Received; accepted 1 Visiting Astronomer, MMT Observatory. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution 2 Visiting Astronomer, Steward Observatory 2.3 m Telescope. ABSTRACTWe present spectra of Eris from the MMT 6.5 meter telescope and Red Channel Spectrograph (5700−9800Å; 5Å pix −1 ) on Mt. Hopkins, AZ, and of Pluto from the Steward Observatory 2.3 meter telescope and Boller and Chivens spectrograph (7100−9400Å; 2Å pix −1 ) on Kitt Peak, AZ. In addition, we present laboratory transmission spectra of methane-nitrogen and methane-argon ice mixtures. By anchoring our analysis in methane and nitrogen solubilities in one another as expressed in the phase diagram of Prokhvatilov & Yantsevich (1983), and comparing methane bands in our Eris and Pluto spectra and methane bands in our laboratory spectra of methane and nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are ∼ 10% and ∼ 90% and Pluto's bulk methane and nitrogen abundances are ∼ 3% and ∼ 97%. Such abundances for Pluto are consistent with values reported in the literature. It appears that the bulk volatile composition of Eris is similar to the bulk volatile composition ofPluto. Both objects appear to be dominated by nitrogen ice. Our analysis also suggests, unlike previous work reported in the literature, that the methane and nitrogen stoichiometry is constant with depth into the surface of Eris. Finally, we point out that our Eris spectrum is also consistent with a laboratory ice mixture consisting of 40% methane and 60% argon. Although we cannot rule out an argon rich surface, it seems more likely that nitrogen is the dominant species on Eris because the nitrogen ice 2.15 µm band is seen in spectra of Pluto and Triton.

We have measured the temperature-dependent onset of strain relief in metastable SijcGei-* strained layers grown on Ge substrates. On the basis of these measurements, and physical arguments, we propose that strained-layer breakdown is most directly determined not by thickness and lattice mismatch, but rather by (l) an "excess" stress (the difference between that due to misfit strain and that due to dislocation line tension) and (2) temperature. With use of these parameters, observed regimes of stability and metastability are shown to be described within a simple, unified framework. PACS numbers: 68.65.+g, 68.55.Bd, 81.40.Lm Strained epitaxial films, first studied theoretically nearly four decades ago, 1 have attracted much interest recently. Partly, this interest stems from observations of structural metastability in films grown by state-of-theart techniques. In this regard, an outstanding question has been how to correlate growth conditions with subsequent structural perfection of the film. The original equilibrium theories of Ball and van der Merwe, 2 Matthews and Blakeslee, 3 and co-workers predicted that, below a critical thickness, lattice mismatch between substrate and film would be accommodated entirely by film strain. Above this thickness, film strain would be partly relieved by misfit dislocations.The pioneering work of Kasper, 4 Bean, 5 and coworkers in the SiGe system showed, however, that under some growth conditions strain in films above the critical thickness is not measurably relieved. Only above a second critical thickness does measurable relief occur, and even then, the amount of relief is not in accord with equilibrium theory. Most recently, the work of Fritz 6 and of Dodson and Tsao 7 suggests that the observed metastability can be explained by sluggish plastic deformation rates accompanied by a finite experimental resolution. The second critical thickness is that for which strain relief is just sufficient to be observable.A full treatment of the kinetics of plastic deformation of thin epitaxial films, however, is nontrivial. Even deformation of bulk materials occurs by a number of complex mechanisms, and little is known about whether deformation in thin films occurs by the same mechanisms. Nevertheless, it is clear that any mechanism must be governed principally by the two parameters shear stress (the driving force for deformation) and temperature. Indeed, for bulk materials, deformation rates can be elegantly expressed with the stress-temperature diagrams (or "deformation mechanism maps") introduced by Frost and Ashby. 8 In this Letter, we argue that the stability and metastability of thin strained layers is determined mainly by the kinetics of plastic deformation and hence is governed by stress and temperature. However, we propose that the stress which actually drives dislocation motion is the difference between the usual stress due to misfit strain and an "effective" stress due to dislocation-line tension. Observable strain relief occurs only if this "excess" stress exceeds a critical value ...

No abstract

Received; accepted 1 Visiting Astronomer, MMT Observatory. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution 2 Visiting Astronomer, NASA IRTF -3 - ABSTRACTWe present three near-infrared spectra of Pluto taken with the IRTF and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model, and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phases − one highly-diluted by nitrogen and the other rich in methane.For Pluto, we find bulk, hemisphere-averaged, methane abundances of 9.1 ± 0.5%, 7.1 ± 0.4%, and 8.2 ± 0.3% for sub-Earth longitudes of 10 • , 125 • , and 257 • . Application of the Wilcoxon rank sum test to our measurements finds these small differences are statistically significant. For Triton, we find bulk, hemisphere-averaged, methane abundances of 5.0 ± 0.1% and 5.3 ± 0.4% for sub-Earth longitudes of 138 • and 314 • . Application of the Wilcoxon rank sum test to our measurements finds the differences are not statistically significant.For Eris, we find a bulk, hemisphere-averaged, methane abundance of 10 ± 2%.Pluto, Triton, and Eris do not exhibit a trend in methane-nitrogen mixing ratio with depth into their surfaces over the few cm range probed by these obser- vations. This result is contrary to the expectation (Grundy & Stansberry 2000)that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth.

X-ray photoelectron spectroscopy (XPS) has been used to investigate the chemical structure of thin polyaniline films grown using a vacuum evaporation process that used chemically prepared polyaniline powder as the starting material. Analysis shows that the as-deposited films are in the completely reduced, leucoemeraldine state. This chemical structure is contrasted with that of the initial and residual powders, which XPS analysis shows are both in a state close to that of protoemeraldine. Thus, the results indicate that the reduction takes place either in the gas phase or, more likely, as a reaction on the surface of the substrate, but does not occur in the quartz crucible as the initial powder is being heated. Results are also presented concerning the oxidation (in pure oxygen and iodine environments) and the protonation (using HCl) of these vapor-deposited polyaniline thin films. Scanning tunneling microscopy was also used to examine the in situ growth of submonolayer coverages of polymer. Evidence for large scale structure growth, possibly resulting from crosslinking of small oligomer components, was observed.

We describe optical spectroscopic observations of the icy dwarf planet Eris with the 6.5-m MMT telescope and the Red Channel Spectrograph. We report a correlation, that is at the edge of statistical significance, between blue shift and albedo at maximum absorption for five methane ice bands. We interpret the correlation as an increasing dilution of methane ice with another ice component, probably nitrogen, with increasing depth into the surface. We suggest a mechanism to explain the apparent increase in nitrogen with depth. Specifically, if we are seeing Eris 50 degrees from pole-on [Brown, M.E., Schaller, L., 2008. Science 316, 1585], the pole we are seeing now at aphelion was in winter darkness at perihelion. Near perihelion, sublimation could have built up atmospheric pressure on the sunlit (summer) hemisphere sufficient to drive winds toward the dark (winter) hemisphere, where the winds would condense. Because nitrogen is more volatile and scarcer than methane, it sublimated from the sunlit hemisphere relatively early in the season, so the early summer atmosphere was nitrogen rich, and so was the ice deposited on the winter pole. Later in the season, much of the nitrogen was exhausted from the summer pole, but there was plenty of methane, which continued to sublimate. At this point, the atmosphere was more depleted in nitrogen, as was the ice freezing out on top of the earlier deposited nitrogen rich ice. Our increasing nitrogen abundance with depth apparently contradicts the Licandro et al. [Licandro, J., Grundy, W.M., Pinilla-Alonso, N., Leisy, P., 2006. Astron. Astrophys. 458, L5-L8] result of a decreasing nitrogen abundance with depth. A comparison of observational, data reduction, and analysis techniques between the two works, suggests the difference between the two works is real. If so, we may be witnessing the signature of weather on Eris. The work reported here is intended to trigger further observational effort by the community.

No abstract

The technique of impact-collision ion-scattering spectrometry (ICISS) was used to study the 4X 1 reconstruction of In on the Si(111) surface. The top layer of adatoms is arranged in double-row ridges, with three equivalent orientations running in (110) directions. Several models have been simulated for both -'-monolayer (ML) and 1-ML coverage of the surface. Our ICISS polar-angle scans do not agree with models containing substitutional In in the first Si layer. Instead, a z-ML model with In adatoms sitting in inequivalent sites provides the closest agreement with experiment. The vertical displacement between the In adatoms and the first Si layer has been determined experimentally to be 1. 15+0.15 A.