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Beamline Description

Manipulator and Sample holder

The sample manipulator has four degree of freedom (xyz translations and polar rotational axes). Since October 2009, an additional angular degree of freedom (azimuthal rotational axes) is available using a suitable sample holder. Different sample holders, capable of accomodating transferable samples, can be mounted on a cryostat that reaches with liquid helium a temperature lower than 5 K. Since April 2012, a new sample holder with motorized azimuthal angle, based on an attocube rotator (ANR200/RES), has been successfully assembled in our liquid-helium cryostat manipulator and tested. It allows to acquire computer-controlled Fermi surface maps with high angular accuracy (about 0.02°) and it is now available for Users beamtimes (see Figure 1). Since December 2017, the manipulator movement is fully motorized, by stepper motors for the polar rotation and xyz translations and by the piezo motor for the azimuthal rotation, and it can be remotely controlled.

The temperature can be measured by a C-type thermocouple and by a standard Lake Shore silicon diode installed next to the sample and on the cold finger, respectively. To improve the reliability of the readings at low temperatures, the thermocouple has been additionally calibrated with the help of the silicon diode. The head of the cryostat includes also a cartridge heater allowing a remote control of the temperature in the range 5-400 K.

Samples must be resistant to radiation damage and conductive for photoemission measurements. Using the transfer system, samples must be mounted on a suitable sample flag (see Figure 2) and the maximum sample size is of about 10 mm in diameter and thickness. If special sample mountings are required, please contact the beamline responsible well in advace in order to plan suitable solutions. Sample annealing at high temperature (> 400 K) can be performed transfering the sample in a dedicated heating stage (see Figure 3) where temperature up to 2500 K can be reached by electron bombardment.

Insulating samples are practically impossible to measure due to charging effects. Therefore, insulating thick (bulk) crystals are not welcome. Metallic, two-dimensional thin films or layered crystals with small Brillouine zone are the sample of choice for this beamline.

Fig. 1: Sample holder with motorized azimuthal angle

Fig. 2: Base sample flag

Fig. 3: Heating stage

Ultima modifica il Lunedì, 15 Gennaio 2018 18:05