  We demonstrate the possibility in quantifying the Raman intensities for both
specimen and substrate layers in a common stacked experimental configuration
and, consequently, propose a general and rapid thickness identification
technique for atomic-scale layers on dielectric substrates. Unprecedentedly
wide-range Raman data for atomically flat MoS2 flakes are collected to compare
with theoretical models. We reveal that all intensity features can be
accurately captured when including optical interference effect. Surprisingly,
we find that even freely suspended chalcogenide few-layer flakes have a
stronger Raman response than that from the bulk phase. Importantly, despite the
oscillating intensity of specimen spectrum versus thickness, the substrate
weighted spectral intensity becomes monotonic. Combined with its sensitivity to
specimen thickness, we suggest this quantity can be used to rapidly determine
the accurate thickness for atomic layers.
