  We investigated 10 to 200 nm thick black phosphorus flakes on SiO2/Si and
polyimide substrates by Angle-resolved Polarized Raman spectra (ARPRS) using
442 nm excitation wavelength. The results revealed that ARPRS with 442 nm
excitation can provide unambiguous, convenient, non-destructive and fast
determination of BP's crystallographic orientation. The substrate and thickness
dependencies of Raman spectra and Raman tensor elements were studied. These
dependencies were shown to be influenced by Raman excitation laser heating
effect. By comparing with in-situ Raman measurements at elevated temperatures,
we were able to quantify the laser-heating effect, which is significant and
hard to avoid for Raman measurements of BP on polyimide substrates due to the
poor thermal conductivity of the substrate. Thermal processing by substrate
heating was shown to have a significant impact on BP on SiO2/Si substrate, but
not for BP on polyimide due to smaller thermal expansion mismatch. Our results
give important insights on Raman Spectroscopy characterizations of BP on
different substrates.
