Samples must be ultra-high vacuum compatible. The PEEM operates at pressures better than 1x10^-9 mbar and hence any material that degasses is not allowed.

Sample surfaces must be CONDUCTIVE. There is no possibility of imaging insulating surfaces because of charging effects. Ultra-thin oxide layers on metals and doped semiconductors can be used. In case of doubt, please ask your local contact.

Samples can be cooled with liquid Nitrogen down to ~ 100 K and can be heated radiatively or with e-beam. Temperatures of approx 1000 K can be reached with radiative heating and 1900 K with e-beam flashing of thin samples. The temperature is measured either with a W/Re thermocouple type C spot-welded on a Ta in thermal contact with the backside of the sample surface or with an optical pyrometer in the preparation chamber.

The sample is mounted on customized cartridges and is kept in position with Mo-caps as shown in figure 1. The outer diameter of the cap is 14 mm and the inner is 6 mm (alternatively inner diameters of 4 and 10 mm are available; please ask your local contact for more details). Please refer to figure 1 for a schematic design or ask your local contact for more details. The thickness of the sample should not exceed 2 mm.

Figure 1: left, image of the sample cartridge. Right: schematic drawing of the range of suitable sample sizes.

Samples with a diameter smaller than 4 mm can be mounted using UHV compatible and conductive glue (usually silver paste) to a Ta foil. However, please refer to the beamline staff for more details.

INSTRUMENT SPECIFICATIONS

The specifications of the PEEM are meant as guidelines for ideal experimental conditions. These conditions can be summarized as: good sample conductivity, clean surface and atomically flat, high contrast and stability. Achievement of high-resolution requires a lot of effort and has to be discussed with the beamline staff.

The fields of view may vary between 80 and 2 mm. For XPEEM and LEEM, the largest field of view is limited by the size of the illumination source of 10 mm (x-rays) and 50 mm (LEEM), respectively.

EVAPORATION SOURCES

One evaporation source is available in the main chamber and two in the preparation chamber. EFM 3 evaporators are currently fitted. For available evaporants and crucibles, please discuss your needs with the beamline staff. The access to the chambers is through a DN40 flange with an inner bore diameter is 38 mm. For the distances to the sample, please contact the beamline staff.

Evaporation of most metallic compounds is allowed (Au, Ag, Co, Cu, Fe, ...). Volatile metals are NOT allowed. Details must be discussed with beamline staff before experiment starts.

Dosing of gasses is possible and has to be agreed with the beamline staff well in advance of the experiment starting.

Evaporation of volatile organic molecules is not permitted in the PEEM or the PEEM Preparation Chamber.

PREPARATION CHAMBER

The preparation chamber is equipped with LEED, AES, VT-STM, two EFM3 evaporators, thickness monitor, gas dosing, sample annealing and sputtering.

The transfer of the sample is done through a load-lock system and the complete transfer from air to measuring position in PEEM takes approximately 15 minutes. 

Photo of PEEM, preparation chamber and load-lock.