Strain engineering of graphene on rigid substrates.

Graphene with a large tensile strain is a promising candidate for the new "straintronics'' applications. The current approaches of strain engineering on graphene are mainly realized by flexible or hollow substrates. In this work, a novel method for strained graphene on a rigid substrate assisted by PDMS stretching and interface adjustments is proposed. The Raman spectra show that the maximum strain of graphene on the SiO2/Si substrate is ∼1.5%, and multiple characterizations demonstrate its high cleanness, flatness, integrity, and reliable electrical performance. The successful strain engineering is attributed to the protection of a layer of formvar resin and the interfacial capillary force of the buffering liquid. We believe this technique can advance strain-related fundamental studies and applications of two-dimensional materials.

Using Scalable Graphene via Press-and-Peel: A Robust and Storable Tape.

The independent expertise required by the preparation and application of graphene has brought a challenge to the more fluent development of graphene devices. We combine the advantages of chemical vapor deposition and micromechanical exfoliation methods of synthesizing graphene to develop a "graphene tape" for the fast utilization of graphene, which is robust, storable, and user-friendly. Prepared by pretransferring graphene to the surface of a polymer carrier film with weak interfacial adhesion, this graphene tape enables the acquisition, patterning, and layer-by-layer epitaxy of scalable graphene on a target substrate through simple cutting, pressing, and peeling off. Multiple characterizations demonstrate its comparable quality with as-synthesized graphene even after stored for over 30 days, overcoming the time and space limitations of acquiring a graphene sample. We believe that this graphene tape can bridge the current gap between graphene synthesis and applications and promote industrial progress of graphene-based devices in the post-Moore era.

High-quality graphene transfer via directional etching of metal substrates.

Large-scale applications of graphene require its high-efficiency transfer from growth metal substrates to any other substrates of interest. The wrinkles and folds generated during the transfer process of graphene by the well-known poly(methyl methacrylate) (PMMA)-assisted technique is a critical issue. Here, we report an improvement of this method by applying a directional etching process for the removal of the growth Cu substrates, using a pair of electrodes inserted into the etchant with a constant current to form an electrochemical system. The controlled redox reactions between the Cu and the solution environment result in the etching of Cu in a part-by-part manner strictly from one end to the other. The consistency of the Cu etching direction can avoid the formation of an easily destroyable Cu structure and release the stress concentration that is usually generated during the random etching process, and finally yield significantly improved quality of the transferred graphene film with a lowered density of wrinkles, cracks/folds, adlayers, reduced root-mean-square of surface roughness, and increased performance in sheet resistance and carrier mobility.