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Tracking Optical and Electronic Behaviour of Quantum Contacts in Sub-Nanometre Plasmonic Cavities

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ABSTRACT

Plasmonic interactions between two metallic tips are dynamically studied in a supercontinuum dark-field microscope and the transition between coupled and charge-transfer plasmons is directly observed in the sub-nm regime. Simultaneous measurement of the dc current, applied force, and optical scattering as the tips come together is used to determine the effects of conductive pathways within the plasmonic nano-gap. Critical conductances are experimentally identified for the first time, determining the points at which quantum tunnelling and conductive charge transport begin to influence plasmon coupling. These results advance our understanding of the relationship between conduction and plasmonics, and the fundamental quantum mechanical behaviours of plasmonic coupling.

No MeSH data available.


(a,b) Optical scattering spectra of a compressed sub-nm dimer cavity at the onset of conductive contact (same run as Fig. 3), showing (c) quantised conductance in units of G0. Deviation from the mean spectrum is shown in (b) to make the steps in spectra clearer; colour scale runs from −0.2 to 0.2 in the units of (a). (d–f) Extracted mode shifts, amplitudes, and linewidths for the longer wavelength (blue) and shorter wavelength (red) plasmon modes. Quantum tunnelling onset in blue shaded region, conduction in yellow shaded region.
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f4: (a,b) Optical scattering spectra of a compressed sub-nm dimer cavity at the onset of conductive contact (same run as Fig. 3), showing (c) quantised conductance in units of G0. Deviation from the mean spectrum is shown in (b) to make the steps in spectra clearer; colour scale runs from −0.2 to 0.2 in the units of (a). (d–f) Extracted mode shifts, amplitudes, and linewidths for the longer wavelength (blue) and shorter wavelength (red) plasmon modes. Quantum tunnelling onset in blue shaded region, conduction in yellow shaded region.

Mentions: Further compression of a plasmonic nano-cavity reduces the gap width to below 0.5 nm, leading to the onset of quantum tunnelling. A representative approach in Fig. 4(a) between two spherical Au AFM tips, shows both screening of hybridised dimer and quadrupolar plasmons (BDP, BQP) and CTP formation once in the quantum regime. Experimental plasmon modes appear at similar wavelengths to QCM predictions. The rate of redshift of each coupled mode reduces with the onset of tunnelling, along with the mode intensity, revealing that the interparticle current has risen sufficiently to begin neutralising surface charge and screening gap coupling.


Tracking Optical and Electronic Behaviour of Quantum Contacts in Sub-Nanometre Plasmonic Cavities
(a,b) Optical scattering spectra of a compressed sub-nm dimer cavity at the onset of conductive contact (same run as Fig. 3), showing (c) quantised conductance in units of G0. Deviation from the mean spectrum is shown in (b) to make the steps in spectra clearer; colour scale runs from −0.2 to 0.2 in the units of (a). (d–f) Extracted mode shifts, amplitudes, and linewidths for the longer wavelength (blue) and shorter wavelength (red) plasmon modes. Quantum tunnelling onset in blue shaded region, conduction in yellow shaded region.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016779&req=5

f4: (a,b) Optical scattering spectra of a compressed sub-nm dimer cavity at the onset of conductive contact (same run as Fig. 3), showing (c) quantised conductance in units of G0. Deviation from the mean spectrum is shown in (b) to make the steps in spectra clearer; colour scale runs from −0.2 to 0.2 in the units of (a). (d–f) Extracted mode shifts, amplitudes, and linewidths for the longer wavelength (blue) and shorter wavelength (red) plasmon modes. Quantum tunnelling onset in blue shaded region, conduction in yellow shaded region.
Mentions: Further compression of a plasmonic nano-cavity reduces the gap width to below 0.5 nm, leading to the onset of quantum tunnelling. A representative approach in Fig. 4(a) between two spherical Au AFM tips, shows both screening of hybridised dimer and quadrupolar plasmons (BDP, BQP) and CTP formation once in the quantum regime. Experimental plasmon modes appear at similar wavelengths to QCM predictions. The rate of redshift of each coupled mode reduces with the onset of tunnelling, along with the mode intensity, revealing that the interparticle current has risen sufficiently to begin neutralising surface charge and screening gap coupling.

View Article: PubMed Central - PubMed

ABSTRACT

Plasmonic interactions between two metallic tips are dynamically studied in a supercontinuum dark-field microscope and the transition between coupled and charge-transfer plasmons is directly observed in the sub-nm regime. Simultaneous measurement of the dc current, applied force, and optical scattering as the tips come together is used to determine the effects of conductive pathways within the plasmonic nano-gap. Critical conductances are experimentally identified for the first time, determining the points at which quantum tunnelling and conductive charge transport begin to influence plasmon coupling. These results advance our understanding of the relationship between conduction and plasmonics, and the fundamental quantum mechanical behaviours of plasmonic coupling.

No MeSH data available.