  Barrier films preventing permeation of gases and moistures are important for
many industries ranging from food to medical and from chemical to electronic.
From this perspective, graphene has recently attracted particular interest
because its defect free monolayers are impermeable to all gases and liquids.
However, it has proved challenging to develop large-area defectless graphene
films suitable for industrial use. Here we report barrier properties of
multilayer graphitic films made by chemical reduction of easily and cheaply
produced graphene oxide laminates. They are found to provide a practically
perfect barrier that blocks all gases, liquids and aggressive chemicals
including, for example, hydrofluoric acid. In particular, if graphene oxide
laminates are reduced in hydroiodic acid, no permeation of hydrogen and water
could be detected for films as thin as 30 nm, which remain optically
transparent. The films thicker than 100 nm become completely impermeable. The
exceptional barrier properties are attributed to a high degree of
graphitization of the laminates and little structural damage during reduction.
This work indicates a close prospect of thin protective coatings with stability
and inertness similar to that of graphene and bulk graphite, which can be
interesting for numerous applications.
