Recent Advances in Ultrathin Chiral Metasurfaces by Twisted Stacking

Abstract

chiral plasmonic nanoparticles and their self-assembled structures as colloidal suspensions. [6][7][8][9] Recently, beyond noble metal plasmonics, solid-state layered nanomaterials that are rotationally aligned with a defined twist angle are becoming increasingly investigated (Figure 1). Among these are twisted 2D van der Waals (vdW) materials, [10][11][12] twisted single-crystal slabs, [13,14] twisted aligned nanowire thin films, [15][16][17][18] and twisted metasurfaces with periodic subunits [19][20][21] (Figure 2). These chiral stacked materials possessing geometric handedness and optical chirality can be seen as truncated and minimalistic versions of supramolecular liquid crystals in the chiral nematic phase or of 3D chiral photonic crystals. [22][23][24] Compared to their bulk or multiple-layer counterparts, the fabrication becomes greatly simplified for bilayer or few-layer chiral metamaterials, enabling precise control over the interlayer twist angle to manipulate lightmatter interactions. Ultrathin chiral metamaterials and metasurfaces with tunable optical and chiroptical responses are thus an active field for study.Twisting achiral layered nanostructures in parallel planes enables engineering of the extrinsic chirality and related optical performance. Specifically, the twist angle from counterclockwise rotation of an upper layer with respect to the beneath one is defined to be positive, θ > 0°, leading to a left-handed stacking geometry. [10,18] Accordingly, negative twist angle from clockwise rotation gives rise to the right-handed counterpart. Accurate control over the interlayer rotation angle offers flexible manipulation of properties, especially optical activity, of twisted layered systems of a wide variety of monolayer constituents and dimensions. A well-studied system is twisted bilayer graphene (TBG), catalyzing the research on twisted stacked nanostructures over the past few years, especially as many intriguing properties of magic-angle graphene are uncovered. [28][29][30] The twist angle dependencies of phonon dispersion, [31] optical absorption and reflection, [32,33] circular dichroism (CD) and birefringence, [10,34] second harmonic generation (SHG), [35] and photoresponse [36,37] of TBG have been extensively explored in the past few years. Similar realizations have been reported for twisted nanostructures of other 2D materials such as transition metal dichalcogenides, [38,39] graphitic carbon nitride, [40] and hexagonal boron nitride (hBN), [41] as well as non-2D systems like polymeric thin films or patterned plasmonic nanohole arrays. [42,43] Therefore, there exists fertile ground for chiral metasurface design Artificial chiral nanostructures have been subjected to extensive research for their unique chiroptical activities. Planarized chiral films of ultrathin thicknesses are in particular demand for easy on-chip integration and improved energy efficiency as polarization-sensitive metadevices. Recently, controlled twisted stacking of two or more layers of nanomaterials, such as 2D van der ...

Circularly Polarized Light-Enabled Chiral Nanomaterials: From Fabrication to Application

“…Lots of chiral materials, such as chiral nematic mesoporous materials [43], chiral liquid crystals [44], chiral helical structures [45,46], chiral gold nanoclusters [47], chiral biointerface materials [48], and chiral plasmonic materials [48][49][50][51], have been prepared using wet-chemical method. Many comprehensive reviews on chiral materials have been published recently [50][51][52][53][54][55][56][57][58][59][60][61][62][63], most of them highlighted the synthetic strategy and optical properties of chiral materials, as well as their applications.…”

Dielectric chiral metasurfaces for enhanced circular dichroism spectroscopy at near infrared regime

“…6,7,[9][10][11][12] However, fabrication ease and extra freedom in chiral metasurfaces (the planar version of chiral metamaterials) made them the more convenient solution for application in chiral optics. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] In chiral light-matter interaction, metasurfaces introduce chiro-optical effects, mainly categorized as circular-birefringence, circular dichroism (CD), or circular conversion dichroism (CCD). Circular birefringence, also termed optical activity (OA) is dened as the change in polarization of light passing through the optically active material, whereas CD is the differential absorption of both spins of circularly polarized (CP) light.…”

Advances in Meta-Optics and Metasurfaces: Fundamentals and Applications

“…Recent advances in meta-optics have been applied in the demonstrations of many exotic optical manipulations and various useful meta-devices [ 101 , 102 , 103 , 104 , 105 , 106 ]. Metasurface-based applications are promising alternatives to replacing existing optical devices, owning to the ultrathin, ultracompact, and multifunctional properties of meta-devices based on the principles of meta-optics [ 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 ]. Meta-optics offer the possibility to address the limitations of conventional optics and a new paradigm to achieve on-chip integrated meta-devices with multi-functional and parallel control of light beams [ 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 ].…”