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    Pb arachidate Langmuir-Blodgett coatings of silicon wafers: relation between Pb particle density and subphase composition

    Year: 2018

    Journal: Colloid Polym. Sci., Volume 296, APR, page 771–780

    Authors: Klimova, Svetlana A.; Sreij, Ramsia; Bratashov, Daniil; Bookhold, Johannes; Teichert, Niclas; Gorobets, Anna S.; Hellweg, Thomas

    Organizations: German Academic Exchange Service (DAAD) [A/12/86233]

    Keywords: Lead arachidate coatings; Lead inclusions; Langmuir-Blodgett; SEM; AFM; XRR; AES; XRD

    The formation of lead arachidate (Pb(AA)(2)) coatings produced by Langmuir tensiometry (LT) was studied in dependence of lead nitrate (Pb(NO3)(2)) concentration in the aqueous subphase at pH 5.5. The stable Pb(AA)(2) monolayers were transferred to Si wafers and TEM grids at 35 mN/m in the liquid condensed phase of the AA monolayer applying the Langmuir-Blodgett (LB) (ten monolayers) or the Langmuir-Schaefer (LS) technique, respectively. The most homogeneous monolayer was obtained at a Pb(NO3)(2) concentration of 0.1 mM by using the LS method. Most homogeneous films (five bilayers) were obtained for a Pb(NO3)(2) concentration of 0.01 mM by using the LB method. The formed films are investigated by transmission electron microscopy (monolayer produced by LS), X-ray reflectivity (XRR), and atomic force microscopy (films produced by LB). These methods revealed the formation of homogeneously distributed lead inclusions in the formed monolayers and films. Pb aggregates increase in number whereas their average size stays constant at ae 50 nm(2) with increasing Pb(NO3)(2) concentration. Thickness parameters were determined by XRR. With increasing Pb(NO3)(2) concentration, the bilayer thickness was found to increase. Furthermore, the patterns (111) and (200) for a cubic lead structure were found. The experimental results are compared with simulations obtained from geometry optimization on a semi-empirical quantum level to discuss the lead-ion binding to the AA molecules at pH 5.5.
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