Chenglong Yang

Microsecond-pulsed Grimm glow discharge as a source for time-of-flight mass spectrometry

A Grimm-type glow discharge ion source has been constructed for a time-of-flight mass spectrometer (TOF-MS). This source was operated in the microsecond-pulsed mode. Special features of pulsed Grimm GD-TOF-MS are described, including resolving power, stability, sensitivity and the temporal separation of discharge gas species and analyte ions. The analytical characteristics of a pulsed Grimm GD-TOF-MS system were also evaluated. These preliminary studies demonstrate the potential of this technique for the elemental analysis for solids.

A pulsed Grimm glow discharge as an atomic emission source

A high voltage, microsecond regime pulse dc glow discharge was applied to a standard Grimm source on a modified LECO SA-2000 direct reader spectrometer and to a duplicate Grimm source coupled to a scanning monochromator. The effects of experimental conditions, including pulse voltage, pulse frequency, pulse width and Ar pressure, on Cu atomic and ionic emission intensities were examined and compared with continuous discharge results. The pulsed Grimm source has a higher sputtering rate, greater signal intensity and lower detection limits. The pulsed signal for atomic lines shows a different temporal response from ionic lines. Pulsed Grimm GD-AES also offers control features advantageous in the measurement of thin surface layers.

Microsecond pulsed glow discharge optical emission spectrometry — investigation of temporal emission characteristics

A high voltage, microsecond regime, pulsed glow discharge has been applied to a standard Grimm type source on a LECO SA-2000 multichannel optical spectrometer. The spectrometer system has been equipped with fast time-resolved electronics in order to study the temporal response of the elemental emission lines. The aim of the research was to investigate possible gains in signal-to-background ratio (S/B) and detection limits compared to a conventional direct current (dc) mode of operation. It was found that the high instantaneous pulse power in itself gives approximately a factor 2 increase in S/B. By utilising time-resolved detection, gains in the range 5–10 are achieved. For nitrogen, it was found that the background from leakage of air could be reduced to approximately 1/3 compared with the dc mode. Another interesting observation was that certain nearly non-conducting materials, which cannot be run in dc mode, could be run in the microsecond pulsed mode.

Quantitative depth analysis using microsecond pulsed glow discharge atomic emission spectrometry

The development of microsecond pulsed glow discharge atomic emission spectrometry (GD-AES) for quantitative depth profile analysis is described. The quantification method, which is based on sputtering rates, has been previously applied to depth analysis employing a dc glow discharge source. Optimal conditions of the glow discharge source, including voltage, pressure, pulse width and pulse frequency, are utilized in order to give the best depth resolution. Pulsed operation of the glow discharge affords the advantages of two additional parameters, pulse width and pulse frequency, which allow better control over the amount of sample being removed via cathodic sputtering. This allows thin layer samples to be analyzed that are very difficult using the dc source. Under the optimized parameters, thin coatings of varying depths of Cu deposited on steel were quantified. The quantitative method predicted Cu deposition depths in accord with the nominal depths.

Depth profiling of thin films with pulsed glow discharge atomic emission spectrometry.

The application of microsecond pulsed Grimm glow discharge atomic emission spectrometry for depth profiling of thin films is examined. The effects of pulsed conditions including pulse voltage, pulse frequency, pulse width, and Ar pressure on depth profiling performance were characterized for Zn and Cu coatings on steel. Using optimized conditions, linear calibration curves of coating thickness for Zn (6.1-26.9 μm) and Cu (50-500 nm) on steel were achieved. A precision of 2-5% relative standard deviation was determined. An ultrathin coating of Cu (10 nm) on steel was also measured by this technique.

A double pulse method for glow discharge enhancement

The already established technique of pulsed glow discharge spectroscopy is extended in these studies to the application of a second pulse applied at a variable delay after a first pulse. The net discharge then consists of a series of double pulses in which each second pulse in the series enhances the emission intensity of the analyte atoms produced by the first pulse. A copper hollow cathode is used to show high emission enhancement for atom and ion lines of the sputtered species and the neon discharge gas species. The technique shows promise for further study by both atomic emission and mass spectrometry.