Zetian Mi and Mathieu Brochu describe their cutting-edge research

Fall 2009

McGill Engineering has an ambitious program to recruit world-class researchers with expertise in areas vital to the education of our students.

One of the tools being used to attract and retain these first-in-class professors is a three-year, $75,000 prize called the Faculty Scholar Award. The award augments funding that professors obtain from external agencies or other sources at McGill. It helps to pay for such items as laboratory expenses and technician support, graduate student support, undergraduate research projects and publication costs.

Five prizes have been awarded to date. If funding is obtained, the Faculty would like to create at least 20 such positions.

The first three recipients, titled Hatch Faculty Fellows, are being supported through a gift from alumnus Gerald G. Hatch, BEng’44, DSc’90 (see Spring 2009 Dean’s Report). In this issue, the two newest Faculty Scholars, Zetian Mi and Mathieu Brochu, explain the objectives of their cutting-edge research. Both are being funded through gifts from Hydro-Québec.

Zetian Mi’s research could lead to major reductions in global energy consumption

The U. S. Department of Energy cast down the research gauntlet recently when it announced a goal of replacing light bulbs by 2025 with solid state lighting that draws on electricity converted directly from semiconductors. And professor Zetian Mi has answered the challenge.

A stunning range of potential applications – Zetian Mi

A stunning range of potential applications – Zetian Mi

Since arriving at the Electrical and Computer Engineering Department in September 2007, Mi has established the only facility at a Canadian university for researching gallium nitride (GaN) nanoscale materials, making him a leading researcher in the field of GaN semiconductors.

Semiconductors such as these could provide an inexpensive, long-lasting light source that is 50% more energy-efficient than current technology. “Since almost 20% of global electricity use is due to lighting, the energy savings would be significant,” Mi says.

Research on GaN and other nitride-based semiconductors dates only from the 1990s, so they still pose many questions. “But that means that they also offer a lot of potential,” Mi says.

“To use them effectively, however, we must understand GaN more thoroughly and develop the technology that would make it more appropriate for the market.” While some companies are commercializing this technology, concerns about efficiency, cost and yield remain among the major roadblocks.

Doctoral students Yi-Lu Chang (left), Feng Li (centre) and professor use a sophisticated Nitride Molecular Beam Epitaxial Growth System to grow nanostructures in Mi’s McConnell Engineering Building laboratory.

Doctoral students Yi-Lu Chang (left), Feng Li (centre) and professor Zetian Mi use a sophisticated Nitride Molecular Beam Epitaxial Growth System to grow nanostructures in Mi’s McConnell Engineering Building laboratory.

Mi, who was recently named a Hydro-Québec Nano-Engineering Scholar, is exploring inexpensive fabrication strategies that involve growing highly efficient nanostructures — such as nanowires and quantum dots — on a large-area silicon substrate, an innovative approach that could scale up to levels demanded for industrial manufacturing. Mi’s group (three doctoral students, a post-doctoral fellow and an undergraduate) has already grown green, yellow, amber and red-emitting indium gallium nitride nanowires on a silicon substrate, with these nanowires showing internal quantum efficiencies of more than 45%, as opposed to currently reported values of less than 10% for other approaches.

GaN nanostructures offer a stunning range of potential applications. “The nanowires we grow here are just a little larger than DNA sequences, and when they are combined with DNA, their electrical properties change,” Mi explains.

Harvesting solar energy

“This characteristic can be used to tell us detailed information about the DNA that may not be obtained otherwise. As such, ultra-sensitive DNA sensors are being developed.” Mi’s unique nanowire research was featured with a photo on a recent cover of the prestigious international journal Nanotechnology. In addition, Mi’s research group is investigating GaN’s potential for harvesting solar energy.

Most solar panels absorb only a portion of the solar spectrum, and even the most advanced solar energy technologies, such as those used on the International Space Station, can take advantage of the entire spectrum only by using a combination of different materials – an approach that is far too expensive for more mundane applications. Systems using nitride-based materials, such as GaN, indium nitride, aluminum nitride and their alloys, can absorb the entire solar spectrum.

“The major problem in tackling this issue is growing sufficiently high-quality nanomaterials, and that is exactly the edge my group has gained in the last two years,” Mi says.

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Brochu’s team engineers an advanced welding process

Manipulating nanomaterials to manufacture large-scale components

Nanomaterials are, by definition, tiny, but professor Mathieu Brochu has taken on the challenge of using nanomaterials to fabricate large objects as well.

The Mining and Materials Engineering Department researcher says that “fabricating laboratory-scale nanomaterials is easy, but to make an actual large-scale component economically — such as a mechanical device or an aircraft part — is no simple task.”

Materials Engineering doctoral student Bamidele Akinrinlola is one of 13 graduate students helping professor Mathieu Brochu develop manufacturing processes that employ nanomaterials. She is seen here working an electrospark welder.

Materials Engineering doctoral student Bamidele Akinrinlola is one of 13 graduate students helping professor Mathieu Brochu develop manufacturing processes that employ nanomaterials. She is seen here working an electrospark welder.

While they boast extremely useful features for large-scale objects, bulk nanomaterials also present daunting problems. For instance, because of their low fracture toughness, an impact could cause something constructed with bulk nanomaterials to break. As a result, such materials are restricted to applications having a static load, which is a significant constraint to their widespread use.

Brochu’s research explores different ways of manipulating and applying nanomaterials to enhance their exceptional qualities — including hardness, strength and oxidation resistance — for use in bulk applications.

Brochu, who is a Canada Research Chair in Manufacturing Nanomaterials as well as a Hydro Québec Nano-Engineering Scholar, says that one way of dealing with low fracture toughness is to develop a type of nanocladding, in which the bulk of a component is made of conventional materials, while the surface uses nanostructures.

“This approach gives us the desired toughness for the component, along with the nano characteristics we want for the surface.”

From aircraft parts to wheels on buses

Professor Mathieu Brochu (right) and master’s student Pat Vespa at the controls of a CSC MIG Welding Process Controller that is housed in Brochu’s W. H. Wong Building nanomaterials laboratory.

Professor Mathieu Brochu (right) and master’s student Pat Vespa at the controls of a CSC MIG Welding Process Controller that is housed in Brochu’s W. H. Wong Building nanomaterials laboratory.

Practical applications are easy to find. “For example, the de-icing sand used on roads in winter accumulates inside the rims of bus wheels and erodes their surface. I am working on a project to make wheels out of conventional materials, but with a nanomaterial coating that would provide higher resistance to abrasion.”

Applying this nanocladding to conventional material is challenging in its own right, but last summer Brochu and members of his research team — including 13 graduate students and an undergraduate from the Summer Undergraduate Research in Engineering (SURE) program — engineered an advanced welding process capable of depositing nanomaterials on a surface.

An arc weld with a high-frequency pulse having a duration of a few microseconds provides the energy to deposit and fuse materials without causing them to lose their nanostructure — as would be the case with a longer duration or different cooling period.

“This sort of freeforming has never been done before, so I am really proud of it,” Brochu says. “But the concept is very new, so there are still issues to address, such as a low deposition rate that demands a time-consuming layering process.”

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