Nanomechanical mass spectrometry has proven to be well suited for the analysis of high mass species such as viruses. Still, the use of one-dimensional devices such as vibrating beams forces a trade-off between analysis time and mass resolution. Complex readout schemes are also required to simultaneously monitor multiple resonance modes, which degrades resolution. These issues restrict nanomechanical MS to specific species. We demonstrate here single-particle mass spectrometry with nano-optomechanical resonators fabricated with a Very Large Scale Integration process. The unique motion sensitivity of optomechanics allows designs that are impervious to particle position, stiffness or shape, opening the way to the analysis of large aspect ratio biological objects of great significance such as viruses with a tail or fibrils. Compared to top-down beam resonators with electrical read-out and state-of-the-art mass resolution, we show a threefold improvement in capture area with no resolution degradation, despite the use of a single resonance mode.
We study the evolution of the surface-plasmon resonances of individual ion-beam-shaped prolate gold nanoparticles embedded in a dielectric SiO 2 environment by electron-energy-loss spectroscopy mapping in a scanning transmission electron microscope. The controlled symmetric dielectric environment obtained through the ion-beam-shaping method allows a direct quantitative comparison with numerical results obtained through simulations (auxiliary differential-equation finite-difference time-domain and boundary-element method) and with theoretical results obtained through analytical models (quasistatic model for prolate nanoellipsoids and waveguide model for infinite one-dimensional plasmonic waveguides), with which our experimental results are in very good agreement. We confirm the accuracy of state-of-the-art numerical tools and analytical theories that establish ion-beam shaping as a very promising method to design metal-dielectric nanocomposites with well-predicted optical properties, and with many possible applications in surfaceenhanced Raman spectroscopy and second-harmonic generation, as well as in conventional applications of metamaterials like negative refraction, superimaging, and invisibility cloaking.
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