  Memristive devices have drawn considerable research attention due to their
potential applications in non-volatile memory and neuromorphic computing. The
combination of resistive switching devices with light-responsive materials is
considered a novel way to integrate optical information with electrical
circuitry. On the other hand, 2D materials have attracted substantial
consideration thank to their unique crystal structure, as reflected in their
chemical and physical properties. Although not the major focus, van der Waals
solids were proven to be potential candidates in memristive devices. In this
scheme, the majority of the resistive switching devices were implemented on
planar flakes, obtained by mechanical exfoliation. Here we utilize a facile and
robust methodology to grow large-scale vertically aligned MoS$_2$ (VA-MoS$_2$)
films on standard silicon substrates. Memristive devices with the structure
silver/VA-MoS$_2$/Si are shown to have low set-ON voltages (<0.5V),
large-retention times ($>2\times10^4$ s) and high thermal stability (up to 350
$^\circ$C). The proposed memristive device also exhibits long term potentiation
/ depression (LTP/LTD) and photo-active memory states. The large-scale
fabrication, together with the low operating voltages, high thermal stability,
light-responsive behaviour and long-term potentiation/depression, makes this
approach very appealing for real-life non-volatile memory applications.
