Design and fabrication of compositionally graded inorganic oxide thin films: The mechanical, optical and permeation characteristics films
Journal
Acta Materialia
Date
2010.09.29
Abstract
Different types of inorganic oxide films composed of a
chemical composition gradient single layer have been
designed, fabricated, and characterized. Compositionally
graded thin films were created by power-controlled co-
sputtering of alumina (Al2O3) and silica (SiO2) at room
temperature, allowing us to tailor the structural design of
the film at the nanometer scale. Two distinct graded thin
films were fabricated: one with a compositionally asymmetric
structure consisting of a SiO2-rich bottom interface and a
Al2O3-rich top surface and the other one with a
compositionally balanced sandwich structure consisting of
both the top surface and bottom interface rich in SiO2 and a
core rich in Al2O3 (referred to as SGS for ‘sandwich graded
structure’). Smoothly graded thin films without interfacial
boundaries were verified by Auger electron spectroscopy (AES)
profiles. X-ray photoelectron spectroscopy (XPS) demonstrated
that the Al2O3/SiO2 graded structures consisted of Si-O and
Al-O bonds, as well as Al-O-Si bonds in the transition layer.
Neat Al2O3 or SiO2 and their graded ones were all
investigated for the mechanical, optical, and permeation
properties. A SGS thin film presented the best mechanical
stability (i.e. about 3 times improved film toughness than a
neat Al2O3 single layer), demonstrating that balanced
internal stresses and alternating bonding structures,
achieved via a graded structure without interfaces, are
crucial for enhancing mechanical stability. Furthermore, neat
and graded thin films exhibited the similar level of optical
transmittance and the permeation properties for the graded
films were well matched with the behaviors of mechanical
stability.