| 1. |
- 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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| 2. |
- Stark, T. H., et al.
(författare)
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Generalization of Classic Question Order Effects Across Cultures
- 2020
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Ingår i: Sociological Methods & Research. - : SAGE Publications. - 0049-1241 .- 1552-8294. ; 49:3, s. 567-602
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Tidskriftsartikel (refereegranskat)abstract
- Questionnaire design is routinely guided by classic experiments on question form, wording, and context conducted decades ago. This article explores whether two question order effects (one due to the norm of evenhandedness and the other due to subtraction or perceptual contrast) appear in surveys of probability samples in the United States and 11 other countries (Canada, Denmark, Germany, Iceland, Japan, the Netherlands, Norway, Portugal, Sweden, Taiwan, and the United Kingdom;N= 25,640). Advancing theory of question order effects, we propose necessary conditions for each effect to occur, and found that the effects occurred in the nations where these necessary conditions were met. Surprisingly, the abortion question order effect even appeared in some countries in which the necessary condition was not met, suggesting that the question order effect there (and perhaps elsewhere) was not due to subtraction or perceptual contrast. The question order effects were not moderated by education. The strength of the effect due to the norm of evenhandedness was correlated with various cultural characteristics of the nations. Strong support was observed for the form-resistant correlation hypothesis.
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| 3. |
- 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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| 4. |
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| 6. |
- Lockyer, Nicholas P., et al.
(författare)
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Secondary ion mass spectrometry
- 2024
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Ingår i: Nature Reviews Methods Primers. - 2662-8449. ; 4
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Forskningsöversikt (refereegranskat)abstract
- Secondary ion mass spectrometry (SIMS) is a technique for chemical analysis and imaging of solid materials, with applications in many areas of science and technology. It involves bombarding a sample surface under high vacuum with energetic primary ions. The ejected secondary ions undergo mass-to-charge ratio (m/z) analysis and are detected. The resulting mass spectrum contains detailed surface chemical information with sub-monolayer sensitivity. Different experimental configurations provide chemically resolved depth distribution and 2D or 3D images. SIMS is complementary to other surface analysis techniques, such as X-ray photoelectron spectroscopy; chemical imaging techniques, for example, vibrational microspectroscopy methods such as Fourier transform infrared spectroscopy and Ramanspectroscopy; and other mass spectrometry imaging techniques, including desorption electrospray ionization and matrix-assisted laser desorption ionization. Features of SIMS include high spatial resolution, high depth resolution and broad chemical sensitivity to all elements, isotopes and molecules up to several thousand mass units. This Primer describes the operating principles of SIMS and outlines how the instrument geometry and operational parameters enable different modes of operation and information to be obtained. Applications, including materials science, surface science, electronic devices, geosciences and life sciences, are explored, finishing with an outlook for the technique.
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| 7. |
- 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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