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Sample mounting

Metal crystals

Polished metal single crystals are usually mounted on Ta heating wires (diameter 0.25 or 0.4 mm) annealed by passing current.

Round shape and 5-10 mm diameter is optimal, the thickness in the range 1-2 mm. The smaller the crystal the higher annealing temperatures can be easily reached. The annealing limit for small and thin crystals (5 mm diameter) is about 1100 °C/1400 K, larger crystals (10 mm diameter) will hardly reach 700 °C/1000 K.

The crystal should have 2 slits (0.3-0.5 mm width). If not it can be spot-welded directly to the heating wires (only some materials). Spot-welding improves the heating contact and provides easier annealing and cooling.

The thermocouple can touch the crystal from the backside like a spring or be spot-welded to the crystal (only some materials). Spot-welding improves the thermal contact and provide more precise temperature reading. The error can be up to 100 K/°C.

For annealing usually the 70 V×24 A DC power supply is sufficient. Maximum annealing current is 20 A. The centre of the sample is theoretically at half of the annealing voltage so it is difficult to acquire spectra during annealing.

In the following pictures Cu (8 mm diameter × 2 mm thickness) and Ir (5 mm diameter × 1 mm thickness) crystals are shown.

Last Updated on Thursday, 25 March 2021 09:19