Atomistic models of hydrogenated amorphous silicon nitride from first principles

We present a theoretical study of hydrogenated amorphous silicon nitride (a-SiNx:H), with equal concentrations of Si and N atoms (x=1), for two considerably different densities (2.0 and 3.0 g/cm3). Densities and hydrogen concentration were chosen according to experimental data. Using first-principles molecular-dynamics within density-functional theory the models were generated by cooling from the liquid. Where both models have a short-range order resembling that of crystalline Si3N4 because of their different densities and hydrogen concentrations they show marked differences at longer length scales. The low-density nitride forms a percolating network of voids with the internal surfaces passivated by hydrogen. Although some voids are still present for the high-density nitride, this material has a much denser and uniform space filling. The structure factors reveal some tendency for the nonstoichiometric high-density nitride to phase separate into nitrogen rich and poor areas. For our slowest cooling rate (0.023 K/fs) we obtain models with a modest number of defect states, where the low (high) density nitride favors undercoordinated (overcoordinated) defects. Analysis of the structural defects and electronic density of states shows that there is no direct one-to-one correspondence between the structural defects and states in the gap. There are several structural defects that do not contribute to in-gap states and there are in-gap states that do only have little to no contributions from (atoms in) structural defects. Finally an estimation of the size and cooling rate effects on the amorphous network is reported.

Local spin-flip spectral distribution obtained by resonant x-ray Raman scattering

We show that resonant x-ray Raman (RXR) scattering can be used to study the local spin-flip excitation spectral distribution in magnetically ordered 3d transition-metal compounds. We demonstrate with realistic calculations on the 3p x-ray absorption edge of a Cu^2+ compound and the 2p edge of a Ni^2+ compound that the scattered x-ray energy and intensity distribution contains the excitation spectrum resulting from a single local spin flip, as well as dd excitations accompanied by local spin flip satellites. We develop the theory describing this effect and discuss the polarization conditions that can be used to observe these effects

Reversed spin polarization at the Co(001)-HfO2(001) interface

Ab initio electronic-structure calculations on the Co(001)-HfO2(001) interface are reported. The spin polarization of conduction electrons is positive at the interface, i.e., it is reversed with respect to the spin polarization in bulk Co. The electronic structure is very sensitive to the interface structure; without atomic relaxations the reversed spin polarization is not found. The possible relation with spin-polarized tunneling and magnetoresistance is discussed

Understanding responsible innovation in small producers’ clusters in Vietnam through Actor Network Theory (ANT)

Innovation is increasingly recognised as an alternative for poverty alleviation in developing countries. However, cases of innovation in small producers’ clusters in Vietnam imply negative externalities that conflict with today’s notions of sustainable and inclusive development. This article analyses how small producers innovate while taking environmental and social considerations into account through an interactive societal process towards a community network, conceptualised as responsible innovation. Existing multi-faceted theoretical insights do not provide sufficient basis to construct and test explanations. We apply a grounded theory involving Actor-Network Theory (ANT) to seek explanations as to why some small producers behave opportunistically while others acknowledge responsibility for the negative externalities. ANT enables us to see the critical details of the network creation process including the agenda of the key actors, push and pull factors, the type of innovation and the informal institutional context

Understanding Responsible Innovation in Small Producers’ Clusters in Vietnam through Actor Network Theory (ANT)

There is increasing evidence that innovation offers perspectives for poverty alleviation in small producers’ contexts in developing countries. However, innovations sometimes imply additional harmful environmental and social consequences, which are not in line with broader poverty alleviation and sustainable development notions. In this paper, we explore the question how small producers in northern Vietnam, as innovators in a cluster context, innovate and take broader societal considerations into account in the innovation process. We found that traditional institutional theories show a number of shortcomings for our analysis into the multifaceted meta-textual societal process towards responsible innovation. Instead, we applied Actor‐Network Theory (ANT) which describes the shaping of the human interaction in detail providing a better understanding why in some networks innovatorsbehave opportunistically while in others they acknowledge responsibility for harmful innovation outcomes. The ANT lens reveals the role of informal institutions in innovations systems and the role of materiality in network development. Lastly, ANT demonstrates how the creation and falling apart of actor networks is essential in the dynamics of a five‐stage model of the responsible innovation societal process. We conclude with factors and conditions steering the societal process and emerging questions concerning power, allowing human and non-human actants into the network, and the issue whether a network in the responsible innovation zone is also desirable in terms of economic competitiveness

Anomalous behavior of the semiconducting gap in WO3 from first-principles calculations

Several crystal structures of tungsten trioxide have been studied with a first-principles pseudopotential method. The electronic band gap increases significantly with the distortion of the octahedra that are the building blocks of the various crystal structures. Moreover, the tilting of the octahedra in the more complex structures leads to a strong increase of the gap upon compression

Fern spore longevity in saline water: can sea bottom sediments maintain a viable spore bank?

Freshwater and marine sediments often harbor reservoirs of plant diaspores, from which germination and establishment may occur whenever the sediment falls dry. Therewith, they form valuable records of historical interand intraspecific diversity, and are increasingly exploited to facilitate diversity establishment in new or restored nature areas. Yet, while ferns may constitute a considerable part of a vegetation’s diversity and sediments are known to contain fern spores, little is known about their longevity, which may suffer from inundation and - in sea bottoms - salt stress. We tested the potential of ferns to establish from a sea or lake bottom, using experimental studies on spore survival and gametophyte formation, as well as a spore bank analysis on sediments from a former Dutch inland sea. Our experimental results revealed clear differences among species. For Asplenium scolopendrium and Gymnocarpium dryopteris, spore germination was not affected by inundated storage alone, but decreased with rising salt concentrations. In contrast, for Asplenium trichomanes subsp. quadrivalens germination decreased following inundation, but not in response to salt. Germination rates decreased with time of storage in saline water. Smaller and less viable gametophytes were produced when saline storage lasted for a year. Effects on germination and gametophyte development clearly differed among genotypes of A. scolopendrium. Spore bank analyses detected no viable spores in marine sediment layers. Only two very small gametophytes (identified as Thelypteris palustris via DNA barcoding) emerged from freshwater sediments. Both died before maturation. We conclude that marine, and likely even freshwater sediments, will generally be of little value for long-term storage of fern diversity. The development of any fern vegetation on a former sea floor will depend heavily on the deposition of spores onto the drained land by natural or artificial means of dispersal

Pilot genetische analyse van verspreidingspatronen bij muskusratten

Voor het optimaliseren van het beheer van de muskusrat (Ondatra zibethicus) in Nederland, en het aansturen van gerichte bestrijding per (deel)regio, is het van grote waarde om de migratiepatronen en migratie-afstanden van deze soort beter te begrijpen. Genetische analyse kan daar in veel gevallen beter zicht op geven, maar voor de muskusratten in Nederland was onduidelijk of voldoende verschillen tussen individuen en regio’s aanwezig zijn om deze methode echt bruikbaar te maken.Deze notitie beschrijft de resultaten van een pilot, waarbij voor 90 dieren van verspreide herkomst een genetisch profiel werd opgesteld op basis van een groot aantal SNP (single nucleotide polymorfism) DNA-merkers. De resultaten laten zien dat het goed mogelijk is om individuele dieren uit elkaar te houden, en dat duidelijke ruimtelijke verschillen in aanwezig zijn, al lijkt geen sprake van duidelijk afgebakende subpopulaties maar meer geleidelijke overgangen als gevolg van uitwisseling over afstanden van meestal enkele kilometers. Op basis van de resultaten verwachten we dat het haalbaar is om, via een vervolgstudie met meer monsters die beter overlappen met het huidige verspreidingsgebied in Nederland, meer zicht te krijgen op o.a.: de plekken in het landschap die fungeren als opening of barrière voor migratie, de meest gebruikte dispersieroutes naar en binnen Nederland, de afstand waarover dieren verspreiden, en kunnen helpen bij een betere afbakening van effectieve bestrijdingsregios.We verwachten dat een dergelijk onderzoek op verschillende manieren zal helpen om een doel van complete verwijdering eerder te behalen, namelijk via: meer mogelijkheid om gerichter te werken, betere onderbouwing van het gesprek met zowel Nederlandse betrokkenen als ook met buurlanden, en via verhoging van de motivatie bij bestrijders

In situ XPS analysis of various iron oxide films grown by NO2-assisted molecular-beam epitaxy

We report on a systematic analysis of x-ray photoelectron spectroscopy (XPS) core- and valence-level spectra of clean and well-characterized iron oxide films, i.e., a-Fe2O3, y-Fe2O3, Fe3- dO4, and Fe3O4. All iron oxide films were prepared epitaxially by NO2-assisted molecular-beam epitaxy on single crystalline MgO(100) and a-Al2O3(0001) substrates. The phase and stoichiometry of the films were controlled precisely by adjusting the NO2 pressure during growth. The XPS spectrum of each oxide clearly showed satellite structures. These satellite structures were simulated using a cluster-model calculation, which could well reproduce the observed structures by considering the systematic changes in both the Fe 3d to O 2p hybridization and the d-d electron-correlation energy. The small difference in the satellite structures between a-Fe2O3 and y-Fe2O3 resulted mainly from changes in the Fe-O hybridization parameters, suggesting an increased covalency in g-Fe2O3 compared to a-Fe2O3. With increasing reduction in the y-Fe2O3-Fe3O4 system, the satellite structures in XPS became unresolved. This was not only due to the formation of Fe21 ions, but also to nonhomogeneous changes in the hybridization parameters between octahedral and tetrahedral Fe^3+ ions