Sample suitability issues

It is important to carefully consider the following issues about the suitablity of your samples for measurements with XPEEM/LEEM.

  • Samples must be conductive. Insulators cannot be imaged due to surface charging under e-beam or photon beam irradiation.

  • Semiconductor substrates must be doped, so that their conductivity is few ohm·cm.

  • Oxides might not be suitable for experiments, depending on the thickness of the film and the material under study. Increasing the sample temperature might reduce charging under irradiation with photons or electrons. Please note that many oxides do reduce under irradiation with the photon beam, an aspect which needs to be considered when evaluating the experiment feasibility.

  • Samples must be flat, without tips. Please consider that tips may act as field emitters, which may result in a continuous HV leakage to the objective lens. In the worst cases, tips can prodice severe arcing between sample and objective lens.

  • In general, faceted samples might be difficult to deal with, because it is often impossible to align the e-beam normal to one the crystallographic faces. Nonetheless, it is possible to align the beam to the optical face.

The samples must fulfill some basic geometric requirements that are given by the hosting sample cartirdges. Square sample must have a minimum size of 6 mm x 6 mm; max size is 9mm x 9 mm. Round samples must have a diameter between 6 mm and 13 mm. The sample thickness has to be smaller than 4 mm, but for efficient heating at temperatures higher than 1000°C a thickness of less than 0.5 mm is recommended. A photo of the standard cartridge is shown in Figure on the left. The sample is sandwiched between the cartridge body and a Mo cap. Caps with 4 (left) and 7 mm hole (right) diameter are available. The cartridge is equipped with a filament for radiative sample heating. Furthermore, the filament can be biased to allow sample heating by electron bombardment. Using thin samples one can reach a max temperature of 1600°C in rapid flashes. A type C thermocouple (W5%Re/W26%Re) is fixed to the cartridge in close proximity to the sample, to allow measuring the sample temperature. Notice that the thermocouple is not spotwelded on the sample, but on a Mo ring in contact with the sample. For this reason the temperature readout may not be correct (plus or minus 50°C than actual sample temperature). For special applications, we can provide a special sample holder which allows applying voltage/current to electrodes onto the sample (shown on the right hand side). For this purpose, the filament and the thermocouple leads are used. This implies that with the modified sample holder, the sample cannot be heated.

Last Updated on Thursday, 11 February 2016 22:08