Sample mounting

Page 5 of 7

Pocket with clamps


pocket with clampspocket with clamps One or two samples of irregular shape, with low conductivity or with other properties preventing them from mounting like crystals or silicon wafers can be mounted to the "metallic pocket", usually spot-welded from Ta wires and sheets. A specially designed broad pocket permits to insert two samples at the same time.

In the example you can see a silicon wafer in the single pocket and a silicon wafer plus a hat-shaped crystal in the double pocket.
 
pocket with clampspocket with clamps The sample is simply clamped by the pre-stressed sheet so thermal contact with pocket is not always excellent and uniform. It can also cause difference between thermocouple reading and the real temperature of the sample surface. The error can be up to 100 K/°C.

Maximum annealing temperature is about 700 °C/1000 K and the maximum annealing current is 20 A.
 
The sample is theoretically at half of the annealing voltage so it is difficult to acquire spectra during annealing.
 
pocket with clamps

Assembly:

item count name material notes
S1,2 2 samples silicon wafer or any plate
S3 1 metal hat-shaped crystal
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 thicker
4 8 nut molybdenum M1.2 thread
5 1 thermocouple chromel
(non magnetic)
alumel
(magnetic)		 0.1-0.25 mm diameter wires, spot-welded together and touching the pocket or spot-welded to it
6 4 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 1 single pocket tantalum spot-welded from 0.1-0.25 mm sheet and 0.25-0.4 mm wires
8.2 1 double pocket
9 2 clamp tantalum 0.25 mm thickness

pocket with clampspocket with clamps		 For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface.
pocket with clampspocket with clamps 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).

Check in the areas labelled by green circles that the pocket (8.1 or 8.2) is not touching directly the annealing contacts (7ab). In such case the annealing current would not flow through the annealing wires but directly through the pocket which would make the annealing inefficient and high temperatures could not be reached.


Last Updated on Thursday, 09 March 2023 10:32