... new experiments conducted at MIT show that a one-atom-thick material called graphene, a form of pure carbon whose atoms are joined in a chicken-wire-like lattice, behaves quite differently depending on the nature of material it’s wrapped around. When sheets of graphene are placed on substrates made of different materials, fundamental properties — such as how the graphene conducts electricity and how it interacts chemically with other materials — can be drastically different, depending on the nature of the underlying material.
“We were quite surprised” to discover this altered behavior, says Michael Strano, the Charles and Hilda Roddey Professor of Chemical Engineering at MIT, who is the senior author of a paper published this week in the journal Nature Chemistry ("Understanding and controlling the substrate effect on graphene electron-transfer chemistry via reactivity imprint lithography").
“We expected it to behave like graphite” — a well-known form of carbon, used to make the lead in pencils, whose structure is essentially multiple layers of graphene piled on top of each other.
But its behavior turned out to be quite different. “Graphene is very strange,” Strano says. Because of its extreme thinness, in practice graphene is almost always placed on top of some other material for support. When that material underneath is silicon dioxide, a standard material used in electronics, the graphene can readily become “functionalized” when exposed to certain chemicals. But when graphene sits on boron nitride, it hardly reacts at all to the same chemicals.
“It’s very counterintuitive,” Strano says. “You can turn off and turn on graphene’s ability to form chemical bonds, based on what’s underneath.”
The reason, it turns out, is that the material is so thin that the way it reacts is strongly affected by the electrical fields of atoms in the material beneath it.[ No kidding...] This means that it is possible to create devices with a micropatterned substrate — made up of some silicon dioxide regions and some coated with boron nitride — covered with a layer of graphene whose chemical behavior will then vary according to the hidden patterning.
Strano says. For example, the one-atom-thick material, when bonded to copper, completely eliminates that metal’s tendency to oxidize (which produces the characteristic blue-green surface of copper roofs). “It can completely turn off the corrosion,” he says, “almost like magic … with just the whisper of a coating.”
To explain why graphene behaves the way it does, “we came up with a new electron-transfer theory”
... said IBM scientist Leo Gross. “The second contrast mechanism really came as a surprise: Bonds appeared with different lengths in AFM measurements. With the help of ab initio calculations we found that the tilting of the carbon monoxide molecule at the tip apex is the cause of this contrast.”
.IBM Research scientists imaged the bond order and length of individual carboncarbon bonds in C60, also known as a buckyball for its football shape and two planar polycyclic aromatic hydrocarbons (PAHs), which resemble small flakes of graphene
As in their earlier research ("The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy") the IBM scientists used an atomic force microscope (AFM) with a tip that is terminated with a single carbon monoxide (CO) molecule. This tip oscillates with a tiny amplitude above the sample to measure the forces between the tip and the sample, such as a molecule, to create an image. The CO termination of the tip acts as a powerful magnifying glass to reveal the atomic structure of the molecule, including its bonds. This made it possible to distinguish individual bonds that differ only by 3 picometers or 3 × 10-12 meters, which is about one-hundredth of an atom’s diameter.
errghh??Comparison with theory shows that Pauli repulsion is the source of the atomic resolution, whereas van der Waals and electrostatic forces only add a diffuse attractive background.
Thereby they calculated the tilting of the CO molecule at the tip apex that occurs during imaging.
a process of mediation by an aethereal field,
So that's a surface effect which involves only a tiny fraction of the total mass of carbon in the powder--just 0.0001 per cent of the mass, according to Esquinazi and co.
Graphene joins the race to redefine the ampere
A new joint innovation by the National Physical Laboratory (NPL) and the University of Cambridge could pave the way for redefining the ampere in terms of fundamental constants of physics. The world's first graphene single-electron pump (SEP), described in a paper today in Nature Nanotechnology ("Gigahertz quantized charge pumping in graphene quantum dots"), provides the speed of electron flow needed to create a new standard for electrical current based on electron charge.
The international system of units (SI) comprises seven base units (the metre, kilogram, second, Kelvin, ampere, mole and candela).
[no unit for magnetism ??]
Ideally these should be stable over time and universally reproducible. This requires definitions based on fundamental constants of nature which are the same wherever you measure them.
The present definition of the Ampere, however, is vulnerable to drift and instability. This is not sufficient to meet the accuracy needs of present and certainly future electrical measurement. The highest global measurement authority, the Conférence Générale des Poids et Mesures, has proposed that the ampere be re-defined in terms of the electron charge.
A good SEP pumps precisely one electron at a time to ensure accuracy, and pumps them quickly to generate a sufficiently large current. Up to now the development of a practical electron pump has been a two-horse race. Tuneable barrier pumps use traditional semiconductors and have the advantage of speed, while the hybrid turnstile utilises superconductivity and has the advantage that many can be put in parallel. Traditional metallic pumps, thought to be not worth pursuing, have been given a new lease of life by fabricating them out of the world's most famous super-material - graphene.
Previous metallic SEPs made of aluminium are very accurate, but pump electrons too slowly for making a practical current standard. Graphene's unique semimetallic two-dimensional structure has just the right properties to let electrons on and off the quantum dot very quickly, creating a fast enough electron flow - at near gigahertz frequency - to create a current standard. The Achillies heel of metallic pumps, slow pumping speed, has thus been overcome by exploiting the unique properties of graphene.
The realisation of the ampere is currently derived indirectly from resistance or voltage, which can be realised separately using the quantum Hall effect and the Josephson Effect. A fundamental definition of the ampere would allow a direct realisation that National Measurement Institutes around the world could adopt. This would shorten the chain for calibrating current-measuring equipment, saving time and money for industries billing for electricity and using ionising radiation for cancer treatment.Current, voltage and resistance are directly correlated. Because we measure resistance and voltage based on fundamental constants – electron charge and Planck's constant -
being able to measure current would also allow us to confirm the universality of these constants on which many precise measurements rely.
...Also, any redefinition will have to wait until the Kilogram has been redefined. This definition, due to be decided soon, will fix the value of electronic charge, on which any electron-based definition of the ampere will depend.
,,, and for answering fundamental questions in quantum mechanics.
In this case, they employed small single crystals of a molecular magnet— each magnetic molecule being just one billionth of a meter—that could be magnetized, much like the needle of a compass.
The researchers provided a pulse of heat as the spark, causing molecular spins near the heaters to flip in a magnetic field, a process that released energy and transmitted it to nearby material.
“When the molecules’ spins are aligned opposite the applied field direction, they possess a high level of energy,” explained Andrew Kent, a professor in NYU’s Department of Physics and the study’s senior researcher. “And then when the spins ‘flip,’ energy is released and dispersed into surrounding magnetic material that can cause a runaway reaction.”
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