Characterization of X-ray Damage to Perfluorosulfonic Acid Using Correlative Microscopy

Abstract

Polymer electrolytes such as perfluorosulfonic acid (PFSA) are key to a variety of electrochemical and clean energy applications. Many analytical techniques for characterizing nanostructured devices containing polymer electrolytes use high-energy electrons or X-rays, which can severely damage soft matter. To better analyze these materials, it is important to understand the chemical, physical, and spectroscopic changes that occur due to radiation damage. Soft X-ray damage to PFSA was characterized using a combination of X-ray microscopy, X-ray absorption spectroscopy, infrared spectroscopy, fluorescence imaging, and atomic force microscopy. X-ray exposure induces substantial and selective loss of fluorine, preferential cleavage of the side chains, and physical ablation of the polymer. The combination of multiple imaging and spectroscopy modalities provides detailed insight into radiation damage mechanisms.

Development of a scanning soft X-ray spectromicroscope to investigate local electronic structures on surfaces and interfaces of advanced materials under conditions ranging from low vacuum to helium atmosphere

“…Similar to the case described in Section 3.4, we deduced the corresponding values using the tabulated photoabsorption cross sections (Henke et al, 1993) for the elements contained in Nafion 117, and then we obtained the photoabsorption cross section Calc: Nafion at 685 eV (705 eV) as 2916 cm 2 g À1 (11320 cm 2 g À1 ) accordingly. By referring the measured optical density of perfluorosulfonic acid (PFSA) at the F 1s peak at 690 eV (Martens et al, 2019), we could estimate the photoabsorption cross section Exp: Nafion at 690 eV to be about 23540 cm 2 g À1 . By using these photoabsorption cross sections and the density of Nafion 117, we calculated the transmission T(E x ) for each excitation energy as shown in Table 1.…”

“…‡ Calculated based on the Beer-Lambert law. § Evaluated from the measured optical density (Martens et al, 2019). } A 50 nm layer thickness was assumed.…”

“…As reported by Yamane et al (2019), we estimated the absorbed dose rate for the first 50 nm-thick layer of the stack to be about 1560 MGy s À1 . As Martens et al (2019) have pointed out, PFSA is very sensitive to X-ray exposure and results in changes to their physical morphology and chemistry even at low nominal dose (5-6 MGy). Thus, if we set the critical absorbed dose for Nafion 117 to be 5 MGy, we need to measure the sample surface for chemical state mapping by quick-scan, i.e.…”

Visualization of elemental distributions and local analysis of element-specific chemical states of an Arachnoidiscus sp. frustule using soft X-ray spectromicroscopy

“…We should note here that radiation damage is always a problem in SX spectromicroscopy, especially for biological and polymer samples. To advance the microspectroscopic study of polymer samples, Wang and Hitchcock et al quantitatively evaluated the radiation-induced damage of polymer samples by using scanning TXM and X-PEEM [35][36][37]. We also study the radiation-induced damage of resinous samples here at SPring-8 [38,39].…”

Additive Nano-Lithography with Focused Soft X-rays: Basics, Challenges, and Opportunities

“…Photo-absorption leads to excitation of electrons and subsequent decay channels that are dominated by the release of lowenergy secondary electrons and, thus, the basic processes of radiation damage are very similar to those in electron beam methods [17,24,79]. Several studies have investigated radiation damage in Xray microscopy with respect to resonant and non-resonant excitation, radiation chemistry and fundamental decomposition principles-mainly for soft organic matter [79][80][81][82][83][84][85][86][87][88][89][90][91][92]. All investigations found that X-ray induced chemistry can be quantitatively correlated with the absorbed dose d that is calculated by [83,87]: An important limitation in X-ray microscopy is radiation damage.…”