In the electronics world, diodes are a versatile and ubiquitous component. Appearing in many shapes and sizes, they are used in an endless array of devices and are essential ingredients for the semiconductor industry. Making components including diodes smaller, cheaper, faster and more efficient has been the holy grail of an exploding electronics field, now probing the nanoscale realm.
Smaller size means cheaper cost and better performance for electronic devices. The first generation computer CPU used a few thousand transistors, Tao says noting the steep advance of silicon technology. "Now even simple, cheap computers use millions of transistors on a single chip."
But lately, the task of miniaturization has gotten much harder, and the famous dictum known as Moore's law—which states that the number of silicon-based transistors on a chip doubles every 18-24 months—will eventually reach its physical limits. "Transistor size is reaching a few tens of nanometers, only about 20 times larger than a molecule," Tao says. "That's one of the reasons people are excited about this idea of molecular electronics."
Diodes are critical components for a broad array of applications, from power conversion equipment, to radios, logic gates, photodetectors and light-emitting devices. In each case, diodes are components that allow current to flow in one direction around an electrical circuit but not the other. For a molecule to perform this feat, Tao explains, it must be physically asymmetric, with one end capable of forming a covalent bond with the negatively charged anode and the other with the positive cathode terminal.
The new study compares a symmetric molecule with an asymmetric one, detailing the performance of each in terms of electron transport. "If you have a symmetric molecule, the current goes both ways, much like an ordinary resistor," Tao observes. This is potentially useful, but the diode is a more important (and difficult) component to replicate (Fig 1).
The idea of surpassing silicon limits with a molecule-based electronic component has been around awhile. "Theoretical chemists Mark Ratner and Ari Aviram proposed the use of molecules for electronics like diodes back in 1974," Tao says, adding "people around world have been trying to accomplish this for over 30 years."
Most efforts to date have involved many molecules, Tao notes, referring to molecular thin films. Only very recently have serious attempts been made to surmount the obstacles to single-molecule designs. One of the challenges is to bridge a single molecule to at least two electrodes supplying current to it. Another challenge involves the proper orientation of the molecule in the device. "We are now able to do this—to build a single molecule device with a well defined orientation," Tao says.
The technique developed by Tao's group relies on a property known as AC modulation. "Basically, we apply a little periodically varying mechanical perturbation to the molecule. If there's a molecule bridged across two electrodes, it responds in one way. If there's no molecule, we can tell."
The interdisciplinary project involved Professor Luping Yu, at the University of Chicago, who supplied the molecules for study, as well as theoretical collaborator, Professor Ivan Oleynik from the University of South Florida. The team used conjugated molecules, in which atoms are stuck together with alternating single and multiple bonds. Such molecules display large electrical conductivity and have asymmetrical ends capable of spontaneously forming covalent bonds with metal electrodes to create a closed circuit.
The project's results raise the prospect of building single molecule diodes – the smallest devices one can ever build. "I think it's exciting because we are able to look at a single molecule and play with it, " Tao says. "We can apply a voltage, a mechanical force, or optical field, measure current and see the response. As quantum physics controls the behaviors of single molecules, this capability allows us to study properties distinct from those of conventional devices."
Chemists, physicists, materials researchers, computational experts and engineers all play a central role in the emerging field of nanoelectronics, where a zoo of available molecules with different functions provide the raw material for innovation. Tao is also examining the mechanical properties of molecules, for example, their ability to oscillate. Binding properties between molecules make them attractive candidates for a new generation of chemical sensors. "Personally, I am interested in molecular electronics not because of their potential to duplicate today's silicon applications, " Tao says. Instead, molecular electronics will benefit from unique electronic, mechanical, optical and molecular binding properties that set them apart from conventional semiconductors. This may lead to applications complementing rather than replacing silicon devices.Written by Richard Harth
Richard Harth | EurekAlert!
Further reports about: > ASU > Small Molecule > diodes > key electrical component > molecular diode > molecular electronics > molecule-based electronic component > multiple bonds > phenomenally tiny scale > semiconductor industry > silicon technology > single molecule > single-molecule diode > symmetric molecule
What the world's tiniest 'monster truck' reveals
23.08.2017 | American Chemical Society
Treating arthritis with algae
23.08.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
23.08.2017 | Life Sciences
23.08.2017 | Life Sciences
23.08.2017 | Physics and Astronomy