Visco, Craig Jacobson, and Lutgard DeJonghe have
developed an innovative method for making a highly
dense film of a metal oxide or mixed metal oxide
by applying a porous film composed of fine metal
or metal alloy and metal oxide particles to a
substrate. In the Berkeley Lab technique, a metal
powder corresponding to a conductive metal oxide
is mixed with the conductive oxide material and
applied to the substrate by one of a variety of
deposition methods: colloidal aerosol spray, electrophoretic
deposition, slurry dip-coat, or vacuum infiltration.
Sintering of the bilayer is initiated in a reducing
environment. During sintering, oxygen is bled
into the furnace and the metal in the membrane
oxidizes and expands, closing off pores in the
film. In response to the heat, the oxide particles
decrease their surface area and densify. These
expanding and contracting effects essentially
cancel each other out so that no film shrinkage
occurs. This technique produces high quality,
gas-tight, dense films in a single step.
Berkeley Lab method has a combination of benefits
that makes it preferable to other practices. It
is preferable to sol-gel techniques because it
produces thicker films and enables the use of
porous substrates. Unlike plasma spray methods
of deposition, it can produce very thin films.
Compared to bulk reaction bonding, it provides
greater oxygen access in the thin film and therefore
greater homogeneity. Because co-firing is unnecessary,
the sintering profiles of the substrate and film
do not need to match.