Escher is a state-of-the-art spectroscopic LEEM/PEEM facility at Leiden University. In May 2008, this research project was funded by the Dutch NWO-Groot Program for large investments. Escher is an exciting set-up with a broad range of possibilities, enabling us to apply LEEM/PEEM to various fascinating research questions in surface science, nanoscience, transport physics and exploratory bioscience. LEEM stands for low energy electron microscopy. This imaging technique was originally developed by Ernst Bauer and later improved by Ernst Bauer, Ruud Tromp and others. In LEEM, an electron beam is first accelerated (typically to 15 keV) and focused towards a sample (see Figure). Just before the sample, however, the electrons are decelerated again, to almost zero energy (~eV). Hence, the incoming electrons can probe the sample surface with very high sensitivity. The electrons returning from the sample, are re-accelerated, focused and finally imaged. Imaging can be done in real space, as well as in reciprocal space (Low energy electron diffraction, LEED). In the Figure, we show a schematic image of Tromp's LEEM design. The electrons run from top to bottom, via the sample (green) which is at a 90o angle.

PEEM denotes photo-electron emission microscopy. In this case, the electrons are released from the sample via the photo-electric effect, and subsequently imaged using the same electron optics as for LEEM.

We aim for a combined LEEM/PEEM instrument featuring aberration-corrected optics with < 2 nm spatial resolution, energy filtered spectroscopic real space imaging, full 3D k-space electron spectroscopy, on sub-micron length scales, and a 10-1800 K operating range. For this, we will not only build up a state-of-the-art set-up, we will also invest deeply in instrument development. Our focus is to build a low-temperature sample holder (a Leiden tradition), as well as to improve the detection technology. The scientific program will address issues in molecular and organic electronics, transport physics, surface, thin film, and interface science, novel materials, and exploratory bioscience.

Introductions of low energy electron microscopy can be found e.g. at the LEEM research website at IBM and Michael Altman's website at HKUST

facility.txt · Last modified: 2013/09/24 12:34 (external edit)