Of silicon dioxide

For some materials, the most notable being silicon, heating alone sufiBces to clean the surface. Commercial Si wafers are produced with a thin layer of silicon dioxide covering the surface. This native oxide is inert to reaction with the atmosphere, and therefore keeps the underlying Si material clean. The native oxide layer is desorbed, i.e. removed into the gas phase, by heating the wafer in UHV to a temperature above approximately 1100 °C. This procedure directly fonus a clean, well ordered Si surface. 

Sand consists mainly of silicon dioxide. When sand is heated with an excess of coke (carbon), pure silicon and carbon monoxide are produced. 

Write a balanced equation for the reaction of hydrofluoric acid with Si02. What volume of 2.0 M HF is required to react with one gram of silicon dioxide ... 

Another example of a cold-wall reactor is shown in Fig. 5.9. It uses a hot plate and a conveyor belt for continuous operation at atmospheric pressure. Preheating and cooling zones reduce the possibility of thermal shock. The system is used extensively for high-volume production of silicon-dioxide coatings for semiconductor passivation and interlayer dielectrics. 

Beta SiC (PSiC) has good chemical resistance, particularly to oxidation owing to the formation of a thin adherent and protective film of silicon dioxide on the surface. Its characteristics are summarized in Table 9.6. 

A recent competitor to CVD in the planarization of silicon dioxide is the sol-gel process, where tetraethylorthosilicate is used to form spin-on-glass (SOG) films (see Appendix). This technique produces films with good dielectric properties and resistance to cracking. Gas-phase precipitation, which sometimes is a problem with CVD, is eliminated. 

CVD, the other major deposition process, is used on a large scale. A typical low-E glass is obtained by depositing a thin film of silicon dioxide followed by another thin film of fluorine-doped tin oxide. The Si02 acts as a diffusion barrier and the Sn02 reduces the emissivity. A typical CVD apparatus is shown in Fig. 

These spherical nano-particles about 55 nm in diameter have a fluorescent material of ruthenium pyridine inside, and the shell of silicon dioxide, as shown in Fig. 36. The excitation wavelength of the ruthenium pyridine is 480 nm and the emission wavelength is 592 nm [81]. In order to get a clear image of nano-particles, the mass concentration of the fluorescent particles should be limited to a very low level. 

Mass Concentration of Fluorescent Particles Mass Concentration of Silicon Dioxide Particles... 

Quartz left) is a crystalline form of silicon dioxide containing a regular three-dimensional array of Si02... 

Silicon, like carbon, is relatively inactive at ordinary temperatures. But, when heated, it reacts vigorously with the halogens (fluorine, chlorine, bromine, cmd iodine) to form halides and with certain metals to form silicides. It is unaffected by all acids except hydrofluoric. At red heat, silicon is attacked by water vapor or by oxygen, forming a surface layer of silicon dioxide. When silicon and carbon are combined at electric furnace temperatures of 2,000 to 2,600 °C (3,600 to 4700 °F), they form silicon carbide (Carborundum = SiC), which is an Importeint abrasive. When reacted with hydrogen, silicon forms a series of hydrides, the silanes. Silicon also forms a series of organic silicon compounds called silicones, when reacted with various organic compounds. 

The arrangement of oxygen atoms in ice I is isomorphous with the wurtzite form of zinc sulphide, and also with the silicon atoms in the tridymite form of silicon dioxide. Hence, ice I is sometimes referred to as the wurtzite or tridymite form of ice (Eisenberg Kauzmann, 1969). 

Geothermal processes give rise to the most impressive form of silicon dioxide rock (or mountain) crystal. This quartz form can also be worked into jewelry. 

There are some exceptions. The diatoms are unicellular microorganisms that protect themselves with a filigree skeleton of silicon dioxide (silicic acid). The sometimes major fossil deposits of kieselguhr (diatomaceous earth or diatomite)... 

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... 

Any two samples of a particular mineral, whatever their source or place of origin, have the same basic composition and characteristic crystal structure moreover, no two different minerals have identical chemical composition and crystal structure (see Textboxes 8 and 21). Quartz, for example, is a common and abundant mineral composed of silicon dioxide, a compound that occurs naturally not only as quartz but also in other crystal structures, known as polymorphs (polymorphs are minerals that have the same chemical composition but different crystal structure), some of which, listed in Table 23, have been used for a variety of purposes. The crystal structure, which is essential for the characterization of solid materials, is just one of a wide range of physical properties, that is, properties not involving chemical differences, which provide convenient criteria for characterizing and identifying solids. 

Flint is a hard and easily split variety of the mineral quartz (composed of silicon dioxide), which occurs not only as flint but also in a wide range of other varieties. Some of these exhibit different colors and colored patterns and have characteristic crystalline structures, while others are amorphous (see Textbox 21). In all its varieties, nevertheless, the hardness of quartz is very high, being graded as 7 on the Mohs scale (see Textbox 23). Almost all varieties are either transparent or translucent and display a distinctive luster. These properties made quartz an attractive material for making ornamental... 

Sol-gel technology makes it possible to deposit onto glass substrates two-component coatings that consist of a mixture of silicon dioxide and an indicator (a dye that changes color as a function of the pH)48. The spectral and operational characteristics of the resulting coatings are similar to one-component coatings. 

Nakano et al. have demonstrated that Fe(III) spin crossover complexes adsorbed on the surface of silicon dioxide retain their spin crossover behaviour [220]. EPR and 57Fe Mossbauer spectral data indicated that the spin transitions observed are similar to those of the neat solid materials used, i.e. [Fe(acpa)2]PF6, [Fe(acpa)2]BPh4 (Hacpa=N-(l-acetyl-2-propylidene)(2-pyri-dylmethyl)amine) and [Fe(bzpa)2]PF6 (Hbzpa=(l-benzoylpropen-2-yl)(2-pyridylmethyl)amine). 

Figure 4.2 Schematic diagram of a charge-coupled device (CCD) imaging sensor. It consists of a semiconducting substrate (silicon), topped by a conducting material (doped polysilicon), separated by an insulating layer of silicon dioxide. By applying charge to the polysilicon electrodes, a localized potential well is formed, which traps the charge created by the incident light as it enters the silicon substrate.

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