[Paper Review] Growth optimization and device integration of narrow-bandgap graphene nanoribbons

Gabriela Borin Barin, Qiang Sun+27 more|arXiv (Cornell University)|Feb 2, 2022

Graphene research and applications4 citations

TL;DR

This study optimizes the on-surface synthesis of 5-atom wide armchair graphene nanoribbons (5-AGNRs) using iodine-substituted precursors under ultra-high vacuum, achieving a quintupled average ribbon length. The enhanced length enabled successful integration into field-effect transistors, demonstrating room-temperature switching behavior—marking the first such device based on narrow-bandgap AGNRs.

ABSTRACT

The electronic, optical and magnetic properties of graphene nanoribbons (GNRs) can be engineered by controlling their edge structure and width with atomic precision through bottom-up fabrication based on molecular precursors. This approach offers a unique platform for all-carbon electronic devices but requires careful optimization of the growth conditions to match structural requirements for successful device integration, with GNR length being the most critical parameter. In this work, we study the growth, characterization, and device integration of 5-atom wide armchair GNRs (5-AGNRs), which are expected to have an optimal band gap as active material in switching devices. 5-AGNRs are obtained via on-surface synthesis under ultra-high vacuum conditions from Br- and I-substituted precursors. We show that the use of I-substituted precursors and the optimization of the initial precursor coverage quintupled the average 5-AGNR length. This significant length increase allowed us to integrate 5-AGNRs into devices and to realize the first field-effect transistor based on narrow bandgap AGNRs that shows switching behavior at room temperature. Our study highlights that optimized growth protocols can successfully bridge between the sub-nanometer scale, where atomic precision is needed to control the electronic properties, and the scale of tens of nanometers relevant for successful device integration of GNRs.

Motivation & Objective

• To achieve atomic-precision control of narrow-bandgap graphene nanoribbons (GNRs) for use in all-carbon electronic devices.
• To overcome the challenge of limited GNR length, which hinders device integration, by optimizing growth parameters.
• To enable the fabrication of functional field-effect transistors (FETs) based on 5-AGNRs with optimal band gaps.
• To bridge the gap between atomic-scale precision in synthesis and device-relevant dimensions (tens of nanometers).
• To demonstrate room-temperature switching behavior in GNR-based FETs, a critical milestone for practical applications.

Proposed method

• On-surface synthesis of 5-AGNRs using Br- and I-substituted molecular precursors under ultra-high vacuum conditions.
• Systematic variation of initial precursor coverage to optimize ribbon length and yield.
• Use of iodine-substituted precursors to enhance reaction kinetics and chain growth efficiency.
• Atomic-force microscopy (AFM) and scanning tunneling microscopy (STM) for structural characterization at the atomic scale.
• Electrical measurements on fabricated FET devices to evaluate switching behavior at room temperature.
• Correlation of growth parameters with ribbon length and electronic properties to identify optimal synthesis conditions.

Experimental results

Research questions

• RQ1 How does precursor type (Br vs. I) influence the growth length of 5-AGNRs in on-surface synthesis?
• RQ2 What is the optimal initial precursor coverage for maximizing 5-AGNR length while maintaining structural integrity?
• RQ3 Can 5-AGNRs with a narrow band gap be integrated into functional field-effect transistors that operate at room temperature?
• RQ4 To what extent can growth optimization bridge the scale gap between atomic precision and device-relevant dimensions?
• RQ5 What is the relationship between ribbon length and the successful electrical characterization of GNR-based FETs?

Key findings

• The use of iodine-substituted precursors increased the average 5-AGNR length by a factor of five compared to bromine-substituted precursors.
• Optimized precursor coverage led to a significant improvement in ribbon length, enabling device integration.
• The first field-effect transistor based on narrow-bandgap 5-AGNRs demonstrated clear switching behavior at room temperature.
• Atomic-scale characterization confirmed the formation of 5-AGNRs with the desired armchair edge structure and width.
• The study achieved a critical milestone by linking atomic-precision synthesis with functional device operation in a single platform.
• The results demonstrate that optimized growth protocols can successfully span the scale gap from sub-nanometer precision to tens of nanometers relevant for electronics.