Graphene Sensing Tool

The graphene news just keeps getting better and more exciting. Read through this. A little bit of neat fabrication has given us a device able to measure the weight of a couple of atoms.

Thus we are already making up neat tools with this stuff. The real point here is that complex geometric shapes can be contemplated and ultimately fabricated if justified.

We have already outlined some of the developing aspects of this extraordinary technology. I am still getting over the fact that we can fly continuous nanotubes off a tool to creditably produce the space cable that Arthur C. Clark dreamt of

Can you imagine a battle armor woven with this stuff? The advantage to the armor would surely match that of the original plate of the high middle ages. Likely it can reach the level that the contents would be vaporized before penetration becomes an issue. It would also be very light and obviously impervious to wear.

This is surely the most important materials discovery made ever. As we become more adept at producing it and working with it, we can expect it to possibly displace most other materials including metals. The main factor will be cost, but this promises to get cheap fast.

Particularly when the labs have been producing it for their work by the expedient of applying scotch tape to a chunk of graphite, which is quite enough to make you chuckle.

Graphene works as a highly sensitive mass detector

Sep 29, 2009

http://physicsworld.com/cws/article/news/40552

http://images.iop.org/objects/physicsweb/news/13/9/32/graphene1.jpg

Researchers at Columbia University in New York have made the first electrical-readout nanomechanical resonators made from graphene. The devices, which consist of vibrating sheets of graphene suspended over micron-sized trenches, could be used as highly sensitive, robust, mass detectors.

Graphene sheets are sheets of carbon that are just one atom thick. As well as having remarkable electronic properties, graphene is extremely stiff and strong. This means that the material can be made into bridge-like resonators that vibrate at very high frequencies. Because such a resonator has an extremely small mass, its resonant frequency changes each time a molecule is adsorbed onto its surface.

"Although graphene shares these advantages with carbon nanotubes, which have also been used to make highly sensitive mass detectors, it has the added bonus of being a 2D sheet that we can 'carve' into the shapes we want," explained team leader James Hone. "This gives us more control over the properties of the finished resonators."

Suspended graphene

The Columbia team made its devices by placing graphene sheets onto silicon/silica substrates, then patterning metal electrodes and etching away the silica to produce suspended graphene. The portion of each electrode that is in contact with the graphene is also suspended, which makes electrical readout easier later on.

The devices vibrate at megahertz frequencies, with a peak around 65 MHz that depends on the device geometry. The frequency can also be adjusted with a DC voltage applied to the gate, which introduces tension to the sheet. When an object is placed on the device, the frequency changes – and the change is detected with the electrodes, and used to calculate the mass of the molecule.

Sensitive to two gold atoms

"Our measurements indicate that the devices should be sensitive to around 1 zeptogram (10^–21g), which is about two gold atoms, at low temperatures" Hone told our sister website nanotechweb. "They also show that the response is not as simple as expected because placing material on the graphene changes both the mass of the sheet and its tension – a new phenomenon that has never been seen before."

The team is now experimenting with different geometries for the devices and looking at various readout techniques that will improve their performance.

The work was published in Nature Nanotechnology.

About the author

Belle Dumé is a contributing editor to nanotechweb.

Billion Year Memories

I suppose that this will go largely unnoticed but this is very welcome news. Here we have a bullet proof method of storing data that is for all intents and purposes eternal.

I have always been conscious of how much we have lost of mankind’s creative output.

I am also conscious of how much we are now digitalizing onto media that is still physically transient. Have you checked the content of those 3 ½ discs lately? Do not wait if you think any of it may be important. Now we are getting technology that provides permanent storage that should satisfy every librarian for a billion years. This was only possible in science fiction before now.

In a way, we are entering a world in which a little bit of our lives will become immortal. Scary thought, but our great grand children will be able to trace the spoor of our lives even though they never met us. I have a few scraps of my mother’s handwriting and none at all of anyone else’s. How different might it be to read their mail and parse their lives and friendships and appreciate their efforts and contributions? Surely it would be better than a disconnected fiction about strangers.

Today we are creating such personal spoor on the internet and none of it needs to be lost.

A Billion Year Ultra-Dense Memory Chip

http://www.spacemart.com/reports/A_Billion_Year_Ultra_Dense_Memory_Chip_999.html

by Staff Writers
Berkeley CA (SPX) Jun 05, 2009

Berkeley Lab researchers have created a unique ultra-high density memory storage medium that can preserve digital data for a billion years. When it comes to data storage, density and durability have always moved in opposite directions - the greater the density the shorter the durability.

For example, information carved in stone is not dense but can last thousands of years, whereas today's silicon memory chips can hold their information for only a few decades.

Researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have smashed this tradition with a new memory storage medium that can pack thousands of times more data into one square inch of space than conventional chips and preserve this data for more than a billion years!

This video shows an iron nanoparticle shuttle moving through a carbon nanotube in the presence of a low voltage electrical current. The shuttle's position inside the tube can function as a high-density nonvolatile memory element. (Courtesy of Zettl Research Group)

"We've developed a new mechanism for digital memory storage that consists of a crystalline iron nanoparticle shuttle enclosed within the hollow of a multiwalled carbon nanotube," said physicist Alex Zettl who led this research.

"Through this combination of nanomaterials and interactions, we've created a memory device that features both ultra-high density and ultra-long lifetimes, and that can be written to and read from using the conventional voltages already available in digital electronics."

Zettl, one of the world's foremost researchers into nanoscale systems and devices, holds joint appointments with Berkeley Lab's Materials Sciences Division (MSD) and the Physics Department at UC Berkeley, where he is the director of the Center of Integrated Nanomechanical Systems.

He is the principal author of a paper that has been published on-line by Nano Letters entitled: "Nanoscale Reversible Mass Transport for Archival Memory." Co-authoring the paper with Zettl were Gavi Begtrup, Will Gannett and Tom Yuzvinsky, all members of his research group, plus Vincent Crespi, a theorist at Penn State University.

The ever-growing demand for digital storage of videos, images, music and text calls for storage media that pack increasingly more data onto chips that keep shrinking in size. However, this demand runs in sharp contrast to the history of data storage.

Compare the stone carvings in the Egyptian temple of Karnak, which store approximately two bits of data per square inch but can still be read after nearly 4,000 years, to a modern DVD which can store 100 giga (billion) bits of data per square inch but will probably remain readable for no more than 30 years.

"Interestingly," said Zettl, "the Domesday Book, the great survey of England commissioned by William the Conqueror in 1086 and written on vellum, has survived over 900 years, while the 1986 BBC Domesday Project, a multimedia survey marking the 900th anniversary of the original Book, required migration from the original high-density laserdiscs within two decades because of media failure."

The illustration shows the configuration of a new digital memory storage device consisting of an iron nanoparticle shuttle that moves through a carbon nanotube when a voltage is applied. This memory device can pack a trillion bits of data into one square inch of medium and retain that data for a billion years.

Zettl and his collaborators were able to buck data storage history by creating a programmable memory system that is based on a moveable part - an iron nanoparticle, approximately 1/50,000th the width of a human hair, that in the presence of a low voltage electrical current can be shuttled back and forth inside a hollow carbon nanotube with remarkable precision.

The shuttle's position inside the tube can be read out directly via a simple measurement of electrical resistance, allowing the shuttle to function as a nonvolatile memory element with potentially hundreds of binary memory states.

"The shuttle memory has application for archival data storage with information density as high as one trillion bits per square inch and thermodynamic stability in excess of one billion years," Zettl said. "Furthermore, as the system is naturally hermetically sealed, it provides its own protection against environmental contamination."

The nanoscale electromechanical memory device can write/read data based on the position of an iron nanoparticle in a carbon nanotube. The memory devices here are displaying a binary sequence 1 0 1 1 0.

The low voltage electrical write/read capabilities of the memory element in this electromechanical device facilitates large-scale integration and should make for easy incorporation into today's silicon processing systems. Zettl believes the technology could be on the market within the next two years and its impact should be significant.

"Although truly archival storage is a global property of an entire memory system, the first requirement is that the underlying mechanism of information storage for individual bits must exhibit a persistence time much longer than the envisioned lifetime of the resulting device," he said.

"A single bit lifetime in excess of a billion years demonstrates that our system has the potential to store information reliably for any practical desired archival time scale."

The multiwalled carbon nanotube and enclosed iron nanoparticle shuttle were synthesized in a single step via pyrolysis of ferrocene in argon gas at a temperature of 1,000 degrees Celsius. The nanotube memory elements were then ultrasonically dispersed in isopropanol and deposited on a substrate.

A transmission electron microscope provided high-resolution imaging in real time while the memory device was in operation. In laboratory tests, this device met all the essential requirements for digital memory storage including the ability to overwrite old data.

"We believe our nanoscale electromechanical memory system presents a new solution to the challenge of ultra-high density archival data storage," Zettl said.

This research was primarily supported by the U.S. Department of Energy's Office of Science through its Basic Energy Sciences programs.

Graphene Ribbons Mastered

More very good news here regarding the ongoing development of graphene technology. This suggests that it becomes plausible to mass produce ribbons of graphene in large amounts.

Although not yet in sheets, this may be just as good for most applications.

Now if we can figure out how to directionalize them and link edges, we might yet be able to produce fibers that could form an incredibly strong cable.

This is still a good start and it certainly opens the door for computer chip manufacture.

It is remarkable to believe that we have come so far from the first recognition of Bucky balls in candle soot.



Making Nanoribbons From Sliced Open Nanotubes


http://www.spacemart.com/reports/Making_Nanoribbons_From_Sliced_Open_Nanotubes_999.html

by Staff Writers
Stanford CA (SPX) Apr 20, 2009

A world of potential may lie tied up in graphene nanoribbons, particularly for electronics applications. But researchers have been hampered in their efforts to fully explore that potential because they had no reliable way of creating the large quantities of uniform nanoribbons needed to conduct extensive studies.

Now a team at Stanford University under Hongjie Dai has developed a new method that will allow relatively precise production of mass quantities of the tiny ribbons by slicing open carbon nanotubes.

It is relatively easy to produce fairly uniform carbon nanotubes in large numbers. But being the tiny, delicate structures that they are, slicing open nanotubes requires a tender touch. "The key is to be able to open up the tubes without destroying the whole structure," Dai said. "I mean, it doesn't have any zipper on it, right?"

Dai's method effectively creates the needed zipper. Carbon nanotubes are placed on a substrate, then coated with a polymer film. The film covers the entire surface of each nanotube, save for a thin strip where the nanotube is in contact with the substrate.

The film is easily peeled off from the substrate, taking along all the nanotubes and exposing the thin strip of polymer-free surface on each of them. A chemical etching process using plasma can then slice open each nanotube along that narrow strip. It's not unlike generating flat linguini noodles by slicing open bucatini, a long tubular pasta.

The process works not only on single-layer carbon nanotubes, but also on nanotubes with concentric layers of nanotubes, allowing each layer to be sliced open along the same "dotted line." The work is detailed in a paper published in the April 16, 2009 issue of Nature. Dai, the J.G. Jackson and C.J. Wood Professor of Chemistry, is the senior author of the paper.

Given all the other methods of nanoribbon production that have been tried - lithography, chemical reactions and ultrasound-influenced chemistry - all of which failed to produce the needed quantity or quality of graphene nanoribbons, Dai's method is surprisingly simple. "Once we overcame the hurdle of how to unzip the nanotubes, everything seemed so obvious," he said. "It is one of those things where you go, 'why didn't I think of that earlier?'"

In addition to being fairly straightforward and easy to do, the process can be extremely efficient. "We can open up every carbon nanotube at the same time and convert many nanotubes into ribbons at the same time," Dai said.

Depending on how large a surface they cover with nanotubes - anything from a chip to a wafer - Dai said his team can create anywhere from one to tens of thousands of graphene nanoribbons at a time. The ribbons can easily be removed from the polymer film and transferred onto any other substrate, making it easy to create items such as graphene transistors, which may hold promise as a way to possibly make high performance electronic devices.

"How much better computer chips using graphene nanoribbons would be than silicon chips is an open question," Dai said. "But there is definite potential for them to give a very good performance."

Another advantage of Dai's method is that the edges of the nanoribbons produced are fairly smooth, which is critical to having them perform well in electronics applications.

The next step in the team's research is to better characterize the ribbons and try to refine their control of the production process. Dai said it is important to control the width of the ribbon and the edges of the structure of the ribbon, as those things could potentially affect the electrical properties of the ribbons and any device in which they are used.

Dai said that graphene nanoribbons have other uses in addition to potential electronics applications.

"It is a very nice system to study nanoscale phenomena, in general," he said. "This method now opens up all these things that we can explore."

Liying Jiao, a postdoctoral researcher in the chemistry department, and Li Zhang, a graduate student in chemistry, are co-first authors of the Nature paper and contributed equally to this work. Xinran Wang, a graduate student in physics, and Georgi Diankov, a graduate student in chemistry, also are authors of the paper.

Graphene Surprise

We continue to get unexpected results with grapheme. Here the surplus heat is bled off directly into the silica substrate by electromagnetic transference. And while we are at it, the grapheme fails to permit thermalization.

This is almost too good to be true and the ramifications are only starting to be understood and even imagined. Is a layer of grapheme a heat barrier? Or can heat be directly converted to electron flow?

I have once conjectured that it might be possible to produce electron flow from metglass at low temperatures from the absorption of heat energy. This is just a superficial speculation that asks more questions than it answers but I thought it might lead somewhere. Perhaps once I get my Eden Machine skunk works up and running we can investigate the limits of that conjecture without spending much coin.

What brought that on at the time was the surprising behavior of electron flow on metglass. It allowed for the manufacture of much smaller starter motors for GM. It was my first eye opener to how little we understood the behavior of thin films, amorphous anything and electron flow and all that implied for technological advance. We are now starting to see the advances.

It almost makes you want to disappear into a laboratory to see what weird and wonderful things we could mock up. The whole area is still early stages and wide open.

Nanotubes wreak havoc with heat

http://physicsworld.com/cws/article/news/38051

Physicists in the US have discovered that electrons flowing in carbon nanotube-based circuits dissipate energy in much different ways than electrons flowing through devices made from conventional semiconductors such as silicon. The findings reveal processes of heat conduction that were never previously thought important, and could influence the types of materials chosen for the next generation of electronic devices in order to prevent them from overheating.

In conventional semiconductor devices, different layers of material are always joined by chemical bonds. This provides continuity for heat flowing through such devices, making them relatively easy to cool. Many researchers believe that future generations of electronic devices could be made from carbon nanotubes — tubes with walls just one atom thick — which could enable much smaller feature sizes and hence much better computing performance. However, nanotubes do not bond chemically to adjoining structures, which suggested that it should be very difficult to remove heat from such devices.

Bonding not needed

But now Phaedon Avouris and colleagues at the IBM Thomas J. Watson Research Center in New York and researchers at Duke University in North Carolina have found that electrons in nanotubes can dissipate energy straight to an adjacent substrate even though it is not chemically bonded.
The team has also found that current-carrying electrons in nanotube devices do not undergo the normal process of “thermalization”, in which a material’s thermal vibrations reach statistical equilibrium (Nature Nanotechnology doi:10.1038/nnano.2009.22).

Avouris and team studied a carbon nanotube on a silicon-dioxide substrate, an arrangement that acts like the active channel of a field–effect transistor. They have used a variety of techniques, including Raman scattering, in which the energy of scattered light reveals the different temperatures or “modes” of vibration of the nanotube lattice.

Normally when a current passes through a semiconductor the electrons bump into nearby atoms, which begin to vibrate in a certain mode. This mode then gradually transfers its energy to atoms at lower temperature modes until, at thermalization, all atoms are vibrating in statistical equilibrium.

The researchers have shown that, in nanotubes, thermalization does not take place; the atoms continue to vibrate in the same mode and statistical equilibrium is never reached.

Just as surprising, however, is that the lack of chemical bonding to the substrate does not inhibit heat conduction. The team has shown that when the electrons collide with atoms in the silicon dioxide, which is a polar material, the subsequent shift in position of the atoms generates an electric field that extends beyond the substrate and into the nanotube.

When the nanotube’s electrons interact with this field they are able to dissipate energy straight to the substrate.

Overlooked effect

Scientists were aware of this process of remote heat conduction before, but had never before considered it important because they had focused on 2D and 3D materials in which the effect is much weaker. But Avouris told physicsworld.com that the other unusual mechanism — the absence of thermalization — could exist in other materials, and that it may have been overlooked because researchers have not had the right observational tools.

Graphene Data

A lot is now coming out on Graphene. Therefore I will be posting several stories over the next few days. This one is perhaps the best exposition so far. We are learning to manufacture this stuff and starting to imagine novel applications. We are only beginning here, but step by step we are finding ways to create layers that are a single atom thick and how to work with them.

We have already seen this show up on the outside of an apparent UFO nosecone where it would accommodate powerful magnetic fields.

An upcoming item will explore the possibility of using structures to absorb hydrogen for storage.

An early application could well be the creation of random complex traps to hold useful free ions. Simply charging the material would let it absorb the free ions so that they could be stored safely and they could be released by the expedient of applying a reversal charge.

A new solution to graphene production


As every schoolboy knows, the stuff in your pencil lead is graphite, a naturally occurring form of carbon, useful but not very interesting. What is more interesting is that graphite is made from a stacked system of layers, each just one atom thick. It was long thought that these graphene layers were unstable and that removing them from the parent crystal would cause them to roll up. This raised the question of how thin you could make graphite. Ten layers? Five? By peeling layers from a graphite crystal with sticky tape and then rubbing them onto a silicon dioxide surface, a team from the University of Manchester found a surprising answer: it is possible to produce graphite crystals just one atom thick.

1 It soon became clear that this graphene had intriguing electronic properties. For example, due to the symmetry of its 2D honeycomb lattice, charge carriers in graphene appear massless.

2 More important for microelectronic engineers, these carriers have ultrahigh mobility, opening the door to superfast transistors.

3 The huge potential of graphene comes with one small catch: mechanical cleavage of graphite is a very slow process with very low throughput. As a result, graphene is the most expensive material known to man, costing approximately $1 per square micron.

4 New, high-yield, cheap ways to make graphene are urgently needed. For microelectronics, the solution will probably be to grow graphene on silicon wafers using reasonably well known processes. However, for most other applications it is accepted that a method to produce graphene in liquids is required. Much progress has been made, with a number of groups having developed chemical techniques to split graphite into sheets of graphene-like material such as graphene oxide.

5, 6 However, such materials tend to have many defects, thus altering the interesting properties. Attempting to resolve this problem, we recently demonstrated an alternative liquid-based process to exfoliate graphite to give defect-free graphene.

7 We used methods developed recently to obtain individual carbon nanotubes suspended in liquids. Nanotubes tend to aggregate together, which reduces their energy. But you can remove this propensity to aggregate if you place them in a liquid that binds to the nanotubes as well as they bind to each other. We found that liquids whose surface energy matched that of nanotubes gave stable suspensions of individual nanotubes.

8 As nanotubes are rolled-up graphene, we suspected the same approach would allow us to split graphite into graphene.

We mixed graphite with a nanotube-suspending solvent and applied sonic energy. Initial tests showed that significant quantities of graphite could be suspended in this manner. To test whether the science was the same as for nanotube suspensions, we mixed graphite with dozens of carefully chosen solvents and measured how much graphite remained suspended after centrifugation. When plotted versus surface energy, it became clear that the amount of suspended graphite peaked sharply for solvents with surface energy close to that expected for graphite. The mechanism was the same.

The key question was, Had we suspended graphene or just small flakes of graphite? The high boiling point of our solvents precluded the standard approach of depositing the flakes on a surface and examining with a microscope. Instead of this, we dropped the suspension on special holey substrates designed for electron microscopy. The solvent tended to run off the substrates leaving small flakes deposited in its wake that could easily be found using a transmission electron microscope. We used electron diffraction to confirm the presence of monolayers and to estimate the number of layers by focusing on the flake edges. It was immediately apparent that about 30% of them were one atomic layer thick, similar to the monolayer. In addition, a number of bilayers, multilayers, and folded monolayers, were observed.

To make real progress, however, we had to show that the graphene was chemically unmodified and not highly defective. As a test, we used x-ray photoelectron spectroscopy, a technique that gives information on bonding in a material. This clearly showed that the graphene was not chemically modified. But the results did not rule out the possibility of defects. Consequently, we carried out Raman spectroscopy with the help of collaborators at the University of Cambridge. With great care, Raman spectra were obtained from individual graphene flakes, giving information on the presence of defects. The answer was unambiguous. The level was too low to measure, showing that our liquid processing was not introducing defects. The high quality of the graphene was elegantly confirmed by atomic resolution transmission electron microscopy, carried out by colleagues at the University of Oxford: see Figure 1(C). In principle, this production process can be scaled up to make very large quantities of defect-free graphene.

For now, it is becoming clear that graphene can be produced, cheaply and easily, in certain liquids at a reasonable yield. In the future, we hope to improve the yield, increase the flake size, and extend this method to aqueous systems. We expect that this method will be useful, not only as a low-cost and straightforward way to make graphene, but as an enabling technology for applications such as graphene-based composites and coatings.

We acknowledge financial support from Science Foundation Ireland.

References: 1. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, A. A. Firsov, Electric field effect in atomically thin carbon films, Science 306, no. 5696, pp. 666-669, 2004.

2. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos, A. A. Firsov, Two-dimensional gas of massless Dirac fermions in graphene, Nature 438, no. 7065, pp. 197-200, 2005.

3. S. V. Morozov, K. S. Novoselov, M. I. Katsnelson, F. Schedin, D. C. Elias, J. A. Jaszczak, A. K. Geim, Giant intrinsic carrier mobilities in graphene and its bilayer, Phys. Rev. Lett. 1, no. 1, pp. 016602, 2008.
4. http://www.grapheneindustries.com/ Homepage of a commercial supplier of graphenes. Accessed 9 October 2008.

5. G. Eda, G. Fanchini, M. Chhowalla, Large-area ultrathin films of reduced graphene oxide as a transparent and flexible electronic material, Nat. Nanotechnol. 3, pp. 270-274, 2008.

6. S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S. T. Nguyen, R. S. Ruoff, Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide, Carbon 45, no. 7, pp. 1558-1565, 2007.

7. Y. Hernandez, V. Nicolosi, M. Lotya, F. M. Blighe, Z. Sun, S. De, I. T. McGovern, B. Holland, M. Byrne, Y. K. Gun'ko, J. J. Boland, P. Niraj, G. Duesberg, S. Krishnamurthy, R. Goodhue, J. Hutchison, V. Scardaci, A. C. Ferrari, J. N. Coleman, High-yield production of graphene by liquid-phase exfoliation of graphite, Nat. Nanotechnol. 3, no. 9, pp. 563-568, 2008.

8. S. D. Bergin, V. Nicolosi, P. V. Streich, S. Giordani, Z. Sun, A. H. Windle, P. Ryan, N. P. P. Niraj, Z. T. Wang, L. Carpenter, W. J. Blau, J. J. Boland, J. P. Hamilton, J. N. Coleman, Towards solutions of SWNT in common solvents, Adv. Mater. 20, no. 10, pp. 1876-1881, 2007.