BORON NITRIDE MATERIALS FOR TRIBOLOGICAL AND HIGH TEMPERATURE HIGH POWER DEVICES

摘要

Boron nitride thin films on sapphire substrates were investigated for their tribological and optoelectronic applications. A gridless end Hall gun source and an electron cyclotron resonance (ECR) source were used for nitrogen species delivery while pure boron was evaporated at a rate of 0.2 A/s. The surface stability of these thin films was investigated by high temperature annealing. Atomic force microscopy (AFM), friction force microscopy (FEM), and Knoop microhardness measurements were performed on the materials in order to assess their merits as tribological coatings. Finally, BN thin films were subjected to laser transient photoconductivity (TPC) experiments to determine both their optical laser damage threshold as well as their photoconductivity characteristics. For both single-pulse shot and multiple-pulse irradiation regimes, preliminary tests showed the higher the ion beam current used during growth (70-150 mA), the higher the optical damage threshold. The lower damage threshold was typical of BN films grown using an ECR plasma source and was measured to be in the range of approx 50 MW/cm~2. Optical damage of films grown at ion beam currents above 100 mA was not observed at laser intensities up to few hundreds MW/cm~2. A multiphoton excitation technique was utilized to obtain PC signals from this wide band gap material and preliminary results show that unusual PC voltage amplitudes as high as 0.5 V were observed.