Exotic applications of optical thin films: (Left) Scanning electron microscope image of a columnar microcavity with quantum dots produced from a planar structure by a complex etching procedure. The reflecting stacks were deposited in an ion-beam sputtering system. (Right) Microcavity organic light emitting diodes with double sided light emission of different colors. J. Vac. Sci. Technol. A 22, 764-7 (2004).
This equipment is now able to deposit layers with intermediate refractive indices within homogeneous multilayer systems. Such layers are of particular importance in systems designed for use at oblique angles of incidence of light. The reproducibility and degree of control of thickness and refractive index achieved with this apparatus is now sufficient for the deposition of rugate filters.32
The ion beam sputtering system has proved to be an excellent research tool. The advantage of using in situ ion beam etching to remove thickness overshoots during the manufacture of multilayers was convincingly demonstrated in 2003.33 This system has been used with great success to produce a variety of coatings for colleagues in the Institute. Some examples of the special coatings produced in this way are facet coatings for lasers,34 mirrors for VCSELs and micro-cavity devices,35 coatings to increase the contrast and efficiency of OLEDs, and microcavity OLEDs with double-sided light emission of different colors36 and coatings for the Gemini North telescope (Altair).
In 1968, the Bank of Canada was looking for ideas about how to enhance the security of the nation’s currency. The group offered a proposal that would take advantage of the iridescent behavior of thin films.37,38 Normally this is an undesirable property that designers strive to minimize. However, when optical coatings are incorporated into a bank note, they change color with the angle of viewing in a way that cannot be reproduced by photography or xerography. Identicard Ltd., a company producing identification documents and drivers’ licenses, also expressed an interest in the invention. This proposal was destined to become the group’s largest project.39,40
Unfortunately, at the time, no equipment manufacturers were willing or able to supply coating machines that would produce the required large areas of accurate multilayer coatings at a low enough per-unit-area cost. A period of intense engineering efforts followed as the group successfully designed and developed two different processes.
Optical security devices: (Left) First- and (right) second-generation optical security devices on Canadian banknotes. The colors of the thin film systems change from gold to green to blue with increasing angle of viewing.
We developed the system for the Bank of Canada in conjunction with the Canadian Vacuum Corporation Ltd., Gastops Ltd., Lembo Corporation of Canada Ltd. and Vadeco International. The system was a semi-continuous roll-coater based on electron beam evaporation onto a Mylar web.41 The group developed a batch-type RF- magnetron sputtering system for Identicard Ltd., in conjunction with Corona Vacuum Coaters Inc. In it, a large sheet of Mylar was draped over a 1.8 m-diameter, 1.8 m-high cylindrical drum that was rotating about a horizontal axis. Currently, Canadian banknotes carry the second generation of optical thin film security devices. The group has also suggested that optical thin films be used to protect optical media.
Other special products and collaborations
Over the years, the Thin Film Group has developed a number of special multilayer systems that have been of interest to industry. For example, in the late 1980s, the group introduced thin metal layers into dielectric stacks to reduce the reflectance of various generic filter types.42,43 This technology is used in the construction of high-contrast TFEL and OLED displays,44 as well as black layer coatings for the artificial vision systems of the CanadArm for use in space shuttles and the space station.
The group has written many scientific articles about antireflection coatings, polarizing and non-polarizing beam splitters and cutoff filters. One outstanding recent development has been the Li Li polarizing beam splitter, which offers an unprecedented performance over a broad spectral region and a wide range of angles.45
The group has also had many other significant institutional interactions. Some of the companies or institutions we have worked with include Luxell, Environment Canada, FISO, KAO, the Institute of Optics in Quebec, JDS-Fitel, Lumonics Optical, Nortel and, last but not least, its own spin-off, Iridian Spectral Technologies.
NRC Thin Films Group in 2006. Left to right: Frances Lin, Li Li, George Dobrowolski, Yanen Guo, Kamil Mroz, Pierre Verly, Daniel Poitras, Xiaoshu Tong, Bob Simpson, Dan Dalacu and Penghui Ma.
Through the years
During the past 50 years, the Thin Films Group has been involved in a number of academic and commercial projects of national and international significance. It has published about 125 refereed papers and has about 25 U.S. patents to its credit. There can be no doubt that the successes of the group were due to its excellent staff and the stimulating working conditions at the NRC.
NRC scientists who belonged to the group or collaborated closely with it during the past 50 years include K.M. Baird, P.D. Carman, G. Clarke, D. Dalacu, J.A. Dobrowolski, P.D. Grant, G.R. Hanes, F. Ho, M. Laubitz, L. Li, P. Ma, N. Osborne, D. Poitras, B.T. Sullivan and P.G. Verly.
Technical staff frequently made all the difference between success and failure. They include T. Cassidy, D.G. Charbonneau, Y. Guo, L. Howe, G. Laframboise, S.H. Lewis, F. Lin, G.E. Marsh, G. Marshall, L.M. Plante, T. Quance, M. Ranger, J.D. Sankey, R.H. Simpson, X. Tong, H.T. Tran, C.J. Van der Hoeven, A. Waldorf and R.L. Wilkinson.
The group also hosted a number of guest workers who helped to expand its horizons. These include T. Akiyama, J. Ciosek, C. Holm, D. Menagh, C. Montcalm, Z. Pang, J. Shao, A.V. Tikhonravov and M.K. Trubetskov.
Last but not least, the group benefited from the influx of “young blood”—summer students who, with their enthusiasm, contributed to the projects and were frequently invited to be co-authors of scientific publications. All of these people contributed to the successes of the group and the present staff express their appreciation to them.
J.A. Dobrowolski, Dan Dalacu, Li Li, Penghui Ma, Daniel Poitras and Pierre G. Verly are with the Institute for Microstructural Sciences, National Research Council of Canada, Ontario, Canada.