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Ge with a quasi-direct band gap can be realized by strain engineering, alloying with Sn, or ultrahigh n-type doping. In this work, we use all three approaches together to fabricate direct-band-gap Ge-Sn alloys. The heavily doped n-type Ge-Sn is realized with CMOS-compatible nonequilibrium material processing. P is used to form highly doped n-type Ge-Sn layers and to modify the lattice parameter of P-doped Ge-Sn alloys. The strain engineering in heavily-P-doped Ge-Sn films is confirmed by x-ray diffraction and micro Raman spectroscopy. The change of the band gap in P-doped Ge-Sn alloy as a function of P concentration is theoretically predicted by density functional theory and experimentally verified by near-infrared spectroscopic ellipsometry. According to the shift of the absorption edge, it is shown that for an electron concentration greater than 1x10^20 cm-3 the band-gap renormalization is partially compensated by the Burstein-Moss effect. These results indicate that Ge-based materials have high potential for use in near-infrared optoelectronic devices, fully compatible with CMOS technology., 20 pages, 6 figures

Single quantum dots in the core of freestanding semiconductor nanowires is a promising scheme for the realization of on-demand sources of single photons or entangled photon pairs in quantum technology systems. Here, we demonstrate that complex quantum-dots can be grown in self-catalyzed III-As nanowires and their emission can be tuned in a wide range of wavelengths. The quantum dots are formed inside self-catalyzed GaAs nanowires (grown on Si substrates by molecular beam epitaxy) by first growing an axial AlxGa1-xAs/GaAs/AlxGa1-xAs heterostructure in pulsed mode . The AlxGa1-xAs segments are grown as digital alloys with a precise control of the composition, the thickness, and the crystal structure (absence of stacking faults). Then, the nanowires are overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. Owing to the large lattice-mismatch with the shell, the thin core develops tensile hydrostatic strain and the emission from the dot is strongly red-shifted. Furthermore, distinct exciton-biexciton features are identified in photoluminescence measurements.

Silicides have been widely used for CMOS devices in order to provide a stable Ohmic contact with a low contact resistivity. With the integration of Ge on Si the focus also shifted to germanides as a low resistivity contact material. In addition, ferromagnetic germanides may serve as spin injector materials for Ge-based spintronic devices. Usually, germanides have been fabricated by furnace or rapid thermal annealing in literature. In this contribution we investigate the formation process of Ni germanides using a combination of magnetron sputtering and flash lamp annealing (FLA). Three different types of Ge served as a substrate for the deposition of the transition metal: amorphous Ge made by magnetron-sputtering on a SiO2-Si substrate, polycrystalline Ge made by magnetron-sputtering followed by FLA, and monocrystalline Ge in the form of a (100) Ge wafer. After metal deposition samples are in-situ annealed by FLA without breaking the vacuum, which triggers the formation of germanides and prevents a possible, but unwanted oxidation. In order to investigate the crystallization behavior, the structures have been characterized by Raman spectroscopy, X-ray diffraction, ellipsometry, current-voltage and Hall effect measurements.

Non-reciprocity of wave phenomena describes the situation where wave dispersion depends on the sign of the wave-vector, i.e., counter-propagating waves exhibit di↵erent wavelengths for the same frequency. Such behavior has been recently observed in heavy-metal/ferromagnetic interfaces with Dzyaloshinskii-Moriya coupling, and has also been known for coupled magnetic bilayers, where non-reciprocity is enhanced when the two layers are antiparallel aligned. Besides the conventional uses of spin-waves, non-reciprocity adds further functionalities, such as its potential applications in communications technologies and logical operations. In the current manuscript, we thus examine the spin-wave non-reciprocity induced by dipolar interactions in a coupled bilayer consisting of two ferromagnetic layers separated by a non-magnetic spacer. We derive an easy-to-use formula to estimate the frequency di↵erence provided by the non-reciprocity, which allows for choosing an optimal system in order to maximize the e↵ect. For small wave-numbers, non-reciprocity scales linearly, while for larger wave-vectors the non-reciprocity behaves non-monotonically, with a well-defined maximum. The study is carried out by means of analytical calculations that are complemented by micromagnetic simulations. Furthermore, we confirmed our model by experimental investigation of the spin-wave dispersion in a prototype antiparallel-coupled bilayer system. Since the relative magnetic orientation can be controlled through a bias field, the magnon non-reciprocity can be then turned on and o↵, which lends an important functionality to the coupled ferromagnetic bilayers.

Although significant advances in the tailoring of BaSO4-based nanoparticles have been achieved, the synthesis of particles is strongly dependent on the use of templates, surfactants, and additives, especially when radiolabeled with 133Ba or 224Ra. Herein, direct facile preparation of radiolabeled alendronate-functionalized BaSO4 nanoparticles in an aqueous medium in a one-pot reaction is developed. Remarkably, the size of the formed BaSO4 nanoparticles can be controlled by the type of the organic solvent used. Upon the addition of alendronate, amine functionalities were introduced into the nanoparticles. Additionally, a fluorescence dye-containing alendronate was used to evidence the introduction of the alendronate during the formation of the nanoparticles. The variations in the functionalities were investigated by IR and the morphology of the resulting BASO4 nanoparticles are investigated in detail by transmission electron microscopy. DLS and TEM measurements provided an average diameter of the nanoparticles of approx. 140 nm. Radium-doped alendronate nanoparticles were successfully obtained in a one-pot labeling procedure from [224Ra]RaCl2, Na2SO4 Ba(NO3)2 and alendronate.

We report on the experimental observation and theoretical studies of a self-assembled Fe-rich (In,Fe)As nano-lamellar structure that is driven by anisotropic spinodal decomposition at the growth front during laser heating-induced recrystallization of Fe-implanted InAs [1]. Pseudomorphically embedded in the InAs lattice, those Fe-rich nano-lamellae are perpendicular to the (001) surface and parallel to the in-plane [110] crystallographic direction. The Fe atoms are substitutionally incorporated at the indium sites. Magnetic measurements indicate a typical blocked superparamagnetic behavior suggesting strong ferromagnetic orderings inside the Fe-rich nanostructures, but weak coupling between the nano-lamellae. Our findings explain the surprisingly high apparent Curie temperatures and unexpected eight-fold symmetry of crystalline anisotropic magnetoresistance found previously in Be-doped n-type (In,Fe)As grown by molecular beam epitaxy [2]. Prompted by these results we discuss how a different d-level electronic configuration of Fe in InAs and Mn in GaAs [3] affects the magnetic ion incorporation and spatial distribution and, thus, magnetism and anisotropy. Our results also indicate that the directional distribution of impurities or alloy components setting in during the growth may account for the observed nematicity in other classes of correlated systems. Reference [1] Y. Yuan, R. Hübner, M. Birowska, C. Xu, M. Wang, S. Prucnal, R. Jakiela, K. Potzger, R. Böttger, S. Facsko, J.A. Majewski, M. Helm, M. Sawicki, S. Zhou, T. Dietl, Nematicity of correlated systems driven by anisotropic chemical phase separation, in Phys. Rev. Materials 2, 114601 (2018). [2] Pham Nam Hai, D. Sasaki, Le Duc Anh, and M. Tanaka, Crystalline anisotropic magnetoresistance with twofold and eight-fold symmetry in (In,Fe)As ferromagnetic semiconductor, Appl. Phys. Lett. 100, 262409 (2012). [3] M. Birowska, C. Śliwa, J. A. Majewski, and T. Dietl, Origin of Bulk Uniaxial Anisotropy in Zinc-Blende Dilute Magnetic Semiconductors, Phys. Rev. Lett. 108, 237203 (2012).

We report a strong shift of the plasma resonance in highly doped GaAs/InGaAs core/shell nanowires for intense infrared excitation observed by scattering-type scanning near-field infrared microscopy. The studied nanowires show a sharp plasma resonance at a photon energy of about 125 meV in the case of continuous-wave excitation by a CO₂ laser. Probing the same nanowires with the pulsed free-electron laser with peak electric field strengths up to several 10 kV/cm reveals a power-dependent redshift to about 95 meV and broadening of the plasmonic resonance. We assign this effect to a substantial heating of the electrons in the conduction band and subsequent increase of the effective mass in the nonparabolic Γ-valley.

The n-type doping of Ge and Ge-based alloys is a self-limiting process due to the formation of vacancy-donor complexes (DnV with n ≤ 4) that deactivate the donors. This work clearly demonstrates that the dissolution of the DnV clusters in a heavily n-doped Ge, GeSn and SiGeSn layers can be achieved by millisecond-flash lamp annealing. This DnV cluster dissolution results in a considerable increase of the electrical activation together with a suppression of donor diffusion. Using electrical measurements and positron annihilation lifetime spectroscopy, combined with theoretical calculations, it is possible to address, understand and solve the fundamental problem of achieving ultra-high doping level in Ge, that has hindered so far the full integration of Ge and Ge-based alloys with complementary-metal-oxide-semiconductor technology.

Magnetic nanoclusters in amorphous carbon have promising applications for highly responsive magnetic sensors, where decreasing the size of the nanoclusters can lead to superparamagnetism and therefore low remanence. The insulating properties (wide bandgap) of amorphous carbon are also potentially useful for designing high frequency components. Both these properties are crucial to achieve ultra-high density magnetic data storage. High fluence (1.2×1017 Co/cm2) near-surface implantation of 30 keV Co ions into amorphous carbon results in the formation of complex magnetic nanostructures and multiple magnetic phases. Next to small segregated cobalt carbide nanoclusters, starting forming at a depth of 25 nm within the amorphous carbon film, a nearly continuous network of cobalt carbide thin nanocrystalline regions can be observed at a depth of 8 nm. On the surface a 3 nm thin cobalt oxide nanostructured layer is seen separated from the cobalt carbide by a 1 nm thin Co-depleted region. TEM and magnetic measurements show superparamagnetic nanoclusters with a blocking temperature of 5 K. However, a small proportion of larger cobalt carbide nanoclusters exhibits magnetic hysteresis even at room-temperature. The magnetic saturation moment is as high as 0.51 µB/Co at 2 K and 0.32 µB/Co at room temperature - ten times larger than previously reported on hydrogenated amorphous carbon [1]. The structural disorder of the nanoparticles results in a spin glass behaviour with a range of transition temperatures below ~70 K, suggesting a spin disordered shell model [2]. Thus high fluence Co-implantation into amorphous carbon at room temperature created complex magnetic nanostructures consisting of cobalt oxide and cobalt carbide. Multiple magnetic phases such as superparamagnetism, spin glass, ferromagnetism and also antiferromagnetism can be observed. References: 1. P.G. Sridhar Gupta, G.V.M. Williams and A. Markwitz, Journal of Physics D: Applied Physics, 2016, 49, 5, 055002. 2. T. Prakash, G.V.M. Williams, J. Kennedy and S. Rubanov, Materials Research Express, 2016, 3, 12, 126102.

There is a broad palette of applications for thin Si and Ge films ranging from photovoltaics over various microelectronic devices to sensor applications. Both amorphous and polycrystalline thin films are of interest for thin film photovoltaics, and thin film poly-Si transistors are the heart piece for driving LCDs and OLEDs [1]. In addition, the ability to deposit SiO2 and Si layers in an alternating order and to process them allows to extend the device density without further downscaling [2]. Amorphous thin film deposition methods are the most cost-effective ones, the subsequent crystallization is the most critical process step with regard to microstructure, defect density, and electrical properties. Potentially, flash lamp annealing (FLA) is a very suitable method due to the short process time, the qualification for temperature-sensible substrates and the possibility to take advantage of non-equilibrium crystallization modes [3]. In this work thin amorphous Si and Ge films have been deposited on SiO2 by DC-magnetron sputtering and crystallized by in-situ FLA in a new FLA sputter tool recently installed by the Rovak GmbH at HZDR (Fig. 1). The in-situ-processing suppresses the influence of surface oxidation effects after deposition prior to FLA. In order to investigate the crystallization behaviour, the thin films have been characterized by Raman spectroscopy, X-ray diffraction, ellipsometry, current-voltage and Hall effect measurements. Based on these results and in combination with temperature simulations, a model for the crystallization of thin amorphous Si and Ge films is derived.

III-As semiconductors in the form of free-standing nanowires have exhibited new potentials for a wide variety of future applications in nanotechnology, ranging from energy-efficient electronic switches to entangled-photon-pair sources for quantum information technology, including the possibility for monolithic integration in the mainstream Si technology. Using molecular beam epitaxy, we developed an in situ procedure (substrate annealing – Ga deposition – substrate annealing) in order to modify the surface of Si substrates and, thus, to achieve highly synchronized nucleation of self-catalyzed GaAs nanowire ensembles with well controlled dimensions and number density. Specifically, the radius can be as low as 10 nm, the distribution of lengths can be sub-Poissonian (due to the so-called nucleation anti-bunching), and the number density can be varied from 10 ⁶ to 10 ⁹ cm-2. Furthermore, the GaAs nanowires can be hydrostatically strained when they are overgrown all-around with lattice-mismatched shells. The high surface-to-volume ratios allow for growing highly mismatched combinations without dislocations, beyond to what is possible in thin-film heterostructures. Here, we show that the mismatch strain inside the GaAs core can be engineered via the composition and the thickness of an (In, Ga)As or (In, Al)As shell. As a result, the electronic properties of GaAs can be widely tuned; the band gap and the electron effective mass can be reduced down to 60% of the strain-free values, rendering GaAs nanowires suitable for photonic devices across the near-infrared (800 – 1400 nm) range or for high-speed transistors.

To complement scaling of field effect transistors, new device concepts were introduced recently. One such concept is the reconfigurable field effect transistor (RFET). These transistors are based on nickel silicide-Si-nickel silicide Schottky junctions and their polarity can be switched between p- and n- type at runtime by the application of an electrostatic potential [1]. Control over silicide length and phase is important for scaling and proper functioning of these devices [2]. NiSi2 is the desirable silicide phase as its metal work function aligns itself near mid bandgap of Si, which enables reconfigurability of the device [1, 3]. We report on fabrication and electrical characterization results of RFETs. Si nanowires (SiNWs) are fabricated on undoped silicon-on-insulator (SOI) substrates by a top-down process based on electron beam lithography and inductively coupled plasma etching. Then, Ni is placed at both ends of the SiNWs by metal evaporation and lift-off processes. Afterwards, flash lamp annealing (FLA) is performed for silicidation of the NWs. FLA has enabled better control over silicidation length since flash times are much shorter (of the order of milli-seconds) than rapid thermal annealing (RTA) times. Transmission electron microscopy (TEM) shows the formation of the desired NiSi2 phase near the silicide-Si interface. Electrical characterization of the devices with back gating shows ambipolar behaviour. For unipolar behaviour, top gates need to be fabricated, results of which will be presented at the conference.

Gallium is an essential element in many semi-conducting products, electronic devices and opto-electronic components. It is mostly applied as GaAs and GaN. Despite it’s growing demand it is currently not recycled. The development of novel biocomposites based on magnetite and biopolymers for the selective binding of Ga and As from diluted flushing solutions of the semi-conducting industry offers a promising concept for the efficient, economical and sustainable recycling of these metal(loids). In this study several magnetite based-biocomposites for an efficient and easy separation in magnetic field were developed and optimized regarding an effective sorption behavior for Ga and As from complex but highly diluted industrial wastewaters (each 4 mg/L, pH 8.4). Combinations of magnetite nanoparticles and S-layer proteins removed up to 100% of both elements depending on the used amount of material. Additionally, the S-layer-magnetite-composites showed a better stability compared to pure magnetite during the sorption process. The materials showed a preferred sorption of Ga compared to As. An optimization of (selective) sorption and stability of the materials was achieved by addition of a second biomolecule (bovine serum albumin, phosvitin, chitosan) to S-layer-magnetite-composites. Raman spectroscopy and transmission electron microscopy with electron diffraction of the biocomposites revealed pure magnetite particles with size between 5-10 nm surrounded by the biocomponent. The zeta-potential of the biocomposites is negative which favors the binding of Ga3+ compared to negatively charged As species. Sustainability of the biocomposites is given as bound Ga and As could be completely removed from the composites with EDTA, so that the biocomposites could be reused for several sorption-desorption cycles. In conclusion, these regenerative materials enable an efficient and selective removal of gallium and arsenic from highly diluted industrial wastewaters. The combination of magnetite with biomolecules provides a promising approach to improve metal recycling and contribute to environmentally friendly and sustainable processes.

Short period superlattices (SPSs) of InxGa1-xN/GaN quantum wells (QW) with a thickness of one up to just a few atomic monolayers (MLs) are promising for bandgap and strain engineering towards advanced optoelectronics devices and novel topological insulators. We have considered 5-period InxGa1-xN/GaN SPSs deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates under metal-rich conditions. The nominal QW thickness was 1 ML and the GaN barriers were 10 nm thick. The SPSs were grown at various growth temperatures keeping the same temperature for both QWs and GaN barriers. Cs-corrected high resolution transmission electron microscopy (HRTEM), and probe-corrected scanning TEM (HRSTEM) observations were carried out in order to elucidate the effect of growth temperature on the structural quality, composition, and strain state of the QWs. Cross-sectional observations were conducted along the and projection directions. Atomic positions were identified on images using a peak finding algorithm and were employed in order to extract nanoscale strain maps. Furthermore, quantification of the Z-contrast of atomic columns on the HRSTEM observations was employed for the direct determination of the indium content in QWs. The thin foil relaxation phenomenon was considered in the analysis. Composition dependent strain graphs were calculated theoretically in order to associate the experimental strain measurements to the indium content. For that purpose, a series of energetically relaxed InxGa1-xN/GaN supercells were constructed taking into account several indium contents, and the QW thickness limited to 1 ML. For the relaxation of the supercells a ternary empirical interatomic potential was utilized using molecular dynamics simulations.

Der Vortrag stellt das Helmholtz Innovation Lab für Ultrakurzzeitausheilung vor. Im zweiten Teil werden experimentelle Ergebnisse bei der Kristallisation von dünnen amorphen Halbleiterschichten (Si, Ge, NiGe) mittels magnetron sputtering und Blitzlampenausheilung diskutiert.

In recent days, due to increased use of hadron therapy for cancer and tumor treatment, precise online dose monitoring is an important issue for safety purpose. Regarding hadron therapy, recently carbon ion beam with high Linear Energy Transfer (LET) is found to be more effective than the photon beams. Among several known TL/OSL oxides phosphors, C-doped alumina (Al2O3) is favorable for radiation dosimetry, especially in medical field due to its tissue equivalent in terms of radiation absorption, simple glow curve, and high sensitivity. A facile approach to improve thermoluminescence sensitivity of electrochemically anodized porous Al2O3 (AAO) is presented by introducing carbon ions for ion beam dosimetry. Initially, ion implantation technique has been carried out for Carbon doping in AAO in controlled manner. HAADF-STEM, EDS mapping, SEM studies reveal the evolution of a porous structure followed by the carbon distribution up to 200 nm. However, the evolution of optically active F+ centres with increasing ion fluence has been examined by photoluminescence investigation at room temperature and thermoluminescence (TL) measurement while the chemical nature of such defect centres has been extracted by depth dependent XPS analysis.

The catalytic graphitization with layer exchange (LE) of amorphous carbon in thin film stacks with Ni was investigated as a function of the initial stacking order. Bilayer and triple layer stacks were exposed to heating ramps up to 700 °C. Raman spectroscopy showed the formation of a layered graphitic structure after the annealing. During outwards LE, as C is transported towards the sample surface, a smooth layer with graphitic planes parallel to the interface with the substrate has formed through a 2D growth. A significant restructuring of the Ni layer appeared during inwards LE, as C is transported towards the substrate. Here, the fragmentation of the Ni layer, as well as the regions with turbulence-like and folding defects indicated a 3D growth. The degree of LE, quantified by ion beam analysis, is 95 % and 80 % for the outand inwards direction, respectively. Based on the calculation of surface and interface energies of the initial and final states, thermodynamic estimations pointed to the wetting of Ni grain boundaries by C atoms as the initial driving force for the LE and allowed a consistent understanding of the LE directionality and of the final thin film microstructure.

Radionuclides occur naturally and can be released into nature through anthropogenic effects. Through leaching and migration, also the anthropogenically released radionuclides can enter the groundwater and endanger the environment, animals and humans. However, the microbial community living in the soil may influence the mobility and thus the migration behaviour of radionuclides. Since the Chernobyl accident at the latest, it became clear that various fungi are able to accumulate considerable amounts of heavy metals and radionuclides in their fruiting bodies [1-3]. However, it has not yet been determined, which processes lead to this significant accumulation in the fungal fruiting body. For this reason, the interaction of a model fungus, namely Schizophyllum commune, with various radionuclides was studied in detail in the steps of binding and uptake by the fungal cells and transport within the mycelium. For the visualization of the radionuclide and heavy metal transport through the hyphae, TEM and STEM imaging in combination with Energy-dispersive X-ray spectroscopy analysis were used to locate accumulation sites within the cells and to identify the formed species. The first results with uranium show that it is accumulated in form of phosphate minerals mainly on the cell membrane. Furthermore, microcosm experiments were conducted in which the bidirectional growth of the fungus was exploited: parts of the mycelium were growing upwards, while the other parts were growing into the contaminated soil. In order to check the transport of soil contaminants through the hyphae, the part of the mycelium that has no direct contact with the soil was sampled and analysed by ICP-MS. First results show that uranium could be detected in the samples, suggesting transport through the hyphae. In addition to the transport of uranium, the experiments also investigate the transport of europium as an analogue for trivalent actinides, as well as the transport of inactive caesium and strontium within the mycelium.

The organic permeable base transistor (OPBT) is currently the fastest organic transistor with a transition frequency of 40 MHz. It relies on a thin aluminum base electrode to control the transistor current. This electrode is surrounded by a native oxide layer for passivation, currently created by oxidation in air. However, this process is not reliable and leads to large performance variations between samples, slow production, and relatively high leakage currents. Here, for the first time it is demonstrated that electrochemical anodization can be conveniently employed for the fabrication of high-performance OPBTs with vastly reduced leakage currents and more controlled process parameters. Very large transmission factors of 99.9996 % are achieved, while excellent on/off ratios of 5 × 105 and high on-currents greater than 300 mA cm−2 show that the C60 semiconductor layer can withstand the electrochemical anodization. These results make anodization an intriguing option for innovative organic transistor design.

Free-standing nanowires are promising platforms for hosting three-dimensional heterostructures such as single quantum dots for quantum photonics, modulation doped heterostructures for gate-all-around high mobility transistors, etc. The peculiarity of heteroepitaxy in nanowires is the existence of multiple growth interfaces with different crystallographic orientations (usually one top- and six side-facets), where the growth can take place in different modes (e.g. vapor-liquid-solid on the top- and vapor-solid on the side-facets) and can be controlled independently. Furthermore, strained epilayers in nanowires can relax elastically both at the lateral free surface and by stretching the substrate, which in this case are the thin nanowires. All these features open up new possibilities for complex three-dimensional heterostructures with loose strain restrictions. Here, we have investigated the growth of radial and axial heterostructures, as well as combinations of the two, within III-As nanowires. The radial ones consist of thin GaAs nanowires overgrown all-around with an InxAl1-xAs layer in a core/shell fashion. In agreement with theory, the small volume of the core allows for strain engineering both in the core and the shell, and for realization of highly-mismatched/strained heterostructures (with misfits up to 4%) without dislocations. The manipulation of the growth kinetics is necessary in order to suppress strain-driven phenomena, such as the preferential shell-growth and In-incorporation on one side of the core. The axial heterostructures consist of single or multiple GaAs/AlxGa1-xAs quantum dots. The width and the thickness of these dots can be controlled independently. The AlxGa1-xAs segments were grown as digital alloys using pulsed epitaxy in order to achieve sharper interfaces and to avoid the formation of stacking faults. Finally, we realized complex heterostructures with single GaAs/AlxGa1-xAs quantum dots inside the core of core/shell nanowires, aiming at engineering the electronic properties of the dots depending on the composition and thickness of the shell. Besides MBE experiments, our investigations involved transmission electron microscopy (HR-TEM, STEM, EDX, STEM tomography), X-ray diffraction, Raman scattering spectroscopy, and photoluminescence spectroscopy.

Introduction/Purpose: Short period superlattices (SPSs) comprising ultrathin InGaN/GaN quantum wells (QW) with thicknesses ranging from one to few (0002) monolayers (MLs) are promising for novel applications ranging from band gap engineering in optoelectronic devices to topological insulators. The strain relaxation behavior of a range of samples grown by varying the growth temperatures for the QWs and GaN barriers has been considered. Methods: In(Ga)N/GaN SPSs were deposited by plasma-assisted molecular beam epitaxy (PAMBE) on c-GaN/Al2O3 templates. Structural characterization was performed by high resolution transmission and scanning transmission electron microscopy (HRTEM/HRSTEM). Results: Strain relaxation through formation of stacking fault domains was observed with decreasing growth temperature. For the quantification of strain versus composition, peak finding with a recently established approach was implemented. This involves quantification of Z-contrast from HRSTEM observations by comparison with calculated composition-dependent graphs of InxGa1-xN/GaN atomic column intensity ratios obtained from multislice image simulations of energetically relaxed supercells under the frozen lattice approximation. Energetical relaxation was performed by molecular dynamics using an empirical interatomic potential, considering the ordered, disordered, and island models of QW structure. Comparison to the experimental observations was performed along the a-type zone axis that is appropriate to deduce average values for the QW composition and strain. Conclusions: The investigation concluded to the influence of growth temperature in the composition and structural properties of ultra-thin In(Ga)N/GaN QWs.

Helium Ion Microscopy (HIM) [1, 2] is best known for its high resolution imaging capabilities of both conductive as well as insulating samples. However, since the introduction of Ne as an imaging gas for the gas field ion source (GFIS) an increasing number of nano-fabrication applications are realized. While the use of Neon as an imaging gas results in a somewhat lower lateral resolution (1.8 nm for 25 keV Ne compared to 0.5 nm for 30 keV He) the user usually benefits from the much higher cross section for nuclear stopping. The latter results in a larger number of sputtered atoms and bonds broken directly by small impact parameter collisions. After a brief introduction of the technique I will present results obtained using direct write milling low fluence ion beam irradiation and ion beam based mixing. In all three cases the electronic or magnetic properties of the target material will be altered at the nano-scale in a controlled way to achieve new functionality. The examples comprise ∙ The fabrication of semiconducting graphene nano-ribbons by direct milling [3] ∙ The fabrication of a lateral spin valve structure using low fluence ion irradiation [4] ∙ The formation of individual 3 nm Si clusters for a room temperature single electron transistor [5] For all presented examples the critical length scale of the nanostructure is smaller or in the range of collision cascade. This size regime can not be accessed with traditional broad beam based ion irradiation and holds many promises but also challenges that need to be overcome to enable new device concepts and new functional materials on the nano-scale. This work is supported by the European Union’s H-2020 research project ‘IONS4SET’ under Grant Agreement No. 688072

We report terahertz response of photoexcited core/shell nanowires. The obtained parameters of the localized surface plasmon mode allow us to estimate electron mobilities, concentrations and recombination lifetimes. The extracted mobilities reach 4000 cm²/V·s at room temperature, while the carrier lifetimes range from 80 to 300 ps, depending on the shell composition and the photoexcitation level.

The n-type doping of Ge is self-limiting process due to formation of the vacancy-donor complexes (Dn V with n≤4). Here we report on experiments and density functional theory (DFT) calculations solving the basic problem of donor deactivation in heavily doped Ge. The self-healing process of heavily doped n-type Ge is achieved by rear-side flash lamp annealing (r-FLA) for 20 ms with the peak temperature of about 1050 K. The positron-annihilation lifetime spectroscopy (PALS) reveals that the P4V clusters are main defects in the as-grown Ge:P samples. Millisecond range high-temperature treatment dissociates the phosphorus-vacancy cluster (P4V) and, as shown by SIMS, fully supress the P diffusion. The electrochemical capacitance-voltage (ECV) profiling shows that the effective carrier concentration in P doped Ge (P concentration - 1×1020 cm-3) increases from about 3×1019 cm-3 in as-grown sample to above 8×1019 cm-3 after r-FLA. For the first time using structural (PALS, SIMS) and electrical (ECV) characterization combined with DFT calculations we were able to addressed, explained and solved the fundamental problem hindering the full integration of Ge with CMOS technology.

Compact tellurium (Te) thin films show important applications in micro-thermoelectric modules, which are able to convert waste heat to electrical energy (μTEG) or vice versa to use electricity to generate cooling (μTEC). The as-fabricated μTECs, which are based on electrochemically deposited n-type Bi2(TexSe1-x)3 (in short BiTeSe) and p-type tellurium, demonstrate a rapid response time of 1ms, a high cycling reliability of up to 10 million cycles and a long-term cooling stability of more than 1 month at constant electric current. However, a mismatch of electrical conductivity between pure Te and BiTeSe often leads to some difficulties in the geometry design of micro-thermoelectric modules. In order to enhance the electrical property of Te, we have introduced an atomic bismuth (Bi) doping. In this report, we have performed transmission electron microscopy (TEM, FEI Tecnai G2/ 200 kV) analysis to observe the presence and distribution of Bi within Te. To this end, cross-sectional TEM specimens were prepared using the Focused Ion Beam technique (FIB, FEI Helios NanoLab 600i). The Bi-doped Te samples have a columnar grain structure. Selected-area electron diffraction proves the presence of crystalline Te. Results of Nanodiffraction in numerous areas also suggest Te (hexagonal, space group 152, a = b = 0,4458 nm, c = 0,5925 nm, α = ß = 90°, γ = 120°) but could be explained with Bi (rhomboedral, space group 166, a = b = 0,4550 nm, c = 1,1850 nm, α= ß = 90°, γ = 120°), too. Unfortunately, the geometry of the Bi and Te unit cells differ only in the length of the c-axis. In addition, HRTEM images show lattice fringes, which could belong to Bi or Te. To unambiguously distinguish between both elements, chemical analysis is necessary. Performing energy-dispersive X-ray spectroscopy (EDXS) analysis with a conventional Si(Li) detector, no Bi counts appear in the EDX spectra during reasonable measuring times of several minutes. To finally get the distribution of Bi in the Te matrix, we employed a FEI Talos F200X microscope operated at 200 kV and equipped with an X-FEG electron source and a Super-X EDX detector system and performed spectrum imaging analysis based on EDXS.

The chemically ordered B2 Fe50Rh50 alloy is antiferromagnetic. By inducing chemical disorder its structure can be changed to the ferromagnetic A2 structure. Following the laser writing method published here [1] we used a pulsed laser to induce ferromagnetism locally in Fe50Rh50 thin films of 10, 20, and 30nm thickness. XMCD measurements on the laser-treated region revealed the formation of an annulus of FM contrast and a non-FM center. Transmission electron microscopy (TEM) on a section through the annulus found the FM region to be A2 and the enclosed non-contrast region of the fcc A1 structure. The surrounding untreated region remained in the B2 structure.

Si hyperdoped with chalcogens (S,Se,Te) is well known to possess unique properties such as an insulator-tometal transition and a room-temperature sub-band-gap absorption. These properties are expected to be sensitive to a postsynthesis thermal annealing, since hyperdoped Si is a thermodynamically metastable material. Thermal stability of the as-fabricated hyperdoped Si is of great importance for the device fabrication process involving temperature-dependent steps such as Ohmic contact formation. Here, we report on the thermal stability of the as-fabricated Te-hyperdoped Si subjected to isochronal furnace anneals from 250 to 1200 °C. We demonstrate that Te-hyperdoped Si exhibits thermal stability up to 400 °C for 10 min, which even helps to further improve the crystalline quality, the electrical activation of Te dopants, and the room-temperature sub-band-gap absorption. At higher temperatures, however, Te atoms are found to move out from the substitutional sites with a maximum migration energy of EM = 2.3 eV forming inactive clusters and precipitates that impair the structural, electrical, and optical properties. These results provide further insight into the underlying physical state transformation of Te dopants in a metastable compositional regime caused by postsynthesis thermal annealing. They also pave the way for the fabrication of advanced hyperdoped Si-based devices.

Due to the multifaceted use of radionuclides in research, medicine and industry, there is an increased risk of a release into the environment during the extraction and use of radioactive materials, but also during the storage of the resulting radioactive waste. If radionuclides are released into the soil, they can migrate through soil layers to the groundwater or can be absorbed by crops. In any case, it endangers the environment, animals and humans. For this reason, an effective precautionary radiation protection method must be found which can limit the mobility of possible released radionuclides in the environment. Since the Chernobyl accident at the latest, it became clear, that fungi influence the migration behavior of radionuclides in the soil by accumulating them in large quantities. Due to other positive properties of fungi, such as the spread of one organism over several square kilometers and their high life expectancy, they provide a good basis for a bio-based precautionary radiation protection. Nevertheless, previous studies have also shown, that the effectiveness of radionuclide accumulation depends on the respective fungal strain [1-3]. For this reason, the molecular interactions of four different fungi with uranium were investigated and compared. First TEM and STEM images of the fungus Schizophyllum commune, which is widely used as a model organism, show mineralization of uranium in form of needles at the cell membrane. Energy-dispersive X-ray spectroscopy analysis and time-resolved laser-induced fluorescence spectroscopy (TRLFS) have shown, that uranium is mineralized with phosphate. A second fungus, called Leucoagaricus naucinus, shows a different form of mineralization and localization of uranium in the cell. However, first TRLFS experiments suggest that it is a phosphate mineral as well. Together with two other fungi, Pleurotus ostreatus and Macrolepiota procera, a better understanding of the interactions of different fungi with radionuclides will be generated in order to evaluate the potential of fungi for the precautionary radiation protection of soils and to lay the basis for the development of a practicable process.

Noble metal aerogels (NMAs), as the most important class of noble metal foams (NMFs), appear as emerging functional porous materials in the field of materials science. Combining the irreplaceable roles of noble metals in certain scenarios, as well as monolithic and porous features of aerogels, NMAs can potentially revolutionize diverse fields, such as catalysis, plasmonics, and biology. Despite profound progress, grand challenges remain in their fabrication process, including the efficient structure control, the comprehensive understanding of the formation mechanisms, and the generality of the fabrication strategies, thus inevitably retarding the material design and optimization. This Perspective focuses on the key progress, especially of the fabrication strategies for NMAs during the last two decades, while other NMFs are also succinctly introduced. Challenges and opportunities are summarized to highlight the unexploited space and future directions in expectation of stimulating the broad interest of interdisciplinary scientists.

The graphitization of amorphous carbon in thin film stacks with Ni was investigated in situ as a function of the initial stacking order, temperature and time by Rutherford backscattering spectrometry and Raman spectroscopy. Four different bilayer and triple layer stacks were exposed to heating ramps up to 700 °C. The graphitization occurred simultaneously with a layer exchange (LE) and was completed during the applied heating ramp. The temperature-resolved measurements allowed the determination of the onset temperatures and transition rates for the respective stacking order. Finally, the activation energies for the graphitization of the amorphous carbon were estimated for both LE directions. In combination with thermodynamic calculations, this in situ study allowed to identify metal-induced crystallization with LE via wetting and diffusion along grain boundaries as mechanism responsible for the graphitization of amorphous carbon thin films in contact with Ni, instead of bulk dissolution/precipitation. The proposed model can potentially be used to estimate the catalytic transformation of group 14 elements in contact with transition metals.

In Uranus and Neptune methane and other hydrocarbons are highly abundant. Their planetary interior conditions can be mimicked using high intensity lasers in the laboratory on a nanosecond timescale. Nanodiamond formation from shock-compressed polystyrene (~150GPa, ~5000K) was demonstrated via in situ X-ray diffraction with a XFEL. The lower size estimate is 4nm. 60% of the carbon atoms in the plastic are transferred to a diamond lattice. However, in total a maximum of ~16μg of nanodiamonds are expected from a 125nm CH foil and a 500μm focal spot. In order to understand the underlying hydrocarbon separation mechanism the physical recovery of nanodiamonds is pursued to learn from their shape, size, surface modifications and defects.