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Surface photovoltage spectroscopy of ultrawide bandgap materials
No full textTechniques of surface photovoltage spectroscopy allow for the highly sensitive characterization of transitions in ultra wide bandgap materials without the need for contact preparation. Furthermore, SPV techniques can give access to electronic transitions at buried interfaces. Tools for continuous measurements of dc, ac modulated and ac transient SPV signals with the same perforated electrode and a charge amplifier are developed for spectral ranges from the near infrared up to the deep ultraviolet and for time domains from the ns to s h to ranges. The analysis of modulated SPV transients is applied. The high empirical potential of SPV spectroscopy is demonstrated by studies of a diamond single crystal, a layer of amp; 61538; Ga2O3 grown by pulsed laser deposition and an AlN layer epitaxially grown on sapphire. Defect related transitions are characterized over the entire bandgap for all mentioned materials. Several phonon assisted transitions near the bandgap of diamond are well detected. Different defect transitions dominating near the amp; 61538; Ga2O3 surface or near the amp; 61538; Ga2O3 sapphire interface are distinguished. Several defect transitions near the bandgap of AlN are observed. Uncertainties for interpretation of transition energies are discusse
Corrigendum Effects of disorder on the magnetic properties of the Heusler alloy V2FeAl
No full textCorrigendu
Buried hole selective interface engineering for high efficiency tin lead perovskite solar cells with enhanced interfacial chemical stability
No full textMixed Sn Pb perovskites are attracting significant attention due to their narrow bandgap and consequent potential for all perovskite tandem solar cells. However, the conventional hole transport materials can lead to band misalignment or induce degradation at the buried interface of perovskite. Here we designed a self assembled material 4 9H carbozol 9 yl phenylboronic acid 4PBA for the surface modification of the substrate as the hole selective contact. It incorporates an electron rich carbazole group and conjugated phenyl group, which contribute to a substantial interfacial dipole moment and tune the substrate s energy levels for better alignment with the Sn Pb perovskite energy levels, thereby promoting hole extraction. Meanwhile, enhanced perovskite crystallization and improved contact at bottom of the perovskite minimized defects within perovskite bulk and at the buried interface, suppressing non radiative recombination. Consequently, Sn Pb perovskite solar cells using 4PBA achieved efficiencies of up to 23.45 . Remarkably, the 4PBA layer provided superior interfacial chemical stability, and effectively mitigated device degradation. Unencapsulated devices retained 93.5 of their initial efficiency after 2000 h of shelf storag
Morphological Evolution of Sn Metal Based Anodes for Lithium Ion Batteries Using Operando X Ray Imaging
Get PDFSn based electrodes are promising candidates for next generation lithium ion batteries. However, it suffers from deleterious micro structural deformation as it undergoes drastic volume changes upon lithium insertion and extraction. Progress in designing these materials is limited to complex structures. There is a significant need to develop an alloy based anode that can be industrially manufactured and offers high reversible capacity. This necessitates a profound understanding of the interplay between structural changes and electrochemical performance. Here, operando X ray imaging is used to correlate the morphological evolution to electrochemical performance in foil and foam systems. The 3D Sn foam like structure electrode is fabricated in house as a practical approach to accommodate the volume expansion and alleviate the mechanical stress experienced upon alloying dealloying. Results show that generating pores in Sn electrodes can help manage the volume expansion and mitigate the severe mechanical stress in thick electrodes during alloying dealloying processes. The foam electrode demonstrates superior electrochemical performance compared to non porous Sn foil with an equivalent absolute capacity. This work advances the understanding of the real time morphological evolution of Sn bulky electrode
Investigation of Ti nanostructures via laboratory scanning free GEXRF
Get PDFThe ability to characterize periodic nanostructures in the laboratory gains more attention as nanotechnology is widely utilized in a variety of application fields. Scanning free grazing emission X ray fluorescence spectroscopy GEXRF is a promising candidate to allow non destructive, element sensitive characterization of sample structures down to the nanometer range for process engineering. Adopting a complementary metal oxide semiconductor CMOS detector to work energy dispersively via single photon detection, the whole range of emission angles of interest can be recorded at once. In this work, a setup based on a Cr X ray tube and a CMOS detector is used to investigate two TiO2 nanogratings and a TiO2 layer sample in the tender X ray range. The measurement results are compared to simulations of sample models based on known sample parameters. The fluorescence emission is simulated using the finite element method together with a Maxwell solver. In addition, a reconstruction of the sample model based on the measurement data is conducted to illustrate the feasibility of laboratory scanning free GEXRF as a technique to non destructively characterize periodic nanostructures in the tender X ray rang
Conformational Plasticity and Binding Affinity Enhancement Controlled by Linker Derivatization in Macrocycles
No full textMacrocycles are abundantly used by nature to enable cell permeable bioactive molecules. Synthetic non peptidic macrocycles are also increasingly considered as modalities for difficult to bind proteins but guidelines for macrocyclization are only beginning to emerge. Macrocycles are thought to constrain the available conformations but also to allow for residual flexibility, the latter being poorly understood. Here we show that even medium sized macrocycles display an unexpected high conformational plasticity, even when bound to their protein target. Minor modification of the linker region of macrocycles can shift the conformational ensemble to distinct conformational subclasses, each constituting distinct three dimensional scaffolds for further optimization. This led to several new ligands with improved affinity and beneficial physicochemical parameters for the FK506 binding protein 51, a promising target for depression, obesity and chronic pain. Importantly, none of the beneficial modifications could have been identified by classical medicinal chemistry as they only work in the macrocyclic context. Our results show that macrocyclization can do more than keeping loose ends together but rather provide a platform for multiple series of macrocycles with distinct binding mode
Understanding the Role of Varying Ti3C2Tx MXene in Ni Ti3C2Tx for the Oxygen Evolution Reaction
Get PDFThe current state of the art catalysts for the oxygen evolution reaction OER in an anion exchange membrane AEM electrolyser are not efficient enough to surpass green H2 produced by other electrolyser technologies, such as Proton Exchange Membrane PEM electrolysers. One reason for this is due to the AEM catalysts not being active enough and lacking long term stability. In this work, we combine Ni based material with Ti3C2Tx MXene at different loadings 1, 5 and 10 amp; 8201; to understand the effect of the MXene on the OER activity and stability. Our results show that the amount of MXene not only affects the OER performance, but the materials surface is also altered. Interestingly, the Ti3C2Tx is still present in the bulk for all composites but the surface of the composites contains different amounts of oxidized Ti3C2Tx i.e. TiO2. The optimum material in this study for the OER is the NiOx 1 amp; 8201; Ti3C2Tx which can be rationalized by the lower Ti Ni ratio in the starting materials hence producing less overall surface TiO2 during OER. Additionally, when the pure NiOx and the 1 amp; 8201; Ni Ti3C2Tx are compared by operando Raman spectroscopy, the NiOx 1 amp; 8201; Ti3C2Tx exhibits amp; 946; NiOOH at lower overpotentials, which is known to be present for efficient OER on Ni material
Component dependent lattice distortions and atomic scale insights in multi component Au Cu Ni Pd Pt based alloys
Get PDFIn our study, the composition dependent effects of atomic displacements in Au Cu Ni Pd Pt based alloys, comprising elements with large differences in atomic radii, are investigated at the atomic scale. Two alloys the equimolar AuCuNiPdPt and AuCuNiPd have been characterized using multi edge extended X ray absorption fine structure EXAFS spectroscopy in conjunction with reverse Monte Carlo RMC simulations at room temperature. The statistically averaged component dependent pair distribution functions PDFs , which represent the distribution of atoms around the assumed regular face centered cubic fcc lattice positions, reveal a shift of their peaks to shorter distances and a pronounced asymmetry in atomic distribution only for atoms with small radii Cu Ni . The analysis demonstrates that small atoms Cu Ni are significantly more displaced from the expected lattice positions as compared to large atoms Au Pt . Furthermore, there are indications of preferential next neighbour bonding that changes depending on the alloy composition. The most pronounced changes in the PDFs were found solely for Pd. With this study, we provide a basis for a deeper understanding of the composition dependent atomic arrangement in chemically complex solid solution
Structure and magnetic properties of the maple leaf antiferromagnet Ho3ScO6
Get PDFHo3ScO6 harbors a frustrated maple leaf lattice MLL . It crystalizes in the Mg3TeO6 type structure and has a centrosymmetric trigonal space group R3 . This system contains stacked layers of magnetic rings along the c axis consisting of six magnetic Ho3 ions forming Ho hexagons, which are connected into a two dimensional network by equilateral and isosceles triangles to form a rare example of a MLL. Long range magnetic order is reached below TN 4.1 K with a 120 amp; 9702; spin arrangement on the equilateral triangles, resulting in a positive vector chirality ground state configuratio
Exploring Electronic States and Ultrafast Electron Dynamics in AlInP Window Layers The Role of Surface Reconstruction
Get PDFAlInP 001 is widely utilized as a window layer in optoelectronic devices, including world record III V multi junction solar cells and photoelectrochemical PEC cells. The chemical and electronic properties of AlInP 001 depend on its surface reconstruction, which impacts its interaction with electrolytes in PEC applications and passivation layers. This study investigates AlInP 001 surface reconstructions using density functional theory and experimental methods. Phosphorus rich P rich and indium rich In rich AlInP surfaces are prepared with in situ monitoring of the process by reflection anisotropy RA spectroscopy and confirmed by low energy electron diffraction and photoemission spectroscopy. The experimental RA spectra closely match the theoretical predictions obtained by solving the Bethe Salpeter equation. It is shown that missing hydrogen on P rich surfaces and formation of In In 1D atomic chains on In rich surfaces introduce mid gap surface states that pin the Fermi level and induce band bending. Time resolved two photon photoemission measurements reveal ultrafast near surface electron dynamics for both P rich and In rich surfaces, demonstrating photoexcited electrons reaching the surface conduction band minimum and relaxing to mid gap surface states on about hundreds of fs. This work provides the most extensive AlInP surface analysis to date, allowing for more targeted surface and interface engineering, which is crucial for the optimization and design of III V heterostructure