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  • Pauw, Brian Richard (5)
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Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene (2020)
Reed, B. P. ; Cant, D.J.H. ; Spencer, J. ; Carmona-Carmona, A. J. ; Bushell, A. ; Herrara-Gómez, A. ; Kurokawa, A. ; Thissen, A. ; Thomas, A.G. ; Britton, A.J. ; Bernasik, A. ; Fuchs, A. ; Baddorf, A. P. ; Bock, B. ; Thellacker, B. ; Cheng, B. ; Castner, D.G. ; Morgan, D.J. ; Valley, D. ; Willneff, E.A. ; Smith, E.F. ; Nolot, E. ; Xie, F. ; Zorn, G. ; Smith, G.C. ; Yasukufu, H. ; Fenton, J. L. ; Chen, J. ; Counsell, J..D.P. ; Radnik, Jörg ; Gaskell, K.J. ; Artyushkova, K. ; Yang, L. ; Zhang, L. ; Eguchi, M. ; Walker, M. ; Hajdyla, M. ; Marzec, M.M. ; Linford, M.R. ; Kubota, N. ; Cartazar-Martínez, O. ; Dietrich, P. ; Satoh, R. ; Schroeder, S.L.M. ; Avval, T.G. ; Nagatomi, T. ; Fernandez, V. ; Lake, W. ; Azuma, Y. ; Yoshikawa, Y. ; Shard, A.G.
We report the results of a Versailles Project on Advanced Materials and Standards interlaboratory study on the intensity scale calibration of x-ray photoelectron spectrometers using low-density polyethylene (LDPE) as an alternative material to gold, silver, and copper. An improved set of LDPE reference spectra, corrected for different instrument geometries using a quartz-monochromated Al Kα x-ray source, was developed using data provided by participants in this study. Using these new reference spectra, a transmission function was calculated for each dataset that participants provided. When compared to a similar calibration procedure using the NPL reference spectra for gold, the LDPE intensity calibration method achieves an absolute offset of ∼3.0% and a systematic deviation of ±6.5% on average across all participants. For spectra recorded at high pass energies (≥90 eV), values of absolute offset and systematic deviation are ∼5.8% and ±5.7%, respectively, whereas for spectra collected at lower pass energies (<90 eV), values of absolute offset and systematic deviation are ∼4.9% and ±8.8%, respectively; low pass energy spectra perform worse than the global average, in terms of systematic deviations, due to diminished count rates and signal-to-noise ratio. Differences in absolute offset are attributed to the surface roughness of the LDPE induced by sample preparation. We further assess the usability of LDPE as a secondary reference material and comment on its performance in the presence of issues such as variable dark noise, x-ray warm up times, inaccuracy at low count rates, and underlying spectrometer problems. In response to participant feedback and the results of the study, we provide an updated LDPE intensity calibration protocol to address the issues highlighted in the interlaboratory study. We also comment on the lack of implementation of a consistent and traceable intensity calibration method across the community of x-ray photoelectron spectroscopy (XPS) users and, therefore, propose a route to achieving this with the assistance of instrument manufacturers, metrology laboratories, and experts leading to an international standard for XPS intensity scale calibration.
Versailles Project on Advanced Materials and Standards Interlaboratory Study on Measuring the Thickness and Chemistry of Nanoparticle Coatings Using XPS and LEIS (2016)
Belsey, N. A. ; Cant, D. J. H. ; Minelli, C. ; Araujo, J. R. ; Bock, B. ; Brüner, P. ; Castner, D. G. ; Ceccone, G. ; Counsell, J. D. P. ; Dietrich, Paul M. ; Engelhardt, M. H. ; Fearn, S. ; Galhardo, C. E. ; Kalbe, H. ; Kim, J. W. ; Lartundo-Rojas, L. ; Luftman, H. S. ; Nunney, T. S. ; Pseiner, J. ; Smith, E. F. ; Spampinato, V. ; Sturm, J. M. ; Thomas, A. G. ; Treacy, J. P. W. ; Veith, L. ; Wagstaffe, M. ; Wang, H. ; Wang, M. ; Wang, Y.-C. ; Werner, W. ; Yang, L. ; Shard, A. G.
We report the results of a Versailles Project on Advanced Materials and Standards (VAMAS) interlaboratory study on the measurement of the shell thickness and chemistry of nanoparticle coatings. Peptide-coated gold particles were supplied to laboratories in two forms: a colloidal suspension in pure water and particles dried onto a silicon wafer. Participants prepared and analyzed these samples using either X-ray photoelectron spectroscopy (XPS) or low energy ion scattering (LEIS). Careful data analysis revealed some significant sources of discrepancy, particularly for XPS. Degradation during transportation, storage, or sample preparation resulted in a variability in thickness of 53%. The calculation method chosen by XPS participants contributed a variability of 67%. However, variability of 12% was achieved for the samples deposited using a single method and by choosing photoelectron peaks that were not adversely affected by instrumental transmission effects. The study identified a need for more consistency in instrumental transmission functions and relative sensitivity factors since this contributed a variability of 33%. The results from the LEIS participants were more consistent, with variability of less than 10% in thickness, and this is mostly due to a common method of data analysis. The calculation was performed using a model developed for uniform, flat films, and some participants employed a correction factor to account for the sample geometry, which appears warranted based upon a simulation of LEIS data from one of the participants and comparison to the XPS results.
Combined pressure and temperature denaturation of ribonuclease A produces alternate dentatured states (2016)
Ryan, T. M. ; Xun, Y. ; Cowieson, N. P. ; Mata, J. P. ; Jackson, A. ; Pauw, Brian Richard ; Smith, A. J. ; Kirby, N. ; McGillivray, D.
Protein folding, unfolding and misfolding have become critically important to a range of health and industry applications. Increasing high temperature and high pressure are used to control and speed up reactions. A number of studies have indicated that these parameters can have a large effecton protein structure and function. Here we describe the additive effects of these parameters on the small angle scattering behaviour of ribonuclease A. We find that alternate unfolded structures can be obtained with combined high pressure and temperature treatment of the protein.
Extending SAXS instrument ranges through addition of a portable, inexpensive USAXS module (2019)
Pauw, Brian Richard ; Smith, A. J. ; Snow, T. ; Shebanova, O. ; Sutter, J. P. ; Hermida-Merino, D. ; Smales, Glen Jacob ; Terrill, N. J. ; Thünemann, Andreas F. ; Bras, W.
Ultra-SAXS can enhance the capabilities of existing SAXS/WAXS beamlines and laboratory instruments. A compact Ultra-SAXS module has been developed, which extends the measurable q-range with 0:0015 < q 1/nm) < 0:2, allowing structural dimensions between 30 < D(nm) < 4000 to be probed in addition to the range covered by a high-end SAXS/WAXS instrument. By shifting the module components in and out on their respective motor stages, SAXS/WAXS measurements can be easily and rapidly interleaved with USAXS measurements.
The modular small-angle X-ray scattering data correction sequence (2017)
Pauw, Brian Richard ; Smith, A. J. ; Snow, T. ; Terril, N. J. ; Thünemann, Andreas F.
Data correction is probably the least favourite activity amongst users experimenting with small-angle X-ray scattering: if it is not done sufficiently well, this may become evident only during the data analysis stage, necessitating the repetition of the data corrections from scratch. A recommended comprehensive sequence of elementary data correction steps is presented here to alleviate the difficulties associated with data correction, both in the laboratory and at the synchrotron. When applied in the proposed order to the raw signals, the resulting absolute scattering cross section will provide a high degree of accuracy for a very wide range of samples, with its values accompanied by uncertainty estimates. The method can be applied without modification to any pinhole-collimated instruments with photon-counting direct-detection area detectors.
Simultaneous SAXS and SANS Analysis for the Detection of Toroidal Supramolecular Polymers Composed of Noncovalent Supermacrocycles in Solution (2016)
Hollamby, M. J. ; Aratsu, K. ; Pauw, Brian Richard ; Rogers, S. E. ; Smith, A. J. ; Yamauchi, M. ; Lin, X. ; Yagai, S.
Molecular self-assembly primarily occurs in solution. To better understand this process, techniques capable of probing the solvated state are consequently required. Smallangle scattering (SAS) has a proven ability to detect and characterize solutions, but it is rarely applied to more complex assembly shapes. Here, small-angle X-ray and neutron scattering are applied to observe toroidal assemblies in solution. Combined analysis confirms that the toroids have a core–shell structure, with a p-conjugated core and an alkyl shell into which solvent penetrates. The dimensions determined by SAS agree well with those obtained by (dried-state) atomic force microscopy. Increasing the number of naphthalene units in the molecular building block yields greater rigidity, as evidenced by a larger toroid and a reduction in solvent penetration into the shell. The detailed structural analysis demonstrates the applicability of SAS to monitor complex solution-based selfassembly.
The aggregation of an alkyl–C60 derivative as a function of concentration, temperature and solvent type (2018)
Hollamby, M. J. ; Smith, C. F. ; Britton, M. M. ; Danks, A. E. ; Schnepp, Z. ; Grillo, I. ; Pauw, Brian Richard ; Kishimura, A. ; Nakanishi, T.
Contrast-variation small-angle neutron scattering (CV-SANS), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR) measurements of diffusion and isothermal titration calorimetry (ITC) are used to gain insight into the aggregation of an alkyl–C60 derivative, molecule 1, in n-hexane, n-decane and toluene as a function of concentration and temperature. Results point to an associative mechanism of aggregation similar to other commonly associating molecules, including non-ionic surfactants or asphaltenes in non-aqueous solvents. Little aggregation is detected in toluene, but small micelle-like structures form in n-alkane solvents, which have a C60-rich core and alkyl-rich shell. The greatest aggregation extent is found in n-hexane, and at 0.1 M the micelles of 1 comprise around 6 molecules at 25 °C. These micelles become smaller when the concentration is lowered, or if the solvent is changed to n-decane. The solution structure is also affected by temperature, with a slightly larger aggregation extent at 10 °C than at 25 °C. At higher concentrations, for example in solutions of 1 above 0.3 M in n-decane, a bicontinuous network becomes apparent. Overall, these findings aid our understanding of the factors driving the assembly of alkyl–π-conjugated hydrophobic amphiphiles such as 1 in solution and thereby represent a step towards the ultimate goal of exploiting this phenomenon to form materials with well-defined order.
Neutron activation cross sections on lead isotopes (2009)
Semkova, V. ; Reimer, P. ; Altzitzoglou, T. ; Plompen, A.J.M. ; Quétel, C. ; Sudár, S. ; Vogl, Jochen ; Koning, A.J. ; Qaim, S.M. ; Smith, D.L.
Near-Edge X-ray Absorption Fine Structure Spectroscopy on Ordered Films of an Amphiphilic Derivate of 2,5-Diphenyl-1,3,4-Oxadiazole (1999)
Giebler, Rainer ; Unger, Wolfgang ; Schulz, B. ; Reiche, J. ; Brehmer, L. ; Wühn, M. ; Wöll, Ch. ; Smith, A.P. ; Urquhart, S.G.
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