The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth.

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The hydrogen economy is seen as a potential alternative to overcome the depletion of traditional fossil fuels and environmental pollution; therefore, the demand for high-purity hydrogen has rapidly increased. To produce hydrogen in a sustainable and environmentally friendly manner, numerousThe metallic 1T phase of WS 2 (1T-WS 2 ), which boosts the charge transfer between the electron source and active edge sites, can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER). As the semiconductor 2H phase of WS 2 (2H-WS 2 ) is inherently stable, methods for synthesizing 1T-WS 2 are limited and complicated. Herein, a uniform wafer-scale 1T-WS 2 film is prepared using a plasma-enhanced chemical vapor deposition (PE-CVD) system. The growth temperature is maintained at 150 °C enabling the direct synthesis of 1T-WS 2 films on both rigid dielectric and flexible polymer substrates. Both the crystallinity and number of layers of the as-grown 1T-WS 2 are verified by various spectroscopic and microscopic analyses. A distorted 1T structure with a 2a 0 × a 0 superlattice is observed using scanning transmission electron microscopy. An electrochemical analysis of the 1T-WS 2 film demonstrates its similar catalytic activity and high durability as compared to those of previously reported untreated and planar 1T-WS 2 films synthesized with CVD and hydrothermal methods. The 1T-WS 2 does not transform to stable 2H-WS 2 , even after a 700 h exposure to harsh catalytic conditions and 1000 cycles of HERs. This synthetic strategy can provide a facile method to synthesize uniform 1T-phase 2D materials for electrocatalysis applications.

Graphene has recently been attracting considerable interest because of its exceptional conductivity, mechanical strength, thermal stability, etc. Graphene-based devices exhibit high potential for applications in electronics, optoelectronics, and energy harvesting. In this paper, we review various growth strategies including metal-catalyzed transfer-free growth and direct-growth of graphene on flexible and rigid insulating substrates which are "major issues" for avoiding the complicated transfer processes that cause graphene defects, residues, tears and performance degradation in graphene-based functional devices. Recent advances in practical applications based on "direct-grown graphene" are discussed. Finally, several important directions, challenges and perspectives in the commercialization of 'direct growth of graphene' are also discussed and addressed.