| 1. |
- Aoyagi, M., et al.
(författare)
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Systematic effects on a Compton polarimeter at the focus of an X-ray mirror
- 2024
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- XL-Calibur is a balloon-borne Compton polarimeter for X-rays in the ∼15–80 keV range. Using an X-ray mirror with a 12 m focal length for collecting photons onto a beryllium scattering rod surrounded by CZT detectors, a minimum-detectable polarization as low as ∼3% is expected during a 24-hour on-target observation of a 1 Crab source at 45° elevation. Systematic effects alter the reconstructed polarization as the mirror focal spot moves across the beryllium scatterer, due to pointing offsets, mechanical misalignment or deformation of the carbon-fiber truss supporting the mirror and the polarimeter. Unaddressed, this can give rise to a spurious polarization signal for an unpolarized flux, or a change in reconstructed polarization fraction and angle for a polarized flux. Using bench-marked Monte-Carlo simulations and an accurate mirror point-spread function characterized at synchrotron beam-lines, systematic effects are quantified, and mitigation strategies discussed. By recalculating the scattering site for a shifted beam, systematic errors can be reduced from several tens of percent to the few-percent level for any shift within the scattering element. The treatment of these systematic effects will be important for any polarimetric instrument where a focused X-ray beam is impinging on a scattering element surrounded by counting detectors.
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| 2. |
- Shard, A. G., et al.
(författare)
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Measuring Compositions in Organic Depth Profiling: Results from a VAMAS Interlaboratory Study
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:33, s. 10784-10797
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of a VAMAS (Versailles Project on Advanced Materials and Standards) interlaboratory study on the measurement of composition in organic depth profiling. Layered samples with known binary compositions of Irganox 1010 and either Irganox 1098 or Fmoc-pentafluoro-L-phenylalanine in each layer were manufactured in a single batch and distributed to more than 20 participating laboratories. The samples were analyzed using argon cluster ion sputtering and either X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (ToF-SIMS) to generate depth profiles. Participants were asked to estimate the volume fractions in two of the layers and were provided with the compositions of all other layers. Participants using XPS provided volume fractions within 0.03 of the nominal values. Participants using ToF-SIMS either made no attempt, or used various methods that gave results ranging in error from 0.02 to over 0.10 in volume fraction, the latter representing a 50% relative error for a nominal volume fraction of 0.2. Error was predominantly caused by inadequacy in the ability to compensate for primary ion intensity variations and the matrix effect in SIMS. Matrix effects in these materials appear to be more pronounced as the number of atoms in both the primary analytical ion and the secondary ion increase. Using the participants' data we show that organic SIMS matrix effects can be measured and are remarkably consistent between instruments. We provide recommendations for identifying and compensating for matrix effects. Finally, we demonstrate, using a simple normalization method, that virtually all ToF-SIMS participants could have obtained estimates of volume fraction that were at least as accurate and consistent as XPS.
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| 3. |
- Petersson, A, et al.
(författare)
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Compositional variation of AlGaN epitaxial films on 6H-SiC substrates determined by cathodoluminescence.
- 2002
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Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- High quality epitaxial films of A(l)xGa(1-x)N, grown on SiC substrates, were investigated using spatially resolved cathodoluminescence (CL), scanning electron microscopy, and atomic force microscopy. A variation in the observed peak energy position of the CL was related to alloy fluctuations. CL was used to reveal relative alloy fluctuations of approximately 1% on a sub-micrometer scale, with a precision difficult to surpass with other available techniques. By correlating data from the different techniques, a model was derived. The main feature of it is an alloy fluctuation on the micrometer scale, seeded during the initial growth and extending through the epitaxial film. These alloy fluctuations seems to be related to terrace steps ( approximate to5 nm in height), formed preferentially at scratches on the SiC surface. This investigation indicates that the initial growth of epitaxial films is critical and structures formed at the beginning of the growth tend to persist throughout the growth. Further, a strain gradient from the SiC interface extending towards the surface, was observed.
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| 4. |
- Yokoyama, Y., et al.
(författare)
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Peptide Fragmentation and Surface Structural Analysis by Means of ToF-SIMS Using Large Cluster Ion Sources
- 2016
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 88:7, s. 3592-3597
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Tidskriftsartikel (refereegranskat)abstract
- Peptide or protein structural analysis is crucial for the evaluation of biochips and biodevices, therefore an analytical technique with the ability to detect and identify protein and peptide species directly from surfaces with high lateral resolution is required. In this report, the efficacy of ToF-SIMS to analyze and identify proteins directly from surfaces is evaluated. Although the physics governing the SIMS bombardment process precludes the ability for researchers to detect intact protein or larger peptides of greater than a few thousand mass unit directly, it is possible to obtain information on the partial structures of peptides or proteins using low energy per atom argon duster ion beams. Large cluster ion beams, such as Ar dusters and C-60 ion beams, produce spectra similar to those generated by tandem MS. The SIMS bombardment process also produces peptide fragment ions not detected by conventional MS/MS techniques. In order to clarify appropriate measurement conditions for peptide structural analysis, peptide fragmentation dependency on the energy of a primary ion beam and ToF-SIMS specific fragment ions are evaluated. It was found that the energy range approximately 6 <= E/n <= 10 eV/atom is most effective for peptide analysis based on peptide fragments and [M + H] ions. We also observed the cleaving of side chain moieties at extremely low-energy E/n <= 4 eV/atom.
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