Resistivity metal films

With the help of cholesteric liquid crystals, intensity distributions of microwave fields can be rendered visible [12]. A suitable detector (Fig. 2) consists of a thin resistive metal film with a surface resistance of 200 12/a, to 400 2/d coated with a 10 jLtm to 20 jum layer of a cholesteric liquid crystal. A polyester film deposited on both sides protects the device. When this foil is introduced into a microwave field of sufficient power density, absorption in the metal film produces a temperature profile proportional to the field intensity distribution. The liquid crystal temperature indicator then makes this profile visible. 

The wide range of soHd lubricants can generally be classified as either inorganic compounds or organic polymers, both commonly used in a bonded coating on a matching substrate, plus chemical conversion coatings and metal films. Since solid-film lubricants often suffer from poor wear resistance and inabihty to self-heal any breaks in the film, search continues for improved compositions. 

Cavitation Formation of transient voids or vacuum bubbles in a liquid stream passing over a surface is called cavitation. This is often encountered arouna propellers, rudders, and struts and in pumps. When these bubbles collapse on a metal surface, there is a severe impact or explosive effec t that can cause considerable mechanical damage, and corrosion can be greatly accelerated because of the destruction of protective films. Redesign or a more resistant metal is generally required to avoid this problem. 

Tubeside fouling Shellside fouling Tube metal wall Tubeside film resistance Shellside film resistance... 

Anodizing—the formation of a hard, corrosion-resistant oxide film on metals via anodic oxidation of the metal in an electrolytic solution. 

Cellulose Acetate Butyrate H F F Molded with plasticizers Excellent moisture resistance-metallized sheets and film, automobile industry... 

Attempts made to produce an alloy more resistant to hydrochloric acid have resulted in alloys containing 17-18% silicon or 14-5% silicon and chromium plus 3% molybdenum. The first is produced in Britain, and the second in the United States. The reason for the increase in resistance to hydrochloric acid of the Fe-18 Si alloy is thought to lie primarily in the increased density of the silica-rich film left on the metal by initial corrosion. The addition of 6% chromium with some molybdenum to Fe-14-5 Si causes the formation of extremely stable complex carbides with the consequent complete elimination of graphite plus the formation of a more penetration-resistant silica film, probably containing chromium in substantial quantity. 

Many of the alloys of copper are more resistant to corrosion than is copper itself, owing to the incorporation either of relatively corrosion-resistant metals such as nickel or tin, or of metals such as aluminium or beryllium that would be expected to assist in the formation of protective oxide films. Several of the copper alloys are liable to undergo a selective type of corrosion in certain circumstances, the most notable example being the dezincification of brasses. Some alloys again are liable to suffer stress corrosion by the combined effects of internal or applied stresses and the corrosive effects of certain specific environments. The most widely known example of this is the season cracking of brasses. In general brasses are the least corrosion-resistant of the commonly used copper-base alloys. 

Tantalum is one of the most versatile corrosion-resistant metals. Its corrosion behaviour can be compared with that of glass in most environments. This behaviour is attributed to the stable passive film of TajO, produced on the surface during exposure. 

Thin metal films (e.g., copper films) on insulating materials are employed in remote-controlled resistors. The electrical resistance of such a film can be regulated in both directions, by cathodic growth of the film or by anodic dissolution of the film, leading to a decrease in film thickness. 

MIC depends on the complex structure of corrosion products and passive films on metal surfaces as well as on the structure of the biofilm. Unfortunately, electrochemical methods have sometimes been used in complex electrolytes, such as microbiological culture media, where the characteristics and properties of passive films and MIC deposits are quite active and not fully understood. It must be kept in mind that microbial colonization of passive metals can drastically change their resistance to film breakdown by causing localized changes in the type, concentration, and thickness of anions, pH, oxygen gradients, and inhibitor levels at the metal surface during the course of a... 

Continuous (barrier, passivation) films have a high resistivity (106Q cm or more), with a maximum thickness of 10 4cm. During their formation, the metal cation does not enter the solution, but rather oxidation occurs at the metal-film interface. Oxide films at tantalum, zirconium, aluminium and niobium are examples of these films. 

In 1987, Swartz [73] measured the thermal boundary resistance between metal films and the dielectric substrates onto which the films were deposited, in the range 0.6-200 K. A typical example is the measurement of the thermal contact resistance between indium and sapphire [72]. To minimize the dependence on surface irregularities, indium was vacuum deposited onto the sapphire rods the two surfaces were then pressed together and annealed. Analogous measurements have been carried out also with lead and aluminium. In all these cases, it has been clear that the contact resistance was strongly dependent on the sample preparation. In particular, obtained data suggest that the contact between the two materials was not complete. 

TES are based on the steep temperature dependence of the resistance of superconducting metallic films. The useful temperature range is very narrow. These thermometers which may have a very low intrinsic noise, are fabricated by a vacuum deposition process at very low pressure and are patterned either by photolithography technique (see e.g. ref. [21]) or by micromechanical machining (see e.g. ref. [22]). The dimensionless parameter a = T/R-dR/dT defines the DC quality of a sensor. TES with a as high as 1000 have been built [23],... 

The reactivity hazards of this well defined group of oxidants towards other materials decrease progressively from fluorine, which reacts violently with most materials (except for those metals on which resistant fluoride films form), through chlorine and bromine to iodine. Astatine may be expected to continue this trend. The individual entries are ... 

A shadow-mask technique has been applied for the local metal deposition to exclude metal residues on other designs processed on the same wafer (Fig. 4.2b). Such metal residues may be caused by imperfections in the patterned resist due to topographical features on the processed CMOS wafers or dust particles. The metal film is only deposited in those areas on the wafer, where it is needed for electrode coverage on the microhotplates. This also renders the lift-off process easier since no closed metal film is formed on the wafer, so that the acetone has a large surface to attack the photoresist. Another advantage of the local metal lift-off process is its full compatibility with the fabrication sequence of chemical sensors based on other transducer principles [20]. 

Almost all metallic materials in practical environments perform their service in the state of spontaneous passivation, in which hydrated oxygen moleciiles or hydrogen ions act as oxidants to passivate the surfaces. Stainless steel is a good and widely known example of corrosion resistant metals it is spontaneously passivated and remains in the passive state with a thin passive oxide film even in fairly corrosive environments. 

Although the sputter deposition technique can provide a cheap and directly controlled deposition method, the performance of PEM fuel cells with sputtered CLs is still inferior to that of conventional ink-based fuel cells. In addition, other issues arise related to the physical properties of sputtered catalyst layers, such as low lateral electrical conductivity of the thin metallic films [96,108]. Furthermore, the smaller particle size of sputter-deposited Ft can hinder water transport because of the high resistance to water transport in a thick, dense, sputtered Ft layer [108]. Currently, the sputter deposition method is not considered an economically viable alternative for large-scale electrode fabrication [82] and further research is underway to improve methods. 

Four-point probe is the most commonly used method to measure sheet resistance for metal films in silicon processing. Given known resistivities of each material, the film thickness can be obtained. Table VI lists the resistivities for the films often used in the back-end interconnect processes. The theory in four-point prohe originally comes from Ohm s law ... 

If a single metal film is deposited on an oxide, the sheet resistance measurement results can by easily interpreted and converted to the thickness. In practice, however, this is not usually the case. For example, in W CVD, the tungsten is not directly deposited on oxide due to high residual stress and unreliable adhesion. A titanium (Ti) layer must be first deposited as a glue layer. In addition, to prevent the fluorine in the CVD-precursor WFg from directly reacting with Ti (a strong catalytic reaction will occur), a barrier layer of titanium nitride (TiN) must be deposited on top of the Ti. As a result, we have a trilayer film of W on TiN on Ti on oxide, as shown schematically in Fig. 21. This poses some problems in accuracy in the four-point probe measurements. Based on the resistivities in Table VI, the... 

Aluminum is a soft, ductile, and relatively inexpensive metal. The surface of aluminum readily oxidizes in the air and water to form a highly resistant oxide film. This oxide film serves to make aluminum resistant to attack when used in environments containing sulfides, sulfur dioxide, carbon dioxide, and other corrosive gases. It is highly resistant to water-initiated corrosion, but is susceptible to galvanic corrosion by trace amounts of copper, tin, lead, nickel, or carbon steel. The reaction of aluminum in water to form Bayerite is shown in FIGURE 9-2. 

Cylinder and piston ring wear have been observed when using alcohol fuels. Metal loss could be due to wear caused by removal of the lubricating oil film by liquid alcohol during cold starting or by the corrosive action of formic acid or other acids formed during the combustion process. Use of more corrosion- and wear-resistant metal alloys in engine construction have helped resolve this problem. 

The behavior of the bias circuit of Fig. 4 is of some interest. Let (RD)0 be the equivalent detector resistance at zero signal. The quantity RL is the load resistance (preferably wire-wound or metal film see Stewart, 1970) and V0 is the background detector voltage that corresponds to a detector resistance Rd = (Rd)0. Then the output signal of the bias circuit, Fsig(a), is given by... 

In the diode the cathode is usually a W filament which can be flashed and maintained as a reference electrode at a temperature above which adsorption occurs. The anode may be of similar construction or take the form of a metal film evaporated from an adjacent filament. Experimentally, current polarization curves are obtained, first for the clean anode surface A and then for the covered anode surface A. Alternatively, resistance-voltage characteristics are measured (SO). The potential difference comprises the applied polarization and the C.P.D. between the emitter and collector. For a given anode current j,... 

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