Letter pubs.acs.org/NanoLett
Programmable Extreme Chirality in the Visible by Helix-Shaped Metamaterial Platform Marco Esposito,†,‡ Vittorianna Tasco,*,† Francesco Todisco,†,‡ Massimo Cuscunà,† Alessio Benedetti,§ Mario Scuderi,∥ Giuseppe Nicotra,∥ and Adriana Passaseo† †
CNR NANOTEC- Istituto di Nanotecnologia, Polo di Nanotecnologia, c/o Campus Ecotekne, via Monteroni, I-73100 Lecce, Italy Dipartimento Mat-Fis Ennio De Giorgi, Università del Salento, I-73100 Lecce, Italy § Dipartimento D.I.E.T., “Sapienza: Università di Roma”, Via Eudossiana 18, I-00184 Rome, Italy ∥ CNR-IMM Sezione di Catania, Strada VIII, 5, I-95121 Catania, Italy ‡
S Supporting Information *
ABSTRACT: The capability to fully control the chiro-optical properties of metamaterials in the visible range enables a number of applications from integrated photonics to life science. To achieve this goal, a simultaneous control over complex spatial and localized structuring as well as material composition at the nanoscale is required. Here, we demonstrate how circular dichroic bands and optical rotation can be effectively and independently tailored throughout the visible regime as a function of the fundamental meta-atoms properties and of their three dimensional architecture in a the helix-shaped metamaterials. The record chiro-optical effects obtained in the visible range are accompanied by an additional control over optical efficiency, even in the plasmonic context. These achievements pave the way toward fully integrated chiral photonic devices. KEYWORDS: Chiral metamaterials, dielectric chiral metamaterials, circular dichroism, optical rotation, plasmonics
C
using circularly polarized light at the chip-scale, as well as the study of innovative optically active drugs,9,10 would potentially benefit from such a technology. However, for this purpose nanoscaling must be applied to complex-shape structures, resulting a particularly challenging fabrication issue. We have recently demonstrated how the focused ion beam induced deposition (FIBID) of metallic deposits, upgraded with the dose compensation11 and the tomographic rotatory growth12 concepts, is an effective tool to artificially craft helix-shaped and even multibundled nanostructures. Here, we show the achievement in helix-based metamaterials of extremely high circular dichroism and optical rotation in the VIS, obtained by matching the structural features of the metaatom with inspecting light. The versatility of this advanced approach offers the additional capability to program on demand the chiral response in this spectral range, as a function of the spatial architecture and the material composition of its building block, providing simultaneously the unique advantage to preserve optical transmission levels suitable for practical operation of photonic devices, such as filters, rotators, polarizers, or optical diodes.
hiral metamaterials are an emerging class of metamaterials capable of interacting with circularly polarized light because of the three-dimensional (3D) variation of the metaatom structure along the light propagation direction. The most pronounced chiral response can be obtained when incident light matches the geometrical features of the chiral metamaterial building block, as demonstrated by the chiral 3D photonic crystals 1,2 and the gold helix photonic metamaterial3 in the near- and mid-infrared, respectively. These results paved the way toward chiral photonic devices with potential applications in the telecommunication field. Metamaterials with large rotatory power or circular dichroism in the visible spectral range, enabling effective light polarization manipulation, are widely demanded for the development of integrated photonic circuits where they can operate, for example, as miniature polarization controllers, optical isolators, and circular polarizers. This would counterbalance the lack of naturally occurring circularly birefringent materials, providing compact solutions as an alternative to commonly used multi optical component systems. Photonic metamaterials with large circular polarization discrimination in the VIS are also required for the recognition and the analysis of optically active biological systems,4,5 such as natural amino acid structures or proteins, where the intensity of this effect is extremely small and difficult to detect.6 A number of applications in polarimetric imaging,7 emission,8 and sensing © 2016 American Chemical Society
Received: June 23, 2016 Revised: August 20, 2016 Published: August 26, 2016 5823
DOI: 10.1021/acs.nanolett.6b02583 Nano Lett. 2016, 16, 5823−5828
Letter
Nano Letters FIBID is a unique technology providing direct and fast production and integration of nanostructures within patterned substrates and optical devices. With respect to solution processes that demonstrated strong capability in manufacturing highly anisotropic nanostructures,13,14 this approach enables the full control, along all the three space dimensions and with nanometer accuracy, of the chiral nanostructures geometrical parameters and the shaping into even more complex fashion than the helix geometry.12 Most relevantly, the technology can be applied not only to different metals but also to various dielectric materials such as carbon or silicon dioxide, thus allowing the management of optical losses and the development of nanoscale 3D dielectric chiral metamaterials.15,16 We employed this technique to spatially assemble chiral building blocks with nanoscale features, both along the vertical direction and on the growth plane. The former approach leads to continuous, uniform, single wire, and multiloop helix nanosystems, obtained by 3D proximity effect compensation.11 With the latter scheme, complex concentric ordering of intertwined helices was accomplished by the tomographic rotatory growth method.12 Two material systems, providing different fundamental behaviors from metal to low loss dielectric, were used for a comparative study. The metallic helical metamaterials were grown using a Pt metal−organic precursor ((CH3)3(CH3C5H4)-Pt). This metal intrinsically presents catalytic activity17 that can be potentially combined with plasmonic effects in the visible18,19 and can find applications such as synthesis of chiral drugs or chiral molecules catalyzed by the chiro-optical activity. The analogue dielectric helical systems were built up by phenanthrene (C14H10). This has been reported to dissociate into diamond-like carbon20 deposits of significant interest as dielectric medium because of its high refractive index.21 The material composition of FIBID deposit results from the complex interplay between shape-dependent beam and precursor parameters.20,22,23 The different growth dynamics in the two material systems leads to significantly different nanostructure features, as revealed by scanning transmission electron microscopy (STEM) inspection, combined with energy dispersive X-ray (EDX) analysis (Figure 1 and Supplementary Figure S1). In the metal case (Figure 1a), the nanowire consists of Pt nanograins embedded into an amorphous carbon matrix.20,22,23 The overall volume composition, uniform across the nanowire section, is 50% of Pt and 45% of amorphous carbon (Figure 1c−e, and Supporting Information S1). In the Supporting Information S2, we analyze the plasmonic response of the single achiral Pt grains in the low-k dielectric matrix with respect to their absorption, extinction, and scattering cross sections in the visible spectral range, and we assume these elements as the fundamental plasmonic cornerstone of the metallic metamaterial. Following the helix growth along the vertical direction, the Pt nanograins assemble forming chiral plasmonic dipoles, which are expected to exhibit circular dichroism and optical activity,14,24 as confirmed by experimental results shown in the following. The helix nanowire from carbon precursor (Figure 1b) consists of a thick amorphous shell of carbon (classified as diamond-like carbon, i.e., a low loss dielectric) enveloping a tiny core with small precipitates of amorphous gallium (Figure
Figure 1. (a,b) STEM-HAADF image of two reference nanohelices, grown by FIBID starting from a Pt-precursor and a C-precursor, respectively, realized on a copper TEM grid for high resolution structural and compositional characterization. (c−e) High-magnification STEM-HAADF image of Pt-based nanowire; C and Pt EDX qualitative elemental maps exhibit uniform composition across the wire section section with Pt nanograins embedded in an amorphous carbon matrix. (f−h) High-magnification STEM-HAADF image of Cbased nanowire and related C, Ga EDX qualitative elemental maps showing Ga precipitates (diameter 1.5−4 nm) incorporated within a 30 nm core.
1f−h and Supporting Information S1), as an intrinsic effect of the FIBID growth dynamics.25 The first degree of freedom in the chiral metamaterial construction we present, is the evolution of the nanowire segment along the vertical axis in a helical shape with an external diameter (ED) of 300 nm and a full revolution vertical pitch (VP) of 500 nm. The vertical evolution is accomplished by varying the pitch number N from 0.5 to 1.5 in both the material systems under investigation. The geometrical size range has been engineered to maximize chiro-optical response in the VIS, following the periodic effective dipole model26 for the metal case and the effective refractive index model for the dielectric2,27 system. Three exemplary scanning electron microscopy (SEM) images of the Pt structures are reported in Figure 2. Identical structural features and fabrication tolerance characterize the correspondent carbon-based arrays (Supplementary Figure S3). The in-plane lattice constant of the fabricated arrays (500 nm) was sufficiently large to neglect the plasmonic interaction among the structures.28,29 Normal incidence transmittance measurements were conducted with circularly polarized light spanning the visible range and the related spectra of circular dichroism (CD) were calculated and expressed in terms of the ellipticity θ as CD = tan θ =
TLCP −
TRCP
TLCP +
TRCP
where TLCP and TRCP are the transmission of left- and rightcircularly polarized light, respectively. The experimental results, expressed in degree units, are shown, for the metallic and dielectric arrays, respectively, in Figure 3a,b. In addition, optical activity (OA), intended as the rotation angle of linearly polarized incident light, was measured in the same spectral range and plotted in Figure 3c,d. 5824
DOI: 10.1021/acs.nanolett.6b02583 Nano Lett. 2016, 16, 5823−5828
Letter
Nano Letters
Figure 2. SEM bird eye views of 3D helical nanosystem arrays with (a) N = 0.5, (b) N = 1, and (c) N = 1.5. The helix arrays were fabricated by FIBID using platinum-based precursors. The corresponding arrays in carbon are shown in the Supplementary Figure S3. The geometrical dimensions are ED = 300 nm, WD = 100 nm, lattice period (LP) = 500 nm and VP for one full revolution = 500 nm.
Figure 3. (a,b) Boost of experimentally measured CD, expressed in degree units, induced by the stacking of chiral dipoles along the normal to the substrate, in the metallic and dielectric arrays. Hybridization of plasmonic modes is highlighted by the bandwidth increase in the metallic metamaterials. (c,d) OA, measured as the polarization rotation angle of the linearly polarized incident light, for platinum and carbon based helical metamaterials. The side SEM images show the corresponding helix types with box color recalling the corresponding measured spectra.
When two unit metallic elements are vertically stacked (N = 1), the two dichroic bandwidths are increased with respect to the ones of the half-pitch structure (Figure 3a) because the plasmonic mode-hybridization induces the resonance splitting and generation of new dichroic modes of plasmonic origin.31,32 The continuity between the two stacked elements in our structures maximizes the coupling strength.33,34 The mode hybridization is further boosted up to an ellipticity of 10° when three metallic unit elements are stacked (pitch number N = 1.5), and the related dichroic bands result further broadened by additional oscillators contributing to the plasmonic resonances (more hybridized modes). It is worth noting that these results are a factor of 2 larger with respect to state of the art technology,35 enabled by the material choice (platinum) along with geometrical sizes matching this spectral range. In the dielectric system, the experimental difference among the transmission curves (Supplementary Figure S4b) for each circular polarization in the investigated range (400−900 nm)
In the platinum case, the half-pitch helix circular dichroism spectrum manifests the typical Cotton effect30 with two circular dichroic bands crossing at 600 nm. The corresponding circularly polarized transmission curves are shown in Supplementary Figure S4a. The dipole formation theory26 in plasmonic nanohelices suggests the onset of strong chirooptical effects when the overlapping of dipole moments within the structure with the incident light is boosted by the geometrical matching between structure and light handedness. For our geometry, a quarter pitch helical element does not exhibit circular dichroism (Supplementary Figure S5), whereas a metallic half pitch helical element shows a resonant chiral behavior, thus indicating the formation of a light-interacting plasmonic dipole moment. These observations suggest that the helix half pitch can be considered with a good approximation as the fundamental unit element (building block) characterizing the overall optical behavior of this metamaterial. 5825
DOI: 10.1021/acs.nanolett.6b02583 Nano Lett. 2016, 16, 5823−5828
Letter
Nano Letters
Figure 4. (a,b) SEM bird-eye views of chiral dipoles intertwined by the tomographic rotatory growth in both material systems. The geometrical dimensions are ED = 300 nm, WD = 100 nm, N = 1, and VP = 700 nm. The nanostructures were further spaced (LP = 900 nm) with respect to the analysis above in order to keep nearly constant the overall areal density of dipoles. (c,d) Measured CD and OA curves for platinum- and carbonbased triple helix arrays.
In the low-k dielectric case (Figure 3d), the multi-meta-atom system induces an impressively large OA boost, with the loop number increment, up to 11° (for N = 1.5). To the best of our knowledge, such a large rotation has not been reported by any other existing approach. In particular, a peak value is evident near the short wavelength CD maximum (550 nm). A second OA peak emerges concomitantly with the CD resonance depth increment at 700 nm for N = 1.5 because of a greater confinement of the light field into the dielectric. These results endorse that CD and OA of zero-order transmitted light are substantially linked to the transmitted resonances, following the Kramers−Kronig relations and the principle of causality.36 The OA spectra also evidence the different material behavior and the presence of plasmonic effects in the Pt system; as opposed to the dielectric systems, metallic chiral structures are intrinsically limited toward further enhancement of their rotatory power because of their large optical losses in this spectral range. Finally, the two presented metamaterial systems with the same vertical arrangement but differing in composition, demonstrate the possibility to accomplish a number of extremely large chiro-optical effects in the visible range. As noted before, a critical issue of the metallic system with respect to practical device applications is the decreasing trend in the average transmission level for both the circular polarizations, observed as the dipole number increases (i.e., the number of stacked elements, see Supplementary Figure S4a). Because of the intrinsic metal absorption, OA (as well as the pure difference between the two polarized transmissions) saturates after the coupling of two meta-atoms, thus evidencing a threshold-like behavior for the plasmonic losses prevalence. A widely spaced planar organization is the most obvious approach to compensate this negative trend, but even though the average transmission level arises the total number of dipoles per unit area drops down, as well as the observable chiro-optical
leads to two circular dichroic bands with sign inversion (corresponding to the zero circular dichroism wavelength) at 560 nm (Figure 3b), induced by the light effective wavelength matching with the structure vertical pitch (Supporting Information, S7).2,27 The transmission bands do not shift with the number of stacked elements, while the CD peak value evolves from 1° for the unit cell (N = 0.5) up to 6° for a 1.5 turn helix. These remarkably high values in the visible range, also from dielectric systems, which, to the best of our knowledge, have not been reported by other existing fabrication methods, result from the combination of high refractive index contrast medium with 3D nanoscale arrangement of chiral structures, and structural features matching light effective wavelength even in the visible range. The measured CD spectra for both material systems agree with numerical calculations conducted with the FDTD model shown in Supporting Information, S6. A comparison with other theoretical models on nanohelix optical behavior is discussed in the Supporting Information, S7, for both metallic and dielectric contexts. In particular, a quantitative agreement between the experimental data of the plasmonic system and the effective periodic dipole proposed by Zhang26 has been found. The other signature of the chiral electromagnetic material response is the OA. In the platinum system, the OA spectra show maximum values at 575 and 850 nm, near the plasmonic CD peaks (Figure 3a,c). The dipole plasmon number increment results in an initial OA enhancement from 0.5° up to 5° corresponding to a 5-fold increment in rotatory power for just a couple of stacked elements. No further improvement is observed for N = 1.5. Remarkably, the optical activity of this metamaterial has a broadband operation, covering the entire VIS range, as required for applications like integrated superachromatic optical rotators. 5826
DOI: 10.1021/acs.nanolett.6b02583 Nano Lett. 2016, 16, 5823−5828
Letter
Nano Letters effects.28 Therefore, the simultaneous control of giant chirooptical effects and optical efficiency (i.e., transmission levels useful for practical application) by metallic nanohelix arrays in the visible is particularly challenging.37 A second degree of freedom in the chiral metamaterial construction can be applied to this purpose, represented by the possibility to intertwine single and concentric nanohelices, as we recently demonstrated12 realizing chiral metamaterial with increased symmetry.38,39 Figure 4a,b shows the application of this concept in both the material systems investigated in the present work. In this case, the chiral dipoles are spatially located within the growth plane, always with nanometer scale geometrical features (wire diameter (WD) = 100 nm, ED = 300 nm, N = 1). While in the dielectric system the triple helix configuration still holds the bisignated CD spectrum induced by the material polarizability, a single and highly selective CD band extending throughout the visible range arises in the metallic counterpart (Figure 4c), as an effect of extra dipole−dipole interactions among the single plasmonic helices.33 Consequently, the OA spectrum exhibits the bisignated shape only in the metallic system (Figure 4d), because of the Kramers−Kronig relations.36 The 3D spatial dipole placing adds further flexibility in the design and manipulation of chiral effects as evident by the enhanced OA for both the material systems and, most relevantly, by the high optical efficiency expressed by a transmission level of allowed circular polarization larger than 50% (Supplementary Figure S8). Therefore, this additional degree of freedom in metamaterial design effectively allows the simultaneous control of giant chiro-optical effects in the visible and application driven transmission levels. In this article, we have demonstrated the full molding of chiral properties at the nanoscale by engineering helical-shaped metamaterials. The 3D spatial dipole placing, by the vertically stacked or multibundled organization of the unit cell, is encoded in strongly modulated optical spectra with tailored and unprecedented chirality effects in the visible range, intrinsically linked to the geometrical matching of the system with the interacting light. Moreover, this approach turns out strategic with respect to the issue, particularly challenging in the metallic context, of achieving large chiro-optical effects while preserving the optical efficiency required for practical device applications. To the best of our knowledge, this pronounced chiral response has never been experimentally reported by any other metamaterials in this spectral range. Two photon lithography allows for chiral3 and multibundled shaping40 but diffraction limits spectral operation to the IR range. The elegant integration of glancing angle deposition27,41 with colloidal nanolithography13 is a powerful tool for nanoscaling of helix and complex structures but fine local arrangement of properly seeded or intertwined helices is intrinsically hindered. Several fields of application are envisioned for this scheme. At first sight, it can be employed for compact, practical, and optically efficient nanophotonic devices for conversion and filtering of light circular polarization. The highly localized spatial control peculiar of FIBID process suggests potential integration with single photon nanoemitters in the field of quantum computing.42 Finally, the scheme can be employed for ultrasensitive chiral biodetection improvement based on the superchirality concept,43 while the combination with chemically active metals (such as catalysts) can lead to new methods of asymmetric syntheses.9,10
Methods. Sample Fabrication. Indium tin oxide-on-glass substrate was employed in a Carl Zeiss Auriga40 Crossbeam FIB/SEM system, equipped with the gas injection system. For the two material systems investigated in this work, trimethyl(methylcyclopentadienyl)-platinum(IV) precursor and phenantrene (C14H10) precursor, respectively, were locally injected on the sample. We optimized the injection distance between the substrate and nozzle and the scanning direction to obtain, respectively, high growth control by a suitable gas density and high-dimensional uniformity between nanohelices. The chamber pressure ranged from 1 × 10−5 to 8 × 10−6 mbar during the deposition time. The nanostructure arrays were grown with ion beam current of 1 pA, accelerating voltage of 30 keV, and step size of 10 nm.11,44 TEM/EDX Characterization. STEM and EDX analyses were performed in a Cs-probe-corrected JEOL ARM200CF at a primary beam energy of 200 keV and equipped with a 100 mm2 silicon drift detector for EDX spectroscopy. In order to obtain Z contrast sensitiveness from the images, the microscope was configured in high-angle annular dark-field mode (HAADF) with a convergence angle of 33 mrad and a collection angle comprised between 64 and 172 mrad (inner and outer collection angles of the dark-field detector). For EDX mapping, signal was collected by scanning the same region multiple times with a dwell time of 1 ms. The chemical composition radially along the nanohelix section was determined by EDX punctual spectra in addition to linescan performed across the nanohelix as described in Supporting Information, S1. Optical Characterization. To quantify the CD in the chiral structures, the transmission spectra were recorded in a confocal configuration by illuminating the sample with light from a tungsten lamp focalized with a condenser with NA < 0.1 and collecting the transmitted light using a 10× objective lens with numerical aperture (NA) = 0.45. Circular polarization excitation was achieved using a combination of a linear polarizer and an achromatic quarter-wave plate. The microscope output image is collected and reconstructed on the entrance slits of a 200 mm spectrometer coupled to a chargecoupled device camera for measurements in the visible range. The light transmission was calculated with respect to light transmitted by the unpatterned substrate. The OA was measured by the same experimental setup using linearly polarized incident light. The transmitted light was analyzed using an achromatic half-wave plate, mounted on a mechanical rotator with 1mdeg sensitivity, cascaded with a linear polarizer. Light intensity spectra were recorded by rotating the half waveplate with 2° steps, between 0° and 180°, with respect to the linear polarizer axis. Modeling. To evaluate the spectral properties of the FIBID helix samples, we simulated their electromagnetic response in the visible using a commercial finite difference time-domainbased software (Lumerical FDTD Solutions), whereas the postprocessing of data has been completed by means of several Matlab codes. The material permittivities employed in the simulations are discussed in details in Supporting Information, S6. The substrate has not been included in the simulations.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.nanolett.6b02583. 5827
DOI: 10.1021/acs.nanolett.6b02583 Nano Lett. 2016, 16, 5823−5828
Letter
Nano Letters
■
(21) Yun, J. G.; Jung, D. H.; Kim, H. J.; Choi, W. S.; Hong, B. Y.; Noda, S.; Song, B. S. Microelectron. Eng. 2014, 126, 99−102. (22) De Teresa, J. M.; Córdoba, R.; Fernández-Pacheco, A.; Montero, O.; Strichovanec, P.; Ibarra, M. R. J. Nanomater. 2009, 2009, 1−11. (23) Fernández-Pacheco, A.; De Teresa, J. M.; Córdoba, R.; Ibarra, M. R. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79 (17), 174204. (24) Fan, Z.; Govorov, A. O. J. Phys. Chem. C 2011, 115 (27), 13254−13261. (25) Kometani, R.; Ichihashi, T.; Kanda, K.; Suzuki, T.; Niihara, K.; Ishihara, S.; Kaito, T.; Matsui, S. J. Vac. Sci. Technol. B 2008, 26 (6), 2628−2631. (26) Zhang, Z.-Y.; Zhao, Y.-P. Appl. Phys. Lett. 2011, 98 (8), 083102. (27) Robbie, K.; Broer, D. J.; Brett, M. J. Nature 1999, 399 (6738), 764−766. (28) Esposito, M.; Tasco, V.; Todisco, F.; Benedetti, A.; Tarantini, I.; Cuscunà, M.; Dominici, L.; De Giorgi, M.; Passaseo, A. Nanoscale 2015, 7 (43), 18081−18088. (29) Sersic, I.; Frimmer, M.; Verhagen, E.; Koenderink, A. F. Phys. Rev. Lett. 2009, 103 (21), 213902. (30) Fan, Z.; Govorov, A. O. Nano Lett. 2012, 12 (6), 3283−3289. (31) Prodan, E.; Radloff, C.; Halas, N. J.; Nordlander, P. Science 2003, 302 (5644), 419−422. (32) Yin, X.; Schäferling, M.; Metzger, B.; Giessen, H. Nano Lett. 2013, 13 (12), 6238−6243. (33) Li, Y. R.; Ho, R. M.; Hung, Y. C. IEEE Photonics J. 2013, 5 (2), 2700510−2700510. (34) Liu, N.; Kaiser, S.; Giessen, H. Adv. Mater. 2008, 20 (23), 4521−4525. (35) Gibbs, J. G.; Mark, A. G.; Lee, T.-C.; Eslami, S.; Schamel, D.; Fischer, P. Nanoscale 2014, 6 (16), 9457. (36) Gorkunov, M. V.; Dmitrienko, V. E.; Ezhov, A. A.; Artemov, V. V.; Rogov, O. Y. Sci. Rep. 2015, 5, 9273. (37) Gibbs, J. G.; Mark, A. G.; Eslami, S.; Fischer, P. Appl. Phys. Lett. 2013, 103 (21), 213101. (38) Yang, Z.; Zhao, M.; Lu, P. Opt. Express 2011, 19 (5), 4255. (39) Kaschke, J.; Gansel, J. K.; Wegener, M. Opt. Express 2012, 20 (23), 26012. (40) Kaschke, J.; Wegener, M. Opt. Lett. 2015, 40 (17), 3986. (41) Robbie, K.; Brett, M. J.; Lakhtakia, A. Nature 1996, 384 (6610), 616−616. (42) O’Brien, J. L.; Furusawa, A.; Vučković, J. Nat. Photonics 2009, 3 (12), 687−695. (43) Tang, Y.; Cohen, A. E. Science 2011, 332 (6027), 333−336. (44) Esposito, M.; Tasco, V.; Cuscunà, M.; Todisco, F.; Benedetti, A.; Tarantini, I.; Giorgi, M. D.; Sanvitto, D.; Passaseo, A. ACS Photonics 2015, 2 (1), 105−114.
Detailed structural analysis, discussion on the origin of plasmonic resonances in the metallic system, SEM images of Carbon nanohelices arrays, transmission spectra, numerical calculations, and compared discussion with nanohelix theoretical models (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The work was partially supported by Italian projects PON R&C 2007−2013 “MAAT” Molecular NAnotechnology for HeAlth and EnvironmenT (PON02 00563 3316357).
■
REFERENCES
(1) Turner, M. D.; Saba, M.; Zhang, Q.; Cumming, B. P.; SchröderTurk, G. E.; Gu, M. Nat. Photonics 2013, 7 (10), 801−805. (2) Thiel, M.; Decker, M.; Deubel, M.; Wegener, M.; Linden, S.; von Freymann, G. Adv. Mater. 2007, 19 (2), 207−210. (3) Gansel, J. K.; Thiel, M.; Rill, M. S.; Decker, M.; Bade, K.; Saile, V.; von Freymann, G.; Linden, S.; Wegener, M. Science 2009, 325 (5947), 1513−1515. (4) Hendry, E.; Carpy, T.; Johnston, J.; Popland, M.; Mikhaylovskiy, R. V.; Lapthorn, A. J.; Kelly, S. M.; Barron, L. D.; Gadegaard, N.; Kadodwala, M. Nat. Nanotechnol. 2010, 5 (11), 783−787. (5) Maoz, B. M.; Chaikin, Y.; Tesler, A. B.; Bar Elli, O.; Fan, Z.; Govorov, A. O.; Markovich, G. Nano Lett. 2013, 13 (3), 1203−1209. (6) Barron, L. D. Molecular Light Scattering and Optical Activity, 2nd ed.; Cambridge University Press: New York, 2004. (7) Snik, F., Craven-Jones, J., Escuti, M., Fineschi, S., Harrington, D., De Martino, A., Mawet, D., Riedi, J., Tyo, J. S. Proc. SPIE 2014; 9099, Polarization: Measurement, Analysis, and Remote Sensing XI, 90990B (May 21, 2014); 10.1117/12.2053245. (8) Rodrigues, S. P.; Cui, Y.; Lan, S.; Kang, L.; Cai, W. Adv. Mater. 2015, 27 (6), 1124−1130. (9) Noorduin, W. L.; Bode, A. A. C.; van der Meijden, M.; Meekes, H.; van Etteger, A. F.; van Enckevort, W. J. P.; Christianen, P. C. M.; Kaptein, B.; Kellogg, R. M.; Rasing, T.; Vlieg, E. Nat. Chem. 2009, 1 (9), 729−732. (10) Amabilino, D. B. Chirality at the Nanoscale; Amabilino, A. D. B., Ed.; Wiley-VCH: New York, 2009. (11) Esposito, M.; Tasco, V.; Todisco, F.; Benedetti, A.; Sanvitto, D.; Passaseo, A. Adv. Opt. Mater. 2014, 2 (2), 154−161. (12) Esposito, M.; Tasco, V.; Todisco, F.; Cuscunà, M.; Benedetti, A.; Sanvitto, D.; Passaseo, A. Nat. Commun. 2015, 6, 6484. (13) Mark, A. G.; Gibbs, J. G.; Lee, T.-C.; Fischer, P. Nat. Mater. 2013, 12 (9), 802−807. (14) Kuzyk, A.; Schreiber, R.; Fan, Z.; Pardatscher, G.; Roller, E.-M.; Högele, A.; Simmel, F. C.; Govorov, A. O.; Liedl, T. Nature 2012, 483 (7389), 311−314. (15) Boltasseva, A.; Atwater, H. A. Science 2011, 331 (6015), 290− 291. (16) Jahani, S.; Jacob, Z. Nat. Nanotechnol. 2016, 11 (1), 23−36. (17) Larsson, E. M.; Langhammer, C.; Zorić, I.; Kasemo, B. Science 2009, 326 (5956), 1091−1094. (18) Zorić, I.; Zäch, M.; Kasemo, B.; Langhammer, C. ACS Nano 2011, 5 (4), 2535−2546. (19) Manchon, D.; Lermé, J.; Zhang, T.; Mosset, A.; Jamois, C.; Bonnet, C.; Rye, J.-M.; Belarouci, A.; Broyer, M.; Pellarin, M.; Cottancin, E. Nanoscale 2015, 7 (3), 1181−1192. (20) Matsui, S. In Springer Handbook of Nanotechnology; Bhushan, P. B., Ed.; Springer: Berlin Heidelberg, 2010; pp 211−229. 5828
DOI: 10.1021/acs.nanolett.6b02583 Nano Lett. 2016, 16, 5823−5828
