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 units. Utilizing a direct-write scanning tunneling microscopy (STM) based mostly course of, the nanometer-scale steel contacts have 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 creating steel contacts to particular GNRs with certainty and that these contacts induce system performance wanted for transistor operate.
The outcomes of this analysis, led by electrical and pc engineering (ECE) professor Joseph Lyding, together with ECE graduate pupil Pin-Chiao Huang and supplies science and engineering graduate pupil Hongye Solar, have been not too long ago printed within the journal ACS Nano.
“Graphene has been round for some time and it has been regarded as one thing that would doubtlessly 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 could be the thinnest identified materials, additionally it is 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 have been synthesized by co-author Alexander Sinitskii and his group on the College of Nebraska.
The method of creating a transistor out of the GNRs contains 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 crucial 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 most effective. This technique, nonetheless, introduces a number 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 instrument) 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 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 may be very exact. Once we see a GNR, we are able to simply outline a sample that we would like, after which we’ll join it. It isn’t simply blindly throwing electrodes on the floor,” says Huang.
One other benefit of this technique is that it’s finished in ultra-high vacuum (UHV). This ensures that the fabric stays clear from atmospheric water and different “junk” that degrades system 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 alter its digital properties. Solar explains, “One method to dope GNRs is to make use of completely different chemical reactions to alter the GNR properties. However that course of is difficult. The way in which we do it’s by depositing steel. And we are able to really select the type of steel that we wish to placed on the GNRs which might additionally tune the GNR traits. That is one method to basically dope our GNRs, with out really utilizing dopants.”
Lyding says, “The following 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 creating the electrodes which are completely crucial for system operate.”
