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High-performance neutron supermirrors deposited using an automatic accurate-thickness monitoring technique

High reflectivity neutron mirrors require perfectly smooth, sharp interfaces, uniform layer thicknesses and densities and high stack regularity. For this, the multilayers were deposited on water cooled glass substrates using a D-C low energy (300 - 700 V) triode sputtering unit equipped with an accurate thickness monitoring system. This last one is based on the dependence of the deposition rate on the target current. During deposition, the target current is sampled and converted to a digitalized voltage. This voltage value is then fed to a computer where a real-time numerical integration is made. The target current is integrated and the film thickness is given by the integration time. All sputtering parameters are regulated. A feed- back system between anode current and filament heating supply keeps the plasma current constant. The computer also automatically controls the setting and the timing of the runs. Thicknesses can be controlled to an accuracy of better than 1A. Reproducibility is better than 1%. Therefore, a high stack regularity can be achieved with sharp interfaces as will be shown by the characteristics of a 10[Ni-Ti] neutron monochromator. The experimental and theoretical reflection profiles are in perfect agreement indicating a high stack regularity. This technique is also efficient at producing high reflectivity aperiodic media: supermirrors. A 15[Ni-Ti] supermirror in Hayter-Mook configuration gives a neutron reflectivity of the order of 95% with an effective critical angel of 1.9(theta) cNi. The characteristics of the previous monochromator and supermirror have been measured also using secondary ion mass spectrometry, grazing angle x-rays reflectometry, and resistivity measurements.