CO₂-promoted transfer-free growth of conformal graphene

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 barriers 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 kΩ·sq⁻¹ at an optical transmittance of ~ 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.