Growth of single and multilayer sesquioxide crystal films for lasing applications via pulsed laser deposition

Sesquioxides, materials of the form RE2O3 (RE: rare earth), are of great interest for lasing applications. These materials offer high thermal conductivities, are mechanically stable, can easily be doped with various rare earth ions and are optically isotropic. Members of the sesquioxide family have the same crystal structure but differing refractive indices, and hence are ideal candidates for multilayer as well as single film growth. Sesquioxides can be challenging to grow from the melt, however, due to their high melting points (>2400 °C)

Imaging Pulsed Laser Deposition oxide growth by in-situ Atomic Force Microscopy

To visualize the topography of thin oxide films during growth, thereby enabling to study its growth behavior quasi real-time, we have designed and integrated an atomic force microscope (AFM) in a pulsed laser deposition (PLD) vacuum setup. The AFM scanner and PLD target are integrated in a single support frame, combined with a fast sample transfer method, such that in-situ microscopy can be utilized after subsequent deposition pulses. The in-situ microscope can be operated from room temperature (RT) up to 700$^\circ$C and at (process) pressures ranging from the vacuum base pressure of 10$^{-6}$ mbar up to 1 mbar, typical PLD conditions for the growth of oxide films. The performance of this instrument is demonstrated by resolving unit cell height surface steps and surface topography under typical oxide PLD growth conditions.Comment: 8 pages, 8 figure

Spatiotemporal variability in Swedish lake ecosystems

Studying ecosystem dynamics is critical to monitoring and managing linked systems of humans and nature. Due to the growth of tools and techniques for collecting data, information on the condition of these systems is more widely available. While there are a variety of approaches for mining and assessing data, there is a need for methods to detect latent characteristics in ecosystems linked to temporal and spatial patterns of change. Resiliencebased approaches have been effective at not only identifying environmental change but also providing warning in advance of critical transitions in social-ecological systems (SES). In this study, we examine the usefulness of one such method, Fisher Information (FI) for spatiotemporal analysis. FI is used to assess patterns in data and has been established as an effective tool for capturing complex system dynamics to include regimes and regime shifts. We employed FI to assess the biophysical condition of eighty-five Swedish lakes from 1996–2018. Results showed that FI captured spatiotemporal changes in the Swedish lakes and identified distinct spatial patterns above and below the Limes Norrlandicus, a hard ecotone boundary which separates northern and southern ecoregions in Sweden. Further, it revealed that spatial variance changed approaching this boundary. Our results demonstrate the utility of this resilience-based approach for spatiotemporal and spatial regimes analyses linked to monitoring and managing critical watersheds and waterbodies impacted by accelerating environmental change

Characterisation of the porous structure of Gilsocarbon graphite using pycnometry, cyclic porosimetry and void-network modeling

file: :C$$:/pdf/1-s2.0-S000862231400164X-main.pdf:pdfThe cores of the fourteen Advanced Gas-cooled nuclear Reactors (AGRs) within the UK comprise Gilsocarbon graphite, a manufactured material surrounded predominantly by CO2 at high pressure and temperature to provide heat exchange. The intense ionising radiation within the reactors causes radiolytic oxidation, and the resulting mass loss is a primary factor in determining reactor lifetime. The void structure of the porous Gilsocarbon graphite affects the permeability and diffusion of the carbon dioxide, and the sites of oxidation. To model this void structure, the porosities and densities of ten virgin Gilsocarbon graphite samples have been measured by powder and helium pycnometry. For comparison, results are also presented for highly ordered pyrolytic graphite (HOPG), and a fine-grained Ringsdorff graphite. Samples have been examined at a range of magnifications by electron microscopy. Total porosities and percolation characteristics have been measured by standard and cyclic mercury porosimetry up to an applied mercury pressure of 400MPa. Inverse modelling of the cyclic intrusion curves produces simulated void structures with characteristics which closely match those of experiment. Void size distributions of the structures are presented, together with much Supplementary Information. The simulated void networks provide the bases for future simulations of the radiolytic oxidation process itself

Apparatus to control and visualize the impact of a high-energy laser pulse on a liquid target

We present an experimental apparatus to control and visualize the response of a liquid target to a laser-induced vaporization. We use a millimeter-sized drop as target and present two liquid-dye solutions that allow a variation of the absorption coefficient of the laser light in the drop by seven orders of magnitude. The excitation source is a Q-switched Nd:YAG laser at its frequency-doubled wavelength emitting nanosecond pulses with energy densities above the local vaporization threshold. The absorption of the laser energy leads to a large-scale liquid motion at timescales that are separated by several orders of magnitude, which we spatiotemporally resolve by a combination of ultra-high-speed and stroboscopic high-resolution imaging in two orthogonal views. Surprisingly, the large-scale liquid motion at upon laser impact is completely controlled by the spatial energy distribution obtained by a precise beam-shaping technique. The apparatus demonstrates the potential for accurate and quantitative studies of laser-matter interactions.Comment: Submitted to Review of Scientific Instrument

Ultrasonic Scattering from a Hemispherical Pit Theory and Experimental Measurement Precision

The accuracy and precision of ultrasonic thickness measurement systems are influenced by systematic and environmental factors including the back-wall reflection surface profile. The scattering amplitude from a relatively flat and smooth back-wall surface can be characterized by the acoustic impedance ratio of the two materials at the interface. If the back-wall surface increases in roughness due to internal corrosion, then the arrival time of the incident wave upon the various surface heights will be slightly different, resulting in slight phase changes within the reflected field. In addition, the roughness of the internal surface will result in various impingement anglesrelative to the incident wave causing some mode conversion. The reflected wave field is composed of the coherent field (same phase and same relative angle as the incident wave) and the diffuse field (random phase and random angle). As roughness increases, more energy is converted to the diffuse field resulting in a decrease in the reflected coherent field. This reduction in energy from the coherent field can be observed with a transducer by a decrease in voltage amplitude as well as a change in the frequency component of the received signal. A single corrosive pit can be represented as a hemisphere in a half-space to model the initiation point of rough surface corrosion, or to model isolated pitting degradation as possible with naphthenic acid corrosion in oil refineries. The case of a single hemispherical pit with a normal incident compression wave has been studied in NDE applications and in the seismology community with a recent presentation of a full analytical solution. This paper looks to present the thickness measurement accuracy and precision of various time-of-flight thick- ness calculation methods taking into consideration asymmetric measurement uncertainty for the case of a normal incident compression wave on both a relatively smooth back-wall surface and on a hemispherical pit. In addition, this paper looks to compare a full analytical solution, various scattering approximations (such as Kirchoff), as well as experimental measurements presented as scattering coefficients relative to normalized frequency for the case of a hemispherical pit

Ultrasonic Sol-Gel Arrays for Monitoring High-Temperature Corrosion

Corrosion of oil refinery equipment operating at high temperature is a growing challenge linked to an increase in sulfur concentration and acidity within the world supply of crude oils. Improved high temperature monitoring tools are needed to continuously measure the local minimum wall thickness of steel pipe subject to non-uniform internal corrosion. Thickness measurements must be sufficiently accurate to calculate the maximum allowable stress permissible as to avoid failure. Thickness measurements must also be sufficiently reliable and precise to correlate the rate of wall-loss with process conditions as to improve future corrosion rate predictions. Permanently installed structural health monitoring (SHM) technologies have the potential to meet these needs and an ultrasonic sensor technology based on the sol-gel ceramic fabrication process will be presented. The sol-gel thin-film sensor fabrication process is described: aerosol printing of high-temperature piezoceramic material, heat curing, polarization, electrode deposition, and wiring. The sensors are characterized with the photoelastic visualization method by first, recording the propagating elastic waves as a sequence of images, then, processing the image frames to reconstruct a beam profile through identification of the maximum optical intensity for each pixel via normalizing, filtering, and smoothing. A sol-gel transducer is shown to be similar to a traditional manual contact transducer. The systematic and environmental factors that impact ultrasonic thickness measurement accuracy, precision, and reliability are discussed. An experiment is conducted using a flat-bottom-hole calibration pipe at ambient temperature with sol-gel transducer arrays in pulse-echo and pitch-catch configuration for various time-of-flight thickness calculation methods. A weighted censored relative maximum likelihood statistical method incorporating the propagation of asymmetric uncertainty is used to report thickness measurement results with confidence limits analogous to the a90/95 terminology used in Probability-of-Detection (POD) assessments. Future work is discussed to apply the statistical analysis technique to complex back-wall surfaces at high temperature representative of naphthenic acid corrosion in oil refineries