Ultraclean transfer of graphene by mechanically exfoliating polymer with modified crosslink density

The transfer of graphene from metallic substrates onto application-specific substrates is usually inevitable for the applications of high-quality graphene films derived from chemical vapour deposition (CVD) approaches. Commonly used to support the graphene films during the transfer, the coating of the polymer would produce the surface contaminations and hinder the industrially compatible transfer. In this work, through the thermal imidization of polyamide acid (PAA) to polyimide (PI) and tuning of the concentration of dangling chains, we achieved the ultraclean and crack-free transfer of graphene wafers with high electronic quality. The resulting contamination-free and hydrophilic surface also enabled the observed improved cell viability in a biomedical applications. By avoiding aqueous etching or the usage of strong bases, our proposed transfer method is industrially compatible for batch transfer of graphene films towards the real applications.