TIME OF FLIGHT SECONDARY-ION MASS SPECTROSCOPY (TOF-SIMS)
Time of flight secondary-ion mass spectroscopy (ToF-SIMS) is a nondestructive surface-specific analytical technique used to determine chemical composition of the outermost 1-2 nm of a sample.
The technique falls within the broad class of secondary-ion mass spectroscopy (SIMS) experiments, which identify ion fragments ablated from a sample surface according to their mass. In a Time-of-Flight (ToF) instrument, a pulsed primary ion beam is rastered over the surface, creating pulses of secondary atomic and molecular ions that separate during their transit through a specialized mass analyzer. Low-mass secondary ions move through the analyzer fastest and arrive at the detector before the higher-mass particles. The measured times-of-flight of the secondary species are then converted to a mass scale, and the resulting mass spectrum – a histogram binned by mass – reflects the chemical makeup of the sample surface, enabling detailed chemical analysis.
ToF-SIMS can be performed on any solid material stable under ultrahigh vacuum conditions. This includes: semiconductor devices, polymers, dried paint and coatings, biomaterials, pharmaceuticals, glasses, papers, polymers and rubbers, ceramics, metals, etc.
It is often used in industry to investigate sources of component failure, in quality control and analyses, process and part development, reverse-engineering and in fundamental research. ToF-SIMS can identify reagents and byproducts involved in sample synthesis, as well as contaminants and adsorbed materials on the surface. It has fast-growing applications in biochemistry and bioengineering for its imaging and chemical mapping capabilities. It is used in a variety of other industries in assaying adhesion, corrosion, diffusion, and segregation of different chemical compounds.
- Identification of trace-level contaminants
- Identification of monomeric or repeating structural chemical units at a sample surface
- Fingerprint identification of polymers
- Spatial maps of the distribution of chemical species on sub-micron scale (lateral resolution < 100 nm in imaging mode)
- Non-quantitative differentiation of different isotopes of an element or compound
- Ultra-thin depth-profiling (depth resolution <2nm)
USES & LIMITATIONS:
- What it is great for:
- ToF-SIMS can identify elemental composition and chemical status at the sample surface
- Instrument is optimally equipped to detect trace metals or compounds with unrivaled mass resolution (up to 10,000 +) with up to 800 ppb sensitivity
- Technique is nondestructive outside of depth-profiling experiments
- Tool accommodates conductive and insulating materials
- Lateral resolution and mass resolution trade-off
- Technique is not quantitative
- Ultra-high vacuum requirement limits utility for volatile samples
- Very rough samples may have compromised data quality
Instruments We Use for ToF-SIMS
ION-TOF Model IV ToF-SIMS
The Model IV ToF-SIMS from Ion-TOF comes equipped with a patented reflectron-type TOF analyzer with non-linear reflection to promote high transmission and highest possible mass resolution in both positive and negative ion experiments.A liquid metal ion gun (LMIG) is used to generate the primary ion beam, and provides multiple options for primary ion species (e.g. Bi1+, Bi3+, Bi7++). The LMIG can also operate in either bunched or un-bunched beam modes, facilitating either maximal mass (spectroscopy) or lateral (imaging) resolution experiments. Depth profiling capability has been added with optional Cs+or O+ sputtering from surface-ionization source components that produce the greatest brightness and lowest chromatic aberration (enabling beam focus below 1µm at the surface). Data are analyzed in the comprehensive ToF-SIMS Analyzer package from Ion-TOF.