ORCID Profile
0000-0002-5529-1250
Current Organisations
IT University of Copenhagen
,
Københavns Universitet
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Publisher: Oxford University Press (OUP)
Date: 08-2022
DOI: 10.1017/S1431927621013714
Abstract: Well-defined reconstruction parameters are essential to quantify the size, shape, and distribution of nanoscale features in atom probe tomography (APT) datasets. However, the reconstruction parameters of many minerals are difficult to estimate because intrinsic spatial markers, such as crystallographic planes, are not usually present within the datasets themselves. Using transmission and/or scanning electron microscopy imaging of needle-shaped specimens before and after atom probe analysis, we test various approaches to provide best-fit reconstruction parameters for voltage-based APT reconstructions. The results demonstrate that the length measurement of evaporated material, constrained by overlaying pre- and post-analysis images, yields more consistent reconstruction parameters than the measurement of final tip radius. Using this approach, we provide standardized parameters that may be used in APT reconstructions of 11 minerals. The adoption of standardized reconstruction parameters by the geoscience APT community will alleviate potential problems in the measurement of nanoscale features (e.g., clusters and interfaces) caused by the use of inappropriate parameters.
Publisher: Wiley
Date: 26-02-2020
DOI: 10.1111/GGR.12313
Publisher: Wiley
Date: 08-2022
DOI: 10.1111/JMG.12686
Abstract: The trace‐element composition of rutile is commonly used to constrain P – T – t conditions for a wide range of metamorphic systems. However, recent studies have demonstrated the redistribution of trace elements in rutile via high‐diffusivity pathways and dislocation‐impurity associations related to the formation and evolution of microstructures. Here, we investigate trace‐element migration in low‐angle boundaries formed by dislocation creep in rutile within an omphacite vein of the Lago di Cignana unit (Western Alps, Italy). Zr‐in‐rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain the conditions of rutile deformation to around the prograde boundary from high pressure to ultra‐high pressure (~2.7 GPa) at temperatures of 500–565°C. Crystal‐plastic deformation of a large rutile grain results in low‐angle boundaries that generate a total misorientation of ~25°. Dislocations constituting one of these low‐angle boundaries are enriched in common and uncommon trace elements, including Fe and Ca, providing evidence for the diffusion and trapping of trace elements along the dislocation cores. The role of dislocation microstructures as fast‐diffusion pathways must be evaluated when applying high‐resolution analytical procedures as compositional disturbances might lead to erroneous interpretations for Ca and Fe. In contrast, our results indicate a trapping mechanism for Zr.
Publisher: Geological Society of America
Date: 07-07-2020
Abstract: Additional information on results, acquisition conditions and visualization of the APT mass spectrum, and 3D digital reconstructions. br
Publisher: Elsevier BV
Date: 04-2022
Publisher: Oxford University Press (OUP)
Date: 02-2019
DOI: 10.1017/S1431927618015477
Abstract: Since the introduction of laser-assisted atom probe, analysis of nonconductive materials by atom probe tomography (APT) has become more routine. To obtain high-quality data, a number of acquisition variables needs to be optimized for the material of interest, and for the specific question being addressed. Here, the rutile (TiO 2 ) reference material ‘Windmill Hill Quartzite,’ used for secondary ion mass spectrometry U–Pb dating and laser-ablation inductively coupled plasma mass spectrometry, was analyzed by laser-assisted APT to constrain optimal running conditions. Changes in acquisition parameters such as laser energy and detection rate are evaluated in terms of their effect on background noise, ionization state, hit-multiplicity, and thermal tails. Higher laser energy results in the formation of more complex molecular ions and affects the ionization charge state. At lower energies, background noise and hit-multiplicity increase, but thermal tails shorten. There are also correlations between the acquisition voltage and several of these metrics, which remain to be fully understood. The results observed when varying the acquisition parameters will be discussed in detail in the context of utilizing APT analysis of rutile within geology.
Publisher: Geological Society of America
Date: 07-07-2020
DOI: 10.1130/GEOL.S.12620615.V1
Abstract: Additional information on results, acquisition conditions and visualization of the APT mass spectrum, and 3D digital reconstructions. br
Publisher: Wiley
Date: 18-07-2021
DOI: 10.1111/GGR.12398
Abstract: Xenotime (YPO 4 ) is an accessory phase common in low to high‐temperature geological environments. Xenotime is an established geochronometer, though its small size, low modal abundance and textural complexity make it more difficult to analyse with traditional techniques but makes a prime candidate for nanoscale analysis. In this study, we develop an atom probe tomography (APT) protocol to determine the 206 Pb/ 238 U and 207 Pb/ 206 Pb ages of micro‐scale xenotime crystals with analytical volumes four to six orders of magnitude smaller than typical geochronology techniques. A linear correlation between the 206 Pb/ 238 U fractionation and 238 UO 2 2+ / 238 UO 2+ was used to correct for the atom probe instrument parameters variability between specimens. For 207 Pb/ 206 Pb ages, we employed two methods of background correction owing to the 206 Pb 2+ thermal tail contribution to the 207 Pb 2+ counts: A constant background correction for the younger (˜ 1000 Ma) Y1 reference material and a variable correction of background for Archaean age reference material xtc to correct for the thermal tail influence. This contribution also proposes strategies for optimisation of xenotime analysis using APT and permits us to explore the various geological problems in the nanoscale realm. This methodology potentially allows determining the age of small xenotime crystals in sedimentary rocks, low metamorphic grade settings and deformation microstructures.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-9404
Abstract: & & The trace-element composition of rutile is commonly used to constrain & em& P-T-t& /em& conditions for a wide range of metamorphic systems. Recent studies have highlighted the importance of micro- and nanostructures in the redistribution of trace elements in rutile via high-diffusivity pathways and dislocation-impurity associations. In this contribution, we investigate the effect of crystal-plastic deformation of rutile on its composition by combining microstructural and petrological analyses with atom probe tomography. The studied s le is from an omphacite vein of the ultrahigh-pressure metamorphic Lago di Cignana unit, Western Alps, Italy. Zr-in-rutile thermometry and inclusions of quartz in rutile and of coesite in omphacite constrain rutile deformation to around the prograde HP-UHP boundary at 500& #8211 & #176 C. Crystal-plastic deformation of a large rutile grain resulted in low-angle boundaries that generate a total misorientation of ~25& #176 . Dislocations constituting the low-angle boundary are enriched in common (Fe, Zr) and uncommon trace elements (Ca). The Ca is interpreted to be derived from the grain exterior, suggesting diffusion of trace elements along the dislocation cores. The potential for dislocation microstructures to act as fast diffusion pathways must be evaluated when applying traditional geochemical analyses as compositional disturbances caused by the presence of dislocation might lead to erroneous interpretations.& &
No related grants have been discovered for Rick Verberne.