Thin-film silicon anodes

Ohara S, Suzuki J, Sekine K, Takamura T (2004) A thin film silicon anode for Li-ion batteries having a very large specific capacity and long cycle life. J Power Sourc 136 303-306... 

The reaction channels were made in silicon by several photolithographic steps, followed by potassium hydroxide etching [13,14]. Silicon oxide was thermally grovm over the silicon. Nickel thin films were vapor-deposited. Pyrex was anodically bonded to such a modified micro structured silicon wafer. 

Methods have been developed for fabrication of the highly-ordered titania nanotuhe arrays from titanium thin films atop a substrate compatible with photolithographic processing, notably silicon or FTO coated glass [104]. The resulting transparent nanotuhe array structure, illustrated in Fig. 5.16, is promising for applications such as anti-reflection coatings and dye sensitized solar cells (DSSCs). Fig. 5.17 shows the typical anodization behavior of a 400 nm Ti thin film anodized at 10 V in an HE based electrolyte. Eor a fixed HE concentration, the dimensions of the tube vary with respect to... 

Usually the nanotube arrays have been made from a titanium thick film or foil, in which case the resulting nanotubes rest upon an underlying Ti substrate as separated by a barrier layer. The nanotube arrays have also been fabricated from a titanium thin film sputtered onto a variety of substrates, such as silicon and fluorine doped tin oxide (FTO) coated conductive glass. This extends the possibility for preparing technical catalysts by deposing a thin Ti layer over a substrate (a foam, for example) and then inducing the formation of the nanostructured titania film by anodic oxidation. ... 

In nonalkaline and nonfluoride aqueous solutions, silicon substrates behave as essentially inert electrodes due to the presence of a thin oxide film. Even in alkaline solutions, silicon is passivated by an oxide film at anodic potentials beyond the passivation peak. Very small current can pass through the passivated silicon surface of n- or p-type materials in the dark or under illumination. Depending on the pH of the electrolyte, oxidized surface sites Si—OH are more or less ionized into anionic species Si—0 owing to the acido-basic properties of such radicals so that the passivation current can vary in a wide range from a few... 

Baranchugov V, Markevich E, Poliak E, Salitra G, Aurbach D. Amorphous silicon thin films as a high capacity anodes for Li-ion batteries in ionic liquid electrolytes. Electrochem Commun 2007 9 796-800. 

The dual-channel reactor is a silicon chip device and was manufactured by photolithography and potassium hydroxide etching [274]. Silicon oxide was thermally grown on silicon and thin films of nickel were evaporated for passivation because direct fluorination was carried out in this device. Pyrex was bonded anodically to the modified microstructured silicon wafer (see Figure 4.34, top). 

This will be called the thick anode film throughout this paper to distinguish it from the thin film which is present during electropolishing silicon. The thick film can grow to a thickness of as much as several tenths of a millimeter, whereas the thin film is probably less than 100 A in thickness. 

An example of local anodic oxidatition (LAO) on 10 nm thick carbon stripe on silicon oxide in air is shown in Fig. 1 [2]. The depth and width of the oxidized gaps depend on the probe tip radii. The LAO method for carbon thin films is attractive because carbon oxide is a result of oxidation. 

Anodic behavior of sihcon can best be characterized by i-V curves. Neglecting the details associated with a silicon substrate such as doping, the current-potential relationship of silicon in aqueous solutions can be considered to be principally determined by the pH and HE concentration as illustrated in Pig. 5.1. In nonalkaline and nonfluoride aqueous solutions, silicon as an electrode is essentially inert, showing a very small current at anodic potential due to the presence of a thin oxide film. In alkaline solutions, silicon is also passivated by an oxide film at anodic potentials but is active below the passivation potential, Vp. In fluoride solutions, the silicon electrode is active in the whole anodic region as shown by the large anodic current. 

Passive films formed on a silicon surface in aqueous solutions are in general oxide films. There is rather limited systematic information on the structure and properties of thin silicon anodic oxide films, particularly those formed in solutions of high silicon solubilities. On the other hand, the thicker oxide films formed at large potentials have been better characterized (see Chapter 3) and the information associated can be used for understanding the thin oxide films formed at relatively low potentials. 

Electroless deposition of the catalytic Pt or Pt-Ru layer was proposed for the preparation of electrodes in microdirect methanol fuel cells.53 A porous silicone substrate is prepared by the anodic etching in HF-ethanol-water (1 1 1) solution. After the etching, at the surface of porous silicon substrate, a thin film of titanium is sputtered and then a film of Pt or Pt-Ru alloy with thickness of about 150-200 nm was electroless deposited. The electrodes prepared in this way helped in minimization of the fuel cell size and increased the reactive area of the catalyst over the silicon electrode surface. 

A. Hanneborg, M. Nese, H. Jakobsen, R. Holm, Silicon-to-thin film anodic bonding, I. Micromech. Microeng. 1992, 2/3, 117-121. 

The samples with porous layers were fabricated by electrochemical anodic etching of p-type, 12 Ohmcm and n-type 0.01 Ohmcm monocrystalline silicon wafers in 48 % water solution of HF at the current density of 50 mA/cm2. The anodized area of 1 cm in diameter was defined by the window in a Si3N4 thin film mask deposited onto the wafers. The anodization time was chosen in the range of 15-90 min in order to get porous layers of a thickness from 30 to 180 pm. The integral porosity was estimated by gravimetry to be of about 60 %. 

Anodic porous alumina is conventionally grown on aluminum foils, as indicated in Fig. 2. Similar self-assembled growth is achieved on Si by depositing an A1 thin film on the front side of a silicon wafer and forming an ohmic contact on the back side that is used as anode. The electrochemical solutions currently used are oxalic or sulfuric acid aqueous solutions. Details for the fabrication of thin alumina templates on Si with adjustable pore size and density are given elsewhere [8]. Electrochemical oxidation of A1 starts from the A1 surface and continues down to the Al/Si interface, following an anodization current density/time curve as shown in Fig. 3. 

On the other hand, when using Ti thin film onto silicon substrates (Fig. 5.8), self-organized Ti02 nanotubes layers with thickness of about 600 nm are obtained after anodization under the same conditions. Moreover, the nanotube diameter and wall thickness are in the range 50-200 nm and about 20 nm, respectively. Hence, a layer of titania nanotubes is successfully fabricated on Ti foils and Ti thin films. Moreover, the titania nanotubes were heated at 450°C in air for 3 h and the nanotube morphology remained unmodified, as we will discuss later. 

The main approaches used to date for investigating silicon-based anodes were summarized that is, the composite approach and thin-film approach. The composite approach relies on the use of silicon in the form of tiny silicon cores, uniformly... 

Abel, P. R. Lin, Y.-M. CeUo, H. Heller, A. Mullins, C. B. Improving the stability of nanostructured silicon thin film lithium-ion battery anodes through their controlled oxidation, ACS Nano 2012, 6, 2506-2516. 

Doped diamond is the alternative carbon material to glassy carbon for ozone generation [20,21], but the technology is much less developed. Boron-doped diamond is prepared by chemical vapor deposition and has been used as an anode when (i) deposited as a thin film on substrates such as silicon, titanium, or niobium or (ii) fabricated as a bulk plate - for example. Element Six supplies Diafilm EP as a free-standing polycrystalline plate capable of supporting current densities of >1 Acm [25]. Typically, the boron-doping concentration is 10 °-10 atoms cm when its resistivity is of the order of 0.05 cm. These boron-doped... 

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