Evidence of Optical Circular Dichroism in GaAs‐Based Nanowires Partially Covered with Gold

Abstract

thus paves the way for the important applications spreading from negative refraction, [1][2][3] chiral sensing [4,5] to production of optical field carrying out optical angular momentum for quantum information applications. [6] It has been shown that plasmonic nanostructures forming 1D [7] elements, 2D metasurfaces, [8][9][10] and 3D metamaterials [11] can exhibit linear chiral response due to their own, intrinsic chirality. Also semiconductor nanostructures can exhibit chiral features. [12][13][14][15][16] From the optical point of view, chiral structures possess the ability to rotate the plane of the polarization of electromagnetic waves (optical activity), and give rise to circular dichroism-i.e., the difference in the absorption of right-and lefthanded circular polarized light.Apart from 3D chiral objects, the possibility to obtain optical chirality, i.e., optical activity, with nonchiral elements was studied in the past, [17] but only recently reconsidered. [18,19] This phenomenon is obtained when the experimental configuration composed by both the nonchiral object and the optical incident field is nonsuperimposable on its mirror image. [20] This is called "extrinsic" chirality; in our previous works we have investigated this type of chirality in tilted golden nanowires by means of both linear (reflection and absorption) and nonlinear (second harmonic generation) measurements. [20][21][22][23] III-V semiconductor nanowires (NWs) have been widely investigated since they exhibit good waveguiding properties thus offering a light manipulation at nanoscale. Coupling of the incident light to the discrete leaky waveguide modes above the bandgap in NWs leads to increased resonant absorption, thus paving the way for important applications such as energy harvesting, spectral selectivity, lasing, spin angular momentum generation, etc. [24][25][26][27] Metallic NWs have also been investigated for plasmonic laser applications [28][29][30] and possibility of surface plasmon polaritons excitation. [31] One step further is the partial covering of such NWs with gold: this can induce, along with the proper experiment setup, the symmetry breaking which leads to chiral response.In this paper, for the first time to our knowledge, we report on a circular dichroism behavior from semiconductor hexagonal Semiconductor nanostructures hybridized with metals have been known to offer new opportunities in nonlinear optics, plasmonics, lasing, biosensors; among them GaAs-based nanowires (NWs) hybridized with gold can offer new functionalities, as chiral sensing and light manipulation, as well as circular polarization sources. This study investigates GaAs-AlGaAs-GaAs NWs fabricated by self-catalyzed growth on Si substrates, and partially covered with gold, thus inducing the symmetry breaking and a potential chiral response. Three different samples are investigated, each of them with a different morphology, as the length and the overall diameter ranging from 4.6 to 5.19 µm and from 138 up to 165 nm, respectively. The samples are first char...

Circular Dichroism in Low-Cost Plasmonics: 2D Arrays of Nanoholes in Silver

“…Plasmonics is promising for that matter as it can enhance interaction with electromagnetic fields at the nanoscale. Chirality can be designed [19] by breaking the symmetry in plasmonic nanomaterials during their fabrication, or with a proper oblique incidence set-up, as it was experimentally observed previously [20][21][22][23][24]. When a sample exhibits CD at normal incidence, it is said to be intrinsically chiral; on the contrary, in achiral samples the symmetry breaking can be induced by properly tilting the experimental set-up (extrinsic chirality).…”

Chiral near-field manipulation in Au-GaAs hybrid hexagonal nanowires

“…4(a). We have investigated such NW in [11] where optical circular dichroism was measured by means of photo-acoustic technique. It was shown that in such NW there is still an absorption peak due to the excitation of weakly guided mode, and the experimental results were shown to be in good agreement with numerical simulations.…”

“…The fabrication of such NWs by molecular beam epitaxy on p-Si(111) wafers using lithography-free Si/SiOx patterns has already proved that high quality samples with desired geometrical parameters can be produced [22]. Moreover, we recently reported experimental results on circular dichroism in the same kind of structures [11,23]: in reference [23] we applied the photo acoustic spectroscopy to measure the resonant absorption peaks due to the excitation of weakly-guided modes, while in [11] we reported on circular dichroism when these NW are hybridized with Au.…”

“…The collective effects in these nanostructures can be characterized by means of e.g. photo-acoustic technique or second harmonic generation [11][12][13][14][15][16]; however, applications based on the enhanced interaction between nanostructures and chiral molecules require more profound investigation and understanding of near field chiral effects. In fact it has been shown that the local value of the optical chirality governs the processes of circular dichroism: different absorption for differently headed fields in a medium [17].…”

Self-Organized Conductive Gratings of Au Nanostripe Dimers Enable Tunable Plasmonic Activity

“…Plasmonic nanoantennas have collected a strong research and technological interest within the last decade, due to their unique capability to achieve resonant light scattering and near-field confinement at the nanoscale level, enabling novel functionalities in nano-optics, biosensing and energy harvesting [1][2][3][4][5][6][7][8]. In particular, the possibility to tune localized plasmon resonances of subwavelength noble metal nanostructures over a broadband spectrum has been investigated for the selection and local amplification of weak molecular signals in linear and/or nonlinear optical spectroscopies [2,[6][7][8][9][10][11][12]. One possibility for the nanofabrication of highly sensitive biosensing templates and nanodevices is given by lithographic techniques, which allow the increased complexity of the individual meta-atoms, controlling the shape and/or the inter-particle spacing at the nanoscale level [13][14][15][16].…”