Nanomaterials Aboard the Space Shuttle

Can you imagine working with materials that are only nanometers in length and can sort out different types of molecules? Dr. Geoffrey Ozin and Ph.D. student Carol Bowes at the University of Toronto do because they work with these materials in their lab. They are working with a new class of materials called nanoporous semiconductors. The nanomaterials are important because their optical and electronic properties can be modified through the absorption of gases.

The nanomaterials, metal suphides of germanium and tin, are semiconductors that contain a regular arrangement of pores ranging in size from 3 - 20 angstroms (1 angstrom = 1 x 10^-10 m). The pores can be modified to different sizes! The different pore sizes in the semiconductors will be used to differentiate molecules electronically since only certain sized molecules can pass through each pore. Thus, different molecules in a gas can be detected and quantified according to their size and shape-selective adsorption behaviour.

These types of semiconductors, also called chalcogenides, are actually self-assembling crystals which means that crystal formation occurs by itself. However, the formation and growth of crystals isn't always perfect. Under normal conditions, the crystals are often small and have imperfections caused by gravitational effects such as the settling of sediment and the convection of heat. In order find better conditions to grow these crystals , Dr. Ozin has been working jointly with the Canadian Space Agency and COM DEV Atlantic of New Brunswick, to determine whether the crystals will grow more perfectly in near zero (micro) gravity.

An automated system has been developed that will conduct and observe 38 crystal growth experiments. This experiment, NANOGAS, will be activated by Marc Garneau, a Canadian astronaut, on the NASA Shuttle mission in May 1996. It is predicted that the crystals will become larger and more perfectly shaped when grown in a micro gravity environment. This experiment will be the first to simultaneously synthesize and grow crystals in space. After the crystals are retrieved from space they will be compared to crystals that have been grown on earth using the same procedure.

The work by Ozin, Bowes and two post-doctoral fellows, David Young and Andy Holmes, has included characterization and synthesis of tin and germanium sulphides. Bowes has concentrated on the characterization and understanding of the tin sulphide SnS-1. Other members of the group are working on other tin chalcogenides containing sulphur and/ or selenium and novel germanium chalcogenides. Current research in Ozin's group is on the synthesis of thin films, mesoporous chalcogenides and synthesis of novel structures.

Hopefully, with the investigation of new semiconductors and perfection of the growth of the crystals these novel material can be put to use. The variability of pore size in the crystals will provide a number of uses for these semiconductors. One obvious use would be for the detection and quantification of molecules. They could be detectors for air quality, freshness of food, hidden illegal substances, or even chemical purity of gases. In other words, they could act like an electronic nose and "sniff-out" any type of molecule!