Minimizing damage during FIB sample preparation of soft materials

Abstract

SummaryAlthough focused ion beam (FIB) microscopy has been used successfully for milling patterns and creating ultra-thin electron and soft X-ray transparent sections of polymers and other soft materials, little has been documented regarding FIB-induced damage of these materials beyond qualitative evaluations of microstructure. In this study, we sought to identify steps in the FIB preparation process that can cause changes in chemical composition and bonding in soft materials. The impact of various parameters in the FIB-scanning electron microscope (SEM) sample preparation process, such as final milling voltage, temperature, ion beam overlap and mechanical stability of soft samples, was evaluated using two test-case materials systems: polyacrylamide, a low melting-point polymer, and Wyodak lignite coal, a refractory organic material. We evaluated changes in carbon bonding in the samples using X-ray absorption near-edge structure spectroscopy (XANES) at the carbon K edge and compared these samples with thin sections that had been prepared mechanically using ultramicrotomy. Minor chemical changes were induced in the coal samples during FIB-SEM preparation, and little effect was observed by changing ion-beam parameters. However, polyacrylamide was particularly sensitive to irradiation by the electron beam, which drastically altered the chemistry of the sample, with the primary damage occurring as an increase in the Correspondence to: N. D.

X-ray absorption near edge structure spectroscopic study of Hayabusa category 3 carbonaceous particles

“…Their spectral patterns of aromatic/ olefinic carbon, aromatic ketone, and carboxyl carbon are typical of those observed from terrestrial coal (Cody et al 1998;Bassim et al 2012) and kerogen (Bernard et al 2012) and even extraterrestrial organic solids from chondritic meteorites and IDPs (e.g., Flynn et al 2003;Cody et al 2011). This does not necessarily imply that our category 3 particles are coal or chondritic organics, but the findings do suggest the presence of some form of heterogeneous macromolecule formed through chemical processing in a natural environment.…”

“…Similarly to TEM electron beam damage, ion beam damage from the FIB extraction of the samples is possible, although such damage is expected to be much smaller (Bassim et al 2012). Nevertheless, identical FIB conditions were applied for all the samples in this study, so it is unlikely that spectral differences between the samples could be attributed to the FIB procedure alone.…”

Strategies for transmission electron microscopy specimen preparation of polymer composites

“…The main challenge in preparing a TEM specimen of nanocomposite material is making a thin section of nanocomposite material without causing significant damage in the prepared specimen [13]. The following sections describe the general procedure for preparing a TEM specimen from a polymer nanocomposite material.…”

Recent advances in focused ion beam technology and applications

“…Mitigation strategies include the use of low beam currents, 79 changes in beam overlap during milling, 80 and use of mechanically supportive frames to maintain mechanical rigidity. 81 It was also shown that electron beam imaging during preparation of soft materials may chemically modify the structures.…”