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The fabrication of thin organic films covalently grafted onto silicon substrates is of significant interest, as they are expected to give access to a broad range of new materials for integration into microelectronic applications. Covalent layer-by-layer (LbL) assembly offers a high degree of freedom when designing such thin films. In this work an approach for the preparation of covalent redox active molecular multilayers on silicon (100) surfaces is presented using a highly branched decaallylferrocene and thiol-ene click chemistry. The multilayers are analyzed by ellipsometry, X-ray photoelectron sprectroscopy, and cyclic voltammetry. The results indicate that the multilayer growth is linear for at least sixteen layers and the density of ferrocenes per layer is in the range of 6 × 10⁻¹¹ mol cm⁻². Moreover, this method for LbL assembly is extended to surfaces which have been locally passivated by microcontact printing. By atomic force microscopy measurements it is possible to show that the covalent LbL deposition proceeds exclusively in the nonpassivated areas.

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a change in its optical constants during lithiation. However, a quantification of the optical properties and their tailoring via dis/charging has not been probed yet.The present study aims at the quantification of the optical constants, that is, the complex refractive index (CRI) and its change during intercalation by varying the lithium content of Li x Mn 2 O 4 from x = 0 to x = 1. Furthermore, an attempt is made to establish a link between this change in optical constants to the band structure of the material, learned from various sources. [11,15,[18][19][20][21] Similar characteristics have been reported for other electrochromic materials, such as Nb 2 O 5 , WO 3 , V 2 O 5 , and MoO 3, [22] which are known to change their optical properties, namely the real (n) and imaginary (k, or extinction coefficient) part of the CRI during an electrochemical reaction. In these materials, intercalation of charged species results in the generation of different electronic absorption bands in the optical spectrum or insertion of additional bound charges acting as harmonic oscillators. [22] For the present study, the reflection spectrum is measured at different stages of intercalation to clarify such electrochromic phenomenon. The measured spectra are evaluated to extract the CRI of the material for different lithium contents. Furthermore, an innovative method of recording the reflectance spectrum in situ during the electrochemical reaction is demonstrated (Figure 1c) that provides an additional time resolution to the spectrometry. Results Structural CharacterizationThe X-ray diffractogram (XRD) spectra of representative samples of LMO in the as-deposited and annealed states are shown in Figure 2a. No characteristic LMO diffraction peaks are observed for the as-deposited layer (bottom curve of Figure 2a). Only a small hump, observed at 61.98° (marked with *), could be due to the LMO structure corresponding to {440} planes. This reflection is very broad and shifted in comparison to the work of Wickhamt and Croft. [23] (JCP2 database) that predicts the position at 63.78°. The shape and the shift in the reflection suggest that the LMO layer is nanocrystalline and stressed, as it is usually the case for sputter-deposited layers.The optical response of lithium manganese oxide (LiMn 2 O 4 , LMO) on intercalation with Li ions is quantitatively characterized. For this purpose, a layer of LMO and a layer of platinum, acting as current collector/reflector, are deposited on oxidized silicon wafers. The active layer is structurally characterized using X-ray diffractogram and transmission electron microscopy. Well-defined intercalation states are prepared electrochemically and investigated by optical spectrometry in reflectance geometry. The measured dispersion curves are described by the Clausius-Mossotti dispersion equation to derive the complex refractive index as a function of wavelength and intercalation state. The observed variation of the effective resonant wavelength is consistent with the change in the band structure of LMO with l...

Thin film battery electrodes of the olivine structure LiFePO4 and the spinel phase LiMn2O4 are deposited through ion-beam sputtering. The intercalation kinetics is studied by cyclo-voltammetry using variation of the cycling rate over 4 to 5 orders of magnitude. The well-defined layer geometry allows a detailed quantitative analysis. It is shown that LiFePO4 clearly undergoes phase separation during intercalation, although the material is nano-confined and very high charging rates are applied. We present a modified Randles–Sevcik evaluation adapted to phase-separating systems. Both the charging current and the overpotential depend on the film thickness in a systematic way. The analysis yields evidence that the grain boundaries are important short circuit paths for fast transport. They increase the electrochemical active area with increasing layer thickness. Evidence is obtained that the grain boundaries in LiFePO4 have the character of an ion-conductor of vanishing electronic conductivity.

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From x-ray photoelectron spectroscopy (XPS) measurements of thermally evaporated cerium films on polypropylene (PP) we conclude that an ion bombardment pretreatment of the substrate significantly improves the deposited amount of cerium. The metal–polymer interface state is dependent upon the ion bombardment of the PP substrate. For a mild bombardment (Ar+ ions of kinetic energy less than 500 eV and doses less than 1015 ions/cm2) we observed the formation of Ce–C bonds, which are not observed if we apply a more energetic ion bombardment (ions kinetic energy 3 keV, doses≳1016 ions/cm2). The effect of the ion bombardment on the cerium film formation can be summarized in an increased coverage of the polymeric substrate for the same thickness of the cerium film. We find that the cerium film grows with a Volmer–Weber mechanism and the difference between treated and untreated samples consists in an increased coverage of the substrate by cerium for the treated samples. A new kind of plot of the XPS data is used to discriminate between different surface coverages. The XPS measurements have also shown that an oxidation of the cerium films takes place during the XPS measurements. Mass spectrometry of the residual gas composition of the ultrahigh vacuum system, where the XPS measurements are performed, shows that the x-rays induce an outgas of H2, water, OH, CO, and CO2 originating from the polypropylene substrate. Water in the PP is dissociated by x-ray influence and therefore is responsible for the oxidation of the cerium film.