  Two-dimensional layered semiconductors have recently emerged as attractive
building blocks for next-generation low-power non-volatile memories. However,
challenges remain in the controllable sub-micron fabrication of bipolar
resistively switching circuit components from these novel materials. Here we
report on the scalable experimental realisation of lateral on-dielectric
memtransistors from monolayer single-crystal molybdenum disulfide (MoS2)
utilising a focused helium ion beam. Site-specific irradiation with the probe
of a helium ion microscope (HIM) allows for the creation of charged defects in
the MoS2 lattice. The reversible drift of these locally seeded defects in the
applied electric field modulates the resistance of the semiconducting channel,
enabling versatile memristive functionality on the nanoscale. We find the
device can reliably retain its resistance ratios and set biases for hundreds of
switching cycles at sweep frequencies of up to 2.9 V/s with relatively low
drain-source biases. We also demonstrate long-term potentiation and depression
with sharp habituation that promises application in future neuromorphic
architectures. This work advances the down-scaling progress of memristive
devices without sacrificing key performance parameters such as power
consumption or its applicability for synaptic emulation.
