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Using low-temperature cathodoluminescence spectroscopy, we study the properties of N- and Al-polar AlN layers grown by molecular beam epitaxy on bulk AlN{0001}. Compared to the bulk AlN substrate, layers of both polarities feature a suppression of deep-level luminescence, a total absence of the prevalent donor with an exciton binding energy of 28 meV, and a much increased intensity of the emission from free excitons. The dominant donor in these layers is characterized by an associated exciton binding energy of 13 meV. The observation of excited exciton states up to the exciton continuum allows us to directly extract the $\Gamma_{5}$ free exciton binding energy of 57 meV.

Financial information is generated and distributed across the world, resulting in a vast amount of domain-specific multilingual data. Multilingual models adapted to the financial domain would ease deployment when an organization needs to work with multiple languages on a regular basis. For the development and evaluation of such models, there is a need for multilingual financial language processing datasets. We describe MULTIFIN– a publicly available financial dataset consisting of real-world article headlines covering 15 languages across different writing systems and language families. The dataset consists of hierarchical label structure providing two classification tasks: multi-label and multi-class. We develop our annotation schema based on a real-world application and annotate our dataset using both ‘label by native-speaker’ and ‘translate-then-label’ approaches. The evaluation of several popular multilingual models, e.g., mBERT, XLM-R, and mT5, show that although decent accuracy can be achieved in high-resource languages, there is substantial room for improvement in low-resource languages.

An accurate knowledge of the optical constants (refractive index $n$ and extinction coefficient $k$) of ScN is crucial for understanding the optical properties of this binary nitride semiconductor as well as for its use in optoelectronic applications. Using spectroscopic ellipsometry in a spectral range from far infrared to far ultraviolet (0.045-8.5 eV), we determine $n$ and $k$ of ScN layers grown on Al$_{2}$O$_{3}$(0001) substrates by plasma-assisted molecular beam epitaxy. Fits of ellipsometry data return the energies of four oscillators representing critical points in the band structure of ScN, namely, 2.03, 3.89, 5.33, and 6.95 eV. As the infrared range is dominated by free carriers, the vibrational properties of the layers are examined by Raman spectroscopy. Despite the rocksalt structure of ScN, several first-order phonon modes are observed, suggesting a high density of point defects consistent with the high electron density deduced from Hall measurements. Finally, photoluminescence measurements reveal an emission band slightly above the lowest direct bandgap. We attribute the redshift of the peak emission energy from 2.3 to 2.2 eV with increasing layer thickness to a reduction of the O concentration in the layers.

We study the molecular beam epitaxy of AlN nanowires between 950 and 1215 {\deg}C, well above the usual growth temperatures, to identify optimal growth conditions. The nanowires are grown by self-assembly on TiN(111) films sputtered onto Al$_2$O$_3$. Above 1100 {\deg}C, the TiN film is seen to undergo grain growth and its surface exhibits {111} facets where AlN nucleation preferentially occurs. Modelling of the nanowire elongation rate measured at different temperatures shows that the Al adatom diffusion length is maximised at 1150 {\deg}C, which appears to be the optimum growth temperature. However, analysis of the nanowire luminescence shows a steep increase in the deep-level signal already above 1050 {\deg}C, associated with O incorporation from the Al$_2$O$_3$ substrate. Comparison with AlN nanowires grown on Si, MgO and SiC substrates suggests that heavy doping of Si and O by interdiffusion from the TiN/substrate interface increases the nanowire internal quantum efficiency, presumably due to the formation of a SiN$_x$ or AlO$_x$ passivation shell. The outdiffusion of Si and O would also cause the formation of the inversion domains observed in the nanowires. It follows that for optoelectronic and piezoelectric applications, optimal AlN nanowire ensembles should be prepared at 1150 {\deg}C on TiN/SiC substrates and will require an ex situ surface passivation., Comment: Main Paper: 13 pages, 5 figures Supporting Information: 4 pages, 4 figures

Capitalizing on the directed nature of the atomic fluxes in molecular beam epitaxy, we propose and demonstrate the sequential directional deposition of lateral (In,Ga)N shells on GaN nanowires. In this approach, a sub-monolayer thickness of each constituent atomic species, i.e. Ga, In, and N, is deposited subsequently from the same direction by rotating the sample and operating the shutters accordingly. Using multiple iterations of this process, we achieve the growth of homogeneous shells on a single side facet of the nanowires. For higher In content and thus lattice mismatch, we observe a strain-induced bending of the nanowire heterostructures. The incorporation of In and the resulting emission spectra are systematically investigated as a function of both the growth temperature and the In/Ga flux ratio.

Using molecular beam epitaxy, we demonstrate the growth of (In,Ga)N shells emitting in the green spectral range around very thin (35 nm diameter) GaN core nanowires. These GaN nanowires are obtained by self-assembled growth on TiN. We present a qualitative shell growth model accounting for both the three-dimensional nature of the nanostructures as well as the directionality of the atomic fluxes. This model allows us, on the one hand, to optimise the conditions for high and homogeneous In incorporation and, on the other hand, to explain the influence of changes in the growth conditions on the sample morphology and In content. Specifically, the impact of the V/III and In/Ga flux ratios, the rotation speed and the rotation direction are investigated. Notably, with In acting as surfactant, the ternary (In,Ga)N shells are much more homogeneous in thickness along the NW length than their binary GaN counterparts.

GaAs-based nanowires are among the most promising candidates for realizing a monolithical integration of III-V optoelectronics on the Si platform. To realize their full potential for applications as light absorbers and emitters, it is crucial to understand their interaction with light governing the absorption and extraction efficiency, as well as the carrier recombination dynamics determining the radiative efficiency. Here, we study the spontaneous emission of zincblende GaAs/(Al,Ga)As core/shell nanowire arrays by $\mu$-photoluminescence spectroscopy. These ordered arrays are synthesized on patterned Si(111) substrates using molecular beam epitaxy, and exhibit an exceptionally low degree of polytypism for interwire separations exceeding a critical value. We record emission spectra over more than five orders of excitation density for both steady-state and pulsed excitation to identify the nature of the recombination channels. An abrupt Mott transition from excitonic to electron-hole-plasma recombination is observed, and the corresponding Mott density is derived. Combining these experiments with simulations and additional direct measurements of the external quantum efficiency using a perfect diffuse reflector as reference, we are able to extract the internal quantum efficiency as a function of carrier density and temperature as well as the extraction efficiency of the nanowire array. The results vividly document the high potential of GaAs/(Al,Ga)As core/shell nanowires for efficient light emitters integrated on the Si platform. Furthermore, the methodology established in this work can be applied to nanowires of any other materials system of interest for optoelectronic applications.

An accurate knowledge of the lattice parameters of the new nitride Sc$_\textit{x}$Al$_\textit{1-x}$N is essential for understanding the elastic and piezoelectric properties of this compound as well as for the ability to engineer its strain state in heterostructures. Using high-resolution x-ray diffractometry, we determine the lattice parameters of 100-nm-thick undoped Sc$_\textit{x}$Al$_\textit{1-x}$N layers grown on GaN(0001) templates by plasma-assisted molecular beam epitaxy. The Sc content $\textit{x}$ of the layers is measured independently by both x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy and ranges from 0 to 0.25. The in-plane lattice parameter of the layers linearly increases with increasing $\textit{x}$, while their out-of-plane lattice parameter remains constant. Layers with $\textit{x}$ $\approx$ 0.09 are found to be lattice matched to GaN, resulting in a smooth surface and a structural perfection equivalent to that of the GaN underlayer. In addition, a two-dimensional electron gas is induced at the Sc$_\textit{x}$Al$_\textit{1-x}$N/GaN heterointerface, with the highest sheet electron density and mobility observed for lattice-matched conditions.

The self-assembly of heteroepitaxial GaN nanowires using either molecular beam epitaxy (MBE) or metal-organic vapor phase epitaxy (MOVPE) mostly results in wafer-scale ensembles with ultrahigh ($>10$ $μ$m$^{-2}$) or ultralow ($

In the molecular beam epitaxy of oxide films, the cation (Sn, Ga) or dopant (Sn) incorporation does not follow the vapor pressure of the elemental metal sources, but is enhanced by several orders of magnitude for low source temperatures. Using line-of-sight quadrupole mass spectrometry, we identify the dominant contribution to the total flux emanating from Sn and Ga sources at these temperatures to be due to the unintentional formation and evaporation of the respective suboxides SnO and Ga$_{2}$O. We quantitatively describe this phenomenon by a rate-equation model that takes into account the O background pressure, the resulting formation of the suboxides via oxidation of the metal source, and their subsequent thermally activated evaporation. As a result, the total flux composed of the metal and the suboxide fluxes exhibit an \textsf{S}-shape temperature dependence instead of the expected linear one in an Arrhenius plot, in excellent agreement with the available experimental data. Our model reveals that the thermally activated regimes at low and high temperatures are almost exclusively due to suboxide and metal evaporation, respectively, joined by an intermediate plateau-like regime in which the flux is limited by the available amount of O. An important suboxide contribution is expected for all elemental sources whose suboxide exhibits a higher vapor pressure than the element, such as B, Ga, In, La, Si, Ge, Sn, Sb, Mo, Nb, Ru, Ta, V, and W. This contribution can play a decisive role in the molecular beam epitaxy of oxides, including multicomponent or complex oxides, from elemental sources. Finally, our model predicts suboxide-dominated growth in low-pressure chemical vapor deposition of Ga$_{2}$O$_{3}$ and In$_{2}$O$_{3}$.

Prayer marks are asymptomatic callosities resulting from repeated, extended pressure, and friction exerted on bony prominences when praying on hard ground. A 41-year-old woman with ulcerative colitis treated with infliximab was referred to our clinic due to skin changes on her feet that were suspected to be drug eruptions. The patient presented several asymptomatic, hyperpigmented, and hyperkeratotic plaques over the lateral malleoli suggesting that the lesions had a mechanical cause. Further exploration revealed that the patient, a practicing Muslim, prays in a sitting position called "Julus" several times a day. After color marking, the lesions over the lateral feet left a precise imprint on the underlay when the patient was asked to imitate the praying posture-thus proving the origin of the skin lesions. We searched the database on July 31, 2019 using the terms «prayer marks» OR «prayer nodules» OR "prayer callosities." Only electronically available publications were reviewed. Recognition of prayer marks is important to avoid misdiagnosis, performance of unnecessary diagnostic procedures, and to enhance the intercultural competence of clinicians who practice in multicultural societies.

We investigate the impact of threading dislocations with an edge component (a or a+c-type) on carrier recombination and diffusion in GaN(0001) layers close to the surface as well as in the bulk. To this end, we utilize cathodoluminescence imaging of the top surface of a GaN(0001) layer with a deeply buried (In,Ga)N quantum well. Varying the acceleration voltage of the primary electrons and comparing the signal from the layer and the quantum well enables us to probe carrier recombination at depths ranging from the close vicinity of the surface to the position of the quantum well. Our experiments are accompanied by fully three-dimensional Monte Carlo simulations of carrier drift, diffusion, and recombination in the presence of the surface, the quantum well, and the dislocation, taking into account the dislocation strain field and the resulting piezoelectric field at the dislocation outcrop. Near the surface, this field establishes an exciton dead zone around the dislocation, the extent of which is not related to the carrier diffusion length. However, reliable values of the carrier diffusion length can be extracted from the dipole-like energy shift observed in hyperspectral cathodoluminescence maps recorded around the dislocation outcrop at low acceleration voltages. For high acceleration voltages, allowing us to probe a depth where carrier recombination is unaffected by surface effects, we observe a much stronger contrast than expected from the piezoelectric field alone. This finding provides unambiguous experimental evidence for the strong nonradiative activity of edge threading dislocations in bulk GaN and hence also in buried heterostructures.

We determine the diffusion length of excess carriers in GaN by spatially resolved cathodoluminescence spectroscopy utilizing a single quantum well as carrier collector or carrier sink. Monochromatic intensity profiles across the quantum well are recorded for temperatures between 10 and 300 K. A classical diffusion model accounts for the profiles acquired between 120 and 300 K, while for temperatures lower than 120 K, a quantum capture process has to be taken into account in addition. Combining the diffusion length extracted from these profiles and the effective carrier lifetime measured by time-resolved photoluminescence experiments, we deduce the carrier diffusivity as a function of temperature. The experimental values are found to be close to theoretical ones for the ambipolar diffusivity of free carriers limited only by intrinsic phonon scattering. This agreement is shown to be fortuitous. The high diffusivity at low temperatures instead originates from an increasing participation of excitons in the diffusion process.

We investigate, both theoretically and experimentally, the drift, diffusion, and recombination of excitons in the strain field of an edge threading dislocation intersecting the GaN{0001} surface. We calculate and measure hyperspectral cathodoluminescence maps around the dislocation outcrop for temperatures between 10 to 200 K. Contrary to common belief, the cathodoluminescence intensity contrast is only weakly affected by exciton diffusion, but is caused primarily by exciton dissociation in the piezoelectric field at the dislocation outcrop. Hence, the extension of the dark spots around dislocations in the luminescence maps cannot be used to determine the exciton diffusion length. However, the cathodoluminescence energy contrast, reflecting the local bandgap variation in the dislocation strain field, does sensitively depend on the exciton diffusion length and hence enables its experimental determination.

International audience

We present a systematic study of the influence of elastic strain relaxation on the built-in electrostatic potentials and the electronic properties of axial (In,Ga)N/GaN nanowire heterostructures. We employ and evaluate analytical and numerical approaches to compute strain and polarization potentials. These two ingredients then enter an eight-band k.p model to compute electron and hole ground states and energies. Our analysis reveals that for a sufficiently large ratio between the thickness of the (In,Ga)N disk and the diameter of the nanowire, the elastic relaxation leads to a significant reduction of the built-in electrostatic potential in comparison to a planar system of similar layer thickness and In content. However, a complete elimination of the built-in potential cannot be achieved in axial nanowire heterostructures. Nevertheless, the reduction of the built-in electrostatic potential leads to a significant modification of the electron and hole energies. Our findings indicate that the range of accessible ground state transition energies in an axial (In,Ga)N/GaN nanowire heterostructure is limited due to the reduced influence of polarization potentials for thicker disks. Additionally, we find that strain and polarization potentials induce complex confinement features of electrons and holes, which depend on the In content, shape, and dimensions of the heterostructure.

We investigate the luminescence of Ga- and N-polar In$_{x}$Ga$_{1-x}$N/In$_{y}$Ga$_{1-y}$N quantum wells (QWs) grown by plasma-assisted molecular beam epitaxy on freestanding GaN as well as 6H-SiC substrates. In striking contrast to their Ga-polar counterparts, the N-polar QWs prepared on freestanding GaN do not exhibit any detectable photoluminescence. Theoretical simulations of the band profiles combined with resonant excitation of the QWs allow us to rule out carrier escape and subsequent surface recombination as the reason for the absence of luminescence. To explore the hypothesis of a high concentration of nonradiative defects at the interfaces between wells and barriers, we analyze Ga- and N-polar QWs prepared on 6H-SiC as a function of the well width. Intense luminescence is observed for both Ga- and N polar samples. As expected, the luminescence of the Ga-polar QWs quenches and red-shifts with increasing well width due to the quantum confined Stark effect. In contrast, both the intensity and the energy of the luminescence from the N-polar samples are essentially independent of well width. Transmission electron microscopy reveals that the N-polar QWs exhibit abrupt interfaces and homogeneous composition, excluding emission from In-rich clusters as the reason for this anomalous behavior. The microscopic origin of the luminescence in the N-polar QWs is elucidated using spatially resolved cathodoluminescence spectroscopy. Regardless of well width, the luminescence is found to not originate from the N-polar QWs, but from the semipolar facets of v-pit defects. These results cast serious doubts on the potential of N-polar QWs grown by plasma-assisted molecular beam epitaxy for the development of long-wavelength light emitting diodes. What remains to be seen is whether unconventional growth conditions may enable a significant reduction in the concentration of nonradiative defects., 12 pages, 10 figures

International audience; In contrast to epitaxial layers, single-crystalline GaN can be grown in the form of nanowires on Si substrates. In addition, the sub-wavelength diameter of nanowires facilitates light extraction, which is advantageous for the realization of efficient nanowire-based light emitting diodes. However, the ionization energies of dopants are different in nanostructures compared to the bulk. This effect may seriously affect the operation of nanowire-baseddevices relying on a controlled doping [1]. First, the combination of surface and dielectric mismatch effects results in a strong and non-monotonic variation of the donor binding energy, when going from the core to the surface of a nanostructure [2]. Second, surface states pin the Fermi level at the surface of the nanowire. This causes the formation of internal electric fields and the depletion of nanowires, as demonstrated by photoconductivity experiments [3]. We emphasize that this depletion is incomplete at low temperature, as donor bound exciton luminescence is observed even for GaN nanowires with a diameter of 30 nm [4].In this work, we investigate the impact of surface and internal electric fields on the binding energy of donor atoms in GaN nanowires. Using Monte-Carlo simulations, we first examine the validity of the assumption that depletion leads to a parabolic potential across the section of nanowires. For instance, we show that for nanowires with a doping of 2 x 1015 cm-3 and with a diameter and a length of 80 nm and 1.5 μm, respectively, the potential cannot be described by a parabola. In contrast, for a doping of the order of 1017 cm-3, the potential is nearly parabolic and is well described using the Poisson equation, where one assumes a spatially homogeneous distribution of dopants.Using envelope function calculations, we then compute the binding energy of donors in thin GaN slabs bounded by air. We take into account surface, confinement, and the dielectric mismatch, similarly to what has been reported in Refs. [2,5]. Based on the evolution of the spatial extent of the electron wave function as a function of the electric field at the nanowire surface, we deduce the magnitude of the electric field required for the ionization of surface donors. In particular, we show that surface donors are ionized for doping densities typically larger than 3 x 1016 cm-3, irrespectively of the nanowire diameter. Finally, the result of our calculations is compared with low-temperature photoluminescence experiments on ensemble of nanowires.[1] M. Pierre et al., Nature Nanotechnology 5, 133, (2010).[2] P. Corfdir and P. Lefebvre, J. Appl. Phys. 112, 106104 (2012).[3] R. Calarco et al., Nano Letters 5, 981 (2005).[4] P. Corfdir et al., J. Appl. Phys. 105, 013113 (2009).[5] P. Corfdir et al., Phys. Rev. B 80, 153309 (2009).

We investigate the origin of the fast recombination dynamics of bound and free excitons in GaN nanowire ensembles by temperature-dependent photoluminescence spectroscopy using both continuous-wave and pulsed excitation. The exciton recombination in the present GaN nanowires is dominated by a nonradiative channel between 10 and 300 K. Furthermore, bound and free excitons in GaN NWs are strongly coupled even at low temperatures resulting in a common lifetime of these states. By solving the rate equations for a coupled two-level system, we show that one cannot, in practice, distinguish whether the nonradiative decay occurs directly via the bound or indirectly via the free state. The nanowire surface and coalescence-induced dislocations appear to be the most obvious candidates for nonradiative defects, and we thus compare the exciton decay times measured for a variety of GaN nanowire ensembles with different surface-to-volume ratio and coalescence degrees. The data are found to exhibit no correlation with either of these parameters, i. e., the dominating nonradiative channel in the GaN nanowires under investigation is neither related to the nanowire surface, nor to coalescence-induced defects for the present samples. Hence, we conclude that nonradiative point defects are the origin of the fast recombination dynamics of excitons in GaN nanowires., Comment: 10 pages, 5 figures

GaN nanowire ensembles with axial InGaN multi-quantum wells (MQWs) were grown by molecular beam epitaxy. In a series of samples, we varied the In content in the MQWs from almost zero to about 20%. Within the nanowire ensemble, the MQWs fluctuate strongly in composition and size. Statistical information about the composition was obtained from x-ray diffraction and Raman spectroscopy. Photoluminescence at room temperature was obtained in the range from 2.2 eV to 2.5 eV depending on In content. Contrary to planar MQWs, the intensity increases with increasing In content. We compare the observed emission energies with transition energies obtained from a one-dimensional model, and conclude that several mechanisms for carrier localization affect the luminescence of these three-dimensional structures., Comment: This is an author-created, un-copyedited version of an article accepted for publication in Nanotechnology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.1088/0957-4484/23/45/455203

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Im Rahmen des EU-Projekts PROTOWET* wurde, als Teil einer Feuchtgebiets-Ökosystemanalyse, von Juli 1996 bis Juni 1999 die Verteilung, Mobilität und Dynamik von Schwermetallen und Arsen in Böden und im Oberflächen-, Boden- und Grundwasser der Muldeaue bei Bitterfeld/Wolfen untersucht. Nach der Fertigstellung des Muldestaudamms 1979 und infolge des Rückbaus der Altindustrien im Ostteil Deutschlands nach 1989/90 hat sich die Schadstoffbilanz durch den Rückgang der Mulde-Schadstoffbelastung verändert. Demnach ist meist ein höheres Potential an mobilen Schwermetallen und Arsen in Bodenlösungen und Grundwasser als im Fließgewässer anzutreffen. Entsprechend berücksichtigten die Untersuchungen die saisonal stark variierende Hydrodynamik und Hydrochemie in lithofaziell, pedologisch und hydrogeomorphologisch unterschiedlichen Auebereichen sowie das Schadstoffverhalten während der Hochwasserphasen im März 1998, November 1998 und März 1999. Untersuchungen der Elementverteilung in humosen Oberbodenhorizonten der Muldeaue belegen die Existenz zweier Elementverteilungsmuster. Die Oberböden sind vorrangig durch die chemisch-metallurgische Industrie Bitterfeld/Wolfens mit Ag, Cr, Sn, W, V (Cu, Pb) und über den Muldeoberlauf aus dem Erzgebirge (Bergbau, Industrie) mit As, Cd, Cu, Ni, Pb, U und Zn belastet. Ältere Verteilungsmuster der Unterböden dokumentieren dagegen Einträge von Ag, Cr aus Bitterfeld/Wolfen und As, Cd, Cu, Ni, Pb, Sn und Zn aus dem Erzgebirgsraum. Hohe Bodengehalte in der Muldeaue waren insbesondere für die Elemente Cd (10 - 20 mg/kg), As (100 - 300 mg/kg), Cr (200 - 2000 mg/kg) und Zn (250 - 2500 mg/kg) nachweisbar, die bis in die Grundwasser-gesättigte Zone hinabreichen können. Die Gewässersedimente des Spittelwassers bei Bitterfeld/Wolfen sind extrem hoch mit Zn und die Uferbereiche mit Cr kontaminiert (Maximalwerte: Zn 10.044 mg/kg und Cr 10.117 mg/kg). Nach Überschwemmungen im März 1998 bestätigten hohe Cr-Konzentrationen von 0,44 - 0,17 mg/l in den Bodenlösungen die hohe Belastung der sandig-humosen und versauerten Bodenhorizonte (pH-Werte: 4 - 5). Hohe As-Konzentrationen von durchschnittlich 1,5 mg/l (max. 29 mg/l) sind die Folge mikrobiologisch gesteuerter Reduktionsprozesse im Boden- und Grundwasser stark anoxischer, Grundwasser-gesättigter Bereiche der Muldeaue. Elutions- und Extraktionsuntersuchungen an Bodenmaterial aus stark anoxischen Bereichen bestätigen zum Teil die hohe Arsenmobilität. Im Verlauf von Hochwasserphasen bewirken Sickerwasserzuflüsse vermutlich eine partielle Aufoxidation und einen Grundwassertransport von reduziertem As(III) in Richtung Mulde. Die As-Konzentrationen in der Mulde, benachbarter Grundwasserbereiche und Altarmgewässer korrelieren während der Hochwasserperioden signifikant miteinander. In schwach anoxisch bis oxischen Auebereichen verursachen Überschwemmungen einen Transport von Cd mit dem Sickerwasser. Das Schwermetall weist in den schwach gepufferten Oberböden der karbonatfreien Muldeaue bei pH-Werten zwischen 4,0 - 6,5 erhöhte Konzentrationen von 3 - 21 µg/l (Median) auf. Überschwemmungen und die Versickerung von sauerstoffreichem Oberflächenwasser haben in stark anoxischen Auebereichen eine Senkung des pH-Werts und Erhöhungen der Cd-Konzentration im Boden- und Grundwasser zur Folge. Höhere Cd-Konzentrationen im Grundwasser des Uferbereichs können auf Austauschprozesse zwischen der Infiltrationszone des Muldeufers und den hochbelasteten Gewässersedimenten zurückgeführt werden. Überschwemmungen in Auebereichen mit hoher Schadstoffmobilität führen zu höheren Austrägen von Schwermetallen und Arsen. Eingriffe in den Wasserhaushalt einer Flußaue durch Deiche/Wehre und unterschiedliche Nutzungen (Landwirtschaft, Kies-/Sandgewinnung) beeinflussen die Schadstoffmobilität und Wasserqualität. Die Folgen und mögliche Schutzmaßnahmen für Flußaue-Ökosysteme lassen sich durch eine detaillierte Gefährdungsanalyse zur Schadstoffdynamik ermitteln. *PROTOWET: Procedures for the Operationalisation of Techniques for the Functional Analysis of European Wetland Ecosystems (Kontakt-Nr.: ENV4-CT95-0060) The distribution, mobility and dynamics of heavy metals and arsenic in soils/sediments and the aquatic environment in wetlands of the River Mulde were investigated during the period June 1996 - July 1999, under the scope of the European wetland ecosystem research project PROTOWET* . The relationships of element input/output changed due to the decrease of River Mulde pollution resulting from the completion of the River Mulde Dam (1979) and the shutdown of old industrial facilities in Eastern Germany after 1989/90. Therefore the potential of mobile phases of investigated pollutants is particularly higher in soil solutions and groundwater of wetland areas than in river water. The field investigations in differing wetland areas (lithofacies, soils, morphology) consider the seasonal variable hydrodynamics and hydrochemistry as well as the element behaviour during inundations in March 1998, November 1998 and March 1999, respectively. The element distribution in humose topsoils represents different element patterns. On the one hand, the River Mulde is affected by pollution from the chemical and metal industry in Bitterfeld/Wolfen (Ag, Cr, Sn, W, V) and secondly by the input from mining and metal industry in the Ore Mountains of Saxony (As, Cd, Cu, Ni, Pb, U, Zn). Subsoil layers represent an older historical impact from Bitterfeld/Wolfen (Ag, Cr) and from upstream tributaries in the Ore Mountains (As, Cd, Cu, Ni, Pb, Sn, Zn). High concentrations of Cd (10 - 20 mg/kg), As (100 - 300 mg/kg), Cr (200 - 2000 mg/kg) and Zn (250 - 2500 mg/kg) were measured in topsoils and partially in waterlogged subsoils. River sediments of Spittelwasser (Bitterfeld/Wolfen) represent high concentrations of Zn up to 10044 mg/kg. Topsoils of natural levees contain Cr up to 10117 mg/kg. After the inundation in March 1998 Cr-concentrations in solutions of sandy and acid topsoils (pH 4 - 5) range from 0.17 to 0.44 mg/l. High As-concentrations of 1.5 mg/l (max. 29 mg/l) in soil solution and groundwater result from microbially controlled reduction processes in waterlogged and anoxic subsoils of River Mulde wetlands. Investigations of the element mobility in anoxic soils represent a comparable behaviour of As. Floods control the groundwater infiltration, which partially effects oxidation and movement of As(III)-species. During inundations the As-Concentration in River Mulde correlate with concentrations in adjacent groundwater zones and ox-bow lakes. The floodwater infiltration in weak anoxic-oxic wetland soils controls the Cd-transport. Weakly buffered, acid topsoils (pH 4.0 - 6.5) represent Cd-concentrations of 3 - 21 µg/l (Median). Cd-concentrations in the aquatic environment of strongly anoxic wetland soils increase during the infiltration of oxygen-rich seepage water. Higher Cd-concentrations in the groundwater area of the River Mulde bank result most likely from interactions between infiltration zones and contaminated river sediments. Inundations increase the removal of heavy metals and arsenic in wetland areas forming a high potential of mobile pollutants. Additionally, floodwater regulation by dams/weirs and land use (agriculture, gravel extraction) influences the mobility of pollutants and also the water quality. A risk assessment for a better understanding of heavy metal and arsenic dynamics represents a decision-making tool for the protection of river marginal wetland ecosystems. *PROTOWET: Procedures for the Operationalisation of Techniques for the Functional Analysis of European Wetland Ecosystems (Contract-nr. ENV4-CT95-0060)