Sample mounting
General
In general, suitable samples are flat plates of max. 10×10 mm² surface area (depending on the sample holder used). The materials to be analyzed must be UHV compatible, electrically conductive and if possible homogeneous. Some other types of samples can be studied only if deposited on flat conductive substrates, e.g. evaporated or sputtered thin films, powders pressesd into indium foil etc. Samples sensitive to air exposure might be mounted in a nitrogen-filled glove bag but such option must be discussed in advance.Several sample holders are available. The base plate, which is the same for all sample holders, is grounded, but sample can be mounted on insulated supports with electrical contacts using molybdenum M1.2 nuts. It allows sample to be heated and/or grounded or biased. The thermocouple (K-type, chromel-alumel) is available for temperature measurement. The design can be further developed depending on sample properties and user requirements (cooling, heating, thermocouple reading...).
Sample holder selection table
Sample requirements |
![]() Plain mounting |
![]() Crystals |
![]() Silicon wafers |
![]() Pocket with clamps |
![]() Sapphire plates |
![]() STM type |
number of samples on one holder | many | 1 | 1 | 1-2 | 1 | 1 |
can be grounded | yes | yes | yes | yes | yes | yes |
can be biased | no | yes | yes | yes | no | yes |
annealing up to 400 °C (700 K) | no | yes | yes | yes | yes | yes |
annealing up to 1000 °C (1300 K) | no | yes | yes | yes | no | yes |
measurement while annealing ≤400 °C (700 K) | no | maybe | no | maybe | yes | yes |
measurement while annealing ≥400 °C (700 K) | no | no | no | no | no | yes |
maximum annealing current | – | 20 A | 10 A | 20 A | 5 A | 5 A |
Sample mounting
- Mount the sample(s) on the selected holder.
- Check that all nuts are properly tightened. Do not exaggerate with the force in order not to break the fragile ceramic insulators.
- Measure the distances for the annealing and thermocouple pins according to the instructions for each sample holder.
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Check electrical connections (if installed):
- sample to ground: infinity resistance, depending on the cleanliness of the ceramic insulators, several kΩ can still be fine
- heating element contacts: low resistance, <1Ω for metals, higher for Si wafers
- thermocouple contacts: low resistance, several Ω at maximum
- sample to thermocouple: low resistance, several Ω at maximum
- Blow away any dust from the sample surface.
- Proceed with sample insertion.
Plain mounting
Four sample holders for the samples that do not need to be annealed are available.
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The samples can cover up to the area marked in red. | |||||||||||||||||||||||||||||||||||||||||||
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The sample(s) can be glued on the baseplate surface using a double-sided carbon of copper adhesive tape or held in place using a metallic clamp fixed with a screw or rod+nut to any of the 16 M1.2 threaded holes. | |||||||||||||||||||||||||||||||||||||||||||
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The metallic clamp assures a good electric contact between the sample surface and the plate to avoid charging effects. However, it occupies some space so the number of samples is more limited. | |||||||||||||||||||||||||||||||||||||||||||
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Many samples can fit on one base plate, depending on their shapes and sizes. Bear in mind that too small samples might be difficult to correctly align with respect to the photon beam and energy analyzer. Using only the adhesive plate you can fit for example up to 11 disc-shaped samples of 6 mm diameter on one sample holder (covering at most the red area noted above). Because of the thick insulating glue layers the electrical contact might be poor, resulting in charging effects, unless you strongly press the tape and the samples. | |||||||||||||||||||||||||||||||||||||||||||
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Assembly:
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The thermocouple pins help holding the sample holder in the manipulator, however not as strongly as other sample holders where annealing contacts are assembled. The rod(s) or the screw(s) holding the clamp(s) must not be screwed to much in because the botom surface must remain flat. The thermocouple pins can stick out between 3-4 mm below the bottom surface. |
Metal crystals
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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. |
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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 |
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Example of Cu crystal (8 mm diameter × 2 mm thickness) mounted. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Example of Ir crystal (5 mm diameter × 1 mm thickness) mounted. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Assembly:
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For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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 (too big) sample (S) is not touching directly the annealing contacts (7ab). In such case the annealing current would not flow through the thin annealing wires (8) but directly through the thick crystal (S) which would make the annealing inefficient and high temperatures could not be reached. |
Silicon wafers
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Silicon wafers may be clamped between the annealing contacts and heated by current passing directly through the sample. It requires self-supporting sample of rectangular shape approximately 10 mm long and 3-10 mm wide. The best width is 5-7 mm. The suggested thickness is about 0.5 mm. The electrical resistance should be in the range 0.1-1000 Ω depending on required temperature (in the case of silicon it means that it must be sufficiently doped). If the resistance is too high it is impossible to anneal the sample. |
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For annealing we usually use the 70 V×24 A power supply. The centre of the sample is theoretically at half of the annealing voltage so it is difficult to acquire spectra during annealing. The temperatures up to about 1100 °C/1400 K can be reached. Maximum annealing current is 10 A. Thermocouple is optional. Some users prefer to estimate the temperature during high-temperature annealing by eye or use a pyrometer. They claim that at high temperatures nickel from the thermocouple alloys migrates on the sample and contaminates it. So if you want to use the thermocouple place a thin tantalum spacer to avoid the direct contact of the thermocouple with the sample. |
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Example of Si sample 10×6×0.5 mm³ mounted. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Assembly:
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For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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) |
Pocket with clamps
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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. |
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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. |
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Assembly:
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For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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. |
Sapphire plates
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The sample on this holder is annealed by a Ta spiral closed between two insulating sapphire plates. The sample of maximum 10×10 mm2 size is clamped by two wires that are fixed by screws to the base plate. Therefore the sample is permanently grounded and the spectra can be measured during annealing. |
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The thermocouple is touching the sample surface which makes the temperature reading more accurate than on the pocket sample holder. However, the error can be up to 50 K/°C so you can consider spot-welding of the thermocouple to the sample if your material permits to. Maximum temperature is about is about 500 °C/800 K. Maximum annealing current is 5 A. |
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Example of stainless steel disc sample mounted. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Assembly:
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For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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) |
STM type
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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. |
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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. |
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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:
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For the correct thermocouple pin contact the pins must stick out 3.8-4 mm below the baseplate bottom surface | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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