Etching in hydrofluoric acid

In one embodiment patented by Makrides et al., tantalum foils were electrolyti-cally etched in hydrofluoric acid, washed with acetone and, while still wet with acetone, placed in vacuum and dried by evacuation. Using an argon plasma at a pressure of about 1 mm Hg (133.3 Pa), palladium was deposited onto both sides of the membranes to recommended thicknesses between 10 and 100 nm. Membranes of niobium and vanadium were prepared in the same manner, except that, in addition, vanadium was degassed in vacuum at 1273 K (1000 °C) to remove oxygen. Unalloyed palladium as well as Pd-Ag, Pd-Au and Pd-B, were also patented as hydrogen dissociation catalysts and as protective layers for the highly reactive niobium, tantalum and vanadium. 

The effect of etch time (30 sec vs. 180 sec) on the composition of a Ti-6-4 surface etched in hydrofluoric acid/ammonium orthophosphate solution was followed by two SIMS spectra shown in Figure 29.(33) The aluminum signal decreases with increasing etch time while the vanadium signal increases. Preferential etching of the aluminum-rich a phase relative to the vanadium-rich p phase by the etch leads to the decreased aluminum signal. 

FIGURE 29. SIMS spectra of titanium-6-4 etched in hydrofluoric acid/ammonium orthophosphate for 30 sec (b) and titanium-6-4 etched in the same acid mixture for 180 sec (a). Reprinted with permission from Reference 33. Copyright 1981 Gordon and Breach Science Publishers. 

The fiber bundles used for the electronic nose platform are polished and chemically etched with hydrofluoric acid to create an ordered array of micrometer sized wells on the tip of the fiber (Figure 3)4. The etching process takes advantage of the difference in reactivity of the core and the... 

A spatial distribution of Pb centres (g = 2.0029, g — 2.0086) has been revealed in porous silicon formed by anodic etching of crystalline silicon in hydrofluoric acid.144 Oxygen ions were also implanted using accelerator at 2 MeV and compared with photoluminescence. 

P. Lim, J. R. Brock, and I. Trachtenberg, Laset-induced etching of silicon in hydrofluoric acid, Appl. Phys. Lett. 60(6), 1992. 

The fact that mica (and fused silica) can serve as solid state track detector (SSTD) of fission fragments was reported shortly before the final stage of development of the method for element 104 [12-14], In the dielectric solids, fission fragments produce tiny tracks visible by electron microscopy. Mica and silica are very resistant to active chemical reagents and elevated temperatures. The tracks proved to stay in hostile conditions of real experiments for a reasonably long time. Thanks to this, after the end of bombardment (EOB), the mica sheets could be etched with hydrofluoric acid to enlarge the tracks to micrometer size they were distinct in appearance and were searched out by scanning the surface of the detectors with an... 

Bard and coworkers studied Si(lll) in hydrofluoric acid under potential control in 1992. They studied silicon surface etching in dependence on HF concentration and electrode potential. In the cathodic potential range they observed atomic cormgation of silicon surface, cf. Fig. 27, which with time disappeared due to the surface rearrangement because of the hydrogen evolution. 

The substrate is first coated, for instance, via electroless or physical vapor deposition with a thin (< 1 pm) metallic layer, which in turn is patterned by photolithography and wet etching. This layer serves two roles, as a plating base and as an electrically conducting layer for the finished structures. In the subsequent step a sacrificial layer, of about 5 pm in tliickness, is deposited on the substrate and also patterned by photolithography and wet etching. Titanium is used most often as the sacrificial material because it adheres well to the resist and to the electrodeposited layer and can be etched with hydrofluoric acid that does not attack other materials such as chromium, silver, nickel, copper, and which are usually used in the LIGA process. 

Acids have many uses. For example, phosphoric acid is used to make gasoline additives and carbonated beverages. The textile industry uses oxalic acid (found in rhubarb and spinach) to bleach cloth, and glass is etched by hydrofluoric acid. Dyes and many other chemicals are made with sulfuric acid and nitric acid, and corn syrup, which is... 

Silicon oxides (SiOx) are the most widely used thin films in silicon microelectronic and micromechanical devices. Similar to silicon nitride (Section 5.5.4), these amorphous films exhibit dielectric properties. Silicon oxide is often utilized as part of a dielectric membrane, as a passivation or insulating layer, or as a sacrificial layer, which can be etched with hydrofluoric acid (HF)-containing etchants. Two different approaches to forming a silicon oxide thin film are... 

Fig. 9.7.4 Typical microchannel trapezoidal cross-section generated from wet etching in hydrofluoric (HF) acid baths. (Reprinted from Ref. [35], 2004, with permission from Elsevier.)...

Fluoride-liberating chemicals are used in some automobile wheel cleaners, glass etching solutions, insecticides, rodenticides, aluminum production, vitamins or dietary supplements, and products to prevent dental caries. Most toothpaste contains up to 5 mg fluoride per teaspoon. Fluoride is commonly added to community drinking water. It is also found in hydrofluoric acid (see p 221), which is used for etching glass and cleaning silicon chip products. Soluble fluoride salts are rapidly absorbed and are more acutely toxic (Table 11-25). 

Fig. 8. Isotopic compositions of nitrogen and neon released from a lunar ilmenite separate subjected to stepwise etching by hydrofluoric acid. Close to grain surfaces, on the right of the plot, isotopically heavy nitrogen is associated with neon whose Ne/ Ne ratio equals that observed directly in the solar wind, whereas at greater depths within the grains, lighter nitrogen is associated with isotopically heavier neon, attributed by Wieler et al (1986) to solar energetic particles. From Mathew et al (1998).

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