Manipulating nanoribbons on the molecular stage

slim strips of graphene referred to as nanoribbons exhibit first rate properties that cause them to important applicants for destiny nanoelectronic technology. A barrier to exploiting them, however, is the issue of controlling their form at the atomic scale, a prerequisite for many feasible programs.

  Now, researchers at the united states department of electricity's (DOE) Lawrence Berkeley country wide Laboratory (Berkeley Lab) and the university of California, Berkeley, have evolved a brand new precision method for synthesizing graphene nanoribbons from pre-designed molecular building blocks. using this process the researchers have constructed nanoribbons that have superior properties -- along with function-dependent, tunable bandgaps -- which are probably very beneficial for next-era electronic circuitry.

The results appear in a paper titled "Molecular bandgap engineering of bottom-up synthesized graphene nanoribbon heterojunctions," published in Nature Nanotechnology.

"This work represents development in the direction of the intention of controllably assembling molecules into whatever shapes we need," says Mike Crommie, senior scientist at Berkeley Lab, professor at UC Berkeley, and a frontrunner of the have a look at. "For the first time we have created a molecular nanoribbon where the width modifications precisely how we designed it to."

Nanoribbons beyond and gift

formerly, scientists made nanoribbons which have a regular width in the course of. "That makes for a pleasing cord or a simple switching element," says Crommie, "but it does not offer quite a few functionality. We wanted to peer if we should exchange the width within a single nanoribbon, controlling the shape inside the nanoribbon on the atomic scale to provide it new behavior this is doubtlessly useful."

Felix Fischer, Professor of Chemistry at UC Berkeley who jointly led the observe, designed the molecular additives to find out whether or not this will be possible. together, Fischer and Crommie located that molecules of various widths can certainly be made to chemically bond such that width is modulated alongside the length of a unmarried resulting nanoribbon.

"think of the molecules as special sized Lego blocks," explains Fischer. each block has a positive defined structure and when pieced collectively they bring about a specific form for the whole nanoribbon. "We want to look if we are able to understand the exceptional properties that emerge whilst we assemble those molecular structures, and to peer if we are able to make the most them to construct new useful devices."

until now, nanoribbon synthesis has in the main worried etching ribbons out of larger 2nd sheets of graphene. The hassle, in step with Fischer, is this lacks precision and every ensuing nanoribbon has a completely unique, barely random structure. some other approach has been to unzip nanotubes to yield nanoribbons. This produces smoother edges than the "top-down" etching method, however it's far difficult to manipulate due to the fact nanotubes have exclusive widths and chiralities.

a third direction, discovered by way of Roman Fasel of Swiss Federal Laboratories for materials technology & technology along together with his co-employees, entails putting molecules on a metal surface and chemically fusing them collectively to shape flawlessly uniform nanoribbons. Crommie and Fischer changed this ultimate method and feature shown that if the shapes of the constituent molecules are numerous then so is the shape of the ensuing nanoribbon.

"What we have executed this is new is to show that it's far possible to create atomically-unique nanoribbons with non-uniform shape by using converting the shapes of the molecular constructing blocks," says Crommie.

Controlling quantum residences

Electrons in the nanoribbons set up quantum mechanical status-wave patterns that decide the nanoribbon's electronic residences, including its "bandgap." This determines the energetics of how electrons circulate through a nanoribbon, inclusive of which areas they collect in and which regions they avoid.

within the past, scientists spatially engineered the bandgap of micron-scale devices through doping, the addition of impurities to a cloth. For the smaller nanoribbons, however, it's miles possible to trade the bandgap with the aid of enhancing their width in sub-nanometer increments, a technique that Crommie and Fischer have dubbed "molecular bandgap engineering." This kind of engineering permits the researchers to tailor the quantum mechanical homes of nanoribbons so they might be flexibly used for destiny nanoelectronic devices.

to check their molecular bandgap engineering, Crommie's institution used scanning tunneling microscopy (STM), a method which could spatially map the behavior of electrons inner a unmarried nanoribbon. "We had to realize the atomic-scale shape of the nanoribbons, and we additionally had to recognise how the electrons inside adapt to that form," says Crommie. UC Berkeley professor of physics Steven Louie and his student Ting Cao calculated the digital shape of the nanribbons in order to properly interpret the STM pix. This "closed the loop" between nanoribbon design, fabrication, and characterization.

New instructions towards new gadgets

a main query on this work is how excellent to construct useful gadgets from those tiny molecular structures. whilst the group has proven the way to fabricate width-various nanoribbons, it has not but included them into real electronic circuits. Crommie and Fischer hope to apply this new form of nanoribbon to subsequently create new device elements -- along with diodes, transistors, and LEDs -- which are smaller and more effective than those in modern-day use. in the end they desire to include nanoribbons into complex circuits that yield better overall performance than today's computer chips. To this cease they're collaborating with UC Berkeley electric engineers such as Jeffrey Bokor and Sayeef Salahuddin.

the specified spatial precision already exists: the crew can modulate nanoribbon width from zero.7 nm to 1.4nm, developing junctions wherein slender nanoribbons fuse seamlessly into wider ones. "varying the width through a aspect of two permits us to modulate the bandgap by way of more than 1eV," says Fischer. for many programs that is enough for building useful devices.

while the ability packages are thrilling, Crommie factors out that a relevant motivation for the studies is the preference to reply primary medical questions like how nanoribbons with non-uniform width truely behave. "We set out to answer an thrilling query, and we responded it," he concludes.