Composition and thickness of surface layer on molybdenum tips for scanning tunnelling microscopy (STM) studied by SEM/AES/(AR)XPS

A combination of SEM, AES and angle-resolved XPS (ARXPS) has been applied to analyse the distribution of chemical compounds in the surface region of electrochemically etched molybdenum tips and to determine the contamination layer thickness. Carbon monoxide, graphite, molybdenum carbide and molybdenum oxide were found to be the main surface contaminants on molybdenum tips. Auger line profiling revealed a significant enrichment of carbon and oxygen upon the tip. The thickness of the oxygen-carbon contamination layer on the tip was estimated to be 13.5 ± 1.0 nm as measured by AES. The thickness of the contamination layer on a molybdenum sheet was found to be 8.0 ± 1.5 and 6.8 nm using AES and ARXPS respectively. Quantitative analysis of the surface concentrations of carbon, oxygen and molybdenum has been performed

Exploring the trade-off between quality and fairness in human partner choice

Partner choice is an important force underpinning cooperation in humans and other animals. Nevertheless, the mechanisms individuals use to evaluate and discriminate among partners who vary across different dimensions are poorly understood. Generally, individuals are expected to prefer partners who are both able and willing to invest in cooperation but how do individuals prioritize the ability over willingness to invest when these characteristics are opposed to one another? We used a modified Dictator Game to tackle this question. Choosers evaluated partners varying in quality (proxied by wealth) and fairness, in conditions when wealth was relatively stable or liable to change. When both partners were equally fair (or unfair), choosers typically preferred the richer partner. Nevertheless, when asked to choose between a rich-stingy and a poor-fair partner, choosers prioritized fairness over wealth—with this preference being particularly pronounced when wealth was unstable. The implications of these findings for real-world partner choice are discussed

Structural and chemical evolution of single-wall carbon nanotubes under atomic and molecular deuterium interaction

The interaction of atomic (D) and molecular (D2) deuterium, as present in a (D + D2) gas mixture, with single-wall carbon nanotubes (SWNTs) has been studied by means of a combination of scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The SWNT samples were exposed to the gas mixture, produced by thermal dissociation of D2 on a hot W filament, its temperature, TW, being kept at 1020 and 1550 K for a deuterium pressure of 0.6 and 60 Pa, respectively. Prolonged interaction of the low-pressure (D + D2) gas mixture produced at TW = 1020 K leads to a conglomeration of the SWNT bundles into larger diameter ropes of square and triangular cross-section, covered by nano-aggregates of graphite material. Both the coalescence of single SWNTs and a massive reconstruction of bundles of SWNTs into a “coral reef”-like structure were found to occur after prolonged exposure of SWNTs to the high-pressure (D + D2) gas mixture produced at TW = 1550 K. This structure is formed by the encapsulated Fe nanoparticles and deuterocarbon-like species appearing as a result of the deuterium interaction with the SWNT bundles accompanied by partial erosion of the SWNT material. The XPS valence-band spectra disclose electronic features characteristic for a hydrogen-plasma modified multi-wall carbon nanotube (MWNT)-like structure as a result of an intensive (D + D2) induced transformation of the SWNTs into the “coral reef”-like structure

In depth compositional analysis of ceramic (Bi2O3)0.75(Er2O3)0.25 by AES and XPS

The chemical composition of dense ceramics of erbia-stabilized δ-Bi2O3 was analyzed by Auger electron spectroscopy (AES) depth profiling using Ar+ ion sputtering. The relative sensitivity factors (rsf) and sputter rates of bismuth and erbium in this material have been determined by electron probe microanalysis (EPMA) and chemical analysis. These results, supplemented by data from angle resolved X-ray photoelectron spectroscopy (ARXPS), shows a bismuth enrichment at the surface. Evidence has been found for reduction of the bismuth-oxide at the outermost part of the surface layer

Structural and chemical characterisation of titanium deuteride films covered by nanoscale evaporated palladium layers

Thin titanium deuteride (TiDy) films, covered by an ultra-thin palladium layer, have been compared with the corresponding titanium and palladium films using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TiDy layers were prepared under ultra-high vacuum (UHV) conditions by precisely controlled deuterium sorption at 298 K on a Ti film evaporated onto a Si(100) substrate. Both Ti and TiDy films were then covered in situ by a nanoscale Pd layer. It was found that a 10- to 12-nm-thick Pd layer protects the TiDy films efficiently against extensive air interaction. The morphology of both the surface and bulk Pd/TiDy (Ti) films have been observed using SEM and cross-sectional TEM analysis, respectively. A polycrystalline bulk morphology in both Ti and TiDy films accompanied by a fine-grained Pd surface was observed. High-magnification cross-sectional TEM images reveal the TiDy film to be plastically deformed leading to an increase in the roughness of the top Pd layer. Complex structures, including Moiré patterns, have been identified within the Pd/TiDy interface. The chemical nature of this interface has been analysed after partial sputtering of the Pd top layer using XPS. Besides TiDy and Pd, TiO and PdO were found to be the main chemical species in the interface region of the Pd/TiHy film. The XPS valence-band spectra of the Pd/TiDy interface reveal electronic features characteristic of a Pd–Ti bimetallic structure

Microstructural and chemical transformation of thin Ti/Pd and TiDy/Pd bi-later films induced by vacuum annealing

Using a combination of scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS), we made a comparative study of the high-temperature annealing impact on thin titanium deuteride (TiD y ) films covered by an ultrathin Pd layer, and on Ti/Pd bilayer films. The bilayer films were prepared under ultrahigh vacuum conditions and were in situ annealed using the same annealing procedure. It was found that the surface and the bulk morphology of both films undergo different annealing-induced transformations, leading to an extensive intermixing between the Ti and Pd layers and the formation of a new PdTi2 bimetallic phase. Energy-filtered TEM imaging and energy-dispersive X-ray spectrometry analysis, as well as XPS depth profiling all provided evidence of a different distribution of Pd and Ti in the annealed TiD y /Pd film compared with the annealed Ti/Pd film. Our results show that thermal decomposition of TiD y , as a consequence of annealing the TiD y /Pd film, modifies the intermixing process, thereby promoting Ti diffusion into the Pd-rich top layer of the TiD y film and thus providing a more likely path for the formation of the PdTi2 phase than in an annealed Ti/Pd fil