Abstract
Near-field manipulation in plasmonic nanocavities can provide various applications in nanoscale science and technology. In particular, a gap plasmon in a scanning tunneling microscope (STM) junction is of key interest to nanoscale imaging and spectroscopy. Here we show that spectral features of a plasmonic STM junction can be manipulated by nanofabrication of Au tips using focused ion beam. An exemplary Fabry–Pérot type resonator of surface plasmons is demonstrated by producing the tip with a single groove on its shaft. Scanning tunneling luminescence spectra of the Fabry–Pérot tips exhibit spectral modulation resulting from interference between localized and propagating surface plasmon modes. In addition, the quality factor of the plasmonic Fabry–Pérot interference can be improved by optimizing the overall tip shape. Our approach paves the way for near-field imaging and spectroscopy with a high degree of accuracy.
Highlights
Manipulation of near-field properties, such as a spectral response, optical coupling to far fields, and local field enhancement, by using metallic nanostructures is a foundation of plasmonics, providing a wide range of applications in nanooptics,[1] single-molecule sensing,[2] and enhancement of photovoltaics,[3] and photochemistry.[4]
Tip-enhanced Raman spectroscopy (TERS) has attracted increasing attention as powerful vibrational nanospectroscopy.[11−14] In addition, scanning tunneling luminescence (STL) can be used to investigate localized surface plasmon resonance (LSPR) confined in nanoscale cavities[15] and more recently has demonstrated highly accurate single-molecule spectroscopy.[16−23] These studies open up new opportunities to elucidate fundamental aspects of near-field physics and chemistry withnanometer spatial resolution
Active control of plasmonic properties in scanning tunneling microscope (STM) junctions is one important technical milestone but the correlation between the LSPR and the tip geometry has been examined only qualitatively.[24−26] Here we report an attempt to manipulate LSPR in STM junctions by nanofabricating Au tips using focused ion beam (FIB) and demonstrate spectral modulation through a Fabry−Perot type interference of surface plasmons
Summary
The STL spectra and the emission intensity becomes stronger at higher voltages. Quenching of light emission at short wavelengths arises from the quantum cutoff[28] at low voltages and from the 5d → 6sp interband transition of Au at high voltages.[29]. The simulated wavelength dependence of the electric field in the junction (see top panel of Figure 2d) shows that the peak positions coincide with experiment This result corroborates that the spectral modulation of the grooved tip occurs through the plasmonic Fabry−Peŕ ot interference. The STM geometry provides a unique opportunity to study remote generation of a spatially separated localized plasmon modes by tunneling electrons (as shown in Figure 4), whereby conventional diffraction-limited plasmonic couplers can be omitted This mechanism can be incorporated in plasmonic optoelectronic devices utilizing remote excitation of surface plasmons.[47−50] The control of the near-field spectral response in STM junctions makes it possible to match the plasmonic resonance with resonances in the electronic structure of molecular systems. We believe that our approach paves the way for improving apertureless SNOM performance and investigating near-field physics and chemistry in (sub)nanoscale plasmonic cavities with a high degree of accuracy
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
