Storage of ultracold neutrons in a volume coated with diamondlike carbon

Ultracold neutrons (UCN) with energy up to the Fermi potential were stored for the first time in a volume coated with diamondlike carbon. As a function of the UCN energy and wall temperature of the storage volume, we measured the wall loss parameter eta and obtained eta=(3.1 +/- 0.9)center dot 10(-4) at T=290 K and eta=(1.8 +/- 0.2)center dot 10(-4) at T=115 K.