Surface-insoluble layer

From the time of the inception, chemical amplified positive resists suffered from formation of a surface-insoluble layer, which typically showed up as a skin or T-top profile (Fig. 49). The problem has been ascribed to contamination by... 

Chemically amplified resist system is a promising technology to attain hi resolution and high sensitivity for sub-quarter micron device fabrication. However, air-borne contamination (1-3), such as ammonia mainly generated from conventional adhesion promoter, hexamethyldisilazane (HMDS), severely affects this kind of resist. It causes surface insoluble layer of resist patterns, which results in failure of the pattern fabrication. 

Contamination by airborne basic substances such as amines and N-methylpyrrolidone (NMP) has been shown to be responsible for the formation of the surface insoluble layer. Because of the catalytic nature of the imaging chemistries, a trace amount on the order of 10 ppb of airborne basic substances absorbed in the resist film interfaces with desired acid-catalyzed reactions, and also certain polymers and groups can function as internal contamination. Activated carbon filtration of the enclosing atmosphere can alleviate the contamination problem. Application of a protective... 

The reaction product SiF4 would be gaseous, but it reacts with two HF to Si I7 and two protons and stays in solution [Mellj. The solubility of Si 17, which is in the order of mol 1 1 is significantly reduced in the presence of alkali metal ions. Especially for Rb, K or Cs, a micrometer thick, insoluble layer of metal hexafluoro-silicate may be formed on the electrode surface [Hal2j. The divalent electrochemical dissolution reaction is dominant during PS formation. The effects of the reaction products SiFg and H2 on pore growth are discussed in Section 9.5. 

Addition of fuel oil no. 2 to a laboratory marine ecosystem showed that the insoluble, saturated hydrocarbons in the oil were slowly transported to the sediment on suspended particulate material. The particulate material contained 40-50% of the total amount of aliphatics added to the system and only 3-21% of the aromatic fraction (Oviatt et al. 1982). This indicates that most aromatic hydrocarbons are dissolved in the water (Coleman et al. 1984), whereas the aliphatic hydrocarbons are not (Gearing et al. 1980 Oviatt et al. 1982). In a similar experiment, when fuel oil no. 2 was added continuously to a marine ecosystem for 24 weeks, oil concentrations in the sediment remained low until 135 days after the additions began, but then increased dramatically to levels that were 9% of the total fuel oil added (108 g/tank) and 12% of the total fuel oil saturated hydrocarbons. The fuel oil concentrations in the sediment began to decrease quite rapidly after the maximum levels were reached. The highest sediment concentrations of saturated hydrocarbons (106-527 g/g) were found in the surface flocculent layer, with concentrations decreasing with sediment depth from 22 g/g to not detectable at 2-3 cm below the sediment surface. 

In sulfuric acid solutions alone, the formation of an insoluble layer of the sulfate on the electrode surface may serve to inhibit the rapid bulk corrosion which has been observed in the presence of acetic acid. 

The adsorption kinetics are slow in a surfactant concentration range around CAC and become fast again close to the CMC of the pure surfactant, where the surface layers with and without polymer become similar. Below CAC, they behave as incompressible layers. When subjected to small compression-expansion cycles, the layers exhibit a viscoelastic response, similar with the different polymers. Appreciable differences are seen only when the compression is more important (decrease of the surface area by a factor up to five) the layers with xanthan still behave as insoluble layers (even above CAC), whereas those with PAMPS appear as partially soluble. 

Fixation of metals as their insoluble sulfides is clearly evident for Fe and is considered the likely method for fixing the other trace metals, except for Mn. The blackened sediment beneath the thin-surface-oxidized layer, the lower SO4/CI ratio than that of marine water, and the presence of pyrite framboids (FeS2> show that sulfate is actively reduced to sulfide in the salt marsh. No discrete metal sulfides, besides pyrite framboids, were detected by microprobe examination however, the simultaneous appearance of S04 and trace metals in the interstitial water of cores stored in air suggests that other trace metals may be present as finely dispersed insoluble sulfides. 

These potential limitations, however, have been largely eliminated. Early attempts describe modifications of the metal surface with thin insoluble layers, such as silica with subsequent functionalization via silane compounds [16]. The SAM approach created a tool for convenient introduction of various surface functionalities that can be used for immobilization [6j. Examples include SAMs that are cw-terminated with hydroxyl or carboxyl groups, which can be activated for covalent coupling via nucleophilic reactions. In addition, this modification with epoxy groups leads to activated surfaces that can be directly used for nucleophilic linkage. 

Typical cyclic voltammograms for a silver electrode in 0.1 M KC1 and in 0.1 M K2S04 supporting electrolytes are shown in Fig. 10. These are produced under ORC conditions typically used for SERS activation. During the oxidation half-cycle, the Ag° electrode surface is oxidized to Ag+, which forms an insoluble layer of AgCl or Ag2S04 on the surface. The amount of... 

All these cathodic stripping processes involve an initial deposition of an insoluble layer on the surface of the electrode. If too much material is deposited the quality of the stripping peak will deteriorate and the height of the peak will cease to be proportional to the original concentration. The method is highly sensitive but is suited only to these very low levels. 

Microstreaming, shock waves, and liquid microjets in the vicinity of solid surfaces lead to very efficient cleaning. This effect has been used in industry for more than forty years. Insoluble layers of inorganic salts, polymers, or liquids can be removed by the ultrasonic cleaning effect. In heterogeneous systems such a clean reactive surface leads to improved dissolution rates of metals in acids and enhanced reaction rates. Chemical reactions giving insoluble products are freed from these mass-transport-limiting layers and react rapidly. 

The radionuclides incorporated into the oxide layers, which lead to a radiation field in the surrounding area, are mainly the activated corrosion product nuclides, above all Co and Co. Out of the fission products present in the primary coolant during plant operation with failed fuel rods in the reactor core, iodine and cesium isotopes are not deposited into the surface oxide layers this reactor experience is consistent with the general chemical properties of these elements which do not allow the formation of insoluble compounds under the prevailing conditions (with the sole exception of Agl, see Section 4.3.3.1.2.). On the other hand, fission product elements that are able to form insoluble compounds (such as oxides, hydroxides or ferrites) in the primary coolant are incorporated almost quantitatively into the contamination layers (see Section 4.3.3.1.4.). However, because of the usually low concentrations of polyvalent fission products in the primary coolant, only in very rare cases will these radionculides make a measurable contribution to the total contamination level for this reason, they will not be treated in this context. 

The anions also play a very important role in the corrosion process. If they react with metal ions, produced during the anodic corrosion reaction, 2md form an insoluble salt precipitate on the metsd surface, this layer could act as an effective barrier against corrosion. This is the case of corrosion of lead sheathing for power and communications cables in a soU solution that contains sulfate ions (S04 ). The most corrosive anion for metals is the chloride ion (Cl"), which is usually naturally present in soils and sands of the marine-coastal regions, or it may be present as a result of external sources such as de-icing salts applied to roadways. Its attack is localized and more dangerous than the uniform corrosion, because the formed pits could perforate the metal surface. The chloride ion concentration in corrosive soil electrol3 tes (moisture) varies as soil conditions alternate between wet and dry. 

Chromium is enriched in the inner rust layer together with copper and phosphorus. They promote the formation of a dense layer of amorphous FeOOH next to the steel surface. This layer acts as a barrier to the transport of water, oxygen, and pollutants. Nickel is supposed to act by forming insoluble basic sulfates in pores of the rust layer. 

Polyamide surfaces yellow under thermal-oxidative aging. Over time, the intensity of the discoloration increases. Yellowing can assume intensive brown, even black coloring at elevated temperatures, which turns into crosslinked, insoluble layers that are very brittle. Thus, molded parts become notch-sensitive and break when bent. 

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