Magnetic sector secondary ion mass spectrometry (SIMS) generates isotopic and elemental information from solid surfaces with depth profiling capabilities to measure the concentration of isotopes and elements as a function of depth into the film.
Magnetic sector SIMS uses high energy “primary” ions to bombard the surface and liberate “secondary” ions much like in ToF-SIMS, but the ion beam is operated continuously to maximize duty cycle. The high ion dose is preferred for depth profiling, where the concentration of elements and isotopes are determined as a function of depth. This is one of the very few techniques where the depth resolution can approach 1 nm in inorganic films. The separation of “secondary” ions by mass occurs through a double-focusing lens, first through an electrostatic sector to filter the ions by energy, then through a magnetic sector to filter the ions by mass. Quantification is achieved by applying relative sensitivity factors (determined from standard samples) to convert secondary ion intensities to concentrations. Precision and accuracy better than 1% can be achieved with detection limits in the parts-per-million (ppm) to parts-per-billion (ppb) for most elements in the periodic table.
Creating a test pattern for an effective automated particle mapping capability
Oftentimes, characterization of the size, morphology, and elemental composition of thousands of particles and aerosols become necessary. Automation allows collection of particle data with certain characteristics, such as size, shape, composition, and/or isotopic signature. The SIMS instrument operating in the ion imaging mode SIMS has the sensitivity and image resolution to precisely characterize these particles. However, this ability to characterize particles depend heavily on user setup of the instrument, such as proper image calibration and optimized instrument setup, failure of which may lead to inaccurate results regarding the particles. A standardized test pattern (Figure B) that contains features with known sizes, shapes, height, and composition is currently being produced so that instruments around the world equipped with the automated particle mapping capability can be calibrated to output the same results.
Nanoparticle Detection in Organisms
Release of nanoparticles into the environment presents a potential health hazard that is not yet well understood. Sensitive measurement tools are needed for the assessment of risk and regulatory decision making. SIMS image depth profiling was used to monitor and visualize the uptake of Au nanoparticles by Caenorhabditis elegans (C. elegans), a simple multicellular organism useful as a model in environmental toxicology studies. The high spatial resolution and sensitivity of makes SIMS a powerful tool for the in-situ study of nanoparticle uptake at environmentally relevant concentrations.