How surface tension matters in polymer-free graphene transfer

The main goal of this work is to achieve a direct transfer of graphene and examine the exact effect of surface tension (ST) on graphene during this type of transfer. To reach this target, we designed a specific transfer container with two-sided ports to facilitate replacing liquids underneath graphene and monitor the effect of ST. We prepared liquids with various STs by mixing pure deionized-water with different ratios of isopropanol (IPA). Our results indicate that high ST does not break the graphene structure if graphene has good quality. Besides, a ST gap (STG) can be applied to graphene at a specific level without damaging the graphene monolayer. Comparing those results to the defective graphene features after applying high ST and varied STGs confirms that standing high ST and STG can be considered as a key feature of good quality graphene. Thus, good-quality graphene can be transferred at high ST (ST of water: 72 dyne/cm) with no sign of structural damage. In addition, this type of graphene can stand STG <= 40 dyne/cm. This new understanding of the ST effect on graphene could simplify the current direct transfer techniques and widen the graphene applications by expanding the choices of the target substrates and transfer liquids.