Doping and alloying amorphous carbon (a-C) thin films are ways to tailor their mechanical and tribological properties. However, few studies have focused on doping/alloying with rare-earth elements. This study shows that a-C films containing europium (Eu) or gadolinium (Gd) can have promising tribological properties.
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Dopants and alloying elements are commonly introduced in amorphous carbon (a-C) thin-film materials to tailor the mechanical and tribological properties. While most studies have focused on doping and/or alloying a-C coatings with metals and metalloids, the introduction of rare-earth elements into the a-C matrix is largely unexplored. Here, the friction response of a-C films containing europium ([Eu] = (2.4±0.1) at.%) or gadolinium ([Gd] = (2.3±0.1) at.%) was evaluated as a function of applied normal load in open air and at room temperature. The friction results indicated that alloying a-C films with Gd or Eu leads to a significant reduction of the shear strength of the sliding interfaces. To shed light on the origin of the promising tribological properties of Eu- and Gd-alloyed a-C films, near-edge X-ray absorption fine structure (NEXAFS) spectromicroscopy measurements were performed. The surface-analytical results indicated that no stress-assisted sp3-to-sp2 rehybridization of carbon atoms was induced by the sliding process in the near-surface region of undoped a-C, while the amount of sp2-bonded carbon increased in Eu- and Gd-alloyed a-C films. Based on the spectroscopic results, a model is proposed for the effect of introduction of Gd and Eu into the a-C matrix on the resulting tribological response.
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Filippo Mangolini, Ph.D., Associate Professor Cockrell Family Fellowship