Accurate in situ calibration of the energy bandwidth and the zero-energy offset in SIMS analysis using magnetic sector field instruments

Abstract

Instruments used for basic studies in secondary ion mass spectrometry (SIMS) are usually not very well characterized in terms of important experimental parameters like the energy bandwidth and the origin of the energy scale. A proof-of-concept is presented which shows that in magnetic sector field mass spectrometers this kind of information can be obtained rather easily by determining the spectral features of ions generated by primary ion impact on a gas deliberately introduced in the extraction region above the sample. Owing to the negligible kinetic energy of the gas atoms, the measured energy spectrum exhibits a well-defined edge which corresponds to moving the energy bandpass through the gas–solid interface at the target surface. The energy resolution function can be derived as the derivative of the measured data. For high accuracy it is mandatory that the detected ions originate from a volume that is uniformly illuminated by the primary ion beam. The validity of the concept is demonstrated by evaluating recently published literature data. Even though the experiments were performed with a rather large bandwidth, shown to be 30.2 eV, the highly symmetric resolution function allowed the origin of the energy scale to be determined with an accuracy of ±0.2 eV. The potential of the approach needs to be explored in more detail by varying the relevant experimental parameters.