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

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

Statistical Analysis and Discovery of Heterogeneous Catalysts Based on Machine Learning from Diverse Published Data

The literature provides insights for catalyst design and discovery. Effective analysis of reported data using machine learning (ML) methods offers the ability to gain valuable information. However, utilizing the literature in this way has obstacles such as lack of compositional overlaps, bias from prior published data, and low sample counts for many elements. The present study describes an ML approach that considers elemental features as input representations instead of inputting catalyst compositions directly. This ML method has the potential for catalyst discovery, including catalytic reactions with limited catalyst composition overlap in the available data. Oxidative coupling of methane (OCM), water gas shift (WGS), and CO oxidation reactions were chosen to confirm the effectiveness of the proposed method by analysis using several state-of-the-art ML methods. Among the ML methods tested, gradient boosting regression with XGBoost (XGB) provided the best results, and prediction accuracy was improved by the proposed approach for all three reaction types. In addition, a quantitative value of "feature importance score" was calculated to evaluate the most influential input variables on catalyst performance. Finally, catalyst optimization was explored using ML as a "surrogate" model, and the top 20 promising candidate catalysts were identified for the OCM reaction based on the optimization. The advantages of ML in catalysis analysis as well as the difficulties and limitations originating from the complexity of heterogeneous catalysis were explored

Topological Investigation of Two-dimensional Amorphous Materials

Real space image data of two-dimensional amorphous networks have become available in high resolution. We review a number of systems regarding ring size distribution, pair correlation function and characteristic structural clusters. We present similarities and differences that can help identify general descriptors for amorphousnes

Atomic structure of a metal-supported two-dimensional germania film

The growth and microscopic characterization of two-dimensional germania films is presented. Germanium oxide monolayer films were grown on Ru(0001) by physical vapor deposition and subsequent annealing in oxygen. We obtain a comprehensive image of the germania film structure by combining intensity-voltage low-energy electron diffraction (I/V-LEED) and ab initio density functional theory (DFT) analysis with atomic-resolution scanning tunneling microscopy (STM) imaging. For benchmarking purposes, the bare Ru(0001) substrate and the (2×2)3O covered Ru(0001) were analyzed with I/V-LEED with respect to previous reports. STM topographic images of the germania film reveal a hexagonal network where the oxygen and germanium atom positions appear in different imaging contrasts. For quantitative LEED, the best agreement has been achieved with DFT structures where the germanium atoms are located preferentially on the top and fcc hollow sites of the Ru(0001) substrate. Moreover, in these atomically flat germania films, local site geometries, i.e., tetrahedral building blocks, ring structures, and domain boundaries, have been identified, indicating possible pathways towards two-dimensional amorphous networks

Atomic structure of a metal-supported two-dimensional germania film

The growth and microscopic characterization of two-dimensional germania films is presented. Germanium oxide monolayer films were grown on Ru(0001) by physical vapor deposition and subsequent annealing in oxygen. We obtain a comprehensive image of the germania film structure by combining intensity-voltage low-energy electron diffraction (I/V-LEED) and ab initio density functional theory (DFT) analysis with atomic-resolution scanning tunneling microscopy (STM) imaging. For benchmarking purposes, the bare Ru(0001) substrate and the (2×2)3O covered Ru(0001) were analyzed with I/V-LEED with respect to previous reports. STM topographic images of the germania film reveal a hexagonal network where the oxygen and germanium atom positions appear in different imaging contrasts. For quantitative LEED, the best agreement has been achieved with DFT structures where the germanium atoms are located preferentially on the top and fcc hollow sites of the Ru(0001) substrate. Moreover, in these atomically flat germania films, local site geometries, i.e., tetrahedral building blocks, ring structures, and domain boundaries, have been identified, indicating possible pathways towards two-dimensional amorphous networks

Determination of Silica and Germania Film Network Structures on Ru(0001) at the Atomic Scale

The detailed structure of silica and germania films supported on Ru(0001) metal substrates are compared to each other. Surface science techniques together with density functional theory calculations have been used to gain insights into the atomic arrangement of these prominent glass-forming materials. The monolayer films of these materials both show predominantly crystalline hexagonal lattices with characteristic domain boundary structures. For the germania monolayer films a large variety of ring elements within domain boundaries have been observed. Density functional calculations predict stronger interaction with the metal substrate for bilayer germania as compared to bilayer silica films. Scanning tunneling microscopy images with atomically resolved structural features have given access to silica and germania bilayer film structures. Both bilayer films form characteristic amorphous ring structures. However, the germania bilayer films appear to be more corrugated, pointing to a stronger interaction with the metal support thus giving rise to slightly different connectivity rules

Bending Rigidity of 2D Silica

A chemically stable bilayers of SiO2 (2D silica) is a new, wide band gap 2D material. Up till now graphene has been the only 2D material where the bending rigidity has been measured. Here we present inelastic helium atom scattering data from 2D silica on Ru(0001) and extract the first bending rigidity, κ, measurements for a nonmonoatomic 2D material of definable thickness. We find a value of κ=8.8  eV±0.5  eV which is of the same order of magnitude as theoretical values in the literature for freestanding crystalline 2D silica