Interference effect and Raman depolarization behavior in MoO2 bubbles

Abstract

Here, MoO2 bubbles are firstly found in MoO2 nanosheets (NSs) synthesized by chemical vapor deposition and exposed to air for 2–3 years. Interestingly, the Newton’s rings are clearly observed in Raman map of MoO2 bubbles. Meanwhile, it’s found that the height of bright rings close to the 1/2, 2/2, 3/2 of the laser wavelength, confirming that the Newton’s rings in Raman map are caused by the laser interference on the surface of bubbles. At the same time, based on simple membrane theory, the adhesion energy 0.15 and 1.08 J/m2 between MoO2 NSs and different SiO2/Si substrates are extracted. Moreover, Raman depolarization effect is observed on the surface of MoO2 bubbles. As the aspect ratio of bubbles increases from 0.16 to 0.21, the relative-depolarization ratios of 205 cm−1 and 750 cm−1 phonon modes are gradually increased from 18% to 46% and 10–36%, respectively. The Raman depolarization behavior should be ascribed to the surface strain of MoO2 bubbles leading to the asymmetric changes of photoelastic tensor in all directions of the crystal. This finding maybe provides a reference for regulating the polarization characteristics of MoO2 by adjusting its surface strain and ultimately achieving application in the field of photonics.