Surface Conductivity of Si(100) and Ge(100) Surfaces Determined from Four-Point Transport Measurements Using an Analytical N-Layer Conductance Model

An analytical N-layer model for charge transport close to a surface is derived from the solution of Poisson's equation and used to describe distance-dependent electrical four-point measurements on the microscale. As the N-layer model comprises a surface channel, multiple intermediate layers and a semi-infinite bulk, it can be applied to semiconductors in combination with a calculation of the near-surface band-bending to model very precisely the measured four-point resistance on the surface of a specific sample and to extract a value for the surface conductivity. For describing four-point measurements on sample geometries with mixed 2D-3D conduction channels often a very simple parallel-circuit model has so far been used in the literature, but the application of this model is limited, as there are already significant deviations, when it is compared to the lowest possible case of the N-layer model, i.e. the 3-layer model. Furthermore, the N-layer model is applied to published distance-dependent four-point resistance measurements obtained with a multi-tip scanning tunneling microscope (STM) on Germanium(100) and Silicon(100) with different bulk doping concentrations resulting in the determination of values for the surface conductivities of these materials.Comment: 11 pages, 6 color figure

Surface and Step Conductivities on Si(111) Surfaces

Four-point measurements using a multi-tip scanning tunneling microscope (STM) are carried out in order to determine surface and step conductivities on Si(111) surfaces. In a first step, distance-dependent four-point measurements in the linear configuration are used in combination with an analytical three-layer model for charge transport to disentangle the 2D surface conductivity from non-surface contributions. A termination of the Si(111) surface with either Bi or H results in the two limiting cases of a pure 2D or 3D conductance, respectively. In order to further disentangle the surface conductivity of the step-free surface from the contribution due to atomic steps, a square four-probe configuration is applied as function of the rotation angle. In total this combined approach leads to an atomic step conductivity of $\sigma_\mathrm{step} = (29 \pm 9)$ $\mathrm{\Omega}^{-1} \mathrm{m}^{-1}$ and to a step-free surface conductivity of $\sigma_\mathrm{surf} = (9 \pm 2) \cdot 10^{-6}\,\mathrm{\Omega}^{-1}/\square$ for the Si(111)-(7$\times$7) surface.Comment: Main paper: 5 pages, 4 figures, Supplemental material: 6 pages, 3 figures. The Supplemental Material contains details on the sample preparation and measurement procedure, additional experimental results for Si(111) samples with different doping levels, and the description of the three-layer conductance mode

Using Geographically Referenced Data on Environmental Exposures for Public Health Research: A Feasibility Study Based on the German Socio-Economic Panel Study (SOEP)

Background: In panel datasets information on environmental exposures is scarce. Thus, our goal was to probe the use of area-wide geographically referenced data for air pollution from an external data source in the analysis of physical health. Methods: The study population comprised SOEP respondents in 2004 merged with exposures for NO2, PM10 and O3 based on a multi-year reanalysis of the EURopean Air pollution Dispersion-Inverse Model (EURAD-IM). Apart from bivariate analyses with subjective air pollution we estimated cross-sectional multilevel regression models for physical health as assessed by the SF-12. Results: The variation of average exposure to NO2, PM10 and O3 was small with the interquartile range being less than 10µg/m3 for all pollutants. There was no correlation between subjective air pollution and average exposure to PM10 and O3, while there was a very small positive correlation between the first and NO2. Inclusion of objective air pollution in regression models did not improve the model fit. Conclusions: It is feasible to merge environmental exposures to a nationally representative panel study like the SOEP. However, in our study the spatial resolution of the specific air pollutants has been too little, yet.SOEP, Geographically Referenced Data, Feasibility Study, Air Pollution, EURAD-IM, Physical Health

Strong and Weak 3D Topological Insulators Probed by Surface Science Methods

The contributions of surface science methods to discover and improve 3D topological insulator materials are reviewed herein, illustrated with examples from the authors’ own work. In particular, it is demonstrated that spin-polarized angular-resolved photoelectron spectroscopy is instrumental to evidence the spin-helical surface Dirac cone, to tune its Dirac point energy toward the Fermi level, and to discover novel types of topological insulators such as dual ones or switchable ones in phase change materials. Moreover, procedures are introduced to spatially map potential fluctuations by scanning tunneling spectroscopy and to identify topological edge states in weak topological insulators. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

The impact of regional and neighbourhood deprivation on physical health in Germany: a multilevel study

Voigtländer S, Berger U, Razum O. The impact of regional and neighbourhood deprivation on physical health in Germany: a multilevel study. BMC Public Health. 2010;10(1): 403.Background There is increasing evidence that individual health is at least partly determined by neighbourhood and regional factors. Mechanisms, however, remain poorly understood, and evidence from Germany is scant. This study explores whether regional as well as neighbourhood deprivation are associated with physical health and to what extent this association can be explained by specific neighbourhood exposures. Methods Using 2004 data from the German Socio-Economic Panel Study (SOEP) merged with regional and neighbourhood characteristics, we fitted multilevel linear regression models with subjective physical health, as measured by the SF-12, as the dependent variable. The models include regional and neighbourhood proxies of deprivation (i.e. regional unemployment quota, average purchasing power of the street section) as well as specific neighbourhood exposures (i.e. perceived air pollution). Individual characteristics including socioeconomic status and health behaviour have been controlled for. Results This study finds a significant association between area deprivation and physical health which is independent of compositional factors and consistent across different spatial scales. Furthermore the association between neighbourhood deprivation and physical health can be partly explained by specific features of the neighbourhood environment. Among these perceived air pollution shows the strongest association with physical health (-2.4 points for very strong and -1.5 points for strong disturbance by air pollution, standard error (SE) = 0.8 and 0.4, respectively). Beta coefficients for perceived air pollution, perceived noise and the perceived distance to recreational resources do not diminish when including individual health behaviour in the models. Conclusions This study highlights the difference regional and in particular neighbourhood deprivation make to the physical health of individuals in Germany. The results support the argument that specific neighbourhood exposures serve as an intermediary step between deprivation and health. As people with a low socioeconomic status were more likely to be exposed to unfavourable neighbourhood characteristics these conditions plausibly contribute towards generating health inequalities

Rehabilitative Versorgung und gesundheitsbedingte Frühberentung von Personen mit Migrationshintergrund in Deutschland: Abschlussbericht

Dieser Abschlussbericht stellt die Ergebnisse des Projektes "Rehabilitative Versorgung und gesundheitsbedingte Frühberentung von Personen mit Migrationshintergrund in Deutschland" vor. Auf Basis eines quantitativen und qualitativen Forschungszugangs wurde untersucht, inwiefern sich einzelne Gruppen von ausländischen Staatsangehörigen bzw. Menschen mit Migrationshintergrund hinsichtlich der Häufigkeit von Arbeitsunfällen und Berufskrankheiten, der Inanspruchnahme beruflicher und medizinischer Rehabilitationsmaßnahmen, des Rehabilitationserfolges und der Frühberentung von Deutschen bzw. Menschen ohne Migrationshintergrund unterscheiden. Unter Bezugnahme auf Prozess- und Individualdaten unterschiedlicher Rehabilitationsträger zeigt der Bericht, dass Menschen mit Migrationshintergrund im Durchschnitt weniger häufig Maßnahmen der medizinischen Rehabilitation in Anspruch nehmen sowie einen geringeren Rehabilitationserfolg und höhere Frühberentungsquoten aufweisen als die Mehrheitsbevölkerung. Auf Basis einer systematischen Literaturrecherche und mittels qualitativer Experten- und Fokusgruppeninterviews werden darüber hinaus unterschiedliche Zugangs-, Durchführungs- und Wirksamkeitsbarrieren in der Rehabilitation von Menschen mit Migrationshintergrund identifiziert, welche die quantitativen Ergebnisse zumindest teilweise erklären können. Handlungsempfehlungen für die Verbesserung der rehabilitativen Versorgung von Menschen mit Migrationshintergrund werden abgeleitet

Regionale Ungleichverteilung von Gesundheit und ihre Determinanten

Razum O, Voigtländer S. Regionale Ungleichverteilung von Gesundheit und ihre Determinanten. Sozialer Fortschritt. 2009;58(2-3):36-43.DEUTSCH: Die regionale Gleichwertigkeit der Lebensverhältnisse ist ein sozialpolitisches Leitprinzip in Deutschland. Während sich bei einem Ost-West-Vergleich Lebensverhältnisse und gesundheitliche Situation tendenziell angleichen, zeigen sich unterhalb dieser großräumigen Entitäten erhebliche Disparitäten. Diese haben mit großer Wahrscheinlichkeit Auswirkungen auf die Gesundheit der jeweiligen Bevölkerung. Die Analyse daraus resultierender gesundheitlicher Ungleichheiten erfordert kleinräumige sozialepidemiologische Untersuchungen. Die zentrale methodische Anforderung an solche Analysen besteht darin, gesundheitliche Ungleichheit als das Ergebnis eines kausalen Zusammenspiels sowohl ökologischer als auch individueller Merkmale zu modellieren. Hierzu können gemischte Modelle eingesetzt werden, auch multilevel models genannt, ergänzt um Verfahren der Räumlichen Statistik. Parallel dazu müssen theoretische Modelle zur Erklärung sozial bedingter gesundheitlicher Ungleichheit so weiterentwickelt werden, dass sie den gesundheitlichen Einfluss spezifischer individueller und ökologischer Merkmale in Form expliziter kausaler Pfade konzeptualisieren. ENGLISH: A guiding socio-political principle in Germany is that of equality of living conditions betweens regions. While a comparison between East and West Germany shows declining socio-economic and health disparities, widening differences can be found below the level of these large entities. It is highly likely that these differences have an influence on the health of the respective populations. Small-area socio-epidemiological studies are needed to analyse resulting health inequalities. The key methodological challenge is to model health inequalities as a result of a causal interplay of ecological as well as individual characteristics. For this purpose one can apply mixed models, also called multilevel models, complemented by spatial modelling techniques. At the same time, it is necessary to further develop theoretical models that attempt to explain the social determination of health inequalities. The extension of such models should enable the influence of specific individual and ecological characteristics on health to be conceptualized in the form of explicit causal pathways

External Evaluation of System-Wide Cooperation and Capacity-Building within the Framework of the Estonian HIV/AIDS Prevention System

Voigtländer S, Abel K. External Evaluation of System-Wide Cooperation and Capacity-Building within the Framework of the Estonian HIV/AIDS Prevention System.; 2004