physical phenomena, engineer novel functionalities, and address critical technological challenges across diverse fields. Over the past two decades, the exploration of 2D materials has expanded beyond graphene, encompassing a vast library of atomically thin crystals and their heterostructures. These materials exhibit extraordinary electronic, optical, thermal, mechanical, and chemical properties, and hold promise for breakthroughs in electronics, optoelectronics, quantum technologies, energy storage, catalysis, thermal management, filtration and separation, and beyond. Many exciting new physics and phenomena continue to emerge, while select 2D materials, such as graphene, h-BN, and the semiconducting transition metal dichalcogenides (TMDCs), are transitioning from laboratory-scale demonstrations to industrial applications. In this context, a holistic understanding of synthesis, structure-property relationships, integration, and performance optimization is essential. This roadmap reviews the multifaceted challenges and opportunities in 2D materials research, focusing on the synthesis, properties and applications of representative systems including graphene and its derivatives, TMDCs, MXenes as well as their heterostructures and moiré systems.