An in-situ study was performed of the growth kinetics of individual
crystallites during the deposition of iron onto electron-transparent
singlecrystalline α-Al2O3
(sapphire) substrates. Clean sapphire films were produced in-situ under UHV
conditions by electron-beam induced crystallization of amorphous
Al2O3 (1). Iron was
electron-beam vapor-deposited at constant rates (0.2-0.5 nm/min) and
elevated substrate temperatures (750 – 900°C) immediately following the
crystallization. The nucleation, growth, and eventual coalescence of the
metal particles were observed in-situ by transmission electron microscopy
and recorded on video tape at 30 frames per second. In fig. 1, a growth and
coalescence sequence of several Fe-particles on
[100]-α-Al2O3 is shown. The
images were selected and photographed from the TV monitor during video
playback. The particles marked with letters were analyzed in detail.
Noteworthy is that particle A (after about 30 min. of growth) started a
rapid increase of its length-to-width ratio. Particle H, formed in a
coalescence event, exhibited a preferred growth in a special direction,
presumably in order to develop a certain crystallographic habit. Particle K
developed a fast lateral growth ab-initio and remained a thin platelet until
it coalesced with a neighboring particle about 25 min. after the beginning
of the deposition.