The adsorption of sodium dodecyl sulfate (SDS) and poly(viny1pyrrolidone) (PVP) at the air/water interface from an aqueous solution containing both components is studied by using the radiotracer technique and surface tension measurements. The increase in surface tension accompanying the conversion of a micellar solution of SDS (in the presence of M NaCI) to a solution containing PVP-SDS assemblies in the bulk phase by the addition of PVP is explained on the basis of desorption of SDS and adsorption of the polymer at the air/water interface. The concentration of SDS at the interface is reduced to 2/3 of the value in the absence of the polymer. The results suggest that SDS and PVP form two-dimensional aggregates at the interface similar in structure to the assemblies in the bulk phase.
IntroductionIn recent years, a number of papers'-3 have dealt with the properties of aqueous solutions containing a mixture of nonionic polymer and anionic surfactant. The most widely studied systems have been those containing poly(ethy1ene oxide) (PEO) and sodium dodecyl sulfate (SDS) or poly(vinylpyrro1idone) (PVP) and SDS. The changes occurring in bulk water upon the addition of PVP or PEO to a micellar solution of SDS are now well-characterized in terms of the structure of the polymer-surfactant complex that is formed and also in terms of the distribution of surfactant between the monomer or free amphiphile state and the aggregate ~t a t e .~*~ In contrast, no attempt has been made to
The effect of rapid thermal annealing ͑RTA͒ temperature on the formation of the cobalt silicide ͑CoSi͒ was investigated using x-ray photoelectron spectroscopy ͑XPS͒ and micro Raman spectroscopy. With 125 Å of Co deposited on single-crystalline Si wafers and capped by a Ti thin film, the wafers were rapid thermal annealed at 450, 460, 470, 480, and 490°C. These wafers were then stripped with a sulfuric acid peroxide mixture treatment. XPS was used to determine the chemical composition of the CoSi thin films, and the Co Auger parameter was continuously monitored along with ion sputtering to provide a chemical-state depth profile. Micro-Raman spectroscopy was used as a nondestructive method to characterize the film thickness and uniformity of the CoSi thin films on Si wafers. The Raman shifts at 204 and 220 cm Ϫ1 due to CoSi and the Raman shift at 150 cm Ϫ1 due to Co 2 Si are reported. The product ␣d (␣ is the absorption coefficient, d is the film thickness͒, which indicates the CoSi film thickness, was calculated from the Si excitation wavelength of 520 cm 1 . The behavior of the calculated ␣d as a function of the RTA temperature confirms the XPS result.
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