Delayed extraction for improved resolution of ion/surface collision products by time-of-flight mass spectrometry

Abstract

A time-of-flight mass spectrometer is described which contains a collision surface located behind the reflectron. This collision device uses delayed extraction (DE) to improve the instrument resolving power for ion/surface collision products formed by secondary ion mass spectrometry (SIMS) and surface induced dissociation (SID). Comparisons are made between spectra acquired using delayed and continuous extraction. SIMS spectra were acquired by bombarding a perfluoropolyether (PFPE) surface with 1.5 keV ferrocene molecular ion projectiles. Sputtered fluorocarbon ions were detected with resolving powers ( m/Δ m, FWHM) of 150 and 950 using continuous and delayed extraction, respectively. SID spectra were acquired using naphthalene projectile ions which collide upon the PFPE surface at 50 eV. Naphthalene fragments were detected with a resolving power of 130 using continuous extraction and 350 with DE. For both the high- and low-energy experiments, the instrument resolving power showed a strong dependence on extraction delay. Energy resolved SID mass spectra collected using ferrocene molecular ions show that fragmentation of this projectile is similar to that observed while using other instrument geometries.