Evaluation of an X-ray-Excited Optical Microscope for Chemical Imaging of Metal and Other Surfaces

Abstract

The application of a modular system for the nondestructive chemical imaging of metal and other surfaces is described using heritage metals as an example. The custom-built X-ray-excited optical luminescence (XEOL) microscope, XEOM 1, images the chemical state and short-range atomic order of the top 200 nm of both amorphous and crystalline surfaces. A broad X-ray beam is used to illuminate large areas (up to 4 mm(2)) of the sample, and the resulting XEOL emission is collected simultaneously for each pixel by a charge-coupled device sensor to form an image. The input X-ray energy is incremented across a range typical for the X-ray absorption near-edge structure (XANES) and an image collected for each increment. The use of large-footprint beams combined with parallel detection allows the power density to be kept low and facilitates complete nondestructive XANES mapping on a reasonable time scale. In this study the microscope was evaluated by imaging copper surfaces with well-defined patterns of different corrosion products (cuprite Cu2O and nantokite CuCl). The images obtained show chemical contrast, and filtering the XEOL light allowed different corrosion products to be imaged separately. Absorption spectra extracted from software-selected regions of interest exhibit characteristic XANES fingerprints for the compounds present. Moreover, when the X-ray absorption edge positions were extracted from each spectrum, an oxidation state map of the sample could be compiled. The results show that this method allows one to obtain nondestructive and noninvasive information at the micrometer scale while using full-field imaging.

Synchrotron X-ray diffraction investigation of the surface condition of artefacts from King Henry VIII's warship the Mary Rose

“…XEOL-XANES data were also acquired on XMaS using the broadband photomultiplier (H8259-01, Hamamatsu Photonics KK) fitted to our XEOL full-field microscope system XEOM 1 (Dowsett et al, 2015;Sabbe et al, 2014). X-rays were incident at 60 to the surface, and take-off was at 45 .…”

“…Therefore, in a parallel study we used a microscope (XEOM 1) (Dowsett et al, 2015) based on X-ray excited optical luminescence (XEOL) to examine the copper K-edge X-ray near-edge absorption structure (XANES). Some of these data have been published elsewhere (Dowsett et al, 2015;Sabbe et al, 2014).…”

XEOM 1 - A novel microscopy system for the chemical imaging of heritage metal surfaces

“…The copper surface was cleaned as described elsewhere [28] and heated to a dull red in a reducing Bunsen flame. A patina of >90% cuprite with a residue of tenorite forms immediately on air exposure [29].…”

X‐ray Excited Optical Fluorescence and Diffraction Imaging of Reactivity and Crystallinity in a Zeolite Crystal: Crystallography and Molecular Spectroscopy in One

“…If excited by X‐rays, these molecules undergo photoemission in the optical region (UV/Vis), a phenomenon that is generally known as X‐ray excited optical luminescence,33, 34, 35 here referred to as XEOF. Recently, several strategies were developed at synchrotrons to utilize the XEOF emission of visible light for studies of functional materials 36, 37, 38, 39, 40, 41, 42, 43, 44. Our method makes use of a less common method to simultaneously excite electronic transitions in organic molecules and resolve the crystallographic structure of a single crystal.…”

“…Recently,s everal strategies were developed at synchrotrons to utilize the XEOF emission of visible light for studies of functional materials. [36][37][38][39][40][41][42][43][44] Our method makes use of al ess common method to simultaneously excite electronic transitions in organic molecules and resolve the crystallographic structure of asingle crystal. Figure 1illustrates the approach for measuring m-XRD/m-XEOF maps of asingle steamed ZSM-5 crystal stained with 4methoxystyrene in one experiment.…”