S ingle crystalline graphene (SCG) has proven its potential as an ideal candidate toward high-performance electronic, spintronic, and optoelectronic devices owing to its extremely high intrinsic carrier mobility and significantly wavelengthindependent absorption. 1−4 By chemical vapor deposition (CVD), large-area SCG can be controllably prepared, which is promising to fulfill the industrial-level demands by top-down processing. Through controlling nucleation density on catalytic metal substrates, especially on Cu foil, large SCG up to centimeter-scale has been obtained so far. 5−7 However, the approaches employed to suppress graphene nucleation, such as long-time annealing, 8−10 prepolishing before growth, 11,12 and exquisite substrate design, 6,13−17 inevitably increase the fabrication period and complicate the preparation procedure.Recently, it has been reported that the utilization of single crystal metal substrate, for example, Cu(111), 18−21 high-index surfaces Cu(114) 22 or Ge(110), 23 could allow graphene domains aligning into the same orientation. Such behavior is very similar to the epitaxial growth of graphene on h-BN, in which the negligible lattice mismatch between the substrate and the two-dimensional (2D) material guides the 2D material nucleates with a fixed stacking orientation. 24,25 In addition, the different single crystal Cu substrates would endow graphene with specific properties, such as the unique pentagonal singlecrystal graphene domains formation on Cu(114) 22 and the strong interfacial coupling of the commensurate graphene on Cu(111) for anticorrosion. 26 More importantly, the stitching between aligned graphene domains is "boundary-free" to enable them coalesce into a single crystal. Thus, no extra treatment for nucleation control is required and large SCG with high crystallinity up to wafer-scale dimensions can be obtained in relative short duration. 18,20 However, the availability of single crystal metal, either directly purchased with high price or produced by repeated annealing process at high temperature, is still far from the request of industrial applications. In addition, the controllability and reliability of this strategy is reported to be challenging as single crystal substrate with high lattice perfection is difficult to obtain and remain in CVD system.Liquid copper, Cu foil in molten phase, is considered as an effective substrate to catalyze CVD graphene growth in recent years. 27−32 Compared with solid Cu, liquid Cu has advantages of higher surface uniformity, faster carbon precursor decomposition rate, and faster graphene growth rate; thus,

Direct chemical vapor deposition growth of high quality graphene on dielectric substrates holds great promise for practical applications in electronics and optoelectronics. However, graphene growth on dielectrics always suffers from the issues of inhomogeneity and/or poor quality. Here, we first reveal that a novel precursormodification strategy can successfully suppress the secondary nucleation of graphene to evolve ultrauniform graphene monolayer film on dielectric substrates. A mechanistic study indicates that the hydroxylation of silica substrate weakens the binding between graphene edges and substrate, thus realizing the primary nucleationdominated growth. Field-effect transistors based on the graphene films show exceptional electrical performance with the charge carrier mobility up to 3800 cm 2 V −1 s −1 in air, which is much higher than those reported results of graphene films grown on dielectrics.