A new method that controls the phase of titanium dioxide at room temperature could make the material more efficient in applications such as photovoltaic cells, smart sensors, optical communication technologies, hydrogen production and antimicrobial coatings. Titanium dioxide is most commonly available in either an anatase or rutile phase. The arrangement of atoms dictates the material’s optical, chemical and electronic properties. As a result, each phase has different features. The anatase phase is suitable for applications such as hydrogen production and can be used as an antibacterial agent, while the rutile phase is ideal for applications including optical communication technologies, smart sensors and photovoltaic cells. The technique, developed by scientists at North Carolina State University, precisely controls titanium dioxide’s phase at room temperature and stabilizes it so that it will not change during temperature fluctuations. The new technique allows researchers to control the phase of the titanium dioxide by modifying the structure of the titanium trioxide and sapphire substrate. (Image: NCSU) “Traditionally, it has been a challenge to stabilize titanium dioxide in the desired phase,” said Dr. Jay Narayan, the Jon C. Fan Distinguished Chair Professor of materials science and engineering at NC State. “The material tends to transform into the anatase phase below 500 degrees Celsius and transform into the rutile phase at temperatures above 500 Celsius.” In the process, a sapphire substrate with desired crystalline structure is used, and a template layer of titanium trioxide is grown over the substrate; the structure of the titanium trioxide is similar to that of the substrate. Finally, titanium dioxide is grown on top of the titanium trioxide layer. The structure of titanium dioxide differs from the titanium trioxide layer, so titanium dioxide can be created in any phase simply by altering the structure of the sapphire substrate and titanium trioxide. This works because of a process called domain matching epitaxy, a method in which lattice planes in the template layer line up with the lattice planes of the material being grown on the template. The team also has demonstrated how the method can be integrated with silicon computer chip substrates, which can be included in electronic devices such as smart sensors. The research appeared online June 20 in Applied Physics Letters. For more information, visit: www.ncsu.edu