Optical reflectivity and hardness improvement of hafnium nitride films via tantalum alloying

It is found that incorporation oftantalum in a hafnium nitridefilm induces a tunable opticalreflectivity and improves thehardness. The underlying mechanism can be illustrated by a combination of experiments andfirst-principles calculations. It is shown that the evolution of opticalreflectivity and the increase inhardness arise from the formation of Hf1 −xTaxNsolid solutions and the resulting changes in the electronic structure. The increase in infrared reflectance originates from the increase in concentration of freeelectrons (n) becauseTa (d3s2) has one more valenceelectron than Hf (d2s2). The sharp blue-shift in cutoff wavelength is attributed to the increase inn and the appearance oft2g→eg interband absorption. These results suggest that alloying of a second transition metal renders an effective avenue to improve simultaneously the optical and mechanical properties of transition metal nitridefilms. This opens up a door in preparing high-reflectance yet hardfilms.

Source: Applied Physics Letters - December 5, 2016 Category: Physics Authors: Zhiqing Gu, Haihua Huang, Sam Zhang, Xiaoyi Wang, Jing Gao, Lei Zhao, Weitao Zheng and Chaoquan Hu Source Type: research