Search results for "photoemission"
showing 10 items of 174 documents
High Tolerance of Double-Decker Phthalocyanine toward Molecular Oxygen
2018
Because organic electronics suffer from degradation-inducing oxidation processes, oxygen-tolerant organic molecules could solve this issue and be integrated to improve the stability of devices during operation. In this work, we investigate how lutetium double-decker phthalocyanine (LuPc2) reacts toward molecular oxygen and we report microscopic details of its interaction with LuPc2 film by combining X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and density functional theory. Surprisingly, LuPc2 molecules are found to weakly physisorb below 120 K and appear rather inert to molecular oxygen at more elevated temperatures. We are able to draw a micros…
Spin structure and spin Hall magnetoresistance of epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO 3
2019
We report a combined study of imaging the antiferromagnetic (AFM) spin structure and measuring the spin Hall magnetoresistance (SMR) in epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO3. X-ray magnetic linear dichroism photoemission electron microscopy measurements reveal that the AFM spins of the SmFeO3(1 1 0) align in the plane of the film. Angularly dependent magnetoresistance measurements show that SmFeO3/Ta bilayers exhibit a positive SMR, in contrast to the negative SMR expected in previously studied collinear AFMs. The SMR amplitude increases linearly with increasing external magnetic field at higher magnetic fields, suggesting that field-induced canting of …
Effect of Composition on the Photoelectrochemical Behavior of Anodic Oxides on Binary Aluminum Alloys
2006
The photoelectrochemical behavior of anodic films on Al alloys, containing titanium, tantalum, and tungsten (valve metals), has been studied as a function of alloy composition and anodizing conditions. Photocurrent spectroscopy has been used to get information on bandgap and the flatband potential values of different mixed oxides. Both insulator-like and semiconducting behavior has been observed for anodic oxides grown on Al-W and Al-Ti alloys dependent on alloy initial composition. Optical bandgap values, E opt g , of different oxides are in accordance with predictions based on the correlation between E opt g and the difference of electronegativities of the oxide constituents, indicating p…
Magnetization dynamics in polycrystalline Permalloy and epitaxial Co platelets observed by time-resolved photoemission electron microscopy
2009
We studied the dynamic magnetization response in rectangular polycrystalline Permalloy and also epitaxial Co structures (lateral sizes comprised tens of microns at a thickness of tens of nanometers) during the action of a magnetic field pulse, using time-resolved X-ray photoemission electron microscopy with a time resolution of 10 ps. In the case of Permalloy platelets the restoring torque that is necessary for the stroboscopic image acquisition is provided by the Landau flux closure structure representing a minimum of the free energy. We investigated the dynamic response of 90° Neel domain walls. The main results are: the maximum velocity of the domain wall is 1.5 × 104 m/s, the intrinsic …
Sub-nanosecond resolution x-ray magnetic circular dichroism photoemission electron microscopy of magnetization processes in a permalloy ring
2005
Fast magnetization processes in a microstructured permalloy ring with 80 µm o.d. and 30 nm thickness have been observed by photoemission electron microscopy exploiting x-ray magnetic circular dichroism as the magnetic contrast mechanism. As a high speed probe we employed synchrotron radiation pulses at the ESRF (Grenoble) operated in 16-bunch mode, yielding photon pulses of 105 ps FWHM with a period of 176 ns. Fast magnetic field pulses have been generated by means of current pulses through coplanar waveguides with the magnetic structure being lithographically prepared on their surface. A stroboscopic pump–probe set-up with a variable time delay between the field pulse and photon pulse allo…
Time-resolved X-ray photoemission electron microscopy: imaging magnetodynamics on the 100 ps scale and below
2005
Abstract We present recent results of time-resolved X-ray photoemission electron microscopy (TR-XPEEM) investigations on magnetic systems. Our studies of microstructured permalloy particles employ a magnetic pump XPEEM probe approach. The stroboscopic experiments feature a time resolution of Δ τ ≤ 130 ps and yield magnetic domain images with a surprising richness of details. We observe a strong influence of incoherent magnetization rotation processes, which lead to complicated transient domain structures with a blocked relaxation behavior.
Stroboscopic XMCD–PEEM imaging of standing and propagating spinwave modes in permalloy thin-film structures
2007
Abstract Using synchrotron-based stroboscopic photoemission electron microscopy with X-ray circular dichroism as contrast method, we have investigated the high-frequency response of permalloy thin-film structures. Standing precessional modes have been studied in rectangular elements (16 × 32 μm 2 , 10 nm thick) with a high time resolution of about 15 ps in the low- α mode of BESSY. With increasing amplitude of the applied magnetic AC field the particle is driven from an initial symmetric Landau flux-closure state into an asymmetric state and finally into a single-domain state magnetized perpendicular to the applied field H AC . The electromagnetic microwave field thus can induces a net magn…
Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy
2010
By example of a Permalloy particle (40 × 40 μm(2) size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cau…
Verwey-type transition in EuNiP
2006
High temperature 151Eu Mossbauer measurements provide proof for inhomogeneous mixed-valent behaviour in EuNiP. We observed that EuNiP undergoes a Verwey-type charge delocalisation transition when heated above 470 K prior to the structural γ-β phase transition at T ≈ 510 K. This finding confirms the results of photoemission spectroscopy in the isostructural compound EuPdP and of TB-LMTO-ASA band structure calculations. We discuss the role of a van Hove singularity associated with a high density of 4f states close to the Fermi energy in inhomogeneous mixed europium valency, and the microscopic mechanism of γ-β phase transition in compounds analogous to EuNiP.
Direct Measurement of Electron-Phonon Coupling with Time-Resolved ARPES
2020
Time- and angular- resolved photoelectron spectroscopy is a powerful technique to measure electron dynamics in solids. Recent advances in this technique have facilitated band and energy resolved observations of the effect that excited phonons, have on the electronic structure. Here, we show with the help of ab initio simulations that the Fourier analysis of the time-resolved measurements of solids with excited phonon modes enables the determination of the band- and mode-resolved electron-phonon coupling directly from the experimental data without any additional input from theory. Such an observation is not restricted to regions of strong electron-phonon coupling and does not require strongl…