Graphene mixer can speed up future electronics

Researchers at Chalmers University of Technology (Sweden) have for the first time demonstrated a novel subharmonic graphene FET mixer at microwave frequencies. The mixer provides new opportunities in future electronics, as it enables compact circuit technology, potential to reach high frequencies and integration with silicon technology.

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​A mixer is a key building block in all electronic systems – a device that combines two or more electronic signals into one or two composite output signals. Future applications at THz frequencies such as radar systems for security and safety, radio astronomy, process monitoring and environmental monitoring will require large arrays of mixers for high-resolution imaging and high-speed data acquisition. Such mixer arrays or multi-pixel receivers need new type of devices that are not only sensitive but also power-efficient and compact.

The ability in graphene to switch between hole or electron carrier transport via the field effect enables a unique niche for graphene for RF IC applications. Thanks to this symmetrical electrical characteristic, the researchers at Chalmers have managed to build the G-FET subharmonic resistive mixer using only one transistor. Hence, no extra feeding circuits are required, which makes the mixer circuit more compact as opposed to conventional mixers. As a consequence, the new type of mixer requires less wafer area when constructed and can open up for advanced sensor arrays, for example for imaging at millimetre waves and even sub millimetre waves as G-FET technology progress.

Schematic picture of a subharmonic graphene-FET mixer. The LO and RF signals are fed to the gate and drain terminals, respectively, and the IF signal is extracted from the drain terminal.

"The performance of the mixer can be improved by further optimising the circuit, as well as fabricating a G-FET device with a higher on-off current ratio", says Jan Stake, professor of the research team. "Using a G‐FET in this new topology enables us to extend its operation to higher frequencies, thereby exploiting the exceptional properties of graphene. This paves the way for future technologies operating at extremely high frequencies."

In addition to enabling compact circuits, the G-FET provides potential to reach high frequencies thanks to the high velocity in graphene, and the fact that a subharmonic mixer only requires half the local oscillator (LO) frequency compared to a fundamental mixer. This property is attractive especially at high frequencies (THz) where there is a lack of sources providing sufficient LO-power.

Moreover, the G-FET can be integrated with silicon technology. For example, it is CMOS compatible (Complementary Metal Oxide Semiconductor) and among other things it can be used in CMOS electronics for backend processing on a single chip.

How Molecules Move Energy After Light Absorption

Chemists Solve an 84-Year-Old Theory On How Molecules Move Energy After Light Absorption

ScienceDaily (Dec. 22, 2011) — The same principle that causes figure skaters to spin faster as they draw their arms into their bodies has now been used by Michigan State University researchers to understand how molecules move energy around following the absorption of light.

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Conservation of angular momentum is a fundamental property of nature, one that astronomers use to detect the presence of satellites circling distant planets. In 1927, it was proposed that this principle should apply to chemical reactions, but a clear demonstration has never been achieved.

In the current issue of Science, MSU chemist Jim McCusker demonstrates for the first time the effect is real and also suggests how scientists could use it to control and predict chemical reaction pathways in general.

"The idea has floated around for decades and has been implicitly invoked in a variety of contexts, but no one had ever come up with a chemical system that could demonstrate whether or not the underlying concept was valid," McCusker said. "Our result not only validates the idea, but it really allows us to start thinking about chemical reactions from an entirely different perspective."

The experiment involved the preparation of two closely related molecules that were specifically designed to undergo a chemical reaction known as fluorescence resonance energy transfer, or FRET. Upon absorption of light, the system is predisposed to transfer that energy from one part of the molecule to another.

McCusker's team changed the identity of one of the atoms in the molecule from chromium to cobalt. This altered the molecule's properties and shut down the reaction. The absence of any detectable energy transfer in the cobalt-containing compound confirmed the hypothesis.

"What we have successfully conducted is a proof-of-principle experiment," McCusker said. "One can easily imagine employing these ideas to other chemical processes, and we're actually exploring some of these avenues in my group right now."

The researchers believe their results could impact a variety of fields including molecular electronics, biology and energy science through the development of new types of chemical reactions.

Dong Guo, a postdoctoral researcher, and Troy Knight, former graduate student and now research scientist at Dow Chemical, were part of McCusker's team. Funding was provided by the National Science Foundation.

Nutrino faster than loght disputed?

The announcement of opera team about the discovery of Nutrino faster than light vreated a futter in Science world.

 Carlo Contaldi of Imperial College London says that it’s likely the OPERA team failed to take gravity into account in their  equations and its effect on the clocks used to time the experiment. This because the degree of gravity at Italy and Geneva ,the two stations involved in the experiment  were different. There for one of the clocks would have been running slightly faster than the other, resulting in faulty timing. .

Andrew Cohen and Sheldon Glashow, says that if the neutrinos in the study were in fact traveling as fast as claimed, they should have been radiating particles as they went, leaving behind a measurable trail; this due to the energy transfer that would occur between particles moving at different speeds. And since the OPERA team didn’t observe any such trail ,it follows that the neutrinos weren’t in fact traveling as fast as were claimed and the resultant speed measurements would have to be attributed to something else.
Neither of these papers actually disproves the results found by the OPERA team of course, the first merely suggests there may be a problem with the way the measurements were taken, the second takes more of a “it can’t be true because of…” approach which only highlight the general disbelief in the physics community regarding the very possibility of anything, much less the speed of neutrinos traveling faster than the speed of light, messing with Einstein’s most basic theories. The first can be addressed rather easily by the OPERA team if it so desires, and the second, well, if the neutrinos did in fact travel faster than the speed of light and did so without leaving a trail, a lot of physics theory will have to be rethought. Though that may not necessarily be a bad thing, physics is supposed to be about finding answers to explain the natural world around us after all, even if it means going back to the drawing board now and then.
Courtesy Physics.org

Is it rational to believe in God?

Is it rational to believe in God?

Giovanni Serritella, Banda Aceh | Thu, 12/22/2011 9:48 AM

The world’s most famous physicist Prof. Stephen Hawking has declared that God does not exist.

Hawking joins the opinion of several other world-class scientists like Richard Dawkins, Peter Atkins, James Watson, Victor Stenger and many others who deny the existence of God in the name of the latest advancements in physics, biology and other scientific domains.

The so-called “New Atheism” (championed by Richard Dawkins) sees God as a delusion, a by product of the mind of superstitious and scientifically uneducated people.

“Because there is a law like gravity, the universe can and will create itself from nothing ... Spontaneous creation is the reason there is something rather than nothing, why the universe exists and why we are here”. This is the conclusion of The Grand Design, Hawking’s latest book.

Hawking’s assertion is based on the predictions of his famous M-theory. But is Hawking’s theory really an ultimate explanation? Has the grand master of physics checkmated the grand master of the universe? Let’s examine things in more detail.

Einstein’s theory of relativity says that time is not the same for everyone but is “relative” to how fast one is moving. At variable speeds or in the presence of weak and strong gravity time behaves elastically, it can stretch and shrink and even stop.

This phenomenon has been observed by measuring the rate of atomic clocks mounted on supersonic jet planes moving at different speeds at various distances from the Earth’s surface.

Under extreme gravity like at the moment of the birth of the universe (the big bang), gravity was so intense that time was “compressed” to a zero point. Not only space but time itself was born at that moment. There was no “before”.

Hawking states that a “law of gravity” exists and this (not God) creates the universe. Hawking surely also believes that gravity itself exists (since a law of gravity without “gravity” to describe would be meaningless). Now, if we say that X creates Y, we must presuppose the existence of X in the first place to bring Y into existence. Likewise, we must presuppose the existence of gravity to bring the universe into existence.

But Einstein’s theory of relativity shows that this is illogical because it is like saying that gravity existed “before time” which is absurd. Did gravity spontaneously generate itself then? It is important to realize that it is logically impossible for a cause (gravity) to bring about an effect (its own creation) without already being in existence.

Hawking sustains that “the universe creates itself out of nothing”. But Hawking’s nothing is actually something: “Gravity” (first self-contradiction). Hawking then says that the universe creates itself (second self-contradiction). Thus, the conclusion of The Grand Design is actually a double self-contradiction.

Let’s consider an Apple computer. Should we account for it by mentioning its inventor (Steve Jobs) or should we follow Hawking’s reasoning and say that the Apple computer arose naturally from the laws of physics?

It actually makes no sense to choose between Jobs and the laws of physics to account for the existence of the Apple computer since both levels of explanation are needed. Jobs is needed to conceive and design the machine and the laws of physics are needed to make the computer processor work.

These two levels of explanations are not mutually exclusive but they complement each other. Science is concerned with “how” questions (how does the computer work?) and with functional questions (why is that circuit there?).

But science does not ask the “why” question of purpose (why was the computer built?) Purpose (Jobs in this case) does not even appear in the scientific account. But it would be ridiculous to say that Jobs did not exist. He is the actual reason why there is an Apple computer in the first place.

This is exactly what many scientists (including Hawking) do with God. They ask questions which exclude God (“how” questions and “functional” questions) and then they claim that God is unnecessary. This reasoning shows that offering a choice between God and the law of gravity is, in fact, illogical as both are needed.

Hawking in his book confuses two levels of explanation; “personal agency” and “physical law” and he attributes creative power (which is a personal agency) to a physical law.

 Let’s look at another example. If I put ¤1 in my bank account and another euro, the next the law of arithmetic 1+1=2 will explain “why” I have ¤2 in my account, it will not “create” ¤2 for me and it will surely not tell me anything about the purpose of me having ¤2 in my account.

Likewise, the law of gravity does not “create” gravity it only “explains” what’s already there (gravity) and “predicts” how gravity behaves.

The bottom line is that the laws of physics cannot create anything or cause anything to happen. Rather than ultimate creators of the universe, they are just descriptions of how things behave.

What actually needs explaining is the logical characteristics and intelligibility of nature and the universe, not whether the universe generates itself spontaneously out of nothing or not.

Nobel laureate in physics Richard Feynman once stated: “The fact that there are rules like the law of gravity is some sort of miracle as it leads to the possibility of prediction; it tells you what you would expect to happen in an experiment you have not yet done”.

Not denying the genius of Hawking, it appears that self-contradiction is possible even for world-famous scientists. The problem is that sometimes the illogicality of certain statements is obscured by the authority of those who make such statements and the general public often fails to see this.

World-wide prestige and distinguished scientific authority do not compensate for faulty logic and far from being a delusion the God hypothesis remains a rational explanation of why there is a universe rather than nothing.

The writer, an environmental scientist, works for the European Union Delegation to Indonesia. The opinions expressed are his own.

• Physicists see hints that Higgs boson exists

  John Heilprin, Associated Press
  Tuesday, December 13, 2011
  Geneva --
  Physicists are closing in on an elusive subatomic particle that, if found, would confirm a long-held understanding about why matter has mass and how the universe's fundamental building blocks behave.
  Few people outside physics can fully comprehend the search for the Higgs boson, which was first hypothesized 40 years ago. But proving that the "God particle" actually exists would be "a vindication of the equations we've been using all these years," said one Nobel laureate.
  Scientists announced Tuesday that they had found hints but no definitive proof of the particle, which is believed to be a basic component of the universe. They hope to determine whether it exists by next year.
  It's hard to find, not because it is especially tiny but because it is hard to create, said physicist Howard Gordon of the Brookhaven National Laboratory in Upton, N.Y. He works with the ATLAS experiment, one of two independent teams looking for the Higgs boson at CERN, the European Organization for Nuclear Research near Geneva.
  CERN runs the Large Hadron Collider under the Swiss-French border, a 17-mile tunnel where high-energy beams of protons are sent crashing into each other at incredible speeds.
  A fraction of those collisions could produce the Higgs particle, assuming it exists.
  CERN's director-general, Rolf Heuer, said that "the window for the Higgs mass gets smaller and smaller" as scientists learn more.
  "But be careful - it's intriguing hints," he said. "We have not found it yet. We have not excluded it yet."
  Tuesday's revelations were highly anticipated by thousands of researchers, but the ideas behind the Higgs boson date back to the 1960s.
  British physicist Peter Higgs and others theorized its existence to explain why the fundamental particles in matter have mass. Those particles, such as electrons, are the building blocks of the universe. Mass is a trait that combines with gravity to give an object weight.
  Frank Wilczek, a Nobel laureate and physics professor at the Massachusetts Institute of Technology, said finding the Higgs boson would tie up a loose end of the standard model of physics, which requires that a Higgs-like particle exist.

New Switch for Electronics

New Switch Could Improve Electronics

ScienceDaily (Dec. 1, 2011) — Researchers at the University of Pittsburgh have invented a new type of electronic switch that performs electronic logic functions within a single molecule. The incorporation of such single-molecule elements could enable smaller, faster, and more energy-efficient electronics.

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The research findings, supported by a $1 million grant from the W.M. Keck Foundation, were published online in the Nov. 14 issue of Nano Letters.
"This new switch is superior to existing single-molecule concepts," said Hrvoje Petek, principal investigator and professor of physics and chemistry in the Kenneth P. Dietrich School of Arts and Sciences and codirector of the Petersen Institute for NanoScience and Engineering (PINSE) at Pitt. "We are learning how to reduce electronic circuit elements to single molecules for a new generation of enhanced and more sustainable technologies."
The switch was discovered by experimenting with the rotation of a triangular cluster of three metal atoms held together by a nitrogen atom, which is enclosed entirely within a cage made up entirely of carbon atoms. Petek and his team found that the metal clusters encapsulated within a hollow carbon cage could rotate between several structures under the stimulation of electrons. This rotation changes the molecule's ability to conduct an electric current, thereby switching among multiple logic states without changing the spherical shape of the carbon cage. Petek says this concept also protects the molecule so it can function without influence from outside chemicals.
Because of their constant spherical shape, the prototype molecular switches can be integrated as atom-like building blocks the size of one nanometer (100,000 times smaller than the diameter of a human hair) into massively parallel computing architectures.
The prototype was demonstrated using an Sc3N@C80 molecule sandwiched between two electrodes consisting of an atomically flat copper oxide substrate and an atomically sharp tungsten tip. By applying a voltage pulse, the equilateral triangle-shaped Sc3N could be rotated predictably among six logic states.
The research was led by Petek in collaboration with chemists at the Leibnitz Institute for Solid State Research in Dresden, Germany, and theoreticians at the University of Science and Technology of China in Hefei, People's Republic of China. The experiments were performed by postdoctoral researcher Tian Huang and research assistant professor Min Feng, both in Pitt's Department of Physics and Astronomy.

way to concentrate sun's heat

 

December 2, 2011

Most technologies for harnessing the sun’s energy capture the light itself, which is turned into electricity using photovoltaic materials. Others use the sun’s thermal energy, usually concentrating the sunlight with mirrors to generate enough heat to boil water and turn a generating turbine. A third, less common approach is to use the sun’s heat — also concentrated by mirrors — to generate electricity directly, using solid-state devices called thermophotovoltaics, which have their roots at MIT dating back to the 1950s.

Now, researchers at MIT have found a way to use thermophotovoltaic devices without mirrors to concentrate the sunlight, potentially making the system much simpler and less expensive. The key is to prevent the heat from escaping the thermoelectric material, something the MIT team achieved by using a photonic crystal: essentially, an array of precisely spaced microscopic holes in a top layer of the material.

The approach mimics Earth’s greenhouse effect: Infrared radiation from the sun can enter the chip through the holes on the surface, but the reflected rays are blocked when they try to escape. This blockage is achieved by a precisely designed geometry that only allows rays that fall within a very tiny range of angles to escape, while the rest stay in the material and heat it up.
The new device was described in a paper by Research Laboratory of Electronics research scientist Peter Bermel and other MIT researchers, published in October in the journal Nanoscale Research Letters.
Bermel explains that if you put an ordinary, dark-colored, light- and heat-absorbing material in direct sunlight, “it can’t get much hotter than boiling water,” because the object will reradiate heat almost as fast as it absorbs it. But to generate power efficiently, you need much higher temperatures than that. By concentrating sunlight with parabolic mirrors or a large array of flat mirrors, it’s possible to get much higher temperatures — but at the expense of a much larger and more complex system.
“What I’m looking at is an alternative to that paradigm,” Bermel says, by “concentrating the sunlight thermally”: capturing it and reflecting it back into the material. The result, he says, is that the device can absorb as much heat as a standard black object, but “in practice, we can get it extremely hot, and not reradiate much of that heat.”
Such a system, he says, “at large scale, is efficient enough to compete with more conventional forms of power. This is an alternative to concentrators.”