Thin metal film electrode

Owing to the toxicity of mercury and its disposal problem, solid electrodes are now very popular. In particular, electrodes made of carbon such as glassy carbon, graphite, carbon paste, and carbon fibers have gained popularity. Mercury, gold, bismuth, and other metals can be deposited as thin metal films on carbon and serves as thin metal film electrodes (TMFE) with excellent analytical advantages in trace metal analysis. The choice of working electrode is determined by the redox... 

The (nonelectrochemical) SEIRAS effect was first reported by Hartstein and coworkers in 1980 [110], after which Suetaka and coworkers published a number of papers from 1982 exploiting Kretschmann coupling (Fig. la) to effect SPP excitation and the concomitant enhancement of the infrared absorptions of species adsorbed at the thin metal film electrode surface [69, 111-113], effectively SEIRAS. The authors commented that the short-range enhancement afforded by the technique enabled species at the metal-aqueous solution interfaces to be preferentially observed . Similarly, Neff and coworkers [48] reported the study of water at the electrode-electrolyte interface using SPP excitation. As with the SERS effect, SEIRAS is limited, so far, to the coinage metals [5,10]. 

EQCM [172] significantly contributed to the elucidation of mechanisms of electrochemical reactions of fullerene films. The principle of the method is simple and based on frequency measurement of a piezoelectric quartz crystal. The frequency is sensitive to mass and viscosity changes on a thin metal film (electrode) deposited on the quartz crystal. Most commonly any contribution from shear forces is neglected and the observed fi-equency changes are regarded as being... 

After tq is passed, the second step starts by scanning the potential from Ed to a potential when all the deposited metals are re-oxidized (the reverse of reaction 25). The oxidation current recorded as a function of potential is the anodic stripping voltammogram (ASV). A typical ASY of three metals (Cd, Pb, and Cu) deposited on a mercury film electrode is shown in Fig. 18b.12b. The sensitivity of ASY can be improved by increasing the deposition time and by using the pulse technique to record the oxidation current. ASV in Fig. 18b. 12b was obtained by using the square wave voltammetry. In most cases a simple linear or step ramp is sufficient to measure sub-ppm level of metals in aqueous solution. The peak current of a linear scan ASV performed on a thin mercury film electrode is given by... 

Although the sputter deposition technique can provide a cheap and directly controlled deposition method, the performance of PEM fuel cells with sputtered CLs is still inferior to that of conventional ink-based fuel cells. In addition, other issues arise related to the physical properties of sputtered catalyst layers, such as low lateral electrical conductivity of the thin metallic films [96,108]. Furthermore, the smaller particle size of sputter-deposited Ft can hinder water transport because of the high resistance to water transport in a thick, dense, sputtered Ft layer [108]. Currently, the sputter deposition method is not considered an economically viable alternative for large-scale electrode fabrication [82] and further research is underway to improve methods. 

Reactions of Amalgam-Forming Metals on Thin Mercury Film Electrodes... 

For reversible stripping reactions, the applied potential controls the concentration at the mercury-solution interface (according to the Nernst equation). Because of the rapid depletion of all the metal from thin mercury films, the stripping behavior at these electrodes follows a thin-layer behavior. The peak current for the linear scan operation at thin mercury film electrodes is thus given by... 

The first step in sample preparation is the deposition of a thin metal film on an insulating substrate (e.g. a glass microscope slide). This base electrode is deposited by conventional vacuum deposition techniques with the electrode geometry defined by a shadow mask. Next, this electrode is oxidized either by exposing the film to room air or oxygen, or by establishing an oxygen plasma within the vacuum chamber. In the case of Al-electrodes, a remarkably uniform oxide layer is formed, typically 1-2 nm thick. The oxide film may then be dosed with the compound of interest this is achieved in one of three ways. 

The mixer was made by wet-chemical etching of glass substrates, following a photolithographic step, yielding channels for the fluid flow and for the electrodes. The electrodes (100 Q resistors) were made by an electron-beam evaporation process generating thin metallic films in the etched channels [92], Holes were drilled into the cover plate for inlet and outlet connection. Fusion bonding was used to seal the plates. 

Consider the polymer-on-metal interface, which might be prepared by coating a thin metal film with polymer in a polymer-based LED. The case of the counter electrode, formed by vapor-deposition, is discussed subsequently. First, assume that the substrates have clean surfaces hydrocarbon and oxide free, or naturally oxidized but still hydrocarbon free (pointed out as necessary). Typically, in connection with polymer-based LEDs, the metallic substrate could be gold, ITO (indium tin oxide) coated glass, the clean natural oxide of aluminum ( 20 A in thickness), the natural oxide which forms upon freshly etched Si( 110) wafers ( 10 A), or possibly even a polyaniline film. Dirt , which may be either a problem or an advantage, will not be taken up here. Discussions will alternate between coated polymer films and condensed model molecular solid films, as necessary to illustrate points. 

Several transparent electrode materials were tried, including indium-tin oxide, or 5-nm-thick layers of Cr or Nb. Although the thin-metal films have an optical density of 0.2 - 0.3, they produce less debris on the surface during laser writing. The opposite electrode was typically a 20-30-nm-thick film of Cr or Nb deposited by evaporation or ion-beam deposition, respectively. For test purposes, this layer was patterned with a shadow mask in 3.5-mm-diameter circles that could be connected independently to the voltage source. 

Y. Nakato H. Tsubomura, The photoelectrochemical behavior of an n-Ti02 electrode coated with a thin metal film, as revealed by measure-... 

DPASV equipped with the Thin Mercury Film Electrode (TMFE) plated onto a Rotating Glassy Carbon Disc Electrode (RGCDE), is one of the most sensitive and powerful techniques at present available for the determination of ultra-trace metals in real time samples (59, 60). Cadmium, Cu, Pb and Zn are the most frequently determined metals at subnanomolar or even picomolar concentration in sea water, without any preconcentration step (17, 61, 62), but other elements can also be determined (63-66). Detection limits lower than 0.5 ng/1 are normally reached (17, 60). 

The method closely related to voltammetry is voltohmmetry, which is based on the fact that the lateral resistance of a thin metal film depends on the presence or absence of interacting species at its surface. Resistance measurements show a specific selectivity in the electrode potentials, and magnitude of resistance change depends linearly on analyte concentrations in solution from p.p.b. to p.p.m. range.58 This method is alternative for voltammetry, not only for heavy metals determinations, but also for nonelectroactive species that can be deposited or dissolved under defined potential of resistance. 

Both metallic and membrane electrodes have been used to detect end points in potentiometric titrations involving complex formation. Mercury electrodes are useful for EDTA titrations of cations that form complexes that are less stable than HgY- . See Section 21D-1 for the half-reactions involved and Equation 21-5 for the Nernst expression describing the behavior of the electrode. Hanging mercury drop and thin mercury film electrodes appropriate for EDTA titrations are available from a number of manufacturers. As always, whenever mercury is used in experiments like these, we must take every precaution to avoid spilling it, and it must be stored in a well-ventilated hood or a special cabinet to remove the toxic vapors of the liquid metal. Before working with mercury, be sure to read its Materials Safety Data Sheet (MSDS), and follow all appropriate safety procedures. 

Quartz crystal microbalance is operated in typical resonant frequencies ranging from 1 to 10 MHz, with most of them operating in 5-10 MHz. A typical QCM is a disk in the size of 10-16 mm in diameter with a thickness of approximately 0.15 mm. A thin metal film, gold, aluminum, or others, is deposited onto the surface of the quartz serving as electrodes. The metal... 

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