10 research outputs found
Hard x-ray nanoprobe of beamline P06 at PETRA III
Thehard x-ray scanning microscope at beamline P06 of PETRAIII at DESY in Hamburg serves a large user community, from physics, chemistry, and nanotechnology to the bio-medical, materials, environmental, and geosciences. It has been in user operation since 2012, and is mainly based on nanofocusing refractive x-ray lenses. Using refractive optics, nearly gaussian-limited nanobeams in the range from 50 to 100 nm can be generated in the hard x-ray energy range from 8 to 30 keV. The degree of coherence can be traded off against the flux in the nanobeam by a two-stage focusing scheme. We give a brief overview on published results from this instrument and describe its most important components and parameters
X-ray vision of Cu(In,Ga)Se: from the Ga/In ratio to solar-cell performance
Cost efficiency and defect passivation are the two major challenges that thin-film solar cells have to overcome for economic competitiveness. For Cu(In,Ga)Se solar cells, the first is addressed by an increase of the Ga/In ratio, which widens the bandgap favorably for tandem applications and reduces the requirement of costly, rare In. The second is addressed by heavy alkali post-deposition treatments. However, the maximum device efficiency is typically achieved with a comparably low Ga/In ratio, which is in contrast to the economic interest of a higher Ga/In ratio and makes it paramount to identify, understand and mitigate the sources of local underperformance in Ga-rich cells. In this work, we investigate a series of Cu(In,Ga)Se cells with varying Ga/In concentration in the absorber, using multi-modal scanning x-ray microscopy. In particular, we analyze differences in chemical composition and electrical performance on the nanoscale, with a focus on the effect of Rb. We find that In-rich cells show, along with a greater overall performance, a more homogeneous distribution of the nanoscale performance compared to the Ga-rich cells. Our analysis on Rb suggests that this effect is due to a more effective passivation of structural defects in the absorbers, i.e. voids and grain boundaries. These results shine light on the causes of the superiority of Ga-poor/In-rich absorbers and substantiate the trend to higher defect density for Ga-rich absorbers
LPPLS Bubble Indicators over Two Centuries of the S&P 500 Index
The aim of this paper is to present novel tests for the early causal diagnostic of positive
and negative bubbles in the S&P 500 index and the detection of End-of-Bubble signals
with their corresponding confidence levels. We use monthly S&P 500 data covering the
period from August 1791 to August 2014. This study is the first work in the literature
showing the possibility to develop reliable ex-ante diagnostics of the frequent regime
shifts over two centuries of data. We show that the DS LPPLS (log-periodic power law
singularity) approach successfully diagnoses positive and negative bubbles, constructs
efficient End-of-Bubble signals for all of the well-documented bubbles, and obtains for
the first time new statistical evidence of bubbles for some other events. We also compare
the DS LPPLS method to the exponential curve fitting and the generalized sup ADF test
approaches and find that DS LPPLS system is more accurate in identifying well-known
bubble events, with significantly smaller numbers of false negatives and false positives.http://www.elsevier.com/locate/physa2017-09-30hb2016Economic