Development of plasma imaging for 2D elemental analysis

Maxim Voronov, Volker Hoffmann

In the frames of NIMESA project

Imaging technology for Glow Discharge (GD) Optical Emission Spectrometry (OES) is intensively developing in the last few years because this technique can potentially perform cheap and fast 2D and 3D analyses of solid materials [1]. In plasma the atoms are sputtered from the cathode, excited and emit light. In this way the elemental structure of the cathode may be reproduced in the plasma image. Pulsed Glow Discharge (PGD) is preferred because the sputtered atoms have no time to diffuse far from the initial sputtering point until they are excited and radiate. This increases the spatial resolution of the detected images [2].

Target of the project “International collaboration in chemistry: Novel Instrumentation for Modern Elemental Speciation Analysis” (NIMESA) was the development of an rf PGD imaging system for metallomics and speciation analysis. The samples to analyze are 5x5 cm size thin polyvinylidene fluoride or nitrocellulose membranes, which are results from a 2-dimensional gel electrophoresis on them. The project included an international collaboration of groups in the University of Bloomington (group of G. Hieftje), University of Münster (group of W. Buscher), and IFW Dresden (group of V. Hoffmann).

The development in the group of IFW Dresden included the improvement of a discharge source with a cathode diameter of 8 cm, the development of a new discharge source with a cathode diameter of 4 cm [3], the investigation of electrical properties of PGDs in the different sources [4], the development of a novel acousto-optical spectrometer (AOS) [4] (in collaboration with IfU Diagnostic Systems GmbH) and the development of plasma imaging methods with different discharge systems [3,4]. Additionally some complimentary investigations were carried out: experimental and modelling investigations of pressure waves in PGDs [5,6] including the explanation of the electrical prepeak existing in athe leading edge of PGD [6].

Fig. 1. Left: Sample consisting of copper lines on the surface of Al2O3 plate. Right: plasma image of the sample in rf PGD in the new 4-cm discharge source measured by the developed AOS. Pressure = 6.5 hPa, pulse duration = 50 μs, instantaneous power = 800 W.

  1. G. Gamez, M. Voronov, S.J. Ray, V. Hoffmann, G.M. Hieftje, J. Michler, “Surface elemental mapping via glow discharge optical emission spectroscopy”, Spectrochimica Acta Part B, 70 (2012), 1–9.
  2. M.R. Webb, V. Hoffmann, G.M. Hieftje, “Surface elemental mapping using glow discharge – optical emission spectrometry”, Spectrochimica Acta Part B, 2006, 61, 1279–1284.
  3. M. Voronov, V. Hoffmann, T. Steingrobe, W. Buscher, C. Engelhard, S.J. Ray, G.M. Hieftje, “Development of a new discharge source with a 4-cm cathode size for plasma imaging”, 2013 European Winter Conference on Plasma Spectrochemistry, February 10–15, 2013, Kraków, Poland, oral presentation.
  4. M. Voronov, V. Hoffmann, T. Wallendorf, S. Marke, J. Mönch, C. Engelhard, W. Buscher, S.J. Ray, G.M. Hieftje, “Glow discharge imaging spectroscopy with a novel acousto-optical imaging spectrometer”, J. Anal. At. Spectrom., 2012, 27, 419–425.
  5. M. Voronov, V. Hoffmann, W. Buscher, C. Engelhard, S.J. Ray, G.M. Hieftje, “Pressure waves generated in a Grimm-type pulsed glow discharge source and their influence on discharge parameters”, J. Anal. At. Spectrom., 2011, 26, 811–815.
  6. M. Voronov, V. Hoffmann, W. Buscher, C. Engelhard, S.J. Ray, G.M. Hieftje, “Thermal mechanism for formation of electrical prepeak and pressure waves in a microsecond direct current pulsed glow discharge with a Grimm-type source: a modeling investigation”, J. Anal. At. Spectrom., 2012, 27, 1225–1233.