Ferro enough!

US researchers have found a way to induce switching in nanoscale materials, a discovery that could lead the way to new types of memory devices for computer information storage, tiny sensors, and even nano motors to power microelectromechanical (MEMS) systems. The team comprises Sergey Prosandeev, Inna Ponomarena, Igor Kornev, Ivan Naumov, and Laurent Bellaiche of the University of Arkansas.

“The properties of nanoscale objects are often different from the properties of objects at the macroscopic scale,” Prosandeev explains, “We try to study the new properties of objects at the nanoscale to understand how to apply them to technology.” Prosandeev and his colleagues are investigating so-called ferroelectric compounds, materials that adopt electrical dipoles all lying along the same direction. Such materials are currently used in medical ultrasound, naval sonar and smart memory cards. Until now, scientists had assumed that the ferroelectric effect would fail if the crystals were close to the nanoscopic because of size effects.

Laurent Bellaiche

Laurent Bellaiche

However, in a nanodot, a sub-microscopic sliver of ferroelectric crystal, this “loss” is governed by the swirling of charges within the nanodot, which cancel each other out. The Arkansas team decided to calculate the possibility of switching the direction of the charge vortex, which would open up the possibility of using these nanoscale materials in switches, sensors and other devices. The team used very complex but extremely close to nature computational techniques. “We use what are called methods from first-principles, which are known for their accuracy and microscopic insights,” Bellaiche told Spotlight.

First, the team investigated whether they could observe switching in their model using an inhomogeneous, or non-uniform, electric field formed by two different charges located at one side of the nanodot. They found that the external charges could be used to direct the vortex. When the charges were moved, the vortex moved, and when they swapped the two charges, the vortex swirled in the opposite direction.

Swirling fields make nanoswitches (Credit: Prossandeev et al)

Swirling fields make nanoswitches (Credit: Prossandeev et al)

The researchers explain that such vortex switching could be key to designing memory cards with phenomenal storage capacity far greater than currently possible. Such cards might be controlled by using a scanning tunnelling microscope (STM) tip close to nanodots laid out in array, and using the tip to generate the inhomogeneous electric fields.

Further reading

Phys Rev Lett, 2006, 96, 237601
http://dx.doi.org/10.1103/PhysRevLett.96.237601

Laurent Bellaiche
http://www.uark.edu/depts/physics/faculty/index.php?name=bellaiche

Computational Condensed Matter Physics Group, University of Arkansas
http://www.uark.edu/misc/aaron5/

Suggested searches

nanotechnology
elctric fields

Ringing the changes for e-paper

The development of new energy-efficient and high-resolution full-colour displays for portable computing and communications applications, even flexible electronic paper, will rely on finding novel organic molecules that produce colour when a voltage is applied. Such molecules could ultimately lead to a whole new range of display devices that are currently not possible with conventional liquid crystal displays.

Now, Wei-Qiao Deng and William Goddard III of California Institute of Technology have used quantum mechanics based molecular modelling to design a molecule that changes between red, green, and blue, as an increasing voltage is applied. This three-colour molecule could circumvent the need to have three different molecules for each of the primary display colours by encompassing all three in a single unit and so reducing device complexity and ultimately cost. Fraser Stoddart and Amar Flood of the University of California at Los Angeles are in the process of synthesizing this molecule to test and optimize the performance of this system.

J Fraser Stoddart

Fraser Stoddart

The design is based on the invention by Stoddart and his colleagues of interlocking ring-shaped molecules that can change properties with electrical control. In order to make a colour change molecule they interlocked two rings that could flip between two states. The resulting molecule is either green or red depending on the voltage. Adding a third colour is much more difficult and to accomplish this, the team turned to chemical computation to find the design that would achieve exactly the right colours and would progress through three colours as the voltage is ramped.

Goddard, Stoddart and their colleagues propose a new concept for the pixel component in what they call an E-PAD. The device would consist of a film of their single RGB dye compound, with areas of film controlled by the device electronics. The researchers suggest that compared with other systems, their approach would be much simpler because of the need for only one pixel unit. Moreover, the molecules could be embedded into simple polymer layers or even actual paper so that technology related to ink-jet printing could be used in manufacturing rather than sophisticated layering processes.

William A. Goddard, III

William A. Goddard, III

Achieving a design experimentally is normally an enormous task. However, by combining theory and experiment in the way the Caltech and UCLA scientists have done they can carry out rapid prototyping for the best design using the computer. The whole process is greatly simplified by starting with the computationally optimized system, Goddard explains. This technique, he adds, is likely to become a powerful method for developing new materials and systems.

A dye molecule cycles between red, green, and blue forms depending on the voltage (Adapted from Stoddart et al/ACS)

A dye molecule cycles between red, green, and blue forms depending on the voltage (Adapted from Stoddart et al/ACS)

Further reading

J Am Chem Soc, 2005, in press
http://dx.doi.org/10.1021/ja0431298

Prof. William A. Goddard, III
http://www.wag.caltech.edu/home/wag/index.html

Tangled quantum talk

Quantum communication holds the promise of highly secure information transfer making eavesdroppers almost a thing of the past. The problem facing those hoping to develop such a system is in exploiting the property of quantum entanglement in the real world. Now, physicists at the Georgia Institute of Technology have entangled a photon and a single atom located in an atomic cloud and demonstrated that it passes the crucial validity test known as the Bell inequality violation.

Relying on photons or atoms to carry information from one place to another, network security relies on a method known as quantum cryptographic key distribution. In this method, the two information-carrying particles, photonic qubits or atomic qubits, are entangled. Entanglement invokes the odd quantum effect that should one of a pair of entangled particles be observed then the other will be affected and the entanglement destroyed and the eavesdropper revealed.

Alex Kuzmich

Alex Kuzmich

Quantum bits, qubits, the currency of quantum communication, can travel long distances if they’re made from photons and so carry information over long distances but longevity is a problem. Atomic qubits, on the other hand, are much more stable and so can store information for much longer but long-distance travel is a problem for them. An entangled system using both photons and atoms offers the best of both worlds. The trick is how to get them entangled in a simple way without resorting to masses of hardware.

Physicists Alex Kuzmich and Brian Kennedy reasoned that a collective approach would work because this avoids the issue of having to isolate an atom to get it into an excited state ready for entanglement with a photon. A cloud of atoms would be the key.

Brian Kennedy

Brian Kennedy

Using a collective atomic qubit is much simpler than the single atom approach, explains Kuzmich. It requires less hardware because we don’t have to isolate an atom. In fact, we don’t even know, or need to know, which atom in the group is the qubit. We can show that the system is entangled because it violates Bell inequality. Collective excitation needs minimal initial preparation in other words.

Quantum cryptography

Quantum cryptography

In addition to having the system pass the rigorous test of Bell inequality, the researchers were able to increase the length of time the atomic cloud can store information to several microseconds. This is long enough by fifty times to prepare and measure the atom-photon entanglement. The next step will be to put systems like this together and confirm that they behave quantum mechanically.

Further reading

Phys Rev Lett, 2005, 95, 040405
http://link.aps.org/doi/10.1103/PhysRevLett.95.040405

Alex Kuzmich
http://www.physics.gatech.edu/people/faculty/akuzmich.html

Brian Kennedy
http://www.physics.gatech.edu/people/faculty/bkennedy.html