Exploring Properties of MoS2 Transferred onto Periodically Patterned Substrates

Abstract

This project aimed to characterize the strain in few-layer MoS2 via Raman spectroscopy. Periodic patterns were etched into Si/SiO2 wafers using photolithography, after which MoS2 flakes were exfoliated and transferred on top of the patterns, leading to a mechanical deformation of the layers. We investigated the topography of the flakes via atomic force microscopy, and discovered that the sudden drop-off of the flakes had led to an increased presence of air bubbles. By investigating our samples with Raman spectroscopy, we first confirmed the presence of the two characteristic peaks E1_2g and A1g. Comparison with other studies indicates that our MoS2 flakes are thinner than our AFM measurements suggested, which we attribute to presence of air bubbles, which can both artificially increase the step heights as well as disturb the vibrational modes. Modulations in the Raman response around the location of the bubbles shows a softening of the difference of the peak position, although the change is not significant enough. Similarly, no significant change in the Raman response was observed at the edges of the patterns, due to the shallow etch depth, which does not induce a strain important enough to be resolved by our Raman system. These results highlight the challenges associated with strain characterization of crystalline systems.