Andrej Grubisic

Plasmonic Near-Electric Field Enhancement Effects in Ultrafast Photoelectron Emission: Correlated Spatial and Laser Polarization Microscopy Studies of Individual Ag Nanocubes

Electron emission from single, supported Ag nanocubes excited with ultrafast laser pulses (λ = 800 nm) is studied via spatial and polarization correlated (i) dark field scattering microscopy (DFM), (ii) scanning photoionization microscopy (SPIM), and (iii) high-resolution transmission electron microscopy (HRTEM). Laser-induced electron emission is found to peak for laser polarization aligned with cube diagonals, suggesting the critical influence of plasmonic near-field enhancement of the incident electric field on the overall electron yield. For laser pulses with photon energy below the metal work function, coherent multiphoton photoelectron emission (MPPE) is identified as the most probable mechanism responsible for electron emission from Ag nanocubes and likely metal nanoparticles/surfaces in general.

Polarization-dependent scanning photoionization microscopy: ultrafast plasmon-mediated electron ejection dynamics in single Au nanorods.

This work investigates plasmon-enhanced multiphoton scanning photoelectron emission microscopy (SPIM) of single gold nanorods under vacuum conditions. Striking differences in their photoemission properties are observed for nanorods deposited either on 2 nm thick Pt films or 10 nm thick indium tin oxide (ITO) films. On a Pt support, the Au nanorods display fourth-order photoionization when excited at 800 nm, a wavelength corresponding to their plasmon resonance in aqueous solution. A cos(8)(θ) dependence of the photoelectron flux on laser polarization implies photoemission mediated by the dipolar plasmon; however, no plasmon resonance signature is exhibited over the 750-880 nm range. Electromagnetic simulations confirm that the resonance is severely broadened compared to aqueous solution, indicative of strong interactions between the Au nanorod and propagating surface plasmon modes in the Pt substrate. On ITO substrates, by way of contrast, sharp plasmon resonances in the photoemission from individual Au nanorods are observed, with widths limited only by fundamental internal electron collision processes. Furthermore, the ensemble-averaged plasmon resonance for Au nanorods on ITO is almost unshifted compared to its frequency in solution. Both findings suggest that plasmonic particle-substrate interactions are suppressed in the Au/ITO system. However, Au nanorods on ITO exhibit a surprising third-order photoemission (observed neither in Au nor ITO by itself), indicating that electrostatic interactions introduce a substantial shift in the work function for this fundamental nanoparticle-substrate system.

Multi-wavelength laser transmitter for the two-step laser time-of-flight mass spectrometer

We are developing a multi-wavelength laser for the two-step laser time-of-flight mass-spectrometer (L2MS). The L2MS is designed to detect hydrocarbons in organically-doped analog minerals, including cryogenic Ocean World-relevant ices and mixtures for future astrobiology missions.