Stain-free mapping of polymer-blend morphologies via application of high-voltage STEM-EELS hyperspectral imaging to low-loss spectra

• Published in: Polymer journal Vol. 55; no. 9; pp. 997 - 1006
• Main Authors: Umemoto, Hiroki, Arai, Shigeo, Otobe, Hirohide, Muto, Shunsuke
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2023; Nature Publishing Group
• Subjects: 639/301/357; 639/638/455/958; Absorption spectra; Biomaterials; Bioorganic Chemistry; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Electron beams; Electron energy; Electron energy loss spectroscopy; Electron irradiation; Electrons; High voltages; Hyperspectral imaging; Industrial applications; Morphology; Original Article; Physical properties; Polymer blends; Polymer Sciences; Polymers; Radiation damage; Scanning electron microscopy; Scanning transmission electron microscopy; Spectrum analysis; Surfaces and Interfaces; Thin Films; Transmission electron microscopy
• ISSN: 0032-3896; 1349-0540
• DOI: 10.1038/s41428-023-00786-5

Polymer blends composed of multiple types of polymers are used for various industrial applications; therefore, their morphologies must be understood to predict and improve their physical properties. Herein, we propose a spectral imaging method based on scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy to map polymer morphologies with nanometric resolution as an alternative to the conventional electron staining technique. In particular, the low-loss spectra of the 5–30 eV energy-loss region were measured to minimize electron irradiation damage rather than the core-loss spectra, such as carbon K-shell absorption spectra, which require significantly longer recording times. Medium-voltage (200 kV) and high-voltage (1000 kV) STEM was used at various temperatures to compare the degrees of electron-beam damage resulting from various electron energies and sample temperatures. A multivariate curve resolution technique was used to isolate the constituent spectra and visualize their distributions by distinguishing the characteristic peaks derived from various chemical species. High-voltage STEM was more useful than medium-voltage STEM for analyzing thicker samples while suppressing ionization damage. We propose a method for analyzing the morphology of polymer blends with nanometric resolution using scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopic imaging in the low energy-loss region (5–30 eV). Furthermore, we employed medium-voltage (200 kV) and high-voltage (1000 kV) STEMs at different temperatures to compare the extent of electron-beam damage. This comparison highlighted the utility of the ultra-high voltage electron microscope for suppressing thermal damage and analyzing thicker samples.