Near-Field Mapping of Localized Plasmon Resonances in Metal-Free, Nanomembrane Graphene for Mid-Infrared Sensing Applications

Abstract

Graphene, as an optically transparent material, typically defies any attempt for mid-infrared (mid-IR) absorption, which limits its applications in mid-IR biosensing. Although remarkable evidence for mid-IR nanopatterned graphene plasmons has been reported via the induction of free charge carriers, no study so far has investigated plasmonic excitation in nanopatterned graphene without employing induced voltage, high chemical doping, or metallic reflectors. In this work, we show that localized plasmon resonance (LSPR) can be probed in metal-free, naturally doped, nanomembrane graphene (NMG) without induced voltage or using metallic layers. We rely on facile, lithography-free, fabrication methodology to pattern nanoscale holes in a single sheet of graphene using Au nanoislands with hole dimensions as small as 10 nm. We image the LSPR at the graphene membrane edges via scanning near-field optical microscopy. Our experimental findings are confirmed by theoretical electromagnetic field mapping at the graphene membrane edges leading to noticeable absorption. We demonstrate the dependence of this absorption wavelength on the hole diameter and interhole distance; hence, we present a new avenue to fundamentally boost light harvesting with naturally doped NMG which is pivotal for mid-IR sensors. We show that our designed NMG can be used as a mid-IR biosensor with theoretically calculated sensitivity of 825 nm/RIU.

Graphene Nanoplatelet–Au Nanoparticle Hybrid as a Capacitive-Metal–Oxide–Semiconductor pH Sensor

“…At 4 nm thickness, gold is not a continuous layer, but rather a group of islands; because of the clustering mechanism of gold, these islands shrink upon annealing. 32 Therefore, the Au layer was annealed at 300 °C for 30 min in vacuum, using a UniTemp RTP 150 system. The hybrid film was prepared by depositing the nanoislands on the Si chips, as described above, followed by spin coating the GP film.…”

“…29 Graphene is known to have a zero band gap, and in electronic applications, having a gap is one of the important properties, which can be obtained in graphene by achieving regular or irregular holes. 30,31 In our previous work, we created a nanomesh graphene with an easy and low-cost method, 32 and the same method was followed here, however, using a graphene nanoplatelet (GP) film. GPs have the advantage of combining the properties of graphite and graphene, such as the high electrical conductivity, the electron mobility, and stability.…”

Infrared Polaritonic Biosensors Based on Two-Dimensional Materials

“…Later in 2018, nanomembrane graphene (NMG) has also been proposed as an efficient way to develop mid-IR biosensing applications and it has been proved that LSPR can be probed in NMG without the need of external chemical doping, induced potential or even thick reflective metallic layers [ 70 ]. The synthesis procedure of NMG is as follows, (i) firstly covering the graphene with Au layer and then annealing to obtain the Au nano-islands, (ii) then the rest of the graphene was protected by Cr layer, and (iii) finally the NMG was fabricated by removing the Au and Cr layers.…”

“…( a – d ) Reproduced with permission [ 33 ], Copyright 2015, AAAS. ( e – h ) Reproduced with permission [ 70 ], Copyright 2018, American Chemical Society. …”

High Temperature Mid‐IR Polarizer via Natural In‐Plane Hyperbolic Van der Waals Crystals

“…Phonons have a relatively long lifetime compared to plasmons resulting in lower optical losses than their analogous plasmonic-based metamaterials [7][8][9] in which photons are coupled with plasmons. Many NHMs [1][2][3] exhibit hyperbolic anisotropy in mid-IR spectral region (3-30 µm) which has diverse applications like polarized IR imaging, [10] molecular sensing, [11,12] free space communication, [13] and quantum interference. [14] Unlike h-BN, which possesses uniaxial hyperbolic anisotropy (i.e., ε xx = ε yy ≠ ε zz ), α-MoO 3 exhibits in-plane hyperbolic anisotropy (i.e., ε xx ≠ ε yy ≠ ε zz ) which is particularly beneficial for planar mid-IR optical devices.…”