Chapter Five - Time-of-Flight Mass Spectrometry and Composition Measurements

Abstract

Time-of-flight mass spectrometry enables the mass over charge ratio of detected ions to be determined by measuring their time of flight from the specimen surface to the detector. The accuracy of composition measurements relies on the ability to detect all the chemical species of the material with the same efficiency, to calculate properly the mass over charge ratio of the evaporated ions from their time of flight and to associate each peak of the mass spectrum obtained to the chemical nature of the detected ions. In the first part, the main quantities related to time-of-flight mass spectrometry will be defined. Then, the phenomena controlling the quality of mass spectra will be highlighted. Hardware methods (reflectron, local electrode), which allow improving the quality of the mass spectrum will be briefly discussed. The measurement of composition based on the time-of-flight mass spectrometry will be presented in the last part of this chapter. This section will review the background subtraction, the definition of intervals (for simple or not trivial cases), the formulation of standard deviation associated to a measurement, and the detection limit of the technique.