Gold arsenide

Gold arsenides.—Arsenic precipitates from auric-chloride solution an arsenide, AugAs.6 Fusion of thus substance with potassium cyanide converts it into a yellow arsenide, Au4As3, of density 16-2. Both substances have the character of alloys. 

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

AuSn has the nickel arsenide structure, B8, with abnormally small axial ratio (c/a = 1.278, instead of the normal value 1.633). Each tin atom is surrounded by six gold atoms, at the corners of a trigonal prism, with Au-Sn = 2.847 A. and each gold atom is surrounded by six tin atoms, at the corners of a flattened octahedron, and two gold atoms, at 2.756 A., in the opposed directions through the centers of the two large faces of the octahedron. 

Villegas, I. Stickney, J. L. 1992. Preliminary studies of gallium arsenide deposition on gold (100), (110), and (111) surfaces by electrochemical atomic layer epitaxy. J. Electrochem. Soc. 139 686-94. 

Formation of SA monolayers of phospholipids [217,242] and surface-active viologens [244, 245] on gold substrates, those of long-chain zirconium-phosphonates on silicon substrates [243], and those of alkanethiols on gallium arsenide substrates [246] have also been reported. 

As mentioned in Chapter II, many metallic arsenides are found in Nature. Arsenic combines directly with most metals to form stable compounds, those of the heavy metals being the most stable. The latter may be obtained by allowing an aqueous solution of a salt of the appropriate metal to drop into an atmosphere of arsine, air being completely absent, and the vessel continually shaken.1 Precipitation by passing arsine into the salt solution is not satisfactory as, in the case of copper, silver, gold, mercury and lead, a secondary reaction with the excess of metallic ions occurs ... 

The reaction commences at a temperature above 400° C., before the melting temperature is reached, and the fused product therefore always contains some arsenious oxide.1 When heated in hydrogen, the pentoxide is reduced first to arsenious oxide and then to free arsenic. Similar reduction occurs when it is heated with carbon or phosphorus with sulphur, arsenious sulphide is formed. Arsenic and metallic arsenides result when the pentoxide is heated with alkali metals,2 zinc, lead, iron or most other heavy metals mercury and silver react only at high temperature gold and platinum do not react. 

In the arsenide and antimonide derivatives Na2AuAs or Na2AuSb there are zigzag (AuX)2 -chains, with structures like the gold(I) halides (4), while AuSb2 has metallic properties and has the cubic fluorite structure.325-327... 

Other materials that are normally etehed in a mieroelectronics environment are poly-silieon, silicon nitride, doped poly-silieon, aluminum, gallium arsenide, and gold. The plasma chemistry involved is... 

Davidson F.M., III Schricker, A.D. Wiacek, R.J. Korgel, B.A. Supercritical fluid-liquid-solid synthesis of gallium arsenide nanowires seeded by alkanethiol-stabilized gold nanocrystals. Adv. Mater. 2004, 16 (7), 646-649. 

The use of NEXAFS to provide structure information in molecular electronics has appeared only recently. Krapchetov et al. performed a NEXAFS analysis of the assembly of terphenyldithiol and quaterphenyldithiol on gold and gallium arsenide... 

Krapchetov, D.A. et al., Solvent-dependent assembly of terphenyl- and qnaterphe-nyldithiol on gold and gaUinm arsenide, Langmuir 21 (13), 5887-5893, 2005. 

Silver and gold occur native, and in sulfide, arsenide and telluride ores, e.g. argentite (Ag2S) and sylvanite ((Ag,Au)Te2). Silver is usually worked from the residues of Cu, Ni or Pb refining and, like Au, can be extracted from all its ores by reaction 22.4, the cyano complex being reduced to the metal by Zn. ... 

Ruthenium, osmium, rhodium, iridium, palladium and platinum are the six heaviest members of Group VII1. They are rare elements platinum itself is the commonest with an abundance of about 10-6% whereas the others have abundances of the order of 10"7 % of the earth s crust. They occur in Nature as metals, often as alloys such as osmiridium, and in arsenide, sulfide and other ores. The elements are usually associated not only with one another but also with the coinage metals copper, silver and gold. The main suppliers are South Africa, Canada and the USSR. 

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