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XEOM 1 : a novel microscopy system for the chemical imaging of heritage metal surfaces

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Abstract
Background: We describe a novel microscopy system which can obtain chemical maps from the surfaces of heritage metals in air or a controlled environment. The microscope, x-ray excited optical microscope Mk 1 (XEOM 1), forms images from x-ray excited optical luminescence (XEOL) induced by illuminating a few square millimetres of the sample with monochromated x-rays (broad beam or macroprobe illumination). XEOL is a spectroscopy tool in its own right and can, under the right circumstances, also be a vehicle for x-ray absorption spectroscopy. This (usually) synchrotron based technique provides information on the chemical state and short-range atomic order of the top few microns of a surface. It is thus well suited to heritage metal corrosion studies and is complementary to synchrotron x-ray diffraction. Results: Imaging can be performed by scanning the sample under an x-ray microprobe. We show elsewhere that the power density needed for image acquisition on a reasonable time-scale is high enough to damage a patina and modify its chemistry. Although the damaged region may be invisible to the human eye, the data are characteristic of the damage and not the native chemistry of the surface. A macrobeam power density can be 4 orders of magnitude smaller than that for a microbeam and no surface modification was observed on test samples. Features of the instrument are demonstrated using copper test surfaces with a spatially varying patination to establish the ground work for the imaging of copper, cuprite, nantokite and atacamite/paratacamite and a first application from a bronze chain mail link. In parallel we have developed a suite of imaging software which can process XEOM image stacks to produce reduced data sets characteristic of various aspects of the surface chemical map. These include edge-shift (oxidation state) images and edge height (high contrast) images and spectra from user defined regions of interest. Conclusions: The technique can map the oxidation state of a surface from shifts in the absorption edge energy across columns of pixels in an image set, and map particular compounds from their characteristic XANES spectra. Optically filtered images give improved chemical selectivity and the data sets contain as yet untapped information sources.
Keywords
SYNCHROTRON, XANES, Patina Mapping, X-Ray excited optical luminescence (XEOL), EXCITED OPTICAL LUMINESCENCE, XEOL-XANES, RADIATION X-RAY

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MLA
Dowsett, Mark, et al. “XEOM 1 : A Novel Microscopy System for the Chemical Imaging of Heritage Metal Surfaces.” HERITAGE SCIENCE, vol. 3, 2015.
APA
Dowsett, M., Hand, M., Sabbe, P.-J., Thompson, P., & Adriaens, M. (2015). XEOM 1 : a novel microscopy system for the chemical imaging of heritage metal surfaces. HERITAGE SCIENCE, 3.
Chicago author-date
Dowsett, Mark, Matt Hand, Pieter-Jan Sabbe, Paul Thompson, and Mieke Adriaens. 2015. “XEOM 1 : A Novel Microscopy System for the Chemical Imaging of Heritage Metal Surfaces.” HERITAGE SCIENCE 3.
Chicago author-date (all authors)
Dowsett, Mark, Matt Hand, Pieter-Jan Sabbe, Paul Thompson, and Mieke Adriaens. 2015. “XEOM 1 : A Novel Microscopy System for the Chemical Imaging of Heritage Metal Surfaces.” HERITAGE SCIENCE 3.
Vancouver
1.
Dowsett M, Hand M, Sabbe P-J, Thompson P, Adriaens M. XEOM 1 : a novel microscopy system for the chemical imaging of heritage metal surfaces. HERITAGE SCIENCE. 2015;3.
IEEE
[1]
M. Dowsett, M. Hand, P.-J. Sabbe, P. Thompson, and M. Adriaens, “XEOM 1 : a novel microscopy system for the chemical imaging of heritage metal surfaces,” HERITAGE SCIENCE, vol. 3, 2015.
@article{7053047,
  abstract     = {Background: We describe a novel microscopy system which can obtain chemical maps from the surfaces of heritage metals in air or a controlled environment. The microscope, x-ray excited optical microscope Mk 1 (XEOM 1), forms images from x-ray excited optical luminescence (XEOL) induced by illuminating a few square millimetres of the sample with monochromated x-rays (broad beam or macroprobe illumination). XEOL is a spectroscopy tool in its own right and can, under the right circumstances, also be a vehicle for x-ray absorption spectroscopy. This (usually) synchrotron based technique provides information on the chemical state and short-range atomic order of the top few microns of a surface. It is thus well suited to heritage metal corrosion studies and is complementary to synchrotron x-ray diffraction. 
Results: Imaging can be performed by scanning the sample under an x-ray microprobe. We show elsewhere that the power density needed for image acquisition on a reasonable time-scale is high enough to damage a patina and modify its chemistry. Although the damaged region may be invisible to the human eye, the data are characteristic of the damage and not the native chemistry of the surface. A macrobeam power density can be 4 orders of magnitude smaller than that for a microbeam and no surface modification was observed on test samples. Features of the instrument are demonstrated using copper test surfaces with a spatially varying patination to establish the ground work for the imaging of copper, cuprite, nantokite and atacamite/paratacamite and a first application from a bronze chain mail link. In parallel we have developed a suite of imaging software which can process XEOM image stacks to produce reduced data sets characteristic of various aspects of the surface chemical map. These include edge-shift (oxidation state) images and edge height (high contrast) images and spectra from user defined regions of interest. 
Conclusions: The technique can map the oxidation state of a surface from shifts in the absorption edge energy across columns of pixels in an image set, and map particular compounds from their characteristic XANES spectra. Optically filtered images give improved chemical selectivity and the data sets contain as yet untapped information sources.},
  articleno    = {14},
  author       = {Dowsett, Mark and Hand, Matt and Sabbe, Pieter-Jan and Thompson, Paul and Adriaens, Mieke},
  issn         = {2050-7445},
  journal      = {HERITAGE SCIENCE},
  keywords     = {SYNCHROTRON,XANES,Patina Mapping,X-Ray excited optical luminescence (XEOL),EXCITED OPTICAL LUMINESCENCE,XEOL-XANES,RADIATION X-RAY},
  language     = {eng},
  pages        = {8},
  title        = {XEOM 1 : a novel microscopy system for the chemical imaging of heritage metal surfaces},
  url          = {http://dx.doi.org/10.1186/s40494-015-0042-5},
  volume       = {3},
  year         = {2015},
}

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