Air Gap-Based Cavities Dramatically Enhance the True Intrinsic Spectral Signals of Suspended and Pristine Two-Dimensional Materials

Abstract

The properties of two-dimensional (2D) materials are readily affected by their surroundings. Therefore, the underlying substrates and surrounding materials always disturb the pristine properties of 2D materials. Herein, we describe how the pristine properties of suspended 2D materials can be precisely extracted from Raman and photoluminescence (PL) spectra with great signal enhancements by taking advantage of both air gap suspension and nanocavity enhancement effects. The modes of the Raman emission lines were enhanced to almost the same degree when the 2D materials were positioned over the nanocavity: the 2D/G peaks of suspended single-layer graphene (SLG) and the E 1 2g /A 1g peaks of MoS 2 were significantly enhanced almost equally. Moreover, recording Raman and PL spectra at different positions of the suspended 2D materials was a very powerful tool for observing charge transfer between the pristine 2D materials and the surrounding materials. We also found that the residual holes of the suspended SLG could be neutralized by aluminum (Al) at certain positions. By employing the air cavity structure, we could readily locate the charge neutrality point of the suspended 2D materials. In addition, the PL intensity of MoS 2 could be greatly enhanced when using the same nanocavity. The great enhancements in the PL signals from the suspended 2D materials allowed us to further investigate the spectral weights of both the A 0 exciton and A − trion peaks when MoS 2 was suspended or supported upon various metal films. This approach may open up new doors for techniques allowing precise characterization of abundant information from pristine and suspended 2D materials.

Self-Rolling of Monolayer Graphene for Ultrasensitive Molecular Sensing

“…Figure c shows the Raman result of the microtube, in which the D, G, and 2D peaks can be recognized through color distribution. Due to the low yield of Raman scattering and the atomic thickness of graphene, the Raman signals of graphene are supposed to be weak without employing techniques for Raman enhancement. , However, with an air microcavity between suspended graphene and the substrate, its Raman intensity can be greatly enhanced by interference-enhanced Raman scattering (IERS). , Therefore, the Raman intensity of suspended graphene (red region in Figure b) is significantly larger than that of graphene on the Cr strip. Figure d shows a comparison between the Raman spectrum acquired from suspended graphene (red line) and graphene on Cr (black line).…”

“…Due to the low yield of Raman scattering and the atomic thickness of graphene, the Raman signals of graphene are supposed to be weak without employing techniques for Raman enhancement. 18,35 However, with an air microcavity between suspended and the substrate, its Raman intensity can be greatly enhanced by interference-enhanced Raman scattering (IERS). 36,37 Therefore, the Raman intensity of suspended graphene (red region in Figure 3b) is significantly larger than that of graphene on the Cr strip.…”

“…Polycrystalline monolayer graphene grown on the Ge(111) substrate was used for its relatively moderate fracture toughness. , The diameter of the graphene microtubes can be tuned from 5.2 to 13.9 μm by changing the thickness of the strain layers. Due to the suspension of the graphene as well as the tubular structure, large Raman enhancement was achieved. , To highlight the enhanced-Raman scattering of tubular graphene, the molecular sensors based on the GERS effect had been fabricated. Trace amounts of rhodamine 6G (R6G) molecules were detected down to 10 –11 M showing excellent molecular sensing ability.…”

“…Due to the suspension of the graphene as well as the tubular structure, large Raman enhancement was achieved. 18,19 To highlight the enhanced-Raman scattering of tubular graphene, the molecular sensors based on the GERS effect had been fabricated. Trace amounts of rhodamine 6G (R6G) molecules were detected down to 10 −11 M showing excellent molecular sensing ability.…”

Single pixel wide gamut dynamic color modulation based on graphene micromechanical system

“…The use of DBRs in combination with a polymer sacrificial layer enables the achievement of the aircavity [44,57]. On the other hand, multilayer graphene films grown by chemical vapor deposition (CVD) can be transferred into a DBR cavity using a semi-dry transfer technique [34,35,58].…”