To create efficient catalysts, sensing, and separation membranes as well as energy storage devices, scientists often start with particles containing tiny pore channels. However, defects between the particles can hamper performance.

To address this problem, a team at the U.S. Energy Department's Pacific Northwest National Laboratory created a one-pot method that they say produces complex, well-structured microscopic pyramids.

Highly ordered sodium silicate particles (bottom right) with a regular array of spherical pores (bottom left) form on silicon surface. The one-step synthesis is directed by the atomic ordering of the substrate, which induces the formation of a soft template for sodium silicate growth. Sodium silicate, in turn, modifies the structure of the soft template during growth, encapsulating it within its structure (top).Their technique for three-dimensional material growth is similar to that seen in nature. "It's relatively easy to grow thin layers of material," says Dr. Maria Sushko, a materials scientist who worked on the study. "Now, we can grow supported three-dimensional crystals that have a larger word structure on the inside as well – a crystal within the crystal."

This work is important because more efficient energy storage materials would be helpful for renewable energy. In addition, more efficient catalysts, sensors, and separators could reduce the energy demands and waste from manufacturing plants and refineries.

The team’s technique offers a new way for scientists to grow well-defined three-dimensional structures on the surface in a single step. Growing material directly on the surface eliminates steps in testing new ideas for electrodes or catalysts.

The process takes advantage of a relationship among the atomic ordering of the silicon substrate, structure of organic templates, and atomic structure of sodium silicate. Organic molecules and a sodium silicate precursor are combined in controlled proportions. The solution is then heated in the presence of the silicon surface, and the silicon substrate directs the template’s self-assembly along a specific crystallographic direction. The template directs the formation of sodium silicate along the crystallographic direction of the substrate, ensuring near-perfect lattice matching between silicon and sodium silicate.

The organic template ultimately forms an array of well-defined spherical micelles several nanometers in diameter. The micelles are arranged in a cubic lattice and encapsulated into sodium silicate.

The result, confirmed by electron microscopes, is an array of oriented ordered porous pyramids with a well-defined cubic lattice of pores. The scientists are able to vary the structure and size of the particles. Their system makes different structures, with different sizes and compositions, as needed.

The team is now exploring ways to expand this technique beyond sodium silicate to other materials.