A comparison of non-pulsed radiofrequency and pulsed radiofrequency glow discharge orthogonal time-of-flight mass spectrometry for analytical purposes

Abstract

The analytical potential of a radiofrequency glow discharge orthogonal time-of-flight mass spectrometer (RFGD-TOFMS) has been evaluated in both pulsed and non-pulsed modes. A certified reference steel was selected for this study. The operating conditions of the GD plasma (pressure and applied power) were optimized in terms of sensitivity. Additionally, duty cycle and pulse width parameters were investigated in the pulsed RF mode. In this case, high analyte ion signals and improved signal to background ratios were measured after the end of the pulse, in the so-called afterglow domain. The analyte ion signals were normalized to sputtering rates to compare different operating conditions. It was found that the sensitivity in the pulsed mode was improved in comparison to the non-pulsed mode; however, the factor of enhancement is element dependent. Moreover, improved analytical performance was obtained in terms of ion separation capabilities as well as in terms of accuracy and precision in the evaluation of the isotopic ratios, using the pulsed RFGD-TOFMS. Additionally, depth profile analyses of a Zn/Ni coating on steel were performed and the non-pulsed and pulsed RFGD-TOFMS analytical performances were compared.

Depth Profile Analysis of Amorphous Silicon Thin Film Solar Cells by Pulsed Radiofrequency Glow Discharge Time of Flight Mass Spectrometry

“…The optimum conditions were 600 Pa and 90 W, similar to previous experiments [21]. As expected [7,22], higher analytical signals were obtained in the afterpeak region of the pulse profile, and so the afterpeak will be the only temporal region in the GD pulses shown throughout this Results and Discussion section.…”

“…On the other hand, although polyatomics attributable to recombination processes in the GD dynamic plasma are typically produced at the end of the afterglow region, the exact shape depends on the particular polyatomic. Finally, for silicon measurement similar results to those previously reported in experimental works carried out in our group were found [7,21]. Although several polyatomic interferences can occur for the three Si isotopes (e.g., Si + was 18.1, which corresponds to an 8% deviation from the natural isotope abundance ratios.…”

“…In order to motorize the beginning of the pulse, a 150 ns delay was employed to ensure a complete acquisition of MS signals between GD pulses. Further details of GD-MS instrument can be found in previous work [7].…”

“…In particular, the use of pulsed GD (PGD) in combination with time of flight mass spectrometry (TOFMS) has proven to be a recent promising approach for the analysis of thin layers [8]. In this vein, it has to be highlighted that the combination of a PGD (generating a dynamic plasma) to TOFMS (fast enough to collect data at different time intervals during the pulse) can allow the reduction or even removal of spectral interferences by integrating a proper pulse interval [7,9]. Spectral interferences removal is crucial for the quantification of some important analytes, such as .…”

“…Moreover, the application of pulses to the GDs gives rise to Electronic supplementary material The online version of this article (doi:10.1007/s13361-014-1022-9) contains supplementary material, which is available to authorized users. higher analytical sensitivity [7], while reducing the thermal stress in the analyzed samples [4]. In pulsed mode, the plasma is a dynamic system as the discharge is switched on and off periodically, thus producing different ionization mechanisms during the pulse period.…”