Aouadi S M, Zhang Y, Basnyat P, Stadler S, Filip P, Williams M, Hilfiker J N, Singh N, Woollam J A
Department of Physics, Southern Illinois University, Carbondale, IL 62901-4401, USA.
J Phys Condens Matter. 2006 Feb 15;18(6):1977-86. doi: 10.1088/0953-8984/18/6/013. Epub 2006 Jan 25.
The structural, electronic, optical, and mechanical properties of stoichiometric TaC(x)N(y = 1-x) were simulated using an ab initio calculation based on density functional theory (DFT) within the generalized gradient approximation. The calculations revealed the theoretical lattice parameter, density of states, refractive index, and elastic constants as a function of carbon and nitrogen content. TaC(x)N(y) films were subsequently produced on Si wafers using unbalanced magnetron sputtering. The structural, optical, and mechanical properties were measured using x-ray diffraction/transmission electron microscopy, vacuum ultraviolet spectroscopic ellipsometry, and nanoindentation, respectively. The computational and experimental properties were compared. The lattice parameter, the energy of the 2p bands in the density of states, and the energy of the interband transitions were found to decrease with increasing C content. No significant changes in the elastic constants were observed as a result of substituting N atoms with C atoms. The hardness and the elastic modulus were in the 40 and 380 GPa range, respectively. The experimental Young's modulus was much smaller than the computational one and this discrepancy was attributed to the nanocrystalline nature of the films. Also, the elastic constants were found to decrease dramatically for over-stoichiometric films.
基于广义梯度近似下的密度泛函理论（DFT），采用从头算方法模拟了化学计量比TaC(x)N(y = 1 - x)的结构、电子、光学和力学性能。计算揭示了理论晶格参数、态密度、折射率和弹性常数随碳和氮含量的变化关系。随后，利用非平衡磁控溅射在硅片上制备了TaC(x)N(y)薄膜。分别使用X射线衍射/透射电子显微镜、真空紫外光谱椭偏仪和纳米压痕法测量了其结构、光学和力学性能。对计算结果和实验结果进行了比较。发现晶格参数、态密度中2p带的能量以及带间跃迁的能量随碳含量的增加而降低。用碳原子取代氮原子后，未观察到弹性常数有显著变化。硬度和弹性模量分别在约40 GPa和380 GPa范围内。实验测得的杨氏模量远小于计算值，这种差异归因于薄膜的纳米晶性质。此外，还发现对于过化学计量比的薄膜，弹性常数会急剧下降。
