Desorption of deposited species plays a role in determining the evolution of
surface morphology during crystal growth when the desorption time constant is
short compared to the time to diffuse to a defect site, step edge or kink.
However, experiments to directly test the predictions of these effects are
lacking. Novel techniques such as \emph{in-situ} coherent X-ray scattering can
provide significant new information. Herein we present X-ray Photon Correlation
Spectroscopy (XPCS) measurements during diindenoperylene (DIP) vapor deposition
on thermally oxidized silicon surfaces. DIP forms a nearly complete
two-dimensional first layer over the range of temperatures studied (40 - 120
∘C), followed by mounded growth during subsequent deposition. Local
step flow within mounds was observed, and we find that there was a
terrace-length-dependent behavior of the step edge dynamics. This led to
unstable growth with rapid roughening (β>0.5) and deviation from a
symmetric error-function-like height profile. At high temperatures, the grooves
between the mounds tend to close up leading to nearly flat polycrystalline
films. Numerical analysis based on a 1 + 1 dimensional model suggests that
terrace-length dependent desorption of deposited ad-molecules is an essential
cause of the step dynamics, and it influences the morphology evolution.Comment: 21 pages, 9 figures, and one tabl