Resistive memory (ReRAM) based on a solid-electrolyte insulator is a promising nanoscale device and has great potentials in nonvolatile memory, analog circuits, and neuromorphic applications. The underlying resistive switching (RS) mechanism of ReRAM is suggested to be the formation and rupture of nanoscale conductive filament (CF) inside the solid-electrolyte layer. However, the random nature of the nucleation and growth of the CF makes their formation difficult to control, which is a major obstacle for ReRAM performance improvement. Here, we report a novel approach to resolve this challenge by adopting a metal nanocrystal (NC) covered bottom electrode (BE) to replace the conventional ReRAM BE. As a demonstration vehicle, a Ag/ZrO(2)/Cu NC/Pt structure is prepared and the Cu NC covered Pt BE can control CF nucleation and growth to provide superior uniformity of RS properties. The controllable growth of nanoscale CF bridges between Cu NC and Ag top electrode has been vividly observed by transmission electron microscopy (TEM). On the basis of energy-dispersive X-ray spectroscopy (EDS) and elemental mapping analyses, we further confirm that the chemical contents of the CF are mainly Ag atoms. These testing/metrology results are consistent with the simulation results of electric-field distribution, showing that the electric field will enhance and concentrate on the NC sites and control location and orientation of Ag CFs.
Although the kinetics of CF formation/ dissolution is still unclear, it is widely accepted that the CF formation/dissolution is strongly related to the electromigration and electrochemical reaction of anion (i.e., oxygen vacancy) [13][14][15][16] or cation (i.e., Cu 2+ , Ag + or Ni 2+ ). [17][18][19][20][21][22] Generally, RS behavior can be classifi ed as two modes: nonvolatile memory switching (MS) and volatile threshold switching (TS). In the MS mode, both LRS and HRS can be maintained after removing the external voltage, while the LRS in the TS mode will be back to the HRS once the applied voltage is smaller than a critical value. [23][24][25] To avoid confusion with MS, the LRS and HRS in TS are renamed as "TS ON-state" and "TS OFFstate" in this article. The MS device can be used for the non-volatile data storage [1][2][3][4][5] while TS device can be as a selector in series with memory cell to suppress crosstalk effect in the crossbar array. [26][27][28][29][30] Recently, some groups reported that TS and MS can coexist and mutually transform in a single device at suitable external excitation. [23][24][25][26][27][28] Several models have been proposed to explain this phenomenon, including CF thermal instability, [ 23 ] strong electron correlation effect, [ 24 ] quantum-wire model, [ 25 ] interface barrier modulation, [ 26 ] and space charge effect. [ 27 ] However, the underlying mechanism of the phenomenon is still unclear, especially lacking of direct evidences to uncover when and how the two RS modes happen and what is the internal relationship between them.Here, we demonstrate that the TS and MS modes can be modulated in the Ag/SiO 2 /Pt structure by controlling the compliance current ( I CC ) in electroforming. We systematically investigate the morphologies, chemical components, and dynamic growth of the CF using scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) analysis. The results confi rm that the TS and MS modes correspond to the CF consisting of isolated and continuous Ag nanocrystals, respectively. In addition, by Kelvin probe force microscopy (KPFM) studies, the voltage potential distribution of CF in the ON-and OFF-state further indicate that the TS mode is Volatile threshold switching (TS) and non-volatile memory switching (MS) are two typical resistive switching (RS) phenomena in oxides, which could form the basis for memory, analog circuits, and neuromorphic applications. Interestingly, TS and MS can be coexistent and converted in a single device under the suitable external excitation. However, the origin of the transition from TS to MS is still unclear due to the lack of direct experimental evidence. Here, conversion between TS and MS induced by conductive fi lament (CF) morphology in Ag/SiO 2 /Pt device is directly observed using scanning electron microscopy and high-resolution transmission electron microscopy. The MS mechanism is related to the formation and dissolution of CF consisting of continuous Ag...
We propose using graphene electrodes with hydrogenated edges for solid-state nanoporebased DNA sequencing, and perform molecular dynamics simulations in conjunction with electronic transport calculations to explore the potential merits of this idea. The results of our investigation show that, compared to the unhydrogenated system, edge-hydrogenated graphene electrodes facilitate the temporary formation of H-bonds with suitable atomic sites in the translocating DNA molecule. As a consequence, the average conductivity is drastically raised by about 3 orders of magnitude while exhibiting significantly reduced statistical variance. We have furthermore investigated how these results are affected when the distance between opposing electrodes is varied and have identified two regimes: for narrow electrode separation, the
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