3D Time-of-flight Secondary Ion Mass Spectrometry Research Articles

Detection of ZrO₂ Nanoparticles in Lung Tissue Sections by Time-of-Flight Secondary Ion Mass Spectrometry and Ion Beam Microscopy.

The increasing use of nanoparticles (NP) in commercial products requires elaborated techniques to detect NP in the tissue of exposed organisms. However, due to the low amount of material, the detection and exact localization of NP within tissue sections is demanding. In this respect, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Ion Beam Microscopy (IBM) are promising techniques, because they both offer sub-micron lateral resolutions along with high sensitivities. Here, we compare the performance of the non-material-consumptive IBM and material-consumptive ToF-SIMS for the detection of ZrO2 NP (primary size 9–10 nm) in rat lung tissue. Unfixed or methanol-fixed air-dried cryo-sections were subjected to IBM using proton beam scanning or to three-dimensional ToF-SIMS (3D ToF-SIMS) using either oxygen or argon gas cluster ion beams for complete sample sputtering. Some sample sites were analyzed first by IBM and subsequently by 3D ToF-SIMS, to compare results from exactly the same site. Both techniques revealed that ZrO2 NP particles occurred mostly agglomerated in phagocytic cells with only small quantities being associated to the lung epithelium, with Zr, S, and P colocalized within the same biological structures. However, while IBM provided quantitative information on element distribution, 3D ToF-SIMS delivered a higher lateral resolution and a lower limit of detection under these conditions. We, therefore, conclude that 3D ToF-SIMS, although not yet a quantitative technique, is a highly valuable tool for the detection of NP in biological tissue.

Role of Segregated Iron at Grain Boundaries on Mg Corrosion

To elucidate the role of noble metal impurities on corrosion of Mg, 3D time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging in combination with X-ray photoelectron spectroscopy and optical microscopy measurements were carried out on Mg samples (99.9%) before and after Mg polarization at EOCP+0.5 V in 0.1 M NaCl. A significant segregation of Fe (and of Mn and Al) metallic impurities at grain boundaries (GBs) was observed on the Mg surface by 3D ToF-SIMS. A 3-step mechanism of Mg corrosion was proposed, including a catalytic effect of Fe segregated at the GBs on the hydrogen evolution reaction (HER). In the 1st stage, the initiation of Mg corrosion is accompanied by the HER occurring over Fe impurities segregated at GBs leading to formation of small circular defects, and propagation with occurrence of dark filiform-like pattern corrosion enriched in Cl−. In the 2nd stage, segregated Fe metallic particles are released by Mg matrix undermining, and are dissolved into Fe2+ ions and in the 3rd stage a redeposition of Fe in the clear areas of Mg surfaces, corresponding to areas with low concentration of Cl−, takes place.

Three-dimensional failure analysis of high power semiconductor laser diodes operated in vacuum

The damaged region of a semiconductor laser diode that failed in a vacuum environment was analyzed using focused ion beam (FIB) serial sectioning, time-of-flight secondary ion mass spectrometry (ToF-SIMS), high resolution transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), energy dispersive x-ray spectroscopy (EDS), and nanodiffraction. The FIB nanotomography models and the TEM cross sections show a damage structure extending deep into the core and originating at the diode/antireflective (AR) coating interface. Nanocrystalline gold was detected at this interface using both TEM diffraction and EDS, and the localization of gold along the core at the diode/AR interface was corroborated using 3D ToF-SIMS. A thinning of the AR coating above the failure site was observed by TEM with a corresponding increase in carbon content on the AR surface detected with EELS. It is suggested that failure proceeded by pyrolysis of adsorbed hydrocarbons on the AR coating, which, in the presence of a high optical flux, contributed to carbothermal reduction of the AR coating. As the optical flux increased, thermal gradients facilitate metal migration, leading to larger gold clusters. These clusters are sites for deep level traps and may promote catalytic reactions.