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View Full Version : Wonder material could harvest energy from thin air (Peter Shadbolt, CNN)



Tesla_WTC_Solution
24th December 2014, 19:14
http://us.cnn.com/2014/12/23/tech/innovation/tomorrow-transformed-graphene-battery/index.html?hpt=hp_t4

Wonder material could harvest energy from thin air

By Peter Shadbolt, for CNN

updated 5:43 AM EST, Tue December 23, 2014

http://i2.cdn.turner.com/cnn/dam/assets/130429155622-pencil-key-graphene-horizontal-gallery.jpg

Editor's note: Tomorrow Transformed explores innovative approaches and opportunities available in business and society through technology.

(CNN) -- Bold claims for new battery technology have been around since the invention of the lead-acid battery more than 150 years ago.

But researchers at Manchester University in the UK say their latest discovery involving the new wonder material graphene could be the most revolutionary advance in battery technology yet.

According to a study published in the journal Nature, graphene membranes could be used to sieve hydrogen gas from the atmosphere -- a development that could pave the way for electric generators powered by air.

"It looks extremely simple and equally promising," said Dr Sheng Hu, a post-doctoral researcher in the project. "Because graphene can be produced these days in square metre sheets, we hope that it will find its way to commercial fuel cells sooner rather than later."

Pencil power

At the heart of the technology is the remarkable physical properties of graphene -- a substance with the same atomic structure as the lead found in the humble household pencil.








Watch this video


Hyundai to introduce hydrogen fueled car






Watch this video


Solar station, water car

Isolated in 2004 by a team from Manchester University headed by Andrew Geim and Kostya Novoselov -- both of whom won the Nobel Prize for Physics for their discovery in 2010 -- graphene is already well known as a technological game-changer.

The first two-dimensional crystal known to science, graphene is the thinnest, lightest and strongest object ever obtained. It is harder than diamond and 200 times stronger than steel.

Flexible, transparent and able to conduct electricity even better than copper, the ground-breaking substance is set to revolutionize everything from smartphones and wearable technology to green technology and medicine.

Renowned for its barrier qualities, graphene is just one atom thick - more than a million times thinner than a human hair.

Membrane technology

The latest discovery makes graphene attractive for possible uses in proton-conducting membranes which are at the core of modern fuel-cell technology.

Fuel cells work by using oxygen and hydrogen as a fuel, converting the chemical energy produced by its input directly into electricity. However, current membranes that separate the protons necessary for this process are relatively inefficient, allowing contamination in the fuel crossover.

Using graphene membranes could boost their efficiency and durability.

The team found the protons passed through the ultra-thin crystals with relative ease, especially at raised temperatures and with the use of a platinum-based catalyst coated on the membrane film.

Harvesting hydrogen

The most surprising aspect of the research, however, found the membranes could be used to extract hydrogen from the atmosphere. The scientists said such harvesting could be combined with fuel cells to create a mobile electric generator fueled simply by hydrogen present in air.

"When you know how it should work, it is a very simple setup. You put a hydrogen-containing gas on one side, apply small electric current and collect pure hydrogen on the other side. This hydrogen can then be burned in a fuel cell.

"We worked with small membranes, and the achieved flow of hydrogen is of course tiny so far. But this is the initial stage of discovery, and the paper is to make experts aware of the existing prospects. To build up and test hydrogen harvesters will require much further effort."

Currently, hydrogen is obtained nearly entirely from fossil fuels.


Already scientists are finding new ways of processing graphene and new applications for the invisible substance. Because it is flexible and stretchable, it makes it an ideal candidate for solar generation.


New research from the Institute of Photonic Sciences in Spain showed that graphene could be far more efficient in the transformation of light into energy.

The study found that unlike silicon, which generates only one current-driving electron for each photon it absorbs, graphene can produce multiple electrons.

Although the application of graphene in solar cells is only theoretical, the potential could be staggering. Solar cells made with graphene could offer 60% solar cell efficiency -- double the widely-regarded maximum efficiency of silicon cells.

Apart from uses in transportation, where its lightness and strength stands to transform the manufacture of cars and planes to make them more fuel efficient, graphene has been studied as a corrosion-proof coating for packaging and even super-thin condoms.

In medicine, researchers say it could be used to deliver drugs to specific sites in the body and is being developed as a treatment for people with brain conditions.

In industry, its use as a membrane is being studied as a means of purifying water and even as a way of extracting salt and other elements from sea water to make it drinkable.



http://www.teslamotors.com/fr_CH/forum/forums/graphene-supercapacitor-cells-how-pencil-lead-and-dvd-burner-will-change-world


Graphene Super-Capacitor Cells - How Pencil Lead And A DVD Burner Will Change The World.







N. A. Lee | 3 Mars 2013


Tesla currently uses lithium to make batteries that power their vehicles. While lithium is fairly inexpensive to manufacture, it has its drawbacks. Catching fire when exposed to air in a fatal accident, the inability to charge quickly compared to the fueling time of a combustion engine, and a limited life cycle, are but a few of the difficulties that have to be taken into account when using lithium as a power source for electric vehicles. But, what if there were a simplistic, cheap material that equally performs as lithium but is so environmentally friendly that it can be re-used as garden fertilizer? What unimaginable, absurdly fictional material could possibly exist with these properties?

Graphene.

What is graphene? It is essentially composed of the same graphite material found in millions of yellow pencils used by children around the world. The only difference with the writing material is the arrangement of the carbon into single atom-thick sheets rather than a random jumble of atoms. This material does not look like much on the surface but when it is arranged in this fashion, the carbon takes on some strange and amazing properties – such as the ability to hold and disperse large amounts of electrons.

Until recently, graphene was difficult to manufacture on a large scale. Thanks to some ingenious researchers at UCLA, making graphene is as simple as painting a liquid carbon solution on a DVD and running it through a Lightscribe DVD burner. The result is a material that has the same energy density of lithium, but can be charged in a fraction of the time along with the added benefit of being manufactured at pennies on the dollar.

What does this mean for Tesla? Since they would no longer have to base the price of their vehicle on the cost of batteries, Tesla will be able to manufacture cost-effective electric cars for the masses that are equally as powerful as any car that uses lithium batteries.

Please watch and read below for more information:

Breakthrough Announcement In 2012:
http://www.rsc.org/chemistryworld/News/2012/March/graphene-dvd-player-bu...

The Reality As Of 2013:
http://newsroom.ucla.edu/portal/ucla/ucla-researchers-develop-new-techni...

Watch The Creation In Action:
http://vimeo.com/51873011
http://youtu.be/_oEFwyoWKXo





http://www.valuewalk.com/2014/08/tesla-500-mile-graphene-battery/

Tesla Motors Inc (NASDAQ:TSLA) might be looking to develop a 500-mile graphene battery. Graphine has a reputation of being an excellent material. According to a Chinese website, Tesla is already working on the graphene battery. Previously, CEO Elon Musk announced that a 500-mile battery could be launched anytime soon, says a report from Clean Technica.






http://www.graphenetracker.com/us-department-of-energy-files-patent-for-efficient-tesla-coils-with-graphene/

http://www.graphenetracker.com/images/2013/02/tesla_coil.jpg


US Department of Energy files patent for efficient Tesla coils with graphene

By Marko Spasenovic on February 1, 2013


The United States Department of Energy, through its Oak Ridge National Laboratory and its management company UT-Battelle, has filed a patent to use graphene for more efficient high frequency coils, also known as Tesla coils. The graphene would wrap around the wires of the coil to act as protection against unwanted eddy currents, making such coils more suitable for wireless power transmission.

United States Patent Application number 20130020877 relates to the field of wireless power transfer, and in particular to graphene-coated coupling coils for reducing alternating current (AC) resistance for high frequency AC applications. Wireless transmission of electrical energy has been a goal of engineers ever since the Serbian-American scientist Nikola Tesla dreamed it up a century ago. Practical and commercial realization of wireless power has been elusive, but hopefully this patent brings us a step closer to charging our mobile devices out of thin air.

The problem that the inventors attempt so solve is that of eddy currents, which are parasitic electrical currents that creep up into wires carrying high-frequency alternating currents, in particular when several such wires are near each other. The problem is solved by wrapping the wires in graphene, which provides a short circuit for the eddy currents, while leaving the AC currents intact. The hope is that lower losses in the circuits used to generate and receive wireless power will result in more efficient transmission of power. The receiver is said to be on a vehicle. Tesla also worked on using these coils for shooting out lightning bolts and wireless communication.

The patent application is a beautiful example of technology catching up to dreams of a scientific genius, aiming to fulfil those dreams a century later. May the invention serve mankind as Tesla would have wanted it to.









http://www.activistpost.com/2013/04/can-graphene-provide-free-energy.html




Activist Post

The suppression of free energy by corporate interests has been made quite famous by the work of Nikola Tesla; and our subsequent continued reliance on fossil fuels and other inadequate sources of energy remains a serious hurdle to overcome.

There are some very promising developments coming out of the various open source DIY groups. These groups are utilizing the vast potential of lower-cost research and networking to provide a multi-faceted approach to innovation that is becoming far more difficult to suppress than the inventions of a single genius such as Tesla.

There has been particular focus upon how to increase battery life, given the ubiquitous nature of our digital gadgets and high-tech infrastructure. A German student, Dennis Siegel, invented a device that builds upon Tesla's maxim that "throughout space there is energy" by capturing modern-day electromagnetic fields like WIFI and radio waves and converting them to stored energy in batteries. Siegel won a prestigious award when he successfully demonstrated charging one conventional AA battery over the span of a day. Siegel's full story can be found here.

Now, a new technology based upon the amazing properties of graphene to convert light to electricity is showing signs of surpassing silicon as the most efficient path toward potential free energy. And even if it comes up short of that lofty goal, it still might revolutionize computing and electronics.

A new study from Nature Physics journal states the hard science behind this technology:

As hot electrons in graphene can drive currents, multiple hot-carrier generation makes graphene a promising material for highly efficient broadband extraction of light energy into electronic degrees of freedom, enabling high-efficiency optoelectronic applications.

In layman's terms: graphene generates multiple electrons from each photon, whereas silicon - the current source of solar cells - can generate only a single electron per photon.


http://static.neatorama.com/images/2010-03/tesla-master-of-lightning.jpg




http://en.wikipedia.org/wiki/Graphite


Graphite /ˈɡræfaɪt/ is made almost entirely of carbon atoms, and as with diamond, is a semimetal native element mineral, and an allotrope of carbon. Graphite is the most stable form of carbon under standard conditions. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is difficult to ignite.




http://upload.wikimedia.org/wikipedia/commons/thumb/f/f3/GraphiteUSGOV.jpg/240px-GraphiteUSGOV.jpg





Batteries[edit]

The use of graphite in batteries has been increasing in the last 30 years. Natural and synthetic graphite are used to construct the anode of all major battery technologies.[7] The lithium-ion battery utilizes roughly twice the amount of graphite than lithium carbonate.[28]

The demand for batteries, primarily nickel-metal-hydride and lithium-ion batteries, has caused a growth in graphite demand in the late 1980s and early 1990s. This growth was driven by portable electronics, such as portable CD players and power tools. Laptops, mobile phones, tablet, and smartphone products have increased the demand for batteries. Electric vehicle batteries are anticipated to increase graphite demand. As an example, a lithium-ion battery in a fully electric Nissan Leaf contains nearly 40 kg of graphite.



http://en.wikipedia.org/wiki/List_of_Nikola_Tesla_patents

U.S. Patent 0,335,786 - Electric Arc lamp - 1886 February 9 - Arc lamp with carbon electrodes controlled by electromagnets or solenoids and a clutch mechanism; Corrects earlier design flaws common to the industry.
3.U.S. Patent 0,335,787 - Electric arc lamp - 1886 February 9 - Arc lamp's automatic fail switch when arc possesses abnormal behavior; Automatic reactivation.

http://altered-states.net/barry/tesla/





p.s. how many think that Tesla was aware of the properties of graphite even though the patent office may not have a record of this?

Tesla_WTC_Solution
24th December 2014, 19:35
Pencil graphite as a filament under right conditions, home experiment:

http://dwarmstr.blogspot.com/2008/06/updates-tesla-coil-and-light-bulb.html


Dean W. Armstrong


Scientific and other projects in astronomy, geoscience, physics, and electronics.


Friday, June 06, 2008



Updates: Tesla coil and light bulb



Updates.

I tried to help Igor out on his Tesla coil. It's a traditional spark-gap variety coil. The problem was the secondary kept arcing over to the primary or elsewhere from near the bottom, nowhere near the top, and we didn't see any streamers or such from the top. Nothing we tried would insulate the primary from the secondary--styrofoam, electrical tape, plastic cups. When we changed where we connected to the primary the sparks would change their behavior--sometimes we would get a single spark or sometimes we would get what we think was called "racing sparks"--the ones that jump a few inches on the secondary. Also we tried grounding, although we were up on a third story. All this, plus the fun of a spark gap that literally was too loud to operate. Bang-bang-bang! We need to enclose the spark gap in something to absorb the sound, but to do that would mean we'd also have to set up an air flow via a fan to break the arc. No photos of this work.

The other is a revisit to a Scav Hunt item, a homemade light bulb. This was a success on our part. We used a 0.5mm mechanical pencil lead, connected it to a pair of 6V latern batteries wired in series, giving 12V. The filament was enclosed in a Snapple bottle with wire passed through a hole in the cap sealed with hot glue. To remove oxygen in the air we lit a match or two in the bottle until it went out and sealed quickly. This bulb had a nice ruddy glow to it. We only ran it for thirty seconds or so before it was passed on for the judges to see. I don't know where it is now, so I decided to make another one. The basics were the same except for the power source. I used a 15V AC 1A power supply. I put the filament in a Starbucks glass container that I had worries about being airtight enough. This time it lit nicely, but within ten seconds one side of the graphite became brighter. A post-mortem showed it got brighter because the lead got narrower, and more power was dissipated there, increasing the erosion. It got brighter and brighter and then narrowed to nothing, when it broke.


http://www.lib.uchicago.edu/~dean/blog/graphite-thumb.jpg

http://www.lib.uchicago.edu/~dean/blog/graphite-lightbulb-thumb.jpg

http://www.lib.uchicago.edu/~dean/blog/lightbulb-movie.jpg

¤=[Post Update]=¤

US Navy experiments a bit more complicated hehe

http://www.nrl.navy.mil/media/news-releases/2014/nrl-researchers-create-first-homoepitaxial-graphene-tunnel-barrier-transport-channel-device

NRL Researchers Create First Homoepitaxial Graphene Tunnel Barrier/Transport Channel Device

01/28/2014 11:15 EST - 6-14r Contact: Donna McKinney, (202) 767-2541

http://www.nrl.navy.mil/PressReleases/2014/tunnel-device-structure_6-14r_744x262.jpg


A schematic (left) and an optical image (right) of one of the homoepitaxial fluorinated graphene/graphene spin valve devices. The top layer of graphene is used as a tunnel barrier. It is fluorinated to decouple it from the bottom layer of graphene, which is the spin transport channel. Ferromagnetic permalloy (NiFe - red) contacts inject and detect the spin in the channel. The gold contacts are ohmic reference contacts (Ti/Au). The scale bar on the microscope image is 20 microns.
(Photo: U.S. Naval Research Laboratory)

Scientists at the U.S. Naval Research Laboratory (NRL) have created a new type of tunnel device structure in which the tunnel barrier and transport channel are made of the same material, graphene. They show that dilutely fluorinated graphene, a single atomic layer of carbon atoms arranged in a two-dimensional (2D) honeycomb array, acts as a tunnel barrier on another layer of graphene for charge and spin transport. They demonstrate tunnel injection through the fluorinated graphene, and lateral transport and electrical detection of pure spin current in the graphene channel. They further report the highest spin injection values yet measured for graphene, providing evidence for the enhancement of tunnel spin polarization theoretically predicted to occur for certain ferromagnetic metals on graphene. This discovery opens an entirely new avenue for making highly functional, scalable graphene-based electronic and spintronic devices a reality. The research results are reported in a paper published in the journal Nature Communications on January 21, 2014. The coupled imperatives for reduced heat dissipation and power consumption in high-density electronics have rekindled interest in devices based on tunneling, a quantum mechanical phenomenon in which electrons transit through a potential barrier rather than going over it. Because the tunnel barrier and transport channel are typically very different materials, such devices require mating dissimilar materials, raising issues of heteroepitaxy, layer uniformity, interface stability and electronic defect states that severely complicate fabrication and compromise performance. "2D materials such as graphene and hexagonal boron nitride obviate these issues and offer a new paradigm for tunnel barriers", explains Dr. Berend Jonker, Senior Scientist and project leader. In bulk form, these materials are comprised of well-defined layers which exhibit very strong atomic bonding in-plane, but relatively weak bonding between the layers, known as van der Waals bonding. Single layers can be readily separated from the bulk, or grown directly over large areas by a variety of techniques. These layers thus have a strong tendency to be very uniform in thickness down to a single atom, have very few defects, and do not intermix readily with other materials—these are key characteristics for a tunnel barrier, in which the tunnel current depends exponentially on the barrier thickness. The NRL scientists fluorinate the top layer of a graphene bilayer to decouple it from the bottom layer, so that it serves as a single-monolayer tunnel barrier for both charge and spin injection into the lower graphene channel. They deposit ohmic (gold) and ferromagnetic permalloy (red) contacts as shown in the figure, forming a non-local spin valve structure. When a bias current is applied between the left two contacts, a spin-polarized charge current tunnels from the permalloy into the graphene transport channel, generating a pure spin current that diffuses to the right. This spin current is detected as a voltage on the right permalloy contact that is proportional to the degree of spin polarization and its orientation. The vectorial character of spin (compared to the scalar character of charge) provides additional mechanisms for the control and manipulation needed for advanced information processing. The NRL team demonstrated the highest spin injection efficiency ever measured for graphene (63%), and determined spin lifetimes with the Hanle effect. In contrast with most oxide tunnel barriers on graphene, fluorinated graphene provides much larger tunnelling spin polarization efficiency, attributed to interface spin filtering and a more uniform, well-controlled barrier, and allows the observation of the theoretically predicted Hanle voltage and spin lifetime on gate voltage. These results identify a new route towards high quality, next generation graphene electronic/spintronic devices including spin-based transistors, logic, and memory. In addition, the process is completely scalable and easily accomplished. "In the near future," predicts Dr. Adam Friedman, lead author on the project, "We will be able to write entire spintronic circuits in situ on grown, large areas of bilayer graphene simply by selectively chemically modifying the top layer of graphene." Fluorographene/graphene enables realization of homoepitaxial few-layer carbon structures for versatile electronic devices. The NRL research team includes Dr. Adam Friedman, Dr. Olaf van 't Erve, Dr. Connie Li, and Dr. Berend Jonker from the Materials Science and Technology Division and Dr. Jeremy Robinson from the Electronics Science and Technology Division.






http://www.onr.navy.mil/en/Media-Center/Fact-Sheets/Graphene.aspx

Graphene and the Future of Nanoelectronics

With the end of Moore’s law in sight, we can no longer count on the continued shrinking of transistors indefi nitely. As a result, we are facing technical challenges at several levels: materials synthesis and characterization, novel nanodevices circuits, new computing architectures and nanofabrication.

The Office of Naval Research (ONR) nanoelectronics program thrusts are specifically designed to address each of those challenges.

Since 2005, ONR has been supporting various aspects of graphene research, in order to use it as a material platform for future nanoelectronic devices, circuits and systems. For example, one of the key technical issues for graphene-based electronic devices, despite its record mobility, is the lack of an electronic bandgap in bulk graphene (e.g. lateral size of graphene sheet exceeding 1 micron). Early investment in ONR’s program focused on various ways to open a bandgap in graphene, such as using graphene nanoribbons or multi-layer graphene.

More recently we turned our attention to atomic scale molecular engineering of graphene nanostructures using chemical synthesis techniques. This latter approach, while technically more challenging, holds great potential to change the entire landscape of nanoelectronics beyond the transistor era. The anticipated benefi ts for warfi ghters of this high-risk, basic research project include:

Personal electronic aids for individual warfi ghters that are fl exible and lightweight, with extremely low power consumption to enhance battlefield situational awareness
Electronic components that meet and exceed the size weight and power (SWaP) requirements for real-time information processing onboard small unmanned air vehicles (UAV’s), thereby unleashing their power in areal reconnaissance and surveillance missions

The combination of graphene’s superior electronic properties with the other, equally unique, properties in optical (THz to UV), thermal and mechanical domains could lead to completely new and hitherto unforeseen capabilities for both military and civilian applications




Research Challenges and Opportunities:
Understanding the fundamental materials properties and synthesis techniques for graphene
Utilizing graphene’s superior functionalities to build electronic, optoelectronic, magnetic and mechanical devices
Integrating graphene devices and circuits to build components and systems with clear advantages in size, weight and power







http://cleantechnica.com/2012/05/09/u-s-navy-funds-research-using-graphene-to-tap-terahertz-waves/

U.S. Navy Rides the Terahertz Wave to Next-Gen Electronics

http://cleantechnica.com/files/2012/05/navy-graphene-research.jpg

May 9th, 2012 by Tina Casey

The U.S. Navy is behind a push to exploit one of the “hottest” areas of the electromagnetic spectrum, the terahertz band. The Office of Naval Research contributed to a breakthrough project at Lawrence Berkeley National Laboratory last fall with the help of graphene nanoribbons, and just last month a team of ONR-funded researchers at the University of Notre Dame announced another new milestone.

The attraction of the terahertz band

Terahertz waves are situated between the microwave and optical light frequencies, at the “farthest end of the far infrared.” In communications, they could transmit far greater amounts of information than either radio waves or microwaves.

In imaging, terahertz frequencies could lead to the development of diagnostic equipment that avoids the health risks of x-rays.

However, expanding the real-world applications of this part of the spectrum has been stuck for want of a material that can be used to manipulate terahertz waves with precision.

Graphene and terahertz waves

The terahertz worm began to turn in 2004, when a team of researchers in the U.K. literally used sticky tape to lift a one-atom thin sheet of carbon from a chunk of graphite.

Called graphene, the new material possesses outsized strength and unique electrical properties, which have made it the focus for bringing about the next generation of super fast, super small, flexible and even transparent electronic devices.

As Notre Dame researcher Berardi Sensale- Rodriguez explained in a prepared statement:

“A major bottleneck in the promise of THz technology has been the lack of efficient materials and devices that manipulate these energy waves. Having a naturally two-dimensional material with strong and tunable response to THz waves, for example, graphene, gives us the opportunity to design THz devices achieving unprecedented performance.”

Graphene nanoribbons to the rescue

Last fall’s breakthrough at Lawrence Berkeley involved the fabrication of graphene nanoribbons, made by etching patterns into a sheet of carbon atoms laid over a silicon oxide substrate. An overlay of ion gel was used to complete the gated structure of a semiconductor system.

The team was able to “tune” or manipulate the ribbons in to control the movement of electrons. This collective movement, or oscillation, of electrons is referred to as a plasmon.

According to Berkeley research Feng Wang, plasmons can be observed by eye, in the unique glow from medieval-era stained glass which is caused by electrons oscillating on the surface of metal nanoparticles including gold and copper.

A similar effect occurs in graphene but at lower frequencies, which are not visible to the naked eye.

The Berkeley team discovered that altering the width of the graphene nanoribbons will cause the electron waves to “slosh” back and forth at different frequencies, which makes the ribbons absorb different frequencies of light.

The demonstration marked a step along the way to practical, real-world applications partly because the team was able to measure the difference in absorption rates at room temperature, in contrast to other research tracks that require temperatures in the absolute zero range.

The findings of the Notre Dame team, published in mid-April, also involved the development of a practical, room-temperature operation. The team was able to demonstrate proof of concept for a graphene based modulator, building on previous research into the use of an electron gas to manipulate terahertz waves.

The idea of using an electron gas dates all the way back to 2006, so given the pace of research in both the Berkeley and Notre Dame cases a practical graphene/terahertz device is far from bouncing out of the laboratory door and onto retail shelves.

Aside from challenges within the research itself, the commercialization of graphene devices depends on the development of cost effective methods for fabricating mass quantities of graphene, and sticky tape will only get you so far. At this point there have been some promising developments, but the goal has proved elusive.

Not to worry, though – the Navy is all over that one, too. Through a separate ONR-funded program, researchers at Rice University are developing a simple, one-step process for creating nanoscale graphene discs.

Image: Some rights reserved by Laineys Repertoire.

Follow me on Twitter: @TinaMCasey.

Keep up to date with all the hottest cleantech news by subscribing to our (free) cleantech newsletter, or keep an eye on sector-specific news by getting our (also free) solar energy newsletter, electric vehicle newsletter, or wind energy newsletter.

Tesla_WTC_Solution
24th December 2014, 19:45
http://www.mpg.de/7583916/graphene-terahertz-laser

Graphene can emit laser flashes

Individual layers of carbon atoms are suitable as active material for terahertz lasers, as they permit population inversion

October 25, 2013

Graphene is considered the jack-of-all-trades of materials science: The two-dimensional honeycomb-shaped lattice made up of carbon atoms is stronger than steel and exhibits extremely high charge carrier mobilities. It is also transparent, lightweight and flexible. No wonder that there are plenty of applications for it – for example, in very fast transistors and flexible displays. A team headed by scientists from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg have demonstrated that it also meets an important condition for use in novel lasers for terahertz pulses with long wavelengths. The direct emission of terahertz radiation would be useful in science, but no laser has yet been developed which can provide it. Theoretical studies have previously suggested that it could be possible with graphene. However, there were well-founded doubts - which the team in Hamburg has now dispelled. At the same time, the scientists discovered that the scope of application for graphene has its limitations though: in further measurements, they showed that the material cannot be used for efficient light harvesting in solar cells.

<p>Emitting flashes of light: Graphene, a honeycomb lattice made of carbon atoms, is a suitable material for lasers emitting ultrashort terahertz pulses.<br />&nbsp;</p>
Zoom Image




Emitting flashes of light: Graphene, a honeycomb lattice made of carbon atoms, is a suitable material for lasers ... [more]












© Jörg Harms

A laser amplifies light by generating many identical copies of photons – cloning the photons, as it were. The process for doing so is called stimulated emission of radiation. A photon already produced by the laser makes electrons in the laser material (a gas or solid) jump from a higher energy state to a lower energy state, emitting a second completely identical photon. This new photon can, in turn, generate more identical photons. The result is a virtual avalanche of cloned photons. A condition for this process is that more electrons are in the higher state of energy than in the lower state of energy. In principle, every semiconductor can meet this criterion.

The state which is referred to as population inversion was produced and demonstrated in graphene by Isabella Gierz and her colleagues at the Max Planck Institute for the Structure and Dynamics of Matter, together with the Central Laser Facility in Harwell (England) and the Max Planck Institute for Solid State Research in Stuttgart. The discovery is surprising because graphene lacks a classic semiconductor property, which was long considered a prerequisite for population inversion: a so-called bandgap. The bandgap is a region of forbidden states of energy, which separates the ground state of the electrons from an excited state with higher energy. Without excess energy, the excited state above the bandgap will be nearly empty and the ground state below the bandgap almost completely populated. A population inversion can be achieved by adding excitation energy to electrons to alter their energy state to the one above the bandgap. This is how the avalanche effect described above is produced.

Until now, terahertz pulses have only been generated via inefficient non-linear optical processes

However, the forbidden band in graphene is infinitesimal. “Nevertheless, the electrons in graphene behave similarly to those of a classic semiconductor”, Isabella Gierz says. To a certain extent, graphene could be thought of as a zero-bandgap semiconductor. Because of the absence of a bandgap, the population inversion in graphene only lasts for around 100 femtoseconds, less than a trillionth of a second. “That is why graphene cannot be used for continuous lasers, but potentially for ultrashort laser pulses”, Gierz explains.

Such a graphene laser would be particularly useful for research purposes. It could be used to amplify laser light with very long wavelengths; so-called terahertz radiation. This type of laser light could be employed in basic research to study, for example, high-temperature superconductors. To date, terahertz radiation has been produced using comparatively inefficient, so-called non-linear optical processes. In addition, the available wavelength range is often limited by the non-linear material used. The recent findings indicate that graphene could be used for broad bandwidth amplification of arbitrarily long wavelengths.

However, the Hamburg-based team also dashed the hopes of some materials scientists – as it turns out, graphene is probably not suited for converting solar radiation into electricity in solar cells. “According to our measurements, a single photon in graphene cannot release several electrons, as previously expected”, Gierz says. This is a prerequisite for efficient conversion of radiation into electricity.

Silicon carbide can be used to produce graphene for lasers

The scientists in Hamburg studied the graphene using a method called time-resolved photoemission spectroscopy. This involved illuminating the material with ultrashort ultraviolet (UV) light pulses. As a consequence the electrons are forced out of the sample and the physicists measure their energy and angle of exit. The resulting data is used to establish the energy distribution of electrons in the material. Time resolution is achieved by delaying the arrival time of the UV probe pulse with respect to an arbitrary excitation pulse.

In the present experiment, the electrons in the graphene were excited using infrared laser light. Then the scientists employed photoemission spectroscopy to demonstrate the occurrence of population inversion. In a similar way, they established that carrier multiplication could not be achieved by radiation.

The graphene was produced by the scientists through thermal decomposition of silicon carbide. According to Gierz, this procedure can also be used to make a graphene laser, since silicon carbide is transparent and will not interfere with terahertz radiation. However, the physicist admits that a lot of development work remains to produce a graphene laser.

CM/PH





http://www.wired.com/2008/07/fbi-we-dont-hav/

they lied

http://www.wired.com/images_blogs/photos/uncategorized/2008/07/24/tesla.jpg


As part of its centennial celebration, the FBI just released a list of the "Top Ten Myths in FBI History." Among other things, the list debunks the silly urban legend that the FBI spies on innocent Americans — you know, like war protestors and people with phones. "We won’t have a ‘file’ on you unless you’re a spy or terrorist or criminal or are suspected of being one."

This entry, though, is genuinely reassuring:


Myth #10) The FBI has Nikola Tesla’s plans for a "death ray."

If you don’t know the name, Nikola Tesla was a prolific inventor and gifted physicist and engineer — most known for developing the basis for AC power — who was born in Croatia in 1856 and settled in the United States in 1884. When Tesla died in New York in January 1943, his papers — which were thought to include plans for a particle beam weapon, dubbed a
"death ray" by the press — were temporarily seized by the Department of Justice Alien Property Custodian Office ("alien" in this case means "foreigner," although Tesla was a U.S. citizen).





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http://techcrunch.com/2013/01/24/cambridge-university-to-open-graphene-rd-centre-with-backing-from-nokia-plastic-logic-others-plus-12m-u-k-government-grant/

2013

Material scientists and nanotechnologists get very excited about the potential of graphene — a one-atom-thick sheet of bonded carbon atoms which is exceptionally strong, lightweight and flexible and is a better conductor than silicon — but they are not the only ones to see huge potential in it. Nokia, Plastic Logic, Philips, Dyson, and BaE systems are among more than 20 industry partners who have pledged £13 million worth of support for a new graphene R&D centre to be established at Cambridge University. The Centre is also backed by more than £12 million of government funding.



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p.s. watching right now:

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