Organic Molecule Driven Actuators
2019
Lin, H., Zhang, S., Xiao, Y., Zhang, C., Zhu, J., Dunlop, J. W. C., and Yuan, J., 
Macromolecular Rapid Communications, 1800896, 2019. (DOI: 10.1002/marc.201800896)

Inspired by the motions of plant tissues in response to external stimuli, significant attention has been devoted to the development of actuating poly- meric materials. In particular, polymeric actuators driven by organic molecules have been designed due to their combined superiorities of tunable functional monomers, designable chemical structures, and variable structural anisot- ropy. Here, the recent progress is summarized in terms of material synthesis, structure design, polymer–solvent interaction, and actuating performance. In addition, various possibilities for practical applications, including the abilityto sense chemical vapors and solvent isomers, and future directions to satisfy the requirement of sensing and smart systems are also highlighted.

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The Pollen Plasma Membrane Permeome Converts Transmembrane Ion Transport into Speed
Pertl-Obermeyer, H., Lackner, P., Dunlop, J. W. C:, Obermeyer, G.
Advances in Botanical Research, 2018, 87, 215-265

Pollen tubes are the fastest growing cells in nature with elongation rates of>20μm/min. The pollen tubes grow as fast as possible through the stigma tissue towards the egg cells where they release two sperm cells for fertilization. In addition to speed, the growth process has to be precise and well balanced to find the targets and to avoid bursting of the tube, respectively. Transport of ions across the plasma membrane generates a typical polar pattern of endogenous currents that accompanies pollen tube growth, and which is thought to function as a pacemaker to synchronize cellular processes. The endoge- nous currents are generated by the activity of various ion transporters in the plasma membrane, which were investigated by biophysical and molecular biology approaches Using an unbiased database search for pollen-expressed transporter genes in Arabidopsis and Lilium, a large number of putative transporters was identified that might contribute to the current pattern formation. Furthermore, we hypothesize that the distribution of the transporters to specific regions in the pollen tube is the basis for the current pattern and is achieved by a self-organization process based on the electro- phoretic mobility of charged membrane proteins in an electrical field. Thus, the activity of an ion transporter causes a local change in the transmembrane potential, which in turn would attract similar transporters and repel others leading to a heterogeneous distribution of transporters in the plasma membrane and the observed current pattern.

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Microscopic insight into electron-induced dissociation of aromatic molecules on ice
2018
Philipp Auburger, Ishita Kemeny, Cord Bertram, Manuel Ligges, Michel Bockstedte, Uwe Bovensiepen, Karina Morgenstern
Physical Review Letters accepted

We use scanning tunneling microscopy, photoelectron spectroscopy, and ab initio calculations to investigate the electron-induced dissociation of halogenated benzene molecules adsorbed on ice. Dissociation is triggered by delocalized excess electrons that attach to the π^∗ orbitals of the halobenzenes from where they are transferred to σ^∗ orbitals. The latter orbitals provide a dissociative potential surface. Adsorption on ice lowers the energy barrier for the transfer between the orbitals sufficiently to facilitate dissociation of bromo- and chloro-, but not of flourobenzene at cryogenic temperatures. Our results shed light on the influence of environmentally important ice particles on reactivity of halogenated aromatic molecules.

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Structural and spectroscopic characterization of the brownmillerite-type Ca₂Fe_2−xGa_xO₅ solid solution series
2018
Quirin E. Stahl, Günther J. Redhammer, Gerold Tippelt, Andreas Reyer
 Physics and Chemistry of Materials 2018 online.

Here, we present a comprehensive study that encompasses changes within the crystal and magnetic structure in the brownmillerite-type phase Ca₂Fe₂O₅ induced by the substitution of Fe³⁺ with Ga³⁺ synthetic single-crystal samples of Ca₂Fe_2−xGa_xO₅ 0.00 ≤ x ≤ 1.328 have been investigated by single-crystal X-ray diffraction at 25 °C. We find that pure Ca₂Fe₂O₅ and samples up to x ~ 1.0 have space group Pnma, Z = 4, whereas samples with x > 1.0 show I2mb symmetry, Z = 4. The Raman spectroscopic measurements exhibit that the change from Pnma to I2mb space group symmetry is reflected by a significant shift of two Raman modes below 150 cm⁻¹. These Raman modes are obviously linked to changes in the Ca–O bond lengths at the phase transition. ⁵⁷Fe Mössbauer spectroscopy was used to characterize the cation distribution and magnetic structure as a function of composition and temperature. Thereby, the strong preference of Ga³⁺ for the tetrahedral site is verified, as an independent method besides XRD. At room-temperature, Ca₂Fe_2−xGa_xO₅ solid solution compounds with 0 ≤ x ≤ 1.0 are antiferromagnetic ordered, as revealed by the appearance of magnetically split sextets in the Mössbauer spectra; samples with higher Ga³⁺ contents are paramagnetic. Over and above, the substitution of Fe³⁺ by Ga³⁺results in the appearance of sharp, additional magnetic hyperfine split sextets, which can be attributed to cluster configurations within the individual tetrahedral chains. The temperature-dependent (20–720 K) Mössbauer study reveals a transition from the magnetically ordered to the paramagnetic state at a temperature of about 710 K for the Ca₂Fe₂O₅ end-member.

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Ab initio description of highly correlated states in defects for realizing quantum bits
2018
M. Bockstedte, F. Schutz, Th. Garratt, V. Ivady, A. Gali
 Nature Partner Journal Quantum Materials, 2018, 3, 31

Coupled localized electron spins hosted by defects in semiconductors implementquantum bits with the potential to revolutionize nanoscale sensors and quantuminformation processing. The present understanding of optical means of spin statemanipulation and read-out calls for quantitative theoretical description of the activestates, built-up from correlated electrons in a bath of extended electron states.Hitherto we propose a first-principles scheme based on many body perturbationtheory and conguration interaction and address two room temperature point defect qubits, the nitrogen vacancy in diamond and the divacancy in silicon carbide. We provide a complete quantitative description of the electronic structure and analyze the crossings and local minima of the energy surface of triplet and singlet states. Our numerical results not only extend the knowledge of the spin-dependent optical cycle of these defects, but also demonstrate the potential of our method for quantitative theoretical studies of point defect qubits

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Resolving nanoparticle growth mechanisms from size- and time-dependent growth rate analysis
2018
Lukas Pichelstorfer, Dominik Stolzenburg, John Ortega, Thomas Karl, Harri Kokkola, Anton Laakso, Kari E. J. Lehtinen, James N. Smith, Peter H. McMurry, and Paul M. Winkler
 Atmospheric Chemistry and Physics, 2018, 18, 1307-1323.

Atmospheric new particle formation occurs frequently in the global atmosphere and may play a crucial role in climate by affecting cloud properties. The relevance of newly formed nanoparticles depends largely on the dynamics governing their initial formation and growth to sizes where they become important for cloud microphysics. One key to the proper understanding of nanoparticle effects on climate is therefore hidden in the growth mechanisms. In this study we have developed and successfully tested two independent methods based on the aerosol general dynamics equation, allowing detailed retrieval of time- and size-dependent nanoparticle growth rates. Both methods were used to analyze particle formation from two different biogenic precursor vapors in controlled chamber experiments. Our results suggest that growth rates below 10 nm show much more variation than is currently thought and pin down the decisive size range of growth at around 5 nm where in-depth studies of physical and chemical particle properties are needed.

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Interface Instability of Fe-stabilized Li₇La₃Zr₂O₁₂ versus Li Metal
2018
Daniel Rettenwander, Reinhard Wagner, Andreas Reyer, Maximilian Bonta, Lei Cheng, Marca M. Doeff, Andreas Limbeck, Martin Wilkening, Georg Amthauer
 The Journal of Physical Chemistry, C., 2018

The interface stability vs. Li represents a major challenge in the development of next-generation all-solidstate batteries (ASSB), which take advantage of the inherently safe ceramic electrolytes. Cubic Li₇La₃Zr₂O₁₂ garnets represent the most promising electrolytes for this technology. The high interfacial impedance versus Li is, however, still a bottleneck towards future devices. Herein, we studied the electrochemical performance of Fe³⁺-stabilized Li₇La₃Zr₂O₁₂ (LLZO:Fe) versus Li metal and found a very high total conductivity of 1.1 mS cm^-1 at room temperature but a very high area specific resistance of ~1 kΩ cm². After removing the Li metal electrode we observe a black surface coloration at the interface, which clearly indicates interfacial degradation. Raman- and nanosecond laser induced breakdown spectroscopy reveals, thereafter, the formation of a 130 μm thick tetragonal LLZO interlayer and a significant Li deficiency of about 1-2 formula units towards the interface. This shows that cubic LLZO:Fe is not stable versus Li metal by forming a thick tetragonal LLZO interlayer causing high interfacial impedance.

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Tensile forces drive a reversible fibroblast-to-myofibroblast transition during tissue growth in engineered clefts
2018
Philip Kollmannsberger, Cécile M. Bidan, John W. C. Dunlop, Peter Fratzl and Viola Vogel
Science Advances, Vol. 4, no. 1, eaao4881 

Myofibroblasts orchestrate wound healing processes, and if they remain activated, they drive disease progression such as fibrosis and cancer. Besides growth factor signaling, the local extracellular matrix (ECM) and its mechanical properties are central regulators of these processes. It remains unknown whether transforming growth factor–β (TGF-β) and tensile forces work synergistically in up-regulating the transition of fibroblasts into myofibroblasts and whether myofibroblasts undergo apoptosis or become deactivated by other means once tissue homeostasis is reached. We used three-dimensional microtissues grown in vitro from fibroblasts in macroscopically engineered clefts for several weeks and found that fibroblasts transitioned into myofibroblasts at the highly tensed growth front as the microtissue progressively closed the cleft, in analogy to closing a wound site. Proliferation was up-regulated at the growth front, and new highly stretched fibronectin fibers were deposited, as revealed by fibronectin fluorescence resonance energy transfer probes. As the tissue was growing, the ECM underneath matured into a collagen-rich tissue containing mostly fibroblasts instead of myofibroblasts, and the fibronectin fibers were under reduced tension. This correlated with a progressive rounding of cells from the growth front inward, with decreased α–smooth muscle actin expression, YAP nuclear translocation, and cell proliferation. Together, this suggests that the myofibroblast phenotype is stabilized at the growth front by tensile forces, even in the absence of endogenously supplemented TGF-β, and reverts into a quiescent fibroblast phenotype already 10 μm behind the growth front, thus giving rise to a myofibroblast-to-fibroblast transition. This is the hallmark of reaching prohealing homeostasis.