Temperature-dependent Raman studies and thermal conductivity of direct CVD grown non-van der Waals layered Bi2O2Se

Layered materials with the van der Waals gap have been extensively studied due to their fascinating properties. However, non-van der Waals type layered Bi2O2Se exhibiting remarkable properties is challenging to grow due to the weak electrostatic interaction among layers. Herein, we present chemical vapor deposition (CVD) growth of an air-stable ultrathin Bi2O2Se semiconductor with high structural and chemical uniformity. By tuning the growth temperature, we obtained ultra-smooth single crystals of few-layer Bi2O2Se (LBOS) on mica and quartz substrates, as confirmed from x-ray diffraction, micro-Raman, and high-resolution TEM analyses. Furthermore, a low-temperature Raman study has been conducted to better realize phonon dispersion in the as-grown LBOS in the temperature range 78-293 K. It is observed that the A(1g) phonon mode frequency of LBOS varies linearly with the temperature with a first-order temperature coefficient (alpha) of -0.017 87 +/- 0.0011 cm(-1) K-1. The broadening of the Raman spectral linewidth with temperature has been explained based on the phonon decay, and a phonon lifetime of 2.08 ps is found for LBOS at absolute zero temperature. Finally, the in-plane thermal conductivity of LBOS is estimated by a non-contact measurement technique in a relatively straightforward way. Taking advantage of the excitation power dependency of the A(1g) mode and using the first-order temperature coefficient, the in-plane thermal conductivity of LBOS is estimated to be similar to 1.6 W/mK. Our results pave the way for large-area CVD growth of LBOS on arbitrary substrates and developing insights into electron-phonon and phonon-phonon interactions in non-van der Waals 2D materials.

Automated summary

In this study, air-stable ultrathin Bi2O2Se semiconductor was successfully grown by chemical vapor deposition (CVD), showing high structural and chemical uniformity. The phonon dispersion and in-plane thermal conductivity of LBOS were investigated through Raman studies and estimation techniques, providing insights into the electron-phonon and phonon-phonon interactions in non-van der Waals 2D materials.