Substrate passivation

Electroplating passive alloys Another application of strike baths reverses the case illustrated in the previous example. The strike is used to promote a small amount of cathode corrosion. When the passivation potential of a substrate lies below the cathode potential of a plating bath, deposition occurs onto the passive oxide film, and the coating is non-adherent. Stainless steel plated with nickel in normal baths retains its passive film and the coating is easily peeled off. A special strike bath is used with a low concentration of nickel and a high current density, so that diffusion polarisation (transport overpotential) depresses the potential into the active region. The bath has a much lower pH than normal. The low pH raises the substrate passivation potential E pa, which theoretically follows a relation... 

Pitts et al. (1986) exposed five individual PAHs, pyrene, fluoranthene, benz[a]anthracene, BeP, and BaP, deposited on glass fiber and Teflon-impregnated glass fiber filter (TIGF) substrates passively for 3 h in the dark in a 360-L Teflon environmental chamber to 50-300 ppb of 03 in air at several relative humidities. These experimental conditions more nearly resemble the actual exposure of ambient particles to 03 (in the dark) during transport than do exposures in Hi-Vol flow systems. Consistent with earlier studies, BaP, BaA,... 

Properties of thermally modified films. Thermally modified films produced in this work were found to be colourless, glassy materials with extremely strong adhesion to the metal substrate. Passivation tests have shown that the coated metals displayed excellent resistance to corrosive chemicals. Exposure of films to concentrated acids, such as ECt, HNO, H2S0i and H PO for several hours had no visible effect upon their surface. 

Stranski-Krastanov growth mode 219 sub-micron channels 485 substituted oligothiophenes 474 substrates - passivation 442 substrates - Si02 substrate 429 surface... 

These effects can be explained by a reorganization of the immobilized molecule to attain the most favorable thermodynamic state. For example, adsorption to hydrophobic surfaces is driven by rearrangements that optimize contact of hydrophobic segments with the substrate. Passive binding to a surface substrate also opens possibilities for uncontrolled exchange of the immobilized molecule during an analysis cycle. If the modified surface is used for repeated analysis cycles, the probabihty of exchange will be further enhanced and lead to unreliable assays. 

Substrate passivation during coating formation is achieved by treating the surface being covered with special technological fluids, i.e. passivators. The passivation operation precedes the application of the polymer layer to the substrate. 

A broad scope of passive and active mixing schemes for Lab-on-a-Qiip systems has been published in the literature. Many of these schemes may also be applied to centrifugal microfluidic systems. However, due to the technical and economical burden imposed by integrating active compraients onto the rotating, typically disposable substrate, passive mixing schemes are preferred. In this contribution, we focus on schemes that make explicit nature of the rotational motion. 

Challenges to overcome for SFIL include deposition of aoss-linked resist on the mold (fouling), which can cause irreversible adhesion of the mold to the substrate. Passivation of the surface of the mold using fluorinated silanes can promote release of the mold from the pattern, but fewer than f 00 uses per mold is typical. Selectively cleavable cross-linking... 

Molecular adsorbates usually cover a substrate with a single layer, after which the surface becomes passive with respect to fiirther adsorption. The actual saturation coverage varies from system to system, and is often detenumed by the strength of the repulsive interactions between neighbouring adsorbates. Some molecules will remain intact upon adsorption, while others will adsorb dissociatively. This is often a frinction of the surface temperature and composition. There are also often multiple adsorption states, in which the stronger, more tightly bound states fill first, and the more weakly bound states fill last. The factors that control adsorbate behaviour depend on the complex interactions between adsorbates and the substrate, and between the adsorbates themselves. 

Step 11. If no additional metallisa tion layers are required, the substrate is covered with a passivation layer. If additional levels of metallisa tion are to be added to the stmcture, a blanket layer of a intermetal dielectric (IMD) is deposited. The resist is deposited, patterned (mask 5), and vias down to the Al in the first metal layer are etched. Steps 10 and 11 are repeated to form the second metal layer. 

Niobium is used as a substrate for platinum in impressed-current cathodic protection anodes because of its high anodic breakdown potential (100 V in seawater), good mechanical properties, good electrical conductivity, and the formation of an adherent passive oxide film when it is anodized. Other uses for niobium metal are in vacuum tubes, high pressure sodium vapor lamps, and in the manufacture of catalysts. 

In most cases, CVD reactions are activated thermally, but in some cases, notably in exothermic chemical transport reactions, the substrate temperature is held below that of the feed material to obtain deposition. Other means of activation are available (7), eg, deposition at lower substrate temperatures is obtained by electric-discharge plasma activation. In some cases, unique materials are produced by plasma-assisted CVD (PACVD), such as amorphous siHcon from silane where 10—35 mol % hydrogen remains bonded in the soHd deposit. Except for the problem of large amounts of energy consumption in its formation, this material is of interest for thin-film solar cells. Passivating films of Si02 or Si02 Si N deposited by PACVD are of interest in the semiconductor industry (see Semiconductors). 

Nickel strike solutions are used primarily to obtain good adhesion on nickel, stainless steels, and other passive substrates. The most common is... 

Primers for protective coatings may be divided into three broad classes based on the mechanism of substrate protection barrier primers that function by preventing the ingress of moisture and electrolytes, primers that protect the substrate galvanically in the presence of electrolytes, and primers that contain electrochemical inhibitors to passivate the substrate. Each of these approaches requires a distinct primer film structure due to the different mechanisms of protection. 

Fig. 8 shows a primer formulated with a corrosion-inhibiting pigment such as a chromate. As discussed previously, some permeability to moisture is necessary for these pigments to dissolve and be transported to the interface where passivation of the substrate can occur. Optimum performance is generally found at PVC/CPVC Just below 1 [71]. 

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