18 O/ 16 O isotopic separation in anodic tantala films by glow discharge time‐of‐flight mass spectrometry

Glow discharge mass spectrometry has been widely used for trace and ultra‐trace element analysis of high‐purity alloys. A novel pulsed radio frequency glow discharge time‐of‐flight mass spectrometer (rf GD TOFMS) has been developed that retains the pulsed radio frequency analytical ion source to provide ion signal enhancement due to processes involving Penning ionisation. A time‐resolved detection mode has been implemented to sample the afterglow regime of the pulse profile, corresponding to the highest ion signal intensities. Here, the performance of rf GD TOFMS in isotope differentiation is discussed. Anodic tantala films, comprising 18 O‐rich layers of controlled thicknesses and locations, were formed by appropriate combination of anodising of tantalum in electrolytes enriched with 18 O isotopes and of natural O isotopic abundance. Transmission electron microscopy (TEM) and radio frequency glow discharge optical emission spectrometry (rf GD OES) analyses were performed to examine the morphology and elemental distributions of the specimens, while the content of 18 O in the 18 O‐rich layers was determined by elastic recoil detection analysis(ERDA). In pulsed rf GD TOFMS analysis, characteristic ionic species formed in the glow discharge allows differentiation of 18 O‐rich layers. Particularly, the location of 18 O‐rich layers was determined from the 16 O 18 O and Ta 18 O ion signals at masses m / z 34 and 199, respectively. The locations of 18 O‐rich layers in anodic films, controlled by the selected anodising conditions, were probed precisely. The 18 O profiles in anodic tantala were directly compared with those obtained by dual beam time‐of‐flight SIMS. Copyright © 2009 John Wiley & Sons, Ltd.