Calculated phonon modes, infrared and Raman spectra in orthorhombic $\alpha$-MoO$_3$ and monolayer MoO$_3$

TL;DR

This study uses first-principles calculations to analyze vibrational properties, phonon modes, and infrared and Raman spectra of orthorhombic $ ext{MoO}_3$ and its monolayer form, aiding experimental identification.

Contribution

It provides detailed computational insights into the vibrational spectra of $ ext{MoO}_3$, including monolayer form, which were previously unexplored.

Findings

Calculated phonon frequencies and spectra match experimental data.

Identified polarization-dependent features in IR and Raman spectra.

Analyzed frequency shifts in monolayer compared to bulk.

Abstract

Orhorhombic $\alpha$-MoO$_3$ is a layered oxide with various applications and with excellent potential to be exfoliated as a 2D ultrathin film or monolayer. In this paper, we present a first-principles computational study of its vibrational properties. Our focus is on the zone center modes which can be measured by a combination of infared and Raman spectroscopy. The polarization dependent spectra are simulated. Calculations are also performed for a monolayer form in which "double layers" of Mo$_2$O$_6$ which are weakly van der Waals bonded in the $\alpha$-structure are isolated. Shift in phonon frequencies are analyzed.