Andrew Fairbrother | Searcharxiv

arXiv2019

Substrate transfer and ex situ characterization of on-surface synthesized graphene nanoribbons

Recent progress in the on-surface synthesis of graphene nanoribbons (GNRs) has given access to atomically precise narrow GNRs with tunable electronic band gaps that makes them excellent candidates for room-temperature switching devices such as field-effect transistors (FET). However, in spite of their exceptional properties, significant challenges remain for GNR processing and characterization. This contribution addresses some of the most important challenges, including GNR fabrication scalability, substrate transfer, long-term stability under ambient conditions and ex situ characterization. We focus on 7- and 9-atom wide armchair graphene nanoribbons (i.e, 7-AGNR; and 9-AGNR) grown on 200 nm Au(111)/mica substrates using a high throughput system. Transfer of both, 7- and 9-AGNRs from their Au growth sub-strate onto various target substrates for additional characterization is accomplished utilizing a polymer-free method that avoids residual contamination. This results in a homogeneous GNR film morphology with very few tears and wrinkles, as examined by atomic force microscopy. Raman spectroscopy indicates no significant degradation of GNR quality upon substrate transfer, and reveals that GNRs have remarkable stability under ambient conditions over a 24-month period. The transferred GNRs are analyzed using multi-wavelength Raman spectroscopy, which provides detailed insight into the wavelength dependence of the width-specific vibrational modes. Finally, we characterize the optical properties of 7- and 9-AGNRs via ultra-violet-visible (UV-Vis) spectroscopy

cond-mat.mtrl-sci↗

arXiv2017

Short-Channel Field Effect Transistors with 9-Atom and 13-Atom wide Graphene Nanoribbons

Bottom-up synthesized GNRs and GNR heterostructures have promising electronic properties for high performance field effect transistors (FETs) and ultra-low power devices such as tunnelling FETs. However, the short length and wide band gap of these GNRs have prevented the fabrication of devices with the desired performance and switching behaviour. Here, by fabricating short channel (Lch ~20 nm) devices with a thin, high-k gate dielectric and a 9-atom wide (0.95 nm) armchair GNR as the channel material, we demonstrate FETs with high on-current (Ion >1 uA at Vd = -1 V) and high Ion/Ioff ~10^5 at room temperature. We find that the performance of these devices is limited by tunnelling through the Schottky barrier (SB) at the contacts and we observe an increase in the transparency of the barrier by increasing the gate field near the contacts. Our results thus demonstrate successful fabrication of high performance short-channel FETs with bottom-up synthesized armchair GNRs.

cond-mat.mes-hall↗