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Depth of Discharge Dependent Capacity Decay Induced by the Accumulation of Oxidized Lattice Oxygen in Li?Rich Layered Oxide Cathode
No full textMore and more basic practical application scenarios have been gradually ignored disregarded, in fundamental research on rechargeable batteries, e.g. assessing cycle life under various depths of discharge DODs . Herein, although benefit from the additional energy density introduced by anionic redox, we critically revealed that lithium rich layered oxide LRLO cathodes present anomalously poor capacity retention at low DOD cycling, which is essentially different from typical layered cathodes e.g. NCM , and pose a formidable impediment to the practical application of LRLO. We systemically demonstrated that DOD dependent capacity decay is induced by the anionic redox and accumulation of oxidized lattice oxygen On amp; 8722; . Upon low DOD cycling, the accumulation of On amp; 8722; and the persistent presence of vacancies in the transition metal TM layer intensified the in plane migration of TM, exacerbating the expansion of vacancy clusters, which further facilitated detrimental out of plane TM migration. As a result, the aggravated structural degradation of LRLO at low DOD impeded reversible Li intercalation, resulting in rapid capacity decay. Furthermore, prolonged accumulation of On amp; 8722; persistently corroded the electrode electrolyte interface, especially negative for pouch type full cells with the shuttle effect. Once the double edged sword effect of anionic redox being elucidated under practical condition, corresponding modification strategies routes would become distinct for accelerating the practical application of LRL
A Structure and Magnetism Study of MnII3MnIVLnIII3 Coordination Complexes with Ln Dy, Yb
No full textWe report the research results of polynuclear complexes consisting of 3d 4f mixed metal cores that are maintained by acetate ligands and multidentate Schiff base ligands with structurally exposed thioether groups. The presence of the latter at the periphery of these neutral compounds enables their anchoring onto substrate surfaces. Specifically, we investigated the electronic and magnetic properties as well as the structural arrangement in MnII3MnIVLnIII3 with Ln Dy, Yb coordination complexes using various complementary methods. We studied the electronic and atomic structure of the target compounds using the XAS and XES techniques. The molecular structures of the compounds were determined using density functional theory, and the magnetic data were obtained as a function of the magnetic field. Using the XMCD method, we followed the changes in the electronic and magnetic properties of adsorbed magnetic compounds induced by the reaction of ligands through interaction with the substrate. The complexes show antiferromagnetic exchange interactions between Mn and Ln ions. The spectroscopic analyses confirmed the structural and electronic integrity of complexes in organic solution. This study provides important input for a full understanding of the dependence of the magnetic properties and the molecule substrate interaction of single adsorbed molecules on the type of ligands. It highlights the importance of chemical synthesis for controlling and tailoring the magnetic properties of metalorganic molecules for their use as optimized building blocks of future molecular spin electronic
Tunable positions of Weyl nodes via magnetism and pressure in the ferromagnetic Weyl semimetal CeAlSi
Get PDFThe noncentrosymmetric ferromagnetic Weyl semimetal CeAlSi with simultaneous space inversion and time reversal symmetry breaking provides a unique platform for exploring novel topological states. Here, by employing multiple experimental techniques, we demonstrate that ferromagnetism and pressure can serve as efficient parameters to tune the positions of Weyl nodes in CeAlSi. At ambient pressure, a magnetism facilitated anomalous Hall Nernst effect AHE ANE is uncovered. Angle resolved photoemission spectroscopy ARPES measurements demonstrated that the Weyl nodes with opposite chirality are moving away from each other upon entering the ferromagnetic phase. Under pressure, by tracing the pressure evolution of AHE and band structure, we demonstrate that pressure could also serve as a pivotal knob to tune the positions of Weyl nodes. Moreover, multiple pressure induced phase transitions are also revealed. These findings indicate that CeAlSi provides a unique and tunable platform for exploring exotic topological physics and electron correlations, as well as catering to potential applications, such as spintronic
Speed limits of the laser induced phase transition in FeRh
Get PDFWe use ultrafast x ray diffraction and the polar time resolved magneto optical Kerr effect to study the laser induced metamagnetic phase transition in two FeRh films with thicknesses below and above the optical penetration depth. In the thin film, we identify an intrinsic timescale for the light induced nucleation of ferromagnetic FM domains in the antiferromagnetic material of 8ps, which is substantially longer than the time it takes for strain waves to traverse the film. For the inhomogeneously excited thicker film, only the optically excited near surface part transforms within 8ps. For strong excitations, we observe an additional slow rise of the FM phase, which we experimentally relate to a growth of the FM phase into the depth of the layer by comparing the transient magnetization in frontside and backside excitation geometry. In the lower lying parts of the film, which are only excited via near equilibrium heat transport, the FM phase emerges significantly slower than 8ps after heating above the transition temperatur
Visualization of beam position and beam shape
No full textFor 25 years, the HZB cyclotron provides protons for eye tumour treatment in collaboration with the Charit Universitätsmedizin Berlin. Parallel to therapy, there is an on going research and development program for beam dosimetry, medical physics, radiation hardness tests, and PIXE. For all these applications, a visualization of the beam shape and its intensity distribution is essential. In the treatment room a CCD camera, having a weight of about 20 kg is used for the measurements of the two dimensional beam distribution. For experiments, a much lighter 2 kg camera system was developed. The properties of this camera and the data evaluation of the images will be presente
PINK a tender X ray beamline for X ray emission spectroscopy
Get PDFA high flux beamline optimized for non resonant X ray emission spectroscopy XES in the tender X ray energy range has been constructed at the BESSY II synchrotron source. The beamline utilizes a cryogenically cooled undulator that provides X rays over the energy range 2.1 amp; 8197;keV to 9.5 amp; 8197;keV. This energy range provides access to XES [and in the future X ray absorption spectroscopy XAS ] studies of transition metals ranging from Ti to Cu K amp; 945;, amp; 8197;K amp; 946; lines and Zr to Ag L amp; 945;, amp; 8197;L amp; 946; , as well as light elements including P, S, Cl, K and Ca K amp; 945;, amp; 8197;K amp; 946; . The beamline can be operated in two modes. In PINK mode, a multilayer monochromator E amp; 916;E amp; 8771; 30 80 provides a high photon flux 1014 amp; 8197;photons amp; 8197;s amp; 8722;1 at 6 amp; 8197;keV and 300 amp; 8197;mA ring current , allowing non resonant XES measurements of dilute substances. This mode is currently available for general user operation. X ray absorption near edge structure and resonant XAS techniques will be available after the second stage of the PINK commissioning, when a high monochromatic mode E amp; 916;E amp; 8771; 10000 40000 will be facilitated by a double crystal monochromator. At present, the beamline incorporates two von Hamos spectrometers, enabling time resolved XES experiments with time scales down to 0.1 amp; 8197;s and the possibility of two color XES experiments. This paper describes the optical scheme of the PINK beamline and the endstation. The design of the two von Hamos dispersive spectrometers and sample environment are discussed here in detail. To illustrate, XES spectra of phosphorus complexes, KCl, TiO2 and Co3O4 measured using the PINK setup are presente
Orientation of Cobalt Phthalocyanines on Molybdenum Disulfide Distinguishing between Single Crystals and Small Flakes
Get PDFHeterostructures consisting of transition metal dichalcogenides TMDCs and organic molecules are currently of enormous interest for a variety of applications. Comparably weakly interacting molecules, like phthalocyanines, exhibit a high potential for tuning the electronic properties of TMDCs. Knowledge of the molecular orientation is a prerequisite for understanding the nature and strength of the interfacial interaction. We study the molecular orientation of cobalt phthalocyanine CoPc and perfluorinated cobalt phthalocyanine CoPcF16, also denoted F16CoPc , on both large molybdenum disulfide MoS2 single crystals and small MoS2 flakes, using synchrotron based techniques X ray absorption spectroscopy XAS at the Co L3 edge and spectromicroscopy in a photoemission electron microscope PEEM . We show that the orientation can be radically different on both substrates. Whereas on large crystals an almost flat lying orientation is observed, significant tilt angles were found on smaller flakes. It is proposed that the orientation depends crucially on the number of MoS2 layers and or the smaller size of atomically flat terraces on flakes compared to bulk crystal
Bandgap Pairing in Three Terminal Tandem Solar Cells From Limiting Efficiency to Voltage Matched Device Performance
Get PDFThree terminal tandem solar cells 3 amp; 8201;T TSCs have recently sparked increasing interest as they feature a lean monolithic device architecture similar to two terminal TSCs and, like four terminal TSCs, do not require current matching for optimal operation. In this contribution, detailed balance limit calculations for different combinations of top and bottom cell bandgaps are conducted to determine the optimum bandgap pairing and limiting efficiency of 3T TSCs. An experimental realization of a 3T TSC with perovskite and silicon sub cells and a combined efficiency of 28.9 is presented and used to derive a realistic parameterization for non radiative recombination. Herein, the optimum bandgap pairing and resulting maximum efficiency under voltage matched conditions for voltage matching ratios of 1 2 and 2 3, which is relevant for stringing and module integration of 3T TSCs, are further determined. To this end, non radiative recombination is incorporated in the model and quantified by matching theoretical open circuit voltages and those of real world high efficiency solar cells based on different absorber materials and thus bandgaps , including the perovskite top cell of the best in house 3T TS
Soft X ray absorption and fragmentation of tin oxo cage photoresists
Get PDFTin oxo cage organometallic compounds are considered as photoresists for extreme ultraviolet EUV photolithography. To gain insight into their electronic structure and reactivity to ionizing radiation, we trapped bare gas phase n butyltin oxo cage dications [ BuSn 12O14 OH 6]2 in an ion trap and investigated their fragmentation upon soft X ray photoabsorption by means of mass spectrometry. In complementary experiments, the tin oxo cages with hydroxide and trifluoroacetate counter anions were cast in thin films and studied using X ray transmission spectroscopy. Quantum chemical calculations were used to interpret the observed spectra. At the carbon K edge, a distinct pre edge absorption band can be attributed to transitions in which electrons are promoted from C1s orbitals to the lowest unoccupied molecular orbitals, which are delocalized orbitals with strong antibonding Sn C amp; 963; character. At higher energies, the most prominent resonant transitions involve C C and C H amp; 963; valence states and Rydberg 3s and 3p states. In the solid state, the onset of continuum ionization is shifted by amp; 8764;5 eV to lower energy with respect to the gas phase, due to the electrostatic effect of the counterions. The O K edge also shows a pre edge absorption, but it is devoid of any specific features, because there are many transitions from the different O1s orbitals to a large number of vacant orbitals. In the gas phase, formation of the parent [ BuSn 12O14 OH 6]3 radical ion is not observed at the C K edge nor at the O K edge, because the loss of a butyl group from this species is very efficient. We do observe a number of triply charged photofragment ions, some of which have lost up to 5 butyl groups. Structures of these species are proposed based on quantum chemical calculations, and pathways of formation are discussed. Our results provide insight into the electronic structure of alkyltin oxo cages, which is a prerequisite for understanding their response to EUV photons and their performance as EUV photoresist
Two Channel Indirect Gap Photoluminescence and Competition between the Conduction Band Valleys in Few Layer MoS2
Get PDFIn response to the demand in few nanometer MoS2 films on large substrate area, sulfurization of MoO3 layers deposited on SiO2 Si substrate by plasma enhanced atomic layer deposition was performed and the obtained MoS2 films were tested using X ray diffraction, confocal Raman spectroscopy and scanning electron microscopy to ensure identity, thickness and surface morphology of the films. Spectroscopic ellipsometry and steady state, excitation power and temperature dependent photoluminescence technique, supported by band structure calculations with spin orbit coupling included were then applied to trace down the evolution of electronic energy spectrum over the photon energy range 0.07 6.5 eV upon decrease of MoS2 thickness from 30 to 5 and 3 nm. Both experimental approaches solidly verify preservation of the well known, distinctive A, B, C, and D exciton structures at and above the direct energy gap down to 3 nm film thickness or 4 MoS2 layers. Two channels of indirect emission, which involve two competting valleys of the conduction band, are observed. Both 3 and 5 nm MoS2 exhibit switching from two to one channel indirect emission with temperature decrease. The former experiences such indirect to indirect crossover at much higher temperature than the latter, which corroborates our band structure result