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Formation of Enhanced Uniform Chiral Fields in Symmetric Dimer Nanostructures.

Tian X, Fang Y, Sun M - Sci Rep (2015)

Bottom Line: Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals.However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications.It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.

View Article: PubMed Central - PubMed

Affiliation: College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal University, Jinan 250014, China.

ABSTRACT
Chiral fields with large optical chirality are very important in chiral molecules analysis, sensing and other measurements. Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals. However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications. Plasmonic helical nanostructures and blocked squares have been proved to provide uniform chiral near-fields, but structure fabrication is a challenge. In this paper, we show that very simple plasmonic dimer structures can provide uniform chiral fields in the gaps with large enhancement of both near electric fields and chiral fields under linearly polarized light illumination with polarization off the dimer axis at dipole resonance. An analytical dipole model is utilized to explain this behavior theoretically. 30 times of volume averaged chiral field enhancement is gotten in the whole gap. Chiral fields with opposite handedness can be obtained simply by changing the polarization to the other side of the dimer axis. It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.

No MeSH data available.


Related in: MedlinePlus

Gap-dependent optical chirality in the gap of Au block dimers (60 nm × 60 nm × 30 nm) on glass in water environment.(a) Extinction spectra. (b) Volume averaged optical chirality in the gap. Red curves are for the case of RCP excitation. (c and d) Super chiral near-field distributions at the dipole resonant wavelength excited by linear polarized light (c) and RCP light (d). Rows (in (a) and (b)) or columns (in (c) and (d)) of i, ii and iii correspond to Gap d = 2 nm, d = 5 nm and d = 10 nm respectively. The x–y slices are cut from middle of the height; x–z slices are cut from the middle position of the gap.
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f7: Gap-dependent optical chirality in the gap of Au block dimers (60 nm × 60 nm × 30 nm) on glass in water environment.(a) Extinction spectra. (b) Volume averaged optical chirality in the gap. Red curves are for the case of RCP excitation. (c and d) Super chiral near-field distributions at the dipole resonant wavelength excited by linear polarized light (c) and RCP light (d). Rows (in (a) and (b)) or columns (in (c) and (d)) of i, ii and iii correspond to Gap d = 2 nm, d = 5 nm and d = 10 nm respectively. The x–y slices are cut from middle of the height; x–z slices are cut from the middle position of the gap.

Mentions: It is in expectation that as the gap decreases, the chiral field becomes stronger and stronger because the field enhancement becomes larger and larger nonlinearly (Fig. 7). However, when the gap decreases, it becomes harder for the incident light to induce field deep in the gap because of the screen effect of the metal, resulting in the scattered field weak in the middle and strong in the sharp edges, which make the chiral field is less uniform and weaker in the middle (Fig. 7ci). Although the chiral field is non-uniform, it still has the same handedness in the whole gap area, so smaller gap is still a better choice in experiment. The volume averaged chiral field enhancement reaches 30 for the 2 nm gap dimer as well (Fig. 7b–i). For all of the gaps, the volume averaged chiral fields have larger values with linearly polarized light excitation than the RCP excitation.


Formation of Enhanced Uniform Chiral Fields in Symmetric Dimer Nanostructures.

Tian X, Fang Y, Sun M - Sci Rep (2015)

Gap-dependent optical chirality in the gap of Au block dimers (60 nm × 60 nm × 30 nm) on glass in water environment.(a) Extinction spectra. (b) Volume averaged optical chirality in the gap. Red curves are for the case of RCP excitation. (c and d) Super chiral near-field distributions at the dipole resonant wavelength excited by linear polarized light (c) and RCP light (d). Rows (in (a) and (b)) or columns (in (c) and (d)) of i, ii and iii correspond to Gap d = 2 nm, d = 5 nm and d = 10 nm respectively. The x–y slices are cut from middle of the height; x–z slices are cut from the middle position of the gap.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664915&req=5

f7: Gap-dependent optical chirality in the gap of Au block dimers (60 nm × 60 nm × 30 nm) on glass in water environment.(a) Extinction spectra. (b) Volume averaged optical chirality in the gap. Red curves are for the case of RCP excitation. (c and d) Super chiral near-field distributions at the dipole resonant wavelength excited by linear polarized light (c) and RCP light (d). Rows (in (a) and (b)) or columns (in (c) and (d)) of i, ii and iii correspond to Gap d = 2 nm, d = 5 nm and d = 10 nm respectively. The x–y slices are cut from middle of the height; x–z slices are cut from the middle position of the gap.
Mentions: It is in expectation that as the gap decreases, the chiral field becomes stronger and stronger because the field enhancement becomes larger and larger nonlinearly (Fig. 7). However, when the gap decreases, it becomes harder for the incident light to induce field deep in the gap because of the screen effect of the metal, resulting in the scattered field weak in the middle and strong in the sharp edges, which make the chiral field is less uniform and weaker in the middle (Fig. 7ci). Although the chiral field is non-uniform, it still has the same handedness in the whole gap area, so smaller gap is still a better choice in experiment. The volume averaged chiral field enhancement reaches 30 for the 2 nm gap dimer as well (Fig. 7b–i). For all of the gaps, the volume averaged chiral fields have larger values with linearly polarized light excitation than the RCP excitation.

Bottom Line: Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals.However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications.It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.

View Article: PubMed Central - PubMed

Affiliation: College of Chemistry, Chemical Engineering and Materials Science, Shandong Normal University, Jinan 250014, China.

ABSTRACT
Chiral fields with large optical chirality are very important in chiral molecules analysis, sensing and other measurements. Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals. However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications. Plasmonic helical nanostructures and blocked squares have been proved to provide uniform chiral near-fields, but structure fabrication is a challenge. In this paper, we show that very simple plasmonic dimer structures can provide uniform chiral fields in the gaps with large enhancement of both near electric fields and chiral fields under linearly polarized light illumination with polarization off the dimer axis at dipole resonance. An analytical dipole model is utilized to explain this behavior theoretically. 30 times of volume averaged chiral field enhancement is gotten in the whole gap. Chiral fields with opposite handedness can be obtained simply by changing the polarization to the other side of the dimer axis. It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.

No MeSH data available.


Related in: MedlinePlus