Papers by Jörg Zegenhagen
In operando
Physical Review Letters
Kinetic roughening during electrodeposition was studied by grazing incidence small angle x-ray sc... more Kinetic roughening during electrodeposition was studied by grazing incidence small angle x-ray scattering for the case of Au(001) homoepitaxial growth in Cl- containing electrolytes. The formation and coarsening of an isotropic mound distribution on unreconstructed Au(001) and of [110]-oriented anisotropic mounds on the "hex" reconstructed surface was observed. The lateral mound coarsening is described by a well-defined scaling law. On unreconstructed Au a transition in the coarsening exponent from ≈1/4 to ≈1/3 with increasing potential is found, which can be explained by the pronounced potential dependence of surface transport processes in an electrochemical environment.
<i>In Operando</i> GISAXS Studies of Mound Coarsening in Electrochemical Homoepitaxy
Physical Review Letters, 2014
Kinetic roughening during electrodeposition was studied by grazing incidence small angle x-ray sc... more Kinetic roughening during electrodeposition was studied by grazing incidence small angle x-ray scattering for the case of Au(001) homoepitaxial growth in Cl- containing electrolytes. The formation and coarsening of an isotropic mound distribution on unreconstructed Au(001) and of [110]-oriented anisotropic mounds on the &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;hex&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; reconstructed surface was observed. The lateral mound coarsening is described by a well-defined scaling law. On unreconstructed Au a transition in the coarsening exponent from ≈1/4 to ≈1/3 with increasing potential is found, which can be explained by the pronounced potential dependence of surface transport processes in an electrochemical environment.
Journal of the American Chemical Society, 2011
We present in situ X-ray surface diffraction studies of interface processes with data acquisition... more We present in situ X-ray surface diffraction studies of interface processes with data acquisition rates in the millisecond regime, using the electrochemical dissolution of Au(001) in Cl-containing solution as an example. This progress in time resolution permits monitoring of atomic-scale growth and etching processes at solid-liquid interfaces at technologically relevant rates. Au etching was found to proceed via a layer-by-layer mechanism in the entire active dissolution regime up to rates of ∼20 ML/s. Furthermore, we demonstrate that information on the lateral surface morphology and in-plane lattice strain during the electrochemical process can be obtained.
X-ray standing wave microscopy: Chemical microanalysis with atomic resolution
Applied Physics Letters, 2002
Abstract We introduce a microprobe technique based on the x-ray standing wave method (XSW) demons... more Abstract We introduce a microprobe technique based on the x-ray standing wave method (XSW) demonstrating that structural analysis can be achieved with chemical sensitivity on a microscopic scale. We apply this XSW microscopy technique to study an epitaxially grown ...
Exceptional Transport Properties and Flux Pinning by Self-Organization in YBa_2Cu_3O_7-delta films
Combining UHV-scanning tunneling microscopy and transmission electron microscopy we demonstrate h... more Combining UHV-scanning tunneling microscopy and transmission electron microscopy we demonstrate how to control the surface and defect structure of YBa_2Cu_3O_7-delta (YBCO) films on tailored SrTiO_3(001) surfaces. YBCO films are grown by pulsed laser deposition on different vicinal SrTiO_3(001) surfaces with regular, straight step edges spaced 23-600 Å apart and separated by steps of different heights (3.9-11.7 ÅAs an example, we find that the vicinal surface SrTiO_3(106) promotes self-organization of YBCO in a particularly efficient way. An array of antiphase boundaries is formed during coalescence of growth fronts which have nucleated out of registry with one another on adjacent terraces. The microstructure imposed on the films leads to a pronounced in-plane anisotropy of the resistivity and flux pinning. We achieve a substantial enhancement of the critical current density up to j_c=8× 10^11 A/m^2 (4.2 K) as derived from a magneto-optical visualization of the flux penetration. We ...
Preface
Philosophical Magazine Part B, 1994
Hydrogen adsorption on the GaAs(001)-(2×4) surface: A scanning-tunneling-microscopy study
Physical Review B, 1995
ABSTRACT Using scanning tunneling microscopy (STM) we have investigated the process of hydrogen a... more ABSTRACT Using scanning tunneling microscopy (STM) we have investigated the process of hydrogen adsorption on the GaAs(001)-(2×4) surface. Stepwise hydrogen-induced changes in the atomic structure of the surface are revealed in the STM images. In a first step, one or two hydrogen atoms bond per As atom, giving rise to localized protrusions within the As dimer rows. In a second step, after adsorption of a third H atom per As atom, AsH3 forms and desorbs, resulting in depressions and thus a degradation of the As dimer rows. Finally, at high exposures a disordered surface develops.
Transport properties and flux pinning by self-organization in YBa 2 Cu 3 O 7 − δ films on vicinal SrTiO 3 (001)
Physical Review B, 1997
We have observed anisotropic flux pinning and resistivity in the substrate plane of YBaâCuâO{sub ... more We have observed anisotropic flux pinning and resistivity in the substrate plane of YBaâCuâO{sub 7-δ} (YBCO) thin films grown on vicinal SrTiOâ(001) with the c axis oriented along the SrTiOâ [001] direction. Using UHV scanning tunneling microscopy and transmission electron microscopy we demonstrate the influence of a periodic nanoscale step structure of the clean substrate surface on the morphology and defect microstructure of subsequently deposited YBCO films. A linear array of dislocations generated via self-organization of the YBCO leads to an exceptionally large critical current density up to 8Ã10¹¹A/m² at 4.2 K. The findings indicate that the critical current density of high-temperature superconductors can be enhanced in a controlled way growing thin films on tailored substrate surfaces. {copyright} {ital 1997} {ital The American Physical Society}
The lattice constant of crystals depends on their isotopic composition. This is caused by the eff... more The lattice constant of crystals depends on their isotopic composition. This is caused by the effect of zero point motion and anharmonicity. The effect is largest at T = 0 and vanishes above the Debye temperature. In the same way as successfully demonstrated recently [1], we used the x-ray standing wave technique to determine the lattice constant difference between a 0.9 mu ^30Si enriched epitaxial film and a Si substrate crystal with natural isotopic composition in the temperature range from 54K to 300K. The measurements were performed at the RÖMO station at HASYLAB, Hamburg with Synchrotron radiation from the DORIS storage ring, employing a (333) reflection from the substrate at high Bragg angle and detecting electron total yield. The result of the measurements and the data analysis can be compared with two calcutaions [2,3] and are in better agreement with the recent path-integral Monte Carlo simulations [3]. [1] A.Kazimirov, J.Zegenhagen, M.Cardona, Science 282(98)930 [2] S.Bier...
Interface Stress Effect on Superconductivity of GdBa_2Cu_3O7 Films and Antiferrodistortive Phase Transition of SrTiO3 Crystals
Ultrathin single-phase, c-oriented thin films of the high temperature superconductor (HTS) GdBa_2... more Ultrathin single-phase, c-oriented thin films of the high temperature superconductor (HTS) GdBa_2Cu_3O7 (GdBCO) were grown simultaneously on SrTiO3 (STO) and NdGaO3 (NGO) substrates by pulsed laser deposition. The films with thickness up to 42nm grow pseudomorphically on STO substrate, while the films grown on NGO substrate do not, even for the film of 14nm which is the thinnest one in our study. Accordingly, Tc of the GdBCO films is influenced by the interface stress. We also found a correlation between Jc of the HTS film and the interface stress field. Generally we found that the interface stress field affects not only the epitaxial film, but also the substrate crystal. The antiferrodistortive phase transition of STO which usually occurs at around 105K was investigated by x-ray backreflection (Bragg angle thetaB higher than 89.5^o). As discussed in our presentation, the critical behaviour and the domain structure of STO crystals were found to be changed due to the influence of the...
X-ray structural analysis of semiconductor-electrolyte interfaces
The in-situ and ex-situ use of x-ray methods to investigate the structure of semiconductor-electr... more The in-situ and ex-situ use of x-ray methods to investigate the structure of semiconductor-electrolyte interfaces is discussed, with examples of several systems studied. The design of electrochemical cells for investigating in-situ potential controlled and dynamic electrochemical processes is described, together with applications of their use. The variety of metal structures availble from electrochemical depostion is shown, by describing Cu deposition on GaAs, electroless deposition of Au on Si, and potential controlled deposition of Au on Si. Examples of the benefit of using surface x-ray diffraction, and x-ray standing waves to investigate metal depostion on semiconductor surfaces are given.
Inelastic background analysis of HAXPES spectra: towards enhanced bulk sensitivity in photoemission
Surface and Interface Analysis, 2014
ABSTRACT We report on quantitative inelastic background analysis in hard X-ray photoelectron spec... more ABSTRACT We report on quantitative inelastic background analysis in hard X-ray photoelectron spectroscopy at high excitation energy (12–18 keV) using the Tougaard method implemented with careful optimisation of the inelastic scattering cross section. Such a method enables the determination of the in-depth elemental distribution over depths up to70 nm. We studied three parameters and investigate their influence on the results: the depth of the layer increases the uncertainty, the thickness and composition of the layer has an influence on statistics, and the excitation energy that must be chosen as a trade-off between high probing depth and low photoionization cross section. We show how this promising method can be used to follow diffusion of a 1-ML La layer after annealing a technologically relevant sample. Copyright © 2014 John Wiley &amp;amp; Sons, Ltd.
Science (New York, N.Y.), Jan 30, 1998
The molecular volume of crystals depends on their isotopic masses. This influence originates from... more The molecular volume of crystals depends on their isotopic masses. This influence originates from the zero-point motion and the resulting small differences in lattice constants. This effect was measured with high precision by using an x-ray standing wave. The standing wave is generated during Bragg reflection and thus is in phase with the planes of the substrate crystal, which is covered with a homoepitaxial film that has a different isotopic composition than the substrate. The positions of the surface planes of the film with respect to the substrate planes are revealed by the photoelectrons excited by the maxima of the standing wave. For germanium-76 on natural germanium(111), a difference in lattice constant of -1.1 x 10(-5) and -2.5 x 10(-5) at 300 and 54 kelvin, respectively, was found. The results are in good agreement with theoretical predictions.
Hard X-ray Photoelectron Spectroscopy (HAXPES) Al alloys Complex metallic alloys Composition dept... more Hard X-ray Photoelectron Spectroscopy (HAXPES) Al alloys Complex metallic alloys Composition depth profiling Oxide/hydroxide A Hard X-ray Photoelectron Spectroscopy (HAXPES) characterisation of the passivation layers formed by electrochemical polarisation of Al-Cr-Fe complex metallic alloys is presented. By employing X-ray excitation energies from 2.3 to 10.0 keV, the depth distributions of Al-and Cr-oxide and hydroxide species in the (Al,Cr)-containing passive layers could be determined. Simultaneous analyses of the shallow Al 2s and deep Al 1s core level lines (respectively, more bulk-and surface-sensitive) provided complementary information to effectively determine the depth-resolved contributions of hydroxide and oxide species within the passivation layer. A Cr threshold concentration of 18 (at.%) was found for effective passivation at pH 1.
Hard X-ray photoelectron spectroscopy Synchrotron radiation Photoelectric multipole contributions... more Hard X-ray photoelectron spectroscopy Synchrotron radiation Photoelectric multipole contributions Fourier analysis a b s t r a c t Investigations on the geometrical structure, chemical composition and electronic properties of surfaces and interfaces are performed on beamline ID32 at the ESRF. It is a high resolution beamline covering the photon energy range 1.4-30 keV optimized for X-ray standing wave, surface X-ray diffraction, and hard X-ray photoelectron spectroscopy experiments. Fresnel zone plates and compound refractive lens systems are used to focus the monochromatic beam. After outlining the principles of X-ray standing wave measurements the unique features of the ID32 beamline are described. Future developments are discussed and finally some selected examples illustrating the advantages of combining the X-ray standing wave technique with hard X-ray photoelectron spectroscopy are presented.
Atomic structure of GdBaCuO superconductor thin films on NdGaO(0 0 1)Probed by X-ray standing waves and photoelectron spectroscopy
ABSTRACT We characterized the structure of GdBa2Cu3O7-δthin films grown on NdGaO3(0 0 1) substrat... more ABSTRACT We characterized the structure of GdBa2Cu3O7-δthin films grown on NdGaO3(0 0 1) substrates using X-ray standing waves combined with photoelectron spectroscopy. The O 1s and Cu 2p core-level spectra display components that exhibit distinct X-ray standing wave modulations, which we identify as arising from the well-ordered (intrinsic) parts of the oxide films, but also contain nearly unmodulated components arising from reacted, degraded phases (non-intrinsic). The large mean-free paths of high kinetic-energy photoelectrons permits, in addition, the detection of the Nd and Ga atoms near the buried interface below a 3.5-nm film. Our measurements reveal an essentially bulk-terminated NdGaO3 surface at the interface. By considering a pseudomorphically strained, orthorhombic Y123 structure for the 3.5-nm film, we find that our X-ray standing wave data are consistent with an interface composed of CuO–NdO planes, where the Cu–Nd distances are determined to be 0.18 nm. The analysis rules out the possibility for the film to start its stacking with a BaO plane. The X-ray standing wave measurement for the GdBa2Cu3O7-δ valence band yields results nearly identical to the intrinsic part of the Cu 2p core level and therefore confirms the major contribution of Cu 3d to the valence band in high-temperature cuprates. For thicker films, the standing wave analysis on a 17.5-nm sample indicates that the film is partially relaxed, in good agreement with the previous X-ray diffraction results. Repeating the measurements at 60 K suggests that the in-plane lattice mismatch between the film and substrate increases with decreasing temperature.
Hard X-ray photoelectron spectroscopy: sensitivity to depth, chemistry and orbital character
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2005
Photoelectron spectroscopy is growing in importance as a tool for characterizing not only the sur... more Photoelectron spectroscopy is growing in importance as a tool for characterizing not only the surface but also the bulk of solids. Photon fluxes of modern synchrotron radiation sources compensate the cross-section lowering of photoelectrons with kinetic energy in the hard X-ray range, the only electrons able to escape from bulk regions. We present examples of photoelectron emission experiments where we
Microscopic structure of the GaAs(001)-(6 x 6) surface derived from scanning tunneling microscopy
Physical review. B, Condensed matter
Microscopic structure of the GaAs(001)-(6×6) surface derived from scanning tunneling microscopy
Physical review. B, Condensed matter
We have derived a microscopic, structural model for the GaAs(001)-(6×6) surface reconstruction us... more We have derived a microscopic, structural model for the GaAs(001)-(6×6) surface reconstruction using scanning tunneling microscopy. It involves three atomic layers containing both As and Ga dimers. Previous studies suggested the (6×6) structure to be poorly ordered, often it was only described as a (1×6) superstructure. In contrast, we find a well-developed (6×6) superstructure with As-dimer rows in the [11¯0] direction separated by 24 Å. However, this reconstruction may not be a stable equilibrium structure.
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Papers by Jörg Zegenhagen