Graphene Coated Dielectric Hierarchical Nanostructures for Highly Sensitive Broadband Infrared Sensing

Abstract

The nfrared (IR) band contains rich matter information, and has great scientific interest and technological importance in practical applications in various fields, [1] such as thermal imaging, [2] chemical sensor, [3,4,5] optical communication, [6] and medical diagnosis. [7] IR plasmonic nanostructures [8,9] supporting IR light-matter interaction in nanoscale, which contribute strongly enhanced local electromagnetic field, are essential for ultrasensitive IR spectroscopy, photodetections, modulation, and generation.Strong IR absorption can be achieved by exploiting the strong optical near-field in the vicinity of resonant metallic nanostructures. [10][11][12][13] Nevertheless, the metal plasmonic nanostructures [14,15] are ultimately limited by the spatially non-homogenous, relatively poor field confinement and large radiation losses in IR band. In contrast, the electromagnetic fields of graphene plasmonic nanostructures [14,15] display Broadband infrared (IR) absorption is sought after for wide range of applications. Graphene can support IR plasmonic waves tightly bound to its surface, leading to an intensified near-field. However, the excitation of graphene plasmonic waves usually relies on resonances. Thus, it is still difficult to directly obtain both high near-field intensity and high absorption rate in ultra-broad IR band. Herein, a novel method is proposed to directly realize high nearfield intensity in broadband IR band by graphene coated manganous oxide microwires featured hierarchical nanostructures (HNSs-MnO@Gr MWs) both experimentally and theoretically. Both near-field intensity and IR absorption of HNSs-MnO@Gr MWs are enhanced by at least one order of magnitude compared to microwires with smooth surfaces. The results demonstrate that the HNSs-MnO@Gr MWs support vibrational sensing of small organic molecules, covering the whole fingerprint region and function group region. Compared with the graphene-flake-based enhancers, the signal enhancement factors reach a record high of 10 3 . Furthermore, just a single HNSs-MnO@Gr MW can be constructed to realize sensitively photoresponse with high responsivity (over 3000 V W −1 ) from near-IR to mid-IR. The graphene coated dielectric hierarchical micro/nanoplatform with enhanced nearfield intensity is scalable and can harness for potential applications including spectroscopy, optoelectronics, and sensing.

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“…High‐resolution TEM revealed an interatomic spacing of 0.347 nm, confirming the formation of graphene (Figure 2c ; Figure S2 , Supporting Information). [ 31 ] Notably, the FG exhibited a significantly smaller size compared to the original CB (Figure 2d,e ), attributed to the evaporation of heteroatom content during the high‐temperature FJH treatment. X‐ray photoelectron spectroscopy (XPS) analysis can support this, wherein the FG reveals much lower heteroatom content compared to CB (Figure 2f ).…”