Rare-earth modified amorphous carbon films: effects of erbium and gadolinium on the structural evolution and mechanical properties

Tillmann W, Lopes Dias FN, Stangier D, Berndt J, Klemme S, Kesper L, Berges U, Westphal C, Thomann CA, Debus J

Research article (journal)

Abstract

Modifying amorphous carbon (a-C) with rare-earth elements is a highly auspicious concept to synthetize func-tional films with unique characteristics. Among the rare earth elements, Er and Gd demonstrate abundantphysicochemical properties and, hence, are of remarkable interest for the element modification of a-C films.Therefore, Er-containing a-C:Er and Gd-containing a-C:Gd films are prepared in a reactive-free magnetronsputtering process. The a-C:Er and a-C:Gd films have an amount of up to 5 at.-% Er and 4.8 at.-% Gd.High-resolution x-ray photoelectron spectroscopy analyses show the formation of Er–C and Gd–C compo-nents, which rise proportionally with increasing amount of the rare-earth element. The addition of Er and Gdlowers the sp3 content of C bonds. At the highest concentrations of the respective rare-earth elements, the a-C:Erand a-C:Gd films exhibit a reduced sp3 content of 8%. The number and size of sp2‑carbon clusters in theamorphous network are enhanced with increasing amount of Er and Gd which is evaluated by Raman scatteringmeasurements. X-ray diffraction analyses reveal Er and Gd carbide phases, indicating the formation of a nano-composite structure consisting of carbidic nanocrystallites and an a-C network. In nanoindentation tests, the non-modified a-C demonstrates a hardness of (21.7 ± 1.6) GPa and an elastic modulus of (232 ± 10) GPa. Withincreasing Er and Gd contents, the hardness linearly decreases to (16.7 ± 0.9) GPa and (14.8 ± 0.9) GPa,respectively. An analogous behavior is also identified for the elastic modulus. The reduced hardness and elasticmodulus are attributed to the lower sp3 content and the larger number and size of the sp2-hybridized carbonatoms. Additionally, the adhesion was slightly improved by the addition of Er and Gd in comparison to non-modified a-C.

Details zur Publikation

Release year: 2022
Language in which the publication is written: English