Synthesis and Analysis methods
Atomic layer deposition
Atomic layer deposition is a vapor-phase deposition technique in which ultra-thin films are synthesized sub-monolayer by sub-monolayer by repeating two subsequently executed half cycles (Fig. 1). The surface reactions are self-limiting, which leads to excellent growth control (atomic layer precision), uniform deposition over large areas, and conformal deposition in high aspect ratio substrates.
At the institute two ALD systems are present. One home-build thermal ALD system (Fig. 2) and one ALD system from Picosun equipped with a plasma source (Fig. 3).
The thermal ALD system is connected to an UHV system equipped with hemispherical analyzer and a monochromatic X-ray source and He source that allows for, respectively XPS and UPS analyses. The in-line ALD/XPS-UPS system allows for elemental identification and identification of the chemical state of an element during layer-by-layer film growth. An example is shown in Fig. 4. Materials currently under investigation in this system is TiO2 as a hole-conducting corrosion protection layer.
The plasma ALD system is a large scale reactor; it can handle substrates up to 8 inch wafers. The advantage of plasma ALD is that a plasma has higher reactivity towards the surface. This leads to good material properties at lower substrate temperatures and allows to use complex precursors, e.g. for the deposition of ternary metal oxides like BiVO4.