Quartz optically transparent electrode

In a typical spectroelectrochemical measurement, an optically transparent electrode (OTE) is used and the UV/vis absorption spectrum (or absorbance) of the substance participating in the reaction is measured. Various types of OTE exist, for example (i) a plate (glass, quartz or plastic) coated either with an optically transparent vapor-deposited metal (Pt or Au) film or with an optically transparent conductive tin oxide film (Fig. 5.26), and (ii) a fine micromesh (40-800 wires/cm) of electrically conductive material (Pt or Au). The electrochemical cell may be either a thin-layer cell with a solution-layer thickness of less than 0.2 mm (Fig. 9.2(a)) or a cell with a solution layer of conventional thickness ( 1 cm, Fig. 9.2(b)). The advantage of the thin-layer cell is that the electrolysis is complete within a short time ( 30 s). On the other hand, the cell with conventional solution thickness has the advantage that mass transport in the solution near the electrode surface can be treated mathematically by the theory of semi-infinite linear diffusion. 

The development of electrodes that exhibit optical transparency has enabled spectral observations to be made directly through the electrode simultaneously with electrochemical perturbations [19-21]. These electrodes typically consist of a very thin film of conductive material such as Pt, Au, carbon, or a semiconductor such as doped tin oxide that is deposited on a glass or quartz substrate. Miniature metal screens, minigrid electrodes in which the presence of very small holes (6-40 fim) lends transparency, have also been used. Optically transparent electrodes (OTE) and the cells that incorporate them are discussed in Chapters 9 and 11. 

Delta Technologies 13960 N. 47th St. Stillwater, MN 55802-1234 Indium oxide optically transparent electrodes on glass and quartz... 

Optically transparent electrode — (OTE), the electrode that is transparent to UV-visible light. Such an electrode is very useful to couple electrochemical and spectroscopic characterization of systems (- spectroelectro-chemistry). Usually the electrodes feature thin films of metals (Au, Pt) or semiconductors (In203, SnCb) deposited on transparent substrate (glass, quartz, plastic). Alternatively, they are in a form of fine wire mesh minigrids. OTE are usually used to obtain dependencies of spectra (or absorbance at given wavelengths) on applied potentials. When the -> diffusion layer is limited to a thin layer (i.e., by placing another, properly spaced, transparent substrate parallel to the OTE), bulk electrolysis can be completed in a few seconds and, for -> reversible or - quasireversible systems, equilibrium is reached for the whole solution with the electrode potential. Such OTEs are called optically transparent thin-layer electrodes or OTTLE s. 

Finally, optically transparent electrodes comprised of Sn02 or ln203 thin films on glass, quartz, or plastic are widely used to study electrochemical reactions under illumination in solution. Spectral studies of reactants, intermediates, or products can be also performed to gain some molecular insight into electrode kinetics. 

The spectrometer can also incorporate facilities for single beam transmission and reflectance measurements since it is often necessary to determine the amount of light reflected or absorbed in order to calculate the quantum efficiency of photocurrent generation. Optically transparent electrodes (OTEs) are particularly useful substrates since they allow simultaneous measurements of photocurrents and transmission to be made. Metal films can be prepared by vacuum deposition on the OTEs or, in some cases, the material of interest can be electroplated directly. If Sn02-coated quartz electrodes are used, it is essential to check them periodically to make sure that they do not give rise to background photocurrents since aged electrodes... 

These coated glasses can be used as working electrodes [optically transparent electrodes (OTE)] in standard three-electrode arrangements provided that both glass and coating are chemically and electrochemically stable and inert in the used electrolyte solution and the applied range of electrode potentials. The use of a modified infrared spectroscopy transmission cell equipped with quartz windows for UV-Vis spectroelectrochemistry has been described [18]. Platinum layers deposited onto the quartz served as an optically transparent working electrode and an additional platinum layer served as a pseudo-reference electrode. A counter electrode outside the thin layer zone (in one of the tubes used for solution supply) served as a counter... 

Figure 7. Small-volume optically transparent thin layer electrochemical cell. (A) Quartz cover plate, (B) Teflon spacer, (C) gold minigrid optically transparent electrode, (D) quartz disc, (E) plastic body, (F) inlet syringe port, (G) Pt syringe needle for auxiliary electrode. Adapted from Reference (40) with permission.

Optically transparent electrodes are used in spectroelectrochemistry They can be made by evaporating 10-100 nm thick layers of platinum, gold, tin dioxide, silver, copper, mercury and carbon onto glass, or quartz substrates [42] (for more details see Chap. II.7). 

In many spectroelectrochemical studies, optically transparent electrodes, which are transparent to radiation in a particular spectral region, have been widely used. One type of transparent electrode consists of a very thin film of conductive material such as platinum, gold, tin oxide, indium oxide, or carbon, which is deposited on a transparent substrate such as glass (visible), quartz (UV-visible), or germanium (IR). A second type of transparent electrode is the minigrid electrode. 

With optically transparent electrodes (OTE), molecular adsorbates, polymer films, or other modifying layers attached to the electrode surface or being present in the phase adjacent to the electrode can be studied. With opaque electrode materials, internal or external reflection may be applied. Glass, quartz, or plastic substrates coated with a thin layer of semiconductors (indium-doped tin oxide) or conducting metals (gold, platinum) are often used as OTE. The optically transparent electrode is immersed as working electrode in a standard cuvette. 

Figure 7. Equipment geometries for studying the wave and acousto-electrical interactions in nematics (1) substrate (y cut, x oriented quartz), (2) glass plate, (3) interdigital transducer, (4) shear transducer (y cut quartz), (5) compression transducer (x cut quartz), (6) nematics, (7) mirror coating, (8) optically transparent electrode, (9) generator, (10) waveguide (substrate), (11) phase meter.

Figure 2 Transmission spectra of Sn02 coatings on various substrates (curve a) glass, 3Qsq- (curve b) Vicor, 6Qsq- (curve c) quartz, 20 Q sq- Reprinted by courtesy of Marcel Dekker, Inc. from Kuwana T and Winograd N (1974) Spectroelectrochemistry at optically transparent electrodes. I. Electrodes under semi-infinite diffusion conditions. In Bard AJ (ed) Electro-anaiyticai Chemistry. A Series of Advances, Vol 7, pp 1-78. New York Marcel-Dekker.

Rotating optically semii-transparent electrodes for spectroelectro-chemical or photoelectrochemical studies can be fabricated by vapour deposition techniques on a quartz substrate. In this way, tin oxide, platinum and gold electrodes, amongst others, can be made. Electrical contact is with silver paint. 

Figure 9.9 Assembly of sandwich-type optically transparent thin-layer electrochemical cell, a, Glass or quartz plates b, adhesive Teflon tape spacers c, minigrid working electrode d, metal thin-film working electrode, which may be used in place of (c) e, platinum wire auxiliary electrode f, silver-silver chloride reference electrode g, sample solution h, sample cup. [Adapted with permission from T.P. DeAngelis and W.R. Heineman, J. Chem. Educ. 53 594 (1976), Copyright 1976 American Chemical Society.]...

For spectroelectrochemical and photoelectrochemical studies, optically semi-transparent electrodes have been fabricated by vapour deposition techniques on glass or quartz substrates (Chapter 12). Tin and indium oxides, platinum, and gold have been used. 

The working electrode should be derived from a material optically transparent to neutrons (e.g., quartz, silicon, sapphire). 

The hollow cathode is the most frequently used atomic absorption line source. A cupped cathode made of the element to be quantitated and a tungsten anode are positioned in a glass tube which is filled with an inert gas at reduced pressure. The end of the tube is sealed with an optically transparent quartz window. When an electrical potential is struck between the electrodes, the inert gas at the anode is ionized and moves toward the cathode. The element in the cup is sputtered into the gas and excited by the discharge to higher electronic states. The lamp emits intense lines due to resonance radiation. The emission will also show lines characteristic of the electrode itself as an impurity. When feasible, the electrode may be made of the element to be analyzed, thereby avoiding this possible interference. Lamps are available for over 60 different elements and are readily obtainable,... 

F. n.63 Simple in situ UVA s spectroelectrochemical cell based on a quartz cuvette with an optically transparent working electrode, counter electrode, and reference electrode immersed in solution... 

The Raman cell for the study of electrodes in an aqueous electrolyte is relatively simple and more flexible in design compared with the nonaqueous system. Figure 10 shows the two most commonly used cells. Cell (a) is suitable for the front collection mode with different incident angle and the back-scattering mode in the macro-Raman system. Cell (b) is for the micro-Raman system. An optically transparent quartz or glass window may be used, especially to avoid contamination from the ambient atmosphere. Usually, it is not necessary to... 

Another electrode form is a thin film deposited on an optically transparent nondiamond substrate, such as undoped Si for IR or quartz for UV/Vis spectroelectrochemical measurements. Diamond deposition on Si for IR OTEs is rather straightforward and involves growth conditions similar to those described above. The resulting films are 2-4 gm thick with micrometer-sized grains of diamond randomly oriented over the surface. Deposition of thin films of diamond on quartz is a little more involved [118]. Figure 22 shows an optical image of a diamond/quartz OTE. The film has a blue hue to it due to the boron doping level. It is... 

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