This work entails a comparative study of both Li and synthetic graphite electrodes in electrolyte solutions based on ethylene and dimethyl carbonates (EC-DMC) and the impact of the salt used [from the LiAsF,, LiC1O4, LiPF,, LiBF4, and LiN(SO2CF3)2 listi. The presence of some additives in solutions (e.g., Li2CO3, C02, tributylamine) and the effect of the particle size of the carbon on the electrode's behavior were investigated. The correlation between the surface chemistry, the morphology, and the performance of Li and graphite electrodes was explored using surface sensitive Fourier transform infrared and x-ray and photoelectron spectroscopies, impedance spectroscopy, x-ray diffraction and scanning electron microscopy in conjunction with standard electrochemical techniques. Synthetic graphite anodes could be cycled (Li intercalation-deintercalation) hundreds of times at a capacity close to the optimal (x -1 in LiC6) in EC-DMC solutions due to the formation of highly stable and passivating surface films in which EC reduction products such as (CH2OCO2Li), are the major constituents. The cycling efficiency of Li metal anodes in these solutions, however, is lower than that obtained in ethereal solutions and seems to be too low for Li-metal liquid electrolyte, rechargeable battery application. The connection between the solution composition and the electrode's performance is discussed.

Recently, milligram quantities of MoS2 fullerene-like nanotubes and negative curvature polyhedra (generically called inorganic fullerene-like material, IF), were reproducibly obtained by a gas phase reaction from an oxide precursor (Feldman, Y.; Wasserman, E.; Srolovitz, D. J.; Tenne, R. Science 1995, 267, 222. Srolovitz, D. J.; Safran, S. A.; Homyonfer, M.; Tenne, R. Phys. Rev. Lett. 1995, 74, 1778). The present work focuses on the mechanism of the synthesis of IF-MS2 (M = W, Mo). The IF material is obtained from oxide particles smaller than ca. 0.2 μm, while larger oxide particles result in 2H-MS2 platelets. The key step in the reaction mechanism is the formation of a closed layer of MS2, which isolates the nanoparticle from its surroundings and prevents its fusion into larger particles. Subsequently, the oxide core of the nanoparticle is progressively converted into a sulfide nanoparticle with an empty core (IF). Taking advantage of this process, we report here a routine for the fabrication of macroscopic quantities of a pure IF-WS2 phase with a very high yield. As anticipated, the size distribution of the IF material is determined by the size distribution of the oxide precursor. The present synthesis paves the way for a systematic study of these materials which are promising candidates for, e.g., solid lubrication.

Li electrodes prepared in situ in solutions and then stored in them for different periods were studied by X-ray photoelectron spectroscopy (XPS) including depth profiling performed by argon sputtering followed by XPS. A set of solvents, propylene carbonate (PC), ethylene carbonate (EC)−dimethyl carbonate (DMC) mixtures, and 1,3-dioxolane, and a set of salts, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiC(SO2CF3)3, were investigated with respect to the effect of storage time. The results of this study were compared with previous studies of Li electrodes in the same solutions by in situ and ex situ Fourier transform infrared spectroscopy. Basically, the results thus obtained are in line with the previous studies. The Li surface chemistry is dominated by solvent reactions. However, all the above salt anions are also reduced to form insoluble species which also contribute to the build-up of the surface films (e.g., the salt anions of the type MF y - (M = As, P, B) are reduced to LiF and species of the Li x MF z type). The surface reactions of these solvents and the salts on Li are discussed in detail. Depth profiling of the surface films formed on Li in solutions indicates that they have a multilayer structure. The concentration of the organic salts in the surface layers decreases as the layer is closer to the Li−film interface.

Active control over the shape, composition, and crystalline habit of nanocrystals has long been a goal. Various methods have been shown to enable postsynthesis modification of nanoparticles, including the use of the Kirkendall effect, galvanic replacement, and cation or anion exchange, all taking advantage of enhanced solid-state diffusion on the nanoscale. In all these processes, however, alteration of the nanoparticles requires introduction of new precursor materials. Here we show that for cesium lead halide perovskite nanoparticles, a reversible structural and compositional change can be induced at room temperature solely by modification of the ligand shell composition in solution. The reversible transformation of cubic CsPbX3 nanocrystals to rhombohedral Cs4PbX6 nanocrystals is achieved by controlling the ratio of oleylamine to oleic acid capping molecules. High-resolution transmission electron microscopy investigation of Cs4PbX6 reveals the growth habit of the rhombohedral crystal structure is composed of a zero-dimensional layered network of isolated PbX6 octahedra separated by Cs cation planes. The reversible transformation between the two phases involves an exfoliation and recrystalliztion process. This scheme enables fabrication of high-purity monodispersed Cs4PbX6 nanoparticles with controlled sizes. Also, depending on the final size of the Cs4PbX6 nanoparticles as tuned by the reaction time, the back reaction yields CsPbX3 nanoplatelets with a controlled thickness. In addition, detailed surface analysis provides insight into the impact of the ligand composition on surface stabilization that, consecutively, acts as the driving force in phase and shape transformations in cesium lead halide perovskites.

The damage caused to amphiphilic n-alkane monolayers under XPS measurement conditions was assessed in a combined XPS-FTIR study supplemented by additional AFM imaging and contact angle measurements. Nine different self-assembled monolayer/substrate systems were examined, comprising a long chain silane (C18, OTS), a short chain silane (C1, MTS), a functional (COOH-terminated) long chain silane (C18, NTSox), a long chain carboxylic acid (C20, AA), and four different solid substrates (silicon, quartz, glass, and ZnSe). Significant differences were observed in the behavior of the various examined monolayer systems under identical X-ray irradiation conditions. These are interpreted in terms of effects associated with the specific mode of layer-to-surface and intralayer coupling, the size of the monolayer hydrocarbon core, and the presence of radiation-sensitive functional groups in the layer. All these factors and their influence on the degradation path followed by a particular monolayer upon exposure to the X-rays were found to be interrelated, giving rise to a variety of possible damage patterns, including an unexpected overall stabilization effect initiated by the preferential rapid loss of a labile top functional group (NTSox). XPS is shown to be insufficient as a tool for the evaluation of the radiation-induced damage in such ultrathin films, because of its insensitivity to loss of hydrogen and to structural transformations that occur without a net loss of carbon from the surface. Independent methods of surface analysis (mainly FTIR), applied in conjunction with XPS, provide a more comprehensive picture of the induced damage, thus permitting a realistic interpretation of the XPS experimental data as well as the design of improved data acquisition procedures. This could also assist in the tailoring of monolayers with predetermined degradability, for specific purposes. Finally, results of combined AFM-XPS-FTIR-contact angle measurements suggest the possible formation of a “diamond-like” surface film upon extensive X-ray irradiation of an OTS/Si monolayer.

Suberin, a polymer composed of both aliphatic and aromatic domains, is deposited as a rough matrix upon plant surface damage and during normal growth in the root endodermis, bark, specialized organs (e.g., potato [Solanum tuberosum] tubers), and seed coats. To identify genes associated with the developmental control of suberin deposition, we investigated the chemical composition and transcriptomes of suberized tomato (Solanum lycopersicum) and russet apple (Malus x domestica) fruit surfaces. Consequently, a gene expression signature for suberin polymer assembly was revealed that is highly conserved in angiosperms. Seed permeability assays of knockout mutants corresponding to signature genes revealed regulatory proteins (i.e., AtMYB9 and AtMYB107) required for suberin assembly in the Arabidopsis thaliana seed coat. Seeds of myb107 and myb9 Arabidopsis mutants displayed a significant reduction in suberin monomers and altered levels of other seed coat-associated metabolites. They also exhibited increased permeability, and lower germination capacities under osmotic and salt stress. AtMYB9 and AtMYB107 appear to synchronize the transcriptional induction of aliphatic and aromatic monomer biosynthesis and transport and suberin polymerization in the seed outer integument layer. Collectively, our findings establish a regulatory system controlling developmentally deposited suberin, which likely differs from the one of stressinduced polymer assembly recognized to date.

Li samples were freshly prepared (shearing) and stored (2 days) in dimethyl carbonate (DMC), and ethyl carbonate-diethyl carbonate (EC-DEC), and dry (20 ppm of H2O) and wet (500 ppm of H2O) EC-DMC solutions of LiAsF6 (1 M), and were then studied by X-ray photoelectron spectroscopy (XPS). The XPS analysis, including depth profiling of these surface films, appears to be reliable on the qualitative level only, because both the X-ray beam and sputtering should be suspected as being partially destructive to the surface films on lithium. These studies basically confirm previous conclusions obtained by Fourier transform infrared spectroscopy spectroscopic studies of Li surfaces. Surface films formed on Li in alkyl carbonate solutions of LiAsF6 are comprised of ROCO2Li, Li2CO3, LiF, LixAsFy, and Li oxides. XPS could also detect surface species with Li-C bonds (e.g., LiCH2CH2OCO2Li). When EC is present, its reduction dominates the surface film formation. The presence of water suppresses both solvent and salt anion reduction and enriches the surface films with Li2CO3 (because of secondary reactions of water with surface species), LiOH, and Li2O. These studies also confirm that the surface films formed on Li have a multilayer structure.

Experimental evidence derived from a comprehensive study of a self-assembled organosilane multilayer film system undergoing a process of postassembly chemical modification that affects interlayer-located polar groups of the constituent molecules while preserving its overall molecular architecture allows a quantitative evaluation of both the degree of intralayer polymerization and that of interlayer covalent bonding of the silane headgroups in a highly ordered layer assembly of this type. The investigated system consists of a layer-by-layer assembled multilayer of a bifunctional n-alkyl silane with terminal alcohol group that is in situ converted, via a wet chemical oxidation process conducted on the entire multilayer, to the corresponding carboxylic acid function. A combined chemical-structural analysis of data furnished by four different techniques, Fourier transform infrared spectroscopy (FTIR), synchrotron X-ray scattering, X-ray photoelectron spectroscopy (XPS), and contact angle measurements, demonstrates that the highly ordered 3D molecular arrangement of the initial alcohol-silane multilayer stack is well preserved upon virtually quantitative conversion of the alcohol to carboxylic acid and the concomitant irreversible cleavage of interlayer covalent bonds. Thus, the correlation of quantitative chemical and structural data obtained from such unreacted and fully reacted film samples offers an unprecedented experimental framework within which it becomes possible to differentiate between intralayer and interlayer covalent bonding. In addition, the use of a sufficiently thick multilayer effectively eliminates the interfering contributions of the underlying silicon oxide substrate to both the X-ray scattering and XPS data. The present findings contribute a firm experimental basis to the elucidation of the self-assembly mechanism, the molecular organization, and the modes and dynamics of intra- and interlayer bonding prevailing in highly ordered organosilane films; with further implications for the rational exploitation of some of the unique options such supramolecular surface entities can offer in the advancement of a chemical nanofabrication methodology.