Researchers wire up particular person graphene nanoribbons

Researchers have developed a technique of “wiring up” graphene nanoribbons (GNRs), a category of one-dimensional supplies which are of curiosity within the scaling of microelectronic units. Utilizing a direct-write scanning tunneling microscopy (STM) based mostly course of, the nanometer-scale metallic 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 metallic contacts to particular GNRs with certainty and that these contacts induce gadget performance wanted for transistor operate.

The outcomes of this analysis, led by electrical and laptop 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 regarded as one thing that might probably be a high-speed digital materials, maybe even a substitute for silicon,” explains Lyding. “However the issue with graphene itself is that it’s not a semiconductor.”

Graphene is a one-atom-thick layer of carbon atoms and whereas it could be the thinnest recognized materials, it’s also extremely sturdy. Semiconductor properties may be induced in graphene by making it very small or by fabricating it into particular shapes—like ribbons. For this undertaking, 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 consists of placing them on a silicon substrate, connecting wires and operating present by way of the wires to measure the transistor properties. The crew has made the important step of taking the GNRs, which are narrower in diameter than a DNA molecule, and wiring them up. They’ve developed a way 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 very best. This technique, nonetheless, introduces quite a lot 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 in search of 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 circulation between the tip and the floor, and when the tip comes throughout atoms on the floor, like driving over a speedbump, that present circulation turns into modulated. This enables 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 metallic 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, referred to as STM direct-write. “Our wiring technique could be very exact. Once we see a GNR, we will simply outline a sample that we would like, 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 performed 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 metallic 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 difficult. The best way we do it’s by depositing metallic. And we will truly select the sort of metallic that we need to placed on the GNRs which may additionally tune the GNR traits. That is one solution to basically dope our GNRs, with out truly utilizing dopants.”

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