The structure of epitaxial layers of uranium

Epitaxial layers of uranium have been grown on a variety of buffer/seed layers on sapphire substrates by UHV magnetron sputtering and their structure determined using x-ray diffraction. The buffer layers were epitaxial layers of niobium, tungsten and niobium covered by a seed layer of hcp gadolinium, on which uranium layers were grown to a thickness of 600 A. The x-ray diffraction results establish that the α-orthorhombic phase of uranium grows epitaxially in the (110) orientation on the niobium (110) buffer, while on the tungsten (110) buffer the growth planes of the α-uranium were (002) and for the growth on the gadolinium buffer the α-uranium was predominantly (021) oriented. These results show that epitaxial uranium films in selected orientations can be grown by using an appropriate buffer. To our knowledge this is the first report of epitaxial α-uranium films, and it is significant because of the difficulty of growing single crystals of α-uranium due to the occurrence of high temperature structural transformations.