Sample mounting

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STM typeSTM type The design of this sample holder is coming from the STM aparatus at the Charles University in Prague.

The sample on this holder is annealed by a molybdenum block containing a heating spiral made of very thin tantalum wire, which allows reaching high temperatures (up to 1100 °C/1400 K) using quite low currents in comparison to the other sample holders (maximum annealing current is 5 A). Therefore, in many cases the spectra can be measured during annealing although the sample is not permanently grounded.
STM typeSTM type We have two types of clamps available (12a and 12b in the assembly below). The clamp can be modified according to the sample size and shape and it can be grounded to the base plate if requested. The maximum sample dimensions are 10×10 mm2.

The thermocouple is touching the bottom surface of the sample. As it is not spot-welded, the error can be up to 100 K/°C. Also due to oven mass the annealing and cooling is much slower than on other sample holders and extensive degassing is needed.
STM typeSTM typeSTM type Examples of the sample holder with Pd crystal mounted (with clamp 12a in the assembly below), with stainless steel disc sample mounted (with the clamp 12b in the assembly below) and with uncovered heater (without samples and clamps).
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Assembly:

item count name material notes
S1,2 1 sample   up to 10×10 mm² surface
1 1 baseplate molybdenum 1 mm thickness
2A 1 thermocouple
pins		 alumel
(magnetic)		 must stick out 3.8-4 mm below the baseplate bottom surface
2C 1 chromel
(non magnetic)
3a 6 ceramic spacers alumina thinner
3b 2-10 thicker
4 8-16 nut molybdenum M1.2 thread
5 1 thermocouple chromel
(non magnetic)
alumel
(magnetic)		 0.125 mm diameter wires, spot-welded together and touching the sample bottom surface
6 4-8 rod molybdenum M1.2 thread
7a 1 annealing
contacts		 tungsten brushed on the left side, see surfaces highlighted in yellow; must be 3.6-3.8 mm above the baseplate top surface
7b 1
8 1 heater tantalum 0.1 mm diameter wind into 3 coils
9 2 clamp tantalum 0.25 mm thickness
10 3 balls alumina insulating ceramic balls, easy to lose!
11 1 oven molybdenum  
12a 1 clamp tantalum
alumina
tungsten
molybdenum		 fixed with screws 13 to the baseplate
12b 1 tantalum fixed with ceramic spacers 3b and nuts 4 on rods 6 to the baseplate
13 4 screw molybdenum M1.2 thread
STM typeSTM type For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface
STM typeSTM type For the correct connection the annealing contacts must be 3.6-3.8 mm above the baseplate top surface. This distance (if 3.5 mm or lower) can be increased by placing tiny spacers made of properly thick wire below the bottom ceramic spacers (3a) or swapping the thin ceramic spacers (3a) with the thicker ones (3b)
Last Updated on Thursday, 09 March 2023 10:32