  High-quality thin polycrystalline films of the heavy-fermion compound CeCu_6
were prepared by sputter deposition. The thicker of these films (with thickness
up to around 200 nm) reproduce the properties of the bulk compound CeCu_6. As
the thickness of the films is decreased, our measurements display strong
deviations from the bulk properties, namely, a suppression of the heavy-fermion
state. We show that possible `external' effects, like disorder, oxidation and
morphology can be excluded and that this size effect is therefore an intrinsic
property of CeCu_6. In addition, we investigate possible scenarios explaining
the size effect, and find that the proximity of CeCu_6 to a quantum phase
transition can account for this striking result.
