Carbon nanotubes could make efficient solar cells

September 10th, 2009 By Anne Ju

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In a carbon nanotube-based photodiode, electrons (blue) and holes (red) - the positively charged areas where electrons used to be before becoming excited - release their excess energy to efficiently create more electron-hole pairs when light is shined on the device. Image: Nathan Gabor

(PhysOrg.com) -- Cornell researchers fabricated, tested and measured a simple solar cell called a photodiode, formed from an individual carbon nanotube.

Using a carbon nanotube instead of traditional silicon, Cornell researchers have created the basic elements of a solar cell that hopefully will lead to much more efficient ways of converting light to electricity than now used in calculators and on rooftops.

The researchers fabricated, tested and measured a simple solar cell called a photodiode, formed from an individual carbon nanotube. Reported online Sept. 11 in the journal Science, the researchers -- led by Paul McEuen, the Goldwin Smith Professor of Physics, and Jiwoong Park, assistant professor of chemistry and chemical biology -- describe how their device converts light to electricity in an extremely efficient process that multiplies the amount of electrical current that flows. This process could prove important for next-generation high efficiency solar cells, the researchers say.

"We are not only looking at a new material, but we actually put it into an application -- a true solar cell device," said first author Nathan Gabor, a graduate student in McEuen's lab.

The researchers used a single-walled carbon nanotube, which is essentially a rolled-up sheet of graphene, to create their solar cell. About the size of a DNA molecule, the nanotube was wired between two electrical contacts and close to two electrical gates, one negatively and one positively charged. Their work was inspired in part by previous research in which scientists created a diode, which is a simple transistor that allows current to flow in only one direction, using a single-walled nanotube. The Cornell team wanted to see what would happen if they built something similar, but this time shined light on it.

Shining lasers of different colors onto different areas of the nanotube, they found that higher levels of photon energy had a multiplying effect on how much electrical current was produced.

Further study revealed that the narrow, cylindrical structure of the carbon nanotube caused the electrons to be neatly squeezed through one by one. The electrons moving through the nanotube became excited and created new electrons that continued to flow. The nanotube, they discovered, may be a nearly ideal photovoltaic cell because it allowed electrons to create more electrons by utilizing the spare energy from the light.

This is unlike today's solar cells, in which extra energy is lost in the form of heat, and the cells require constant external cooling.

Though they have made a device, scaling it up to be inexpensive and reliable would be a serious challenge for engineers, Gabor said.

"What we've observed is that the physics is there," he said.

Source

Hybrid Carbon Nanotube Metal Oxide Arrays to Improve Lithium Battery Technology

Need to store electricity more efficiently? Put it behind bars.

That's essentially the finding of a team of Rice University researchers who have created hybrid carbon nanotube metal oxide arrays as electrode material that may improve the performance of lithium-ion batteries.

With battery technology high on the list of priorities in a world demanding electric cars and gadgets that last longer between charges, such innovations are key to the future. Electrochemical capacitors and fuel cells would also benefit, the researchers said.

The team from Pulickel Ajayan's research group published a paper this week describing the proof-of-concept research in which nanotubes are grown to look – and act – like the coaxial conducting lines used in cables. The coax tubes consist of a manganese oxide shell and a highly conductive nanotube core.

"It's a nice bit of nanoscale engineering," said Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science.

"We've put in two materials – the nanotube, which is highly electrically conducting and can also absorb lithium, and the manganese oxide, which has very high capacity but poor electrical conductivity," said Arava Leela Mohana Reddy, a Rice postdoc researcher. "But when you combine them, you get something interesting."

That would be the ability to hold a lot of juice and transmit it efficiently. The researchers expect the number of charge/discharge cycles such batteries can handle will be greatly enhanced, even with a larger capacity.

"Although the combination of these materials has been studied as a composite electrode by several research groups, it's the coaxial cable design of these materials that offers improved performance as electrodes for lithium batteries," said Ajayan.

"At this point, we're trying to engineer and modify the structures to get the best performance," said Manikoth Shaijumon, also a Rice postdoc. The microscopic nanotubes, only a few nanometers across, can be bundled into any number of configurations. Future batteries may be thin and flexible. "And the whole idea can be transferred to a large scale as well. It is very manufacturable," Shaijumon said.

The hybrid nanocables grown in a Rice-developed process could also eliminate the need for binders, materials used in current batteries that hold the elements together but hinder their conductivity.

Posted February 9th, 2009

Source

Storing bits of memory in nanotube switches

By Todd Morton
Published: November 17, 2008 - 08:40AM CT

The world of computer memory has been approaching an interesting crossroads. Most people are aware that we are rapidly approaching fundamental limits with both magnetic storage mediums like the hard drive, and in the fabrication of transistors through photolithography, which yields RAM and flash memory. Several areas of research, including fields like phase change memory, may provide the opportunity to move away from both magnetic domains and transistors. To explore a different route to future memory systems, researchers went high-tech and put multiwalled carbon nanotubes (MWCNTs) to use—only to discover that they work through a surprisingly retro mechanism.

The researchers fabricated a device that was rather simple compared to the usual carbon nanotube fare that we cover in Nobel Intent—a single MWCNT was spread across a silicon substrate between two platinum electrodes. Although producing these devices is delicate work, it is a far cry from depositing the multiple layers of exotic materials that make up today's field-effect transistors. When a voltage was swept from negative to positive across the nanocable device, a clear transition between conductive and nonconductive states was observed. This transition proved to be nonvolatile; that is, they didn't have to apply a constant voltage in order to maintain the conductive or non-conductive state.

Obviously, this binary state behavior could act as the foundation for computer memory, so the researchers went to work exploring the properties of the device. Read/write operations were stable over thousands of cycles, and the state of the nanocable could read without changing it, meaning the storage of a bit was stable. non-conductive state.

Moving into other performance metrics, they found that the MWCNT device was stable at ionizing radiations that cause normal electrical devices to fail, pointing to potential applications in extreme environments, like space. They remained stable over the course of several weeks in both vacuum and atmospheric conditions, and operated at temperatures that, if present in your laptop, would sear your favorite OEM's logo into your flesh.

An in-depth characterization of the devices revealed the mechanism behind the behavior, which turned out to be a throwback to the mechanical switches of the first computers. The MWCNT structure can be approximated as a sheet of graphene wrapped around a solid core, which provides mechanical stability. As the initial voltage is applied to one of these devices, the outer sheath of graphene will physically break at a defect site, which explains the significant changes in current flow. Although this mechanical process is not reversible in an absolute sense, applying a voltage in the other direction will cause enough electrostatic attraction to reconnect the two broken pieces.

The authors pointed out that similar behavior can be observed in graphene, which offers several possibilities for the actual fabrication of a real-world device based on this phenomenon. The combination of a relatively simple device fabrication technique, a high on/off current ratio at reasonable voltages, quick switching (as fast as 1 microsecond), non-volatility, and an apparently robust device makes for a formidable contender in the race for the memory systems of the future.

Nature Materials, 2008. DOI: 10.1038/nmat2331

Source

Article abstract
Nature Materials

Published online: 16 November 2008 | doi:10.1038/nmat2331

Electronic two-terminal bistable graphitic memories

Yubao Li^1,3, Alexander Sinitskii^1,3 & James M. Tour^1,2

Abstract

Transistors are the basis for electronic switching and memory devices as they exhibit extreme reliabilities with on/off ratios of 10⁴–10⁵, and billions of these three-terminal devices can be fabricated on single planar substrates. On the other hand, two-terminal devices coupled with a nonlinear current–voltage response can be considered as alternatives provided they have large and reliable on/off ratios and that they can be fabricated on a large scale using conventional or easily accessible methods. Here, we report that two-terminal devices consisting of discontinuous 5–10 nm thin films of graphitic sheets grown by chemical vapour deposition on either nanowires or atop planar silicon oxide exhibit enormous and sharp room-temperature bistable current–voltage behaviour possessing stable, rewritable, non-volatile and non-destructive read memories with on/off ratios of up to 10⁷ and switching times of up to 1 s (tested limit). A nanoelectromechanical mechanism is proposed for the unusually pronounced switching behaviour in the devices.

1. Departments of Chemistry; Computer Science and Mechanical Engineering and Materials Science and the Smalley Institute for Nanoscale Science and Technology, Rice University, MS 222, 6100 Main Street, Houston, Texas 77005, USA
2. These authors contributed equally to this work

Correspondence to: James M. Tour^1,2 e-mail: tour@rice.edu

IBM demonstrates light-emitting nanotube

R. Colin Johnson
EE Times
(08/25/2008 8:42 AM EDT)

PORTLAND, Ore. — Electric control of the spectrum, direction and efficiency of light-emitting nanotubes (LENs) has been demonstrated by researchers at IBM Corp.'s Thomas J. Watson Research Center, bringing silicon photonics one step closer to reality.

IBM Research (Yorktown Heights, N.Y.) previously demonstrated record-breaking silicon optical waveguides and higher electroluminescent efficiency for LENs compared to LEDs. Now, it has put a LEN inside an optical waveguide to achieve directional surface emission, wavelength selectivity and the potential for ultrahigh efficiency.

"Like most light-emission sources, nanotubes emit light in all directions. Their spectrum was relatively broad and their efficiency was not very high," said Phaedon Avouris, IBM Fellow and manager of Nanometer Scale Science and Technology at IBM Research. "We attacked all these problems, making its light directional so it can be coupled to optical filters or to a device to transport it. We controlled its spectrum with an optical cavity and we have proposed a theory to help us achieve higher efficiency."

By fabricating an optical cavity around light-emitting nanotube mirrors at the bottom and top, wavelengths were confined to the desired 1.55-micron communications frequency.

IBM achieved surface emission by combining a single nanotube-based field-effect-transistor with a pair of metallic mirrors, one above and below the nanotube which lies flat on the silicon chip. The bottom mirror was made from silver, with a top half-mirror made from gold. Light was emitted from the nanotube in the cavity, which was filled with transparent dielectric.

The distance between the top and bottom mirrors was calculated to be half of the desired emission wavelength, which was set to be near a communications wavelength of 1.55 microns. Light was reflected upward off the bottom of the cavity, where half was passed as a surface emission from the LEN while the other half was reflected back down to the bottom mirror to reinforce the desired emission wavelength.

"We confined the emission in an optical cavity with two mirrors, so that light forms a standing wave between the mirrors which enhanced the frequencies, whose wavelength were equal to half the size of the cavity," said Avouris. "We used lithography to form the cavities, which achieved a dramatic enhancement--confining the spectrum to about 10 percent of what it was without the cavity, and giving us an overall enhancement [in the efficiency] of the emission of 400 percent."

Nanotubes have slightly different diameters (in this case, about 2 nanometers). As a result, they have slightly different bandgaps, and thus emit light at slightly different frequencies. However, by integrating the nanotube inside a cavity, physical confinement in the structure "eliminates unwanted frequencies thus [solving] the problem of nanotubes having slightly different diameters," according to Avouris.

IBM has demonstrated two methods of light emission in nanotubes: one that injects hot carriers into each end and another in which one end gets electrons while the other end gets holes. Another method injects excitons into one end. By characterizing these two methods, IBM claims to have finally answered the question of how electroluminescence compares to photoluminescence.

"There has always been a controversy over whether electroluminescence and photoluminescence involve the same states, so through comparisons using Raman scattering we have now proven that they both use the same states," said Avouris.

IBM has also proposed a theory for how heat diverts energy from luminescence, thus reducing the efficiency of LENs. While further experimentation will be required to prove the theory, IBM claims it is now only a matter of time until virtually all wasted energy that formerly generated heat can be eliminated by changing the electronic structure of a device.

"There are two types of emission from an object, radiative and nonradiative, with the latter being the energies lost by heat," said Avouris. Radiative emission "was always thought to be a fixed property of the material, but what we realized was that it is not only the material that is quantized--that has discrete states--but the photons also are part of a field that has quantized states.

"Emission comes by coupling these two fields. We now feel that by using an electric field we can change the electronic structure of nanotubes so that heat cannot be generated," he added.

Besides improving the efficiency of future devices by eliminating heat generation, IBM researchers also plan to experiment with methods of aligning nanotubes to a superlattice. This would allow an array of LENs to be fabricated on future silicon photonic chips.

Source

Targeted Single-Wall Carbon Nanotube-Mediated Pt(IV) Prodrug Delivery Using Folate as a Homing Device

Published: 1 hour ago, 14:03 EST, August 15, 2008

Nanotechnology / Bio & Medicine

Platinum-based anticancer agents have a long history as proven therapeutic agents, but their toxicity and short lifetime in the body and the ability of tumors to develop resistance to these drugs limit the ultimate utility of these agents.

In an attempt to overcome these limitations, a multi-institutional research team comprising members from Stanford University, the Massachusetts Institute of Technology (MIT), and the University of Duisburg-Essen in Germany is using targeted carbon nanotubes as delivery agents for an inactive form of platinum that cancer cells themselves convert into a toxic anticancer agent.

Reporting its work in the Journal of the American Chemical Society, the research team headed by Stanford’s Hongjie Dai, Ph.D., a member of the Center for Cancer Nanotechnology Excellence Focused on Therapy Response, and Stephen Lippard, Ph.D., MIT, describes its development of methods to attach platinum-containing compounds firmly to the surface of carbon nanotubes to create what they call a “longboat delivery system” for the platinum warhead.

The particular form of platinum that the researchers use, known as platinum-IV, is capable of binding to other molecules in addition to the nanotube. The investigators use that capability to attach the tumor-targeting agent folic acid to the platinum warhead.

When administered to tumor cells that overexpress a folic acid receptor, the modified nanotubes rapidly enter the target cell. There, enzymes within the cell convert platinum-IV to a far more toxic form known as platinum-II. This chemical conversion has the effect of releasing platinum from the nanotube and enabling it to travel to the cell nucleus, where it reacts with deoxyribonucleic acid (DNA) and eventually kills the cell.

Tests with cancer cells growing in culture showed that this nanotube formulation of platinum is more than 8 times more potent than the approved anticancer agent cisplatin.

This work, which is detailed in the paper “Targeted Single-Wall Carbon Nanotube-Mediated Pt(IV) Prodrug Delivery Using Folate as a Homing Device,” was supported by the NCI Alliance for Nanotechnology in Cancer. An abstract of this paper is available through PubMed.

Provided by National Cancer Institute

Source

It's all about targeting

(WO/2008/082374) CARBON NANOTUBE NANOBOMB

WO 2008082374 20080710

Claims

What is claimed is:

1. A composition comprising bundles of carbon nanotubes and a targeting molecule bound to said nanotubes.

2. The composition of claim 1 wherein said carbon nanotubes are single wall carbon nanotubes.

3. The composition of claim 1 wherein said targeting molecule is an antibody.

4. The composition of claim 1 wherein said composition further comprises a therapeutic compound.

5. The composition of claim lwherein said therapeutic compound is a chemotherapy drug.

6. A method for killing or damaging cells comprising the steps of

(a) delivering carbon nanotubes to cells or a location near said cells, wherein said nanotubes are hydrated prior to or after delivery to said cells or location near said cells;

(b) exposing said carbon nanotubes to light of sufficient intensity and for a sufficient amount of time to cause explosion of said carbon nanotubes, whereby the explosion of said nanotubes exposes said cells to a lethal or damaging dose of heat thereby killing or damaging said cells.

7. The method of claim 6 wherein said cells are mammalian cells.

8. The method of claim 6 wherein said cells are cancer cells.

9. The method of claim 6 wherein said cells are on the surface of the body of a mammal.

10. The method of claim 6 wherein said cells are inside the body of a mammal.

11. The method of claim 6 wherein said nanotubes are single wall carbon nanotubes.

12. The method of claim 6 wherein said nanotubes further comprise a targeting molecule.

13. The method of claim 12 wherein said targeting molecule is an antibody.

14. The method of claim 1 wherein said nanotubes further comprise a therapeutic compound.

15. The method of claim 9 wherein said therapeutic compound is a chemotherapy drug.

16. The method of claim 6 wherein said light is near infra-red light.

17. The method of claim 7 wherein said mammalian cells are human cells.

18. The method of claim 9 wherein said cells are human cells.

19. The method of claim 10 wherein said cells are human cells.

WO/2008/082374

http://medicalphysicsweb.org/cws/article/industry/35088

COPYTELE/CNT/Display/Patent/Videocon

Biblio:
http://tinyurl.com/2fy9kw

Details:
http://tinyurl.com/yoz84o

This Copytele has a Technology License Agreement with an Indian TV maker Videocon:
Technology License Agreement with Videocon Industries Limited

On November 2, 2007, we entered into a Technology License Agreement (the "License Agreement") with Videocon. Under the License Agreement, we provide Videocon with a non-transferable, worldwide license of our technology for thin, flat, low voltage phosphor displays (the "Licensed Technology"), for Videocon (or a Videocon Group company) to produce and market products, including TVs, incorporating displays utilizing the Licensed Technology. Under the License Agreement, we will receive a license fee of $11 million from Videocon, payable in installments over a 27 month period, with the first installment of $2 million
payable 15 days after the License Agreement is effective. The License Agreement
will be effective after Videocon has obtained the necessary regulatory approvals
in India for the payment of the license fees and royalties and may be terminated
if the required approvals are not obtained in a reasonable period of time. We
will also receive an agreed upon royalty from Videocon based on display sales by
Videocon.

We will continue to have the right to produce and market, and to
utilize Volga Svet Ltd., a Russian display company that we have been working
with for more than ten years, and an Asian company that we have been working
with for more than four years, to produce and market, products utilizing the
Licensed Technology. Additional licenses of the Licensed Technology to third
parties require our joint agreement with Videocon.

http://tinyurl.com/32e7yk
http://biz.yahoo.com/e/080115/copy.ob10-k.html

Videocon:
http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=204803434
http://ragingbull.quote.com/mboard/boards.cgi?board=CLB01350&read=1334

Are we and/or Keesmann aware of this and what are we and/or Keesmann doing about it, now, in the past or in the future??

Copytele and nanotubes:
Link to US patent
Link to EPO patent documents

From the Copytele Annual Report

Our new technology improves on our prior carbon nanotube and proprietary
low voltage color phosphor display technology. We have developed various
engineering models using such prior technology, which demonstrated the display's
ability to show movies from DVD players by controlling the brightness of
selected individual pixels. The carbon nanotubes, which are supplied to us by a
U.S. company, require a low voltage for electron emission and are extremely
small - approximately 10,000 times thinner than the width of a human hair. The
5.5 inch (diagonal) display we developed has 960 x 234 pixels and utilizes a new
memory-based active matrix thin film technology with each pixel phosphor
activated by electrons emitted by a proprietary carbon nanotube network located
approximately 10 microns (1/10th of a human hair) from the pixels. As a result,
each pixel phosphor brightness is controlled using a maximum of only 40 volts.
The carbon nanotubes and proprietary color phosphors are precisely placed and
separated utilizing our proprietary nanotube and phosphor deposition technology.
We have developed a process of maintaining uniform carbon nanotube deposition
independent of phosphor deposition. We have also developed a method of enhancing nanotube electron emission to increase the brightness of this type of display.

Some other characteristics of our display technology are as follows:

o We have developed a proprietary system which allows us to evacuate our
display; to rapidly vacuum seal it at a low temperature to accommodate
the matrix; and to create lithographic type spacers to assemble our
display utilizing only 0.7mm glass. We thus obtain a display thickness
of approximately 1/16th of an inch, thinner than LCD (liquid crystal)
and PDP (plasma) displays.
o The display matrix, phosphor excitation system, and drivers are all on
one substrate.
o Our display is able to select and change the brightness of each
individual pixel, requiring only 40 volts on each pixel phosphor to
change the brightness from black to white. This compares to thousands
of volts required for other video phosphor based displays, which leads
to inherent breakdowns and short life.
o Our display has no backlight. Because power is only consumed when a
pixel is turned on, low power is needed to activate the whole display.
The display requires less than 20% the power required by an LCD. This
low power consumption could potentially allow use of rechargeable
batteries to operate TV products for wireless applications and extend
the battery operation time for portable devices.
o The same basic display technology could potentially be utilized in
various size applications, from hand-held to TV size displays.
o Our proprietary matrix structures can be produced by existing mass
production TFT (thin film technology) LCD facilities, or portions of
these facilities.
o Our display eliminates display flicker.
o Our display has an approximately 1,000 times faster video response
time than an LCD, and matches the response time of a cathode ray tube
(CRT).
o Our display can be viewed with high contrast over approximately a 180
degree viewing angle, in both the horizontal and vertical directions,
which exceeds the viewing angle of LCDs.
o Also like CRTs, our display is capable of operating over a temperature
range (-40(degree)C to 85(degree)C) which exceeds the range over which
LCDs can operate, especially under cold temperature conditions.

We believe our displays could potentially have a cost similar to a CRT and
thus less than current LCD or PDP displays (our display does not contain a
backlight, or color filter or polarizer, which represent a substantial portion
of the cost of an LCD).