Researchers create molecular diode – sciencedaily


Recently, at Arizona State University’s Biodesign Institute, NJ Tao and colleagues found a way to manufacture a key electronic component at an incredibly small scale. Their single-molecule diode is featured in this week’s online edition of Chemistry of nature.

In the world of electronics, diodes are a versatile and ubiquitous component. Coming 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 a booming field of electronics, which is now exploring the nanoscale realm.

Smaller size means lower cost and better performance for electronic devices. The first-generation computer’s processor used a few thousand transistors, Tao said, noting the tremendous advancements in silicon technology. “Now even simple, cheap computers use millions of transistors on a single chip.”

But lately the task of miniaturization has become much more difficult, and the famous saying known as Moore’s Law, which states that the number of silicon-based transistors on a chip doubles every 18 to 24 months, will eventually reach their physical limits. “The size of the transistor reaches a few tens of nanometers, only about 20 times the size of a molecule,” explains Tao. “This is one of the reasons people are excited about this idea of ​​molecular electronics.”

Diodes are essential components for a wide range of applications, from power conversion equipment to radios, logic gates, photodetectors and light emitting devices. In either case, diodes are components that allow current to flow in one direction around an electrical circuit but not in the other. In order for a molecule to achieve this feat, explains Tao, 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 terminal of the cathode.

The new study compares a symmetrical molecule with an asymmetric molecule, detailing the performance of each in terms of electron transport. “If you have a symmetrical molecule, the current goes both ways, much like an ordinary resistor,” Tao observes. This is potentially useful, but the diode is a larger (and difficult) component to replicate (Fig 1).

The idea of ​​going beyond the limits of silicon with an electronic component based on molecules has been around for a long time. “Theoretical chemists Mark Ratner and Ari Aviram proposed the use of molecules for electronics like diodes in 1974,” Tao said, adding that “people around the world have been trying to achieve this for over 30 years.” .

Most of the efforts to date have involved many molecules, notes Tao, referring to molecular thin films. It is only very recently that serious attempts have been made to overcome the obstacles to the design of unique molecules. One of the challenges is to connect a single molecule to at least two electrodes that provide it with current. Another challenge relates to the correct orientation of the molecule in the device. “We are now able to do that – to build a single molecule device with a well-defined orientation,” says Tao.

The technique developed by Tao’s group is based on a property known as AC modulation. “Basically we are applying a small, periodically varying mechanical disturbance to the molecule. If there is a molecule bridged between two electrodes, it responds in a way. If there is no molecule, we can tell. “

The interdisciplinary project involved Professor Luping Yu of the University of Chicago, who provided the molecules to be studied, as well as theoretical collaborator, Professor Ivan Oleynik of the University of South Florida. The team used conjugated molecules, in which atoms are stuck together with alternating single and multiple bonds. Such molecules exhibit high electrical conductivity and have asymmetric ends capable of spontaneously forming covalent bonds with metal electrodes to create a closed circuit.

The results of the project open 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 an optical field, measure the current and see the response. Because quantum physics controls the behavior of individual molecules, this ability allows us to study properties distinct from those of conventional devices. “

Chemists, physicists, materials researchers, computer experts and engineers all play a central role in the emerging field of nanoelectronics, where a zoo of available molecules with different functions provides the raw material for innovation. Tao also studies the mechanical properties of molecules, for example their ability to oscillate. The binding properties between molecules make them interesting candidates for a new generation of chemical sensors. “Personally, I’m interested in molecular electronics and not because of its 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 it apart from conventional semiconductors. This can lead to applications supplementing rather than replacing silicon devices.

Source of the story:

Material provided by Arizona State University. Original written by Richard Harth, Scientific Editor of the Biodesign Institute. Note: Content can be changed for style and length.


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