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Results We Can See

Wed, 10/10/2012 - 1:03pm
Paul Livingstone

A careful mix of quality instrumentation, business strategy, and expert help is bringing nanotechnology products to the marketplace.

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Recent improvements in gas field ion source technology at microscope manufacturer Carl Zeiss have given researchers a tool that can remove and deposit material at a much finer scale than previously possible. The new Orion NanoFab relies on an additional neon ion beam that can manipulate nanostructures down to just a few nanometers. Images: Carl Zeiss NTS LLC

In the 1950s we learned about lasers. In the 1960s and 1970s, aerospace and the semiconductor took the spotlight. In the 1980s and 1990s, drug discovery, the Internet, and the cell phone stole the show. What is today’s star of technology? It's possible we'll find the answer in a transmission electron micrograph.

Less than two decades removed from the discovery of carbon nanotubes, monumental steps have been made in understanding how materials function, behave, and interact on the nanoscale. Sub-10-nm resolution is no longer an exotic achievement, and nanoparticle suspensions, nanolithography processes, and extremely detailed thin-film constructions are all becoming commonplace.

Nanotechnology has progressed from the “next big thing” to become actual big business. In a 2010 study of nanotechnology commercialization strategy published by The National Center for Manufacturing Sciences, more than 1,200 nanotechnology organizations, most of them for-profit, were operating in the United States. Despite the 2008 recession that negatively affected more than 80% of the organizations surveyed by the report’s authors, a state of "general exuberance" pervaded the sector. This attitude should be of little wonder. According to a May 2012 report for the Congressional Research Service, an estimated $80 billion in revenues in 2008 were generated by products using nanotechnology. In addition to the billions spent and earned by private industry, since 2001 the U.S. government has steadily increased funding for nanoscale science, engineering, and technology through the National Nanotechnology Initiative, which aids both public and private sectors. For Fiscal Year 2013, $1.8 billion has been requested by the current administration, and in 11 years about $15.6 billion has been spent to guarantee the United States’ role as a global leader in nanotechnology.

The appetite for funds, however, is hardly sated. Successful growth of nanotechnology applications has depended on other factors as well. Developments in instrumentation and approaches to business suggest an increasingly orderly, regimented approach to nanoscale R&D is taking place that promises to yield results far in excess of monetary investment.

Tools of the nanoscale trade
The typical time taken to introduce a new material to the marketplace is long: 15 to 25 years, according Lloyd J. Whitman, deputy director of the Center for Nanoscale Science and Technology (CNST) at the National Institute of Standards and Technology (NIST), Gaithersburg, Md.

"Once a new material has been discovered, it takes time to establish both a supply chain and the knowledge base amongst manufacturers to enable them to make use of the new material," says Whitman, whose organization is an authority on materials standards and development. For several heavily researched materials, such as gold nanoparticles, graphene, and single-walled carbon nanotubes, he says, "we are in the transition period from research to product deployment, with high-volume manufacturing methods starting to become available. This is a critical step because it enables statistically meaningful measurements of material quality and reliability to be made, which can then be used to improve the manufacturing process."

For example, even though the technology for producing gold nanoparticles has been around since the early 19th century, efforts to make them multifunctional are still an active area of research. Only recently have potential medical treatments based on these particles neared the clinical trial stage.

In 2007, NIST formed CNST as way to support U.S. nanotechnology enterprise from discovery to production. The center provides industry, academia, NIST, and other government agencies access to world-class nanoscale measurement and fabrication methods and technology.

CNST's shared-use NanoFab facility gives researchers economical access to and training on a state-of-the-art tool set required for cutting-edge nanotechnology development. A simplified application process allows participants to get projects started in just a few weeks.

"We provide assistance to private organizations through direct collaboration with our measurement research, including formal agreements such as Cooperative Research and Development Agreements [CRADA], and through the NanoFab where we provide access to nanofabrication tools, training, and assistance with process development. We are also able to perform remote work, where private organizations pay for our staff time to perform well-defined tasks," says Whitman.

CNST is not a contract research organization (CRO), but it fills the gap where a CRO, or multiple CROs, might be expected to exist as various fields that rely on nanotechnology mature down the road. In some cases, according to Whitman, access to an expensive instrument like an electron microscope is quite difficult for small companies, and this lack of capability can make or break a product.

Research at CNST is entirely geared toward development of nanoscale measurement instruments and methods, which are made available through collaboration. These efforts may help guide instrument makers as they look to further develop their own products.

Neon brings new light to nanofabrication
While some technologies for nanoscale imaging, such as electron microscopy, have existed for decades, others have languished until recent breakthroughs have allowed them emerge in the marketplace. This is true of gas field ion sources (GFIS), which were first invented in 1955 for possible use in charged particle beam instruments, but could not be developed for commercial ion sources because the sources lacked durability and temporal stability could not be adequately controlled.

Instead, charged particle beams have relied on either beams of electrons or ionized gallium. Both sources can help build and prototype customized devices with nanoscale features by machining materials through sputtering, depositing, or etching metals and insulators, or exposing resist for direct write lithography.

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Tools such as dynamic light scattering particle sizers and this network gas chromatograph from Agilent Technologies help Pixelligent perfect the liquid synthesis it uses to make nanocrystals into numerous shapes, including rods, spheres, flakes, and discs. The size of these nanoparticles is carefully controlled, ranging from 2 to 10 nm. Image: Pixelligent

Five years ago, Carl Zeiss NTS LLC, Peabody, Mass., introduced the Orion Plus Helium Ion Microscope as an improvement to gallium ion beams. The instrument gave users better contrast and surface detail measurements at sub-0.5-nm lateral resolution, allowing direct write fabrication and inspection down below the sub-10-nm level.

These were significant improvements over prior ion sources and were made possible with helium beams created from a GFIS. Because helium is inert, the conductivity of deposited materials—typically metals and insulators—is not altered by the energy of the beam. According to Bipin Singh, product manager at Carl Zeiss, the adoption of helium beam technology has since become a mainstream technique, resulting in more than 100 publications.

Neon, another inert gas, was postulated to potentially produce an even more efficient source of ionic energy. However, it posed an even bigger development challenge, because of the fundamental differences in the two types of atoms. Neon atoms will field ionize at an electric field strength of 3.5 V/Å, or about 20% less than the field required for the field ionization of helium. According to Singh, the reduced field strength gives rise to a limited lifetime of the emitter atoms due to field.

Through research at Carl Zeiss, says Singh, both the fluctuations in the brightness, and the motion of the emission sites, have been reduced by a factor of five. Operation time has been extended to about 10 hours, allowing the neon ion source to be used for imaging and nanomachine applications.

"A distinct advantage of helium and neon ion beam lithography is that there is no proximity effect," says Singh. "This means that when fabricating nested structures, the width of features in the center and periphery of the region of interest will be the same. The user can then focus on designing and fabricating nanostructures of choice rather than engineering elaborate dose adjustments to overcome the proximity effect."

In 2012, the Orion NanoFab was launched, which features both the helium and the neon GFIS in addition to the traditional gallium focused ion beam. Capabilities that have already been demonstrated, says Singh, include the machining of holes less than 3 nm in diameter with aspect ratios of 10:1 or greater. Plasmonic device sidewall features of less than 5 nm and direct write lithography features as narrow as 4 nm have been created with NanoFab, and practical accomplishments include the creation of solid-state nanopores for DNA sequencing devices.

Practical Raman for the nanoscale
Another recent arrival to modern nanotechnology applications is Raman spectroscopy. Although vibrational spectroscopy has been long been a valued resource for determining chemical signatures, its role in product development has been limited by its ability to achieve repeatable results. Scot Ellis has been observing the shift during his 16 years at Thermo Fisher Scientific.

"It's pretty easy to enter the Raman market," says Ellis, marketing manager for microscopy and research spectroscopy at Thermo Fisher Scientific, Waltham, Mass. But, he says, "Raman has historically been a very finicky technique. It's hard to get working properly, and it's challenging to get repeatable."

Times have changed somewhat. After years of seeing high demand for Fourier transform infrared spectrometry, Ellis is seeing a rise in interest for Raman. At Thermo Fisher Scientific, this can range from the TruScan range of handheld spectrometers to full-scale benchtop research Raman instruments such as the DXR.

"We see our microscopes being used in a number of areas in materials, particularly carbon nanotubes. A few years ago, carbon nanotubes drove the market," says Ellis. “Raman can tell you a number of things about nanotubes. Because it is sensitive to physical characteristics, we can see things like the number of carbon nanotubes in multi-wall nanotubes, its length, and its width."

Now, he says, the excitement has shifted to graphene, where Raman spectroscopy can permit the characterization of sheet thickness, uniformity, and functionalization.

In recent years, the market for Raman spectroscopy has grown significantly, but not just because of the demand for nanoscale measurement. Instead, teams at Thermo Fisher Scientific, as well as other companies, have capitalized on the development of compact, rugged Raman technology to deliver spectroscopic accuracy to the handheld market. The instruments, which can search spectral libraries to identify unknowns, have been popular in areas well away from laboratory research, such as homeland security.

But nanotechnology is still a driver for further development of the underlying technology. Notable innovations, says Ellis, include surface-enhanced Raman spectroscopy, which involves the use of molecules adsorbed on rough metal surfaces to increase Raman scattering. This has been shown to increase sensitivity enough to allow detection of single molecules.

Tip-enhanced spectroscopy, meanwhile, brings Raman scattering to the atomic force microscope (AFM) tip and offers true nanoscale chemical characterization. This is still a tricky technique, however, and hasn't resulted in the sort of repeatability expected of mainstream Raman.

"As far as product development goes, Raman is underutilized with respect to nanomaterials analysis," says Ellis. "Raman is sensitive to structural information, and how molecules are put together. That's the nice thing about Raman, it brings two or three different facets to the table."

Nanotech for electrical engineers
Requirements for successful product development typically require more than just quantification of feature size. While many lithographic processes involve known materials with known chemical or electrical properties, some development efforts need more specific information. Spectroscopy can provide chemical information, and electron microscopy can image to nearly the atomic scale. But what about electrical properties?

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These images of a hybrid bipolar junction and CMOS transistor were obtained with Agilent Technologies’ Scanning Microwave Microscopy tool. They show the topography and direct current-direct voltage amplitude (top row, l-r). The bottom images show the phase of the integrated circuit sample and a detail of the previous image that shows the small variations of phase. Images: Agilent Technologies   

In 2009, Agilent Technologies, Santa Clara, Calif., won an R&D 100 Award for an innovative technology, Scanning Microwave Microscopy (SMM), which improved on existing measurement techniques for electrical characteristics. While traditional atomic force microscopy had been used to measure capacitance, its sensitivity was limited by the inherent capabilities of an AFM, which was designed primarily to gauge deflection, not electrical signals. SMM did not depart from AFM; in fact, it uses Agilent’s existing 5420 and 5600 AFM instruments. What it did do was combine the nanoscale spatial resolving power of the AFM with the compound electrical measurement capabilities of a vector network analyzer (VNA). For the first time in one instrument, researchers were able to obtain quantitative data for calibrated capacitance, complex impedance, calibrated dopant density, carrier density, and carrier migration.

What drove Agilent to develop the product, says Matthias Fenner, an applications scientist with Agilent Technologies, was the desire bring the sensitivity of microwave testing for materials down to the nanometer range.

"Microwave characterization of materials has been around for a long while and nanometer measurement has been around for a long while, but combining the two was new. While it has been tried before, nobody had made it a product," says Fenner. A main reason SMM successfully found applications in the marketplace was the ability to calibrate the results generated by the instrument. This effort involved the testing of many different types of AFMs with Agilent’s own VNA so that an appropriate configuration could be found. It also involved the assistance of NIST in developing the calibration standards.

"We have two types of calibration samples at the moment. One is for capacitance measurements and one is for dopant density measurements in semiconductors," says Fenner.

As a result of this effort, Fenner continues, scanning microwaves are the only method of achieving true capacitance measurements on the nanometer-scale. In practice, the VNA sends an incident microwave signal through a diplexer to the sub-7-nm conductive tip of the AFM's platinum-iridium cantilever. The signal is reflected from the tip and measured by the VNA. By calculating the magnitude and phase of the ratio between the incident and reflected signals, SMM applies it to a model to calculate the electrical properties of the sample.

"It really helps with different areas in the search to characterize materials. For instance, when we think of semiconductor devices, very often we find it’s necessary to measure gate capacitance for a transistor. Another interesting application we found is the measurement of ionic conductors," says Fenner. These are solids in which the electrons and ions carry electrical resistance. Ion conductivity is typically difficult to measure, because in a conventional AFM the ions are attracted to a metal tip but do not pass through. The charge builds on the tip but cannot be measured because no contact is made. SMM circumvents this with the sensitivity of the VNA.

In addition to widespread use in the semiconductor field, other areas of nanotechnology R&D are taking notice of SMM. According to Fenner, anyone who is interested in electron transport or dielectric properties could find use in the technique, including those working with organic photovoltaics or polymers.

Nanoscale product realized
Even with multiple innovations in materials characterization, producers of nanotechnology products still face tremendous challenges in launching a product to market. While established corporations have the advantage of size and a broad market, start-ups face the pressure of not only lining up funding and properly executing development, but also getting products to customers quickly.

Pixelligent, a Baltimore, Md.-based company that manufactures two distinct types of nanoparticles, offers a window into the challenges that face a small nanotechnology company, and the strategies that can be used to overcome them.

Like many new technologies, the proprietary process for producing nanoparticles was developed at a university—the University of Maryland—and subsequently launched as a company that intended to specialize in lithography. After experimentation, this avenue did not seem promising. "Lithography is a difficult technology," says Craig Bandes, president and CEO of Pixelligent. "The adoption path is long, from five to 10 years."

Going back to their expertise, the company’s founders decided their best option was to market nanoparticles that could be used in a drop-in fashion immediately.

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One of Thermo Fisher Scientific's most populat research Raman spectrometers is the DXR, which can be used to effectively characterize carbon nanostructures, including nanotubes and graphene. Researchers are have using it in conjunction with the Nicolet iS50 FT-IR spectrometer at the Wisconsin Institutes of Discovery in Madison. Image: Thermo Fisher Scientific

"Our focus was actually to get the product out to customers early, before even they think it’s perfected," says Bandes. "We went out early and presented our capabilities so we could figure out who cares about the product. That really was a defining moment for us and enabled us to really understand what customers care about."

What they learned was that nanoparticle dispersion was the most important characteristic for their potential base of customers. Because that was Pixelligent's strongest capability already, the founders decided to narrow their focus even further. Despite developing expertise in a number of materials types, they launched just two: zirconia and hafnia. And while their methods can produce tetrapods, rods, and spheres, the company tends to focus on spheres.

Sized from 2 to 10 nm, the nanoparticles are actually crystals, designed to be fully transparent, with high optical transmission. The crystals do not agglomerate in suspension, and can be integrate in various polymers. Their customers show the most interest in zirconia nanocrystals, which are being investigated as a way to increase the index of refraction in touch screens and other flat-panel displays. The company hopes to develop a way to increase the production capacity to the kilogram level shortly, and eventually to 1,000 kg per year by 2013. With 24 employees, the company has more than doubled in size since last year.

Bandes acknowledges that the industry of nanomaterial production is still in its infancy, but that customers are out there and looking for these types of solutions. He is frequently asked why nanotechnology can’t move faster, but he points to several possible reasons. For one, he says, global companies need to increase their investments. Two, it’s important for an R&D company to move to a commercial-type of company quickly to get the product to market. Finally, instrument manufacturers, he says, play a big part in helping produce laboratory tools that are affordable for small companies to buy and use.

"It takes longer than people think. In terms of the growth of nanotechnology applications, it affects every sector of industry, and it takes time," says Bandes.

Repeating the need for reproducibility
While good instrumentation, adequate funding, and smart business decisions make the commercialization process easier, reproducible measurement results—bolstered by established standards—are still in short supply for nanotechnology developers. Instrument vendors play a major role in this progression, but, again, an organization like NIST is required to administer standard references. In addition to a number of important nanoscale materials already released, including gold nanoparticles, polystyrene nanoparticles, nanoparticulate titanium dioxide, and nanoporous controlled-pore glass, NIST has also recently released the world’s first reference material for single-wall carbon nanotube soot, the primary industrial source of single-wall carbon nanotubes.

According to Whitman, this was a badly needed source of uniform and well-characterized carbon nanotube soot for material comparisons, as well as chemical and toxicity analysis.

"In the next year NIST plans to release additional nanoscale reference materials, including other carbon nanotube formulations and silver nanoparticles, along with associated protocols for sample preparation and measurements using widely available commercial instruments," says Whitman.

However, he stresses the importance of remembering that these nanomaterials and many others are actually a whole family of materials, with properties controlled by size, shape, and surface functionalization. Whitman believes that as scalable manufacturing processes are now coming on line for the base materials, we can expect large numbers of new applications to emerge as technologists become more skilled in engineering their detailed properties.

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