  Epitaxial films of NdFeAsO were grown on GaAs substrates by molecular beam
epitaxy (MBE). All elements including oxygen were supplied from solid sources
using Knudsen cells. The x-ray diffraction pattern of the film prepared with
the optimum growth condition showed no indication of impurity phases. Only
(00l) peaks were observed, indicating that NdFeAsO was grown with the c-axis
perpendicular to the substrate. The window of optimum growth condition was very
narrow, but the NdFeAsO phase was grown with a very good reproducibility.
Despite the absence of any appreciable secondary phase, the resistivity showed
an increase with decreasing temperature.
