Transition metal doping of aluminium nitride (AlN) type thin films was recently employed to increase the piezoelectric constants for application in micro electromechanical systems. YxAl1−xN thin films were synthesized with varying x up to 11.6% by reactive co-sputtering from elemental Al and Y targets. Ab initio density functional theory studies up to x=50% yttrium in YxAl1−xN suggest increasing piezoelectric constants d33 and d31 with increasing yttrium content. Experimental measurements of d33 yield increasing values for increasing yttrium content though, remaining below the prediction from ab initio calculations. Detailed X-ray diffraction and transmission electron microscopy studies prove that, although the thin films are highly c-axis oriented, their nucleation at the Si (100) substrates leads to the formation of an amorphous interface region with increasing Y

The demand to discover new materials is scientifically as well as industrially a continuously present topic, covering all different fields of application. The recent scientific work on thin film materials has shown, that especially for nitride-based protective coatings, computationally-driven understanding and modelling serves as a reliable trend-giver and can be used for target-oriented experiments. In this study, semi-automated density functional theory (DFT) calculations were used, to sweep across transition metal diborides in order to characterize their structure, phase stability and mechanical properties. We show that early transition metal diborides (TiB₂, VB₂, etc.) tend to be chemically more stable in the AlB₂ structure type, whereas late transition metal diborides (WB₂, ReB₂, etc.) are preferably stabilized in the W₂B_5−x structure type. Closely related, we could prove that point defects such as vacancies significantly influence the phase stability and even can reverse the preference for the AlB₂ or W₂B_5−x structure. Furthermore, investigations on the brittle-ductile behavior of the various diborides reveal, that the metastable structures are more ductile than their stable counterparts (WB₂, TcB₂, etc.). To design thin film materials, e.g. ternary or layered systems, this study is important for application oriented coating development to focus experimental studies on the most perspective systems.

While many research activities concentrate on mechanical properties and thermal stabilities of protective thin films, only little is known about their thermal properties being essential for the thermal management in various industrial applications. Based on the 3ω-method, we show the influence of Al and Cr on the temperature dependent thermal conductivity of single-phase cubic structured TiN and single-phase wurtzite structured AlN thin films, respectively, and compare them with the results obtained for CrN thin films. The dc sputtered AlN thin films revealed a highly c-axis oriented growth for deposition temperatures of 250 to 700 °C. Their thermal conductivity was found to increase strongly with the film thickness, indicating progressing crystallization of the interface near amorphous regions during the sputtering process. For the 940 nm AlN film, we found a lower boundary for the thermal conductivity of $55.3\hspace{0.17em}\mathrm{W}\hspace{0.17em}{\mathrm{m}}^{-1}\hspace{0.17em}{\mathrm{K}}^{-1}$ . By the substitution of only 10 at. % Al with Cr, κ significantly reduces to $\sim 5.0\hspace{0.17em}\mathrm{W}\hspace{0.17em}{\mathrm{m}}^{-1}\hspace{0.17em}{\mathrm{K}}^{-1}$ , although the single-phase wurtzite structure is maintained. The single-phase face centered cubic TiN and Ti_0.36Al_0.64N thin films exhibit κ values of $3.1\hspace{0.17em}\mathrm{W}\hspace{0.17em}{\mathrm{m}}^{-1}\hspace{0.17em}{\mathrm{K}}^{-1}$ and $2.5\hspace{0.17em}\mathrm{W}\hspace{0.17em}{\mathrm{m}}^{-1}\hspace{0.17em}{\mathrm{K}}^{-1}$ , respectively, at room temperature. Hence, also here, the substitutional alloying reduces the thermal conductivity, although at a significantly lower level. Single-phase face centered cubic CrN thin films show κ values of $3.6\hspace{0.17em}\mathrm{W}\hspace{0.17em}{\mathrm{m}}^{-1}\hspace{0.17em}{\mathrm{K}}^{-1}$ . For all nitride based thin films investigated, the thermal conductivity slightly increases with increasing temperature between 200 and 330 K. This rather unusual behavior is based on the high defect density (especially point defects) within the thin films prepared by physical vapor deposition.