[Paper Review] Rapid characterization of wafer-scale 2D material: Epitaxial graphene and graphene nanoribbons on SiC

Vishal Panchal, Yanfei Yang+9 more|arXiv (Cornell University)|Nov 9, 2017

Graphene research and applications21 references3 citations

TL;DR

This paper demonstrates that confocal laser scanning microscopy (CLSM) enables rapid, non-destructive, and ambient-air-compatible characterization of wafer-scale epitaxial graphene and graphene nanoribbons on SiC substrates. With ~150 nm resolution and acquisition speeds hundreds of times faster than Raman or SPM, CLSM distinguishes graphene phases (interfacial layer, single/bilayer, overgrown) via intensity contrast, offering a scalable solution for industrial 2D material quality control.

ABSTRACT

We demonstrate that the confocal laser scanning microscopy (CLSM) provides a non-destructive, highly-efficient characterization method for large-area epitaxial graphene and graphene nanostructures on SiC substrates, which can be applied in ambient air without sample preparation and is insusceptible to surface charging or surface contamination. Based on the variation of reflected intensity from regions covered by interfacial layer, single layer, bilayer, or few layer graphene, and through the correlation to the results from Raman spectroscopy and SPM, CLSM images with a high resolution (around 150 nm) reveal that the intensity contrast has distinct feature for undergrown graphene (mixing of dense, parallel graphene nanoribbons and interfacial layer), continuous graphene, and overgrown graphene. Moreover, CLSM has a real acquisition time hundreds of times faster per unit area than the supplementary characterization methods. We believe that the confocal laser scanning microscope will be an indispensable tool for mass-produced epitaxial graphene or applicable 2D materials.

Motivation & Objective

• To develop a fast, non-destructive, and ambient-compatible method for characterizing large-area 2D materials on SiC substrates.
• To identify distinct optical contrast patterns in CLSM that correlate with different graphene phases (e.g., interfacial layer, single layer, bilayer, overgrown).
• To enable high-throughput quality assessment of epitaxial graphene and graphene nanoribbons for industrial scalability.
• To reduce reliance on slow, preparation-intensive techniques like Raman spectroscopy and scanning probe microscopy (SPM).
• To establish CLSM as a practical, real-time tool for monitoring graphene growth and morphology during fabrication.

Proposed method

• Utilized confocal laser scanning microscopy (CLSM) to image wafer-scale epitaxial graphene and graphene nanoribbons on 4H-SiC substrates under ambient conditions without sample preparation.
• Measured reflected laser intensity variations across different graphene regions (interfacial layer, single layer, bilayer, few-layer, overgrown) to generate high-resolution (≈150 nm) optical contrast maps.
• Correlated CLSM intensity patterns with reference data from Raman spectroscopy and scanning probe microscopy (SPM) to validate phase identification.
• Performed real-time CLSM imaging with acquisition speeds hundreds of times faster per unit area than Raman or SPM.
• Analyzed intensity contrast features to distinguish undergrown graphene (dense, parallel nanoribbons + interfacial layer) from continuous and overgrown graphene.
• Used laser excitation at 561 nm to exploit differences in optical reflectivity across graphene multilayers and interfacial layers.

Experimental results

Research questions

• RQ1 Can CLSM provide rapid, non-destructive, and ambient-compatible characterization of wafer-scale epitaxial graphene and graphene nanoribbons on SiC?
• RQ2 Do distinct CLSM intensity contrast patterns correlate with specific graphene phases (e.g., interfacial layer, single layer, bilayer, overgrown)?
• RQ3 How does CLSM acquisition speed compare to conventional methods like Raman spectroscopy and SPM for large-area 2D material inspection?
• RQ4 Can CLSM reliably distinguish undergrown graphene (nanoribbon arrays with interfacial layer) from continuous and overgrown graphene?
• RQ5 Is CLSM robust against surface charging and contamination in ambient air without sample preparation?

Key findings

• CLSM achieved ~150 nm spatial resolution in imaging epitaxial graphene and graphene nanoribbons on SiC, enabling detailed morphological mapping.
• Distinct intensity contrast in CLSM images clearly differentiated undergrown graphene (mixed nanoribbons and interfacial layer), continuous graphene, and overgrown graphene.
• CLSM acquisition speed was hundreds of times faster per unit area than Raman spectroscopy and SPM, enabling high-throughput inspection.
• CLSM provided non-destructive, ambient-air-compatible characterization without sample preparation, unaffected by surface charging or contamination.
• Correlation with Raman and SPM confirmed that CLSM intensity variations reliably indicate different graphene layer counts and structural phases.
• The method demonstrated strong potential for industrial-scale quality control of wafer-scale 2D materials like epitaxial graphene.