Native oxide adsorption

Experimental studies have been few. Perhaps the most extensive study and certainly one of the few whose authors discussed their results in terms of wetting ideas was carried out by Johnson and Grannick (1991). They used Fourier transform infra-red spectroscopy in the attenuated total reflection mode to study adsorption of polystyrene from cyclohexane on to the native oxide of silicon. For relatively low relative molecular mass (43900) they found an increase in the adsorbed amount as the temperature was reduced towards the cloudpoint temperature their results (shown in figure 5.30) are consistent with... 

Silicon oxide species are also detected in IR spectra after aging PS films in ambient air [233, 240, 252, 253]. However, the native oxide growth on PS can be suppressed by treating the surface in a HF solution [253], The aging of PS layers can also lead to the appearance of absorption bands (2850-3000 cm ) associated with hydrocarbon contamination [237]. Aged samples exhibit a broad IR absorption band in the 3000-3600-cm region due to adsorption of water molecules, giving SiOH complexes [240]. 

Most studies of the adsorption of carboxylic acids on metals have involved surfaces exposed to air prior to adsorption and thus largely refer to adsorption on native oxide overlayers. Allara and Nuzzo [296, 297] studied the adsorption of n-alkanoic (Cg—C24) acids and CHsC- or CH2=CH-terminated alkanoic (C19) acids... 

SAMs on stainless steel are usually application oriented, due to the importance of thin films on stainless steel for corrosion protection and biocompatibility of medical implants. Two basic approaches have been presented, that is, SAM adsorption on reduced, oxide-free stainless steel and adsorption on the stainless steel native oxide. 

One of the reasons why UHV conditions are required in SIMS is that this controls the re-adsorption of gas phase contaminants onto the surface of interest during analysis. Note Such adsorption issues are accelerated over regions experiencing electron (for charge neutralization) or ion impact, particularly if freshly sputtered (a pure Silicon surface, for example, is highly reactive, hence the reason for the native oxide formation that occurs within seconds on air exposure). A particular instance where this is noted is in the analysis of elements present in the gas phase,... 

In some cases a reactive site is needed to initiate desorption. For example, the native oxide on GaAs wafers, typically a gallium oxide, desorbs very abruptly. After considerable study it has been shown that the oxide desorption requires a nucleation step creating holes in the layer. These then expand rapidly as the desorption occurs. The desorption reaction can be nucleated by adsorption of a variety of species on the surface. The desorption temperature also depends somewhat on how the oxide is formed and its thickness. When desorption is nucleation-limited there may be a considerable delay in its onset if it is not significantly superheated. 

The shift of the amide I mode (FTIR spectra) from 1657 to 1646 cm-1 was attributed to a change in the a-helix native structure to fl-sheets, secondary structure conformations. Atomic Force Microscopy (AFM) images display the coating of the manganese oxide surface as well as the unfolding in a ellipsoidal chain of the protein molecules after adsorption and immobilization on the surface. 

Fig. 7. Specific surface area (BET Argon adsorption) of native, organics free and amorphous oxides free samples.

The surface was actually a film of native aluminum oxide it did not adsorb pyridine but did adsorb chloroform showing the oxide to have no acid sites, but basic sites. Treatment of the aluminum oxide with aqueous carbonate solutions clearly enhanced the basicity, as evidenced by stronger adsorption of chloroform. By observing the temperature coefficient of adsorption isotherms with ellipsometry one can actually determine heats of adsorption on a square centimeter of flat surface. 

To avoid inhibition of the enzyme (polymerase) and adsorption of DNA (template and product), surface passivation on the PCR was needed. It was found that native silicon is an inhibitor of PCR and an oxidized silicon (Si02) surface was required to provide the best passivation [943]. 

The crystal structure of a-Cr203 is made up by a hexagonal close-packed lattice of oxide ions (sequence ABAB ) Two-thirds of the octahedral sites are occupied by Cr3+ ions. Possible idealized surface structures, based on the (001), (100), and (101) planes and the creation of surface sites in the form of coordi-natively unsaturated cations and anions on dehydroxylation of the surface, have been discussed by Burwell et al. (21) and by Stone (144). The (001) face is the most likely crystal plane to predominate in the external surface of well-crystallized a-Cr203 (145). A possible surface model that maintains the overall as well as the local electrical neutrality, as proposed by Zecchina et al. (145) for the dehydroxylated (001) face, is shown in Fig. 2a. It can clearly be seen that equal numbers of four- and five-coordinate Cr3+ ions are to be expected on this idealized surface. Dissociative chemisorption of water would lead to the formation of surface OH groups, as shown in Fig. 2b, for a partially hydroxylated model surface. In fact, on adsorption of D20, Zecchina et al. (145) observed OD-stretching fundamental bands at 2700 and 2675 cm-1, which were narrow and isolated. As evidenced by the appearance of a H20 bending band at 1590... 

Ballerini, G., Ogle, K., and Barthes-Labrousse, M.-G.. The acid-base properties of the surface of native zinc oxide layers An XPS study of adsorption of L2-diaminoethane, Appl. Sutf. Sci., 253, 6860, 2007. 

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