Fano resonance-induced asymmetric scissors modes and anharmonic interactions in MoO3 nanostructures

Abstract

MoO3 nanostructures (NSs) have emerged as a potential candidate for field-effect transistors, thermoelectronic, and optoelectronic devices because of their wide range of stoichiometry, exceptional structural, optical, and electrical properties. Controlling electron–phonon (e–ph) interactions in MoO3 NSs by structural phase tuning offers an efficient way to tailor the charge-carrier mobility, heat transport, and non-radiative transitions for these next-generation devices. The present temperature-dependent and laser power-dependent Raman studies on Fano line shapes of oxygen defect-sensitive scissors modes (c axis) revealed significant e–ph interactions in α-MoO3, compared to h/α-MoO3, and h-MoO3 NSs at higher temperatures and laser power. At higher temperatures, the optical phonons in these MoO3 NSs interact with an electronic continuum of thermally excited donor-level electrons, resulting in non-radiative intraband transitions. The temperature-dependent photoluminescence spectroscopy was employed to investigate these non-radiative intraband transitions. The density functional theory calculations revealed that α-MoO3 exhibited a significantly higher oxygen defect stability (c axis) than h/α-MoO3 and h-MoO3. Therefore, the e–ph interactions in α-MoO3 are enhanced by the substantial oxygen defects (c axis) in comparison to other phases. In addition, a method has been proposed to determine the charge density of states [N(EF)] of 59.14 (eV)−1 quantitatively in α-MoO3 using a laser power-dependent study, which can also be applied to similar semiconducting oxides. Through structural phase control, our findings explain e–ph interactions, non-radiative transitions, and thermal transport in MoO3 for field-effect transistors, optoelectronic, and thermal device applications.