Abstract
The angle-resolved composition evolution of Mo-B-C thin films deposited from a Mo2BC compound target was investigated experimentally and theoretically. Depositions were carried out by direct current magnetron sputtering (DCMS) in a pressure range from 0.09 to 0.98 Pa in Ar and Kr. The substrates were placed at specific angles α with respect to the target normal from 0 to ±67.5°. A model based on TRIDYN and SIMTRA was used to calculate the influence of the sputtering gas on the angular distribution function of the sputtered species at the target, their transport through the gas phase, and film composition. Experimental pressure- and sputtering gas-dependent thin film chemical composition data are in good agreement with simulated angle-resolved film composition data. In Ar, the pressure-induced film composition variations at a particular α are within the error of the EDX measurements. On the contrary, an order of magnitude increase in Kr pressure results in an increase of the Mo concentration measured at α = 0° from 36 at.% to 43 at.%. It is shown that the mass ratio between sputtering gas and sputtered species defines the scattering angle within the collision cascades in the target, as well as for the collisions in the gas phase, which in turn defines the angle- and pressure-dependent film compositions.
Highlights
Mo2 BC is classified as a nanolaminated material with an orthorhombic structure [1,2,3]
A model based on TRIDYN and SIMTRA was used to calculate the influence of the sputtering gas on the angular distribution function of the sputtered species at the target, their transport through the gas phase, and film composition
It is shown that the mass ratio between sputtering gas and sputtered species defines the scattering angle within the collision cascades in the target, as well as for the collisions in the gas phase, which in turn defines the angle- and pressure-dependent film compositions
Summary
Mo2 BC is classified as a nanolaminated material with an orthorhombic structure [1,2,3]. It shows a unique combination of mechanical properties, such as an elastic modulus of 470 GPa, a ratio of bulk and shear moduli of 1.73, and a positive Cauchy pressure, which are required for hard and wear-resistant coatings with moderate ductility [3,4]. The lower deposition temperature for the synthesis of a crystalline thin film by HPPMS was attributed to a larger adatom mobility induced by ion bombardment during HPPMS. There are several synthesis approaches for the deposition of compound thin films, such as the utilization of reactive gases [7], co-sputtering from several targets [8,9], or targets with plugs [10].
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