From Crystalline to Amorphous Germania Bilayer Films at the Atomic Scale: Preparation and Characterization

A new two-dimensional (2D) germanium dioxide film has been prepared. The film consists of interconnected germania tetrahedral units forming a bilayer structure, weakly coupled to the supporting Pt(111) metal-substrate. Density functional theory calculations predict a stable structure of 558-membered rings for germania films, while for silica films 6-membered rings are preferred. By varying the preparation conditions the degree of order in the germania films is tuned. Crystalline, intermediate ordered and purely amorphous film structures are resolved by analysing scanning tunnelling microscopy images

From Crystalline to Amorphous Germania Bilayer Films at the Atomic Scale: Preparation and Characterization

A new two-dimensional (2D) germanium dioxide film has been prepared. The film consists of interconnected germania tetrahedral units forming a bilayer structure, weakly coupled to the supporting Pt(111) metal-substrate. Density functional theory calculations predict a stable structure of 558-membered rings for germania films, while for silica films 6-membered rings are preferred. By varying the preparation conditions the degree of order in the germania films is tuned. Crystalline, intermediate ordered and purely amorphous film structures are resolved by analysing scanning tunnelling microscopy images

Ultrathin silica films on Pd(111): Structure and adsorption properties

We studied the preparation of thin silica films on Pd(111) using low energy electron diffraction (LEED), infrared reflection-absorption spectroscopy (IRAS), and scanning tunneling microscopy (STM). The films grow from the onset as a double-layer (bilayer) silicate and show no long-range ordering as judged by LEED, thus bearing close similarities to the silicate films grown on a Pt(111) support. The results provide further evidence that the principal structure (monolayer vs bilayer) of ultrathin silica films on metal substrates is primarily governed by the affinity of a metal substrate to oxygen. Individual adsorption of CO and D2 on the prepared films showed that both molecules penetrate through the film and chemisorb on the Pd(111) surface. Density functional theory (DFT) calculations showed that CO bonding on Pd(111) underneath the silica film becomes weaker as compared to the bare Pd(111) surface, but the vibrational frequencies remain unaffected, that is in nice agreement with the experimental results

Distribution of the North American Porcupine (Erethizon dorsatum) in Northern California

Western Wildlife 4:17–28, 2017: The North American Porcupine (Erethizon dorsatum) is one of the most widely distributed mammals in North America, but recent reports have suggested declines in parts of its range in the West. In California, little is known about the historical or current status of the porcupine, and maps of its distribution conflict considerably. Nevertheless, the species is of interest to natural resource managers. For much of the 1900s, foresters and others primarily treated porcupines as pests because of the undesirable damage they inflict feeding on trees and gnawing on manmade items in search of salt. More recently, porcupines have been recognized for their role in promoting forest structure and diversity, and as potential prey for the Fisher (Pekania pennanti). We collected records of porcupine occurrence in the northern part of California since the beginning of the 20th Century, relying on government and private databases, reports from the public, and other sources. These records confirm that porcupines may occur in most major regions and habitat types across northern California, in contrast to many published range maps. The contemporary distribution of porcupines in the state most closely resembles the California Wildlife Habitat Relationships System (CWHR) range map, which is based on projections of suitable habitat. We are unable to offer deeper insight into trends of abundance and possible changes in distribution because these records are likely spatiotemporally correlated with observer effort. This work is a first step and we recommend that a broader statewide effort be conducted to better understand the distribution, abundance, and ecology of North American Porcupines in California. See below or click here to view data

Reduced sintering of mass-selected Au clusters on SiO2 by alloying with Ti: an aberration-corrected STEM and computational study

Au nanoparticles represent the most remarkable example of a size effect in heterogeneous catalysis. However, a major issue hindering the use of Au nanoparticles in technological applications is their rapid sintering. We explore the potential of stabilizing Au nanoclusters on SiO2 by alloying them with a reactive metal, Ti. Mass-selected Au/Ti clusters (400 000 amu) and Au2057 clusters (405 229 amu) were produced with a magnetron sputtering, gas condensation cluster beam source in conjunction with a lateral time-of-flight mass filter, deposited onto a silica support and characterised by XPS and LEIS. The sintering dynamics of mass-selected Au and Au/Ti alloy nanoclusters were investigated in real space and real time with atomic resolution aberration-corrected HAADF-STEM imaging, supported by model DFT calculations. A strong anchoring effect was revealed in the case of the Au/Ti clusters, because of a much increased local interaction with the support (by a factor 5 in the simulations), which strongly inhibits sintering, especially when the clusters are more than ∼0.60 nm apart. Heating the clusters at 100 °C for 1 h in a mixture of O2 and CO, to simulate CO oxidation conditions, led to some segregation in the Au/Ti clusters, but in line with the model computational investigation, Au atoms were still present on the surface. Thus size-selected, deposited nanoalloy Au/Ti clusters appear to be promising candidates for sustainable gold-based nanocatalysis

Habitat determinants of golden‐headed lion tamarin (Leontopithecus chrysomelas) occupancy of cacao agroforests: Gloomy conservation prospects for management intensification

Organismal distributions in human‐modified landscapes largely depend on the capacity of any given species to adapt to changes in habitat structure and quality. The golden‐headed lion tamarin (GHLT; Leontopithecus chrysomelas) is an Endangered primate from the Brazilian Atlantic Forest whose remaining populations occupy heterogeneous landscapes consisting primarily of shade cacao (Theobroma cacao) agroforestry, locally known as cabrucas. This cash crop can coexist with high densities of native tree species and holds a significant proportion of the native fauna, but its widely extolled wildlife‐friendly status is increasingly threatened by management intensification. Although this potentially threatens to reduce the distribution of GHLTs, the main determinants of tamarin's occupancy of cabrucas remain unknown, thereby limiting our ability to design and implement appropriate conservation practices. We surveyed 16 cabruca patches in southern Bahia, Brazil, and used occupancy modeling to identify the best predictors of GHLT patch occupancy. Key explanatory variables included vegetation structure, critical resources, landscape context, human disturbance, and predation pressure. We found a negative relationship between GHLT occupancy and the prevalence of jackfruit trees (Artocarpus heterophylus), which is likely associated with the low representation of other key food species for GHLTs. Conversely, cabrucas retaining large‐diameter canopy trees have a higher probability of GHLT occupancy, likely because these trees provide preferred sleeping sites. Thus, key large tree resources (food and shelter) are currently the main drivers of GHLT occupancy within cabruca agroecosystems. Since both factors can be directly affected by crop management practices, intensification of cabrucas may induce significant habitat impacts on GHLT populations over much of their remaining range‐wide distribution

pH effects on the electrochemical reduction of CO₍₂₎ towards C₂ products on stepped copper

CO2 conversion to reduced products provides a use for greenhouse gases, but reaction complexity stymies mechanistic studies. Here, authors present a microkinetic model for CO2 and CO reduction on copper, based on ab initio simulations, to elucidate pH’s impact on competitive reaction pathways