  Thin films based on silicon and transition-metal elements dominate the
semiconducting industry and are ubiquitous in all modern devices. Films have
also been produced in the rare-earth series of elements for both research and
specialized applications. Thin films of uranium and uranium dioxide were
fabricated in the 1960s and 1970s, but there was little sustained effort until
the early 2000s. Significant programmes started at Oxford University
(transferring to Bristol University in 2011), and Los Alamos National
Laboratory (LANL) in New Mexico, USA. In this review we cover the work that has
been published over the last ~20 years with these materials. Important
breakthroughs occurred with the fabrication of epitaxial thin films of
initially uranium metal and UO2, but more recently of many other uranium
compounds and alloys. These have led to a number of different experiments that
are reviewed, as well as some important trends. The interaction with the
substrate leads to differing strain and hence changes in properties. An
important advantage is that epitaxial films can often be made of materials that
are impossible to produce as bulk single crystals. Examples are U3O8, U2N3 and
alloys of U-Mo, which form in a modified bcc structure. Epitaxial films may
also be used in applied research. They represent excellent surfaces, and it is
at the surfaces that most of the important reactions occur in the nuclear fuel
cycle. For example, the fuel-cladding interactions, and the dissolution of fuel
by water in the long-term storage of spent fuel. To conclude, we discuss
possible future prospects, examples include bilayers containing uranium for
spintronics, and superlattices that could be used in heterostructures. Such
applications will require a more detailed knowledge of the interface
interactions in these systems, and this is an important direction for future
research.
