Light emission, also known as luminescence, provides access to valuable information about the physical properties and dynamics of atomic, molecular or excited solid systems. Among these properties, the lifetime of an excited state is of fundamental as well as applicative interest. Thus, its measurement has stimulated for decades the development of new instrumental developments. The techniques used have long been based on optical excitation of the sample. However, the limited spatial resolution of optical spectroscopies and the characteristic length scales of the main relaxation processes often below the optical wavelength have motivated the search for alternative strategies.
Historically, light emission measurements have been performed in scanning electron microscopes (SEM). However, despite the significant gains in spatial resolution compared to optical systems, SEM technologies are intrinsically limited, and do not allow, for example, to access atomic structural information in parallel with optical information.
This is what transmission electron microscopy (TEM) technologies allow. Collaboration between researchers from CEMES in Toulouse and LPS-Orsay has made it possible to achieve such a measurement in an ultrafast transmission electron microscope (UTEM).
These time-resolved nanocathodoluminescence experiments in a TEM will provide information at the nanoscale on the connection between structural properties and charge carrier dynamics in semiconductor nanostructures. They will allow for example to study the ultralocal modification of the internal quantum efficiency of semiconductor nanostructures linked to the modulation of the dopant concentration, to stress variations, to electric fields (quantum confined Stark effect), to interfaces or to structural defects such as dislocations. They will deepen our understanding of the physics of excitons in these confined systems, a physics that is at the heart of many applications in photodetection, light emission, single photon sources...
ITEM images of a nanodiamond cluster, the white square represents the scanned area (insert image). Intensity (b) and lifetime (c) map of the light emission detected at each pixel. d) Time-resolved cathodoluminescence signal detected at the locations represented by the red and blue squares in c).
Publication : Time-resolved cathodoluminescence in an ultrafast transmission electron microscope. S. Meuret, L. H.G. Tizei, F. Houdellier, S. Weber, Y. Auad, M. Tencé, H.-C. Chang, M. Kociak and A. Arbouet, Appl. Phys. Lett. DOI : doi.org/10.1063/5.0057861
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