Electrical conductors metals

In contrast to dielectrics, the electromagnetic waves that penetrate metals are damped the extinction coefficient k in the complex refractive index n = n — ik is not equal to zero, but generally greater than n. For the spectral emissivity s Xn normal to the surface, the electromagnetic theory delivers the relationship 

According to this, with metals, significantly smaller emissivities than those for electrical insulators are to be expected. 

At large wavelengths, around A 5 p,m, and small electrical resistivity re, the radiation properties of metals can be described by a simplified version of electromagnetic wave theory, which goes back to P. Drude [5.22]. It is also linked with the names E. Hagen and H. Rubens, who checked its applicability by experiment [5.23]. According to this theory n and k assume large values, and it holds that 

Here c0 is the velocity of light in a vacuum and p0 = An- 10 7N/A2 is the magnetic field constant. These universal constants yield an electrical resistance of R0 = Cq q/A-k = 29.979 fl 

According to Drude s theory, e x only depends on the polar angle (3 and n from (5.85), cf. Fig. 5.36. At polar angles larger than 80°, e x assumes a distinct 

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Unfortunately the electromagnetic theory is only valid under a series of limiting suppositions, so that the emissivities calculated from it frequently differ from reality. Despite this, it provides important, qualitative statements that can be used for the extrapolation from measurements or to estimate for missing data. We will not discuss the electromagnetic theory, see for this [5.4], but will use some of its results in the treatment of emissivities of electrical insulators and electrical conductors (metals). These two material groups differ significantly in their radiation behaviour. 

These elements form two groups, often called the alkali (Group I) and alkaline earth (Group II) metals. Some of the physical properties usually associated with metals—hardness, high m.p. and b.p.—are noticeably lacking in these metals, but they all have a metallic appearance and are good electrical conductors. Table 6.1 gives some of the physical properties. 

In the early 1970s, the first companies to apply low cost, mass production techniques to photovoltaics, a technology that had previously been considered an exotic aerospace technology, emerged. These techniques included the use of electroplated and screen printed metal paste electrical conductors, reflow soldered ribbon interconnects, and by 1977, low cost, automobile windshield-style, laminated module constmction. Such processes benefitted from a substantial existing industrial infrastmcture, and have become virtually ubiquitous in the present PV industry. 

Uranium metal is weaMy paramagnetic, with a magnetic susceptibility of 1.740 X 10 A/g at 20°C, and 1.804 x 10 A/g (A = 10 emu) at 350°C (51). Uranium is a relatively poor electrical conductor. Superconductivity has been observed in a-uranium, with the value of the superconducting temperature, being pressure-dependent. This was shown to be a result of the fact that there are actually three transformations within a-uranium (37,52). 

The physical properties of bismuth, summarized ia Table 1, are characterized by a low melting poiat, a high density, and expansion on solidification. Thermochemical and thermodynamic data are summarized ia Table 2. The soHd metal floats on the Hquid metal as ice floating on water. GaUium and antimony are the only other metals that expand on solidification. Bismuth is the most diamagnetic of the metals, and it is a poor electrical conductor. The thermal conductivity of bismuth is lower than that of any other metal except mercury. 

Other Metals. Ruthenium, the least expensive of the platinum group, is the second best electrical conductor, has the hardest deposit, and has a high melting point. A general purpose bath uses 5.3 g/L of mthenium as the sulfamate salt with 8 g/L sulfamic acid, and is operated at 25—60°C with a pH of 1—2. Osmium has been plated from acid chloride solutions (130) and iridium from bromide solutions, but there are no known appHcations for these baths. 

Electromagnetic Force When the fluid is an electrical conductor, as is the case with molten metals, it is possible to impress an electromagnetic field around the fluid conduit in such a way that a driving force that will cause flow is created. Such pumps have been developed for the handling of heat-transfer hquids, especially for nuclear reactors. 

The way in which materials are used in a developed nation is fairly standard. All consume steel, concrete and wood in construction steel and aluminium in general engineering copper in electrical conductors polymers in appliances, and so forth and roughly in the same proportions. Among metals, steel is used in the greatest quantities by far 90% of all the metal produced in the world is steel. But the non-metals wood and concrete beat steel - they are used in even greater volume. 

This handbook deals only with systems involving metallic materials and electrolytes. Both partners to the reaction are conductors. In corrosion reactions a partial electrochemical step occurs that is influenced by electrical variables. These include the electric current I flowing through the metal/electrolyte phase boundary, and the potential difference A( = 0, - arising at the interface. and represent the electric potentials of the partners to the reaction immediately at the interface. The potential difference A0 is not directly measurable. Therefore, instead the voltage U of the cell Me /metal/electrolyte/reference electrode/Me is measured as the conventional electrode potential of the metal. The connection to the voltmeter is made of the same conductor metal Me. The potential difference - 0 is negligibly small then since A0g = 0b - 0ei ... 

The mechanical properties, especially the internal stresses set up by interaction of substrate and deposit, have a close bearing on the behavior of metallic interconnects (electrical conductors) in integrated circuits. Such interconnects suffer from more diseases than does a drink-sodden and tobacco-crazed invalid, and stress-states play roughly the role of nicotine poisoning. A very good review specifically of stresses in films is by Nix (1989). 

About one-third of the copper used is secondary copper (i.e. scrap) but the annual production of new metal is nearly 8 million tonnes, the chief sources (1993) being Chile (22%), the USA (20%), the former Soviet Union (9%), Canada and China (7.5% each) and Zambia (5%). The major use is as an electrical conductor but it is also widely employed in coinage alloys as well as the traditional bronze (Cu plus 7-10% Sn), brass (Cu-Zn), and special alloys such as Monel (Ni-Cu). 

The third group is the continuum, models, and these are based on simple concepts from classical electromagnetism. It is convenient to divide materials into two classes, electrical conductors and dielectrics. In a conductor such as metallic copper, the conduction electrons are free to move under the influence of an applied electric field. In a dielectric material such as glass, paraffin wax or paper, all the electrons are bound to the molecules as shown schematically in Figure 15.2. The black circles represent nuclei, and the electron clouds are represented as open circles. 

The electrical resistance of most conductors, metals in particular, decreases as the temperature of the conductor decreases. For some pure metals and compounds of the metals, the resistance decreases with temperature as usual, but at some critical temperature the resistance drops identically to zero. The resistance remains zero as long as the material is maintained at a temperature below the critical temperature. Such a material is termed a supercon-... 

In using metallic Pb as an anode the formation and maintenance of a hard layer of PbOj is essential, since it is the PbOj that is the actual inert anode, the Pb acting both as a source of PbOj and an electrical conductor. PbOj is relatively insoluble in seawater and its dissipation is more usually associated with mechanical wear and stress than electrochemical action. 

Metals also possess unusually high thermal conductivity, as anyone who has drunk hot coffee from a tin cup can testify. It is noteworthy that among metals the best electrical conductors are also the best thermal conductors. This is a clue that these two properties are somehow related and, again, the electron configuration proves to be responsible. 

Aluminum has a low density it is a strong metal and an excellent electrical conductor. Although it is strongly reducing and therefore easily oxidized, aluminum is resistant to corrosion because its surface is passivated in air by a stable oxide film. The thickness of the oxide layer can be increased by making aluminum the anode of an electrolytic cell the result is called anodized aluminum. Dyes may be added to the dilute sulfuric acid electrolyte used in the anodizing process to produce surface layers with different colors. 

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

Metallic lead is dark in color and is an electrical conductor. Diamond, the most valuable form of carbon, is transparent and is an electrical insulator. These properties are very different yet both lead and carbon are in Group 14 of the periodic table and have the same valence configuration, s p Why, then, are diamonds transparent insulators, whereas lead is a dark-colored conductor ... 

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