Chemical composition of nanoporous layer formed by electrochemical etching of p-type GaAs

Abstract : We have performed a detailed characterization study of electrochemically etched p-type GaAs in a hydrofluoric acid-based electrolyte. The samples were investigated and characterized through cathodoluminescence (CL), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). It was found that after electrochemical etching, the porous layer showed a major decrease in the CL intensity and a change in chemical composition and in the crystalline phase. Contrary to previous reports on p-GaAs porosification, which stated that the formed layer is composed of porous GaAs, we report evidence that the porous layer is in fact mainly constituted of porous As2O3. Finally, a qualitative model is proposed to explain the porous As2O3 layer formation on p-GaAs substrate

Reviewing the use of resilience concepts in forest sciences

Purpose of the review Resilience is a key concept to deal with an uncertain future in forestry. In recent years, it has received increasing attention from both research and practice. However, a common understanding of what resilience means in a forestry context, and how to operationalise it is lacking. Here, we conducted a systematic review of the recent forest science literature on resilience in the forestry context, synthesising how resilience is defined and assessed. Recent findings Based on a detailed review of 255 studies, we analysed how the concepts of engineering resilience, ecological resilience, and social-ecological resilience are used in forest sciences. A clear majority of the studies applied the concept of engineering resilience, quantifying resilience as the recovery time after a disturbance. The two most used indicators for engineering resilience were basal area increment and vegetation cover, whereas ecological resilience studies frequently focus on vegetation cover and tree density. In contrast, important social-ecological resilience indicators used in the literature are socio-economic diversity and stock of natural resources. In the context of global change, we expected an increase in studies adopting the more holistic social-ecological resilience concept, but this was not the observed trend. Summary Our analysis points to the nestedness of these three resilience concepts, suggesting that they are complementary rather than contradictory. It also means that the variety of resilience approaches does not need to be an obstacle for operationalisation of the concept. We provide guidance for choosing the most suitable resilience concept and indicators based on the management, disturbance and application context

Using assembly rules to measure the resilience of riparian plant communities to beaver invasion in subantarctic forests

The present study measures the resilience of riparian herbaceous communities to beaver invasion in subantarctic forests of southern Chile and Argentina. Divergence in community composition and spatial structure was measured comparing beaver-disturbed and undisturbed vegetation assemblages along a sequence of beaver meadow ages; the former by performing a Principal Component Analysis and the later by estimating a co-occurrence index (C-score). Community composition and spatial structure of vegetation showed an increasingly divergent trend from undisturbed sites to older beaver meadows. These results indicated that understory vegetation in deciduous subantarctic forests was not resilient to beaver invasion. Using “assembly rules” as a conceptual framework, we propose a resilience index of host communities to disturbances caused by herbivore invaders that also can be used for subsequent restoration programs to monitor the effectiveness of intervention and mitigation efforts.Fil: Wallem, Petra K.. Universidad Catolica de Chile. Center For Advanced Studies In Ecology And Biodiversity; ChileFil: Anderson, Christopher Brian. Millennium Institute of Ecology and Biodiversity; Chile. University of Magallanes. Omora Ethnobotanical Park; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentin