Magnetron sputtering of coatings with a composition gradient
Sputtering coating with a gradient
Magnetron sputtering, the working-horse technology adopted by glass industry, is used on a small experimental scale in our lab. By placing the sputter gun under an angle with the substrate, more atoms are deposited close to the gun causing a thickness gradient. By using multiple guns at the same time (co-sputtering) and tuning gun power of the individual guns, a wide composition and doping ion concentration gradient can be made in one deposition. By mixing reactive gasses like O2 and N2 with the Ar plasma, oxides or nitrides can be obtained.
Position dependent composition
Coatings can be analyzed by energy dispersive x-ray spectroscopy to determine the elemental composition as a function of position in terms of the % of the total number of elements. The example to the right the Si, Al and Eu compositions are shown in the contour plots, showing equi-concentration lines as a function of position on the substrate. The composition range in this single films is finally displayed in the triangular ternary phase diagram.
Position dependent properties
We have developed a fully automated experimental facility that can measure crucial optical properties as a function of position on the substrate like emission-, excitation-, decay- and transmission spectra on for example a grid of 20x20 locations. Each measurement on a single location constitutes a whole spectrum as shown here for a Sm2+ doped SiAlO coating. It shows typical 4f-4f and 5d-4f emission transition. Some Sm3+ emission can also be seen. Their ratio can for example be studied as a function of composition.
The recorded composition determined by EDX and properties like the emission spectra, can be combined in so-called phase diagrams that directly link properties to composition instead of position on the substrate. The figure to the right shows how the Sm2+ emission intensity changes with material composition. This technique is useful for efficient material optimization but also new material discovery.