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Microgrooved wafers are available in a choice of two different face angles: 35° and 55°. To identify the face angle of the wafer, observe the ends of the grooves. The ends of the 55° grooves are square, while the ends of the 35° grooves are capped by a triangle. The orientation of the grooves with respect to the wafer length and width is not a reliable indicator of the face angle. Please use the ends of the grooves to identify the wafer face angle.

35 degree	55 degree
The ends of the 35° groove profile are triangular.	The ends of the 55° groove profile are square.

Orienting and Sealing the Wafer in the Cell

The microgrooved wafers can be installed such that the grooves are either parallel or perpendicular to the incident beam. The performance is comparable for both orientations for most applications.

If one orientation is preferred for a given set of experimental conditions, take note of the direction of the grooves with respect to the side-lengths of the wafer. (Some batches of wafers have the grooves aligned parallel to the long side-length of the wafers, while other batches have the grooves aligned parallel to the short side-length.) Place the wafer holder in the VeeMAX III top plate and place the wafer groove-side down in the holder. Rotate the wafer holder in the pocket of the VeeMAX top plate such that the incident beam is oriented with respect to the grooves according to the desired result. Use the table below as a guide to aid installation.

	IR beam parallel to grooves	IR beam perpendicular to grooves
Wafer grooves are parallel to short side- length	Alignment nub faces front of VeeMAX.	Alignment nub faces side of VeeMAX.
Wafer grooves are parallel to long side- length.	Alignment nub faces side of VeeMAX.	Alignment nub faces front of VeeMAX.

In this video, we demonstrate the assembly of a J1 cell (both wafer and FAC options) and provide some pointers to help you get up and running with your first experiment using a J1 cell.

Occasionally, we’ve been asked if our cells are able to be used with hemispherical ATR elements. While there is no fundamental reason preventing the use of a hemisphere in one of our cells, the performance of hemispheres is substantially worse than the Face-Angled Crystals (FACs) that we recommend. This performance difference is apparent by looking at the single channel energy spectrum of the two elements:

Figure 1: Energy curves to compare throughput of internal reflection elements.

Both spectra were collected with the same 2 mm aperture and 128 co-additions. The spectrum collected using the FAC had 12 times the spectral power of the spectrum collected with the hemisphere. Both spectra were collected at an angle of incidence of 60 degrees, which was the face angle of the FAC.

The main reason for the difference in throughput is that the hemisphere is a focusing optic, while the planar surfaces of the FAC do not alter the shape of the wavefront. The stock VeeMAX III configuration is designed to focus the beam onto the surface of a flat mirror or the face of a prism, and the extra optical power provided by the curved surface of the hemisphere reduces the amount of light which is directed onto the detector by the mirrors of the VeeMAX. The anti-reflection coating further helps to boost the throughput compared to an uncoated hemisphere by minimizing reflection losses at the two air/Si interfaces.

For more additional information comparing the performance of a hemispheres and FACs using the VeeMAX II, see the following article:

Sigrist JA, Lins ES, Morhart TA, Briggs JL, Burgess IJ. Optimization of a Commercial Variable Angle Accessory for Entry Level Users of Electrochemical Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS). Applied Spectroscopy. 2019;73(12):1394-1402. 10.1177/0003702819858353