Time of flight secondary ion mass spectrometry is a technique that provides trace molecular analysis of the top surface of various materials. It detects and analyzes low concentrations of molecules and elements at ppm levels. Researchers can use it to understand surface chemistry in organic and inorganic samples. And that’s not all; there is a lot you need to know about ToF-SIMS.
How does ToF-SIMS work?
ToF-SIMS Analysis uses a pulsed ion beam to sputter the sample’s surface. The process produces secondary particles like ions, electrons and neutral particles from the top atomic monolayers. The secondary ions are then collected and accelerated into a flight tube. Measuring their time of flight helps in identifying their mass.
Measuring flight time in nanoseconds allows ToF-SIMS to produce high-mass resolution spectra and identify mass differences as tiny as o.02 atomic mass units. It is surface sensitive, and it’s an effective way to make a relative comparison of a specific element in different samples. Also, ToF-SIMS analysis provides chemical information because it can capture all the ions produced during sputtering.
What is sputtering in ToF-SIMS?
Sputtering is when ions bombard the sample, causing atoms to be knocked off. Bombarding at once makes it difficult for researchers to detect signals in their samples.
How to increase resolution in ToF-SIMS
Using a liquid metal ion source is one of the effective ways to increase ToF-SIMS. It allows ions to be accelerated at lower voltages, meaning the sample won’t require much energy for sputtering. It helps researchers to detect signals from different elements.
Strengths of ToF-SIMS
- It surveys all masses on material surfaces, including single ions, individual isotopes, and molecular compounds.
- The ability for chemical and elemental mapping on a sub-micron scale
- The high mass resolution enables analyzers to distinguish species of similar nominal mass.
- High sensitivity for trace elements and compounds
- Great surface analysis of insulating and conducting samples
- Depth profiling
- Non-destructive analysis
- Retrospective analysis
Limitations of ToF-SIMS
- Sample preparations are prone to contamination
- Practical difficulties
- It does not produce quantitative analysis
- Too much data: any pixel of an image contains a complete mass spectrum for that point. Therefore, you’ll take hours or weeks to analyze the single data set comprehensively.
- Image shift when changing from positive to negative ion data collection mode. The shift makes it difficult to collect positive and negative ion data in the same spot.
- It has limited optical capabilities that make it challenging to find grains or specific regions of interest for analysis.
Mass range of ToF-SIMS
The mass range of the ToF analyzer is unlimited. Again, it has low fluency of primary ion beam, which favors the emission of intact molecular ions and high molecular weight. However, you can only observe masses below 2000 Daltons in practice. That’s due to intermolecular interactions of atoms in your sample that prevent the ejection of large, intact molecules.
Application of ToF-SIMS In automotive
The automotive industry uses various elaborately processed materials such as plastics, glasses, electronic components, etc. ToF-SIMS analysis help solve issues such as:
- Deposits on components of the injection system
- Failure of servomotors
- Lubricant issues
- Plastic composition
Various industries, such as electronics, semiconductors, solar, paints, coating, polymers, and automotive, benefit from ToF-SIMS analysis. The technique has been instrumental in solving the industries’ issues and offering long-term solutions.