Paper AS-WeM3
Chemical Characterisation on the Nanoscale: Imaging XPS and Scanning Auger Microscopy with Ultimate Spatial Resolution

Wednesday, October 17, 2007, 8:40 am, Room 610

In this contribution we briefly summarize the current status of Imaging XPS (iXPS) and Scanning Auger Microscopy (SAM). Novel instrument concepts are presented, one in either field achieving ultimate resolution beyond todays limits. In iXPS a great obstacle for higher resolution is the limited X-ray brilliance in the analysis area in combination with the small electron acceptance angle of current spectrometers. Today commercial laboratory instruments are limited to approx. 3 µm resolution at best. Acquisition times as well as time for experiment set up increase unacceptably when the attempt is made to utilise this kind of resolution routinely. In particular with those instruments acquiring each image pixel sequentially by either scanning the X-ray beam or the analysis spot. We present first results of the NanoESCA instrument recently installed at LETI. A new lens concept provides a huge progress for the acceptance angle of photo electrons. This is combined with a patented abberation compensated analyser allowing the acquisition of typically 640x512 image pixels in a single shot. This offers the unique possibility to achieve sub micron image resolution routinely as well as small spot spectra from well defined areas below 1µm diameter, within reasonable acquisition times. In the field of SAM, the spatial resolution depends mainly on the performance of its electron source. Crucial parameters are the probe diameter, the electron energy, and the beam current density. As state of the art a spatial resolution on the order of 10 nm and slightly below has been demonstrated recently on the most advanced commercial instruments, using beam energies as high as 20 keV. However, the Auger cross section increases for lower beam energies and the scattering volume in the sample decreases. Thus operation at lower beam energies is desirable, but the probe diameter still shall not increase to an counteracting extent. We present SAM measurements acquired with a new electron source employing a patented lens system optimised for low beam energies and high current density. This concept enables the highest so far reported SAM resolution of 5 nm (at 10kV). Even at beam energies as low as 1keV more than 1 nA beam current can be focussed into <10nm spotsize. Furthermore we describe the combination of SEM/SAM with complementary techniques, such as STM/AFM, 4 Probe STM, SEMPA, or EBSD to provide information on topography, electronic structure, magnetic domains, or crystal orientation.