Looking inside the glass

As the demand for smartphones, tablets, and solar panels increases, so too will the need for more high-quality, tough, transparent glass. One of the candidate materials for these applications is called aluminosilicate glass, which is made of aluminum, silicon, and oxygen. As with all amorphous materials, the glass does not form a simple lattice but exists more like a disordered "frozen liquid." However, intricate structures can still form between that have not yet been analyzed by scientists.

Now, a team of researchers at The University of Tokyo have used electron energy loss fine structure spectroscopy with a scanning transmission electron microscope to reveal the local arrangement of atoms within a glass made of 50% aluminum oxide (Al₂O₃) and 50% silicon dioxide (SiO₂).

"We chose to study this system because it is known to phase separate into aluminum-rich and silicon-rich regions" first author Kun-Yen Liao says.

When imaging with an electron microscope, some emitted electrons undergo inelastic scattering, which causes them to lose some of their original kinetic energy. The amount of energy dissipated varies based on the location and type of atom or cluster of atoms in the glass sample it hit. Electron loss spectroscopy is sensitive enough to tell the difference between aluminum coordinated in tetrahedral as opposed to octahedral clusters. By fitting the profile of the electron energy loss fine structure spectra pixel by pixel, the abundance of the various aluminum structures was determined with nanometer precision.

The team also used computer simulations to interpret the data. "Aluminosilicate glasses can be manufactured to resist high temperatures and compressive stresses. This makes them useful for a wide range of industrial and consumer applications, such as touch displays, safety glass, and photovoltaics," senior author Teruyasu Mizoguchi says. Because aluminosilicate is also naturally occurring, this technique can also be used for geological research.

The work is published in The Journal of Physical Chemistry Letters as "Revealing Spatial Distribution of Al Coordinated Species in a Phase-separated Aluminosilicate Glass by STEM-EELS."