Carbon Coated Gas Electron Multipliers
  Gas electron multipliers (GEMs) have been overcoated with a high resistivity 10e14 - 10e15 Ohms / square amorphous carbon layer. The coating avoids charging up of the holes and provides a constant gain immediately after switching on independent of the rate. The gain uniformity across the GEM is improved. Coating opens the possibility to produce thick GEMs of very high gain. 
S. Beirle, U. Werthenbach, G. Zech, T. Zeuner