Humidity thin films

Fig. 10. Schematic of casting machine used to make microporous membranes by watervapor imbibition. A casting solution is deposited as a thin film on a moving stainless steel belt. The film passes through a series of humid and dry chambers, where the solvent evaporates from the solution, and water vapor is absorbed from the air. This precipitates the polymer, forming a microporous membrane that is taken up on a collection roU (25).

Eastman and Zhn [52] performed a study of SisN4 tips, subsequently coated with gold and finally with paraffin thin films, adhering to mica. The study was purely qualitative, because they did not have accnrate valnes for either their lever stiffnesses or their tip radii. By enclosing their AEM in a sealed container and controlling the humidity they found that hydrophobic tips show a lower adhesion with a surface expected to have a thin water film, as also observed by Jarvis and Pethica [51]. Surprisingly they did not see any dependence of adhesion on hnmidity for any of their tips. 

H20, humidity Capacitive polmyer sensors and ceramic sensors Thin film technology and thick film technology... 

Weatherfastness tests on coatings have shown that prolonging the dry and wet periods, i.e., extending the usual 17 minute dry cycle to a full 102 minutes and the wet period to 18 minutes, affords results which correlate much better with the Florida outdoor exposure tests. The humidity that penetrates a layer is known to interact with the various components in the coating, adversely affecting the mechanical properties of the material. The above mentioned cycle apparently corresponds much better with the climatic conditions in areas like Florida. If recirculated water is used in accelerated exposure equipment, suspended particles may adhere to the surface of the coating, producing a thin film. This obviously has a detrimental effect on the test results. 

The weathering of alt-PRC in a weathering chamber was the subject of a further decomposition study, and the results are very relevant for the use of PPC in outdoor applications [23]. A thin film of PPC on a glass substrate was used and subjected to a temperature of 63°C, humidity of 50%, and light of 250-800 nm with an energy of 550 W/m. It was found that the molecular weight decreased by chain scission... 

Carbon surfaces of various types have been the subject of most studies. However, other types of surfaces, including alumina, fly ash, dust, MgO, V2Os, Fe203, and Mn02, have also been shown to oxidize S02 and/or remove it from the gas phase (Hulett et al., 1972 Judeikis et al., 1978 Liberti et al., 1978 Barbaray et al., 1977, 1978 Halstead et al., 1990). As expected, the rate of removal depends on the nature of the particular surface, the presence of copollutants such as N02, and, as in the case of carbonaceous surfaces, the relative humidity. The increase with increasing water vapor suggests that oxidation of the S02 may occur in a thin film of water on the surface of the solid. 

Pitts et al. (1985) first used differential optical absorption spectrometry (DOAS) to establish unequivocally that N02 injected into a mobile home forms HONO. Interestingly, the dependence of the rate of HONO generation on the N02 concentration was similar to that measured in laboratory systems, consistent with production in, or on, a thin film of water adsorbed on surfaces. A number of studies have confirmed that the behavior is similar to that in laboratory systems i.e., the rate of production of HONO increases with N02 and with relative humidity. Indoor levels of HONO as high as 8 ppb as a 24-h average and 40 ppb as a 6-h... 

The effect of humidity on conductivity of thin films of poly(dG)-poly(dC) and poly(dA)-poly(dT) in air was also investigated. It was found that above 20% relative humidity (RH) the conductance increases exponentially with RH [68]. It was concluded that the resistance of the films is not determined by that of the DNA, but rather by conduction through the hydration layers surrounding the DNA molecules in the film [68]. 

Aqueous corrosion can occur even when the metallic object to be protected is ostensibly not immersed in water, if the relative humidity of the atmosphere exceeds 60%. In that case, a film of water will in fact be present on the metal surface. Further, if sulfur dioxide is present in the air, corrosion in the thin film of water will be greatly accelerated, partly because the acidity of the dissolved SO2 facilitates the oxygen absorption reaction... 

Miyoshi, S. Sugihara, T. Jinda, A. Hijikigama, H. "Thin Film Humidity Sensor Composed of Cross-Linked Poly el ectroly te", pp. 451-456, ibid. 

Also polymers which are not lithographically active have shown some useful properties. STM has been used to produce from 0.5 to 2 nm sized structures in thin films of polyvinyl alcohol [456]. The structures were shown to depend strongly on the relative humidity and their origin might involve electrochemical reactions. 

L. Sabbatini, and P. G. Zambonin, NTCDA organic thin-film transistor as humidity sensor weaknesses and strengths , Sensors And Actuators B -Chemical 77, 7 (2001). 

H. Moon, H. E. Katz, and Z. Bao, Humidity effect on electrical performance of organic thin film transistors , Applied Physics Letters... 

Z.-T. Zhu, J. T. Mason, R. Dieckmann, and G. G. Maeeiaras, Humidity sensors based on pentacene thin-film transistors ,... 

In this paragraph we will briefly discuss the stability behavior of silicon thin film solar cells. Two aspects were considered light induced degradation and stability in hot and humid environment. 

Reliable stability data of the p-i-n solar cell itself are not easily obtained, especially for non-encapsulated cells or modules. One of these tests e.g. for EN/IEC 61646 certification of modules is the so-called damp-heat test (85°C, 85% humidity, up to lOOOh). Recent studies were performed by Stiebig et al. [50, 51] exposing different types of cells to harsh conditions. One of the most important results was the excellent stability of silicon thin film solar cells. Remarkably, this is also valid for small area modules even without encapsulation [52]. This is of high interest because costs and efforts for module encapsulation strongly depend on the inherent stability of the solar cells. As a more detailed treatment of this subject is beyond the scope of this chapter, the reader is referred to the original papers [50,51]. 

Even if some polymers might be hydrophobic in the bulk, concerns about possible water adsorption effects in thin films are justified, because of the preponderant role of the interface in confinement. For example, negligible water adsorption is reported in the handbook of polymers for polystyrene in the bulk 0.05% at 23 °C and 50% relative humidity. In spite of this, strong water adsorption-desorption effects were observed in thin polystyrene films the dielectric loss decreased with more than one decade when a thin film was measured in a dry nitrogen atmosphere and after 2 horns of annealing at 135 °C (Fig. 9, example for a film thickness of 223 nm). A pronounced decrease of s ( 20% at 1 Hz) was detected as well. 

These compounds tend to be hydroscopic and must be stored in tightly closed containers. High humidity will interfere with cure, particularly in thin films. The slow cure can be overcome by the addition of bisphenol A, which acts as an acid accelerator. 

Polvimide-Metal Interfaces. Several technological applications including semiconductor packaging and metallization demand a reliable and durable adhesion properties of the metal films. In the development of multilayer devices consist of alternating layers of metal and polyimides several reliable techniques are needed to study both thin films and their interfaces. The usefulness of the nuclear scattering techniques to study the metallization and the associated interfacial elemental diffusion processes under the effects of various temperature and humidity treatments on the metal-polyimide systems, such as Al, Cu, N, and Au on Du Pont Kapton type H have already been reported (21., 22.). Only a couple of examples are presented here to illustrate the ERD application. 

Conventional humidity sensors of the electric resistance variable type use hydrocarbon polyelectrolyte as a moisture sensing material. Therefore, the sensors usually have insufficient heat resistance, and cannot be used at temperatures of 60°C or more. Another problem is that they deteriorate when in contact with cigarette smoke and oil contained in the air [64,65]. When the fluorinated pitch-deposited coating was breathed upon, the electrical resistance quickly decreased, but electrical resistance quickly recovered when this action was stopped. Then, how to develop a humidity sensor excelling in humidity response sensitivity, heat resistance and durability was attempted [66]. Two kinds of comb-like electrodes with different electrode gaps were made, and a thin film was formed on the surfaces by vacuum deposition of fluorinated pitch. The obtained fluorinated pitch sensors were left at rest in a thermostatic chamber, and electrical resistance was determined under the following conditions. 

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