Circular dichroism nano-imaging of two-dimensional chiral metal nanostructures

Narushima, Tetsuya; Okamoto, Hiromi

doi:10.1039/c3cp50854d

Cited by 61 publications

(55 citation statements)

References 21 publications

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“…In addition, the detection system may also distort the CD image, if the aperture of the near‐field probe had structural irregularity. However, it should be noted that similar centrosymmetric distribution of local CD for the S‐shaped structure was observed in our previous studies, with good reproducibility . Also, antisymmetric spatial distribution of local CD with respect to the central axis of the structure was obtained for an achiral 3/4‐arc structure similar to that in Figure b or Figure b .…”

Section: Resultssupporting

confidence: 87%

Optical Activity Governed by Local Chiral Structures in Two‐Dimensional Curved Metallic Nanostructures

2016

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Chiral nanostructures show macroscopic optical activity. Local optical activity and its handedness are not uniform in the nanostructure, and are spatially distributed depending on the shape of the nanostructure. In this study we fabricated curved chain nanostructures made of gold by connecting linearly two or more arc structures in a two-dimensional plane. Spatial features of local optical activity in the chain structures were evaluated with near-field circular dichroism (CD) imaging, and analyzed with the aid of classical electromagnetic simulation. The electromagnetic simulation predicted that local optical activity appears at inflection points where arc structures are connected. The handedness of the local optical activity was dependent on the handedness of the local chirality at the inflection point. Chiral chain structures have odd inflection points and the local optical activity distributed symmetrically with respect to structural centers. In contrast, achiral chain structures have even inflection points and showed antisymmetric distribution. In the near-field CD images of fabricated chain nanostructures, the symmetric and antisymmetric distributions of local CD were observed for chiral and achiral chain structures, respectively, consistent with the simulated results. The handedness of the local optical activity was found to be determined by the handedness of the inflection point, for the fabricated chain structures having two or more inflection points. The local optical activity was thus governed primarily by the local chirality of the inflection points for the gold chain structures. The total effect of all the inflection points in the chain structure is considered to be a predominant factor that determines the macroscopic optical activity. Chirality 28:540-544, 2016. © 2016 Wiley Periodicals, Inc.

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Section: Resultssupporting

confidence: 87%

Optical Activity Governed by Local Chiral Structures in Two‐Dimensional Curved Metallic Nanostructures

2016

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“…[145][146][147] Prominent CD signals on the order of 10 -3 in absorbance units were observed in the macroscopic CD spectra of these samples measured with a propagating light, and the signs of the signals for "S" and mirrored "S" were mutually inverted. 146 Figure 17 shows near-field CD images of S-shaped and its mirrored counterpart gold nanostructures of the same sizes, and the profiles of the CD signals along the curves of the structures.…”

Section: Imaging Of Chiral and Achiral Gold Nanostructuresmentioning

confidence: 88%

“…Recently, we developed an apparatus with higher detection sensitivity of CD signals while maintaining a 100 nm (or higher) spatial resolution. [145][146][147][148] This design enabled a closer approach to the CD of metal nanostructures than has previously been made possible.…”

Section: Methods Of Near-field Measurements Of Local Optical Activitymentioning

confidence: 99%

Local optical responses of plasmon resonances visualised by near-field optical imaging

Okamoto

Narushima

Nishiyama

et al. 2015

Phys. Chem. Chem. Phys.

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The unique optical characteristics of noble metal nanostructures have their origin principally in surface plasmon resonances. To exploit and design the unique characteristics arising from plasmons, an investigation of optical field structures adjacent to the nanostructure is of fundamental importance. As the spatial scale of the optical field structures is essentially smaller than the radiation wavelength in resonance with the plasmon, optical imaging methods that achieve spatial resolution beyond the diffraction limit of light are necessary to visualise the fields. In this article, we review the studies of direct experimental visualisation of plasmon resonances using near-field optical microscopy. We briefly describe the method of near-field optical microscopy used to study noble metal nanoparticles and show with several typical single gold nanoparticles that the spatial features of plasmon resonances, in particular the standing wave functions of the plasmons, can be directly visualised by near-field imaging. We then describe our recent efforts to visualise ultrafast dynamics in metal nanostructures following plasmonic excitation, which are based on near-field ultrafast imaging measurements. Another notable aspect of metal nanostructures that has attracted attention recently is the chirality of plasmons. Here, we describe a method and examples of near-field optical imaging and analyses of chiral plasmons excited on metal nanostructures.

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“…The distribution of the local CD signals coming from chiral nanostructures explained the relation ship between chiroptical signal and nanoscale chirality. [91] A recent work showed that circularly polarized selective near field distribution explained the farfield chiral optical reac tions, in which several propagating waves in different direc tions were observed, and can analogize to nanoantennas (upper part of Figure 4b). [93] In this singlelayered structure which was in rosette geometry, it was believed that a signif icant magnetic mode was lost and thus caused weak chiral response.…”

Section: Quasi-2d Periodic Chiral Nanostructuresmentioning

confidence: 99%

“…[88] The interaction between periodic chiral metallic nanostructures and CPL, gives rise to interesting and unique chiral phenomena. [89][90][91] …”

Section: Periodic Chiral Nanostructuresmentioning

confidence: 99%

Plasmonic Chiral Nanostructures: Chiroptical Effects and Applications

Luo

Chi

Jiang

et al. 2017

Advanced Optical Materials

170

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(circular birefringence) and absorption losses (circular dichroism) with the circu larly polarized light (CPL) illumination. [10] CB arises from the difference in the real part of refractive index, leading to a dif ferent velocity for LCP and RCP compo nents, and thus results in the polarization rotation of the linearly polarized incident light. CD corresponds to the difference in the imaginary part of refractive index, resulting in a distinct absorption loss for LCP and RCP excitations. Besides the con ventional CD and CB, asymmetric trans mission (circular conversion dichroism) is another fundamental chiroptical pheno menon, which exists in the nondiffracting array, referring to different LCPtoRCP and RCPtoLCP conversion efficiencies. [11] All of these chiroptical phenomena have been successfully applied in the spectros copy for identifying special arrangements of chiral matters in biology, chemistry and physics as efficient diagnostic tools. [12][13][14][15][16] However, the chirop tical response in natural chiral materials is relatively weak due to the small electromagnetic (EM) interaction volume, [17] hence limits its further applications.Recent progress in plasmonics paves the way for the enhancement of chiroptical response. [18][19][20] Surface plasmons (SPs), as the collective electrons oscillation at the dielectric and metal interface, [21][22][23] present the capacity of light confine ment and field enhancement, which significantly improve the strength of lightmatter interactions. [24][25][26][27][28] With the uptodate nanofabrication technology, the study field of chirality has been extended from traditional chiral molecules to 3D metallic nanostructures. [29][30][31][32] Chiroptical responses of metallic meta molecules have been widely investigated, [33][34][35] and applied in various fields, such as biosensing, [36] chiral catalysis, [37] polari zation tuning, [38] and chiral photo detection.[39] The 3D metallic structure exhibited giant optical activity response because of the strong interaction between electric and magnetic resonant modes. [40,41] Different from 3D chiral ensembles, planar chiral structures show none chiral effect, as they can always coincide with their mirror images. However, 2D chirality was successfully found in the quasitwodimensional (quasi2D) chiral structure. [42] Moreover, recent reports show that even achiral nanomaterials have the ability to generate strong CD under an oblique CPL illumination. [43] This kind of extrinsic chirality arises from sym metry breaking of the incident light and the quasi2D material, which is quite different from the intrinsic chirality of 3D chiral The plasmonic chiroptical effect has been used to manipulate chiral states of light, where the strong field enhancement and light localization in metallic nanostructures can amplify the chiroptical response. Moreover, in metamaterials, the chiroptical effect leads to circular dichroism (CD), circular birefringence (CB), and asymmetric transmission. Potential applications enabled by chiral plasmonics...

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Circular dichroism nano-imaging of two-dimensional chiral metal nanostructures

Cited by 61 publications

References 21 publications

Optical Activity Governed by Local Chiral Structures in Two‐Dimensional Curved Metallic Nanostructures

Optical Activity Governed by Local Chiral Structures in Two‐Dimensional Curved Metallic Nanostructures

Local optical responses of plasmon resonances visualised by near-field optical imaging

Plasmonic Chiral Nanostructures: Chiroptical Effects and Applications

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