Is the Heyday of Carbon Nanotubes Just Around the Corner?

By Chris Wood, Senior Analyst

A few weeks ago in these pages we ran an article titled The State of Nanotechnology. In the article, we touched on one particular technology that I'd like to delve into more deeply today. Carbon nanotubes (CNTs) warrant additional discussion partly because of the sheer scope of their potential applications and partly because of recent breakthroughs that are bringing their heyday closer to reality.

Although the term "carbon nanotubes" still sounds rather futuristic, scientists have known about their existence for quite some time. Sumio Iijima is typically credited with discovering CNTs by accident in 1991, but a careful reading of the literature actually shows that Russian scientist LV Radushkevich and his collaborators reported on CNTs as early as 1952. Then, in the mid-1970s, a collaborative effort between scientists from Japan and France reported the observation of CNTs via electron microscopy. The actual discovery of CNTs came with little fanfare, however, since nobody at the time thought they could be fabricated in meaningful amounts.

Fast forward about 15 years, to when Huffman in the US and Kratschmer in Germany developed the arc evaporation method to produce macroscopic amounts of C60, a carbon molecule in the shape of a soccer ball; these are often referred to now as "buckyballs." Iijima – who was studying the surfaces of the electrodes used in the arc evaporation process – found large amounts of multi-wall carbon nanotubes (MWCNTs) mixed with other graphite particles. The ability to source MWCNTs was of great importance… but there was more to come.

In early 1993, both Iijima (working at NEC in Japan) and Donald Bethune (of IBM) independently isolated single-wall carbon nanotubes (SWCNTs). MWCNTs are easier to produce in high volume quantities than SWCNTs, but they're less sought after because their structural imperfections tend to diminish their desirable material properties. SWCNTs are more pliable than MWCNTs, and they have unique electronic and mechanical properties which are widely useful. Thus, for the purposes of this article, when we discuss CNTs we'll mostly be referring to SWCNTs.

CNTs are an allotrope of carbon that can be thought of as a sheet of graphene (a hexagonal lattice of carbon) rolled into a seamless cylinder. They are highly flexible and very strong (100 times stronger than steel at one-sixth the weight). They also have high electrical conductivity (as high as copper) and high thermal conductivity (as high as diamond). And they can easily penetrate membranes such as cell walls – in effect acting like a needle at the cellular level.

Due to the incredible properties of CNTs, research labs and companies the world over have been promising technological breakthroughs – in fields ranging from electronics and medicine to construction and aerospace – for the past two decades.

Some of these include:

  • Building transistors from CNTs to enable minimum transistor dimensions of a few nanometers, and developing techniques to manufacture integrated circuits built with nanotube transistors.
  • Creating drug-delivery systems with CNTs. One idea is to fill the tubes with a mixture of drugs and water molecules, then heat up the tubes with an infrared laser to boil the water inside, and once they've reached the desired target in the body, blow them up to release the drugs; i.e., "drug grenades" if you will.
  • Constructing superstrong, lightweight bridges and buildings out of CNTs instead of steel.
  • Replacing silicon with a thin layer of CNTs in window-based solar-energy production for a transparent solar window.

It's true that a few applications of CNTs are commercialized today (some products containing CNTs include paint, vehicle parts, and sports equipment), but these represent bulk applications in which MWCNTs play an auxiliary role to reinforce mechanical, thermal, or electric properties. The technological revolution in products that capitalize on the unique mechanical and electric properties of SWCNTs has been slower to materialize.

The main reason that the most promising applications have not yet come to pass is the lack of reproducibility of quality CNTs. Simply by changing the bonding configuration with itself, carbon can form a large variety of isomers from the same number of atoms. And the number of these isomers increases almost exponentially with the number of carbon atoms. For example, C60 has one isomer, while C120 has about 14,000. According to Dr. Gyula Eres, from the Materials Science and Technology Division of Oak Ridge National Laboratory, "The large number of isomers leads to a non-uniform product distribution that can dramatically change in response to relatively small changes in experimental parameters that are often difficult or impossible to account for. This is why the various methods used for synthesis of CNTs produce such vastly different distributions of single wall and multi-wall CNTs along with other carbon structures that are undesirable side products of the synthesis process."

But the long-awaited CNT revolution may be just around the corner, thanks to a couple of recent improvements to the production process.

Since the early '90s, CNTs have been described as "rolled-up sheets of graphene," except they couldn't actually be made that way. Instead, they were coaxed into self-assembling using the three typical production techniques of arc discharge, laser ablation, and chemical vapor deposition. It was recently reported, however, that researchers from Harvard and the NanoScience Center of the University of Jyvaskyla in Finland have discovered a new way to make CNTs by means of twisting graphene nanoribbons. The basic idea is easily explained: simply twist the ends of a strap on a backpack and you'll understand what's going on. The new method also supposedly allows for stricter experimental control, which would permit scientists selectively to create various types of CNTs.

Just two weeks ago, another – perhaps even more important – breakthrough in the production of CNTs was announced by a group of researchers from Malaysia. The group claims to have successfully created a method of continuously producing high-quality, pure CNTs at a cost of just $15 to $35 per gram, well below current production costs of $100 to $700 per gram. According to the team, "the system is capable of producing up to 1,000 grams of carbon nanotubes a day." It should be noted that details about this new method are hard to come by, and the group's claim is difficult to substantiate. If it is true, however, it represents a giant step forward in CNT research.

In addition to novel production techniques, we've also recently seen advances in the application of CNTs in electronics. It's been common knowledge for years that scaling bulk silicon transistors will be extremely difficult (if not impossible) once we get down to about 15 nm. Intel's new chips, coming out later this week, employ the company's Ivy Bridge 22 nm technology. Thus, we've almost reached the theoretical limit of being able to scale down planar transistors. (Intel's new chips do incorporate 3D transistor technology, but that's a discussion for another day.) One possible solution to this problem is to swap silicon transistors for ones made with CNTs. The problem is that nobody knew whether CNT transistors could offer performance advantages over silicon at sub-10 nm lengths – until now.

Dr. Aaron Franklin and his team at IBM recently showed that CNTs can operate as excellent switches at molecular dimensions of only 9 nm; i.e., less than half the size of the leading silicon technology. And these transistors deliver more current and require less operating power than silicon-based ones of similar size. This is the first experiment to clearly demonstrate that silicon can be replaced with CNTs in future semiconductor technology, and the results propel such devices to the forefront of future microchip technologies.

These recent developments add to our already bullish outlook for the future prospects of CNTs. But it's important to keep in mind that like any technology, it doesn't come without risks. Some studies have shown that CNTs, especially longer ones, can pose health risks similar to asbestos' if inhaled. Other studies have shown that CNT inhalation can also suppress the immune system. Thus, their ultimate use in industry could be significantly curbed by regulation.

Nevertheless, CNTs represent a disruptive technology the likes of which comes along once every few generations (if that). We're convinced that it is poised to reshape industries, create new ones, and make savvy investors very wealthy in the process.

Exciting new technologies offer early investors the opportunity for elephant-sized profits. Attendees at this weekend's Recovery Reality Check Summit in Weston, Florida will hear about a number them from a panel of financial luminaries, including Casey Research Chief Technology Investment Strategist Alex Daley.

Not attending? Not to worry! You can catch every single piece of actionable investment advice with the Summit Audio Collection, which you can get for $100 off if you order before midnight EDT tonight.]

Bits & Bytes

Apple Makes the Best Cider… Again (Apple)

Once again, Apple blew market expectations to smithereens, on Tuesday releasing second-quarter financials that exceeded even the most optimistic expectations. Revenues jumped nearly 60%, while net income skyrocketed up 94%, year over year. The results came on the back of stunning sales of iPhones – 35.1 million units sold, up 88%; and iPads – 11.8 million units sold, up 151% from the year-ago quarter. The stock, which had been selling off of late – down 12% from its early April peak – immediately turned around, tacking on 9% on the news.

When Can Computers Not Replace Humans? (TIME)

When grading essays, for starters. The Education Testing Service (ETS) has begun using computers "in conjunction with" humans to grade the essay portion of the SAT, which college-bound high-school students must take. A human grader can only process about 30 essays an hour, ETS says, while a machine can zip through 16,000 in 20 seconds. That's a big savings, but the results leave a lot to be desired. The computer "doesn’t care if you say the War of 1812 started in 1945," criticizes one reviewer. So right now, fully automated essay reading just doesn't cut it (although how much better a human might be reading a new essay every two minutes is open to question), but it seems likely that the bugs will eventually be worked out.

Microsoft and Facebook Cut a Deal (Facebook)

These days, so much of business is a matter of who owns the IP ("intellectual property"). Of all IP, one of the most important issues is patents, as companies seek to protect themselves from so-called "patent-fishing" lawsuits designed to exploit some loophole and gain an out-of-court settlement. Thus the big deal of the week was Facebook's acquisition of the right to purchase a portion of Microsoft's patent portfolio that it in turn recently picked up from AOL. Facebook ponied up a cool $550 million… in cash.

And Just for Fun (gizmag)

How about living longer by eating some buckyballs? It apparently works with rats. Those rodents who ingested the human equivalent of a tenth of a gram of buckyballs (a naturally occurring form of carbon known as C60) dissolved in olive oil nearly doubled their normal lifespan with no toxic side effects. But hey, maybe it was the olive oil. You know, that Mediterranean diet…

Apr 26, 2012