ZnO-based resistive switching device Ag/ZnO/TiN, and its modified structure Ag/ZnO/Zn/ZnO/TiN and Ag/graphene/ZnO/TiN, were prepared. The effects of inserted Zn layers in ZnO matrix and an interface graphene layer on resistive switching characteristics were studied. It is found that metal ions, oxygen vacancies, and interface are involved in the RS process. A thin inserted Zn layer can increase the resistance of HRS and enhance the resistance ratio. A graphene interface layer between ZnO layer and top electrode can block the carrier transport and enhance the resistance ratio to several times. The results suggest feasible routes to tailor the resistive switching performance of ZnO-based structure.
The phonon density of states （PDOS） and the thermodynamical properties including the heat capacity, the free energy, and the entropy of a single-layer graphene with vacancy defects have been studied theoretically. We first analytically derive the general formula of the lattice vibration frequency, and then numerically discuss the effect of the defects on the PDOS. Our results suggest that the vacancy defects will induce the sawtooth-like oscillation of the PDOS and the specific oscillation patterns depend on the concentration and the spatial distribution of the vacancies. In addition, it is verified that the vacancy defects will cause the increase of the beat capacity because of the vacancy-induced low-frequency resonant peak. Moreover, the influences of the vacancies on the free energy and the entropy are investigated.
