No abstract

The desorption and interactions of ethylene carbonate (EC) and dimethyl carbonate (DMC) with clean and lithiated graphite substrates were measured by temperature-programmed desorption (TPD) and reaction (TPR) methods under UHV conditions. Both EC and DMC interact weakly with the clean C(0001) surface with adsorption energies of 0.60 ± 0.06 and 0.64 ± 0.05 eV, respectively. Addition of Li+ to the C(0001) substrate significantly increases the binding energies of molecular carbonates, and the range of measured values is indicative of EC solvation of lithium ions. EC undergoes complete decomposition on metallic Li films. Organolithium products were quantified by TPR, and the amount of lithium carbonate product was determined by detailed mass balance analysis. Decomposition of 1.5 L of EC resulted in the formation of 0.64 ± 0.12 L of lithium ethylene dicarbonate, 0.40 ± 0.05 L of lithium ethylene glycolate, and 0.5 ± 0.2 L of lithium carbonate. The branching ratio at the immediate EC–metallic lithium interface was determined as 70.% organolithium products vs 30% inorganic lithium product.

In an effort to understand the reaction mechanisms involved in the adsorption of organic aromatic molecules on high-index Si surfaces, the reactions of pyrrole molecules adsorbed onto Si(5 5 12)À2 Â 1 surfaces were studied using scanning tunneling microscopy and first principle calculations. The dissociation of one or two H atom(s) bonded to N (or N and C) from the pyrrole molecules was favored, and adsorption at adatom, tetramer, dimer, or honeycomb Si(5 5 12)À2 Â 1 sites occurred to produce several distinct configurations. Pyrrole was most reactive toward the dimer site, yielding two dissociated hydrogen atoms and a vertical configuration. Pyrrole also adsorbed onto the tetramer and honeycomb sites, yielding two dissociated hydrogen atoms. On the adatom row, however, pyrrole bound to an adatom via a σ bond between the adatom and N to yield one dissociated H atom adsorbed onto a nearby adatom. No other hydrogen dissociation reactions were observed. In all configurations, the aromaticity of pyrrole was retained.

A carbon-nanotube-enabling scanning probe technique/nanotechnology for manipulating and measuring lithium at the nano/mesoscale is introduced. Scanning Li-nanopipette and probe microscopy (SLi-NPM) is based on a conductive atomic force microscope (AFM) cantilever with an open-ended multi-walled carbon nanotube (MWCNT) affixed to its apex. SLi-NPM operation is demonstrated with a model system consisting of a Li thin film on a Si(111) substrate. By control of bias, separation distance, and contact time, attograms of Li can be controllably pipetted to or from the MWCNT tip. Patterned surface Li features are then directly probed via noncontact AFM measurements with the MWCNT tip. The subsequent decay of Li features is simulated with a mesoscale continuum model, developed here. The Li surface diffusion coefficient for a four (two) Li layer thick film is measured as D=8(±1.2)×10(-15) cm(2) s(-1) (D=1.75(±0.15)×10(-15) cm(2) s(-1)). Dual-Li pipetting/measuring with SLi-NPM enables a broad range of time-dependent Li and nanoelectrode characterization studies of fundamental importance to energy-storage research.