Tungsten Inverse Opal Investigated

Daniel S. Burgess

University of Toronto researchers have reported the fabrication of an inverse opal film from tungsten. At the Conference on Lasers and Electro-Optics (CLEO) in San Francisco in May, Georg von Freymann described the work, which included the spectroscopic characterization of the optical properties of the photonic crystal.

Scientists at the University of Toronto have fabricated inverse opal films from tungsten. The material may not be suitable for use in lighting applications, as had been hoped. Images courtesy of Georg von Freymann.

To produce the material, the scientists first created a template of packed silica spheres that they necked with silica by chemical vapor deposition to prevent cracking in the subsequent processing steps. They filled the volumes between the spheres with tungsten using chemical vapor deposition with W(CO)₆, and dissolved the template with a hydrofluoric acid solution to leave behind only the tungsten inverse opal film.

To fabricate the inverse opal, the researchers fill the volumes between packed silica spheres with tungsten using using chemical vapor deposition with W(CO)₆ and then dissolve the silica with hydrofluoric acid.

To characterize the material, they performed reflectance and transmittance measurements with a PerkinElmer Lambda 900 UV-VIS-NIR spectrometer on films created from 550- and 850-nm-diameter spheres and on films with varying degrees of tungsten infiltration. Their measurements revealed a more pronounced peak in the reflectance spectrum for inverse opals created with smaller spheres and a smearing of the reflectance spectrum with increased infiltration.

Von Freymann said that the findings indicate that tungsten-based photonic crystals may never be suitable for use in lighting applications, in which it has been hoped that they might convert wasted thermal emissions into visible light to improve efficiency. The work continues, however, and he hinted that the team believes it now knows what materials will have the right properties for such a purpose.