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Edge Spectroscopy of Graphene Nanoribbons in Insulating Fluid

English title Edge Spectroscopy of Graphene Nanoribbons in Insulating Fluid
Applicant Nirmalraj Peter
Number 190330
Funding scheme Spark
Research institution EMPA
Institution of higher education Swiss Federal Laboratories for Materials Science and Technology - EMPA
Main discipline Physical Chemistry
Start/End 01.02.2020 - 31.01.2021
Approved amount 76'000.00
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All Disciplines (2)

Physical Chemistry
Other disciplines of Physics

Keywords (4)

Graphene nanoribbons; 2D atomic materials and nanoscale devices; Liquid based STM and STS; Edge spectroscopy

Lay Summary (French)

Dr. Peter Nirmalraj
Lay summary
L’émergence des matériauxen nanostructure possédant des fonctionnalités électroniques adaptées est d’une très grande importance pour les nouvelles générations de matériaux électroniques allant de dispositifs logiques aux appareils de détections. Le but de ce projet est d’étudier, sous des conditions standard de laboratoire, de tel matériaux, les nanorubans de graphène (GNRs) avec une résolution spatiale et énergétique élevée. La solidité des GNRs et les changements de leur structure électronique intrinsèque sous condition ambiante sera observée par l’utilisation de microscopie scanning à base liquide et à balayage ainsi que de spectroscopie. Les outils utilisés à cette fin seront également employés pour l’étude d’autre nanomatériaux allant de l’épaisseur d’un atome à des protéines unitaires.

Direct link to Lay Summary Last update: 16.12.2019

Responsible applicant and co-applicants


To bring any electronic grade material closer to device integration it is imperative to read-and-record their structure-function rapport under standard laboratory conditions. The need for implementing go/no-go analytical tests with high information content is becoming increasingly important especially for nanostructured materials comprising just a few atoms. Graphene nanoribbons (GNRs) are one such class of edge orientation-controlled semiconductors (energy gap ranges from 0.5 to 2.7 eV) with immense potential to overcome the lithographic (GNR width < 2nm) and performance (e.g GNR has an electron mobility of ~100 times greater than Si) limit of Si-based electronics. Over the past 10 years theoreticians using density functional theory calculations have predicted the size dependent energy gaps of GNRs, chemists have made massive advances in reliable synthesis of GNRs with designer edges and surface physicists have conducted trend setting studies using scanning tunneling microscopy (STM) and spectroscopy (STS) to investigate GNR physics from width dependent energy splitting, atomic scale details on both arm chair and zigzag type edge structures to band alignment at GNR heterojunctions. A majority of such high resolution STM and STS experiments have been conducted under ultrahigh vaccum and often at cryogenic temperatures (4-10 K) which has been traditionally the preferred platform of choice for atomic scale measurements. Remarkably, despite the promise of GNR integration with lithographically defined devices, there has been very little attempt to understand GNR electronic structure and in particular edge effects on energy gaps in ambient environment. Since ambient exposure tends to contaminate (hydrocarbon contaminants) GNR surface. In addition, the accumulation of water layer at STM tip-sample interface and thermal drift of the STM tip are other issues that tend to impede stable electrical measurements under ambient conditions. Yet, without addressing these challenges the vision of GNR based electronics will remain elusive. Through the proposed Spark project edge spectroscopy of graphene nanoribbons in insulating fluid (E-SPEAR) we will investigate the electronic functions and edge states of GNRs (7-AGNR and 9-AGNR) with the highest possible spatial and energy resolution ever achieved under standard laboratory conditions. For this we will identify and encapsulate the surface bound GNRs in an appropriate high density and clean insulating fluid. The ideal fluid will be electrochemically inert and hence not interfere in the tunneling process, will preserve GNR topology from ambient contamination, prevent water bridge accumation at tip-sample interface and minimise STM tip drift at room-temperature, thereby creating a stable imaging and spectroscopy platform. The benefits for probing semiconducting surfaces in high density liquids through STM was first outlined by P.K Hansma and co-workers in 1987 (PNAS, 84, 4671-4674). However, these methods were never fully exploited to study the zoo of emerging 2D materials. We aim to advance these unorthodox methodologies together with our custom designed low-noise liquid based-STM/STS to reliably extract atom-by-atom spectroscopic data on the GNR edges, verify the width dependent energy gap scaling law and clarify the role of topological effects on GNR electronic structure in ambient conditions. We anticipate that once we demonstrate this level of control in understanding the importance of each atom in GNR electronic structure can embolden more efforts for single atom modification and edge decoration through STM at the liquid-solid interface. Through E-SPEAR we propose to start paving the way towards pursing this challenging vision which, even if the pilot studies are successful will make an important contribution to the field of GNR and related 2D material analytics.