The use of single-crystal substrates as templates for the epitaxial growth of single-crystal overlayers has been a primary principle of materials epitaxy for more than 70 years. Here we report our finding that, though counterintuitive, single-crystal 2D materials can be epitaxially grown on twinned crystals. By establishing a geometric principle to describe 2D materials alignment on high-index surfaces, we show that 2D material islands grown on the two sides of a twin boundary can be well aligned. To validate this prediction, wafer-scale Cu foils with abundant twin boundaries were synthesized, and on the surfaces of these polycrystalline Cu foils, we have successfully grown wafer-scale single-crystal graphene and hexagonal boron nitride films. In addition, to greatly increasing the availability of large area high-quality 2D single crystals, our discovery also extends the fundamental understanding of materials epitaxy.
Batch production of continuous and uniform graphene films is critical for the application of graphene. Chemical vapor deposition (CVD) has shown great promise for mass producing high-quality graphene films. However, the critical factors affected the uniformity of graphene films during the batch production need to be further studied. Herein, we propose a method for batch production of uniform graphene films by controlling the gaseous carbon source to be uniformly distributed near the substrate surface. By designing the growth space of graphene into a rectangular channel structure, we adjusted the velocity of feedstock gas flow to be uniformly distributed in the channel, which is critical for uniform graphene growth. The monolayer graphene film grown inside the rectangular channel structure shows high uniformity with average sheet resistance of 345 Ω sq−1 without doping. The experimental and simulation results show that the placement of the substrates during batch growth of graphene films will greatly affect the distribution of gas-phase dynamics near the substrate surface and the growth process of graphene. Uniform graphene films with large-scale can be prepared in batches by adjusting the distribution of gas-phase dynamics.
Twin crystals, the formation energy of which is much smaller than that of ordinary grain boundaries, widely exist in the annealed copper and are hard to eliminate. The study of the effects of twin boundaries on graphene growth is of great significance to the understanding of graphene epitaxy. However, there are few studies on the effects of twin boundaries on the graphene growth process. Here, this article experimentally demonstrates that graphene islands are subjected to different compressive strains from the opposite copper crystal plane after growing across the twin boundary. Further results reveal that graphene can grow across different twin boundaries, such as atom steps, narrow valleys, and even micron‐scale ridges, without forming linear defect. Therefore, strain‐induced graphene doping can be manipulated with the type of twin boundaries and the location on the twin crystals. The transition region where the degree of doping changes monotonically across the twin boundary further confirms the different spatial doping phenomena of graphene islands. This work provides a new perspective for understanding the effect of twin boundaries on the graphene epitaxy, which is expected to have a potential impact on growing high‐quality graphene on twinned copper substrates.
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