SCIENCE & TECHNOLOGY

Graphene electronics
SS Verma

Silicon is the master base material of present-day electronics involving the transport of electrons and holes across the junction. There are growing complications related with the transport of these current carriers along with the increasing cost involved with miniaturisation of silicon based electronics.



A visitor walks past Cryolophosaurus ellioti on display at the opening of “Dinosaurus exhibition in Tokyo Marunouchi” at the Tokyo’s fashionable shopping district of Marunouchi on February 19, 2009. —AFP

Trends
Mammoth skeleton found

LOS ANGELES
: The nearly complete skeleton of a massive Columbian mammoth who died during the last ice age has been dug out of a construction site near the La Brea Tar Pits in downtown Los Angeles, a remarkable find even in the fossil-rich area, scientists said. The mammoth, dubbed “Zed” by researchers at the Page Museum at the La Brea Tar Pits, likely died in his late 40s some 40,000 years ago and was found near an unprecedented treasure trove of fossils that workers stumbled upon while digging the foundation for an underground parking garage.

  • How Alzheimer’s attacks brain

  • Forests absorb fossil fuel emissions

  • First carbon-free polar station


Prof Yash Pal
Prof Yash Pal

THIS UNIVERSE 
PROF YASH PAL
The earth rotates on its axis at an approximate speed of 800 kmph and revolves around the sun in 24 hrs and the solar system hurtles in space @ 36,000 kmph. (please correct me if I am wrong). Why do we not feel the effect of this collective motion and why are we not thrown off at a tangent? Is it due to gravitational pull and due to centripetal/centrifugal forces?

 


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Graphene electronics
SS Verma

Silicon is the master base material of present-day electronics involving the transport of electrons and holes across the junction.

There are growing complications related with the transport of these current carriers along with the increasing cost involved with miniaturisation of silicon based electronics. Hence, efforts are to look for other base materials which are cheap with advantages similar to silicon as well as nano-electronics making use of the wave nature of particles to generate electronic waves due to electron diffraction instead of electrons diffusion, where particles need not to move and the energy will be transferred in the form of waves. PAM Dirac has established and highlighted the wave nature at quantum level and Dirac’s equation explains the unique phenomena concerning the motion of the electron at nano level.

It is found that an electron which seems to be moving slowly must actually have a very high frequency oscillatory motion of small amplitude superposed on the regular motion.

As a result of this oscillatory motion, the velocity of the electron at any time equals the velocity of light. Carbon being available in plenty in its different forms like diamond and graphite is under investigation as a base material for electronics for a long time. Diamond is very costly and hard but graphite, the material that gives pencils their marking ability, is cheap and flexible and could be the basis for a new class of nanometer-scale carbon based electronic devices which will make use of the attractive properties of carbon nanotubes which can be produced using established microelectronics manufacturing techniques.

Recently, researchers have developed foundation for circuitry and devices based on graphite. Graphene (electronic name given to graphite) is a condensed matter realisation of the Dirac electron relativistic wave equation at quantum level in two dimensions.

Many of the unusual properties of relativistic fermions in quantum electrodynamics (QED) reappear in graphene. The discovery of graphene, followed by observation of an anomalous quantum electronic transport phenomena in it has triggered intense focus of research in this one atomic thin two-dimensional system. The unique electronic band structure of graphene lattice provides a linear dispersion relation where the Fermi velocity replaces the role of the speed of light in usual Dirac’s equation. Because of its high electronic mobility, structural flexibility, and capability of being tuned from p-type to n-type doping by the application of a gate voltage, graphene is considered a potential breakthrough in terms of carbon-based nano-electronics.

Using thin layers of graphite, researchers at the Georgia Institute of Technology in the United States, in collaboration with the Centre National de la Recherche Scientifique (CNRS) in France, have produced proof-of-principle transistors, loop devices and circuitry. Ultimately, the researchers hope to use graphene layers less than 10 atoms thick as the basis for revolutionary electronic systems that would manipulate electrons as waves rather than particles, much like photonic systems control light waves.

From graphene based nano electronics, scientists expect to make devices of a kind that don’t really have an analog as in silicon-based electronics, so this is an entirely different way of looking at electronics. The ultimate goal is integrated electronic structures that work on diffraction of electrons rather than diffusion of electrons. This will allow the production of very small devices with very high efficiencies and low power consumption.

The graphene circuitry demonstrates high electron mobility – up to 25,000 square centimeters per volt-second, showing that electrons move with little scattering. The researchers (Prof. De Heer and his collaborators) have shown electronic coherence at near room temperature, and evidence of quantum interference effects. They expect to see ballistic transport when they make structures small enough. So far, they have built an all graphene planar field-effect transistor.

The key to properties of the new circuitry is the width of the ribbons, which confine the electrons in a quantum effect similar to that seen in carbon nanotubes. Scientists have developed and discovered many exciting properties of carbon nanotubes over the past decade and believe that their (carbon nano tubes) primary value has been in calling attention to the useful properties of graphene. carbon nanotubes conduct electricity with virtually no resistance, they have attracted strong interest for use in transistors and other devices. Nanotubes are simply graphene that has been rolled into a cylindrical shape and using narrow ribbons of graphene, which will give all the properties of nanotubes because those properties are due to the graphene and the confinement of the electrons, not the nanotube structures.

Continuous graphene circuitry can be produced using standard microelectronic processing techniques, potentially allowing creation of a “road map” for high-volume graphene electronics manufacturing. Experts envision using the graphene electronics for specialized applications, potentially within conventional silicon-based systems.

Graphene systems could also be used as the foundation for molecular electronics, helping resolve resistance issues that now affect such systems. There is a huge advantage to making a system out of one continuous material, compared to having different materials with different interfaces.

Researchers expect to continue improving their materials and fabrication processes, while producing and testing new structures towards building a new class of electronics based on graphene.

However, serious obstacles must be overcome before nanotube-based electronic devices could be scaled up into high-volume industrial products.

The writer is from Department of Physics, S.L.I.E.T., Longowal 

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Trends
Mammoth skeleton found

LOS ANGELES: The nearly complete skeleton of a massive Columbian mammoth who died during the last ice age has been dug out of a construction site near the La Brea Tar Pits in downtown Los Angeles, a remarkable find even in the fossil-rich area, scientists said. The mammoth, dubbed “Zed” by researchers at the Page Museum at the La Brea Tar Pits, likely died in his late 40s some 40,000 years ago and was found near an unprecedented treasure trove of fossils that workers stumbled upon while digging the foundation for an underground parking garage.

How Alzheimer’s attacks brain

CHICAGO: American scientists proposed a new theory on of how Alzheimer’s disease kills brain cells they said opens new avenues of research into treatments for the fatal, brain-wasting disease. They believe a chemical mechanism that naturally prunes away unwanted brain cells during early brain development somehow gets hijacked in Alzheimer’s disease.

Forests absorb fossil fuel emissions

LONDON: Tropical trees have grown bigger over the past 40 years and now absorb 20 percent of fossil fuel emissions from the atmosphere, highlighting the need to preserve threatened forests, British researchers said Wednesday. Using data collected from nearly 250,000 trees in the world’s tropical forests over the past 40 years, their study found that tropical forests across the world remove 4.8 billion metric tons of carbon dioxide emissions each year.

First carbon-free polar station

PRINCESS ELISABETH BASE, Antarctica: The world’s first zero-emission polar research station opened in Antarctica on Sunday and was welcomed by scientists as proof that alternative energy is viable even in the coldest regions. Pioneers of Belgium’s Princess Elisabeth station in East Antarctica said if a station could rely on wind and solar power in Antarctica—mostly a vast, icy emptiness—it would undercut arguments by sceptics that green power is not reliable.
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THIS UNIVERSE 
PROF YASH PAL

The earth rotates on its axis at an approximate speed of 800 kmph and revolves around the sun in 24 hrs and the solar system hurtles in space @ 36,000 kmph. (please correct me if I am wrong). Why do we not feel the effect of this collective motion and why are we not thrown off at a tangent? Is it due to gravitational pull and due to centripetal/centrifugal forces?

It is true the earth on which we live is moving at a great speed. I think if you take into account all the motions, this speed might come to a few hundred kilometres per second! And yet we do not feel it. This appears amazing till we realise that this is due to a very fundamental law. This states that all frames of reference in relative uniform motion with respect to each other are equivalent and we cannot distinguish between them through any experiment we do within any frame. When in uniform motion all parts of our body keep moving the same way as they would at what we call rest. We have no internal way of detecting that motion. All of us have had the experience of sitting in a train stopped at a station, looking at another train standing on a parallel line. When the train on the other line starts moving we often feel that it is our train that has begun to move. We realise our mistake as soon as our eyes fall on another stationary object. What we do detect are accelerations. We are very sensitive to changes in motion. When they are strong and sudden we have accidents.

We have been told that the ozone hole is mainly present above Antarctica, but not above much polluted places like India and some other polluted countries, despite the fact that ozone hole occurs due to pollution. Why?

Firstly we have to realise atmospheric pollution in stratosphere is not locally confined. Movement of air is almost global. Secondly the “pollution” that destroys ozone is not of carbon dioxide, sulphur dioxide, smoke, dust or even carbon monoxide. The culprits are the molecules that ultimately release atoms like chlorine into the stratosphere. When a chlorine atom goes next to a molecule of ozone it steals one of its oxygen atoms, leaving behind a good old oxygen atom - O2. While the ozone molecule is destroyed the chlorine atom is freed after a while to go and rob another ozone molecule. It is believed that the reason for enhanced ozone depletion near Antarctica is the following: Upper air winds near the poles are circumpolar and the temperature is very low. Several condensation nuclei act as parking stations for many of the ozone destroying chemicals. These stations act as efficient killing centres for ozone molecules.
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