Electrodes silicon

Figure C3.2.4. Plot of the log of photocurrent against number of methyl units in a alkylsilane based monolayer self-assembled on a n silicon electrode. The electrode is immersed in a solution witli an electron donor. Best fits of experimental data collected at different light intensities ( ) 0.3 mW cm ( ) 0.05 mW cm. From [10].

In studies on Pt dotted silicon electrodes, PMC measurements revealed that tiny Pt dots increased the interfacial charge transfer compared with bare silicon surfaces in contact with aqueous electrolytes. However, during an aging effect, the thickness of the oxide layer between the silicon and the platinum dots gradually increased so that the kinetic advantage again decreased with time.11... 

When relation (28) is properly fitted, B,C, and the flatband potential Up can be determined. For a silicon electrode in contact with 0.6 M nh4f... 

Equation (40) relates the lifetime of potential-dependent PMC transients to stationary PMC signals and thus interfacial rate constants [compare (18)]. In order to verify such a correlation and see whether the interfacial recombination rates can be controlled in the accumulation region via the applied electrode potentials, experiments with silicon/polymer junctions were performed.38 The selected polymer, poly(epichlorhydrine-co-ethylenoxide-co-allyl-glycylether, or technically (Hydrine-T), to which lithium perchlorate or potassium iodide were added as salt, should not chemically interact with silicon, but can provide a solid electrolyte contact able to polarize the silicon/electrode interface. 

A photoelectrochemical cell is an electrochemical cell that uses light to carry out a chemical reaction. This type of cell is being considered for the production of hydrogen from water. The silicon electrodes in a photoelectrochemical cell react with water ... 

Laser D, Bard AJ (1976) Semiconductor Electrodes. IV. Electrochemical behavior of n- and p-type silicon electrodes in acetonitrile solutions. J Phys Chem 80 459 66... 

Nakato, Y., Yano, H., Nishiura, S., Ueda, T., and Tsubomura, H., Hydrogen photoevolution at p-type silicon electrodes coated with discontinuous metal layers, ]. Electroanal. Chem. Interfacial Electrochem., 228,97,1987. 

Figure 11.12. Si electrode and NW hybrid device, (a) Schematic of a single LED fabricated by the method outlined in Fig. 11.11. (b) I-V behavior for a crossed p-n junction formed between a fabricated p+-Si electrode and an n-CdS NW. (c) EL spectrum from the forward biased junction, (d) SEM image of a CdS NW assembled over seven p+-silicon electrodes on a SOI wafer (e) EL image recorded from an array consisting of a CdS NW crossing seven p+-Si electrodes. The image was acquired with +5V applied to each silicon electrode while the CdS NW was grounded. [Reprinted with permission from Ref. 59. Copyright 2005 Wiley-VCH Verlag.]...

Figure 20. Two different reaction paths for a silicon electrode in HF solution...

A particular important property of silicon electrodes (semiconductors in general) is the sensitivity of the rate of electrochemical reactions to the radius of curvature of the surface. Since an electric field is present in the space charge layer near the surface of a semiconductor, the vector of the field varies with the radius of surface curvature. The surface concentration of charge carriers and the rate of carrier supply, which are determined by the field vector, are thus affected by surface curvature. The situation is different on a metal surface. There exists no such a field inside the metal near the surface and all sites on a metal surface, whether it is curved not, is identical in this aspect. 

The diffusion length of electronic grade silicon wafers is about 0.5 mm and therefore in the order of the wafer thickness. Illumination of the backside of a silicon electrode may, as a result, influence the electrochemistry at the front side, as discussed in Section 10.3. 

The product of the dissolution process of silicon electrodes in HF is fluosilicic acid, H2SiF6. In contrast to HF, H2SiF6 is mostly (75%) dissociated into Sily and 2H+ in aqueous solution at RT. The diffusion coefficient of the SiF at RT decreases from 1.2X10 5 cmV1 for 0.83 mol 1 1 to 0.45 cm2s 1 for 2.5 moll-1, with values of activation energy around 0.2 eV [We7]. 

This section deals with the electrodes in the electrochemical set-up, with special emphasis on the silicon electrode and its semiconducting character. An electrochemical cell with its complete electrical connections, as shown in Fig. 1.3 a and b, is similar to the well-known four-point probe used for applying a defined bias to a solid-state device. The two tines that supply the current are connected to... 

Fig. 1.8 I mmersion double cell separated by necessary. Illumination is needed for moder-the fixture of the silicon electrode. Note that ately doped samples, to generate a current in...

Fig. 1.9 For in situ IR vibrational characterization of an electrochemical interface the silicon electrode in the double O-ring cell has to be shaped as an ATR prism.

A special O-ring cell design is needed for in situ infrared (IR) vibrational characterization of an electrochemical interface. The absorption of one monolayer (i.e. <1015 cm 2 vibrators) can be measured if the silicon electrode is shaped as an attenuated total reflection (ATR) prism, which allows for working in a multiple-in-ternal-reflection geometry. A set-up as shown in Fig. 1.9 enhances the vibrational signal proportional to the number of reflections and restricts the equivalent path in the electrolyte to a value close to the product of the number of reflections by the penetration depth of the IR radiation in the electrolyte, which is typically a tenth of the wavelength. The best compromise in terms of sensitivity often leads to about ten reflections [Oz2]. 

Fig. 1.10 A closed double O-ring cell for electrochemical experiments with silicon electrodes, based on a standard optical microbench system. Top and side views of a PVC half-cell...

Fig. 3.1 The I—V characteristic of (a) a p-type and (b) an n-type silicon electrode under the assumption that the current is dominated by the properties of the semiconductor and is not limited by interface reactions or by diffusion in the electrolyte, (c) The characteristic I—V curve in an alkaline electrolyte under the...

In this section the I-V characteristic of a silicon electrode in acidic, and specially hydrofluoric electrolytes is discussed with emphasis on the different charge states of the semiconductor. The accompanying chemical reactions are briefly mentioned, but are discussed in detail in Chapter 4. 

Four different regimes of the I-V curve for moderately doped silicon electrodes in an HF electrolyte are shown in Fig. 3.2. These regimes will now be discussed in terms of the charge state of the electrode, the dependence on illumination conditions, the charge transfer, the mass transport, and accompanying chemical reactions. Transient effects are indicated in Fig. 3.2 by a symbol with an arrow. 

Let us now consider the charge state of the electrode. The emitter is positively biased. A p-type silicon electrode is therefore under forward conditions. If the logarithm of the current for a forward biased Schottky diode is plotted against the applied potential (Tafel plot) a linear dependency with 59 meV per current decade is observed for moderately doped Si. The same dependency of 1EB on VEB is observed at a silicon electrode in HF for current densities between OCP and the first current peak at JPS, as shown in Fig. 3.3 [Gal, Otl]. Note that the slope in Fig. 3.3 becomes less steep for highly doped substrates, which is also observed for highly doped Schottky diodes. This, and the fact that no electrons are detected at the collector, indicates that the emitter-base interface is under depletion. This interpretation is sup-... 

If VEB is increased, IEB increases and the current density at the electrode eventually becomes equal to JPS. It has been speculated that this first anodic current peak is associated with flat-band condition of the emitter-base junction. However, data of flat-band potential of a silicon electrode determined from Mott-Schottky plots show significant scatter, as shown in Fig. 10.3. However, from C-V measurement it can be concluded that all PS formation occurs under depletion conditions independent of type and density of doping of the Si electrode [Otl]. 

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