Zinc selenide crystal

Fig. 1 shows the increase of nitrite band near 780 cm- for various alcohol contents in ethylene-vinyl alcohol copolymers. The analysis of the hydroxyl region of the IR spectra (not shown) indicated that the reaction was not quantitative (residual OH band). The precise analysis of this band ( 34(X) 70 I / mol. cm) as w ell as the nitrite band (e780 639 I / mol. cm) allows to evaluate the reaction yield considering the total film thickness (Transmission 1R). The values decrease when the OH content increases (0.75 0.62 0.59 ans 0.59 for vinyl alcohol contents 2.6,4.9, 7.7 and 10.1% respectively). Complementary analysis by reflexion IR (HATR) showed that the first 5-8 pm (Germanium crystal) were fully transformed while the analysis of the first 20-25 pm (Zinc Selenide crystal) revealed a decrease of the yield from 1 to 0.5 when the alcohol content was increasing. Then, this treatment can be helpfull for surface modification of membranes. 

Fourier Transform Infrared Spectroscopy (FT-IR) measurements were made using a Nicolet Instruments 740 FT-IR spectrometer. A horizontal attenuated toted reflectance cell equipped with a 45° zinc-selenide crystal trough wets used. Spectra of neat solutions were obtained by co-addition of 256 scans at 4 cm- resolution. 

The second sample appeared to be black sooty metallic shavings. Following solvent extractions of this material with xylene and Freon, the solvents were evaporated, and the residues were analyzed by FTIR spectrometry. Because chlorinated solvents attack the epoxy that secures the zinc selenide crystal to the horizontal attenuated total reflectance (HATR) boat. Freon was air dried from the residue. The residue was resolvated in acetone for mounting purposes. 

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. 

Cathodic electrodeposition of microcrystalline cadmium-zinc selenide (Cdi i Zn i Se CZS) films has been reported from selenite and selenosulfate baths [125, 126]. When applied for CZS, the typical electrocrystallization process from acidic solutions involves the underpotential reduction of at least one of the metal ion species (the less noble zinc). However, the direct formation of the alloy in this manner is problematic, basically due to a large difference between the redox potentials of and Cd " couples [127]. In solutions containing both zinc and cadmium ions, Cd will deposit preferentially because of its more positive potential, thus leading to free CdSe phase. This is true even if the cations are complexed since the stability constants of cadmium and zinc with various complexants are similar. Notwithstanding, films electrodeposited from typical solutions have been used to study the molar fraction dependence of the CZS band gap energy in the light of photoelectrochemical measurements, along with considerations within the virtual crystal approximation [128]. 

A few ATR probes are commercially available. In the near-IR ATR probes are mostly used as easy-to-use sticking probes for liquids and solids. As the aim is primarily to identify a material, not to measure low concentrations, probes with typically one or two reflections (Figure 5-d) are used. In the mid-IR, similar layouts can be found, using e.g. zinc selenide, germanium or silicon crystals as sensing elements. More sensitive and generally better suited for industrial process control DiComp -type probes (Figure 5-e). The actual ATR element is in this case a thin diamond disc supported by a suitably shaped ZnSe crystal. ATR probes of that type are available off the shelf with between one and nine reflections. If more... 

Cation holes can also be created by coactivation with trivalent metal ions or by incorporation of oxygen [5.313]. The luminescence band of self-activated zinc sulfide with the zinc-blende structure exhibits a maximum at 470 nm. On transition to the wurtzite structure, the maximum shifts to shorter wavelengths. In the mixed crystals zinc sulfide-cadmium sulfide and zinc sulfide-zinc selenide, the maximum shifts to longer wavelengths with increasing cadmium or selenium concentration. 

Some important functional groups and their region of absorbance are highlighted. Cheddar cheese was scanned by pressing 0.5 g of cheese on a diamond attenuated total reflectance (ATR) crystal. Extracts was scanned by drying 10 pi of the extract on a zinc selenide ATR crystal. 

Another kind of cell, made by Graham and Curran, was based on an internal reflection crystal [80]. A gold minigrid was mounted directly on a prism (9 x 9 x 45 mm) and on top of this was a zinc selenide prism. The distance (observation) between the minigrid and the prism is typically 13-15 pm, which results in a very short response time. For a potential-step experiment, maximum absorbance is achieved within a couple of seconds. The cell is especially well-suited for potential-scan experiments because the intermediate generated at the electrode will rapidly fill out most of the observation distance even when moderately fast sweep rates (50 mV s ) are applied. Some memory effect is, however, present, because the diffusion layer will not be completely evolved on this timescale. At smaller sweep rates (2 mV s ) all of the observation layer behaves like a thin layer, where the concentrations are in equilibrium with the electrode surface concentrations. The cell has been used to study the reduction process of Fe(CO)s by CV, where it was pos-... 

In the semiconductors of greater polarity, the dielectric constants are smaller and the effective masses larger, and the same evaluation leads to 0.07 eV in zinc selenide, for example many of the impurity states can be occupied at room temperature. As the energy of the impurity states becomes deeper, the effective Bohr radius becomes smaller and the use of the effective mass approximation becomes suspect the error leads to an underestimation of the binding energy. Thus, in semiconductors of greatest polarity—and certainly in ionic crystals— impurity states can become very important and are then best understood in atomic terms. We will return to this topic in Chapter 14, in the discussion of ionic crystals. 

The crystals used in ATR cells are made from materials which have low solubility in water and are of very high refractive index. Such materials include zinc selenide (ZnSe), germanium (Ge) and thallium/iodide (KRS-5). The properties of these commonly used materials for ATR crystals are summarised in Table 3.3. Different designs of ATR cells allow both liquid and solid samples to be examined. 

Research Centre (MERC) in collaboration with Remspec Inc. The ATR head consists of a three-inch zinc selenide (ZnSe) crystal, attached to the fiber optic cables, and is held in place by a mechanical seal housed within a plastic sleeve. The perforated stainless steel cover protects the ZnSe crystal, and the fibers are insulated to avoid freeze-fracture. The length of the crystal... 

The ATR crystals are made from materials that have a very high refractive index and low solubility in water. Table 1 summarizes some of the commonly materials used in ATR crystals. Amongst these materials, diamond, zinc selenide (ZnSe) and germanium (Ge) are... 

ATR objective ATR is used for surface analysis using physical contact with a sample surface. The objective utilizes a crystal of material for the actual physical contact with the sample. Typical crystal materials include diamond (Di), germanium (Ge), silicon (Si), and zinc selenide (ZnSe). ATR measurements can yield excellent quality spectra provided that the contact pressures of the ATR crystal and the sample are held constant reproducible data require reproducible contact pressure. Commercial contact gauges are available from suppliers of microscope accessories. One-percent reproducibility is typically achieved when keeping the contact pressure constant. ATR crystals are generally ZnSe with a refractive index of 2.42 and an angle of incidence of 45°. Sample pen-... 

Zinc selenide (ZnSe) crystallizes in the zinc blende structure (see Figure P12.72) and has a density of 5.42 g/cm. ... 

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