Q: MCT detectors used in infrared microscopes have different wavenumber ranges. On what basis should I select my detector?
A : The Shimadzu AIM-8800 infrared microscope offers two types of MCT (HgCdTe) detector: Type 1 and Type 2. Type 1 can measure across a wavenumber range from 5000 to 720 cm-1, whereas Type 2 extends slightly further to the low-wavenumber end and covers a range from 5000 to 650cm-1.
The detector element in an MCT detector comprises mercury, cadmium, and tellurium. The two MCT detector types are created by adjusting the mixing ratio of the mercury and cadmium. However, the sensitivity drops as the wavenumber range expands. So, when selecting your detector, select Type 1 to give priority to sensitivity over a narrower measuring range, or select Type 2 to study target samples with peaks near the 700 to 650 cm-1 range.
As a reference, the diagram below shows the spectra of polymers with absorption in the 700 to 650 cm-1 range. From top to bottom, these polymers are polystyrene (PS), polyethylene (PE), polybutadiene (BR), polyvinyl chloride (PVC), and polyvinylidene chloride (PVDC). The absorption near 700 to 650 cm-1 results from C-H out-of-plane vibrations and C-Cl stretching vibrations.