There have been rapidly increasing demands for flexible lighting apparatus, and micrometer-scale light-emitting diodes (LEDs) are regarded as one of the promising lighting sources for deformable device applications. Herein, we demonstrate a method of creating a deformable LED, based on remote heteroepitaxy of GaN microrod (MR) p-n junction arrays on c-Al₂O₃ wafer across graphene. The use of graphene allows the transfer of MR LED arrays onto a copper plate, and spatially separate MR arrays offer ideal device geometry suitable for deformable LED in various shapes without serious device performance degradation. Moreover, remote heteroepitaxy also allows the wafer to be reused, allowing reproducible production of MR LEDs using a single substrate without noticeable device degradation. The remote heteroepitaxial relation is determined by high-resolution scanning transmission electron microscopy, and the density functional theory simulations clarify how the remote heteroepitaxy is made possible through graphene.

The electron emission of position-controlled grown ZnO nanoflowers was investigated for application in cold cathode electron emission devices. ZnO nanoflower arrays, composed of several nanoneedles with sharp tips, were grown selectively on a conducting glass substrate using a chemical solution deposition method. The morphology and position of the ZnO nanoflowers were controlled by preparing polymethylmethacrylate submicron patterns using electron-beam lithography. Without the patterns, in contrast, vertical ZnO nanoneedles were randomly grown on the substrates with high density. Several samples prepared at the same conditions exhibited almost the same nanoflower morphology and field emission characteristics. Comparison of the field emission characteristics of the ZnO nanoflower arrays and ZnO nanoneedles showed that the arrays had excellent electron emission characteristics, with a low turn-on electric field of 0.13 V µm(-1) at 0.1 µA cm(-2) and a high emission current density of 0.8 mA cm(-2) in an applied electric field of 9.0 V µm(-1). Furthermore, light-emitting devices made using ZnO nanoflower arrays demonstrated strong light emission, and micropixels for display application were clearly displayed.

Two-dimensional atomic layered materials (2d-ALMs) are emerging candidates for use as epitaxial seed substrates for transferrable epilayers. However, the micrometer-sized domains of 2d-ALMs preclude their practical use in epitaxy because they cause crystallographically in-plane disordering of the overlayer. Ultrathin graphene can penetrate the electric dipole momentum from an underlying crystal layer to the graphene surface, which then drives it to crystallize the overlayer during the initial growth stage, thus resulting in substantial energy saving. This study demonstrates the remote homoepitaxy of ZnO microrods (MRs) on ZnO substrates across graphene layers via a hydrothermal method. Despite the presence of poly-domain graphene in between the ZnO substrate and ZnO MRs, the MRs were epitaxially grown on a- and c-plane ZnO substrates, whose in-plane alignments were homogeneous within the wafer's size. Transmission electron microscopy revealed a homoepitaxial relationship between the overlayer MRs and the substrate. Density-functional theory calculations suggested that the charge redistribution occurring near graphene induces the electric dipole formation, so the attracted adatoms led to the formation of the remote homoepitaxial overlayer. Due to a strong potential field caused by long-range charge transfer given from the substrate, even the use of bi-layer and tri-layer graphene resulted in remote homoepitaxial ZnO MRs. The effects of substrate crystal planes were also theoretically and empirically investigated. The ability of graphene, which can be released from the mother substrate without covalent bonds, was utilized to transfer the overlayer MR arrays. This method opens a way for producing well aligned, transferrable epitaxial nano/microstructure arrays while regenerating the substrate for cost-saving device manufacturing.

The In-doped SnTe nanowire surface is composed of In ₂ O ₃ , SnO ₂ , Te and TeO ₂ which can be readily removed by argon ion sputtering.