Ultra-clean graphene for transmission electron microscopy by direct polymer-free adhesion method

Graphene is an ideal sample support for electron microscopy experiments. Its crystalline nature and single atomic thickness make it easy for any objects placed on graphene to be identified and studied. At the same time, these advantages can easily be negated by contamination of the graphene surface, which often occurs during growth and transfer procedures. In this study, we present a new polymer-free transfer method by direct adhesion, which produces contamination-free graphene for sample support in transmission electron microscopy studies. High-angle annular dark-field scanning transmission electron microscopy and convergent beam electron diffraction images of the samples obtained using the new graphene transfer protocol show the absence of any contamination originating from the transfer procedure, and only soft contamination due to hydrocarbons is observed. These observations are supported by simulations of graphene with hydrocarbons. We also compare the new dry transfer method against two other procedures known from the previous literature. The samples prepared using the new direct polymer-free adhesion method demonstrate superior quality when compared to the samples prepared by the two other procedures.