9 research outputs found
Comparing Transmission- and Epi-BCARS: A Transnational Round Robin on Solid State Materials
Broadband coherent anti-Stokes Raman scattering (BCARS) is an advanced Raman
spectroscopy method that combines the spectral sensitivity of spontaneous Raman
scattering (SR) with the increased signal intensity of single-frequency
coherent Raman techniques. These two features make BCARS particularly suitable
for ultra-fast imaging of heterogeneous samples, as already shown in
biomedicine. Recent studies demonstrated that BCARS also shows exceptional
spectroscopic capabilities when inspecting crystalline materials like lithium
niobate and lithium tantalate, and can be used for fast imaging of
ferroelectric domain walls. These results strongly suggest the extension of
BCARS towards new imaging applications like mapping defects, strain, or dopant
levels, similar to standard SR imaging. Despite these advantages, BCARS suffers
from a spurious and chemically unspecific non-resonant background (NRB) that
distorts and shifts the Raman peaks. Post-processing numerical algorithms are
then used to remove the NRB and to obtain spectra comparable to SR results.
Here, we show the reproducibility of BCARS by conducting an internal Round
Robin with two different BCARS experimental setups, comparing the results on
different crystalline materials of increasing structural complexity: diamond,
6H-SiC, KDP, and KTP. First, we compare the detected and phase-retrieved
signals, the setup-specific NRB-removal steps, and the mode assignment.
Subsequently, we demonstrate the versatility of BCARS by showcasing how the
selection of pump wavelength, pulse width, and detection geometry can be
tailored to suit the specific objectives of the experiment. Finally, we compare
and optimize measurement parameters for the high-speed, hyperspectral imaging
of ferroelectric domain walls in lithium niobate.Comment: 12 pages, 8 figure
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Perovskite phase heterojunction solar cells
Modern photovoltaic devices are often based on a heterojunction structure where two components with different optoelectronic properties are interfaced. The properties of each side of the junction can be tuned by either utilizing different materials (for example, donor/acceptor) or doping (for example, p–n junction) or even varying their dimensionality (for example, 3D/2D). Here we demonstrate the concept of phase heterojunction (PHJ) solar cells by utilizing two polymorphs of the same material. We demonstrate the approach by forming γ-CsPbI3/β-CsPbI3 perovskite PHJ solar cells. We find that all of the photovoltaic parameters of the PHJ device significantly surpass those of each of the single-phase devices, resulting in a maximum power conversion efficiency of 20.1%. These improvements originate from the efficient passivation of the β-CsPbI3 by the larger bandgap γ-CsPbI3, the increase in the built-in potential of the PHJ devices enabled by the energetic alignment between the two phases and the enhanced absorption of light by the PHJ structure. The approach demonstrated here offers new possibilities for the development of photovoltaic devices based on polymorphic materials
Comparing transmission- and epi-BCARS: a round robin on solid-state materials
Broadband coherent anti-Stokes Raman scattering (BCARS) is a powerful spectroscopy method combining high signal intensity with spectral sensitivity, enabling rapid imaging of heterogeneous samples in biomedical research and, more recently, in crystalline materials. However, BCARS encounters spectral distortion due to a setup-dependent non-resonant background (NRB). This study assesses BCARS reproducibility through a round robin experiment using two distinct BCARS setups and crystalline materials with varying structural complexity, including diamond, 6H-SiC, KDP, and KTP. The analysis compares setup-specific NRB correction procedures, detected and NRB-removed spectra, and mode assignment. We determine the influence of BCARS setup parameters like pump wavelength, pulse width, and detection geometry and provide a practical guide for optimizing BCARS setups for solid-state applications
The closer object? An information-based dissociation between vision for perception and vision for movement in early infancy.
In human adults two functionally and neuro-anatomically separate systems exist for the use of visual information in perception and the use of visual information to control movements (Milner & Goodale 1995, 2008). We investigated whether this separation is already functioning in the early stages of the development of reaching. To this end, 6- and 7-month-old infants were presented with two identical objects at identical distances in front of an illusory Ponzo-like background that made them appear to be located at different distances. In two further conditions without the illusory background, the two objects were presented at physically different distances. Preferential reaching outcomes indicated that the allocentric distance information contained in the illusory background affected the perception of object distance. Yet, infants' reaching kinematics were only affected by the objects' physical distance and not by the perceptual distance manipulation. These findings were taken as evidence for the two-visual systems, as proposed by Milner and Goodale (2008), being functional in early infancy. We discuss the wider implications of this early dissociation. © 2012 Blackwell Publishing Ltd