Geoffrey A. Ozin
Materials Chemistry Research Group
An exciting new direction in the
Ozin materials chemistry research group concerns their groundbreaking work on
the synthesis, characterization and properties of a novel class of materials
that are referred to as nanoporous electronic materials. These materials have
open-framework crystal lattices that can be structurally viewed as semiconductors
filled with regular arrays of molecular dimension pores (3-20 angstroms size
range). They can also be regarded as the geometrical complement of semiconductor
clusters arranged in periodic lattices, the latter being known in physics as
quantum dot lattices and the former as quantum antidot lattices. The spatial
confinement of charge-carriers in these nanostructures, to length scales
that are small compared to the wavelength of an electron or hole, confers unique
"size and composition-tunable" electronic and optical properties on the
materials that are not found in their bulk semiconductor analogs.
Specifically, the Ozin group has
learned how to synthesize metal sulfide and metal selenide open-framework
materials, through the use of a synergistic integration of organic and inorganic
chemistry. In essence, this involves the spatially controlled co-assembly
of inorganic building-blocks with organic templating molecules to create
a "molecularly imprinted inorganic replica" material. In these solids the patterning
of the pore structure is facilitated by the organic additive whose templating
function is to fill space and balance charge. The properties of such materials
are most interesting. They have, for instance, stimulated the group to investigate
the idea of nanoporous electronic and optical devices, such as, a synthetic
photonic-gap material, which has recently been described in the semiconductor
physics literature to have the intriguing property of being able to trap light
of the right wavelength.
Intensive research on these nanoporous
electronic materials in the Ozin laboratory over the last few years has provided
much information on their combined synthesis-structure-property-function
relationships (i.e., the trade of the solid state chemist).1-10
The group has learned a lot about their materials, including knowledge of their
single crystal and Rietveld powder X-ray diffraction structures, mode of formation,
atomic force microscopy-based images of surface topographies (with molecular
resolution), thermochemical properties, adsorbate-induced framework flexibility,
compositional tuning of their electronic band properties, electrical transport
(ac/dc conductivity) behaviour, Fourier Transform-IR/Raman vibrational
spectroscopy, growth as lattice matched and oriented thin films, synthesis of
epitaxial junctions and studies of their potential for chemical sensing. Most
of this research in the group has been published in materials chemistry journals
and some was recently selected by the German Chemical Society as one of the
materials research highlights of 1995.
The Ozin group are optimistic that
this new class of metal chalcogenide semiconductors, with regular arrays of
size-tunable nanometer dimension holes, will be able to function as discerning
hosts and discriminate between different guest molecules based on their size
and shape-selective adsorption behaviour. The Ozin group is currently exploring
the potential of their new materials for chemoselective sensing applications.
An extension of this research has
led the Ozin group to earth-based 1G and space-based µG investigations
of the synthesis and crystal growth of their self-assembling nanoporous
electronic materials. This work has been funded by the Canadian
Space Agency over the period 1993-1996. The essence of this project,
is to take advantage of the fact that deleterious sedimentation and convection
effects that abound in their earth-based synthesis-crystal growth
experiments, do not exist under the quiescent state of a microgravity-based
analogous experiment. In this way the group hopes to be able to "harvest in
space", larger and higher quality crystals of their nanoporous semiconductors,
that are as free as possible of the unwanted crystal defects that generally
form in their earth-grown crystal samples. Achievement of this goal is
expected to enhance the electrical conductivity and optical properties of their
crystals which should improve their efficacy for future semiconductor device
applications envisaged for these materials.
This materials chemistry microgravity
experiment will be one of the first of its kind to perform a simultaneous synthesis
and crystal growth procedure in space. The experiment will be fully automated.
The specially designed reactor will perform 38 synthesis-crystal growth
experiments with comprehensive on-board computer recording of the progress
of the entire system. Prototype experiments have been optimized in the Ozin
group laboratory. Once the space-grown samples are recovered, the reaction
profiles of the experiments will be evaluated and the syntheses will be immediately
duplicated under earth-based conditions. Analysis of a wide range of the
physicochemical properties of the space and earth-generated nanoporous
semiconductor crystals will allow the group to evaluate the effects of microgravity
on the synthesis-crystal growth process.
This microgravity experiment has
the official name NANOGAS (in the jargon of the Canadian Space Agency, the experiment
is referred to as a "Get-Away-Special"). It is a joint venture between
the Canadian Space Agency (funding, technical support), Communication Development
in New Brunswick (flight hardware), the U.
of T. Chemistry Department (facilities, services) and the Ozin group. The experiment was carried on a NASA
Space Shuttle flight in May 1996, STS-77. The samples were recovered later and
the ground and space-based samples will be analyzed over a period of about
six months. The results of this research will be announced towards the end of
The team of researchers in the Ozin
group that have made invaluable contributions to this exciting self-assembly
experiment in space, is headed by Dr. David Young with the expert assistance
of Dr. Atul Verma, Dr. Srebri Petrov, Dr. Neil Coombs, Dr. Alan Lough, Mr. Holmes
Ahari, Ms. Carol Bowes, Ms. Wendy Huynh, Ms. Tong Jiang and Mr. Scott Kirkby,
and the outstanding technical assistance of Mark Cornish in the departmental
machine shop. Bruce Morton at Communication Development has also made invaluable
contributions to the project. The technical and financial support of the scientific
and management team at the Canadian Space Agency, in particular Ed Sloot, Phil
Gregory and Jack Fisher, is also appreciated.
1Ozin, G. A., Bowes, C.
L., Adv. Mater. (in press)
2Ozin, G. A., Adv.
Mater., 4, 612-649 (1992); Ozin, G. A., in "Materials Chemistry:
An Emerging Subdiscipline," A.C.S. Symposium, Washington, March 1992, A.C.S.
Symp. Ser., Ed. Interrante, L., Washington, 1994; Ozin, G. A., Bowes, C.
L., Mater. Res. Soc. Symp. Proc., 286, 93 (1992)
3Ozin, G. A., Supramolecular
Chemistry, 6, 125-134 (1995)
4Jiang, T., Lough, A.
J., Ozin, G. A., Young, D., Chem. Mater., 7, 245-248 (1995)
5Jiang, T., Ozin, G. A.,
Bedard, R. L., Adv. Mater. 6, 860-865 (1994)
6Bedard, R. L., Enzel,
P., Henderson, G. S., Ozin, G. A., Adv. Mater., 7, 64-68 (1995)
7Jiang, T., Ozin, G. A.,
Bedard, R. L., Adv. Mater., 7, 166-170 (1995)
8Ahari, H., Bedard, R.
L., Bowes, C. L., Jiang, T., Lough, A., Ozin, G. A., Petrov, S., Young, D.,
Adv. Mater., 7, 375-378 (1995)
9Ahari, H., Bedard, R.
L., Lough, A., Petrov, S., Ozin, G. A., Young, D., Adv. Mater., 7,
10Ahari, H., Bedard, R.
L., Bowes, C. L., Jiang, T., Kirkby, S. J., Kuperman, A., Lough, A., Ozin, G.
A., Petrov, S., Verma, A., Young, D., Adv. Mater. (in press)