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Abstract A novel class of transition metal oxides, capable of reversible topotactic phase transition between the oxygen‐deficient brownmillerite and oxygen‐rich perovskite, has emerged as a promising material for memristive and magnetoelectric devices. However, the absence of a local oxygen source in the device structure necessitates an oxygen exchange process between the surrounding atmosphere and the switching layer during operation, which can lead to unreliable device performance. In this study, graphene quantum dots (GQDs) are introduced into a SrFe0.5Co0.5Ox memristive device as an oxygen reservoir for the nanoscale topotactic redox process. The SrFe0.5Co0.5Ox memristive devices with GQDs exhibit reliable resistive switching performance compared to SrFe0.5Co0.5Ox devices without GQDs. To understand the effect of GQDs on the device structure, a pulse endurance test is carried out in a high vacuum. The devices with GQDs show rather good endurance behavior, while devices without GQDs exhibit endurance failure. These results provide a deeper understanding of the potential use of GQDs in enhancing the performance of SrFe0.5Co0.5Ox memristive devices, with implications for tuning nanoscale topotactic phase transition for multi‐functional properties.

Abstract This paper describes the fabrication process and characteristics of dimension- and position-controlled gallium nitride (GaN) microstructure arrays grown on graphene films and their quantum structures for use in flexible light-emitting device applications. The characteristics of dimension- and position-controlled growth, which is crucial to fabricate high-performance electronic and optoelectronic devices, were investigated using scanning and transmission electron microscopes and power-dependent photoluminescence spectroscopy measurements. Among the GaN microstructures, GaN microrods exhibited excellent photoluminescence characteristics including room-temperature stimulated emission, which is especially useful for optoelectronic device applications. As one of the device applications of the position-controlled GaN microrod arrays, we fabricated light-emitting diodes (LEDs) by heteroepitaxially growing InxGa1−xN/GaN multiple quantum wells (MQWs) and a p-type GaN layer on the surfaces of GaN microrods and by depositing Ti/Au and Ni/Au metal layers to prepare n-type and p-type ohmic contacts, respectively. Furthermore, the GaN microrod LED arrays were transferred onto Cu foil by using the chemical lift-off method. Even after being transferred onto the flexible Cu foil substrate, the microrod LEDs exhibited strong emission of visible blue light. The proposed method to enable the dimension- and position-controlled growth of GaN microstructures on graphene films can likely be used to fabricate other high-quality flexible inorganic semiconductor devices such as micro-LED displays with an ultrahigh resolution.