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Al₅C₃N has a nanolaminated crystal structure with layers of AlN separated by layers of Al₂C and Al₂C₂. The physical and chemical properties of Al₅C₃N is more or less unknown due to the high temperatures required to synthesize bulk samples but in analogy with other nanolaminated materials such as MAX-phases, this compound may have potential applications as thin film materials. In this study we have deposited single-phase Al₅C₃N films with magnetron sputtering onto α-Al₂O₃(001) and AlN(001)/α-Al₂O₃(001) substrates at deposition temperatures ranging from 650 °C to 800 °C. The as-sputtered films were analyzed using multiple compositional and structural characterization methods. Epitaxial growth of Al₅C₃N was obtained on AlN(001)/α-Al₂O₃(001) but with a large number of defects mainly with extra stacking planes locally inserted into the structure. Nanoindentation measurements showed a hardness of about 18–19 GPa, which is significantly harder than for the MAX-phases. This can be explained by a high bond strength between the alternating AlN and Al₂C/Al₂C₂ layers giving this compound a more three-dimensional character than the MAX-phases. The band gap measurements show band gaps of 2.2 eV and 2.9 eV for the films deposited at 650 °C, and 1.8 eV and 2.5 eV for films deposited at 800 °C.

We report a rapid and controllable solid-state formation process of copper coordination complex hole-transport materials (HTMs) in dye-sensitized solar cells (DSCs), reducing processing times from over 48 h to 20 min. By thermally-induced phase transition of Cu(I/II)(tmby)2-based liquid electrolytes from 50 °C to 110 °C, we demonstrated that a 70 °C post-treatment for 20 min is ideal for creating an amorphous HTM with minimal crystallization. Time-dependent Raman spectra confirmed near-complete solvent removal within 20 min, while scanning electron microscopy highlighted a compact, defect-minimized HTM morphology when 4-tert-butylpyridine was employed versus N-methylbenzimidazole. Transient absorption spectroscopy revealed ultrafast dye regeneration (t1/2,reg = 487 ns) and near-unity regeneration efficiency (99.2%) for short heat treatments, whereas extended treatments (e.g., 60 min) led to μs-scale recombination (26.8 μs) and lower performance. Electrochemical impedance spectroscopy indicated stable charge-transfer resistances at the TiO2/HTM interface (from 25.6 Ω in liquid state to 27.5 Ω in solid state), confirming efficient hole transport pathways. Under 1 sun illumination, devices retained up to ≈10% power conversion efficiency, while indoor (1000 lux) conditions yielded photocurrents up to 79 μA cm−2 and peak efficiencies of 16%. These findings establish a robust, reproducible route to form Cu-based HTMs in solid-state DSCs with enhanced low-light performance and highlight key design parameters controlling morphology, interfacial charge transfer, and photovoltaic yield.

Environmental magnetism, including the use of magnetic susceptibility (MS), has formed the backbone of analyzing past terrestrial climate dynamics recorded in loess deposits world-wide. However, the nature of MS signal response and frequency dependence (χ_FD) varies between loess sequences, which can limit the applicability of the approach. Here, we explore how measuring MS using multiple alternating-current field frequencies can transform our understanding of the past climate record in loess. We compare loess MS data measured at 15 different frequencies from diverse environments across the Northern Hemisphere, and provide high-resolution data for a late Quaternary loess-paleosol section in Tajikistan. Additionally, we study the magnetic mineral composition in selected Tajik loess samples using rock magnetic methods and Raman spectroscopy and assess the usefulness of calculating superparamagnetic nanoparticle (SP) size distributions from multi-frequency magnetic susceptibility. Our results demonstrate that using this approach to determine χ_FD has several advantages over widely used dual-frequency approaches: (a) Inclusion of a wider grain size range of magnetism-bearing SP particles in measuring χ_FD, allowing for a more complete analysis of the environmental drivers behind the MS signal; (b) Higher sensitivity of the χ_FD palaeoclimate proxy to climatic changes; and (c) Increased statistical meaningfulness of the χ_FD proxy by allowing quantification of uncertainty. Our approach is particularly beneficial for understanding sites characterized by low-susceptibility samples and potentially diverse processes of magnetic enhancement. However, we advocate its routine use even in more typical loess sequences due to its greater sensitivity to climatic changes and better understanding of inherent proxy uncertainties.

Zinc oxide (ZnO) is a well-studied wide band gap semiconductor due to its availability, low cost and chemical stability. The light emission and vibrations of low dimensional ZnO are however less understood. Here we report the photoluminescence emission from ZnO quantum dots and their lattice vibrations, with special emphasis of exciton and defect state emission.  It is shown that the fluorescence emission partly originates from surface states and the positions of these surface states within the bandgap are calculated. In a light emitting material energy can be lost through a conversion into thermal energy. This conversion is facilitated through an interaction between the excited state wave function and the lattice vibrations in the material and is dependent on the electron-phonon coupling. The intensity ratio between the Raman peaks of the fundamental longitudinal optical (LO) mode and its overtones, in resonance Raman spectroscopy, can be used as a measure of the electron-phonon coupling strength and we have used this to investigate how the electron-phonon coupling depends on particle size in nano dimensional ZnO.

We developed a computational framework to extract the Raman spectra of nitrogen reduction and ammonia oxidation intermediates on high-entropy alloy (HEA) surfaces, integrating density functional theory with microstructural representations to account for the inherent lattice randomness in these materials. As a case study, we computed the Raman activities of intermediates (N₂*, NNH*, N*, NH*, and NH₃*) and H* adsorption on CoCuFeMoNi HEA surfaces. A comprehensive map of Raman peaks was generated and assigned to specific vibrational modes. The method highlighted the effects of lattice randomness on the Raman spectra compared to those of adsorbates on single-element catalysts. For instance, our results showed that the adsorbed N₂ exhibits Raman modes that are dependent on whether the adsorption is vertical or horizontal. These peak differences could serve as unique fingerprints to identify nitrogen reduction reaction pathways. Moreover, it is also possible to detect surface poisoning by hydrogen, a common issue in reductive environments, due to the high-frequency peaks of H* compared to the typical N-metal stretching and bending frequencies. These results provide valuable references for identifying intermediates in nitrogen reduction and ammonia oxidation reactions, offering insights into reaction mechanisms and potential surface poisoning. This approach is generalizable to other reactions and surfaces in catalysis, provided that the relevant intermediates can be identified.

Ammonia is a promising energy vector and can be used as a hydrogen storage medium. Electrocatalytic ammonia syntheses using renewable energy are attractive low-temperature options to the Haber-Bosch high-temperature process, which releases CO₂ in the atmosphere and contributes to the greenhouse effect. High-entropy (HEA) alloys belong to a new class of materials that can provide single-phase stabilizations by mixing different species and are promising candidates to overcome scientific challenges posed by electrochemistry. Lithium-mediated ammonia synthesis is a way to get high-performance ammonia electrosynthesis from nitrogen at room temperature. In this work, we investigated lithium-mediated ammonia synthesis of a thin-film high-entropy catalyst of CoCrFeMnNi.

Advanced oxidation processes using photogenerated charges in semiconductors constitute an approach to reduce and oxidize pollutants, with an efficiency that depends on the photo physics and defect chemistry of the photocatalyst. In this study, 2D Cu2O coatings on flat copper metal and on 3D copper nanopillars are created via low-temperature oxidation and compared. The structures are characterized by X-ray diffraction, Raman spectroscopy, and electron microscopy. The thickest surface oxide layers on the 3D structures show outgrowth of high-aspect ratio CuO nano-needles through the Cu2O layer, rationalized through a field-induced copper ion diffusion mechanism. Raman scattering provides details about both the specific copper oxide phase present and the type and extent of defects, with a resolution spanning from hundreds of nanometers to micrometers. We show that defects in Cu2O induce Raman activity in several of its modes that are purely IR-active or optically silent in pristine Cu2O. The experimental results are corroborated by linear response density functional theory (DFT) calculations for full vibrational mode analysis. The Cu-supported 2D copper oxide systems exhibit effective photocatalytic performance at quite low probe pollution concentration (10 mu M), while the 3D nanopillar structures enhance the photocatalytic efficiency by around 30 % compared to their planar counterpart under these conditions.

Micro-Raman spectroscopy is an important analytical tool in a large variety of science disciplines. The technique is suitable for both identification of chemical bonds and studying more detailed phenomena like molecular interactions, material strain, crystallinity, defects, and bond formations. Raman scattering has one major weakness however: it is a very low probability process. The weak signals require very sensitive detection systems, which leads to a high probability of picking up signals from origins other than the sample. This complicates the analysis of the results and increases the risk of misinterpreting data. This work provides an overview of the sources of spurious signals occurring in Raman spectra, including photoluminescence, cosmic rays, stray light, artefacts caused by spectrometer components, and signals from other compounds in or surrounding the sample. The origins of these false Raman peaks are explained and means to identify and counteract them are provided. Raman spectroscopy is a great analysis tool but the spectra are sometimes difficult to interpret due to the occurrence of spectral artefacts. This paper dives into the details of many spurious signals and spectral artefacts that occur in Raman spectra, explains their origin, and provides the tools to identify and avoid them.

Water pollution is a severe problem in many parts of the world. In developed countries the increased use of chemicals and urban densification has started to cause stress of previously well-functioning water systems. Advanced oxidation processes (AOPs), is a promising method for degradation of artificial organic pollutants, which are challenging to remove by conventional water treatment techniques. In AOPs hydroxyl radicals (OH•) and reactive oxygen species (O₂^- and O₂^2-) which are strongly oxidizing species are generated and these subsequently react with and degrade the pollutants. To use nanostructures which are optically active in the visible part of the spectrum is attractive because it both creates a large surface area, promoting surface interface reactions, as well as enables the utilization of a large part of the solar spectrum. In this study flat copper surfaces and 3D nanostructured copper pillars are utilized as base structures. These are subjected to thermal oxidation at low temperature, for a controlled amount of time, creating thin copper oxide layers which makes them photoactive in the visible range. The formed copper oxide and its growth is analysed with SEM, XRD and Raman spectroscopy, and show the formation of Cu₂O with a slight incorporation of CuO for the thickest oxide layers. Formation of CuO nano needles, protruding from the Cu₂O layer, were observed in the SEM imaging. The photocatalytic performance was tested by degradation of methylene blue in aqueous solution and all of the tested systems showed quite effective performance. The highest degradation rate was seen for copper nanopillars annealed for 4 or 8 min, which exhibited 34% faster degradation than the oxidized flat sample. The study shows that simple and inexpensive thermal oxidation processes can be used to create efficient photoactive Cu₂O catalysts even on semi-flat surfaces, and that nanostructuring increases the degradation rates.

The ability to control electronic states by utilizing quantum confinement of one of the material components in heterojunctions is a promising approach to perform energy-level matching. In this work, we report the possibility to achieve optimum energy alignment in heterojunctions made from size-controlled quantum dots (Q-dots) of ZnO in combination with three copper oxides: Cu₂O, Cu₄O₃, and CuO. Quantum confinement effects on the ZnO nanoparticles in the diameter range 2.6–7.4 nm showed that the direct optical band gap decreased from 3.99 to 3.41 eV, with a dominating shift occurring in the conduction band (CB) edge, and thus the possibility to obtain close to 0.6 eV CB edge shift by controlling the size of ZnO. The effect was utilized to align the electronic bands in the ZnO Q-dot/copper oxide heterojunctions to allow for charge transfer between the materials and to test the ability to improve the photocatalytic performance for the system, evaluated by the transformation of a dye molecule in water. The catalyst materials were investigated by X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis), photoluminescence, and Raman spectroscopy. The most promising material combination was found to be the Cu₂O copper oxide in combination with an energy aligned ZnO Q-dot system with approximately 7 nm diameter, showing strong synergy effects in good agreement with the energy-level analysis, outperforming the added effect of its individual components, ZnO-Q-dots and Cu₂O, by about 140%. The results show that utilization of a heterojunction with controllable energy alignment can provide a drastically improved photocatalytic performance. Apart from increased photocatalytic activity, specific surface states of ZnO are quenched when the heterojunction is created. It is anticipated that the same approach can be utilized in several material combinations with the added benefit of a system with controllable overpotential and thus added specificity for the targeted reduction reaction.