Laser Induced Mass Analysis LIMA

In the LIMA technique, the surface of the sample is subjected to a pulsed UV laser which is sufficiently energetic to volatilise a small volume (about 1 im cube) of material. The ionised fragments in this volume are then separated and identified by means of a time of flight mass spectrometer. Both negative and positive fragment data can be obtained. 

The analysis area in a LIMA experiment is typically 1-2 pm, the analysis depth 0.25-0.5 pm and the detection limit 10-100 ppm. The technique has the ability to detect all of the elements in a qualitative way. 

The technique is very useful for determining compounds on the surface by means of these elements and molecule fragments, but it is very sensitive, and care must be taken to ensure that the surface is not contaminated (e.g., by handling without gloves) and that the representative control samples are available to assist in the interpretation of the data. 

Its sensitivity and surface specificity make it ideal in the detection of very low levels of contamination/ modification. For example, the detection of a monolayer of silicone contamination of a plastic part that was hampering the wetting of a paint. It can also be used to analyse particulate impurities, fibres and defects in surface coatings. 

LIMA is also referred to as laser microprobe mass spectroscopy (LAMMS). 

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Laser-induced mass analysis (LIMA) This provides information on elements and various species in a single particle. 

Surface analysis techniques such as secondary ion mass spectrometry (SIMS), laser induced mass analysis (LIMA) and X-ray photoelectron spectroscopy (XPS) are used for failure diagnosis work associated with such things as poor bonding to substrates and for surface characterisation work. 

X-ray Photoelectron Spectroscopy (XPS) and Laser Ion Induced Mass Analysis (LIMA) were used to investigate samples of catalyst A. These techniques can show the extent of potassium and lithium distribution within individual catalyst pellets. Samples that had been subjected to 50,100, and 1000 hours of steam reforming in a molten carbonate environment were analysed. A fresh sample of the catalyst was also examined for purposes of comparison. 

A laser-induced ToF mass spectrometer (LIMA-2A) was manufactured by Cambridge Mass Spectrometry Ltd., Cambridge, UK, for micro local analysis and was used to analyze thin sections of biological samples in the transmission mode or bulk material in the reflection mode.150,151 Typical LIMA applications in microelectronics include identification of impurities in dielectrics, microlocal analysis, depth profiling, thick film analysis and investigations on hybrid circuits. 

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