Food packaging can consist of many layers of materials each engineered for different purposes. The layers may be very thin, in some cases much less than one micron. Principally composed of polymers layers may be composed of inorganics and inorganic particles may be embedded by design or as artifacts. Analysis for quality assurance or failure analysis is difficult due to the complex nature of the sample. Raman can easily identify the polymers used in these products. Raman mapping has a resolution of one micron or better. SEM imaging easily achieves a resolution of ten nanometers and can distinguish different polymers by their appearance in electron imaging. EDS achieves a spatial resolution of a few tens of nanometers. It can identify all elements present here except hydrogen. Together these techniques provide complementary information. In addition imaging and elemental mapping with SEM/EDS may be faster than Raman mapping. For this work a JEOL JSM‐7610F FESEM equipped with a Thermo Scientific NS7 EDS analyzer and 60mm2 area Ultradry silicon drift detector were used for the SEM/EDS data. A Thermo Scientific DXRxi Raman spectrometer with optical microscope was used for the Raman spectroscopy. The SEM conditions were 10 kV acceleration voltage and about 3 nA beam current. The sample used here is a cross section of a commercially available potato chips bag. The sample was sectioned by a fresh razor blade. For SEM/EDS the sample was carbon coated. Figure 1 compares the results from both SEM/EDS and Raman. In this view the interior of the package is towards the top of the image. The right image shows a Backscatter Electron (BSE) image of the cross section overlaid by elemental maps for Al, Ti, Si and O. Twelve layers were identified by inspection ranging from about 25 microns to approximately 175 nm thick. Some are not visible at this low magnification view. An Al layer about 200 nm thick was seen. A 175 nm thick layer containing S and Cl was found (not shown in the figure). Several layers contained Ti rich particles. Some particles of silicon oxide, possibly artifacts, were seen. The live time for this map was 931 seconds. The image at left in Figure 1 shows the results of the Raman mapping analysis. The identified polymers layers and their thicknesses are labeled. In general the two techniques agree well on the overall composition of the sample. The Raman analysis identifies the polymers making up each of the layers which was not possible by SEM/EDS. It also found the inorganic rutile particles embedded in some of the layers. It did not find any of the sub 200 nm layers seen in the SEM.
Because of the effects of Bragg defocusing, accurate quantitative analysis by WDS can only be done with the electron beam in “spot mode” and with samples at the proper analytical working distance. As a result, WDS X‐ray mapping in the SEM has only achieved simple raw counts mapping of a single element by rastering the beam over the sample. More complicated WDS X‐ray mapping (quantitative or otherwise) has been relegated to the electron microprobe. However, modern SEMs and WDS systems permit quantitative WDS mapping in which a complete WDS quantitative analysis, including background and Φ(ρz) corrections, is done at each pixel. Here, we use WDS quantitative analysis to map the concentration of Hf in a zoned zircon grain. Zircon has emerged as the most critical geochronological tool in the earth sciences. These tiny crystals are truly zircon‐halfnon solid solutions and typically contain 10's of thousands of ppm Hf. Zr/Hf ratios are used as an index of magma evolution and Hf isotopes in zircon are an important recent tool employed to explore magma sources and processes. The ability to map Hf concentrations in detail and to pair this data with geochronology and Hf isotopes will yield important insights into the interpretation of zircon geochronology and the magmas from which zircons crystallize. Quantitative WDS maps were acquired using a Thermo Scientific™ MagnaRay™ Parallel beam WDS spectrometer and a JEOL JSM‐7001F FE‐SEM. Data were processed using the Thermo Scientific™ NORAN™ System 7 microanalysis system. The quantitative WDS map was acquired by automatically slewing the SEM stage over a 106×46 grid while keeping the beam at a fixed position. The resulting map is 106×46 pixels with a 2 µm resolution. All measurements were made using a 15 kV beam accelerating voltage and a focused electron beam that was set to 206 nA at the beginning of the run. The beam current was measured at the beginning of each analysis. Standardization was done using a Hf‐bearing zirconia (for Hf Mα and Zr Lα) and quartz (for Si Kα) on a commercially prepared (SPI), carbon coated mineral standards mount. The O concentration for each analysis was calculated by stoichiometry. The zircon sample was picked from a granite from the Cretaceous Cadiz Valley Batholith in the central Mojave Desert. This grain was mounted in epoxy, polished, and carbon coated. SIMS geochronology and spot trace element analyses were previously conducted on two spots on the grain (Economos, pers. comm.) constraining absolute Hf concentrations and indicating that there are trace or minor concentrations of the REEs, Th, and U, which were not included in these analyses and explain the resulting somewhat low analytical totals. For unknown and standard analyses, Si Kα and Zr Lα were each counted on‐peak for 5 s and off‐peak for 2.5 s (at both low and high positions). Hf Mα was counted until the error (background corrected) from counting statistics was better than 2%, which was typically achieved after ~11 s on‐peak. Off‐peak measurement positions were confirmed to be free of higher order reflections or trace element peaks by inspection of WDS energy scans. 4,876 analyses were acquired, from which Zr, Si, Hf, (Fig. 1) and O quantitative concentrations maps were extracted. The maps reveal that the zircon grain is strongly zoned with respect to the Hf concentration. The full range of WDS mapping (raw counts, net counts, and quantitative) is now available to the SEM user. Additionally, an EDS spectrum could be concurrently acquired with the WDS measurements, meaning that any arrangement of EDS or WDS standards‐based, quantitative stage maps could be extracted. For example, when mapping zircon, Zr and Si could be mapped with EDS and trace elements (e.g., Hf) could be mapped with WDS.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.