Structure of mono- and multilayer Langmuir–Blodgett films from Cd arachidate and Ca arachidate

Abstract

Langmuir-Blodgett (LB) films of Cd arachidate and Ca arachidate with thicknesses of 1, 3, 9, and 25 layers were investigated using near edge x-ray absorption fine structure (NEXAFS spectroscopy), small angle x-ray scattering (SAXS), and reflected high energy electron diffraction (RHEED). The results from the x-ray diffraction experiments on layer thickness and interface roughness complement the structural information from NEXAFS on the average tilt angle of the alkyl chains in real space. The RHEED measurements confirm these findings and give additional information on the lateral order in these organic films. We find that the monolayer film shows a substantial degree of disorder, while for three and more LB layers, the molecular orientation is virtually identical to that of the corresponding fatty acid salts, i.e., the hydrocarbon chains are oriented perpendicular to the substrate surface in an all-trans conformation. Furthermore, a simplified and more robust analysis scheme for NEXAFS data obtained for hydrocarbon chains is presented. 7722

Self-Assembled Monolayers of Alkylammonium Ions on Mica: Direct Determination of the Orientation of the Alkyl Chains

“…1 by determining the intensity of the corresponding resonance as a function of the angle of incidence, , this approach is unfavorable in the case of alkyl chains. It requires the decomposition of the spectra into their components by fitting the ionization step and the various transitions (36) and is very sensitive to the exact energy position of the step and an angular independent background (38). The evaluation scheme adopted in this work avoids these problems (27,38).…”

“…where C is a constant that is determined by the degree of polarization, P, physical properties of the adsorbate, and machine specific values (27,38). C is derived from a "standard" (reference system) with a known tilt angle.…”

“…It requires the decomposition of the spectra into their components by fitting the ionization step and the various transitions (36) and is very sensitive to the exact energy position of the step and an angular independent background (38). The evaluation scheme adopted in this work avoids these problems (27,38). Difference spectra of the spectra at the various angles of incidence and a fixed reference angle of incidence, here r ϭ 50°, are taken for each data series, eliminating the isotropic background and the ionization step.…”

“…Difference spectra of the spectra at the various angles of incidence and a fixed reference angle of incidence, here r ϭ 50°, are taken for each data series, eliminating the isotropic background and the ionization step. The difference peaks are then integrated numerically (38). The difference intensities depend on the tilt angles, ␣, of the orbitals according to…”

Amine species on self‐assembled monolayers of ω‐aminothiolates on gold as identified by XPS and NEXAFS spectroscopy

“…All characterised SAMs proved to show the linear dichroism. By using the well-established procedure [11,13,17,18] and the CH * resonance intensity variation vs incident angle of light, a mean tilt angle of 48…”