Near-edge X-ray absorption fine structure
(NEXAFS) spectroscopy has been used to
determine the average near-surface orientation of chains in a buffed
polyimide film. Auger and total
electron yield measurements provide powerful and direct means of
determining the orientation of chains
as a function of depth. In the case of a strongly buffed sample,
the polyimide chains at the film surface
are found to be highly aligned along the buffing direction. We
also find significant alignment of the
phenyl ring planes parallel to the surface. The alignment is
discussed in terms of simple models that
are useful in visualizing the alignment in partially disordered
systems. The chain orientation decays as
a function of distance from the surface, becoming random in the bulk.
The 1/e alignment depth is ≃100
Å. Studies as a function of load applied during buffing and
distance of buffing show that the near-surface orientation saturates at relatively small loads and short
distances. The 1/e buffing load and
buffing distance for the near-surface alignment are 1.2
g/cm2 and 67 cm, respectively.
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