Etching, chemical

As stated in Sec. 3.1, valuable information on the mechanism of chemical etching processes can similarly be obtained by studying the electrochemical behavior of the interface. In the particular case of GaP, the conclusion that open-circuit etching of GaP single crystals in acidic Br2 solutions proceeds via a chemical mechanism arises from two experimental observations. Firstly, current-potential measurements at p-GaP show that Br2 cannot inject holes into the valence band of GaP, so that elec- 

The electrochemical reduction of Br2 occurs via reactions (62) and (56) (photocurrent doubling at p-GaP [72])  

At the n-GaP anode, the reverse dark current increases upon addition of Br2 to indifferent H2SO4 solution [72], analogously to the increase of the reverse current in the presence of an electroless etching agent, i.e., a hole injector (see Sec. 2.3). Since 

The Xi intermediate is assumed to be the same as the first intermediate of the anodic decomposition reaction (see reaction (4)). Similarly, the positive intermediate Xj is first neutralized by water through reaction (46) the neutral species X,-OH is subsequently oxidized by a Br radical  

As in the case of anodic etching, electron injection by Xj (reaction (51)) is considered to occur parallel to reaction (46). Further oxidation of X2 to the final products proceeds analogously. The fact that the decomposition intermediates of the chemical etching process are essentially the same as those of the anodic etching process leads to mixed chemical-anodic etching of the p-GaP anode in acidic Br2 solutions the competitive chemical and anodic reactions are linked via the radical intermediates. This explains why at sufficiently high anodic polarization, the etching of p-GaP consumes neither 3 Br2 molecules per GaP siu face entity nor 6 holes, but 1 Br2 molecule and 4 holes. 

---

Bonding. Surface treatment, such as chemical etch, corona, or flame treatments, is required for adhesive bonding of Tefzel. Polyester and epoxy compounds are suitable adhesives. 

Poly(phenylquinoxaline—arnide—imides) are thermally stable up to 430°C and are soluble in polar organic solvents (17). Transparent films of these materials exhibit electrical insulating properties. Quinoxaline—imide copolymer films prepared by polycondensation of 6,6 -meth5lene bis(2-methyl-3,l-benzoxazine-4-one) and 3,3, 4,4 -benzophenone tetracarboxyUc dianhydride and 4,4 -oxydianiline exhibit good chemical etching properties (18). The polymers are soluble, but stable only up to 200—300°C. 

If the interlace or depth of interest is beyond the capability of sputtering, one can try polishing down, sectioning, or chemical etching the sample before insertion. 

Surface modifications and surfiice roughness Cu, Mo, and Be laser mirrors atomic oxygen modified (corroded) surfaces and films, and chemically etched surfaces. 

Another application involves the measurement of copper via the radioisotope Cu (12.6-hour half-life). Since Cu decays by electron capture to Ni ( Cu Ni), a necessary consequence is the emission of X rays from Ni at 7.5 keV. By using X-ray spectrometry following irradiation, sensitive Cu analysis can be accomplished. Because of the short range of the low-energy X rays, near-surface analytical data are obtained without chemical etching. A combination of neutron activation with X-ray spectrometry also can be applied to other elements, such as Zn and Ge. 

As with chemical etches, developing optimum conversion coatings requires assessment of the microstructure of the steel. Correlations have been found between the microstructure of the substrate material and the nature of the phosphate films formed. Aloru et al. demonstrated that the type of phosphate crystal formed varies with the orientation of the underlying steel crystal lattice [154]. Fig. 32 illustrates the different phosphate crystal morphologies that formed on two heat-treated surfaces. The fine flake structure formed on the tempered martensite surface promotes adhesion more effectively than the knobby protrusions formed on the cold-rolled steel. 

In addition to inspecting for possible contamination, it usually is also of interest to determine whether the chemical etching or anodization process has actually produced the desired oxide. For this purpose, anodization has somewhat of an advantage over etching (FPL, for example) because the thicker oxide developed... 

P. Bonsch, D. Wiillner, T. Schrimpf, A. Schlachletzki, R. Lacmann. Ultrasmooth V-grooves in InP by two-step chemical etching. J Electrochem Soc i45 nn-ni6, i998. 

A. Kumar, G. M. Whitesides. Features of gold having micrometer to centimeter dimensions can be formed through a combination with an elastomeric stamp and an alkanethiol ink followed by chemical etching. AppI Phys Lett (55 2002-2004, 1993. 

Other means of identification sometimes used satisfactorily involve chemical etching of the surface (not to be generally recommended), or the formation of letters or numbers by means of a vibrating stylus. The former is advantageous in studies of stress-corrosion cracking in which stamped symbols could lead to regions of stress concentration. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

The data available up to 1971 have been collected by Carr et al.,m who have also reported apzc value of -0.59 0.02 V (SCE) for a melted, cut, mechanically polished, and finally electrochemically and chemically etched electrode. 

---