Abstract
Research efforts in large area graphene synthesis have been focused on increasing grain size. Here, it is shown that, beyond 1 μm grain size, grain boundary engineering determines the electronic properties of the monolayer. It is established by chemical vapor deposition experiments and first-principle calculations that there is a thermodynamic correlation between the vapor phase chemistry and carbon potential at grain boundaries and triple junctions. As a result, boundary formation can be controlled, and well-formed boundaries can be intentionally made defective, reversibly. In 100 µm long channels this aspect is demonstrated by reversibly changing room temperature electronic mobilities from 1000 to 20,000 cm2 V−1 s−1. Water permeation experiments show that changes are localized to grain boundaries. Electron microscopy is further used to correlate the global vapor phase conditions and the boundary defect types. Such thermodynamic control is essential to enable consistent growth and control of two-dimensional layer properties over large areas.
Highlights
Research efforts in large area graphene synthesis have been focused on increasing grain size
Grain boundaries (GB) and triple junctions that are a part of any polycrystalline material are present in large area monolayer graphene[7,8,9]
Using transmission electron microscopic (TEM) analysis of the boundary along with electrical transport measurements, they reported that the samples grown at higher methane flows had smaller grains, uniform coverage and most importantly, lower grain boundaries (GB) resistance
Summary
Research efforts in large area graphene synthesis have been focused on increasing grain size. Electron microscopy is further used to correlate the global vapor phase conditions and the boundary defect types Such thermodynamic control is essential to enable consistent growth and control of two-dimensional layer properties over large areas. Grain boundaries (GB) and triple junctions that are a part of any polycrystalline material are present in large area monolayer graphene[7,8,9] These GB have been extensively studied and their defect density has been theoretically shown to be mainly dependent on the extent of misorientation between the grains[10,11,12]. The results highlight the importance of GB closure in obtaining graphene with the best of electronic properties over large areas, in the regime in which the yields of increasing grain size start diminishing (Supplementary Note 2)[18]. These include the ability to control molecular permeation and sensitivity to various chemicals[19,20]
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