No abstract

In situ electrochemical atomic force microscopy (ECAFM) was used to study the surface films that form on highly ordered pyrolytic graphite (HOPG) electrodes during cathodic polarization in 1 M LiClO, EC:DMC (1:1) and M LiPF, EC:DMC (1:1) electrolytes. Cyclic voltammetry experiments confirmed that distinct reduction reactions occur when the potential of a fresh HOPG electrode is swept from 2.4 to 0.01.V vs. Li/Li + in a Li/HOPG cell. The reactions appear to be irreversible, since no evidence of corresponding oxidation reactions was observed. ECAFM results, when combined with slow-scan cyclic voltammetry data, suggest that different electrochemical reactions are occurring in these two electrolytes. The deposits were found to be several hundreds of nanometers thick. Auger analysis confirmed the presence of elements consistent with electrolyte reduction products. These observations have implications for understanding the formation of a solid electrolyte interphase on HOPG electrodes in lithium-ion batteries.

Monolayer Langmuir-Blodgett films of a discotic mesogen have been studied with atomic force microscopy (AFM). These measurements confirm the "edge on" arrangement for the disk-shaped molecules suggested by surface pressure-area isotherms and show that the molecules form columns that are separated by 17.7 angstroms +/- 10 percent. Column alignment is found to be predominantly along the film deposition direction, with an angular spread of 35 degrees . The AFM images also show that the mean disk separation within the columns is 5.1 +/- 1.3 angstroms, in good agreement with x-ray diffraction (XRD) results. Roomtemperature XRD measurements on bulk samples of the same material indicate a disordered-hexagonal liquid crystalline mesophase, with a column-to-column spacing of 19.9 +/- 0.2 angstroms.

Atomic force microscopy, a powerful, high-resolution imaging technique for determining the structure of surfaces in gaseous and liquid environments, was used to examine the reactivity of an electropolished surface of a naturally aged aluminum-copper-magnesium alloy (2024-T3) in aqueous hydrochloric acid (0.01, 0.1, and 1 M). When first exposed to acid, the matrix dissolved uniformly. Dissolution then accelerated and pits formed predominately in the vicinity of the secondphase precipitates. The pits developed into characteristic intergranular damage: i.e., elongated pits (incipient corrosion cracks) along grain boundaries. Postexperimental ex situ energy dispersive x-ray analysis and Auger electron spectroscopy were employed to characterize the composition of the various surface features of corroded samples.

We have used pressure-area isotherms, X-ray diffraction, atomic force microscopy, and infrared dichroism to study Langmuir and Langmuir-Blodgett films of 2,3,6,7,10,11-hexaalkoxytriphenylenes which were selectively di-and trifunctionalized with C n H 2n -OH groups at the 2,3-, 2,6-, 3,6-, and 3,6,10-positions. The bulk phase behavior of these compounds was also established with use of polarizing microscopy and differential scanning calorimetry. At the air-water interface, the hydroxy groups make contact with the water, and the Langmuir film stability is strongly correlated with proximity of the hydroxy groups on the molecule. Mixtures of 2,3-and 3,6-isomers display a dramatic increase of the liquid-crystalline mesophase temperature range compared to the pure compounds. The mixtures also have lower molecular areas at the air-water interface and produce thin films with a complex superlattice structure of disk tilts, showing for the first time the ability of triphenylene isomer alloys to self-organize.