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Triple-helical nanowires by tomographic rotatory growth for chiral photonics.

Esposito M, Tasco V, Todisco F, Cuscunà M, Benedetti A, Sanvitto D, Passaseo A - Nat Commun (2015)

Bottom Line: Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy.These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB).Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

View Article: PubMed Central - PubMed

Affiliation: National Nanotechnology Laboratory-NNL, CNR-IMIP, VIA Arnesano, 73100 Lecce Italy.

ABSTRACT
Three dimensional helical chiral metamaterials resulted in effective manipulation of circularly polarized light in the visible infrared for advanced nanophotonics. Their potentialities are severely limited by the lack of full rotational symmetry preventing broadband operation, high signal-to-noise ratio and inducing high optical activity sensitivity to structure orientation. Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy. Here we report three dimensional triple-helical nanowires, engineered by the innovative tomographic rotatory growth, on the basis of focused ion beam-induced deposition. These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB). Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

No MeSH data available.


Related in: MedlinePlus

Device fabrication(a) Fabrication scheme to realize THNs. The basic two-dimensional layout consisting of an empty circle is divided in 6 sections (seeding sites arranged every 60°). During the first step, the circular motion of the beam leads to the 3D growth of three arches arranged every 120° (indicated with numbers 1,3,5). Then, after changing the starting angle from 0 ° to 60° anticlockwise the beam was moved to grow 3 arcs placed again every 120°. The extremely high level of alignment is achieved by setting the pattern parameters for a perfect overlap of consecutive arches. These two steps are repeated three times to get a complete loop of each sub-helix. (b) SEM images of the array showing THNs with ED=375 nm, WD=110 nm, VP=705 nm. The THN array size is 10 μm x10 μm, with LP=700 nm. (c) High magnification image of a small array area evidencing the wire continuity and high dimensional uniformity of THNs in all three spatial directions obtained by the TRG method.
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Figure 1: Device fabrication(a) Fabrication scheme to realize THNs. The basic two-dimensional layout consisting of an empty circle is divided in 6 sections (seeding sites arranged every 60°). During the first step, the circular motion of the beam leads to the 3D growth of three arches arranged every 120° (indicated with numbers 1,3,5). Then, after changing the starting angle from 0 ° to 60° anticlockwise the beam was moved to grow 3 arcs placed again every 120°. The extremely high level of alignment is achieved by setting the pattern parameters for a perfect overlap of consecutive arches. These two steps are repeated three times to get a complete loop of each sub-helix. (b) SEM images of the array showing THNs with ED=375 nm, WD=110 nm, VP=705 nm. The THN array size is 10 μm x10 μm, with LP=700 nm. (c) High magnification image of a small array area evidencing the wire continuity and high dimensional uniformity of THNs in all three spatial directions obtained by the TRG method.

Mentions: FIBID technique was already demonstrated to be a powerful tool for manufacturing 3D chiral structures at the nanoscale22, however, the realization of intertwined helical structures by FIBID presents two additional technological challenges. One is the difficulty to extrude the nanowires in the third dimension because of the presence of blind spots (i.e., the space occupied by the elements already grown). The other one is the extremely close distance of nanowires, introducing strong 3D mutual proximity effects, that prevent dimensional uniformity. These limiting factors were overtaken by developing the TRG method, in which the structure growth is stratified in multiple sections and combined with a split circular beam scan. In this growth mode, the basic scanning design (empty circle) is split into 6 arches arranged every 60° (figure 1a). The first fraction of the THN growth starts with the deposition of 3 platinum arches arranged every 120° (indicated in figure 1a with cyan color and starting from the seeding sites 1, 3, 5). The FIBID beam and pattern parameters were optimized following the procedure reported in ref. 22, where is also described the dose compensation procedure used to strongly reduce the 3D proximity effects that, for the THN growth, was further implemented by using a continuous gradient function for dose correction. For the subsequent beam scan, the same pattern is repeated anticlockwise rotating by 60°, thus inducing the deposition of the arches arranged every 120° (indicated in figure 1a with magenta color and starting from points 2, 4, 6), completing one third of a single helix revolution. For a complete THN loop, this procedure is repeated three times, as shown in the Supplementary Movie 1. Structural continuity between consecutive arcs grown at different times during the circular beam motion is ensured by a careful calibration of pattern parameters that allows to match the seed cross-sectional area of the already grown arc.


Triple-helical nanowires by tomographic rotatory growth for chiral photonics.

Esposito M, Tasco V, Todisco F, Cuscunà M, Benedetti A, Sanvitto D, Passaseo A - Nat Commun (2015)

Device fabrication(a) Fabrication scheme to realize THNs. The basic two-dimensional layout consisting of an empty circle is divided in 6 sections (seeding sites arranged every 60°). During the first step, the circular motion of the beam leads to the 3D growth of three arches arranged every 120° (indicated with numbers 1,3,5). Then, after changing the starting angle from 0 ° to 60° anticlockwise the beam was moved to grow 3 arcs placed again every 120°. The extremely high level of alignment is achieved by setting the pattern parameters for a perfect overlap of consecutive arches. These two steps are repeated three times to get a complete loop of each sub-helix. (b) SEM images of the array showing THNs with ED=375 nm, WD=110 nm, VP=705 nm. The THN array size is 10 μm x10 μm, with LP=700 nm. (c) High magnification image of a small array area evidencing the wire continuity and high dimensional uniformity of THNs in all three spatial directions obtained by the TRG method.
© Copyright Policy - permissions-link
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4374152&req=5

Figure 1: Device fabrication(a) Fabrication scheme to realize THNs. The basic two-dimensional layout consisting of an empty circle is divided in 6 sections (seeding sites arranged every 60°). During the first step, the circular motion of the beam leads to the 3D growth of three arches arranged every 120° (indicated with numbers 1,3,5). Then, after changing the starting angle from 0 ° to 60° anticlockwise the beam was moved to grow 3 arcs placed again every 120°. The extremely high level of alignment is achieved by setting the pattern parameters for a perfect overlap of consecutive arches. These two steps are repeated three times to get a complete loop of each sub-helix. (b) SEM images of the array showing THNs with ED=375 nm, WD=110 nm, VP=705 nm. The THN array size is 10 μm x10 μm, with LP=700 nm. (c) High magnification image of a small array area evidencing the wire continuity and high dimensional uniformity of THNs in all three spatial directions obtained by the TRG method.
Mentions: FIBID technique was already demonstrated to be a powerful tool for manufacturing 3D chiral structures at the nanoscale22, however, the realization of intertwined helical structures by FIBID presents two additional technological challenges. One is the difficulty to extrude the nanowires in the third dimension because of the presence of blind spots (i.e., the space occupied by the elements already grown). The other one is the extremely close distance of nanowires, introducing strong 3D mutual proximity effects, that prevent dimensional uniformity. These limiting factors were overtaken by developing the TRG method, in which the structure growth is stratified in multiple sections and combined with a split circular beam scan. In this growth mode, the basic scanning design (empty circle) is split into 6 arches arranged every 60° (figure 1a). The first fraction of the THN growth starts with the deposition of 3 platinum arches arranged every 120° (indicated in figure 1a with cyan color and starting from the seeding sites 1, 3, 5). The FIBID beam and pattern parameters were optimized following the procedure reported in ref. 22, where is also described the dose compensation procedure used to strongly reduce the 3D proximity effects that, for the THN growth, was further implemented by using a continuous gradient function for dose correction. For the subsequent beam scan, the same pattern is repeated anticlockwise rotating by 60°, thus inducing the deposition of the arches arranged every 120° (indicated in figure 1a with magenta color and starting from points 2, 4, 6), completing one third of a single helix revolution. For a complete THN loop, this procedure is repeated three times, as shown in the Supplementary Movie 1. Structural continuity between consecutive arcs grown at different times during the circular beam motion is ensured by a careful calibration of pattern parameters that allows to match the seed cross-sectional area of the already grown arc.

Bottom Line: Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy.These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB).Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

View Article: PubMed Central - PubMed

Affiliation: National Nanotechnology Laboratory-NNL, CNR-IMIP, VIA Arnesano, 73100 Lecce Italy.

ABSTRACT
Three dimensional helical chiral metamaterials resulted in effective manipulation of circularly polarized light in the visible infrared for advanced nanophotonics. Their potentialities are severely limited by the lack of full rotational symmetry preventing broadband operation, high signal-to-noise ratio and inducing high optical activity sensitivity to structure orientation. Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy. Here we report three dimensional triple-helical nanowires, engineered by the innovative tomographic rotatory growth, on the basis of focused ion beam-induced deposition. These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB). Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

No MeSH data available.


Related in: MedlinePlus