Absolute N atom density measurements in an Ar/N₂ Micro-Hollow Cathode Discharge by means of nanosecond Two-Photon Laser Induced Fluorescence

Hexagonal boron nitride (h-BN) has attracted lots of interest because of its high band gap and compatibility with graphene. To provide the N atoms necessary for the deposition of h-BN, a Micro Hollow Cathode Discharge (MHCD) ignited in an Ar/N₂ gas mixture is used to dissociate the strongly bonded N₂ molecules. The MHCD is placed in a reactor with two chambers communicating only through the hole of the MHCD. A pressure differential between the two chambers, with tens of millibars in the high pressure chamber and 1 mbar in the low pressure chamber, creates a plasma jet towards the low pressure side. The absolute density of N atoms is measured by means of nanosecond Two-Photon Laser Induced Fluorescence (TALIF), scanning along the plasma jet axis over 4 cm from the hole. A parametric study is performed, varying the pressure in the high pressure chamber and the percentage of N₂ in the Ar/N₂ gas mixture. These measurements are compared to those previously obtained by the Vacuum Ultra Violet high resolution Fourier Transform spectrometry set-up of the DESIRS beamline at the SOLEIL synchrotron. These measurements are necessary to better understand and optimize the production of N atoms in the MHCD source and their propagation towards the substrate for h-BN deposition.