additive-manufacturing-enabled-low-cost-particle-detector

Additive Manufacturing-Enabled Low-Cost Particle Detector

As particles with a size of 1 &#181;m or smaller pose a severe health risk to the human body, the detection and regulation of particle emissions are of ...

Silicon Austria Labs

Dynamical scattering effects are observed in grazing-incidence X-ray diffraction experiments using an organic thin film of 2,2':6',2''-ternaphthalene grown on oxidized silicon as substrate. Here, a splitting of all Bragg peaks in the out-of-plane direction (z-direction) has been observed, the magnitude of which depends both on the incidence angle of the primary beam and the out-of-plane angle of the scattered beam. The incident angle was varied between 0.09° and 0.25° for synchrotron radiation of 10.5 keV. This study reveals comparable intensities of the split peaks with a maximum for incidence angles close to the critical angle of total external reflection of the substrate. This observation is rationalized by two different scattering pathways resulting in diffraction peaks at different positions at the detector. In order to minimize the splitting, the data suggest either using incident angles well below the critical angle of total reflection or angles well above, which sufficiently attenuates the contributions from the second scattering path. This study highlights that the refraction of X-rays in (organic) thin films has to be corrected accordingly to allow for the determination of peak positions with sufficient accuracy. Based thereon, a reliable determination of the lattice constants becomes feasible, which is required for crystallographic structure solutions from thin films.

Multiple scattering in grazing-incidence X-ray diffraction: impact on lattice-constant determination in thin films.

For the investigation of photoinduced dynamics in molecules with time-resolved pump-probe photoionization spectroscopy, it is essential to obtain unequivocal information about the fragmentation behavior induced by the laser pulses. We present time-resolved photoelectron-photoion coincidence (PEPICO) experiments to investigate the excited-state dynamics of isolated acetone molecules triggered by two-photon (269 nm) excitation. In the complex situation of different relaxation pathways, we unambiguously identify three distinct pump-probe ionization channels. The high selectivity of PEPICO detection allows us to observe the fragmentation behavior and to follow the time evolution of each channel separately. For channels leading to fragment ions, we quantitatively obtain the fragment-to-parent branching ratio and are able to determine experimentally whether dissociation occurs in the neutral molecule or in the parent ion. These results highlight the importance of coincidence detection for the interpretation of time-resolved photochemical relaxation and dissociation studies if multiple pathways are present. 

Disentangling Multichannel Photodissociation Dynamics in Acetone by Time-Resolved Photoelectron-Photoion Coincidence Spectroscopy.

An aerosol gas exchange system (AGES) for nanoparticle sampling at elevated temperatures was developed, modeled, and further characterized with laboratory tests with respect to gas exchange efficiency and particle losses. The model describing the gas exchange was first verified with oxygen and later studied with several inert gases having molecular masses between 18 and 135 u. The exchange rate of the lightest compounds exceeds 90% efficiency at the flow rates used. In order to reach similarly high removal efficiencies for larger molecules, the residence time in the AGES has to be increased. The removal of sticky gases was studied with gaseous sulfuric acid. Results agreed with the model where the boundary condition is zero concentration on the wall. The AGES exhibits very limited particle losses (<5%) for mono-disperse 6 nm particles. Furthermore, diffusional losses for particles down to 1.2 nm were measured utilizing polydisperse aerosol. The experimental findings are in good agreement with the model derived. As both, gas exchange rate and particle losses, rely on the physical effect of diffusion, an optimization for enhanced gas exchange efficiency will come at the cost of increased diffusional particle losses. The presented model can be used as a tool to redesign and optimize the AGES for a desired application. With an application targeted design, particle dilution can be avoided, which can lead to improved results in many fields of aerosol measurement.

Article	Year
Multiple scattering in grazing-incidence X-ray diffraction: impact on lattice-constant determination in thin films. Journal of synchrotron radiation\| PubMed ID: 27140152	2016
Disentangling Multichannel Photodissociation Dynamics in Acetone by Time-Resolved Photoelectron-Photoion Coincidence Spectroscopy. The journal of physical chemistry. A\| PubMed ID: 27459051	2016
Aerosol gas exchange system (AGES) for nanoparticle sampling at elevated temperatures: Modeling and experimental characterization. Scientific reports\| PubMed ID: 31748564	2019

Markus Bainschab

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