Recent achievement in characterization of micro- and nano-materials by scanning photoemission imaging and spectromicroscopy

author: Luca Gregoratti, ELETTRA - Sincrotrone Trieste
published: Feb. 12, 2008,   recorded: October 2007,   views: 352


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With respect to the other photoelectron microscopy techniques a Scanning PhotoEmission Microscope (SPEM) uses the most direct approach to photoelectron spectromicroscopy which is the use of a small focused photon probe to illuminate the surface. The SPEM at the Elettra synchrotron light source can operate in two modes: imaging and spectroscopy. In the first mode the sample surface is mapped by synchronized-scanning the sample with respect to the focused photon beam and collecting photoelectrons with a selected kinetic energy. The second mode is photoelectron spectroscopy from a microspot. The SPEM on the ESCAmicroscopy beamline at Elettra has a lateral resolution of 150 nm; and an overall energy resolution which is now better than 200 meV. Samples can be heated, cooled (liquid N2) and biased during the measurements. The beamline is open to the public and private research community; two call for proposals of experiment are available per year together with the possibility of dedicated collaborations on specific projects. Some recent achievements in the chemical, physical and electronic characterization of nano- and micro-structured materials will be presented providing an overview of the capabilities of this powerful technique. Metallic adsorbate interaction, oxidation and supporting properties of multiwall carbon, semiconducting and metal-based nanotubes will be presented, showing how even dynamic phenomena such as mass transport along the nanotube surface can be monitored by the SPEM. A special design of the samples allows for the investigation of single nanotubes with diameter down to 60nm. The study of compositional and electronic properties of morphological complex 3D semiconducting structures will be presented as well. Important industrial collaborations with international companies have been established in last years. A first example will report on the study of the degradation processes occurring on Organic Light Emitting Devices (OLEDs). Results on both OLEDs operated in ambient atmosphere and grown and operated in ultra-high-vacuum will be compared. Another example will illustrate the chemical characterization of the cathode surfaces of Solid Oxide Fuel Cells under operating conditions; the elemental distribution and its change under biasing and the observation and explanation of the cathode electrochemical activation have been addressed. Finally an overview of the limits in the applications of the x-ray photoelectron microscopes imposed by the operation principles will be given together with the future developments allowing the investigation of materials at mbar and even ambient pressure.

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