The commonly accepted Stranski-Krastanow model, according to which island formation occurs on top of a wetting layer ͑WL͒ of a certain thickness, predicts for the morphological evolution an increasing island aspect ratio with volume. We report on an apparent violation of this thermodynamic understanding of island growth with deposition. In order to investigate the actual onset of three-dimensional islanding and the critical WL thickness in the Ge/Si͑001͒ system, a key issue is controlling the Ge deposition with extremely high resolution ͓0.025 monolayer ͑ML͔͒. Atomic force microscopy and photoluminescence measurements on samples covering the deposition range 1.75-6.1 ML, taken along a Ge deposition gradient on 4 in. Si substrates and at different growth temperatures ͑T g ͒, surprisingly reveal that for T g Ͼ 675°C steeper multifaceted domes apparently nucleate prior to shallow ͕105͖-faceted pyramids, in a narrow commonly overlooked deposition range. The puzzling experimental findings are explained by a quantitative modeling of the total energy with deposition. We accurately matched ab initio calculations of layer and surface energies to finite-element method simulations of the elastic energy in islands, in order to compare the thermodynamic stability of different island shapes with respect to an increasing WL thickness. Close agreement between modeling and experiments is found, pointing out that the sizeable progressive lowering of the surface energy in the first few MLs of the WL reverts the common understanding of the SK growth onset. Strong similarities between islanding in SiGe and III/V systems are highlighted.

Nanoceria redox properties are affected by particle size, particle shape, surface chemistry, and other factors, such as additives that coat the surface, local pH, and ligands that can participate in redox reactions. Each CeO 2 crystal facet has a different chemistry, surface energy, and surface reactivity. Unlike nanoceria's industrial catalytic applications, biological and environment exposures are characterized by high water activity values and relatively high oxygen activity values. Electrochemical data show that oxygen levels, pH, and redox species affect its phase equilibria for solution and dissolution. However, not much is known about how the many and varied redox ligands in environmental and biological systems might affect nanoceria's redox behaviour, the effects of coated surfaces on redox rates and mechanisms, and whether the ceria solid phase undergoes dissolution at physiologically relevant pH and oxygen levels.Research that could answer these questions would improve our understanding of the links between nanoceria's redox performance and its morphology and environmental conditions in the local milieu.(111) FACE Dissociative water adsorption creates two types of hydroxyl on this face, Ce 1 -OH (sitting on top of a cerium atom) and Ce 3 -OH (sitting on top of the intersection of three co-shows the crystal facets investigated, the method, and the typical conditions considered. Several research groups have studied water adsorption 89-94 and hydroxyl stability 95 on nanoceria. Table 4. Computational studies of nanoceria. QCMD = quantum chemical molecular dynamics; DFT = density functional theory; SRPES = synchrotron radiation photoelectron spectroscopy. Condition Crystal facets Method Ref. Low water activity CO adsorption (110), slab

Oxide ionic conductors typically operate at high temperatures, which limits their usefulness. Colossal room-temperature ionic conductivity was recently discovered in multilayers of yttria-stabilized zirconia (YSZ) and SrTiO3. Here we report density-functional calculations that trace the origin of the effect to a combination of lattice-mismatch strain and O-sublattice incompatibility. Strain alone in bulk YSZ enhances O mobility at high temperatures by inducing extreme O disorder. In multilayer structures, O-sublattice incompatibility causes the same extreme disorder at room temperature.

Although regulation makes audit committees responsible for determining and negotiating audit fees, researchers and practitioners express concerns that CFOs continue to control these negotiations. Thus, regulation may give investors a false sense of security regarding auditor independence. We utilize the recent financial crisis and economic recession as an exogenous shock that allows us to shed light on the relative influence of the audit committee and the CFO on fee negotiations. During the recession, we find larger fee reductions in the presence of more powerful CFOs, and smaller fee reductions in the presence of more powerful audit committees. We also find the CFO or the audit committee primarily influences fees when their counterpart is less powerful. Our findings suggest a more complex relationship between the CFO and the audit committee than current regulations recognize and cast doubt on the ability of regulation to force one structure on the negotiation process. Data Availability: Data are available from public sources identified in the text.

The development of methods for controlling the motion and arrangement of molecules adsorbed on a metal surface would provide a powerful tool for the design of molecular electronic devices. Recently, metal phthalocyanines (MPc) have been extensively considered for use in such devices. Here we show that applied electric fields can be used to turn off the diffusivity of iron phthalocyanine (FePc) on Au(111) at fixed temperature, demonstrating a practical and direct method for controlling and potentially patterning FePc layers. Using scanning tunneling microscopy, we show that the diffusivity of FePc on Au(111) is a strong function of temperature and that applied electric fields can be used to retard or enhance molecular diffusion at fixed temperature. Using spin-dependent density-functional calculations, we then explore the origin of this effect, showing that applied fields modify both the molecule-surface binding energies and the molecular diffusion barriers through an interaction with the dipolar Fe-Au adsorption bond. On the basis of these results FePc on Au(111) is a promising candidate system for the development of adaptive molecular device structures.

Formation energies for Ge/Si(100) pyramidal islands are computed combining continuum calculations of strain energy with first-principles-computed strain-dependent surface energies. The strain dependence of surface energy is critically impacted by the presence of strain-induced changes in the Ge {100} surface reconstruction. The appreciable strain dependencies of rebonded-step {105} and dimer-vacancy-line-reconstructed {100} surface energies are estimated to give rise to a significant reduction in the surface contribution to island formation energies.

Degradation mechanisms limiting the electrical reliability of GaN high-electron-mobility transistors (HEMTs) are generally attributed to defect generation by hot-electrons but specific mechanisms for such processes have not been identified. Here we give a model for the generation of active defects by the release of hydrogen atoms that passivate pre-exisiting defects. We report first-principles density-functional calculations of several candidate point defects and their interaction with hydrogen in GaN, under different growth conditions. Candidate precursor point defects in device quality GaN are identified by correlating previously observed trap levels with calculated optical levels. We propose dehydrogenation of point defects as a generic physical mechanism for defect generation in HEMTs under hot-electron stress when the degradation is not spontaneously reversible. Dehydrogenation of point defects explains (1) observed hot electron stress transconductance degradation, (2) increase in yellow luminescence, and opposite threshold voltage shifts in devices where the material was grown under nitrogen- and ammonia-rich conditions.

Ge deposited on Si(100) initially forms heteroepitaxial layers, which grow to a critical thickness of ϳ3 MLs before the appearance of three-dimensional strain relieving structures. Experimental observations reveal that the surface structure of this Ge wetting layer is a dimer vacancy line (DVL) superstructure of the unstrained Ge(100) dimer reconstruction. In the following, the results of first-principles calculations of the thickness dependence of the wetting layer surface excess energy for the c͑4 ϫ 2͒ and 4 ϫ 6 DVL surface reconstructions are reported. These results predict a wetting layer critical thickness of ϳ3 MLs, which is largely unaffected by the presence of dimer vacancy lines. The 4 ϫ 6 DVL reconstruction is found to be thermodynamically stable with respect to the c͑4 ϫ 2͒ structure for wetting layers at least 2 ML thick. A strong correlation between the fraction of total surface induced deformation present in the substrate and the thickness dependence of wetting layer surface energy is also shown.