Pb arachidate Langmuir-Blodgett coatings of silicon wafers: relation between Pb particle density and subphase composition
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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 ≈ 50 nm2 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.
KeywordsLead arachidate coatings Lead inclusions Langmuir-Blodgett SEM AFM XRR AES XRD
The authors thank Prof. Andreas Hütten for great discussion, Dr. Jan Schmalhorst for AES experiments, and Lars Helmich for X-ray reflectivity experiments. The authors also thank Uwe Güth for help with LB experiments. S.K. gratefully acknowledges funding by the German Academic Exchange Service (DAAD, project No. A/12/86233).
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Conflict of interests
The authors declare that they have no conflicts of interest.
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