Indium-doped tin oxide

The first reports on direct electrochemistry of a redox active protein were published in 1977 by Hill [49] and Kuwana [50], They independently reported that cytochrome c (cyt c) exhibited virtually reversible electrochemistry on gold and tin doped indium oxide (ITO) electrodes as revealed by cyclic voltammetry, respectively. Unlike using specific promoters to realize direct electrochemistry of protein in the earlier studies, recently a novel approach that only employed specific modifications of the electrode surface without promoters was developed. From then on, achieving reversible, direct electron transfer between redox proteins and electrodes without using any mediators and promoters had made great accomplishments. 

M. Buchanan, J.B. Webb, and D.F. Williams, Preparation of conducting and transparent thin films of tin-doped indium oxide by magnetron sputtering, Appl. Phys. Lett., 37 213-215, 1980. 

R.B.H. Tahar, T. Ban, Y. Ohya, and Y. Takahashi, Tin doped indium oxide thin films electrical properties, J. Appl. Phys., 83 2631-2645, 1998. 

Nanoparticles of Ti02 are deposited on to a glass support covered with a transparent conducting layer of tin-doped indium oxide (ITO). Each nanoparticle is coated with a monolayer of sensitising dye based on Ru(II). Photoexcitation of the dye results in the injection of an electron into the CB of the semiconductor. 

Indium-tin oxide (ITO) Tin-doped indium oxide, used as a thin solid film on glass when constructing optically transparent electrodes. 

Kumar A, Zhou C (2010) The race to replace tin-doped indium oxide which material will win ACS Nano 4 11-14... 

Fig. 1.20. Schematic energy band diagram of a two-layer organic light emitting diode (OLED), in which tin-doped indium oxide (ITO) is used to inject holes into the highest occupied molecular orbital (HOMO) and a low work function metal to inject electrons into the lowest unoccupied molecular orbital (LUMO)...

Fig. 2.19. (a) Scheme of a transparent field effect transistor based on ZnO [191]. The gate electrode consists of tin-doped indium oxide (ITO) and the gate dielectric is a multilayer of AECE/TiCE (ATO). (b) Output characteristics (drain-source current as a function of the drain-source voltage) for different gate voltages. The saturation current is about 530 rA at a gate bias of 40 V. From this output characteristics a threshold voltage of 19 V and a field-effect mobility of 27 cm2 V-1 s-1 were calculated [192]... 

Shigesato Y., Takaki S. and Haranoh T., Electrical and structural properties of low resistivity tin-doped indium oxide films, J. Appl. Phys. 71 (1992) pp. 3356-3364. 

Ray S., Banerjee R., Basu N., Batabyal A. K. and Barua A. K., Properties of tin doped indium oxide thin films prepared by magnetron sputtering, J. Appl. Phys. 54 (1983) pp. 3497-3501. 

The first reports on a reversible DET between redox proteins and electrodes were published in 1977 showing that cytochrome c is reversibly oxidized and reduced at tin-doped indium oxide [30] and gold in the presence of 4,4 -bipyridyl [31]. Only shortly after these publications appeared, papers were published describing the DET between electrode and enzyme for laccase and peroxidase [32,33]. It was observed that the overpotential for oxygen reduction at a carbon electrode was reduced by several hundred millivolts compared to the uncatalyzed reduction when laccase was adsorbed. This reaction could be inhibited by azide. The term bioelectrocatalysis was introduced for such an acceleration of the electrode process by... 

Use of modified gold electrodes is not the only approach to achieve cytochrome c electrochemistry. Indeed, a number of studies have been reported on a variety of electrode surfaces. In 1977, Yeh and Kuwana illustrated (23) well-behaved voltammetric response of cytochrome c at a tin-doped indium oxide electrode the electrode reaction was found to be diffusion-controlled up to a scan rate of 500 mV sec Metal oxide electrodes were further studied (24, 25) independently in Hawkridge and Hill s groups. The electrochemical response of cytochrome c at tin-doped indium oxide and fluoride-doped tin oxide was very sensitive to the pretreatment procedures of the electrode surface. At thin-film ruthenium dioxide electrodes, variation of the faradaic current with pH correlating with the acid-base protonation of the electrode surface was observed. 

Cadmium stannate, used as electrodes in photogalvanic cells, is another example of a transparent conductor oxide (TCO) having desirable properties, such as good durability and chemical resistance. It can be produced by the spray pyrolysis CVD method with organic solutions of CdCH and SnCH or [Cd(hfa)2 (TMEDA)] and [Sn(acac)2]. ° It also shows the unexpected effect of improving transparency with increasing Him conductivity higher than tin-doped indium oxide. 

First realization of reversible ET of cytochrome c employing tin-doped indium oxide electrodes... 

There are several different metal oxides with optical band gaps of 2.5 to 4 eV, which are useful for transparent conducting oxide (TCO) coatings. The most common of these are tin-doped indium oxide (ITO), fluorine or antimony-doped tin oxide and doped zinc oxides. The preparation and physical properties of these materials prepared by CVD will be discussed. 

The results in Table 3-9 demonstrate, furthermore, that it is possible to grow fluorine and tin-doped indium oxide films with CVD techniques, which possess a high transmission of light (> 90%) and very low resistivities (< 1 mQcm). They are comparable to ITO films prepared by sputtering or other physical deposition techniques, which are generally used in industry these days. 

Transparent conductive coatings combine high optical transmission with good electrical conductivity. The existence of both properties in the same material is, from the physics point of view, not trivial and is only possible with certain semi-conductors like indium oxide, tin oxide, cadmium oxide, and with thin gold and silver films, e.g. [157]. Particularly antimony or fluorine doped tin oxide (ATO, FTO), tin doped indium oxide (ITO), and aluminium, indium, or boron doped zinc oxide (AZO, IZO, BZO) are of technical importance [157a]. 

Bowden, E. F., Hawkridge, F. M., Chlebowski, J. F., Bancroft, E. E., Thorpe, C., Blount, H. N., Cyclic Voltammetry and Derivative Cyclic Voltabsorptometry of Purified Horse Heart Cytochrome C at Tin-Doped Indium Oxide Optically Transparent Electrodes , J. Am. Chem. Soc. 104 (1982) 7641-7644. 

Indium-tin oxide (ITO, or tin-doped indium oxide) is a solid miture of indium(III) oxide (Iu203) and tin(IV) oxide (Sn02). It is transparent and colorless in thin layers. In bulk form, it is yellowish to grey. It is a transparent conducting material that is usually used in thin coating form. ITO is commonly used in applications such as touch panels, electrochromic, electroluminescent and LCD displays, plasma displays, field emission displays, heat reflective coatings, energy efficient windows, gas sensors and photovoltaics. 

Yeh and Kuwana " were the first to report on the electrochemistry of cytochrome c at doped metal oxide semiconductor electrodes. A nearly reversible electrode reaction was indicated by the cyclic voltammetry and differential pulse voltammetry of cytochrome c at tin-doped indium oxide electrodes. Except for the calculated diffusion coefficient, all of the characteristics of the electrochemistry of cytochrome c at this electrode indicated that the electrode reaction was well-behaved. A value of 0.5 x 10" cmVs was determined for the diffusion coefficient which, like previously determined values at mercury, is lower than the value obtained by nonelectrochemical methods (i.e., 1.1 X 10 cm /s " " ). The electrochemical response of cytochrome c at tin oxide semiconductor electrodes was reported to be quasi-reversible, although no details were given. " ... 

The heterogeneous electron transfer kinetics of cytochrome c at tin-doped indium oxide and fluoride-doped tin oxide optically transparent electrodes... 

Figure 18. (A) Cyclic voltammetry of purified cytochrome c at doped indium oxide optically transparent electrodes. Solution contained 73 /uiM cytochrome c, 0.21 M Tris, 0.24 M cacodylic acid, pH 7.0, 0.20 M ionic strength. Electrode area = 0.71 cm. Potential scan rates in mV/s are (a) 100 (b) 50 (c) 20 (d) 10 (e) 5.0 (f) 2.0. (B) Derivative cyclic voltabsorptometry of purified cytochrome c at a tin-doped indium oxide optically transparent electrode. Same conditions as described above. Circles are calculated derivative cyclic voltabsorptometric responses for 73 /iM cytochrome c, formal potential = 0.260 V, n = 1.0, diffusion coefficient of oxidized and reduced cytochrome c = 1.2 x 10 cm /s, difference molar absorptivity at 416 nm = 57,000 cm" formal heterogeneous electron transfer rate constant = 1.0 x 10 cm/s, and electrochemical transfer coefficient = 0.5. Adapted from Reference (126) with permission.

Roller and Hawkridge used a tin-doped indium-oxide electrode and made measurements over the temperature range 5 to 75 °C at pH 7 using phosphate (I = 0.20 M) or Tris/cacodylate (I = 0.20 M) buffer media [86]. In further work they extended the pH range to 5.3 and 8.0 [87]. 

For electropolymerization an anode made of glassy carbon (CWE), gold (Au), platinum disk or plate (Pt), or tin-doped indium-oxide-coated glass (ITO) are commonly used as working electrodes. A platinum wire or mesh is used as the counterelectrode. The potential is measured vs silver/silver chloride (Ag/AgCl) or saturated calomel (SCE) electrodes. Alternatively, a silver wire can be used as a pseudoreference with calibration to the half-wave potential of the ferrocene/ferrocenium (Fc/Fc ) redox couple. 

A.2.2 Solid electrodes (gold, carbon, metal oxide electrodes). Cytochrome c is also adsorbed irreversibly at solid electrodes, which mostly results in irreversible kinetices of the electrode reaction. A nearly reversible reaction of strongly adsorbed cytochrome c is, however, observed at electrodes of metal oxides (doped metal oxide semiconductor electrodes, tin-doped indium oxide electrode) [202, 203]. 

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