  Thin films of noble-metal-based transition metal dichalcogenides, such as
PtSe$_2$, have attracted increasing attention due to their interesting
layer-number dependent properties and application potential. While it is
difficult to cleave bulk crystals down to mono- and few-layers, a range of
growth techniques have been established producing material of varying quality
and layer number. However, to date, no reliable high-throughput
characterization to assess layer number exists. Here, we use top-down liquid
phase exfoliation (LPE) coupled with centrifugation to produce widely basal
plane defect-free PtSe$_2$ nanosheets of varying sizes and thicknesses.
Quantification of the lateral dimensions by statistical atomic force microscopy
allows us to quantitatively link information contained in optical spectra to
the dimensions. For LPE nanosheets we establish metrics for lateral size and
layer number based on extinction spectroscopy. Further, we compare the Raman
spectroscopic response of LPE nanosheets with micromechanically exfoliated
PtSe$_2$, as well as thin films produced by a range of bottom up techniques. We
demonstrate that the Eg1 peak position and the intensity ratio of the Eg1/ A1g1
peaks can serve as robust metric for layer number across all sample types and
will be of importance in future benchmarking of PtSe$_2$ films.
