Matthée, T.T.MatthéeSchäfer, L.L.SchäferSchmidt, A.A.SchmidtKlages, C.-P.C.-P.Klages2022-03-032022-03-031997https://publica.fraunhofer.de/handle/publica/19055710.1016/S0925-9635(96)00609-7Insulating diamond layers of 5-20 mm thickness are deposited by hot filament-chemical vapor deposition (HF-CVD) on tungsten electrodes. These electrodes of about 150 mm length and 2 mm diameter are used for level sensors in hostile environments like water at 350°C. The increase of the resistivity due to N-doping is compared to resistivity of undoped layers. Studies of the homogeneity and quality of the layers are performed by scanning electron microscopy (SEM) and micro-Raman spectroscopy. The electrical characterization is performed by impedance spectroscopy at room temperature and at elevated temperatures up to 83°C in aqueous NaCl solution (3%). The reduction of pores and pin holes is important in arriving at high values of electrical impedance (|Z| > 1 MO, 30 Hz), which is essential for a level sensor working in poorly conductive liquids (swater ≈ 0.1 mS cm−1). Several cleaning procedures are necessary to reduce the pore density from about 1 per 20 mm2 to less than 1 per 1000 mm2. Highest resistivity values of N-doped diamond layers, averaged over the electrode length and film thickness, amounted to 5 × 1012O· cm.endiamond layerhostile environmentLevel SensorCVDdiamondcoatingelectrical propertyimpedance spectroscopy667553journal article