X-ray diffraction measurements have been made in real time during depo
sition of the rare earth Gd on the non-magnetic substrate Mo(110). For
the clean surface at 300 K, the variation of the specularly reflected
X-ray intensity with deposition time is consistent with the completio
n of a close-packed monolayer followed by increasingly disordered, mul
tilayer, growth. Exposure of the Mo surface to 0.25 langmuir of oxygen
prior to Gd deposition produced better defined intensity oscillations
characteristic of improved layerwise growth. It is suggested that the
oxygen creates nucleation sites which increases interlayer mass trans
port.