Time‐resolved cathodoluminescence in a scanning electron microscope

Abstract

The past decade has witnessed enormous progress in the design and fabrication of nanostructured materials with unique optical properties. These tiny physical structures allow geometrical control over the electromagnetic shape of light well below its own wavelength. A large variety of applications for this field of subwavelength optics known as nanophotonics have already begun to emerge, including solar photovoltaics, chemical sensing, quantum cryptography, and LED lighting. Many fundamental optical interactions are hidden beneath the diffraction limit, however, which makes the retrieval of subwavelength optical behavior impossible with standard microscopy. An alternative approach, known as cathodoluminescence (CL) [1], is to probe nanostructures with an electron beam, which excites optical resonances and transitions and then collects the emitted light. It has recently been used to characterize plasmonic structure [2] or III‐N heterostructures [3]. Thanks to a very efficient CL system, in a scanning electron microscope (SEM), working in free space, we can directly probed many key dimensions of light – including intensity, angle, polarization, and frequency – with ~10 nm resolution [4]. In this presentation we will show how we can use a blanker to modulate a continuous electron beam to generate electron pulses with a resolution of ~10 ns. This approach has several advantages compared to alternatives such as a laser driven pulsed electron gun [5]. It can be easily implemented in any SEM, it requires few experimental modifications, it does not require a dedicated microscope and the pulsed electron beam can be controlled at will (pulse duration and repetition rate). We will show how this pulsed electron gun can be used to explore the dynamics of a single photon emitter, such as a rare earth ion or the NV 0 center of nano‐diamond. An HBT interferometer allows recording of the autocorrelation function of the CL signal [6][7]. Combining secondary electron images with measurements of the CL spectra, emission polarizations, lifetimes and second order correlation function, we are able to fully characterize optically active systems at the nanometer scale.