Optimizing use of the structural chemical analyser (variable pressure FESEM‐EDX raman spectroscopy) on micro‐size complex historical paintings characterization

Abstract

The novel Structural Chemical Analyser (hyphenated Raman spectroscopy and scanning electron microscopy equipped with an X-ray detector) is gaining popularity since it allows 3-D morphological studies and elemental, molecular, structural and electronic analyses of a single complex micro-sized sample without transfer between instruments. However, its full potential remains unexploited in painting heritage where simultaneous identification of inorganic and organic materials in paintings is critically yet unresolved. Despite benefits and drawbacks shown in literature, new challenges have to be faced analysing multifaceted paint specimens. SEM-Structural Chemical Analyser systems differ since they are fabricated ad hoc by request. As configuration influences the procedure to optimize analyses, likewise analytical protocols have to be designed ad hoc. This paper deals with the optimization of the analytical procedure of a Variable Pressure Field Emission scanning electron microscopy equipped with an X-ray detector Raman spectroscopy system to analyse historical paint samples. We address essential parameters, technical challenges and limitations raised from analysing paint stratigraphies, archaeological samples and loose pigments. We show that accurate data interpretation requires comprehensive knowledge of factors affecting Raman spectra. We tackled: (i) the in-FESEM-Raman spectroscopy analytical sequence, (ii) correlations between FESEM and Structural Chemical Analyser/laser analytical position, (iii) Raman signal intensity under different VP-FESEM vacuum modes, (iv) carbon deposition on samples under FESEM low-vacuum mode, (v) crystal nature and morphology, (vi) depth of focus and (vii) surface-enhanced Raman scattering effect. We recommend careful planning of analysis strategies prior to research which, although time consuming, guarantees reliable results. The ultimate goal of this paper is to help to guide future users of a FESEM-Structural Chemical Analyser system in order to increase applications.

Effect of hydroxyapatite nanoparticles on enamel remineralization and estimation of fissure sealant bond strength to remineralized tooth surfaces: an in vitro study

“…Both processes provide spaces that facilitate resin infiltration and suitable bonding between the resin and tooth. When nano-HA solution was used, the ionic form of Ca and P enters the porous enamel and provides seeds for remineralization [25, 28, 34, 35]. SEM images in the present study showed differences between groups in the degree of penetrations of the resin sealant into these spaces.…”

“…Energy dispersive X-ray spectroscopy is a chemical elemental microanalysis technique to measure mineral content at the ultrastructural level, and has been used to investigate the remineralization capacity of different materials [14, 17, 24]. In the present study we used FESEM instead of SEM to obtain more detailed structural data of higher quality and resolution [35]. Our analysis of EDS data focused on changes in Wt% of Ca, P and the Ca/P ratio, given that these ions are important indicators of the effect of nano-HA on enamel remineralization.…”

The Combination of Electron Microscopy, Raman Microscopy and Energy Dispersive X‐Ray Spectroscopy for the Investigation of Polymeric Materials

“…An additional light source and a camera serve for illuminating and viewing of the sample for the sake of correlation between the region imaged with the SEM and the same ROI for Raman. Since the objective lens is parallel to the electron column, Raman measurement can be performed without any intensity or resolution loss contrariwise to the “on‐axis” setup, where the restrictions of the optics due to the SEM pole piece lead to a diminished Raman signal and resolution, which may handicap analysis . The controlling software Control FIVE from WITec enables the collection of single spectra and additionally enables Raman mapping which means imaging with Raman information in each pixel.…”

Hyphenated analytical techniques for materials characterisation

“…Additionally, for performing simultaneous elemental analysis using X-rays, these hyphenated instruments can have an X-ray spectrometer connected to the SEM, making the technique SEM-EDX/Raman. Guerra and Cardell 2015). Figure 14a shows the study by de la Fuente et al (2016) where the different rust morphologies very close to each other like globular formations (A), thin laminas in the form of flower petals, bird nests or honeycombs (B), and thick laminas in the form of worm nests (C) were imaged by SEM and the integrated Raman set-up was used to get the corresponding Raman spectra from these three areas (Figure 14b-d).…”