Many studies have accompanied the emergence of a great interest in flexible or/and stretchable devices for new applications in wearable and futuristic technology, including human-interface devices, robotic skin, and biometric devices, and in optoelectronic devices. Especially, new nanodimensional materials enable flexibility or stretchability to be brought based on their dimensionality. Here, the emerging field of flexible devices is briefly introduced using silver nanowires and graphene, which are famous nanomaterials for the use of transparent conductive electrodes, as examples, and their unique functions originating from the intrinsic property of these nanomaterials are highlighted. It is thought that this work will evoke more interest and idea exchanges in this emerging field and hopefully can trigger a breakthrough on a new type of optoelectronics and optogenetic devices in the near future.

Recently, Ag nanowires (AgNWs) has had a great interest as a conducting material for flexible and transparent devices, but it still shows several problems such as the ultimate detachment of AgNWs from substrate and a high contact resistance on AgNW junctions. Therefore, the novel concept to enhance permanent and closed attachment of AgNWs by silane modification to polydimethylsilaoxane (PDMS) substrate well known as high stretchable film with extremly low adhesive is suggested. According to this experiment, higher sigma (σ)-donating ability and hydrophilicity indicate better electrical and mechanical properties in real device. Especially, densely amine self-assembled PDMS surface exhibits the strongest contact force to the AgNWs, especially for junction side, and the longest maintenance of hydrophilicity by coordination-type bonding. In addition, AgNWs adhere permanently to stretchable substrates while simultaneously maintaining high transparency (87%) and high conductivity (27 Ω sq^–1). Consequently, the resulting AgNW film shows excellent mechanical durability which includes enhanced performance of both flexibility and stretchability.

Thermally doped nitrogen atoms on the sp²-carbon network of reduced graphene oxide (rGO) enhance its electrical conductivity. Atomic structural information of thermally annealed graphene oxide (GO) provides an understanding on how the heteroatomic doping could affect electronic property of rGO. Herein, the spectroscopic and microscopic variations during thermal graphitization from 573 to 1 373 K are reported in two different rGO sheets, prepared by thermal annealing of GO (rGO_therm) and post-thermal annealing of chemically nitrogen-doped rGO (post-therm-rGO). The spectroscopic transitions of rGO in thermal annealing ultimately showed new oxygen-functional groups, such as cyclic edge ethers and new graphitized nitrogen atoms at 1 373 K. During the graphitization process, the microscopic evolution resolved by scanning tunneling microscopy (STM) produced more wrinkled surface morphology with graphitized nanocrystalline domains due to atomic doping of nitrogen on a post-therm-rGO sheet. As a result, the post-therm-rGO-containing nitrogen showed a less defected sp²-carbon network, resulting in enhanced conductivity, whereas the rGO_therm sheet containing no nitrogen had large topological defects on the basal plane of the sp²-carbon network. Thus, our investigation of the structural evolution of original wrinkles on a GO sheet incorporated into the graphitized N-doped rGO helps to explain how the atomic doping can enhance the electrical conductivity.

Graphene is of considerable interest as a next-generation semiconductor material to serve as a possible substitute for silicon. For real device applications with complete circuits, effective n-type graphene field effect transistors (FETs) capable of operating even under atmospheric conditions are necessary. In this study, we investigated n-type reduced graphene oxide (rGO) FETs of photoactive metal oxides, such as TiO₂ and ZnO. These metal oxide doped FETs showed slight n-type electric properties without irradiation. Under UV light these photoactive materials readily generated electrons and holes, and the generated electrons easily transferred to graphene channels. As a result, the graphene FET showed strong n-type electric behavior and its drain current was increased. These n-doping effects showed saturation curves and slowly returned back to their original state in darkness. Finally, the n-type rGO FET was also highly stable in air due to the use of highly resistant metal oxides and robust graphene as a channel.