Investigations of pH-dependent domain structure of lead arachidate Langmuir-Blodgett films by means of x-ray specular and diffuse scattering and atomic force microscopy

Abstract

Articles you may be interested inEffect of subphase pH on Langmuir-Blodgett deposition of graphene oxide monolayers on Si and SiO 2 /Si substrates AIP Conf.Langmuir-Blodgett ͑LB͒ multilayer systems are found to be inhomogeneous in morphology and structure. The most characteristic feature of these multilayer films is the appearance of three-dimensional domains in which the molecules arrange themselves as a result of the film transfer onto the substrate. A series of lead arachidate (PbA 2 ) LB multilayers have been prepared as model systems to study the dependence of film morphology on the pH value in the subphase. Atomic force microscopy ͑AFM͒ and two different x-ray scattering methods ͓specular ͑XSR͒ and diffuse ͑XDS͒ x-ray reflectometry͔ have been used to investigate the intrinsic interface properties, such as the vertical electron density profile and lateral distribution of head groups and chains, as well as the microscopic description of the interface structure, thus providing an overall picture of the investigated multilayers. With AFM, discrete height variations of domains with minimum step widths of one double layer independent of the salt concentration in the films were observed. The lateral domain size shows a dependence on pH. It was found to be maximum at pHϭ4.2 ͑pure acid͒ but minimum at pH 7.0 ͑maximum salt content͒. The AFM pictures were treated by a statistical analysis to extract quantities that can be compared with the x-ray results. A considerable number of Bragg maxima were observed in XSR. The vertical correlation length L Z was calculated from the angular width of Bragg maxima along 2 and was found to vary with pH value. It follows, in general, the tendency of the domain sizes, being maximum at pHϭ4.8 and minimum at pHϭ7.0, respectively. The lateral correlation length L X has been evaluated via XDS from the half widths ⌬ measured by rocking the sample across a fixed 2. It decreases for increasing pH. L X was compared with the respective quantity of the AFM analysis. Estimated by XDS, the correlation lengths for inner interfaces and domains complement one another with the lateral length scales resulting from AFM analysis of the surface.

X-ray and Neutron Reflection Analysis of the Structure and the Molecular Exchange Process in Simple and Complex Fatty Acid Salt Langmuir−Blodgett Multilayers

“…Using the formalism introduced in refs and its slope is inversely proportional to the lateral coherence length L x of the height−height fluctuations of the interface roughness σ. σ itself is taken from the slope of the low angle part of the specular reflectivity curve. From the X-ray experiment, we evaluated L x ,x - ray = 8325 ± 250 Å, which is in similar order of magnitude as found by Geue et al for other fatty acid salt multilayers.…”

Application of a pnCCD in X-ray diffraction: a three-dimensional X-ray detector

“…We have measured a multilayer film of Cd arachidate as a test structure. The material is well investigated and consists of thin Cd 2+ layers separated by a double layer made of CH 3 (CH 2 ) 18 COO À amphiphilic molecules (Geue et al, 1999). Each double layer has a vertical lattice spacing of d = 5.4 nm which provides a set of multilayer Bragg peaks whenever Áq z = 2/d is fulfilled (see Fig.…”

Limited Propagation of Lattice Distortion in Trilayer Langmuir–Blodgett Films: Correlation with Mesoscopic Structure

“…The transfer of Langmuir monolayers onto solid substrates using the Langmuir–Blodgett (LB) technique may lead to various useful applications. , However, the structure of the transferred layers may differ from the one observed on the monolayer at the air–water interface. − Indeed, the monolayer over the water surface can be considered as unstrained. Characterization techniques, such as atomic force microscopy (AFM), allow for detecting defects at the mesoscopic scale resulting from possible molecular rearrangements.…”

“…Indeed, holes may be observed in the layers, thus creating new device–air interfaces. The relationship between these defects and the microscopic structure of the transferred monolayers is not obvious, and connection between their observation by AFM (or similar surface-imaging techniques) and film structure experiment has so far received little attention. , Usually, the structure at the molecular scale of LB films is determined by grazing incidence X-ray diffraction (GIXD) experiments. In the usual setup, X-ray beam impinges the surface with an incidence angle set below the critical angle for total internal reflection of the substrate.…”