Currently, the direct synthesis of inch-scale single-crystal graphene on insulating substrates is limited by the lack of metal catalysis, suitable crystallization conditions, and self-limiting growth mechanisms. In this study, we investigated the direct growth of adlayer-free ultra-flat wafer-scale single-crystal monolayer graphene on insulating substrates by the multi-cycle plasma-etching-assisted chemical vapor deposition (MPE-CVD) method. Firstly, an angstrom-scale growth nanochamber was created by fabricating single-crystal Cu(111) foils on Al2O3(0001) substrates. Graphene was then directly synthesized at the interface between Cu(111) and Al2O3(0001) by MPE-CVD. After growth, the Cu(111) foil was detached using a liquid-nitrogen-assisted separation method, and the ultra-high-quality single-crystal graphene film was experimentally achieved on Al2O3(0001). This work breaks the bottleneck in the direct synthesis of single-crystal monolayer graphene on insulating substrates and paves the way for next-generation carbon-based atomic electronics and semiconductor nanodevices.

and performances of nanodevices highly depend on the shape and quality of 2D materials, [5] various routes have been explored to synthesize high-quality controllable-shaped 2D materials. This has led to the development of different synthesis methods including mechanical exfoliation, [6] liquid-phased exfoliation, [7] and chemical vapor deposition (CVD). [8] CVD has been shown to be the most performant synthetic method, and is currently the most widely used for large-scale fabrication of high-quality 2D materials. [9] Tremendous efforts have been made to control the CVD synthetic process, for example, growing large single crystals of graphene by limiting the growth process to one nucleus, [10] fabricating wafer-scale single crystals of h-BN on liquid-gold substrates, [11] or depositing 2D transitionmetal chalcogenides via adding molten salt. [12] However, to achieve the precise control of the growth process of 2D materials, it is essential to take into account its underlying physical mechanisms. Many attempts have been made to explore the atomic mechanism and grow higher-quality materials by considering the oxygen effect, [13] the hydrogen etching, [14] the edgeenergy equilibrium, [15] the classical Wulff structure, [16] and the phase-field approach in the past years. [17] However, due to a large number of influenced factors and the underlying intricate nanoscale physical mechanisms, the precise control of the shape and quality of CVD-grown 2D materials, till now, is still regarded as a formidable challenge.Our study shows that dendritic-structured patterns commonly appear during the CVD growth processes of various 2D materials. To understand this phenomenon, we investigate the growth mechanisms in the framework of the fractal theory. [18] Although, in the past, this theory has provided an explanation for the sound of irregular or fragmented natural structures and self-similar patterns with the unfolding symmetry, [19] this theory has never been applied, to our knowledge, to the interpretation of growth mechanisms of CVD-grown 2D materials. Here, we demonstrate, both experimentally and theoretically, the existence of fractal growth mechanisms in the CVD growth process of graphene, h-BN, and molybdenum disulfide (MoS 2 ). Based on the classic diffusion-limited aggregation (DLA), [20] a typical model of the fractal theory, we develop an The precise control of the shape and quality of 2D materials during chemical vapor deposition (CVD) processes remains a challenging task, due to a lack of understanding of their underlying growth mechanisms. The existence of a fractal-growth-based mechanism in the CVD synthesis of several 2D materials is revealed, to which a modified traditional fractal theory is applied in order to build a 2D diffusion-limited aggregation (2D-DLA) model based on an atomic-scale growth mechanism. The strength of this model is validated by the perfect correlation between theoretically simulated data, predicted by 2D-DLA, and experimental results obtained from the CVD synthesis of graphene, hexagonal b...

The interconversion between spin and charge degrees of freedom offers incredible potential for spintronic devices, opening routes for spin injection, detection, and manipulation alternative to the use of ferromagnets. The understanding and control of such interconversion mechanisms, which rely on spin–orbit coupling, is therefore an exciting prospect. The emergence of van der Waals materials possessing large spin–orbit coupling (such as transition metal dichalcogenides or topological insulators) and/or recently discovered van der Waals layered ferromagnets further extends the possibility of spin-to-charge interconversion to ultrathin spintronic devices. Additionally, they offer abundant room for progress in discovering and analyzing novel spin–charge interconversion phenomena. Modifying the properties of van der Waals materials through proximity effects is an added degree of tunability also under exploration. This Perspective discusses the recent advances toward spin-to-charge interconversion in van der Waals materials. It highlights scientific developments which include techniques for large-scale growth, device physics, and theoretical aspects.

In article number 1902431, Bo Tian, Weiwei Cai, Xixiang Zhang, and co‐workers reveal the existence of a fractal‐growth‐based mechanism in 2D‐material chemical vapor deposition (CVD) syntheses. Based on a 2D diffusion‐limited aggregation model, perfect correlations between theoretically simulated data and CVD experimental results are obtained. Eventually, the precise control of 2D‐material shapes and qualities is achieved by adjusting single‐domain net growth rates in the CVD‐growth process.

In addition to conventional monolayer or bilayer graphene films, graphene‐mesh metamaterials have attracted considerable research attention within the scientific community owing to their unique physical and optical properties. Currently, most graphene‐mesh metamaterials are fabricated using common lithography techniques on exfoliated graphene flakes, which require the deposition and removal of chemicals during fabrication. This process may introduce contamination or doping, thereby limiting their production size and application in nanodevices. Herein, the controlled production of wafer‐scale high‐quality single‐crystal nucleus‐free graphene‐mesh metamaterial films with zigzag edges is demonstrated. The 13C‐isotopic labeling graphene‐growth approach, large‐area Raman mapping techniques, and a uniquely designed high‐voltage localized‐space air‐ionization etching method are utilized to directly remove the graphene nuclei. Subsequently, a hydrogen‐assisted anisotropic etching process is employed for transforming irregular edges into zigzag edges within the hexagonal‐shaped holes, producing a large‐scale single‐crystal high‐quality graphene‐mesh metamaterial film on a Cu(111) substrate. The carrier mobilities of the fabricated field‐effect transistors on the as‐produced films are measured. The findings of this study enable the large‐scale production of high‐quality low‐dimensional graphene‐mesh metamaterials and provide insights for the application of integrated circuits based on graphene and other 2D metamaterials.