2, University of Houston, Houston, Texas, United States
5, Case Western Reserve University, Cleveland, Ohio, United States
3, Baylor University, Waco, Texas, United States
4, Chinese Academy of Sciences, Ningbo, , China
We demonstrate the orientation control of graphene flakes by a weak static magnetic field and subsequently achieve high order parameter alignment by rotating magnetic field. Several devices such as magnetic field sensor, display, polarizer and graphene pattern were exhibited as example of novel applications of macroscopically aligned graphene. The control is made by weak static magnetic field (hundreds of Gauss) for large diamagnetic susceptibility of exfoliated graphene. Viewed as a non-magnetic material, a liquid suspension of graphene flakes is firstly used for magnetic field sensing and display with sensitivity and spatial resolution higher than traditional iron filings or particles. The graphene suspension is then packaged as a writing and/or display board that can be controlled by magnets or magnetic field. Both applications require no external lighting or polarizing optics because they utilize macroscopic alignment and anisotropic optical properties of graphene.
Then graphene suspension was firstly aligned with high order parameter of 0.8 by rotating magnetic field. Macroscopic optical properties of aligned graphene flakes such as birefringence and diffraction were investigated as graphene flakes was controlled in specific orientation and aligned parallel to each other. After mixing with UV cured resin, graphene flakes suspension was aligned as high performance polarizer. By combination lithography process with rotating magnetic field alignment, graphene flakes were assembled into patterns of different orientations with lithography mask. The macroscopic control and alignment of graphene can not only transfer unique properties of graphene from microscopic to macroscopic scale, but also be used to align other nanomaterials. Thus, our demonstration opens door to enormous new device applications.