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Memristor characteristics have been reported to be enhanced by inserting graphene oxide quantum dots (GOQDs) in oxide layers. However, it has not been studied how the density of GOQDs affects the resistive switching behavior of memristor devices. In this work, memristor devices in the structure of Ag/Zr0.5Hf0.5O2 (ZHO)/GOQDs/ZHO/Pt are fabricated and tested. The device measurement results show that as the applied voltage is scanned, if the density of GOQDs increases, the resistance adjustment of fabricated memristor devices shifts from abruptly to gradually. Moreover, the resistance of a high-GOQD-density device is modulated by controlling the amplitude, width, polarity, and number of applied voltage pulses. Furthermore, the fabricated memristor device demonstrates basic synaptic behavior, including tunable conductance, short-term plasticity, long-term plasticity, spike-timing-dependent facilitation, and paired-pulse facilitation. These phenomena are attributed to the high density of GOQDs, which prevents Ag+ from migrating through the switching layers, and hence, the formation of Ag conductive filaments is slower. This study reveals that the proposed memristor device with an appropriate density of GOQDs has great potential in artificial electronic synaptic applications. [ABSTRACT FROM AUTHOR]

Single photon sources, which are compatible with quantum memories, are important components of quantum networks. In this article, we show optical investigations on isolated GaAs/Al0.25Ga0.75As quantum dots grown via droplet epitaxy, which emit single photons on resonance with the Rb-87-D2 line (780 nm). Under continuous wave resonant excitation conditions, we observe bright, clean, and narrowband resonance fluorescence emission from such a droplet quantum dot. Furthermore, the second-order correlation measurement clearly demonstrates the single photon emission from this resonantly driven transition. Spectrally resolved resonance fluorescence of a similar quantum dot yields a linewidth as narrow as 660 MHz (2.7 μeV), which corresponds to a coherence time of 0.482 ns. The observed linewidth is the smallest reported so far for strain free GaAs quantum dots grown via the droplet method. We believe that this single photon source can be a prime candidate for applications in optical quantum networks. [ABSTRACT FROM AUTHOR]