You can read the paper on http://www.nature.com/nature/journal/v483/n7389/fig_tab/nature10941_F1.html

MENLO PARK, US: Researchers from Stanford University and the US Department of Energy’s SLAC National Accelerator Laboratory have created the first-ever system of ‘designer electrons’- exotic variants of ordinary electrons with tunable properties that may ultimately lead to new types of materials and devices.

“The behaviour of electrons in materials is at the heart of essentially all of today’s technologies. We’re now able to tune the fundamental properties of electrons so they behave in ways rarely seen in ordinary materials,” said Hari Manoharan, Associate Professor, Stanford University.

Their first examples, reported in Nature, were hand-crafted, honeycomb-shaped structures inspired by graphene, a pure form of carbon that has been widely heralded for its potential in future electronics. Initially, the electrons in this structure had graphene-like properties; for example, unlike ordinary electrons, they had no mass and traveled as if they were moving at the speed of light in a vacuum. But researchers were then able to tune these electrons in ways that are difficult to do in real graphene.

To make the structure, which Manoharan calls molecular graphene, the scientists use a scanning tunneling microscope to place individual carbon monoxide molecules on a perfectly smooth copper surface. The carbon monoxide repels the free-flowing electrons on the copper surface and forces them into a honeycomb pattern, where they behave like graphene electrons.

To tune the electrons’ properties, the researchers repositioned the carbon monoxide molecules on the surface; this changed the symmetry of the electron flow. In some configurations, electrons acted as if they had been exposed to a magnetic or electric field. In others, researchers were able to finely tune the density of electrons on the surface by introducing defects or impurities. By writing complex patterns that mimicked changes in carbon-carbon bond lengths and strengths in graphene, the researchers were able to restore the electrons’ mass in small, selected areas.

“One of the wildest things we did was to make the electrons think they are in a huge magnetic field when, in fact, no real field had been applied,” said Manoharan. The Stanford team calculated the positions where carbon atoms in graphene should be to make its electrons believe they were being exposed to magnetic fields ranging from zero to 60 Tesla, more than 30 per cent higher than the strongest continuous magnetic field ever achieved on Earth. The researchers then moved carbon monoxide molecules to steer the electrons into precisely those positions, and the electrons responded by behaving exactly as predicted, as if they had been exposed to a real field.

“Our new approach is a powerful new test bed for physics. Molecular graphene is just the first in a series of possible designer structures. We expect that our research will ultimately identify new nanoscale materials with useful electronic properties,” said Manoharan.

…The drill was using Li-doped Graphene or doping both sides of a Graphene layer with different atoms

http://www.worldofchemicals.com/media/academy/researchers-create-piezoelectri…

CALIFORNIA, US: Graphene, the most studied substance of the last decade, is one-hundred-times-better conductor of electricity than silicon. It is stronger than diamond. And, at just one atom thick, it is so thin as to be essentially a two-dimensional material. Yet, graphene is not piezoelectric. Piezoelectricity is the property of some materials to produce electric charge when bent, squeezed or twisted. Perhaps more importantly, piezoelectricity is reversible. When an electric field is applied, piezoelectric materials change shape, yielding a remarkable level of engineering control.

Piezoelectrics have found application in countless devices from watches, radios and ultrasound to the push-button starters on propane grills, but these uses all require relatively large, three-dimensional quantities of piezoelectric materials. In a paper published in the journal ACS Nano, two materials engineers at Stanford have described how they have engineered piezoelectrics into graphene, extending for the first time such fine physical control to the nanoscale.

“The physical deformations we can create are directly proportional to the electrical field applied. This represents a fundamentally new way to control electronics at the nanoscale. This phenomenon brings new dimension to the concept of ‘straintronics,’ because of the way the electrical field strains, the lattice of carbon, causing it to change shape in predictable ways,” said Evan Reed, Head of the Materials Computation and Theory Group, Stanford University.

“Piezoelectric graphene could provide an unparalleled degree of electrical, optical or mechanical control for applications ranging from touchscreens to nanoscale transistors,” said Mitchell Ong, Post-doctoral Scholar, Stanford University. Using a sophisticated modeling application running on high-performance supercomputers, the engineers simulated the deposition of atoms on one side of a graphene lattice, a process known as doping, and measured the piezoelectric effect.

They modeled graphene doped with lithium, hydrogen, potassium and fluorine, as well as combinations of hydrogen and fluorine and lithium and fluorine on either side of the lattice. Doping just one side of the graphene, or doping both sides with different atoms, is key to the process as it breaks graphene’s perfect physical symmetry, which otherwise cancels the piezoelectric effect.

“We thought the piezoelectric effect would be present, but relatively small. Yet, we were able to achieve piezoelectric levels comparable to traditional three-dimensional materials. It was pretty significant,” said Reed. The researchers were further able to fine tune the effect by pattern doping the graphene, selectively placing atoms in specific sections and not others. “We call it designer piezoelectricity because it allows us to strategically control where, when and how much the graphene is deformed by an applied electrical field with promising implications for engineering,” said Ong.

While the results in creating piezoelectric graphene are encouraging, the researchers believe that their technique might further be used to engineer piezoelectricity in nanotubes and other nanomaterials with applications ranging from electronics, photonics, and energy harvesting to chemical sensing and high-frequency acoustics. “We’re already looking at new piezoelectric devices based on other 2D and low-dimensional materials, hoping they might open new and dramatic possibilities in nanotechnology,” said Reed.