A nanofocused plasmon-driven sub-10 femtosecond electron point source

TL;DR

This paper introduces a nanofocused plasmon-driven electron source from a gold nanotip that produces sub-10 femtosecond electron pulses, enabling advanced ultrafast electron microscopy with high spatial and temporal resolution.

Contribution

It demonstrates nonlinear plasmon-induced electron emission from a gold nanotip with sub-8 fs pulse duration, surpassing previous photoemission efficiencies and enabling new ultrafast microscopy techniques.

Findings

Electron pulses below 10 fs at the sample were estimated.

Plasmon-induced emission has higher quantum efficiency than direct apex illumination.

Application demonstrated in imaging a semiconductor nanowire at micrometer distances.

Abstract

Progress in ultrafast electron microscopy relies on the development of efficient laser-driven electron sources delivering femtosecond electron pulses to the sample. In particular, recent advances employ photoemission from metal nanotips as coherent point-like femtosecond low-energy electron sources. We report the nonlinear emission of ultrashort electron wave packets from a gold nanotip generated by nonlocal excitation and nanofocusing of surface plasmon polaritons. We verify the nanoscale localization of plasmon-induced electron emission by its electrostatic collimation characteristics. With a plasmon polariton pulse duration below 8 fs at the apex, we identify multiphoton photoemission as the underlying emission process. The quantum efficiency of the plasmon-induced emission exceeds that of photoemission from direct apex illumination. We demonstrate the application for plasmon-triggered point-projection imaging of an individual semiconductor nanowire at 3 $\mu$m tip-sample distance. Based on numerical simulations we estimate an electron pulse duration at the sample below 10 fs for tip-sample distances up to few micrometers. Plasmon-driven nanolocalized electron emission thus enables femtosecond point-projection microscopy with unprecedented temporal and spatial resolution, femtosecond low-energy electron in-line holography, and opens a new route towards femtosecond scanning tunneling microscopy and spectroscopy.