Synthesis of Armchair Graphene Nanoribbons on Germanium-on-Silicon

Abstract

The synthesis of graphene nanoribbons on complementary metal− oxide−semiconductor-compatible substrates is a significant challenge hindering their integration into commercial semiconductor electronics. Here, the bottom-up synthesis of armchair graphene nanoribbons on epilayers of Ge on Si(001) via chemical vapor deposition is demonstrated. The synthesis leverages the previous discovery that graphene crystal growth can be driven with an extreme shape anisotropy on Ge(001) surfaces to directly form nanoribbons. However, compared to nanoribbon synthesis on Ge(001), synthesis on Ge/Si(001) is complicated by the possibility of Si diffusion to the Ge surface and the presence of threading dislocations. Herein, we demonstrate that similar to Ge(001), armchair nanoribbons with faceted edges and sub-10 nm widths can indeed be grown on Ge/Si(001). The nanoribbon synthesis proceeds faster than the diffusion of Si to the Ge surface if a sufficiently thick Ge epilayer is used (e.g., 3 μm), thereby avoiding competing reactions that form SiC. Moreover, threading dislocations in the Ge epilayer are not observed to affect the nucleation or anisotropic growth kinetics of the nanoribbons. These results demonstrate that previous successes in graphene nanoribbon synthesis on Ge(001) can be extended to Si(001) by using epilayers of Ge, motivating the future exploration of this promising platform for hybrid semiconducting graphene/Si electronics.

Boundary-directed epitaxy of block copolymers

“…To fabricate the chemical pattern, graphene stripes are synthesized directly on Ge(001) wafers via CVD by decomposing CH 4 at 910 °C in a flow of H 2 and Ar 38 . This bottom-up synthesis yields graphene stripes with tunable width from virtually 0 to 100s of nanometers by adjusting the growth time, with high-aspect ratio due to the anisotropic nature of growth, with single-atom thickness of 3 Å due to a self-limiting growth mechanism, and with atomically sharp edges due to faceting of the graphene crystals (with edge roughness <5 Å over edge lengths >10 nm) 38 – 40 . Furthermore, the surfaces of graphene and Ge are relatively pristine and uncontaminated (Supplementary Fig.…”

Graphene nanoribbons initiated from molecularly derived seeds

“…Therefore, resolving the edges in the future may require either nanoribbon growth in situ within an STM chamber (to avoid contamination of the Ge surface via ambient exposure) or transfer of the nanoribbons from the Ge to a flatter, more passivated surface that is more conducive to atomic resolution STM following ambient exposure. It is worth noting that previous STM studies of wider nanoribbons on Ge(001) have identified long (10 nm) stretches of smooth, faceted edges 31 . Future experiments will also be needed to understand and separate the effects of Schottky barriers, insulating residues introduced by transfer, contact length, edge disorder, and substrate disorder on the charge transport properties of the nanoribbons.…”

“…Beyond the data presented here, future experiments will be needed to directly image the shape and size of PAH-derived seeds, elucidate how these aspects are affected by PAH composition (e.g., pentacene versus PTCDA versus other molecules), and analyze the early stages of seed-to-nanoribbon evolution. Additional work will also be needed to image the edge structure of the nanoribbons with atomic resolution and to understand how both the initiation and anisotropic growth stages can be tailored to ensure that the edges are smooth by exploiting the natural tendency of graphene crystal growth on Ge(001) to produce faceted, armchair edges 30 , 31 , 33 . Resolution of edge structure in the high magnification STM images presented in Fig.…”

“…Recent theoretical work has illuminated how graphene edge–substrate interactions can drive dramatic differences in the growth of graphene by CVD along different crystallographic directions of catalyst surfaces 29 . We recently exploited this phenomenon to directly grow armchair graphene nanoribbons from CH 4 on technologically relevant Ge(001) 30 , Ge(001) epilayer on Si(001) 31 , and vicinal Ge(001) wafer platforms 32 . The anisotropic graphene evolution desirably results in nanoribbons self-aligned along Ge and with faceted armchair edges.…”

Family of Magic‐Sized Carbon Clusters on Transition Metal Substrates

“…[ 5,6 ] To obtain large‐area and high‐quality 2D graphene for various practical applications, such as highly sensitive ultrafast transistors [ 7–9 ] and flexible transparent electrodes, [ 10,11 ] it is imperative to know the mechanism of nucleation in a chemical vapor deposition (CVD) process. In the bottom‐up approaches for synthesizing 1D or 0D carbon materials such as graphene nanoribbons [ 12–15 ] and graphene quantum dots, [ 16–19 ] the carbon clusters formed on a transition metal substrate may serve as both nucleation centers and precursors to facilitate the controllable synthesis of these novel graphene nanostructures. To facilitate experimental design of controllable graphene synthesis, it is essential to explore the structure of carbon nuclei in graphene CVD growth and understand the nucleation mechanism of graphene on transition metal substrates [ 20–24 ] such as Ru, Rh, Pt, and Au.…”