Improvement of the analytical performance in RF-GD-OES for non-conductive materials by means of thin conductive layer deposition and the presence of a magnetic field

Abstract

Radiofrequency glow discharge coupled to optical emission spectrometry (RF-GD-OES) is a wellknown analytical technique for bulk, surface and depth profiling and can be applied in the direct analysis of conductors, semiconductors and non-conductors, however for the latter case limits still exist. The problem is related to the low power deposited in the plasma due to a voltage drop developing inside the material. The voltage transfer coefficient, defined as the ratio between the peak voltage at the front and at the back of the sample. This depends on the sample capacitance, which itself is dependant on the material surface, thickness and permittivity. In order to improve the analysis of such non-conductive materials, thin conductive top layers are deposited on both sides of the sample which increases their voltage transfer coefficient. The aim of this work is to study the influence of these thin layers on the optical and electrical signals measured for the samples with varying thickness and diameter. Additionally, the influence of applying a magnetic field during the GD analysis has been evaluated as an attractive option in order to obtain higher sputtering rates, together with better ionisation and excitation efficiencies and as a consequence give improved emission intensities.

Signal Enhancement with Stacked Magnets for High-Resolution Radio Frequency Glow Discharge Mass Spectrometry

“…17,18,22 Here, we demonstrate the effects of the magnetic field strength under different experiment conditions, namely, the discharge pressure and the rfpower.…”

“…10,16 For a mass spectrometry, the sputtering rate and ionization efficiency play important roles in achieving the optimum analytical performance, 16 which could also be influenced by other factors such as gas pressure, rf-power, sample thickness, lattice binding energy of sample and so on. 17,18 With radio frequency (rf) discharges, nonconducting materials can be analyzed directly. However, the generator power is usually coupled capacitive to the plasma, so that the plasma power decreases with increasing thickness, thus sputtering rates, sensitivities and signal intensity decrease at the same time.…”

Atomic spectrometry update. Industrial analysis: metals, chemicals and advanced materials

“…In one, they discussed the use of pulsed RF-GD-OES for depth-profile quantification of metallic coatings. 303 In addition, the authors determined the effect of applying a magnetic field during the GD analysis and found that it offered the advantages of increased sputtering rates, better ionisation and better excitation efficiencies and, hence, an overall improvement in emission intensity was achieved. A comparison of emission intensities and emission yield parameters was made with the continuous mode of operation.…”

An improved analytical performance of magnetically boosted radiofrequency glow discharge

“…[5][6][7][8][9][10] Additionally, several methodological strategies, such as use of plasma gas mixtures, deposition of conductive thin layers, or magnetically boosted glow discharges, have been investigated using rf-GD spectroscopy to further enhance the analytical capabilities of this technique. [11][12][13][14][15] Particularly, in magnetically boosted GD, the combination of an external magnetic field and the electric field, applied between the anode and the cathode, causes modifications in the charged particle motion within the GD plasma. At the relatively low magnetic fields employed in glow discharge spectroscopy, only electron trajectories are significantly affected as ions are much heavier and their paths more difficult to alter.…”

“…26,27 The magnetic field is usually applied by means of permanent magnets placed behind the sample, which implies that the magnetic field strength generated in the GD plasma is a function of the sample thickness. 11,26 Additionally, the application of axial magnetic fields with this experimental configuration significantly affects the produced crater shapes, which are more crowned, in detriment to the achieved depth resolution. 23,27 On the other hand, in transverse configuration the magnetic field is applied parallel to the sample surface and perpendicular to the axis along the cylindrical anode.…”