▎ 摘　　要

Gaseous promotors have readily been adopted during the direct synthesis of graphene over insulators to enhance the growth quality and/or boost the growth rate. The understanding of the real functions of carbon-containing promotors has still remained elusive. In this study, we identify the critical roles of a representative CO2 promotor played in the direct growth of graphene. The comparative experimental trials validate CO2 as an effective modulator to decrease graphene nucleation density, improve growth kinetics, and mitigate adlayer formation. The first-principles calculations illustrate that the generation of gas-phase OH species in CO2-assisted system helps decrease the energy bafflers of CH4 decomposition and carbon attachment to the growth front, which might be the key factor to allow high-quality direct growth. Such a CO2-promoted strategy enables the conformal coating of graphene film over curved insulators, where the sheet resistance of grown graphene on quartz reaches as low as 1.26 k Omega.sq(-1) at an optical transmittance of similar to 95.8%. The fabricated endoscope lens based on our conformal graphene harvests an apoptosis of 82.8% for noninvasive thermal therapy. The work presented here is expected to motivate further investigations in the controllable growth of high-quality graphene on insulating substrates.