Study of Black Phosphorus Using Angle-Resolved Polarized Raman Spectroscopy with 442 nm Excitation

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.