Summary Electron Compton scattering is a technique that gives information on the electron momentum density of states and is used to characterize the ground state electronic structure in solids. Extracting the momentum density of states requires us to assume the so‐called ‘impulse approximation’, which is valid for large energy losses. Here, the robustness of the impulse approximation in the low energy transfer regime is tested and confirmed on amorphous carbon films. Compared to traditional Compton measurements, this provides additional benefits of more efficient data collection and a simplified way to probe valence electrons, which govern solid state bonding. However, a potential complication is the increased background from the plasmon signal. To overcome this, a novel plasmon background subtraction routine is proposed for samples that are resistant to beam damage. Lay Description Properties of solids depend on their electronic structure which can be studied using electron Compton scattering technique. Here, an electron beam is used to penetrate a very thin sample. During the interaction between the electrons in the beam and electrons in the sample, the former transfer a part of their energy to the latter, resulting in a measurable energy loss of the transmitted beam. The amount of the energy transfer depends on the angle of incidence between the beam and the sample. Typically, the experiments are carried out using high tilt angles and high energy transfer; however, in this work, we show that even smaller angles of incidence are suitable, which improve the signal quality and ease data processing procedures.
Silica aerogels are low density solids with high surface area and high porosity which are ideal supports for catalyst materials. the main challenge in aerogel production is the drying process, which must remove liquid from the pores of the wet gel while maintaining the solid network. in this work, the synthesis of silica aerogels and nickel-doped silica aerogels by a low energy budget process is demonstrated. Silica aerogels are produced by ambient drying using ammonium bicarbonate, rather than a conventional low surface tension solvent. Heating dissociates the ammonium bicarbonate, so generating co 2 and nH 3 within the pores of the wet gel which prevents pore collapse during drying. nickel-doped aerogels were produced by reducing nickel ions within pre-synthesised silica aerogels. the morphology of the resulting nickel particles-spheres, wires and chains-could be controlled through an appropriate choice of synthesis conditions. Materials were characterized using nitrogen adsorption/desorption isotherms, scanning electron microscopy, fourier-transform infrared spectroscopy, thermogravimetric analysis and X-ray diffraction. The surface area of undoped aerogel is found to increase with the concentration of ammonium bicarbonate salts from 360 to 530 m 2 g −1 , and that of nickel-doped silica aerogel varies from 240 to 310 m 2 g −1 with nickel doping conditions. Silica aerogels are ultra-low-density solids with the vast majority (typically > 90% 1) of their volume made up of voids consisting of mesopores and macropores. This unique structure leads to a variety of extraordinary properties such as extremely high specific surface area, low dielectric constant and low thermal conductivity, opening up potential uses including in catalysis, adsorption for pollution remediation, thermal super-insulation and in drug delivery systems 2-8. Practical application of aerogels has, however, been limited by high materials costs and laborious methods for drying. These issues have been solved only recently by the development of a low-cost ambient pressure drying (APD) approach 9 for aerogel production by Han and co-workers. In this method the reaction of sodium bicarbonate with HCl, generated from tetramethylchlorosilane (TMCS), was used to generate pore-supporting carbon dioxide within the wet gel during the drying process, so avoiding the need for low surface tension solvents. Nickel catalysts supported on silica have been employed for the reforming of carbon dioxide and methane to produce synthesis gas (syngas-typically a mixture of H 2 , CO and CO 2) 10 which are important intermediates for the production of synthetic natural gas and methanol. When immobilised within silica aerogels, nickel nanoparticles (NiNPs) and nanowires (NiNWs) have been shown to catalyse the CO 2 hydration reaction (CHR) which has significant potential for carbon capture, storage and utilisation (CCSU) to mitigate anthropogenic climate change 11. Similarly, CO 2 reforming of CH 4 has been demonstrated with nickel doped alumina aerogel catalysts 2. However...
The Compton signal in electron energy loss spectroscopy (EELS) is used to determine the projected electron momentum density of states for the solid. A frequent limitation however is the strong dynamical scattering of the incident electron beam within a crystalline specimen, i.e. Bragg diffracted beams can be additional sources of Compton scattering that distort the measured profile from its true shape. The Compton profile is simulated via a multislice method that models dynamical scattering both before and after the Compton energy loss event. Simulations indicate the importance of both the specimen illumination condition and EELS detection geometry. Based on this, a strategy to minimize diffraction artifacts is proposed and verified experimentally. Furthermore, an inversion algorithm to extract the projected momentum density of states from a Compton measurement performed under strong diffraction conditions is demonstrated. The findings enable a new route to more accurate electron Compton data from crystalline specimens.
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