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Broad ion beams have shown their wide applications for materials modification. Focused ion beams can be used in a similar way while simultaneously providing process monitoring. Here, we demonstrate this on a new kind of ion-induced structural evolution. Sub-micrometer Sn spheres were irradiated in a helium ion microscope with a sub-nm beam of 30 keV He ions. Above a fluence of ~10^17/cm², Sn extrusions appeared on the surface of the spheres, which were imaged using the secondary electron signal. Initially, small, pyramid-like faceted extrusions form at the equator of the spheres (north pole pointing to the ion source). Later, each sphere becomes completely covered by the extrusions. A model was developed that assumes that each He ion generate ~70 Frenkel pairs. The implanted helium atoms, interstitials, and vacancies will be confined by the oxide skin of the spheres. Some He atoms will occupy vacancies, which partially prevent their recombination with interstitials. Furthermore, the ion irradiation leads to erosion and opening of the SnO skin. The interstitials can now escape from the interior of the Sn sphere and form an epitaxial regular Sn lattice on the exterior. Transmission electron microscopy, Auger electron spectroscopy as well as TRI3DYN [1] and 3D kinetic lattice Monte Carlo [2] simulations support these findings. In addition, we provide a perspective on focused ion beams from our in-house development and production of liquid metal alloy ion sources, which can be used for applications from self-organized patterning, over altering magnetic or electrical properties, to quantum photonics and computation [3]. [1] Möller, Nucl. Instr. Meth. B 322 (2014) 23 [2] Strobel et al., Phys. Rev. B 64 (2001) 245422 [3] www.hzdr.de/fib

Novel transistor concepts based on semiconductor nanowires promise high performance, lower energy consumption and better integrability in various platforms in nanoscale dimensions. Concerning the intrinsic transport properties of electrons in nanowires, relatively high mobility values that approach those in bulk crystals have been obtained only in core/shell heterostructures, where electrons are confined inside the core and, thus, their scattering on the nanowire surface is suppressed. Here, we demonstrate that the large strain in core/shell nanowires with significant lattice-mismatch between the core and the shell can affect the effective mass and the scattering of electrons in a way that boosts their mobility to higher levels compared to results obtained by any other means. Specifically, we use GaAs/InAlAs core/shell nanowires with a lattice mismatch in the range of 3%, grown on Si substrates by molecular beam epitaxy. Overgrown with an 80-nm-thick shell, the 22-nm-thick core is hydrostatically tensile-strained as found by both Raman scattering and photoluminescence measurements [1, 2]. The transport properties and dynamics of electrons were probed at room temperature by optical-pump THz-probe spectroscopy, which is an established contactless method that circumvents challenges in the fabrication of electrical contacts on nanowires. We found that the mobility of electrons inside the strained GaAs core undergoes a remarkable enhancement despite the small core thickness, becoming 30 – 50 % higher than in unstrained GaAs/AlGaAs nanowires or bulk GaAs [2]. Our studies are extended to modulation-doped GaAs/InAlAs nanowires and the results will be presented. The reported strain-induced mobility enhancement is of major importance for the realization of transistors with high speed and low power consumption, having the potential to trigger major advancements in high-performance nanowire electronic devices monolithically integrated in Si platforms. [1] L. Balaghi, G. Bussone, R. Grifone, R. Hübner, J. Grenzer, M. Ghorbani-Asl, A. V. Krasheninnikov, H. Schneider, M. Helm, E. Dimakis, Nat Commun 10, 2793 (2019). [2] L. Balaghi, S. Shan, I. Fotev, F. Moebus, R. Rana, T. Venanzi, R. Hübner, T. Mikolajick, H. Schneider, M. Helm, A. Pashkin, E. Dimakis, Nat Commun 12, 6642 (2021).

Thin films of the magnetoelectric insulator α-Cr2O3 are technologically relevant for energy-efficient magnetic memory devices controlled by electric fields. In contrast to single crystals, the quality of thin Cr2O3 films is usually compromised by the presence of point defects and their agglomerations at grain boundaries, putting into question their application potential. Here, we study the impact of the defect nanostructure including sparse small-volume defects and their complexes on the magnetic properties of Cr2O3 thin films. By tuning the deposition temperature, we tailor the type, size, and relative concentration of defects, which we then analyze based on positron annihilation spectroscopy complemented with local electron microscopy studies. The structural characterization is correlated with magnetotransport measurements and nitrogen vacancy microscopy of antiferromagnetic domain patterns. Defects pin antiferromagnetic domain walls and stabilize complex multidomain states with a typical domain size in the sub-micrometer range. Despite their influence on the domain configuration, we demonstrate that neither small open-volume defects nor grain boundaries in Cr2O3 thin films affect the Néel temperature in a broad range of deposition parameters. Our results pave the way towards the realization of spin-orbitronic devices where magnetic domain patterns can be tailored based on defect nanostructures without affecting their operation temperature.

The realization of fourfold anisotropic magnetoresistance (AMR) in 3d-5d heterostructures has boosted major efforts in antiferromagnetic (AFM) spintronics. However, despite the potential of incorporating strong spinorbit coupling, only small AMR signals have been detected thus far, prompting a search for mechanisms to enhance the signal. In this paper, we demonstrate an extraordinarily elevated fourfold AMR of 70% realized in CaMnO3/CaIrO3 thin film superlattices.We find that the biaxial magnetic anisotropy and the spin-flop transition in a nearly Mott insulating phase form a potent combination, each contributing one order of magnitude to the total signal. Dynamics between these phenomena capture a subtle interaction of pseudospin coupling with the lattice and external magnetic field, an emergent phenomenon creating opportunities to harness its potential in AFM spintronics.

The stored data sets represent both the raw data and the evaluated data that were used for the publication about uranium(VI) reduction by a sulfate-reducing bacterium.

A series of CuCr₂O₄ thin films has been successfully synthesized via a facile and cost-effective reactive Direct Current Magnetron Sputtering technique at room temperature. These coatings were deposited to evaluate their suitability as absorber material for the next generation of concentrated solar power plants [1]. The composition of the films was controlled using as key parameters the power ratio between Cu and Cr targets as well as the oxygen flux. The films deposited without intentional substrate heating were initially amorphous and needed to be annealed at 800 °C for one hour to obtain a spinel-like crystal structure [2]. RBS was used to characterize the composition of the as-deposited and annealed coatings. The structural properties were investigated by Raman spectroscopy and XRD. Structural characterization allows us to evidence that slight deviation in stoichiometry promotes the formation of secondary phases in the films. In this concern, we use in-situ Raman spectroscopy and spectroscopic ellipsometry to characterize the structural evolution of the films as a function of temperature in a controlled oxygen atmosphere. The study evidences the evolution from amorphous to fully crystallized material. Additionally, the influence of the film roughness in the optical performance of the coatings with appropriate composition was explored to enhance the optical properties of the film. References: 1) Ramón Escobar Galindo, Matthias Krause, K. Niranjan and Harish Barshilia, in Sustainable Material Solutions for Solar Energy Technologies (ed. Mariana Fraga, Delaina Amos, Savas Sonmezoglu, Velumani Subramaniam, Elsevier, 2021). 2) Matthias Krause, Johanna Sonnenberg, Frans Munnik, Jörg Grenzer, René Hübner, Aurelio Garcia-Valenzuela, Sibylle Gemming in Materialia 18 (2021) 101156.

Transition metal oxides have been extensively explored as novel catalysts for designing electrochemical sensors, but the underlying structure-activity relationship remains poorly understood. Herein, we explore a diverse chemical range of La1-xSrxFeO3 perovskite oxides by evaluating their electrochemical sensing activity toward heavy metals and by determining their electronic structures using density functional theory. We find that tuning perovskite chemistry plays an important role in determining the electrochemical activities and sensitivities, as well as the valence states of Fe. By combining experimental and theoretical analyses, a linear relationship between the Fe−O covalency and the electrochemical activity and sensitivity has been obtained, where LaFeO3 exhibits the highest activity of 109 mA cmoxide-2.Thus, the Fe−O covalency is proposed as a rational activity descriptor for the electrochemical sensing of heavy metals. A novel solid-state gelation method was further developed for the fabrication of perovskite oxide aerogels, based on which a highly efficient electrochemical sensor was constructed with a high sensitivity of 87.06 μM μA-1 and a low detection limit of 1.7 nM. This work unlocks an effective parameter, that is, Fe−O covalency, for rationally designing Fe-based oxides and deepening the understanding of fundamental parameters to develop highly efficient sensing platforms.

INTRODUCTION For a comprehensive safety assessment regarding the deep geological disposal of high-level radioactive waste, various aspects have to be taken into account. Besides geological, geochemical, and geophysical properties, the influence of naturally occurring microorganisms in the surrounding host rock and backfill material play a crucial role in the environment of such a repository. Clay formations are potential host rocks for the long-term storage of this waste, whereas bentonites are supposed to serve as backfill material, not only for a final disposal site in clay formations but also in crystalline rock. In the event of a worst-case scenario, if water enters the disposal site, radionuclides can escape from the waste canisters and thus interact with the microorganisms. This can, for example, lead to changes in the chemical speciation or the oxidation state of the metal ions. RESULTS & DISCUSSION Under repository-relevant conditions, Desulfosporosinus spp. are important representatives of anaerobic, sulfate-reducing bacteria being present in clay formations as well as in bentonites. Various studies show that they are playing a major role in the microbial communities of these surroundings. A closely related microorganism to the isolated species is Desulfosporosinus hippei DSM 8344T. Therefore, this bacterium was used to investigate its interactions with uranium(VI) especially regarding the reduction to the less-mobile uranium(IV) having favorable properties like a reduced mobility. Time-dependent reduction experiments showed the removal of about 80% of the uranium(VI) from the supernatants in artificial Opalinus Clay pore water (100 µM uranium(VI), pH 5.5) within 48 h. Corresponding UV/Vis measurements of the dissolved cell pellets provide clear proof of the formed uranium(IV). The proportion of this oxidation state in the cell-bound uranium increases up to 40% after one week. Therefore, a combined sorption-reduction process is a possible interaction mechanism. Time-resolved laser-induced luminescence spectroscopy reveals the presence of two uranium(VI) species in the supernatant. A comparison with reference spectra leads to an assignment to a uranyl(VI) lactate and a uranyl(VI) carbonate complex. The species distribution shows a decrease of the proportion of the lactate species with time, whereas the proportion of the carbonate species remains almost constant. Uranium aggregates are formed on the cell surface during the process, as determined by scanning transmission electron microscopy (STEM). Furthermore, cells release uranium-containing vesicles as a possible defense mechanism against cell encrustation. CONCLUSIONS The findings of this study help to close existing gaps in a comprehensive safeguards concept for a repository for high-level radioactive waste in clay rock. Moreover, this study provides new insights into the interactions of sulfate-reducing microorganisms with uranium(VI) and thus, contributes to new bioremediation approaches of radionuclide-contaminated environments, as well.

Magnetotactic bacteria are characterized by intracellular magnetic mineral crystals of magnetite (Fe3O4) or greigite (Fe3S4), which helps them to orientate themselves along the Earth's magnetic field for reaching regions of optimal oxygen concentrations. They are facultative anaerobe and usually found in a large abundance in oxic-anoxic transition zones of aquatic environments, in sediments of freshwater, brackish, marine, and hypersaline habitats [1]. Assuming that magnetotactic bacteria can also be found in the far-field of a nuclear waste repository, studies on the interaction of a natural bacterial strain of Magnetospirillum magneticum AMB-1 cells with U were carried out for the first time using a multidisciplinary approach combining microscopy and different spectroscopic techniques to achieve a better molecular understanding. Results of batch sorption experiments show that Magnetospirillum magneticum AMB-1 can survive both in a wide pH range and with relatively high U concentrations of up to 0.1 mM, while effectively and almost completely immobilizing U in the first hours of incubation. (S)TEM/EDXS studies on ultrathin sections of cells loaded with 0.1 mM U clearly indicate that U is predominantly located in the cell wall. Since it is known from previous studies [2] that U often binds to the cell wall of bacteria by interacting with cell wall compounds, important ligands were used, such as peptidoglycan, lipopolysaccharide, L-rhamnose, D-(+) galactose and D-(+) mannose as possible complexants for U and measured by cryo-TRLFS combined with PARAFAC. The results show five U species and highlight the dominant role of peptidoglycan as main sorbent of U on the cell wall of Magnetospirillum magneticum AMB-1 cells, showing three characteristic peptidoglycan species. In-situ ATR FT-IR studies confirm the predominant binding to carboxylic functionalities and reveal that polynuclear species seem to play an important role at higher pH.

This work presents first insights into the dynamics of free-surface release clouds from dynamically compressed polystyrene and pyrolytic graphite at pressures up to 200 GPa, where they transform into diamond or lonsdaleite, respectively. These ejecta clouds are released into either vacuum or various types of catcher systems, and are monitored with high-speed recordings (frame rates up to 10 MHz). Molecular dynamics simulations are used to give insights to the rate of diamond preservation throughout the free expansion and the catcher impact process, highlighting the challenges of diamond retrieval. Raman spectroscopy data show graphitic signatures on a catcher plate confirming that the shock-compressed PS is transformed. First electron microscopy analyses of solid catcher plates yield an outstanding number of different spherical-like objects in the size range between ten(s) up to hundreds of nanometres, which are one type of two potential diamond candidates identified. The origin of some objects can unambiguously be assigned, while the history of others remains speculative.

The data included in the publication are results of SET device simulations, Monte-Carlo simulations of physical processes (ion-beam mixing, phase seepration, Si nanodot formation) and micrographs taken by electron and ion microscopes.

Ge nanocrystals embedded in amorphous TaZrOx matrices were synthesized by a magnetron co-sputtering process in a size-controlled manner, separated from each other by a superlattice approach of alternating TaZrOx-Ge/TaZrOx layers. Ge offers, in contrast to silicon, a large Exciton-Bohr radius, which allows the regulation of the bandgap by the diameter. After annealing at 725 °C, Ge nanostructures were found to phase-separate and crystallize [1]. The addition of Sn to Ge promises a way towards a direct bandgap Ge-based semiconductor material [2] in a wide concentration range between 6 at.-% and 22 at.-% of Sn [3]. A direct bandgap material, which is fully compatible to common Si-CMOS processes would enable the integration in future devices, like light emitters or detectors. The fabrication of GeSn alloys is challenging, due to the low solubility of Sn in Ge [4] but it is known that Ge nanocrystals after annealing contain a higher concentration of foreign atoms than expected in thermodynamic equilibrium [1]. Different structural measurements like EDX or Raman scattering monitor the structural changes within the Ge nanostructures by addition of Sn to the superlattice structure under annealing temperatures between 600 °C and 800 °C. TEM EDX measurements revealed that the TaZrOx, which acts as an efficient diffusion barrier for Ge, does not prohibit the diffusion of the Sn completely. However, the formation of pure Sn nanocrystals was not observed. In addition, crystallization of the matrix material can be avoided for appropriate annealing temperatures. 1. D. Lehninger, F. Honeit, D. Rafaja, V. Klemm, C. Röder, L. Khomenkova, F. Schneider, J. von Borany, and J. Heitmann, MRS Bull. 511–512, 654 (2022). 2. A. Slav, C. Palade, C. Logofatu, I. Dascalescu, A. M. Lepadatu, I. Stavarache, F. Comanescu, S. Iftimie, S. Antohe, S. Lazanu, V. S. Teodorescu, D. Buca, M. L. Ciurea, M. Braic, and T. Stoica, ACS Appl. Nano Mater. 2, 3626 (2019). 3. W.-J. Yin, X.-G. Gong, and S.-H. Wei, Phys. Rev. B 78, 161203(4) (2008). 4. H. Li, J. Brouillet, A. Salas, X. Wang, and J. Liu, Opt. Mater. Express 3, 1385 (2013).

In situ measurements using RBS, ERD, and SE are less explored in characterizing solar absorber materials at high temperatures [1, 2]. In the present work, we report the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating with excellent optical, compositional and structural properties at high temperatures [3, 4]. We have carried out in situ Rutherford backscattering spectrometry, elastic recoil detection and spectroscopic ellipsometry measurements at three different temperatures at 450°C, 650°C, and 800°C. An optical model describing perfectly the reflectance and ellipsometric data was developed. Further, the microstructural properties of the solar absorber coating are evaluated using cross-sectional transmission electron microscopy before and after annealing. Our data obtained before and after the heating experiments demonstrate excellent compositional, optical and structural stability of the coatings under the applied conditions. Furthermore, in situ ellipsometry showed the conservation of the optical properties of the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber up to 800 °C, which is crucial for high-temperature applications. [1] Ramón Escobar Galindo, Matthias Krause, K. Niranjan and Harish Barshilia, in Sustainable Material Solutions for Solar Energy Technologies (ed. Mariana Fraga, Delaina Amos, Savas Sonmezoglu, Velumani Subramaniam, Elsevier, 2021). [2] Lungwitz, F. et al. Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Mater. Solar Cells 196, 84-93, doi:10.1016/j.solmat.2019.03.012 (2019). [3] K. Niranjan, A. Soum-Glaude, A. Carling-Plaza, S. Bysakh, S. John, H.C. Barshilia, Extremely high temperature stable nanometric scale multilayer spectrally selective absorber coating: Emissivity measurements at elevated temperatures and a comprehensive study on ageing mechanism, Solar Energy Mater. Sol. Cells 221 (2021) 110905, doi:10.1016/j.solmat.2020.110905. [4] K. Niranjan, A.C. Plaza, T. Grifo, M. Bordas, A. Soum-Glaude, H.C. Barshilia, Performance evaluation and durability studies of W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating for high-temperature applications: A comprehensive study on thermal and solar accelerated ageing, Solar Energy 227 (2021) 457–467, doi:10.1016/j.solener.2021.09.026.

We present results for direct maskless magnetic patterning of ferromagnetic nanostructures using a special liquid metal alloy ion source for focused ion beam (FIB) systems. We used a Co36Nd64 alloy as the FIB source [1]. A Wien mass filter allows for quick switching between the ion species in the alloy without changing the FIB source. A 5000×1000×50 nm3 permalloy strip served as the sample. Using the FIB we implanted a 300-nm-wide track with Co ions (see Fig.1). We observed the Co-induced changes by measuring the sample with microresonator ferromagnetic resonance before and after the implantation. Structures as small as 30 nm can be implanted up to a concentration of 10 % near the surface. Such lateral resolution is hard to reach for other lithographic methods. This allows for easy magnetic modification of edge-localized spin waves. In another set of samples, we implanted Dy ions to locally increase the damping in a stripe pattern of ~120-nm-wide strips with 400 nm periodicity on a total area of 1×1 mm². Thus, the Gilbert damping parameter can be easily increased by one order of magnitude with a lateral resolution of about 100 nm. In contrast to electron beam lithography in combination with broad-beam ion implantation, the maskless FIB process does not require the cumbersome and difficult removal of the ion-hardened resist if optical measurements like BLS or TR-MOKE are needed.

ZusammenfassungDie interventionelle Emphysemtherapie bietet ein breites Spektrum an chirurgischen und endoskopischen Optionen zur Behandlung von Patienten mit fortgeschrittenem Lungenemphysem. Zur Sicherstellung der Behandlungsqualität ist eine interdisziplinäre Zusammenarbeit von Pneumologie, Thoraxchirurgie und bildgebenden Disziplinen in der Auswahl, Therapie und Nachsorge von Emphysem-Patienten erforderlich. Das vorliegende Positionspapier beschreibt erforderliche Struktur- und Qualitätsvoraussetzungen von Behandlungszentren.

Clay formations are potential host rocks for the long-term storage of high-level radioactive waste in a deep geological repository. Bentonites are supposed to serve as backfill material, not only for a final disposal site in clay formations but also in crystalline rock. For a long-term safety assessment, various aspects must be taken into account. Besides geological, geochemical, and geophysical considerations, also naturally occurring microorganisms play a crucial part in the environment of such a repository. In the event of a worst-case scenario, if water enters the disposal site, they can interact with the radionuclides and change for example the chemical speciation or the oxidation state (Lloyd et al., 2002). Desulfosporosinus spp. are an important representative of anaerobic, sulfate-reducing microorganisms, which are present in clay formations as well as in bentonites. Various studies show that they are playing a major role in the microbial communities of these surroundings (Bagnoud et al., 2016; Matschiavelli et al., 2019). A closely related microorganism to the isolated species is Desulfosporosinus hippei DSM 8344, which was originally found in permafrost soil (Vatsurina et al., 2008). This bacterium was used to investigate its interactions with uranium(VI) especially regarding the reduction to the less mobile uranium(IV). Time-dependent reduction experiments in artificial Opalinus Clay pore water (Wersin et al., 2011) (100 µM uranium(VI), pH 5.5) showed the removal of about 80% of the uranium(VI) from the supernatants within 48 h. Corresponding UV/Vis measurements of the dissolved cell pellets exhibit an increasing proportion of uranium(IV) in the cell-bound uranium. Calculations with the inclusion of extinction coefficients lead to a ratio of 39% uranium(IV) after one week. Therefore, a combined sorption-reduction process is a possible interaction mechanism. Time-resolved laser-induced luminescence spectroscopy verifies the presence of two uranium(VI) species in the supernatant. A comparison with reference spectra leads to an assignment to a uranyl(VI) lactate and a uranyl(VI) carbonate complex. The species distribution shows a decrease of the proportion of the lactate species with time, whereas the proportion of the carbonate species remains almost constant. Uranium aggregates are formed on the cell surface during the process, as determined by transmission electron microscopy (TEM). Furthermore, uranium occurs inside and outside the cells as well as uranium-containing vesicles. These findings help to close existing gaps in a comprehensive safeguards concept for a repository for high-level radioactive waste in clay rock. Moreover, this study provides new insights into the interactions of sulfate-reducing microorganisms with uranium(VI). References Bagnoud, A., Chourey, K., Hettich, R. L., De Bruijn, I., Andersson, A. F., Leupin, O. X., Schwyn, B., and Bernier-Latmani, R.: Reconstructing a hydrogen-driven microbial metabolic network in Opalinus Clay rock, Nat. Commun., 7, 1-10, 2016. Lloyd, J. R. and Macaskie, L. E.: Biochemical basis of microbe-radionuclide interactions, in: Interactions of Microorganisms with Radionuclides, edited by: Keith-Roach, M. J. and Livens, F. R., Elsevier, 313-381, 2002. Matschiavelli, N., Kluge, S., Podlech, C., Standhaft, D., Grathoff, G., Ikeda-Ohno, A., Warr, L. N., Chukharkina, A., Arnold, T., and Cherkouk, A.: The year-long development of microorganisms in uncompacted Bavarian bentonite slurries at 30 °C and 60 °C, Environ. Sci. Technol., 53, 10514-10524, 2019. Vatsurina, A., Badrutdinova, D., Schumann, P., Spring, S., Vainshtein, M.: Desulfosporosinus hippei sp. nov., a mesophilic sulfate-reducing bacterium isolated from permafrost, Int. J. Syst. Evol. Microbiol., 58, 1228-1232, 2008. Wersin, P., Leupin, O. X., Mettler, S., Gaucher, E. C., Mäder, U., De Cannière, P., Vinsot, A., Gäbler, H. E., Kunimaro, T., Kiho, K., Eichinger, L.: Biogeochemical processes in a clay formation in situ experiment: Part A - Overview, experimental design and water data of an experiment in the Opalinus Clay at the Mont Terri Underground Research Laboratory, Switzerland, Appl. Geochemistry, 26, 931-953, 2011.

We report on the surprising observation of a unique perforated lamellar (PL) morphology in a mixture of an asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer and CdSe−CdS quantum dots (QDs). The PL morphology formed by the PS-b-P4VP/CdSe−CdS composites consisted of alternating layers of PS and P4VP, where the layer formed by the minority PS block contained cylindrical perforations of the majority P4VP block. Most interestingly, the CdSe−CdS QDs were localized exclusively in the P4VP perforations. The swelling of the bulk samples in a P4VP selective solvent also allowed the isolation of the perforated PS nanosheets, with QDs localized in the perforations, which further provided strong evidence for the formation of the unique PL morphology. The observed PL morphology was, plausibly, energetically stabilized because of the localization of QDs within the P4VP perforations, which allowed for the conformational entropy minimization of the majority P4VP block. The present work reveals possibilities for the discovery of novel hierarchical structures in block copolymer/nanoparticle composite systems and also provides new opportunities for the application of such materials in nanotechnology.

Armed with merits of the metals (e.g., electrical conductivity, catalytic activity, and plasmonic properties) and aerogels (e.g., monolithic structure, porous network, and large specific surface area), metal aerogels (MAs) have stood out as a new class of porous materials in the last decade. With unparalleled potential in electrocatalysis, plasmonics, and sensing, they are envisaged to revolutionize the energy- and detection-related application fields. However, MA development is severely retarded by the lack of a sufficient material basis. Suffering from the ambiguous understanding of formation mechanisms, big challenges remain for tailoring MAs for task-specific applications. By surveying state-of-the-art developments, this review strives to summarize design principles and arouse interest in broad scientific communities. Moreover, critical challenges and opportunities are highlighted to provide a research roadmap for this young yet promising field.

The tuning and control over the intrinsic magnetic properties, such as saturation magnetization (Ms) and Gilbert damping (α), can be obtained via systematic rearrangement of the lattice at the nanoscale. In certain binary alloys such as B2 Fe60Al40 [1] and B2 Fe50Rh50 [2], the Ms can be tuned by inducing chemical disorder. The disorder caused by the randomization of site occupancies of the atoms can be achieved by ion-irradiation. Here we explore a magnetic phase transition in Fe60V40 thin films caused by ordering of the lattice structure from short-range order to the crystalline state. Fe60V40 films (~ 40 nm) were grown onto SiO2/Si substrate. The as-grown films are weakly ferromagnetic with low Ms of 17 kA/m; whereas irradiation with 25 keV Ne+-ions at fluences of ~ 5 × 1015 ions/cm2 leads to a drastic increase of Ms to ~ 750 kA/m, as shown in Fig. 1. X-ray diffraction as well as transmission electron microscopy reveal a structural short-range order in the as-grown films, that transform to A2 Fe60V40 with increasing Ne+-fluence. The A2 region appears to nucleate at the film top surface and with increasing fluence, it propagates deeper down into the film. The effect of the phase transition on the dynamic behaviour has been investigated using ferromagnetic resonance (Fig. 2). The low value of Gilbert damping (~ 0.002) has been obtained from the frequency dependence of the resonance spectra. Furthermore, the transition can be tracked using Conversion electron Mössbauer spectroscopy to shed light on the variation of local magnetic ordering during the transition. The tunable film structure as well as low damping form the basis for further investigations on nanomagnets embedded within Fe60V40 thin films. Funding by the DFG - 322462997 (BA 5656/1-2 | WE 2623/14-2) is acknowledged. Ion-irradiation was performed at the Ion Beam Centre of the HZDR. References [1] J. Ehrler, et al., New J. Phys., 22, 073004 (2020). [2] B. Eggert, et al., RSC Adv.,10, 14386 (2020).

The anisotropy in semiconductor nanoplatelets (NPLs) is reflected in the anisotropy of their crystal structure and organic ligand shell, which can be used for creating new semiconductor heterostructures. This work demonstrates the synthesis of core/shell NPLs containing zero-dimensional (0D) CdxHg1−xSe domains embedded in CdSe NPLs via cation exchange. The strategy is based on the different accessibility of definite regions of the NPLs for incoming cations upon time-limited reaction conditions. The obtained heterostructures were successfully overcoated with a CdyZn1−yS shell preserving their two-dimensional (2D) morphology. The NPLs exhibit bright photoluminescence in the range of 700-1100 nm with quantum yields up to 55%, thus making them a prospective material for light-emitting applications in the near-infrared spectral range.

Developments in the fabrication techniques like lithography, etching, thin-film deposition, and metallization, etc. have enhanced device the performance of the complementary metal-oxide-semiconductor (CMOS) transistors mainly by the scaling-down. Innovative concepts need to be incorporated to further improve the device performance as the scaling limits are being reached. We report on the development of the atomic layer etching (ALE) process to fabricate smooth SiGe-on-insulator (SiGeOI) nanowire using the conventional dry etching tool. First, nano-patterns were made on SiGeOI samples using electron beam lithography. Then these patterns were transferred into the SiGeOI layer using an inductively coupled plasma reactive ion etching (ICP-RIE) process. Subsequently, the ALE process was developed to smoothen the nanowire and to reduce their widths. For the surface modification step, SF6 was used, while Ar+ was used for the subsequent modified layer removal step. The ALE cycle sequence was: modification with 60 sccm SF6 for 20 s, 60 sccm Ar purge for 15 s, layer removal with 60 sccm Ar for 10 s using 25 W platen power, and 40 sccm Ar purge for 10 s. Various ALE cycles were performed to investigate the effect of ALE on the nanowire roughness and width. The surface of etched features was studied using the atomic force microscopy (AFM) (figure 1 (a)). A reduction in the width of the wire was seen with the increasing number of the ALE cycles. Figure 1 (b) shows the root mean square (r.m.s) surface roughness of the buried oxide after certain numbers of the ALE cycles. The roughness went down from ca. 6 nm to 1 nm or below (exact value could not be calculated due to limitation of the AFM tip) as the number of ALE cycles was increased from 78 to 102. Figure 2 shows sub-12 nm nanowires with smooth sidewalls fabricated after performing 63 ALE cycles. An etch per cycle of 1.1 Å was attained. This process, developed on a conventional ICP-RIE tool, can be used to further scale down the nanowires.

The folder contains the following:1. all the SEM and TEM images. 2. The schematics of fabrication 3. comparison of silicidation with FLA and RTA and 4. temperature simulations to estimate temperature during FLA process.

Single quantum dots embedded in the core of freestanding semiconductor nanowires grown directly on Si offer a novel and promising scheme for the realization of on-demand sources of single photons or entangled photon pairs in quantum technology systems. Here, we have investigated the growth mechanism and optical properties of axial quantum dots embedded in GaAs nanowires grown in self-catalyzed vapor-liquid-solid mode while demonstrating the tuneabilty of their emission energy across a wide range of wavelengths with the potential for telecom band access. We have incorporated GaAs complex quantum dots inside GaAs/In(x)Al(1-x)As and GaAs/Al(x)Ga(1-x)As core/shell nanowires grown via our nanowire growth technique called droplet-confined alternate pulsed-epitaxy (DCAPE)[1] (an adaptation of conventional molecular beam epitaxy (MBE)), which grants precise control over the axial growth rate and droplet composition. Using a combination of conventional MBE and DCAPE the growth of highly symmetrical quantum dots, as little as 10 nm in diameter and just a few nanometers in height, were made possible. Strong axial confinement was achieved in the form of a double axial heterostructure by incorporating two Al(x)Ga(1-x)As/Al(y)Ga(1-y)As short-period superlattices separated by a thin GaAs segment (figure 1(a)). The complexity of our quantum dots is derived from the unique possibility of using different ternary alloys for the axial and radial confinement. By introducing a latticed mismatched ternary alloy shell as the radial barrier (In(x)Al(1-x)As), we demonstrated controlled hydrostatic strain induced redshifts of the highly polarized quantum dot emission energy by adjusting the In content of the shell. For 39% In we measured a redshift in the quantum dot emission of 320 meV, from an unstrained quantum dot reference (Al(x)Ga(1-x)As shell), as shown by the photoluminescence measurements in figure 1 (b). To optimize the emission quality, the compositional grading effect of the constituent superlattice materials across the interfaces must be addressed. High-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and nanowire growth models were utilized to gain an understanding of the compositional grading mechanism at the quantum dot/superlattice interface. We found that interfacial sharpness increases significantly by reducing the superlattice growth temperature and nanowire radius. Notwithstanding, limitations in what can be achieved ensue and possible strategies to overcome them will be presented. [1] Balaghi et al., Nano Lett. 16, 4032 (2016)

B20-type FeGe is one of the noncentrosymmetric materials hosting magnetic skymions. In this work, we have prepared B20-type FeGe films by pulsed laser melting of metal Fe deposited on Ge(100). The formation of the B20 phase is confirmed by X-ray diffraction. The FeGe samples show a superparamagnetic behaviour and their blocking temperatures increase with increasing the pulsed laser energy density. We conclude that this phenomenon is due to the increased grain size of the B20-type FeGe with increasing laser energy density. The presented method can be used to obtain different B20-type transition metal germanides and silicides, which can be magnetic skyrmion-hosting materials for spintronics.

The research on surface-enhanced Raman scattering (SERS) continuously draws wide attention because of its high detection sensitivity. However, the commonly investigated 2D SERS substrates cannot fully utilize the 3D active focal volume and require a tight focus on the correct plane, retarding signal enhancement and flexible use. Here, self-supported gold aerogels of centimeter-dimension with tunable ligament sizes are designed as 3D SERS substrates, featuring hot spots throughout the entire network. Unveiling a universal ligament-size-effect, the optimized gold aerogel showcases much larger enhancement factors compared to a 8 nm Au film toward dyes, pesticides, and carcinogens (up to 109). Aside from an excellent reusability and an exceptional stability (> 1 month), an outstanding misfocus tolerance (>300 μm along the z-axis) is also demonstrated for such aerogel-based SERS substrates for multiplex detection. This work may expand the application scope of metal aerogels and lay the foundation for designing next-generation 3D SERS substrates.

The uploaded data are related to electrical measurements including two- and four-probe, Hall effect, and temperature-dependent measurements. The simulation data is included as well.

The depository contains STEM images, experimental data from charge exchange measurements anddata from charge exchange simulations.

To complement the scaling down of complementary metal-oxide-semiconductor (CMOS), new device concepts have been introduced. One such concept is the reconfigurable field-effect transistor (RFET). In the most general case, an RFET is a silicon nanowire (SiNW) based device. The SiNW is silicided at both ends, which results in silicide-Si-silicide Schottky junctions. Typically, two distinct gate electrodes are placed on silicide-Si junctions. By controlling the electrostatic potential on the gate electrodes, the RFET is programmed to the p- or n- polarity. We report on the fabrication and electrical characterization of top-down fabricated SiNW based RFETs. Flash lamp annealing based silicidation process is developed, which enables control over the silicidation process. Uni-polar transfer characteristics are obtained using two top-gates. The effect of implementing various gate dielectric materials (SiO2, Al2O3 and hBN) is studied to enhance device electrostatics.

The formation of nanopores by highly charged ion impacts on freestanding fluorine-functionalized graphene is demonstrated. The process is driven by potential sputtering, which becomes active by changing the semi-metallic properties of graphene into a strongly insulating state by fluorination. The interaction of fluorographene with highly charged ions is also studied in terms of charge exchange and kinetic energy loss. A higher number of captured electrons and a larger kinetic energy loss than in pristine graphene are observed, which can be well explained by an increase in the ion's neutralization length and in the atomic areal density of the target, respectively. Using a computer code based on a time-dependent scattering potential model, a connection between the efficiency of charge exchange and the fluorine coverage is revealed. Our results suggest a competition of two distinct nanostructure formation processes leading either to pore formation or fluorine desorption.

Flash lamp annealing is, like laser annealing, a non-equilibrium annealing method on the sub-second time scale which excellently meets the requirements of thin film processing: it allows the use of temperature-sensible substrates for thin films, leads to energy and cost savings compared to long-time annealing methods, and enables the formation of new materials in thermal non-equilibrium. Originally developed for microelectronics, flash lamp annealing has opened up new areas of application like thin films on glass, sensors, printed electronics, flexible electronics, batteries etc. In this presentation, we shortly compare the pros and cons of flash lamp and laser annealing for thin film processing and discuss these issues at the example of thin semiconductor films on glass. In detail, the crystallization of amorphous Si on borosilicate glass, the crystallization of amorphous Ge on SiO2/Si substrates, and the formation of NiGe on different Ge substrates (amorphous, polycrystalline and monocrystalline) have been investigated. In all cases, the thin films were deposited by magnetron sputtering, followed by flash lamp annealing. The evolution of microstructure and its electrical properties was traced by corresponding characterization methods such as Raman spectroscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, sheet resistance and Hall effect measurements.

Designing cost-effective, highly active, and durable platinum (Pt)-based electrocatalysts is a crucial endeavor in electrochemical hydrogen evolution reaction (HER). Herein, the low-content Pt (0.8 wt%)/tungsten oxide/reduced graphene oxide aerogel (LPWGA) electrocatalyst with excellent HER activity and durability is developed by employing a tungsten oxide/reduced graphene oxide aerogel (WGA) obtained from a facile solvothermal process as a support, followed by electrochemical deposition of Pt nanoparticles. The WGA support with abundant oxygen vacancies and hierarchical pores plays the roles of anchoring the Pt nanoparticles, supplying continuous mass transport and electron transfer channels, and modulating the surface electronic state of Pt, which endow the LPWGA with both high HER activity and durability. Even under a low loading of 0.81 μgPt cm-2, the LPWGA exhibits a high HER activity with an overpotential of 42 mV at 10 mA cm-2, an excellent stability under 10000-cycle cyclic voltammetry and 40 h chronopotentiometry at 10 mA cm-2, a low Tafel slope (30 mV dec-1), and a high turnover frequency of 29.05 s-1 at η = 50 mV, which is much superior to the commercial Pt/C and the low-content Pt/reduced graphene oxide aerogel. This work provides a new strategy to design high-performance Pt-based electrocatalysts with greatly reduced use of Pt.

B20-type transition-metal silicides or germanides are noncentrosymmetric materials hosting magnetic skyrmions, which are promising information carriers in spintronic devices. The prerequisite is the preparation of thin films on technology-relevant substrates with magnetic skyrmions stabilized at a broad temperature and magnetic-field working window. The canonical example is the B20-MnSi film grown on Si substrates. However, the as-yet unavoidable contamination with MnSi1.7 occurs due to the lower nucleation temperature of this phase. In this work, we report a simple and efficient method to overcome this problem and prepare single-phase MnSi films on Si substrates. It is based on the millisecond reaction between metallic Mn and Si using flash lamp annealing (FLA). By controlling the FLA energy density, we can grow single-phase MnSi or MnSi1.7 or their mixture at will. Compared with bulk MnSi the prepared MnSi films show an increased Curie temperature of up to 41 K. In particular, the magnetic skyrmions are stable over a much wider temperature and magnetic-field range than reported previously. Our results constitute a novel phase selection approach for alloys and can help enhance specific functional properties such as enhancing the stability of magnetic skyrmions.

There are many ideas for using radionuclide- and heavy metal-binding microorganisms to remediate contaminated waters after e.g. uranium mining and processing. In particular, magnetotactic bacteria are moving into the focus of interest since they are able to survive in environments with very limited oxygen. Due to their organelles containing magnetic crystals, they can align themselves along the Earth's magnetic field for reaching regions of optimal oxygen concentrations. In laboratory studies we used the α-proteobacterium Magnetospirillum magneticum AMB-1, which is a motile, magnetotactic, gram-negative bacterium. It is facultative anaerobe and usually found in oxic-anoxic transition zones. In kinetic batch sorption experiments, cells of Magnetospirillum magneticum AMB-1 were contacted with different uranium concentrations and different pH. Independent of the initial U concentration, the cells were able to remove most of the uranium from the solution during the first hours of incubation. Microscopic studies, such as Transmission Electron Microscopy (TEM) in combination with Energy-Dispersive X-ray Spectroscopy (EDXS), clearly indicated that uranium is entirely accumulated in the cell membrane. Using spectroscopic methods like Time-Resolved Laser-Induced Fluorescence Spectroscopy at low temperature (cryo-TRLFS at 153 K), it was shown that uranium is mainly bound to the carboxylic functionality groups of peptidoglycan at the outer membrane of Magnetospirillum magneticum AMB-1 cells. With the obtained results we demonstrate that magnetotactic bacteria may play an important role in the bioremediation of contaminated sites, and probably not only for uranium, but also for other heavy metals.

Broad ion irradiation of nanoobjects can considerably change their shape. Examples are ion-beam hammering [1], ion-induced shaping of buried particles [2], and ion-induced viscous flow of nanopillars [3]. Such shape changes are mainly driven by the kinetics of defects generated by binary collisions of ions and recoils. Here we report a new kind of ion-induced structure evolution. Sub-micrometer Sn spheres were irradiated with 30 keV He+ ions in a Helium Ion Microscope (HIM). Above a He+ fluence of ~ 10E17 /cm², Sn extrusions appear on the surface of the spheres and were imaged with the HIM. Initially, small, pyramid-like facetted extrusions form at the equator of the tin spheres (north pole pointing to the ion source). Later, each sphere becomes completely covered with tin and appears like a facetted single crystal cube. No Sn extrusions were observed for tin spheres with diameters smaller than ~100 nm. Transmission Electron Microscopy and Auger electron spectroscopy studies show that the tin spheres are covered with a few nm thick SnOx skin and that the extrusions are single crystals. A model was developed which assumes that the He+ ions generate Frenkel pairs in the body-centered tetragonal lattice of tin. The point defects are confined to the tin sphere by the SnO skin, and there is no preferred nucleation or annihilation of the point defects at the Sn-SnO interface. The recombination of interstitials with vacancies is partly inhibited by occupation with He atoms. This results in an increasing pressure of the “interstitial gas”. Simultaneously, He+ ion erosion creates openings in the SnO skin. The sputter coefficient increases with the angle of incidence, so that openings in the SnO skin form in the equator regions first. Once the tin interstitials find an opening in the SnO skin, they can escape from the interior of the Sn sphere and form an epitaxial regular Sn lattice on the outside. Due to the high Sn-SnO bond strength, the extruded tin wets the outer SnO surface. Computer simulations were performed based on this model. The Frenkel pair generation and the SnO skin sputtering are simulated with dynamical programs based on the Binary Collision Approximation TRI3DYN [4]. Reaction-diffusion dynamics as well as nucleation and extended defect growth were simulated with a 3D kinetic lattice Monte Carlo program [5] using an RGL-potential for tin. The formation of cavities and their filling with He reproduces the experimentally observed tendency for hollow cube formation. [1] Snoeks et al., Nucl. Instr. Meth B 178 (2001) 62 [2] Schmidt et al., Nucl. Instr. Meth. B 267 (2009) 1345 [3] Xu et al., Semicond. Sci. Technol. 35 (2020) 15021 [4] Möller, Nucl. Instr. Meth. B 322 (2014) 23 [5] Strobel et al., Phys. Rev. B 64 (2001) 245422

INTRODUCTION Clay rock is a possible host rock for the long-term storage of high-level radioactive waste and bentonites are a suitable backfill material for a final repository in clay rock and crystalline rock. For a comprehensive safety assessment of such a repository over a long period, different aspects must be taken into account. Besides intensive research regarding geological, geochemical and geophysical properties, these surroundings represent a habitat for naturally occurring microorganisms. In the event of a worst-case scenario, water can enter the repository. It is possible that microorganisms can interact with the radionuclides and thereby change the chemical speciation or the oxidation state by various processes. Desulfosporosinus spp. play an important role as a representative of anaerobic, sulfate-reducing and spore-forming microorganisms. These bacteria occur in different clay formations as well as in bentonites.1,2 A very closely related bacterium to an isolated species from bentonite is Desulfosporosinus hippei DSM 8344, which was originally found in permafrost soils.3 Therefore, this strain was selected to get a more profound insight into the uranium(VI) interactions with naturally occurring microorganisms from deep geological layers by different microscopic and spectroscopic techniques. DESCRIPTION OF THE WORK For the time-dependent experiments in artificial Opalinus Clay pore water4 (100/500 µM uranium(VI), pH 5.5) the cells were cultivated in specific media and harvested in the late exponential growing phase. After washing, suspensions containing cells, uranium(VI) and lactate, were incubated at room temperature and samples were taken between zero hours and one week. RESULTS AND DISCUSSION The experiments showed the removal of about 80% of the uranium(VI) from the supernatants within 48 h at a concentration of 100 µM. Corresponding UV/Vis measurements of the dissolved cell pellets revealed an increasing proportion of uranium(IV) in the samples with time. After one week round about 40% of the uranium in the cell pellets was reduced. Therefore, the interaction mechanisms can be assigned to a combined sorption-reduction process. TEM images of the uranium-incubated cells reveal the formation of uranium aggregates on the cell surface. Uranium can be found not only outside the cell in vesicles, but also inside the cell. HERFD-XANES measurements show the presence of three oxidation states in the cell pellets. Besides uranium(VI) and uranium(IV), also uranium(V) plays a major role in the cellular reduction process. With the help of EXAFS measurements, three cell-related uranium species were detected. This study helps to close existing gaps in a comprehensive safeguard concept for a final repository for high-level radioactive waste in clay rock. Moreover, new insights into the interaction mechanisms of sulfate-reducing microorganisms with uranium are presented. REFERENCES 1. A. BAGNOUD et al., “Reconstructing a hydrogen-driven microbial metabolic network in Opalinus Clay rock” Nat. Commun., 7, 1-10 (2016). 2. N. MATSCHIVELLI et al., “The year-long development of microorganisms in uncompacted Bavarian bentonite slurries at 30 °C and 60 °C” Environ. Sci. Technol., 53, 10514-10524 (2019). 3. A. VATSURINA et al., “Desulfosporosinus hippei sp. nov., a mesophilic sulfate-reducing bacterium isolated from permafrost” Int. J. Syst. Evol. Microbiol., 58, 1228-1232 (2008). 4. P. WERSIN et al., “Biogeochemical processes in a clay formation in situ experiment: Part A - Overview, experimental design and water data of an experiment in the Opalinus Clay at the Mont Terri Underground Research Laboratory, Switzerland” Appl. Geochemistry, 26, 931-953 (2011).