(Hybrid) Macro-ATR Samples: Essential Information
Each macro-ATR crystal has a facet (or flat spot) that comes into contact with the sample. We routinely use crystals with a facet size of 250 μm or 100 μm, but also have a 1 mm facet available that is suitable for soft samples only. The average maximum area that can be used for measurement acquisition on each of the crystal facet sizes are shown below.
Note: This is only a guide, the working area can change slightly depending on the crystal.
Samples are best mounted on a 25 mm metal disc to ensure correct positioning in the macro-ATR accessory. The sample itself may be mounted on (for example) a glass slide, which can then be mounted on the metal disc with a weak adhesive. The beamline has a number of 25 mm discs of various thicknesses (2 - 10 mm height) available for use during your beamtime, including one heating/cooling mounting disc for temperature controlled studies. (See figure below)
Figure: [Left] 25 mm diameter metal discs for mounting macro-ATR samples. [Right] Temperature controlled macro-ATR sample mounting disc
Sample size and positioning on the disc
The macro-ATR unit has a limited travel range in the xy- and z- directions. Therefore, it is imperative that your sample conforms to the following conditions:
The total height of the sample and mounting must be < 11 mm
The region of interest to measure must be located within the central 5 × 5 mm area of the sample mounting location on the macro-ATR accessory (i.e. in the middle of the 25 mm diameter metal mounting disc)
Again, it is highly recommended to use one of the 25 mm metal mounting discs to ensure correct positioning into the macro-ATR accessory
Our macro-ATR crystal is made of germanium (Ge), which is a relatively soft metal and easily damaged. To avoid damaging the crystal, all samples need to have a flat, non-tilted surface for measurement. For tissue sections and other soft squishy samples, a clean cut with a microtome or scalpel is sufficient as the ATR crystal can gently press into the sample without being damaged.
If you have hard samples that require cutting and polishing to obtain a flat surface (e.g. concrete, geology samples, composite materials), we require a final polishing step to be a minimum of 3 micron or 8,000 grit/mesh. Preferably a 1 micron or 14,000 grit finish. Either a diamond or oxide paste will work, and the polishing compound needs to be completely removed before measurement.