(Post-)nationale Grenzen im städtischen Gefüge: Was wichtig wird und wichtig bleibt, wenn Migration und Nationalität entkoppelt sind

Argentinien hat das Recht auf Migration als Menschenrecht gesetzlich verankert und eröffnet Migrant*innen damit auch den Zugang zu allen sozialen Rechten. Dennoch sind immer Rechte von Migrant*innen immer noch umkämpft. In verschiedenen Arenen wie dem Kampf um Wohnen zeigen sich (Re)Konstitutionen interner Grenzziehungen, die eigentlich in einem Widerspruch zum Recht auf Migration stehen. Die Megacity Buenos Aires ist der Zielort der Migration für viele Migrant*innen und der Ort, an dem diese widerstreitenden Prozesse beobachtete werden können. Die Gleichzeitigkeit von migrantischen Rechten und internen Barrieren und ihre Folgen für Positionierungen von Migrant*innen in sozialen wie in räumlichen Bezügen werden in diesem Artikel untersucht.Like in no other country in Argentina the right to migration as a human right is established in its law. The right to migration implies full access to social rights. Nevertheless fights for rights of migrant subjects are evoked in urban spaces. In various arenas - like in the fight for housing - (re-)configurations of internal frontiers and urban barrieres for migrants are obvious - which is contradictory to the right to migrate. The megacity Buenos Aires is the target space for many migrants and the place, in which those reconfi gurations can be observed. The coexistence of migrants rights and internal barrieres and their constitution and consequences for diverse forms of social and geografical mobility of migrants are figuered out in this article

School as a safe place. Flight as a challenge for social work at school

Der Schulbesuch geflüchteter Kinder und Jugendlicher ist ein nach der UN-Kinderrechtskonvention verbrieft es Recht. Zudem kann die Schule für die Kinder zum Ort der Bewältigung ihrer schwierigen Lebenslage werden. Daher ist sie in ihrer Bedeutung als "sicherer Ort" aufgerufen. Auf der Basis empirischen Materials aus einem Lehrforschungsprojekt werden die besondere Rolle und die Möglichkeiten der Schulsozialarbeit im Fluchtkontext herausgearbeitet und die Perspektiven der verschiedenen Beteiligten auf Schule und Bildung rekonstruiert. (DIPF/Orig.)School attendance of refugee children and juveniles is a chartered right according to the UN Convention on the Rights of the Child. Moreover, the school itself can be a place for the children to cope with their difficult circumstances. Therefore it is addressed in its role as a "safe place". On the basis of empirical findings of a teaching research project we will elaborate the particular role as well as the possibilities of school social work in the context of flight. Furthermore, we will reconstruct the perspectives of the different participants on school and education. (DIPF/Orig.

Surface characterization of epitaxial Cu-rich CuInSe2 absorbers

We investigated the electrical properties of epitaxial Cu-rich CuInSe 2 by Kelvin probe force microscopy (KPFM) under ambient and ultra-high vacuum conditions. We first measured the sample under ambient conditions before and after potassium cyanide (KCN) etching. In both cases, we do not see any substantial contrast in the surface potential data; furthermore, after the KCN etching we observed outgrowths with a height around 2nm over the sample surface. On the other hand, the KPFM measurements under ultra-high vacuum conditions show a work function dependence according to the surface orientation of the Cu-rich CuInSe 2 crystal. Our results show the possibility to increase the efficiency of epitaxial Cu-rich CuInSe 2 by growing the materials in the appropriated surface orientation where the variations in work function are reduced

The impact of Kelvin probe force microscopy operation modes and environment on grain boundary band bending in perovskite and Cu(In,Ga)Se2 solar cells

An in-depth understanding of the electronic properties of grain boundaries (GB) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very high and hence limit the solar cell device performance. Kelvin Probe Force Microscopy (KPFM) is the method of choice to investigate GB band bending on the nanometer scale and thereby helps to develop passivation strategies. Here, it is shown that amplitude modulation AM-KPFM, which is by far the most common KPFM measurement mode, is not suitable to measure workfunction variations at GBs on rough samples, such as Cu(In,Ga)Se2 and CH3NH3PbI3. This is a direct consequence of a change in the cantilever-sample distance that varies on rough samples. Furthermore, we critically discuss the impact of different environments (air versus vacuum) and show that air exposure alters the GB and facet contrast, which leads to erroneous interpretations of the GB physics. Frequency modulation FM-KPFM measurements on non-air-exposed CIGSe and perovskite absorbers show that the amount of band bending measured at the GB is negligible and that the electronic landscape of the semiconductor surface is dominated by facet-related contrast due to the polycrystalline nature of the absorbers

Oxidation as Key Mechanism for Efficient Interface Passivation in Cu (In,Ga)Se2 Thin-Film Solar Cells

Copper-indium-gallium-diselenide (CIGS) thin-film solar cells suffer from high recombination losses at the back contact and parasitic absorption in the front-contact layers. Dielectric passivation layers overcome these limitations and enable an efficient control over interface recombination, which becomes increasingly relevant as thin-film solar cells increase in efficiency and become thinner to reduce the consumption of precious resources. We present the optoelectronic and chemical interface properties of oxide-based passivation layers deposited by atomic layer deposition on CIGS. A suitable postdeposition annealing removes detrimental interface defects and leads to restructuring and oxidation of the CIGS surface. The optoelectronic interface properties are very similar for different passivation approaches, demonstrating that an efficient suppression of interface states is possible independent of the metal used in the passivating oxide. If aluminum oxide (Al2O3) is used as the passivation layer we confirm an additional field-effect passivation due to interface charges, resulting in an efficient interface passivation superior to that of a state-of-the-art cadmium-sulfide (CdS) buffer layer. Based on this chemical interface model we present a full-area rear-interface passivation layer without any contact patterning, resulting in a 1% absolute efficiency gain compared to a standard molybdenum back contact. © 2020 authors. Published by the American Physical Society

Passivation of the CuInSe2 surface via cadmium pre-electrolyte treatment

Effective defect passivation of semiconductor surfaces and interfaces is indispensable for the development of high efficiency solar cells. In this study we systematically investigated the surface and grain boundary properties of CuInSe2 (CISe) with scanning tunneling microscopy (STM) and spectroscopy (STS) after different surface treatments such as potassium cyanide (KCN) etching, pre-electrolyte treatment with cadmium ions, and annealing in ultrahigh vacuum (UHV). We show that air exposed samples with a subsequent KCN etching step exhibits a highly defective surface. However, a Cd pre-electrolyte treatment passivates most of these defects, which manifests itself by a reduction of the high conductance in the STS measurements at positive sample biases. The origin of the improvement can be traced back to an increase in surface band bending, which leads to a type inversion, induced by a change in the concentration of Cu vacancies. We observe a defect passivation at the CISe surface and at the grain boundaries. Our results give a direct explanation of why the CdS buffer layer in CISe thin film solar cells is of utmost importance for high efficiency devices

Rotational UV-lithography using flexible chromium coated polymer masks for the fabrication of microstructured dental implant surfaces: a proof of concept

The purpose of this work was to demonstrate the technical feasibility for the fabrication of microgrooves or micropits on dental implants or dental implant abutment surfaces using a novel fabrication method derived from common UV-lithographic microfabrication. Instead of using a flat and rigid chromium/glass mask to structure a photoresist layer on a small cylindrical part, a flexible chromium-coated polymer mask was introduced into the lithographic setup. Through an elastic deformation of the polymer mask, it was possible to achieve lateral resolutions as small as 1.5 μm on small cylinders and to structure conical parts. By subsequent controlled under-etching of the structured photoresist layer, microgrooves of different cross-sectional geometries can be generated and applied to the implant or implant abutment surface. Such structures can be used for contact guidance of human gingival fibroblasts or endothelia cells to enhance the wound healing process and the overall soft-tissue integration

Doping mechanism in pure CuInSe2

We investigate the dopant concentration and majority carrier mobility in epitaxial CuInSe2thin films for different copper-to-indium ratios and selenium excess during growth. We find that all copper-poor samples are n-type, and that hopping conduction in a shallow donor state plays a significant role for carrier transport. Annealing in sodium ambient enhances gallium in-diffusion from the substrate wafer and changes the net doping of the previously n-type samples to p-type. We suggest that sodium incorporation from the glass might be responsible for the observed p-type doping in polycrystalline Cu-poor CuInSe2solar cell absorbers