  Two-dimensional topological insulators (2DTIs) or quantum spin Hall
insulators are attracting increasing attention due to their potential
applications in next-generation spintronic devices. Despite their promising
prospects, realizable 2DTIs are still limited. Recently, Ta2Pd3Te5, a
semiconducting van der Waals material, has shown spectroscopic evidence of
quantum spin Hall states. However, achieving controlled preparation of few- to
monolayer samples, a crucial step in realizing quantum spin Hall devices, has
not yet been achieved. In this work, we fabricated few- to monolayer
Ta$_2$Pd$_3$Te$_5$ and performed systematic thickness- and
temperature-dependent Raman spectroscopy measurements. Our results demonstrate
that Raman spectra can provide valuable information to determine the thickness
of Ta2Pd3Te5 thin flakes. Moreover, our angle-resolved polarized Raman (ARPR)
spectroscopy measurements show that the intensities of the Raman peaks are
strongly anisotropic due to the quasi-one-dimensional atomic structure,
providing a straightforward method to determine its crystalline orientation.
Our findings may stimulate further efforts to realize quantum devices based on
few or monolayer Ta$_2$Pd$_3$Te$_5$.
