High-resolution imaging with SEM/T-SEM, EDX and SAM as a combined methodical approach for morphological and elemental analyses of single engineered nanoparticles

Abstract

The combination of complementary characterization techniques such as SEM (Scanning Electron Microscopy), T-SEM (Scanning Electron Microscopy in Transmission Mode), EDX (Energy Dispersive X-ray Spectroscopy) and SAM (Scanning Auger Microscopy) has been proven to be a powerful and relatively quick characterization strategy for comprehensive morphological and chemical characterization of individual silica and titania nanoparticles. The selected "real life" test materials, silica and titania, are listed in the OECD guidance manual as representative examples because they are often used as commercial nanomaterials. Imaging by high resolution SEM and in the transmission mode by T-SEM allows almost simultaneous surface and in-depth inspection of the same particle using the same instrument. EDX and SAM enable the chemical characterization of bulk and surface of individual nanoparticles. The core-shell properties of silica based materials are addressed as well. Titania nominally coated by silane purchased from an industrial source has been found to be inhomogeneous in terms of chemical composition.

Nanoparticle Characterization: What to Measure?

“…In SEM, lower beam energies are utilized for sample imaging as compared to TEM characterization, which results in a limited penetration depth of the beam and, hence, in being sensitive solely to the specimen surface. However, this superficial interaction also implies that SEM characterization can be used for the analysis of the morphology of “thick” (>100 nm) samples, which is not possible with TEM . The moderate electron energies employed for SEM analysis limit the resolution to typically >2–3 nm, however at the same time drastically decrease the possibility of beam‐induced sample damage compared to TEM.…”

“…In addition, SEM is by far more user‐friendly and enables faster measurements, and features lower acquisition and maintenance costs than TEM. SEM instruments typically also enable investigating the composition of the sample surface by measuring the amount of elastically backscattered electrons, which depends on the interaction between the focused electrons and the sample material, or by detecting x‐ray emission due to e‐beam ionization …”

Analysis of Nanoscale Wear Particles from Lubricated Steel–Steel Contacts

“…Hence, such a sample arrangement, i.e., a very thin and light film substrate, is readily analyzed by high-resolution EDX due to the strong reduction in the influence of the interaction of the PEs in the substrate, typically in the micrometer range down to 10-20 nm [16]. This type of EDX analysis of very small amounts of substance (nanoparticles on electron-transparent foils) becomes possible in conjunction with the use of a sensitive (large-area) EDS detector.…”

Improved Spatial Resolution of EDX/SEM for the Elemental Analysis of Nanoparticles

“…In order to reach the necessary high spatial resolution of the EDX signals, two prerequisites should be fulfilled: the operation of the transmission mode at SEM, i.e. preparation of the (nano)material on TEM grids, as well as the use of highly-sensitive EDS detectors with increased solid angle to compensate for the low signal-to-noise EDX spectra emitted by nanoparticles.Besides pure nanoparticles with a size well below 100 nm, and nanoparticle mixtures, also nanoparticles with a more complicated form and chemical composition such as core-shell nanoparticles are investigated by high-resolution TSEM/EDX [3]. Also the detection of contaminants/impurities becomes possible up to a certain scale.…”

“…Besides pure nanoparticles with a size well below 100 nm, and nanoparticle mixtures, also nanoparticles with a more complicated form and chemical composition such as core-shell nanoparticles are investigated by high-resolution TSEM/EDX [3]. Also the detection of contaminants/impurities becomes possible up to a certain scale.…”