The influence of H2 flooding on the development of surface roughness during time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling was studied to evaluate the different aspects of ...a H2 atmosphere in comparison to an ultrahigh vacuum (UHV) environment. Multilayer samples, consisting of different combinations of metal, metal oxide, and alloy layers of different elements, were bombarded with 1 and 2 keV Cs+ ion beams in UHV and a H2 atmosphere of 7 × 10–7 mbar. The surface roughness S a was measured with atomic force microscopy (AFM) on the initial surface and in the craters formed while sputtering, either in the middle of the layers or at the interfaces. We found that the roughness after Cs+ sputtering depends on the chemical composition/structure of the individual layers, and it increases with the sputtering depth. However, the increase in the roughness was, in specific cases, approximately a few tens of percent lower when sputtering in the H2 atmosphere compared to the UHV. In the other cases, the average surface roughness was generally still lower when H2 flooding was applied, but the differences were statistically insignificant. Additionally, we observed that for the initially rough surfaces with an S a of about 5 nm, sputtering with the 1 keV Cs+ beam might have a smoothing effect, thereby reducing the initial roughness. Our observations also indicate that Cs+ sputtering with ion energies of 1 and 2 keV has a similar effect on roughness development, except for the cases with initially very smooth samples. The results show the beneficial effect of H2 flooding on surface roughness development during the ToF-SIMS depth profiling in addition to a reduction of the matrix effect and an improved identification of thin layers.
Despite the fact that the methanol synthesis process includes industrially some of the most important catalytic chemical reactions, it is still not clear how different gaseous species impact catalyst ...component structure. With the goal to reduce CO2 emissions through hydrogenation to CH3OH, a higher H2O formation rate than in the production from compressed CO-rich feed should also be considered. It is known that steam accelerates the sintering of metals, several oxide compounds, and their interfaces. To determine the effect of moisture on the Cu/ZnO/Al2O3 catalysts, a commercial catalytic material was systematically aged at various gas compositions and analyzed using transient H2 surface adsorption, N2O pulse efficient chemisorption, X-ray photoelectron spectroscopy, scanning transmission electron microscopy mapping, X-ray powder diffraction, and N2 physisorption, and the mechanisms of deactivation were observed. A strong consistent relation between the compacting of Al2O3, the amount of water in the controlled streamflow, and the activity was found. This connected loss of support resulted in the (re)forming of Cu, ZnO, and Cu/ZnO phases. Copper particle growth was modeled by applying a physical coalescence model. In the presence of CO and/or CH3OH, zinc oxide material started to cover the Cu granules, while H2O promoted the development of separate Cu regions.
The influence of the flooding gas during ToF-SIMS depth profiling was studied to reduce the matrix effect and improve the quality of the depth profiles. The profiles were measured on three ...multilayered samples prepared by PVD. They were composed of metal, metal oxide, and alloy layers. Dual-beam depth profiling was performed with 1 keV Cs+ and 1 keV O2 + sputter beams and analyzed with a Bi+ primary beam. The novelty of this work was the application of H2, C2H2, CO, and O2 atmospheres during SIMS depth profiling. Negative cluster secondary ions, formed from sputtered metals/metal oxides and the flooding gases, were analyzed. A systematic comparison and evaluation of the ToF-SIMS depth profiles were performed regarding the matrix effect, ionization probability, chemical sensitivity, sputtering rate, and depth resolution. We found that depth profiling in the C2H2, CO, and O2 atmospheres has some advantages over UHV depth profiling, but it still lacks some of the information needed for an unambiguous determination of multilayered structures. The ToF-SIMS depth profiles were significantly improved during H2 flooding in terms of matrix-effect reduction. The structures of all the samples were clearly resolved while measuring the intensity of the M n H m –, M n O m –, M n O m H–, and M n – cluster secondary ions. A further decrease in the matrix effect was obtained by normalization of the measured signals. The use of H2 is proposed for the depth profiling of metal/metal oxide multilayers and alloys.
In a proof-of-concept study, we assessed different analytical and spectroscopic parameters for stability screening of differently sized β-NaYF4:20 mol % Yb3+, 2 mol % Tm3+ upconversion nanoparticles ...(UCNPs) exemplarily in the bioanalytically relevant buffer phosphate buffered saline (PBS; pH 7.4) at 37 and 50 °C. This included the potentiometric determination of the amount of released fluoride ions, surface analysis with X-ray photoelectron spectroscopy (XPS), and steady-state and time-resolved fluorescence measurements. Based on these results, the luminescence lifetime of the 800 nm upconversion emission was identified as an optimum parameter for stability screening of UCNPs and changes in particle surface chemistry.
Stable chitosan thin films can be promising substrates for creating nanometric peptide-bound polyglucosamine layers. Those are of scientific interest since they can have certain structural ...similarities to bacterial peptidoglycans. Such films were deposited by spin coating from chitosan solutions and modified by acetylation and N-protected amino acids. The masses of deposited materials and their stability in aqueous solutions at different pH values and water interaction were determined with a quartz crystal microbalance with dissipation (QCM-D). The evolution of the surface composition was followed by X-ray photoelectron (XPS) and attenuated total reflectance infrared (ATR-IR) spectroscopy. Morphological changes were measured by atomic force microscopy (AFM), while the surface wettability was monitored by by static water contact angle measurements. The combination of the characterization techniques enabled an insight into the surface chemistry for each treatment step and confirmed the acetylation and coupling of N-protected glycine peptides. The developed procedures are seen as first steps toward preparing thin layers of acetylated chitin, potentially imitating the nanometric peptide substituted glycan layers found in bacterial cell walls.
TiO2 nanotubular films prepared using the anodic oxidation process applied to various forms of metal titanium are promising materials for photocatalytic applications. However, during successive ...anodizations in batch-anodization cells, the chemical composition of the NH4F- and water-based ethylene glycol electrolyte changes with each subsequent anodization, which greatly affects the final photocatalytic properties of the annealed TiO2 nanotubular films. In the present study, 20 titanium discs (Φ 90 mm) were sequentially anodized in the same anodization electrolyte. The chemical composition of the electrolyte was measured after each anodization and correlated with the anodization current density, temperature, electrical conductivity, and pH of the electrolyte and with the morphology, structure, composition, and photocatalytic activity of the resulting TiO2 nanotube films. It was found that the length of the TiO2 nanotubes decreased with the age of the electrolyte due to its lower conductivity. The subsurface chemical composition was evaluated by time of flight secondary ion mass spectrometry (ToF SIMS) analyses, and the integrated ToF SIMS signals over a depth of 250 nm for the TiO2 nanotube films showed that the concentration of F– in the annealed TiO2 film increased with each subsequent anodization due to the increased pH value of the electrolyte. As a consequence, the concentration of the OH– and O2 – species decreased, which is a major reason for the reduced photocatalytic activity of the TiO2 films. It is proposed that the length of the TiO2 nanotubes does not play a decisive role in determining the photocatalytic activity of the TiO2 nanotube films. Finally, the best measured degradation results of 60% for caffeine were thus achieved for the first anodized titanium discs. After that the efficiency gradually decreased for each subsequent anodized disc.
The high structural and compositional flexibility of metal–organic frameworks (MOFs) shows their great potential for CO2 capture and utilization in accordance with the environmental guidelines of ...low-carbon technology developments. HKUST-1 as one of the most intensively studied representatives of MOFs for such purposes excels because of its simplicity of production and high ability to tune its intrinsic properties by various functionalization processes. In the present work, ethylenediamine functionalization was performed for the first time in order to thoroughly investigate the amine sorption sites’ impact on the CO2 capture performance of HKUST-1. The placement of ethylenediamine moieties on Cu2+ free-metal sites has been examined in detail and confirmed by using various spectroscopic techniques such as Fourier transform infrared spectroscopy, electron paramagnetic resonance, Raman, and Cu K-edge extended X-ray absorption fine structure/X-ray absorption near edge structure. N2 and CO2 sorption tests have proven that the functionalization reduces both the specific surface area and the CO2 sorption capacity, but on the other hand, it increases the binding energy by 85% (from −20.3 kJ/mol to −36.8 kJ/mol) and CO2/N2 selectivity at 0.15/0.85 bar by 100% and notably improves the kinetics of adsorption in comparison to the pristine HKUST-1 material.
Combinations of wood and metal are interesting hybrid composite materials, joining together the low density of wood with the stiffness and strength of metals. Different types of adhesives are used to ...connect wood and metal elements, but the compatibility between adhesives used and load-bearing materials must be sufficient, which often is challenging. In adhesive bonding technology, surface treatments are a crucial step in the process. In this study, an atmospheric plasma discharge was employed to enhance the adhesion strength of joints between common beech (
Fagus sylvatica
L.) wood, metals (steel and aluminum alloy), and four different types of adhesives. The optical properties of plasma discharges and its influence on treated substrates’ surface morphology depended on the inherent properties of the treated materials. X-ray photoelectron spectroscopy revealed the surface oxidation of all the materials after plasma treatment. Consequently, the surface free energy of all materials increased as well. The positive effect of the plasma treatment on the tensile shear strength of single-lap joints shows a high potential of atmospheric plasma treatment technology for enhancement of adhesives strength of joints combining wooden elements, wood and steel, or wood and aluminum alloys. In addition to that, expensive epoxy and polyurethane adhesives could be replaced by more affordable polyvinyl acetate and melamine-urea-formaldehyde adhesives, and still perform at equal levels if the plasma was applied prior to bonding.
Development of a robust photocathode using low-cost and high-performing materials, e.g., p-Si, to produce clean fuel hydrogen has remained challenging since the semiconductor substrate is easily ...susceptible to (photo)corrosion under photoelectrochemical (PEC) operational conditions. A protective layer over the substrate to simultaneously provide corrosion resistance and maintain efficient charge transfer across the device is therefore needed. To this end, in the present work, we utilized pulsed laser deposition (PLD) to prepare a high-quality SrTiO3 (STO) layer to passivate the p-Si substrate using a buffer layer of reduced graphene oxide (rGO). Specifically, a very thin (3.9 nm ∼10 unit cells) STO layer epitaxially overgrown on rGO-buffered Si showed the highest onset potential (0.326 V vs RHE) in comparison to the counterparts with thicker and/or nonepitaxial STO. The photovoltage, flat-band potential, and electrochemical impedance spectroscopy measurements revealed that the epitaxial photocathode was more beneficial for charge separation, charge transfer, and targeted redox reaction than the nonepitaxial one. The STO/rGO/Si with a smooth and highly epitaxial STO layer outperforming the directly contacted STO/Si with a textured and polycrystalline STO layer showed the importance of having a well-defined passivation layer. In addition, the numerous pinholes formed in the directly contacted STO/Si led to the rapid degradation of the photocathode during the PEC measurements. The stability tests demonstrated the soundness of the epitaxial STO layer in passivating Si against corrosion. This study provided a facile approach for preparing a robust protection layer over a photoelectrode substrate in realizing an efficient and, at the same time, durable PEC device.
In the process of wood bonding, the usage of aged and inactivated wooden elements can cause a reduction in mechanical properties of products containing wood-adhesive joints. Treating wood with an ...atmospheric air plasma represents a sophisticated technique for surface activation. With this regard, to enhance the bondability of normal beech wood (
Fagus sylvatica
L.) with urea-formaldehyde (UF) adhesive, a dielectric barrier discharge plasma in floating electrode configuration was implemented. In this study, fresh and aged wood specimen both, untreated and plasma treated, were investigated. X-ray photoelectron spectroscopy revealed promotion of carbon-rich species with ageing, but generation of a new functional oxygen-containing functional groups after plasma treatment. Microscopic observations with scanning electron microscope showed no obvious changes in the wood structure after plasma treatment. Surface oxidation consequently improved the wettability of the wood surface with water and UF adhesive. However, this enhanced wettability slightly diminished over time. As shown with dynamic mechanical analysis, the rheological properties of the UF adhesive in wood-adhesive joints were not affected by aging nor by plasma treatment. The positive influence of plasma treatment and negative impact of substrate ageing to the shear strengths of wood lap-joints were determined using an automated bonding evaluation system. Similarly, the negative effect of wood ageing and the positive effect of plasma pre-treatment were reflected in the bending strengths of the produced laminated veneer lumbers. Results showed that plasma treatment of beech wood improves the bonding performance of both fresh and aged wood.
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