Correlating Atomic Structure and Transport in Suspended Graphene Nanoribbons

Abstract

Graphene nanoribbons (GNRs) are promising candidates for next generation integrated circuit (IC) components; this fact motivates exploration of the relationship between crystallographic structure and transport of graphene patterned at IC-relevant length scales (<10 nm). We report on the controlled fabrication of pristine, freestanding GNRs with widths as small as 0.7 nm, paired with simultaneous lattice-resolution imaging and electrical transport characterization, all conducted within an aberration-corrected transmission electron microscope. Few-layer GNRs very frequently formed bonded-bilayers and were remarkably robust, sustaining currents in excess of 1.5 μA per carbon bond across a 5 atom-wide ribbon. We found that the intrinsic conductance of a sub-10 nm bonded bilayer GNR scaled with width as GBL(w) ≈ 3/4(e2/h)w, where w is the width in nanometers, while a monolayer GNR was roughly five times less conductive. Nanosculpted, crystalline monolayer GNRs exhibited armchair-terminated edges after current annealing, presenting a pathway for the controlled fabrication of semiconducting GNRs with known edge geometry. Finally, we report on simulations of quantum transport in GNRs that are in qualitative agreement with the observations.

Graphene nanodevices for DNA sequencing

“…Patterning graphene at elevated temperatures (>600 • C) provides a way to minimize defects to preserve graphene's crystallinity [84]. Narrow ribbons with crystalline edges were also produced through Joule heating [83,90], where a voltage of ∼2-3 V applied across a ribbon resulted in a local heating of 2000K, leading to recrystallization of the edges [90]. Alternatively, narrow bottom-up graphene nanoribbons that are chemically synthesized with perfect zigzag or armchair edges may represent the ultimate approach for ultra-sensitive graphene devices [105].…”

“…Theoretical studies show that an armchair ribbon will be semiconducting [66][67][68][69] and that a zigzag-edged ribbon is metallic with a current profile that peaks at the edges [66,[69][70][71]. Both armchair and zigzag nanoribbons have been proposed to present promising platforms for DNA sequencing in a large number of theoretical reports [72][73][74][75][76][77][78][79], and experimentalists have begun to explore this approach [80][81][82][83][84][85].…”

“…Alternatively, chemical techniques that involve unzipping of carbon nanotubes or 'bottom up' assembly of ribbons with the use of molecular precursors have been used [89]. Freestanding graphene nanoribbons (of sub-10nm widths) were made using scanning transmission electron microscopy (STEM) to obtain narrow ribbons [82][83][84][85]. It was shown that when the graphene is heated to >600 • C, it can be sculpted with near atomic precision, while maintaining pristine defectfree graphene [84].…”

“…This heating recrystallizes the edges of the nanoribbon that rearrange along either a zigzag or armchair profile [90]. With that approach, armchair ribbons down to 0.7nm in width were made, which were highly conducting and could sustain microampere currents at low voltages [82,83].…”

Inelastic vibrational signals in electron transport across graphene nanoconstrictions

“…With the rapid development in fabrication and electronic characterization of nanostructured graphene [19,20,30] it is interesting to investigate the presence of inelastic vibrational signals for GNCs.…”