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

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.

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Experiment configuration for axial tip scanning.(a) The supercontinuum laser is centred on the aligned tip dimer for dark-field spectroscopy. Tips are illuminated at high angles to the optical axis (a central beam block is imaged into the objective’s back aperture) and scattered light is collected on-axis, using an aperture to reject reflected illumination light. The softer cantilever approaches the stationary stiffer cantilever. A bias is applied across the tip junction and the current through the gap is measured. (b) Diagram of tip dimer indicating separation d. (c) Mechanical configuration of the tip dimer, with electrical measurement. Applied force is measured by reflecting a laser from the softer cantilever and monitoring its deflection on a position sensitive photodiode.
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f2: Experiment configuration for axial tip scanning.(a) The supercontinuum laser is centred on the aligned tip dimer for dark-field spectroscopy. Tips are illuminated at high angles to the optical axis (a central beam block is imaged into the objective’s back aperture) and scattered light is collected on-axis, using an aperture to reject reflected illumination light. The softer cantilever approaches the stationary stiffer cantilever. A bias is applied across the tip junction and the current through the gap is measured. (b) Diagram of tip dimer indicating separation d. (c) Mechanical configuration of the tip dimer, with electrical measurement. Applied force is measured by reflecting a laser from the softer cantilever and monitoring its deflection on a position sensitive photodiode.

Mentions: We have developed a rig in which a pair of conducting AFM tips capped with spherical Au nanoparticles can be brought into sub-nm proximity to investigate the relationship between plasmonics and conductance at optical frequencies (Fig. 2). We assume that conductive behaviour originates from the same location and the same nano-scale structure at both dc and optical frequencies, with a common conductance to describe both. The tips used here are pairs of either 50 nm Au-coated Nanotools B150 AFM probes (300 nm apex diameter diamond-like-carbon tips) or similarly sized AuNP-on-Pt AFM probes fabricated in-house using electrodeposition22. Previously we demonstrated that tips without spherical nanoparticles (i.e. just sharp tips) do not support plasmonic cavity modes at any particular resonant wavelength but offer only broadband response23, hence the need to use these carefully constructed NP plasmonic probes here.


Tracking Optical and Electronic Behaviour of Quantum Contacts in Sub-Nanometre Plasmonic Cavities
Experiment configuration for axial tip scanning.(a) The supercontinuum laser is centred on the aligned tip dimer for dark-field spectroscopy. Tips are illuminated at high angles to the optical axis (a central beam block is imaged into the objective’s back aperture) and scattered light is collected on-axis, using an aperture to reject reflected illumination light. The softer cantilever approaches the stationary stiffer cantilever. A bias is applied across the tip junction and the current through the gap is measured. (b) Diagram of tip dimer indicating separation d. (c) Mechanical configuration of the tip dimer, with electrical measurement. Applied force is measured by reflecting a laser from the softer cantilever and monitoring its deflection on a position sensitive photodiode.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Experiment configuration for axial tip scanning.(a) The supercontinuum laser is centred on the aligned tip dimer for dark-field spectroscopy. Tips are illuminated at high angles to the optical axis (a central beam block is imaged into the objective’s back aperture) and scattered light is collected on-axis, using an aperture to reject reflected illumination light. The softer cantilever approaches the stationary stiffer cantilever. A bias is applied across the tip junction and the current through the gap is measured. (b) Diagram of tip dimer indicating separation d. (c) Mechanical configuration of the tip dimer, with electrical measurement. Applied force is measured by reflecting a laser from the softer cantilever and monitoring its deflection on a position sensitive photodiode.
Mentions: We have developed a rig in which a pair of conducting AFM tips capped with spherical Au nanoparticles can be brought into sub-nm proximity to investigate the relationship between plasmonics and conductance at optical frequencies (Fig. 2). We assume that conductive behaviour originates from the same location and the same nano-scale structure at both dc and optical frequencies, with a common conductance to describe both. The tips used here are pairs of either 50 nm Au-coated Nanotools B150 AFM probes (300 nm apex diameter diamond-like-carbon tips) or similarly sized AuNP-on-Pt AFM probes fabricated in-house using electrodeposition22. Previously we demonstrated that tips without spherical nanoparticles (i.e. just sharp tips) do not support plasmonic cavity modes at any particular resonant wavelength but offer only broadband response23, hence the need to use these carefully constructed NP plasmonic probes here.

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.


Related in: MedlinePlus