  Atomically thin circuits have recently been explored for applications in
next-generation electronics and optoelectronics and have been demonstrated with
two-dimensional lateral heterojunctions. In order to form true 2D circuitry
from a single material, electronic properties must be spatially tunable. Here,
we report tunable transport behavior which was introduced into single layer
tungsten diselenide and tungsten disulfide by focused He$^+$ irradiation.
Pseudo-metallic behavior was induced by irradiating the materials with a dose
of ~1x10$^{16} He^+/cm^2$ to introduce defect states, and subsequent
temperature-dependent transport measurements suggest a nearest neighbor hopping
mechanism is operative. Scanning transmission electron microscopy and electron
energy loss spectroscopy reveal that Se is sputtered preferentially, and
extended percolating networks of edge states form within WSe$_2$ at a critical
dose of 1x10$^{16} He^+/cm^2$. First-principles calculations confirm the
semiconductor-to-metallic transition of WSe$_2$ after pore and edge defects
were introduced by He$^+$ irradiation. The hopping conduction was utilized to
direct-write resistor loaded logic circuits in WSe$_2$ and WS$_2$ with a
voltage gain of greater than 5. Edge contacted thin film transistors were also
fabricated with a high on/off ratio (> 10$^6$), demonstrating potential for the
formation of atomically thin circuits.
