TY  - JOUR
A1  - Zeitz, Maria
A1  - Haacker, Jan M.
A1  - Donges, Jonathan
A1  - Albrecht, Torsten
A1  - Winkelmann, Ricarda
T1  - Dynamic regimes of the Greenland Ice Sheet emerging from interacting melt-elevation and glacial isostatic adjustment feedbacks
JF  - Earth system dynamics
N2  - The stability of the Greenland Ice Sheet under global warming is governed by a number of dynamic processes and interacting feedback mechanisms in the ice sheet, atmosphere and solid Earth. 
Here we study the long-term effects due to the interplay of the competing melt-elevation and glacial isostatic adjustment (GIA) feedbacks for different temperature step forcing experiments with a coupled ice-sheet and solid-Earth model. 
Our model results show that for warming levels above 2 degrees C, Greenland could become essentially ice-free within several millennia, mainly as a result of surface melting and acceleration of ice flow. These ice losses are mitigated, however, in some cases with strong GIA feedback even promoting an incomplete recovery of the Greenland ice volume. We further explore the full-factorial parameter space determining the relative strengths of the two feedbacks: our findings suggest distinct dynamic regimes of the Greenland Ice Sheets on the route to destabilization under global warming - from incomplete recovery, via quasi-periodic oscillations in ice volume to ice-sheet collapse. 
In the incomplete recovery regime, the initial ice loss due to warming is essentially reversed within 50 000 years, and the ice volume stabilizes at 61 %-93 % of the present-day volume. For certain combinations of temperature increase, atmospheric lapse rate and mantle viscosity, the interaction of the GIA feedback and the melt-elevation feedback leads to self-sustained, long-term oscillations in ice-sheet volume with oscillation periods between 74 000 and over 300 000 years and oscillation amplitudes between 15 %-70 % of present-day ice volume. 
This oscillatory regime reveals a possible mode of internal climatic variability in the Earth system on timescales on the order of 100 000 years that may be excited by or synchronized with orbital forcing or interact with glacial cycles and other slow modes of variability. Our findings are not meant as scenario-based near-term projections of ice losses but rather providing insight into of the feedback loops governing the "deep future" and, thus, long-term resilience of the Greenland Ice Sheet.
Y1  - 2022
U6  - https://doi.org/10.5194/esd-13-1077-2022
SN  - 2190-4979
SN  - 2190-4987
VL  - 13
IS  - 3
SP  - 1077
EP  - 1096
PB  - Copernicus Publ.
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Zeiske, Stefan
A1  - Sandberg, Oskar J.
A1  - Zarrabi, Nasim
A1  - Wolff, Christian Michael
A1  - Raoufi, Meysam
A1  - Peña-Camargo, Francisco
A1  - Gutierrez-Partida, Emilio
A1  - Meredith, Paul
A1  - Stolterfoht, Martin
A1  - Armin, Ardalan
T1  - Static disorder in lead halide perovskites
JF  - The journal of physical chemistry letters
N2  - In crystalline and amorphous semiconductors, the temperature-dependent Urbach energy can be determined from the inverse slope of the logarithm of the absorption spectrum and reflects the static and dynamic energetic disorder. Using recent advances in the sensitivity of photocurrent spectroscopy methods, we elucidate the temperature-dependent Urbach energy in lead halide perovskites containing different numbers of cation components. We find Urbach energies at room temperature to be 13.0 +/- 1.0, 13.2 +/- 1.0, and 13.5 +/- 1.0 meV for single, double, and triple cation perovskite. Static, temperature-independent contributions to the Urbach energy are found to be as low as 5.1 ?+/- 0.5, 4.7 +/- 0.3, and 3.3 +/- 0.9 meV for the same systems. Our results suggest that, at a low temperature, the dominant static disorder in perovskites is derived from zero-point phonon energy rather than structural disorder. This is unusual for solution-processed semiconductors but broadens the potential application of perovskites further to quantum electronics and devices.
KW  - Cations
KW  - External quantum efficiency
KW  - Perovskites
KW  - Solar cells
KW  - Solar energy
Y1  - 2022
U6  - https://doi.org/10.1021/acs.jpclett.2c01652
SN  - 1948-7185
VL  - 13
IS  - 31
SP  - 7280
EP  - 7285
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Zeiske, Stefan
A1  - Sandberg, Oskar J.
A1  - Kurpiers, Jona
A1  - Shoaee, Safa
A1  - Meredith, Paul
A1  - Armin, Ardalan
T1  - Probing charge generation efficiency in thin-film solar cells by integral-mode transient charge extraction
JF  - ACS photonics
N2  - The photogeneration of free charges in light-harvesting devices is a multistep process, which can be challenging to probe due to the complexity of contributing energetic states and the competitive character of different driving mechanisms. In this contribution, we advance a technique, integral-mode transient charge extraction (ITCE), to probe these processes in thin-film solar cells. ITCE combines capacitance measurements with the integral-mode time-of-flight method in the low intensity regime of sandwich-type thin-film devices and allows for the sensitive determination of photogenerated charge-carrier densities. We verify the theoretical framework of our method by drift-diffusion simulations and demonstrate the applicability of ITCE to organic and perovskite semiconductor-based thin-film solar cells. Furthermore, we examine the field dependence of charge generation efficiency and find our ITCE results to be in excellent agreement with those obtained via time-delayed collection field measurements conducted on the same devices.
KW  - charge generation
KW  - thin-film solar cells
KW  - organic semiconductors;
KW  - perovskite semiconductors
KW  - external generation efficiency
Y1  - 2022
U6  - https://doi.org/10.1021/acsphotonics.1c01532
SN  - 2330-4022
VL  - 9
IS  - 4
SP  - 1188
EP  - 1195
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Zeimer, Ute
A1  - Pietsch, Ullrich
A1  - Grenzer, Joerg
A1  - Fricke, J.
A1  - Knauer, A.
A1  - Weyers, Markus
T1  - Optimised two layer overgrowth of a lateral strain-modulated nanostructure
N2  - Recently it has been shown that lateral carrier confinement in an InGaAs quantum well (QW) embedded in GaAs can be achieved by using a laterally patterned InGaP stressor layer on top of the heterostructure. To exploit this effect in a device the structure has to be planarized by a second epitaxial step. It has been shown that the lateral strain modulation almost vanishes after overgrowth with GaAs, whereas overgrowth with a single ternary layer of opposite strain compared to the stressor layer suffers from strain induced decomposition. Here we show that the lateral carrier confinement of the initially free standing nanostructure can almost be maintained using a two step process for overgrowth, where a strained thin ternary layer is grown first followed by GaAs up to complete planarization of the patterned structure. Thickness and composition of the ternary layer are adjusted on the basis of finite element calculations of the strain distribution (FEM). The strain field achieved after overgrowth is probed by X-ray grazing- incidence diffraction (GID). (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0925-8388
ER  - 
TY  - JOUR
A1  - Zeimer, Ute
A1  - Grenzer, Jörg
A1  - Pietsch, Ullrich
A1  - Bugge, F.
A1  - Smirnitzki, V.
A1  - Weyers, Markus
T1  - Investigation of strain-modulated InGaAs-nanostructures by grazing-incidence x-ray diffraction and photoluminescence
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Zeimer, Ute
A1  - Bugge, F.
A1  - Gramlich, S.
A1  - Smirnitzki, V.
A1  - Weyers, Markus
A1  - Tränkle, G.
A1  - Grenzer, Jörg
A1  - Pietsch, Ullrich
A1  - Cassabois, G.
A1  - Emiliani, V.
A1  - Linau, Christoph
T1  - Evidence of strain-induced lateral carrier confinement in InGaAs-quantum wells by low-temperature near-field spectroscopy
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Zeimer, Ute
A1  - Bugge, F.
A1  - Gramlich, S.
A1  - Smirnitzki, V.
A1  - Weyers, Markus
A1  - Tränkle, G.
A1  - Grenzer, Jörg
A1  - Pietsch, Ullrich
A1  - Cassabois, G.
A1  - Emiliani, V.
A1  - Lienau, C.
T1  - Evidence for strain-induced lateral carrier confinement in InGaAs quantum wells by low-temperature near-field spectroscopy
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Zeimer, Ute
A1  - Baumbach, Tilo
A1  - Grenzer, Jörg
A1  - Lübbert, Daniel
A1  - Mazuelas, A.
A1  - Pietsch, Ullrich
A1  - Erbert, G.
T1  - In-situ characterization of strain distribution in broad-area high-power lasers under operation by high- resolution x-ray diffrcation and topography using synchrotron radiation
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Zehbe, Rolf
A1  - Zehbe, Kerstin
T1  - Strontium doped poly-epsilon-caprolactone composite scaffolds made by reactive foaming
JF  - The European journal of the history of economic thought
N2  - In the reconstruction and regeneration of bone tissue, a primary goal is to initiate bone growth and to stabilize the surrounding bone. In this regard, a potentially useful component in biomaterials for bone tissue engineering is strontium, which acts as cationic active agent, triggering certain intracellular pathways and acting as so called dual action bone agent which inhibits bone resorption while stimulating bone regeneration. In this study we established a novel processing for the foaming of a polymer (poly-epsilon-caprolactone) and simultaneous chemical reaction of a mixture of calcium and strontium hydroxides to the respective carbonates using supercritical carbon dioxide. The resultant porous composite scaffold was optimized in composition and strontium content and was characterized via different spectroscopic (infrared and Raman spectroscopy, energy dispersive X-ray spectroscopy), imaging (SEM, mu CT), mechanical testing and in vitro methods (fluorescence vital staining, MTT-assay). As a result, the composite scaffold showed good in vitro biocompatibility with partly open pore structure and the expected chemistry. First mechanical testing results indicate sufficient mechanical stability to support future in vivo applications. (C) 2016 Elsevier B.V. All rights reserved.
KW  - Strontium
KW  - Poly-epsilon-caprolactone
KW  - Porous scaffold
KW  - CAL-72 osteoblasts
KW  - L-929 fibroblasts
KW  - Reactive foaming
KW  - mu CT imaging
KW  - Spectroscopy
Y1  - 2016
U6  - https://doi.org/10.1016/j.msec.2016.05.045
SN  - 0928-4931
SN  - 1873-0191
VL  - 67
SP  - 259
EP  - 266
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Zehbe, Rolf
A1  - Zaslansky, Paul
A1  - Mochales, Carolina
A1  - Mueller, Wolf-Dieter
A1  - Fleck, Claudia
T1  - Synchrotron micro tomographic evaluation of multilayered zirconia ceramics-Volumetric effects after indentation
JF  - Journal of the European Ceramic Society
N2  - Electrophoretic deposition was used to produce zirconia specimen consisting of alternating layers of fully stabilized cubic zirconia and partially stabilized tetragonal zirconia. In this configuration, the tetragonal stabilized zirconia layers can undergo transformation toughening upon mechanical induced stresses, while the cubic stabilized layers can act as confining element. To understand the volumetric changes due to transformation toughening in these layered materials after indentation, we used an advanced synchrotron-based X-ray mu CT setup and compared the results with surface sensitive methods like Raman spectroscopy, AFM and white light interferometry. The high spatial resolution and the adapted beam energy between the absorption edges of zirconia and yttria allowed discriminating between individual layers due to differences in their yttria content. Furthermore we were able to identify single indents and link volume changes to different physical effects in the different stabilized zirconia parts and visualize the three dimensional volume around only few micrometre sized indents. (C) 2015 Elsevier Ltd. All rights reserved.
KW  - Yttria stabilized zirconia multilayers
KW  - X-ray mu CT
KW  - Electrophoretic deposition
KW  - Transformation toughening
Y1  - 2016
U6  - https://doi.org/10.1016/j.jeurceramsoc.2015.09.015
SN  - 0955-2219
SN  - 1873-619X
VL  - 36
SP  - 171
EP  - 177
PB  - Elsevier
CY  - Oxford
ER  -