Optical and electronic properties of amorphous silicon dioxide by single and double electron spectroscopy

Abstract An investigation of the optical and electronic properties of amorphous silicon dioxide by means of a combination of reflection electron energy loss spectroscopy (REELS) and secondary electron–electron energy loss coincidence spectroscopy (SE2ELCS) is presented. Optical constants for a-SiO2 were extracted from the REELS measurements and a band gap of 9.1 eV was determined by deconvolution of multiple scattering and fitting the differential inverse inelastic mean free path with a model energy loss function (ELF). The coincidence measurements allow to determine the surface barrier height and the electron affinity was determined to be 0.8 eV. Furthermore, the coincidence measurements show that even in the case of an insulator, plasmon decay is the main mechanism for generation of secondary electrons

High frequency acoustic emission monitoring in nano-impact of bulk ceramics

Acoustic Emission (AE) monitoring is proving a powerful technique in improving our understanding of deformation processes occurring at the nano- and micro-scale [1-3]. The recent development of advanced high frequency AE sensor systems and their integration to commercial nanomechanical test instrumentation has been a catalyst for research into damage processes in scratching thin films [2,3]. In recent studies AE detection revealed the onset of cracking otherwise undetectable but subsequently confirmed by FIB sectioning. In this current study the high frequency AE technique has been used to investigate the cracking behavior of bulk technical ceramics (MgO-partially stabilized zirconia (PSZ) and zirconia-toughened alumina (ZTA)) at low strain rate in nanoindentation and at higher strain rate in the nano-impact test. Although both ceramics were susceptible to indentation or impact-induced cracking it was more prevalent on PSZ. The influence of accelerating force and probe geometry were explored in the higher strain rate tests with cube-corner and 5 mm radius spherical diamond indenters. Large bursts of AE were observed at the abrupt displacement step in repetitive impact with a cube corner but were generally much smaller/absent during other impact events. The AE response with the 5 mm radius probe was quite different with smaller displacement events and AE bursts on most impacts at higher load. References [1] Indentation testing and its acoustic emission response: applications and emerging trends, N.H. Faisal, R. Ahmed and R.L. Reuben, International Materials Reviews 56 (2011) 98. [2] On the importance of combined scratch/acoustic emission test evaluation: SiC and SiCN thin films case study, J. Tomastik et al, Coatings 8 (2018) 196 [3] Effect of nitrogen doping and temperature on mechanical durability of silicon carbide thin films, J. Tomastik et al, Sci Rep 8 (2018) 10428

Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake : Nuclear fuel durability enhancement

In this work, we demonstrate and describe an effective method of protecting zirconium fuel cladding against oxygen and hydrogen uptake at both accident and working temperatures in water-cooled nuclear reactor environments. Zr alloy samples were coated with nanocrystalline diamond (NCD) layers of different thicknesses, grown in a microwave plasma chemical vapor deposition apparatus. In addition to showing that such an NCD layer prevents the Zr alloy from directly interacting with water, we show that carbon released from the NCD film enters the underlying Zr material and changes its properties, such that uptake of oxygen and hydrogen is significantly decreased. After 100–170 days of exposure to hot water at 360 °C, the oxidation of the NCD-coated Zr plates was typically decreased by 40%. Protective NCD layers may prolong the lifetime of nuclear cladding and consequently enhance nuclear fuel burnup. NCD may also serve as a passive element for nuclear safety. NCD-coated ZIRLO claddings have been selected as a candidate for Accident Tolerant Fuel in commercially operated reactors in 2020

A spatially explicit database of wind disturbances in European forests over the period 2000-2018

Strong winds may uproot and break trees and represent a major natural disturbance for European forests. Wind disturbances have intensified over the last decades globally and are expected to further rise in view of the effects of climate change. Despite the importance of such natural disturbances, there are currently no spatially explicit databases of wind-related impact at a pan-European scale. Here, we present a new database of wind disturbances in European forests (FORWIND). FORWIND is comprised of more than 80 000 spatially delineated areas in Europe that were disturbed by wind in the period 2000-2018 and describes them in a harmonized and consistent geographical vector format. The database includes all major windstorms that occurred over the observational period (e.g. Gudrun, Kyrill, Klaus, Xynthia and Vaia) and represents approximately 30% of the reported damaging wind events in Europe. Correlation analyses between the areas in FORWIND and land cover changes retrieved from the Landsat-based Global Forest Change dataset and the MODIS Global Disturbance Index corroborate the robustness of FORWIND. Spearman rank coefficients range between 0.27 and 0.48 (p value < 0.05). When recorded forest areas are rescaled based on their damage degree, correlation increases to 0.54. Wind-damaged growing stock volumes reported in national inventories (FORESTORM dataset) are generally higher than analogous metrics provided by FORWIND in combination with satellite-based biomass and country-scale statistics of growing stock volume. The potential of FORWIND is explored for a range of challenging topics and scientific fields, including scaling relations of wind damage, forest vulnerability modelling, remote sensing monitoring of forest disturbance, representation of uprooting and breakage of trees in large-scale land surface models, and hydrogeological risks following wind damage. Overall, FORWIND represents an essential and open-access spatial source that can be used to improve the understanding, detection and prediction of wind disturbances and the consequent impacts on forest ecosystems and the land-atmosphere system. Data sharing is encouraged in order to continuously update and improve FORWIND

Oxides on plasma-exposed beryllium surfaces

Zsfassung in dt. SpracheBei der Kernfusion zur Energiegewinnung sind die in den Reaktoren verwendeten Materialien extremen Bedingungen ausgesetzt. Ein vielversprechender Kandidat für die innere Reaktoroberfläche ist Beryllium, da es eine niedrige Atommasse sowie generell gute mechanische und thermische Eigenschaften hat.Ein wichtiger Aspekt der Materialeigenschaften in einer Fusionsplasaumgebung ist das Oxidationsverhalten, da Sauerstoff und Wasserdampf einen Hauptanteil des Restgases im Reaktor darstellen.Nachdem ein Großteil des Wissens über die Oxidation von Beryllium aus der Mitte des zwanzigsten Jahrhunderts stammt, hat sich die vorliegende Arbeit zum Ziel gesetzt, diese Daten mittels moderner oberflächenanalytischer Methoden zu überarbeiten. In einem zweiten Schritt werden diese Methoden, zusammen mit den erarbeiteten Daten, in Experimenten zur Wechselwirkung von Beryllium mit Wasserstoff-plasma angewandt.Für die Experimente wurde ein Rohrofen mit externen Elektroden zur Plasmaanregung und einer Gasversorgung für Wasserstoff und Wasserdampf verwendet. Die Oxidations-versuche wurden an Luft bei Temperaturen zwischen 390 und 600°C bei Heizzeiten bis 43 h durchgeführt. Bei den Plasmaversuchen wurde - im gleichen Temperaturbereich - sowohl trockener Wasserstoff als auch Mischungen mit einem Anteil von bis zu 1% Wasserdampf verwendet. Nach diesen Experimenten wurden die Berylliumproben mittels Augerelektronenspektroskopie-Sputtertiefenprofilen und Rasterelektronenmikroskopie untersucht.Bei mit der Temperatur kürzer werdenden Heizdauern (bis zu 1 h bei 600°C) wurde diffusionsbestimmte parabolische Oxidation festgestellt.Die Aktivierungsenergie für die ratenbestimmende Diffusion von Beryllium durch die Oxidschicht konnte bestimmt werden. Über 500°C fand bei längeren Heizdauern Korngrenzenoxidation statt, ein Anzeichen für beginnende katastrophale Oxidation.Im trockenen Wasserstoffplasma wurden natürliche Oxidschichten weiter oxidiert, während dickere voroxidierte Schichten reduziert wurden, wobei die Schichtdicke nach den Versuchen in allen Fällen in einem Bereich von 15-35 nm lag. Die Bildung dieses Quasi-Gleichgewichts mit zugehöriger Oxiddicke wurde der Konkurrenz von Oxidation durch Wasserdampf im Restgas und Reduktion durch atomaren Wasserstoff zugeschrieben. Weitere Beimischung von Wasserdampf verursachte eine starke Erhöhung des Schichtwachstums, zusammen mit einem sehr rauen und zerklüfteten Erscheinungsbild der Oberfläche. Dieser erhebliche Unterschied zur Wechselwirkung mit trockenem Plasma wurde durch die überwiegende Bildung von Berylliumhydroxid bei höherem Wasserdampfanteil erklärt.Im Rahmen der Kernfusionsforschung zeigen die dargestellten Ergebnisse die entschei-dende Rolle der Konzentration von sauerstoffhaltigen Restgasen im Plasmareaktor auf.In nuclear fusion for energy generation the materials used for the reactor vessels are exposed to severely erosive conditions during operation. A promising material for the inner vessel surface, the so-called first wall, is beryllium, due to its low atomic mass and overall good mechanical and thermal properties.An important aspect of material properties under fusion plasma conditions is oxidation behaviour, since oxygen and water vapour are major residual gases in the vessel. As much of the knowledge concerning beryllium oxidation has been acquired in the mid 20th century, the aim of this work is to revise these currently used data by applying modern surface analytical methods. In a second step, the same methods and the obtained data are applied to plasma exposure experiments of beryllium.For this purpose, a tubular furnace with attached electrodes for plasma excitation and a supply for hydrogen and water vapour was set up. The oxidation experiments were carried out in air at temperatures between 390 and 600°C and for durations up to 43 h. Plasma exposure experiments were done in the same temperature range with dry hydrogen and admixed water vapour fractions in hydrogen of up to 1%. After the experiments in the furnace, the beryllium samples were investigated with Auger electron spectroscopy (AES) sputter depth profiling and scanning electron microscopy (SEM).For heating durations decreasing with higher temperatures (down to 1 h at 600°C), diffusion-controlled parabolic oxidation was found to occur, and the activation energy for the rate-controlling diffusion of beryllium through the oxide layer could be determined. At 500°C and above, grain boundary oxidation of the beryllium bulk occurred for longer heating durations, which indicates the onset of non-protective (catastrophic) oxidation.Under dry hydrogen plasma exposure, native oxide layers were further oxidised, whereas thicker oxide layers on pre-oxidised surfaces were reduced, both ending up in a thickness range of 15-35 nm. The formation of this quasi-equilibrium oxide layer was attributed to the competition of oxidation by residual water vapour and reduction by atomic hydrogen.Further admixture of water vapour resulted in a dramatic increase in the thickness of the overlayer, combined with a very rough and jagged appearance of the surface. This striking difference was explained with the formation of beryllium hydroxide instead of oxide at higher water vapour fractions.In the context of fusion research, the results demonstrate the critical role of the concentration of residual oxygen-containing gases in the plasma vessel.9

Nanoscratch test — A tool for evaluation of cohesive and adhesive properties of thin films and coatings

Thin films and coatings play an essential role in the whole range of applications. The example par excellence are optical thin films that broaden the possibilities of design of optical components. Analogically to other applications of thin films their mechanical properties are very important for their successful applicability and reliability. This becomes especially vital when they are employed in rough service conditions. As thin films on substrates inherently create a compact system the strength of the film-substrate interface is of great importance. Several experimental methods have been developed for qualification and quantification of the mechanical stability of the film-substrate system. In this paper, some brief introduction into the nanoscratch test is introduced. It is currently the most widely used method to evaluate and to test cohesive-adhesive properties of thin films and coatings

Influence of concentration and anion alkyl chain length on tribological properties of imidazolium sulfate ionic liquids as additives to glycerol in steel-steel contact lubrication

Commercially available ionic liquids were used as additives in the model lubricant fluid glycerol. The stability of the mixtures was controlled by measuring of turbidity. Tribological experiments have been performed on a reciprocating sliding tribometer in the boundary lubrication regime with three ionic liquid concentrations, as well as with neat glycerol and the neat ionic liquids at 100 °C. Wear and friction were measured, and the worn surfaces were examined with optical microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The results show the influence of the ionic liquid concentration and the anion alkyl chain length on the tribological behavior. Significant improvement in friction and wear reduction at low ionic liquid concentrations was detected and attributed to sulfur species in tribofilm

Possibilities of security measures in museums in the czech republic

The threat of theft of works of art, antiques and books which are always being stolen from museums, galleries and archives in the Czech Republic, as well as abroad, remains present. Given the existence of the current stolen objects markets and the fact that artefacts keep their value which grows in time, theft will continue into the future. Thus, the security of museum collections and buildings is a pressing issue. It is, therefore, important to seek modern, secure and cheap solutions for the smaller museums in the Czech Republic. This paper describes the current state of security in the Czech Republic and proposes appropriate solutions of the problem of security in museums and galleries. The situation is very critical in some museum areas. Historic heritage is not sufficiently protected. The present study solves the analysis of the state of the historical heritage at present. The protection of the historical heritage is better than the Velvet Revolution. The article deals with the protection of monuments currently, analyzes the current security situation in museums in the Czech Republic and suggests a solution that would improve the future security of artefacts. Faculty of Logistics and Crisis Management prepares a workplace to help museums work with risks