Copper coatings, reflectivity

Figure 6. The dependence of the degrees of reflection on the wavelength of visible light for the ideal reflectance of copper (B), the total (o), mirror (A) and diffuse(V) reflections of the copper coating electrodeposited from a pure acid sulfate solution. (Reprinted from Ref.12 with permission from Elsevier.)...

Finally, the reflection of light from the copper coating obtained from a pure sulfate solution is mostly diffuse reflection. The structural characteristics of this copper surfaces which enabled a high degree of diffuse reflection with a negligible degree of mirror reflection are that the lateral parts of the surface were larger than the flat parts. 

Figure 16 shows reflection characteristics of the same copper coatings, but having a 25 pm thickness.12,13... 

Similar reflection and structural characteristics to them showed and 40 pm thick the copper coating obtained from solution Cu I. The line section analysis of this copper coating is shown in Fig. 21. The atomically flat parts of these copper coatings are shown in Fig. 22. 

Also, the brightness of a metal surface depends on the mean size of atomically flat parts. The difference in the maximum degrees of mirror reflection between the copper coatings (above 85 %) and the zinc coatings (below 85 %) can be ascribed to the different mean size of atomically flat parts of the copper and zinc coatings (see Figs. 22 and 29). The smaller mean size of atomically flat parts of a surface, the greater is the ratio of screened parts which do not have the ability to... 

The STM images of the copper coating electrodeposited in the presence of the brightening additives that exhibit high degree of mirror reflection which approached very nearly the ideal reflectance of copper are shown in Fig. 2.30 [87, 91, 96]. 

Interference patterns with the reflective and refractive light occurs that varies with the viewing angle. Thin metallic flakes of, for example, aluminium, copper, bronze, coated with a dye are used extensively in automobile wheel hub-caps, and "metallised" car-body paint finishes. 

Gold is classed as a heavy, noble metal located just below copper and silver in group 11 of the periodic table. Gold is a good conductor of electricity as well as an excellent heat reflector of infrared radiation, which makes it an efircient thin coating on glass in skyscrapers to reflect the heat of sunhght. 

Fourier transform infrared reflection-absorption spectroscopy (FT-IFRAS) is applied to the study of corrosion protection of copper by an organic coating. Poly-N-vinyliroidazole (PVI(D) and poly-4(5)-vinylimidazole (PVI(4)) are demonstrated to be effective new polymeric anti-corrosion agents for copper at elevated temperatures. Oxidation of copper is suppressed even at 400° C. PVI(1) and PVI(4) are more effective anti-oxidants than the most commonly used corrosion inhibitors, benzotriazole and undecyllmldazole, at elevated temperatures. These new polymeric agents are water soluble and easy to treat the metal surface. 

As an example, both monofunctional and multifunctional polymeric mercapto-esters were deposited onto optically smooth silicon wafers coated with vapor-deposited copper. The copper had been oxidized to Cu20, as verified by XPS. Infrared reflectance (RAIRS) at 81° (4 cm-1 resolution, 2000 scans) using an MCT detector yielded information on both the nature and the durability of the mercaptoester bond to the metal oxide film. A 16 cm l shift (1740— 1724 cm-1) was observed in the carbonyl absorption of stearyl thioglycolate (STG) deposited onto the Cu20 mirror. The absorption spectrum of the carbonyl region is illustrated in Fig. 11, both for the pure STG and the reacted monolayer. 

Fundamental studies by reflection angle infrared spectroscopy of the bonding of EME coupling agents to metal oxides reveal a significant shift in the carbonyl absorbance band when the coupling agent is applied as a very thin layer on a metal oxide. The shift is reproducible and the extent varies with the type of oxide. These results were obtained both by use of copper mirrors and from CuzO powder coated with very thin layers of model compounds. The compounds were not removable by isopropanol, a solvent for the bulk compound. The thiol absorbances of thin layers of model compounds were also found to decrease in relative intensity with time. This illustrates that a specific chemical interaction has occurred. 

These common uses only hint at all the things that transition metals can do. The copper penny, for instance, is mostly made of zinc, another transition metal. Chromium provides the shiny, mirror-like metal coating on chrome car bumpers, but is also added to some lasers to make their light shine red. Nickel and chromium combine in an alloy that can be coiled into the wires that heat toasters and hair dryers. Titanium dioxide is a very white reflective compound used in toothpaste and paints. The transition metal cadmium is used in brilliant and permanent colors such as cadmium yellow, red, and orange. Artists have used cadmium-based paints for hundreds of years, and manufacturers used the colors more recently in plastic products. However, the colors are rarely used now that scientists have discovered that cadmium pollution can cause cancer and other health problems. 

ATR studies of the biocorrosion of submerged copper surfaces have been reported. The IRE of a cylindrical internal reflectance cell (CIRCLE) was coated with a thin copper layer via a vacuum deposition technique (105). The copper layer reduces the sampling depth of the radiation outward from the surface of the IRE. Therefore, the intensity of the water bending band will vary with copper layer thicknesses of 4.1 nm or less. The copper layers were shown to be stable to exposure to water alone, but the presence of acidic polysaccahrides in the water caused a reduction in the copper layer thicknesses (106.107). The adsorption of a model compound, Gum Arabic, onto the coated IRE was detected by increases in the C-O stretching band of the pyranose units near 1050 cm"1 (106). 

Yoshida, S., and Ishida, H., A FT-IR Reflection Absorption Spectroscopic Study of an Epoxy Coating on Imidazole Treated Copper, Journal of Adhesion, vol. 16, 1984, p. 217. 

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