Clean structures are fabricated in ultrahigh vacuum conditions by evaporation through a shadow mask, avoiding
contamination by resist, chemicals or exposure to air. Moving the shadow mask with nanometer precision during the
growth of the structures gives additional freedom in determining the lateral shape and the thickness profile. Different
materials can easily be combined and chosen from a large range of metals, semiconductors or insulators. In-situ treated
surfaces or, conversely, ex-situ pre-fabricated samples can be used as substrates.