High resolution electron energy loss microscopy based on ionization of cold atoms: a new tool for surface nanochemistry

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The goal of the HREELM (High Resolution Electron Energy Loss Microscope) project is to combine a novel, highly monochromatic electron source from Laboratoire Aimé Cotton (LAC, France) with the Electron Controlled Chemical Lithography experiment from Institut des Sciences Moléculaires d'Orsay (ISMO, France) and with an innovative high-resolution full-field spectroscopic electron microscope (Mainz University, Germany). This unique combination will allow microfocussing monochromatic (~1 meV), very low energy electrons (0-20 eV) for nanoscale surface structuring and diagnostics. The coupling to an innovative, spectroscopic full-field microscope, with high spatial, energy, momentum and time resolution (20nm, few meV, 0.003 Angstroms-1 and 150ps, respectively), will open the way towards high resolution spectroscopic low energy electron imaging and real-space access to fast switching processes (CEA/IRAMIS/SPCSI, France). The creation of a monochromatic electron source, at the meV level, uses advanced laser cooling techniques for neutral Cs atoms that are then ionized by lasers to provide an ultracold electron beam. The initial phase of the project will be devoted to test two sources: the first at Mainz, to test monochromaticity using the meV energy resolution provided by the microscope and the second at ISMO, based on an atom beam, to test low energy focalization for nanostructuring. The nanostructuring mechanism employs dissociative electron attachment, a resonant process at a specific low energy leading to selective bond breaking in molecular systems. In itself this experiment will represent a breakthrough in the domain of manipulating and controlling chemical reactions on the nanoscale. The next step will be the design and construction of spectroscopic full-field microscope with time-of-flight energy dispersion and 3D(x,y,t)-resolving image detector (SPCSI/Mainz). The implementation of the ultracold electron beam in the microscope will make a novel type of low energy electron imaging with ultimate spectroscopic capabilities, for inelastic full-field imaging at few-meV resolution and, in addition, for time-resolved imaging for real-time probing of dynamic processes. It is a cathode-lens type microscope optimized for best time resolution enabling time-of-flight energy filtering (nominally sub-meV resolution) and sub-ns stroboscopic imaging (150ps resolution) with high real and reciprocal space resolution. In-situ diagnostics of nanostructuring mechanism will be performed using high resolution electron energy loss spectroscopy. Furthermore, the time structure of the ultracold electron source can be exploited in time-resolved imaging electron energy loss spectroscopy experiments on molecules on surfaces or on ferroelectric samples. In conclusion, the proposed project intends to develop sources and microscope with the best beam quality ever produced and to assess them in advanced surface science research domains.