  Voltage-controlled resistive switching is demonstrated in various gap systems
on SiO2 substrate. The nanosized gaps are made by different means using
different materials including metal, semiconductor, and metallic nonmetal. The
switching site is further reduced by using multi-walled carbon nanotubes and
single-walled carbon nanotubes. The switching in all the gap systems shares the
same characteristics. This independence of switching on the material
compositions of the electrodes, accompanied by observable damage to the SiO2
substrate at the gap region, bespeaks the intrinsic switching from
post-breakdown SiO2. It calls for caution when studying resistive switching in
nanosystems on oxide substrates, since oxide breakdown extrinsic to the
nanosystem can mimic resistive switching. Meanwhile, the high ON/OFF ratio
(10E5), fast switching time (2 us, test limit), durable cycles demonstrated
show promising memory properties. The intermediate states observed reveal the
filamentary conduction nature.
