Researchers at the Ioffe Technical Physical Institutehave developed a new method of synthesising composite materials from synthetic opal and vanadium oxides. Such materials have unusual optical properties. Previously, they were generated by depositing vanadium oxides (V₂O₅ and VO₂) from a solution, but in their latest work the researchers demonstrated the greater effectiveness of using melted vanadium oxide V₂O₅.

Synthetic opal presents a porous matrix consisting of silicon dioxide (SiO₂). Two types of such matrixes exist — these are three-dimensional and film. Nanocomposites where opal pores are filled with vanadium oxides invoke significant interest. Such structures can be used as gas sensors, switches and limiters of visible and infrared light emission. In addition, nanocomposites have the properties of three-dimensional photon crystal. It means that their structure is characterised with periodic changes in the refractive index. Such substances are capable of capturing photons and are of great demand in optoelectronics.

Today, nanocomposite opal-V₂O₅ and opal-VO₂ are produced using solution methods, that is, wash the matrix in the oxide solution until its pores are filled. The process must be repeated several times which increases the production time; it also leads to unwanted impurities in the resultant material.

Dmitry Kurdyukov and his colleagues suggested and tested a new method to synthesise such nanocomposites. The study report was published in the Solid-State Physicsmagazine. The researchers used melted vanadium oxide (V₂O₅) and an opal sample previously synthesised on the fused quartz substrate. The substances were put into the crucible at the temperature of 690°С, and were further heated uniformly. The vanadium oxide melt moistens the surface of silicon dioxide which allows it to fill the pores in the opal crystal completely. Cooling of the mixture results in the desired nanocomposite. The metal oxide shrinks with cooling and therefore the opal pores get only 70 per cent filled but this level of filling allows the material to preserve its properties. Based on the resulting opal-V₂O₅ it is possible to produce opal-VO₂ – it requires a reaction of vanadium oxide reduction with hydrogen in the pores of the sample.

In order to confirm that the new methodology resulted in the synthesis of the desired nanocomposite, the researchers used the data provided by electron microscopy and Raman spectroscopy. The created substance was subjected to chemical etching to remove vanadium oxides from the near-surface opal layers. The scientists note that the nanocomposites generated after the synthesis have areas of lower pore filling levels, that concentrate near the surface. At the same time, the level of filling the pores located close to the substrate reaches 100 per cent. It means that the development of the three-dimensional photon-crystal structure begins during the first stage of the nanocomposite processing.

Source of information: D. А. Kurdyukov, S. А. Grudinkin, А. V. Nashchekin, N. Smirnov, Е. Yu. Trofimov, М. А. Yagovkina, А. B. Pevtsov, V. G. Golubev: “Melting Synthesis and Structural Properties of opal-V₂O₅ and opal-VO₂ nanocomposites.” The Solid-State Physics, 2011, vol. 53, issue 2

Further information: Dmitry Kurdyukov, the Ioffe Technical Physical Institute, Russian Academy of Sceinces, (812)292-73-93 E-mail: Kurd@gvg.ioffe.ru. Sergey Grudinkin, the Ioffe Technical Physical Institute, Russian Academy of Sceinces, (812)292-73-93 E-mail: Grudink@gvg.ioffe.ru