Windows zinc selenide

Abrasion and corrosion protection for germanium, magnesium fluoride, cadmium telluride, zinc sulfide, and zinc selenide IR windows. 

Infrared optics is a fast growing area in which CVD plays a maj or role, particularly in the manufacture of optical IR windows. 1 The earths atmosphere absorbs much of the infrared radiation but possesses three important bandpasses (wavelengths where the transmission is high) at 1-3 im, 3-5 im and 8-17 pm. As shown in Table 16.2, only three materials can transmit in all these three bandpasses single crystal diamond, germanium, and zinc selenide. 

The most common IR window materials are zinc sulfide, which is translucent, and zinc selenide, which is transparent. Both of these materials are made by low-pressure CVD by the reaction of vaporized zinc and hydrogen sulfide or selenide (see Ch. 12). Germanium, another common IR window material, is also produced by CVD (see Ch. 8). 

Figure 9.9 Schesatic diagrans of flow-through cell. A, and solvent elimination interfar B, for SFC/FTIR. For A (1) polished stainless steel lig..v.pipe (2) zinc selenide window (3) PTFE spacer (4) viton rubber o-ring (5) graphitized Vespel nicroferrule (6) deactivated fused-silica capillary tubing (7) bolt with Allen nut (8) stainless steel end-fitting and (9) stainless steel body of flow cell.

Optics Issues relative to hygroscopic optics and the need to pay attention to mirror mounts relative to vibration and/or thermal effects have already been addressed. Zinc selenide is an important alternative material, especially when antireflection (AR) coated. If potassium bromide absolutely has to be used for its lower transmission range (down to 400 cm ) then a protective coating such as Parylene must be used. Most process analyzers use protective windows between the spectrometer and the sample interface. If used, back reflections from the window surfaces into the interferometer must be avoided because these will cause photometric errors. Such reflection can be eliminated by wedging or tilting the optical windows, relative to the beam path. 

According to the specific task, different materials are used for the windows. Typical materials are sapphire, calcium fluoride, zinc selenide, diamond, and normal quartz. The selection of the materials depends on the pressure and, for spectroscpic investigations, also on the wavelength corresponding to the bonds of the species to be analysed. 

Observation cell (zinc selenide windows) in IR spectrometer monitors products formed via catalysis... 

At forward biases below 2.5 V, the curve shows a linear region. The deviation from the exponential behavior at bias voltages above 2.5 V can be accounted for by the volume resistance of zinc selenide. Therefore, the barrier height at the p-n junction is 2.5 V. It follows from the I-V data that the p-n junction lies within the zinc selenide layer. Therefore, a p-ZnO/p-ZnSe/w-ZnSe structure was produced. The ZnO serves as an injecting contact to the p-ZnSe layer and as an exit window for radiation. 

Infrared, like the UV and visible regions of the spectrum, provides a useful method for detecting solutes in liquid streams. The detector uses the principle of attenuated total reflectance, with a single beam spectrometer being used in conjunction with a tow volume flow cell. The cell is equipped with sodium chloride, calcium fluoride or zinc selenide windows and can be heated to temperatures greater than 100°C. The detector can... 

The sample cell system for GCIR consists of a micro-light-pipe cell, typically a 12 cm long silica tube with an i.d. of 1mm and reflective gold plated inner surfaces giving a cell volume of approximately 100 pi. The ends of the cell are fitted with spring loaded potassium bromide or zinc selenide windows (Figure 7.13b). The GC transfer line and cell are heated to a preset temperature between 50 and 350°C. 

Additives in polymers were identified by solvent-elimination based coupling of reversed-phase column liquid chromatography(LC) and FTIR spectrometry. A spray-jet interface was used to deposit the effluent from a narrow-bore LC column on a zinc selenide window. The deposited additives were analysed by FTIR transmission microscopy, yielding identification limits in the low-nanogram range. High-quality IR spectra were obtained for components present in PVC and PP samples. 

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