Voltage Offset Sputtering produces secondary ions with a distribution of energies . The voltage offset technique uses the energy analyzer of a mass spectrometer to select secondary ions from the high range of translational energies. The offset is simply a reduction in acceleration voltage. The energy analyzer deflects lower energy ions by a larger angle. Ions that started with higher translational energies pass through to the mass analyzer.
Voltage offset thus discriminates against molecular interferences relative to atomic species.
The operator selects the energy cutoff point. A 30 V offset would eliminate essentially all of the di and triatomic ions from a typical distribution of energies. There is an analytical trade-off for this reduction of isobaric interferences. Most of the monatomic ions are also eliminated. A 30 V offset typically reduces the monatomic ion intensity by a factor of ten.