The formation of highly coherent nanocrystalline semiconductor films on polycrystalline metal substrates has important practical and theoretical implications. Electron diffraction patterns reveal that quantum dots (QDs) of CdSe grown on a gold film on a mica substrate are coherent over several micrometers in the lateral directions (see Figure), while in the case of a glass substrate there is a complete loss of epitaxy for QD layers not in direct contact with the gold.