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Graphene nanogap electrodes have been of recent interest in a variety of fields, ranging from molecular electronics to phase change memories. Several recent reports have highlighted that scaling graphene nanogaps to even smaller sizes is a promising route to more efficient and robust molecular and memory devices. Despite the significant interest, the operating and scaling limits of these electrodes are completely unknown. In this paper, we report on our observations of consistent voltage driven resistance switching in sub-5 nm graphene nanogaps. We find that such electrical switching from an insulating state to a conductive state occurs at very low currents and voltages (0.06 μA and 140 mV), independent of the conditions (room ambient, low temperatures, as well as in vacuum), thus portending potential limits to scaling of functional devices with carbon electrodes. We then associate this phenomenon to the formation and rupture of carbon chains. Using a phase change material in the nanogap as a demonstrator device, fabricated using a self-alignment technique, we show that for gap sizes approaching 1 nm the switching is dominated by such carbon chain formation, creating a fundamental scaling limit for potential devices. These findings have important implications, not only for fundamental science, but also in terms of potential applications. [ABSTRACT FROM AUTHOR]

Phase-change memory (PCM) is an importantclass of data storage, yet lowering the programming current of individualdevices is known to be a significant challenge. Here we improve theenergy-efficiency of PCM by placing a graphene layer at the interfacebetween the phase-change material, Ge2Sb2Te5(GST), and the bottom electrode (W) heater. Graphene-PCM(G-PCM) devices have ∼40% lower RESET current compared to controldevices without the graphene. This is attributed to the graphene asan added interfacial thermal resistance which helps confine the generatedheat inside the active PCM volume. The G-PCM achieves programmingup to 105cycles, and the graphene could further enhancethe PCM endurance by limiting atomic migration or material segregationat the bottom electrode interface. [ABSTRACT FROM AUTHOR]