Sunday, March 3, 2024

Making contact: Researchers wire up particular person graphene nanoribbons


Researchers have developed a way of “wiring up” graphene nanoribbons (GNRs), a category of one-dimensional supplies which are of curiosity within the scaling of microelectronic gadgets. Utilizing a direct-write scanning tunneling microscopy (STM) primarily based course of, the nanometer-scale steel contacts had been fabricated on particular person GNRs and will management the digital character of the GNRs. The researchers say that that is the primary demonstration of constructing steel contacts to particular GNRs with certainty and that these contacts induce gadget performance wanted for transistor perform.

The outcomes of this analysis, led by electrical and pc engineering (ECE) professor Joseph Lyding, together with ECE graduate scholar Pin-Chiao Huang and supplies science and engineering graduate scholar Hongye Solar, had been lately revealed within the journal ACS Nano.

“Graphene has been round for some time and it has been considered one thing that would probably be a high-speed digital materials, even perhaps a alternative for silicon,” explains Lyding. “However the issue with graphene itself is that it isn’t a semiconductor.” Graphene is a one-atom-thick layer of carbon atoms and whereas it might be the thinnest recognized materials, it’s also extremely sturdy. Semiconductor properties will be induced in graphene by making it very small or by fabricating it into particular shapes — like ribbons. For this venture, atomically-precise GNRs had been synthesized by co-author Alexander Sinitskii and his group on the College of Nebraska.

The method of constructing a transistor out of the GNRs contains placing them on a silicon substrate, connecting wires and working present by means of the wires to measure the transistor properties. The crew has made the essential step of taking the GNRs, which are narrower in diameter than a DNA molecule, and wiring them up. They’ve developed a method the place the wires are additionally only a few nanometers large.

Different researchers have labored on this drawback by placing many GNRs on a silicon floor and placing down big electrodes and hoping for the perfect. This technique, nevertheless, introduces a variety of uncertainty. Lyding and his college students used a extra exact technique for wiring up the GNRs. They used a scanning tunneling microscope (an atomic decision imaging device) to scan the floor searching for a GNR to make use of. In STM, a pointy tip is introduced near a floor — on the order of a nanometer — and scanned throughout the floor. There’s a present circulate between the tip and the floor, and when the tip comes throughout atoms on the floor, like driving over a speedbump, that present circulate turns into modulated. This permits for the detection and imaging of the GNRs.

As soon as they discover a GNR, they use the electron beam within the STM to set off steel deposition from hafnium diboride precursor molecules to create the wires. Co-author Gregory Girolami and his group within the UIUC Chemistry Division synthesized the precursor for this course of, known as STM direct-write. “Our wiring technique could be very exact. After we see a GNR, we are able to simply outline a sample that we wish, after which we’ll join it. It is not simply blindly throwing electrodes on the floor,” says Huang.

One other benefit of this technique is that it’s completed in ultra-high vacuum (UHV). This ensures that the fabric stays clear from atmospheric water and different “junk” that degrades gadget efficiency.

The researchers additionally investigated the digital character of the GNRs and located that it was modified by placing the steel contacts on. Semiconductor “doping” is the intentional introduction of impurities to vary its digital properties. Solar explains, “One solution to dope GNRs is to make use of completely different chemical reactions to vary the GNR properties. However that course of is tough. The best way we do it’s by depositing steel. And we are able to really select the form of steel that we wish to placed on the GNRs which may additionally tune the GNR traits. That is one solution to basically dope our GNRs, with out really utilizing dopants.”

Lyding says, “The subsequent step, which we’re engaged on now, is to make an actual transistor and really measure the transistor traits. However we all know that we are able to do that pristine course of, utilizing ultra-high vacuum, of constructing the electrodes which are completely obligatory for gadget perform.”

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