Photosensitization anodic

By analogy with photosensitive anodic films appearing over the surface of silicon during its treatment in fluorine-containing electrolytes, it can be suggested that the built-in film represents a mixed phase of electrochemical reaction products or results from the anodized surface amorphization [27,28]. In its turn, this indicates that under potentiostatic conditions the chemical processes at the SiC/HF junction are predominant. The results obtained emphasize that not every porous-like phase formed as a result of SiC anodization can be considered as PSC. 

A variation of the typical anodized aluminum is Photosensitive Anodized Aluminum. This method uses the porous nature of unsealed anodized aluminum to create a sub-surface image. For this special case, the anodized aluminum is impregnated with a silver compound that creates an activated latent image when exposed to a source of light. After the developing and fixing processes take place... 

Fig. 2 Sub-surface image formed inside of the metal using the photosensitive anodized aluminum technique...

An interesting idea has been to prepare the photosensitive electrode on site having the liquid play the dual role of a medium for anodic film growth on a metal electrode and a potential-determining redox electrolyte in the electrochemical solar cell. Such integration of the preparation process with PEC realization was demonstrated initially by Miller and Heller [86], who showed that photosensitive sulfide layers could be grown on bismuth and cadmium electrodes in solutions of sodium polysulfide and then used in situ as photoanodes driving the... 

PMTs contain a photosensitive cathode and a collection anode that are separated by electrical electrodes called dynodes, which provide electron multiplication or gain. The cathode is biased negatively by 400-2500 V with respect to the anode. An incident photon ejected by the photocathode strikes the first dynode... 

For UV and visible radiation, the simplest detector is a photomultiplier tube. The cathode of the tube is coated with a photosensitive material (such as Cs3Sb, K CsSb, or Na2KSb, etc.) which ejects a photoelectron when struck by a photon. This photoelectron is then accelerated towards a series of anodes of successively greater positive potential (called dynodes). At each dynode, the electron impact causes secondary electron emission, which amplifies the original photoelectron by a factor of 106 or 107. The result is a pulse of electricity of duration around 5 ns, giving a current of around 1 mA. This small current is fed into the external electronics and further amplified by an operational amplifier, which produces an output voltage pulse whose height is proportional to the photomultiplier current. 

Besides silicon, other materials have also been used in micro fuel cells. Cha et al. [79] made micro-FF channels on SU8 sheets—a photosensitive polymer that is flexible, easy to fabricate, thin, and cheaper than silicon wafers. On top of fhe flow channels, for both the anode and cathode, a paste of carbon black and PTFE is deposited in order to form the actual diffusion layers of the fuel cell. Mifrovski, Elliott, and Nuzzo [80] used a gas-permeable elastomer, such as poly(dimethylsiloxane) (PDMS), as a diffusion layer (with platinum electrodes embedded in it) for liquid-electrolyte-based micro-PEM fuel cells. 

If a solution, being in contact with an electrode, contains photosensitive atoms or molecules, irradiation of such a system may lead to photoelectro-chemical reactions or, to be more exact, electrochemical reactions with excited particles involved. In such reactions the electrons pass either from an excited particle to the electrode (the anodic process) or from the electrode to an excited particle (the cathodic process). In this case, an elementary act of charge transfer has much in common with ordinary (dark) electrochemical redox reactions, which opens a possibility of interpreting certain aspects of photochemical processes under consideration with the use of concepts developed for general quantum mechanical description of electrode processes. 

In the other scheme the photosensitive interface operates in the photo-galvanic pair regime (Goryachev et al, 1970 Goryachev and Paritsky, 1973). The method is based on the occurrence of a potential difference between illuminated and nonilluminated areas on the surface of a semiconductor electrode in a solution (cf. Section 1 lb). As a result of nonuniform illumination, local anodes and cathodes arise on the surface and this, in turn, leads to nonuniform deposition of metal onto the surface. 

A photoelectric cell consists of a photosensitive surface (the metal or alloy) deposited inside an evacuated glass bulb fitted with a second metal electrode kept at a positive potential (Figure 2.3). Electrons emitted by the photosensitive surface called the photocathode will then be captured by the positive anode and a current will flow in an external circuit which connects the two electrodes. 

A few other applications of dithiolenes make use of their redox properties. Kumar et a/.219 proposed the use of dithiolenes as photosensitizers. Umezawa et al.22<> coated a Pt cathode with (Et4N)Ni(mnt)2 and saw a modest degree (1.4 x 10 4 %) of light conversion upon irradiation. On the opposite side, Bradley et al.721 used dithiolenes to stabilize n-type Si anodes against photoanodic decomposition. 

X-rays are generated in a so-called X-ray tube. In this vacuum tube a cathode is heated and it will emit electrons. Due to the high voltage difference between the anode and cathode these electrons collide with the anode, at which point the kinetic energy of the electrons is converted into heat and X-rays. The latter are aimed at the object and pass through it, either completely or partially. We place a photosensitive plate under the object and this turns black when it is exposed to X-rays. 

Anodic dehydrogenations, e.g., oxidations of alcohols to ketones, have been treated in Sect. 8.1 and formation of olefins by anodic elimination of C02 and H+ from carboxylic acids was covered in Sect. 9.1. Therefore this section is only concerned with anodic bisdecarboxylations of v/odicarboxylic acids to olefins. This method gives usually good results when its chemical equivalent, the lead tetraacetate decarboxylation, fails. Combination of bisdecarboxylation with the Diels-Alder reaction or [2.2] -photosensitized cycloadditions provides useful synthetic sequences, since in this way the equivalent of acetylene can be introduced in cycloadditions. 

The thin semiconductor particulate film prepared by immobilizing semiconductor nanoclusters on a conducting glass surface acts as a photosensitive electrode in an electrochemical cell. An externally applied anodic bias not only improves the efficiency of charge separation by driving the photogenerated electrons via the external circuit to the counter electrode compartment but also provides a means to carry out selective oxidation and reduction in two separate compartments. This technique has been shown to be veiy effective for the degradation of 4-chlorophenol [116,117], formic acid [149], and surfactants [150] and textile azo dyes [264,265]. 

Fig. 28 Photoelectrochemical cofactor regeneration with simultaneous alcohol oxidation using ADHs from horse liver (HLADH) or Thermoanaerobacter brockii. Ru2+ serves as photosensitizer while MV2+ (methyl viologen) functions as primary electron acceptor which can he reoxidized at the anode...

Vacuum phototubes have two electrodes that have a maintained potential difference. The cathode (negative electrode) consists of a plate coated with a photosensitive metal. Radiation incident upon the photosensitive cathode causes an emission of electrons (the photoelectric effect), which are collected at the anode (the positive electrode). The resulting photocurrent can be readily amplified and measured (Fig. 1-5). 

An Effect of Heat Treatment on the Activity of Titanium Dioxide Film Electrodes for Photosensitized Oxidation of Water Heat treatment in argon atmosphere found to improve performance of both anodic and pyrolytically prepared TiCte films. 241... 

The products of degradation during polarization of HTSC electrodes have not been studied in much detail [44,287,293,476,478], Upon cathodic polarization of cuprates, the reduced forms of copper oxides [44,476], and sometimes metallic copper [293], are formed at considerable rates these processes are photosensitive [453], During anodic polarization, the formation of alkaline-earth compounds on the HTSC surface is accelerated [287,476]. 

Some interesting stereoselective anodic reactions of unsaturated hydrocarbons have been known, although the stereoselectivity is not always high [367-369]. The reaction seems to proceed via radical cations of the diene. Ando and coworkers [368] investigated in detail the stereochemical consequence of anodic (probably EGA) catalyzed oxygenation of stereoisomeric syn and anti) di-/-butyl(bicyclo[3,3,l]non-9-ylidenes) compared with the stereochemistry of the photosensitized oxygenation. 

Photodiode (1) A vacuum tube consisting of a wire anode and a photosensitive surface that produces an electron for each photon absorbed on the surface. (2) A reverse-biased silicon semiconductor that produces electrons and holes when irradiated by electromagnetic radiation. The resulting current provides a measure of the number of photons per. second striking the device. 

The operation of photocells and photomultipliers is based on the external photoelectric effect. Photons impinging on the surface of a photosensitive cathode (photocathode) knock out electrons which are then accelerated in the electrical field between the cathode and the anode and give rise to electric current in the outer circuit. The spectral sensitivity of a photocell depends on the material of the photocathode. The photocathode usually consists of three layers a conductive layer (made, e.g., of silver), a semiconductive layer (bimetallic or oxide layer) and a thin absorptive surface layer (a metal from the alkali metal group, usually Cs). A photocathode of the composition, Ag, Cs-Sb alloy, Cs (blue photocell), is photosensitive in the wavelength range above 650 nm for longer wavelengths the red photocell with Ag, Cs-O-Cs, Cs is used. The response time of the photocell (the time constant) is of the order of 10" s. 

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