Silicon dioxide metal ions

In the structures cited in Table 12.3, except for pure silicon dioxide, metal ions are required for overall electrical neutrality. These metal ions are positioned in tetrahedral, octahedral, etc. positions in the silicate-like lattice. Sometimes they replace the silicon atom. Kaolinite asbestos has aluminum substituted for silicon in the Gibbosite sheet. Further, sites for additional anions, such as the hydroxyl anion, are available. In ring, chain, and sheet structures neighboring rings. 

Oxides Metal ion(s) + oxygen ion Haematite (composed of iron oxide), a red pigment and an iron ore Corundum (composed of aluminum oxide), an abrasive silica (composed of silicon dioxide), common sand... 

Studies of the base-hydrolysis mechanism for hydrolysis of technetium complexes have further been expanded to an octahedral tris(acetylacetonato)techne-tium(III) [30], Although a large number of studies dealing with base hydrolysis of octahedral metal(III) complexes have been published [31], the mechanism of the tris(acetylacetonato)metal complex is still unclear. The second-order base hydrolysis of the cationic complex tris(acetylacetonato)silicon(IV) takes place by nucleophilic attack of hydroxide ion at carbonyl groups, followed by acetylacetone liberation, and finally silicon dioxide production [32], The kinetic runs were followed spectrophotometrically by the disappearance of the absorbance at 505 nm for Tc(acac)3. The rate law has the following equation ... 

The type of attack that occurs in liquid media is highly dependent on the chemical nature of the liquid—that is, molten metal, molten ceramic, or aqueous solution. We will consider two industrially important cases attack by molten metals and attack by aqueous media. The attack of most metal oxide ceramics by molten metals involves a simple exchange of one metal ion for another. For example, silicon dioxide in contact with molten aluminum is susceptible to the following corrosion reaction ... 

Silicon dioxide films have been an essential factor in the manufacture of integrated circuits from the earliest days of the industry. They have been used as a final passivation film to protect against scratches and to getter mobile ion impurities (when doped with phosphorus). Another application has been as an interlayer dielectric between the gate polysilicon and the aluminum metal-ization. Initially, most such films were deposited in atmospheric pressure systems. In recent years, low pressure processes have assumed greater importance. We will begin by examining the atmospheric process. 

Among the transition metals, Pd, Pt, Ir, and Rh in various forms have been reported active in methanol synthesis (32-34), as noted in Section II. Palladium, platinum, and iridium metals were supported on silica, and it has recently been suggested that palladium is present in its valence state Pd(II) which is the active form of the catalyst (70). Under the synthesis conditions the Pd(II) ions could not survive the highly reducing atmosphere of the CO/H2 synthesis gas, and so this valence state would have to be induced by the presence of silicon dioxide. Should this be a general case, silica would not act merely as an inert support, and the silica-supported transition metals would have to be considered binary catalysts whose active state is formed by a support-metal interaction. ... 

James, R. 0. and Healy, T. W. Adsorption of hydrolyzable metal ions at the oxide-water interface. I. Cobalt (II) adsorption on silicon dioxide and titanium dioxide as model systems II. Charge reversal of silicon dioxide and titanium dioxide colloids by adsorbed cobalt (II), lanthanum (III) and thorium (IV) as model systems III. 

Metal-RIE process was/is used in the fabrication of Al inter-coimects on chips." This process is depicted in four steps in Fig. 2. The first step in the metal-RIE process is sputter deposition of a blanket thin film of Al (or Al alloys, such as Al-Cu, Al-Si) over a planerized dielectric (e.g., silicon dioxide). In the next step, the unwanted metal is etched away by reactive ion etching (RIE) through a photoresist mask. The features produced this way are separated, electrically isolated, metal Al conductor lines. In the RIE process chemicaly active ions such as F or Cl bombard the Al surface and form volatile aluminum fluorides or chlorides, which are then pumped away in the vacuum system. After etcliing, a dielectric is deposited in such a fashion that it fills the gaps between the lines as well as above them. In the last step, the dielectric is planarized using the chemical mechanical polishing (CMP) technique. ... 

This comprises a crystalline antimicrobial composition, which consists of a crystalline silicon dioxide containing silver ions and one or two optional metal ions, such as zinc or copper ions, and a polymer. 

The anodic passivation of semiconductors in aqueous solution occurs in much the same way as that of metals and produces a passive oxide film on the semiconductor electrodes. Figure 22.25 shows the anodic dissolution current and the thickness of the passive film as a function of electrode potential for p-type and n-type silicon electrodes in basic sodium hydroxide solution [32,33], As mentioned earlier, silicon dissolves in the active state as divalent silicon ions and in the passive state a film of quadravalent insoluble silicon dioxide is formed on the silicon electrode. The passive film is in the order of 0.2-1.0 nm thick with an electric field of 106 107 V cm 1 in the film within the potential range where water is stable. 

The fabrication of IC devices requires that the n- and p-type regions be formed selectively in the surface of the wafer. Silicon dioxide, silicon nitride, polysilicon, and especially resists are typically used to mask (or cover) specific areas of the wafer surface to prevent them from being penetrated by impurities during ion implantation or diffusion. The wafer areas to be implanted or deposited with conducting metals are defined with the aid of lithography. 

The formal systematic replacement of Si02 units in quartz or other polymorphs of silicon dioxide by AIO(OH) or M A102 (M = monovalent metal) is well known to lead either to sheet silicates or to tectosilicates, the zeolites being the most remarkable representatives.All these solid-state compounds have as a common feature interstitial holes, which are occupied by easily extractable cations, or have three-dimensional frameworks which can be modified and used for many applications (ion exchange, catalysts, specific coordination sites,... 

Several techniques can be used for masking the ions so as to define the area to be implanted. Usually for microelectronics a contact mask is required. Typical masks are silicon dioxide (Si02), silicon nitride (Si3N4), photoresist, or metal films. The basic requirements for a mask include ... 

Semiconductors Materials with electrical conductivity intermediate between that of metals and insulators Semipermeable membrane A membrane that allows water molecules but not ions or larger molecules to pass through Sequestrant Chemical that ties up metal atoms or ions by forming bonds with them used as food additives Shell A principal energy level defined by a given value of n Silica Naturally occurring silicon dioxide Silicates Minerals composed of metal cations and silicon-oxygen anions... 

A wide variety of inorganic materials have been used to precipitate or collect trace metals from solution. The most direct approach is a cementation process, which is one that removes the trace pollutants from solution by reduction with a metal and plating onto that metal surface. Although this process may be slow, the filtration is usually quick, since decantation is often sufficient. Finely divided cadmium extracts copper, selenium, and mercury from nitric and sulfuric acid solutions (66). When copper was used to preconcentrate mercury from water or biological fluids prior to atomic absorption analysis, the detection limit was 1-2 X 10 g (67, 68). Iron (69), zinc (70), and tungsten (71), as metals, have also been used to obtain a deposit of several trace metals from aqueous systems as dilute as 10 ppb for subsequent analysis. Elemental tellurium can be produced in solution by reduction using tin(II) chloride or sulfur dioxide, and coprecipitates silver (72) and selenium (73). Granulated silicon-metal alloys were used to remove metal ions from water and brine by reduction as well (74, 75). 

In the processing of integrated circuits, silicon dioxide (SiOa) can be used as a mask during ion implantation or diffusion of impurity into silicon, for passivation, for protection of the device surface, as interlayers for multilevel metallization, or as the active insulating material — the gate oxide film in metal-oxide-semiconductor (MOS) devices [1, 2], At the present time, several methods have been developed for the formation of Si02 layers, including thermal and chemical oxidation, anodization in electrolyte solutions, and various chemical vapor deposition (CVD) techniques [2, 3],... 

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