Electron Interference via a 4096-Pixel MAPS Detector Designed for High-Energy Physics Experiments

A conventional transmission electron microscope is used as a versatile optical bench in a setup where a pixel recording system, sensitive to single electrons, replaces the final viewing screen. Our detector is based on a custom CMOS chip of 4096 monolithic active pixels designed for applications in vertex detectors of future collider experiments. The chip is equipped with a fast read-out chain able to manage up to 10^8 frames per second. This capability permitted to collect high statistics samples of single electron events within a time interval where the stable operations and the coherence conditions of the microscope were guaranteed. The microscope was configured with an accelerating potential of 60 kV, hence leading to 60 keV electrons. The large fraction of empty events made possible to obtain measurements of the time distribution of electron arrivals and this is what really characterizes this work. In fact, for the first time, conventional interference patterns have been split into single-electron frames according to the time of arrival. In particular, the 4096-pixel sensor has been used to collect diffraction patterns of a single wire, a carbon grating and eventually to reproduce the Young-Feynman two-slit experiment with single electrons instead of light. The experiment has been carried out by inserting two nanometric slits—two 100 x 1500 nm slits, 500 nm spaced apart—in the microscope that provided the electron beam source and the electro-optical lenses for projecting and focusing the pattern on the sensor. The fast readout of the sensor allowed us to record single-electron frames, spaced by several empty frames, and this is an improvement over past single-electron interference works. In this way the time distribution of the single electron arrivals has been measured with a timing resolution of 160 us. This research might also open new detector investigation and development and characterization of pixel sensors.