Billions of Pieces, Billions of Questions
By Paul Livingstone, Editor of R&D Magazine
R&D Magazine - October 12, 2010
An excerpt from Billions of Pieces, Billions of Questions
Measurement for nanomanufacturing
A major question mark facing companies that intend to produce a product that uses nanotechnology is that process control measurements hardly yet exist for many promising areas of industrial application. The shortcomings in particular are highlighted by the lack of knowledge about the health effects of certain nanomaterials used in biotech or food-related industries. But even areas where health is not a problem, nanoscale measurements are typically difficult outside the rigidly controlled environment of the laboratory.
For researchers, there are a wide variety of imaging and measurement tools available. Atomic force microscopy and electron microscopy are particularly well-known, but confocal and Raman optical instruments also contribute. But these instruments are designed primarily for researchers. None are process-oriented.
Craig Schwandt, a scientist with the electron-optics group at McCrone Associates, a Westmont, Ill.-based microscopy consultancy firm, says that techniques for observing materials at the nanoscale are improving quickly to keep up with demand. Electron microprobes can now be used for quantitative analysis rather than just imaging, and energy-dispersive x-rays can do micro- and nano-analysis relatively quickly.
“At the nanoscale, the physical properties of materials are different. They tend to want to adhere in clumps. Isolation is difficult, so coming up with tricks for particles to disperse more is still a challenge,” says Schwandt. Simply watching what particles are doing often inadvertently changes the way they’ll behave in, say, a human body. Sample preparation methods allow researchers to move from around 100 nm to the single nanometer scale, but these typically require embedding the sample or capturing in different types of media. The price of such efforts is the need to analyze the media itself—whether it’s a crystal or liquid, and account for its presence when obtaining data.
Yet, for all of this difficulty, analytical instruments and metrology techniques play a significant part in developing nanotechnology, and Liddle certainly can’t do without them for his work at NIST.
Measurements play two critical roles. First, they give us a way to gain a deep understanding of the way materials behave at the nanoscale, as well as the way the processes used to make them work, sometimes down to the atomic scale,” says Liddle.
“Once we have that kind of information, then we’re in a position to design the right nanostructure for a particular application, as well as a robust process for its manufacture.” Second, measurements are required during manufacturing to control the process to ensure that manufacturers are making exactly what they planned to make. This is process control, and while these measurements are nothing new, the unique challenge in nanomanufacturing is the combination of scale and speed. For any given nanomanufacturing process, says Liddle, the default starting estimate is billions of components, all of which (within some set of carefully defined tolerances) must have the same size, shape, and composition.
To close the process loop, Liddle continues, manufacturers must have measurements that can determine those characteristics, at least in terms of an average and standard deviation, at speed. Imagine, for example, a roll-to-roll process like letterpress printing that runs at 10 m2/s), in line and affordably, generating nanopatterned circuitry at high volume.
Research for process like these are either recently underway or just beginning.
Although there will be some commonalities, new measurement methods will likely have to be developed to suit each set of new materials and devices, as well as the particular processes used in their manufacture,” says Liddle.
Part of the problem, according to Schwandt, is that some developers are unaware of the availability, or appropriate application of the tools at hand. He often sees people go to transmission electron microscopes to perform quality control tasks. They don’t necessarily need to jump through the hoops of sample preparation to the get the data they need. A field-emission scanning electron microscope is typically enough to sample particles just a few nanometers in diameter.
“Recent advances in field emission electron microscopy is something nanotechnologists might not be aware of. This technology has only been available for the last three years, so I don’t think that many fabricators of nanoscale materials understand that these instruments are available for their use, whether they go buy them or buy the service,” says Schwandt, who is accustomed to helping clients perform these sorts of analyses.
Another segment of the microscopy market, scanning probes and atomic force microscopes, are enjoying a renaissance because their ability to provide quantitative data on the nanoscale. Unfortunately for those who want a process-oriented tool, these are typically more comfortably employed in the research lab than the factory floor. “My feeling is that there is very little [manufacturing] as far as the SPM (scanning probe microscopy) business is concerned, says Sergei V. Kalinin, a researcher at Oak Ridge National Laboratory, Oak Ridge, Tenn., who is a frequent user of nanoscale imaging tools as co-theme leader for functional imaging on the nanoscale at The Center for Nanophase Materials Sciences and the Oak Ridge Lab’s Materials Sciences and Technology Division. “Most companies,” he says, “primarily sell to R&D in academia, labs or industry, not manufacturing.”
He believes that analytical instruments are a key and enabling component for the successful joining of nanotechnology and manufacturing, but widespread of adoption and use of these tools has not caught up with the demand of commercialization.
“The fact that people started to talk about nanotechnology at all is largely driven by the fact that SPM measurements have become available, and with them the relatively easy to use, low-cost benchtop instrumentation for probing and manipulating materials locally. All of these characteristics are important,” says Kalinin. He anticipates the SPM will continue to a great bearing on how fast nanotechnology develops, more so than electron microscopy in large part because of the cost.