- The paper presents a bottom-up synthesis method that yields uniform 7-carbon-wide graphene nanoribbons with a ~2.5 eV bandgap on Au(111) substrates.
- The paper fabricates three-terminal FETs using e-beam lithography, showing gate-modulated conductance despite challenges from short-channel effects and device yield.
- The paper demonstrates that vacuum annealing improves device performance by switching conduction types and emphasizes the impact of a significant ~1.25 eV Schottky barrier.
Overview of Bottom-up Graphene Nanoribbon Field-Effect Transistors
The paper presents a comprehensive examination of field-effect transistors (FETs) utilizing bottom-up chemically synthesized graphene nanoribbons (GNRs). This investigation contributes to the ongoing efforts to explore alternative materials capable of enhancing the performance of nanoelectronic devices through the unique physical properties of GNRs.
Synthesis and Transfer Methodology
The authors detail an overview technique that leverages the bottom-up chemical synthesis of GNRs from the 10,10’-dibromo-9,9’-bianthryl (DBBA) precursor by thermal sublimation under ultrahigh vacuum conditions. This approach produces GNRs with a uniform width of 7 carbon atoms, leading to precise edge structures and a band gap of approximately 2.5 eV when grown on Au(111) substrates. A significant advancement reported here is the successful layer transfer of GNRs from metallic substrates onto insulating ones while preserving their structural integrity. This is achieved through a PMMA-assisted delamination and etching process to place the nanoribbons on various target substrates.
Device Fabrication and Characterization
Three-terminal GNR FETs were fabricated with defined nanoscale gaps using e-beam lithography. The devices exhibited gate-modulated conductance with on-currents ranging from pA to nA at a 1V bias across source-drain junctions, demonstrating potential transistor behavior despite short-channel lengths. The study highlights a low device yield, attributed to the average ribbon length and lack of inter-ribbon charge transfer, with improvements anticipated by optimizing synthesis and contact methodologies.
Electrical characterization under diverse environmental conditions revealed the transistors initially exhibited large variations in conductance due to adsorbed molecules. Nonetheless, subsequent vacuum annealing improved device performance, transforming the devices from p-type to n-type conduction. These findings are intrinsic to Schottky junction-dominated transport and substantiate the presence of a considerable Schottky barrier (~1.25 eV), accentuated by the narrow GNRs.
Implications and Future Perspectives
The study demonstrates that by varying the local environment and precursor materials during synthesis, it is possible to engineer both the electronic characteristics of GNRs and their coupling with contact metals, advancing their application in electronic and optoelectronic devices. Interestingly, the narrow GNRs show increased environmental sensitivity, potentially offering heightened sensor applications.
The use of wider GNRs synthesized through similar methods is anticipated to improve device performance due to smaller Schottky barriers and reduced effective mass. Furthermore, the developed transfer method allows for extensive examinations beyond traditional transport studies, such as optoelectronic and spintronic analyses, and even potentially transformative applications within the field of nanoscale materials science and device engineering.
In summary, this work underscores the potential of atomically precise GNRs in developing advanced electronic devices. It establishes a foundation for further research into optimizing GNR synthesis and integration into practical applications, contributing significantly to the evolution of high-performance nanoelectronics.