Sub‐nanosecond electron beam blanking for deep‐subwavelength lifetime probing of nanophotonical devices and nanoparticles

Abstract

Optical techniques are used to probe carrier or excited energy dynamics down to femtosecond time‐scales, but they lack the resolution to address nanoscopic length scales [1]. Higher spatial resolution can be obtained using pulsed beams of electrons, but this typically requires dedicated microscopes with laser‐triggered electron sources [2]. Here, we use a standard scanning electron microscope equipped with an electrostatic beam blanker operated in conjugate mode (Fig. 1). We show the generation of sub‐nanosecond electron pulses (Fig.2). This system is used to probe nanophotonical devices and nanoparticles using time‐resolved cathodoluminescence (CL). In these devices, optical emitters couple with the nanoscale environment leading to a position‐dependent excited state lifetime. The pulsed electron beam excites the emitters, giving rise to CL. The CL emission is detected using an integrated light microscope [3]. Photon arrival histograms are obtained using time‐correlated single photon counting, synchronized with the input signal of the electron beam blanker, thus measuring spatially resolved CL lifetime. We demonstrate the ability to identify nanoparticles based on their lifetime as well as their emission wavelength, which provides an additional source of information in nanoparticle‐based biological imaging. Moreover, we conduct a nanoscopic version of the seminal work performed in the 1960s and 1970s by Drexhage, who showed that the lifetime of emitters depends on their distance to a metallic mirror [4]. We locally excite Ce 3+ emitters in YAG, which is partially covered with a thin aluminum film (Fig. 3). We then measure the CL lifetime as a function of distance d to the metal, with deep subwavelength (<λ/10) resolution (Fig. 4). Our results firmly establish time‐resolved electron spectroscopy of nanophotonical devices as a powerful characterization tool for nanophotonics.