Surface and trace analysis by high-resolution time-of-flight secondary ion mass spectrometry

Abstract

We have developed a high-performance time-of-flight secondary ion mass spectrometer that consists of an electron impact ion gun, a pulsed 90°-deflection producing mass separated subnanosecond ion pulses, a single-stage reflectron time-of-flight analyzer, a postacceleration detector, and an 800-MHz time-to-digital converter. This instrument offers a unique combination of high mass resolution, high transmission, and high-mass range, which opens new fields of application. A charge compensation system with a pulsed low-energy electron gun and a pulsed extraction for the secondary ions provides the analysis of insulating materials also. The fields of application range from trace analysis of elements and molecules in the uppermost monolayer of a solid, the characterization of polymer materials, study of surface reactions, and contaminations on all kind of materials (metals, ceramics, polymers, etc.), to the identification and structure analysis of biomolecules with sensitivities in the subpicomole range which is important for a wide variety of applications in life sciences. The performance of the instrument, regarding sensitivity, mass resolution, exact mass measurement, mass range, dynamic range, and abundance sensitivity, is discussed. Characteristic examples as trace element analysis on Si and GaAs wafers, and structural and surface investigations of polymers are presented.