**9. Influence of nitrogen and oxygen on mechanical properties**

The influence of the nitrogen admixture on the elastic modulus of the deposited films was measured by nanoindentation.

The films that were deposited with additional nitrogen are less stiff compared to films where no additional nitrogen was used. The elastic modulus of the UNCD films deposited with 2.5 % nitrogen in the plasma was measured to be around 370 GPa and increasing the nitrogen admixture even higher to 7.5 % in the plasma resulted in UNCD films with values for the elastic modulus as low as 100 GPa. Thus it was shown that UNCD films deposited with additional nitrogen are unsuitable for the application as SAW device.

An opposite trend can be found when oxygen is used as admixture to the process gas. It was shown that the Young's modulus can be increased up to 950 GPa (ca. 75 % of single crystalline diamond). The reason can be found in the effective etching of sp2-bonded carbon by the oxygen in the plasma and thus bigger diamond crystals (Shen et. al., 2006).
