  Atomically thin two-dimensional (2D) van der Waals semiconductors are
promising candidate materials for post-silicon electronics. However, it remains
challenging to attain completely uniform monolayer semiconductor wafers free of
over-grown islands. Here, we report the observation of the energy funneling
effect and ambient photodelamination phenomenon in inhomogeneous few-layer
WS$_2$ flakes under low illumination fluencies down to several nW/$\mu$m$^{2}$
and its potential as a non-invasive post-etching strategy for selectively
stripping the local excessive overlying islands. Photoluminescent tracking on
the photoetching traces reveals relatively fast etching rates around
$0.3-0.8\,\mu$m/min at varied temperatures and an activation energy of
$1.7\,$eV. By using crystallographic and electronic characterization, we also
confirm the non-invasive nature of the low-power photodelamination and the
highly preserved lattice quality in the as-etched monolayer products, featuring
a comparable average density of atomic defects (ca.$4.2\times
10^{13}\,$cm$^{-2}$) to pristine flakes and a high electron mobility up to
$80\,$cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$) at room temperature. This approach
opens a non-invasive photoetching route for thickness uniformity management in
2D van der Waals semiconductor wafers for electronic applications.
