Multi-technique surface analysis for structural and chemical characterization of 2D materials

Significance of the Topic

Two-dimensional materials such as hexagonal boron nitride (h-BN) are pivotal in next-generation electronics and heterostructure devices due to their atomic thickness and tunable properties. Reliable surface analysis that combines chemical fingerprinting and lattice structure probing is essential for material development, process optimization, and quality assurance in both research and industrial settings.

Objectives and Study Overview

This work demonstrates a streamlined approach to locate, identify, and characterize discrete boron nitride flakes grown on copper foil by integrating X-ray photoelectron spectroscopy (XPS) SnapMap imaging with coincident Raman spectroscopy. Key goals include rapid flake localization, full-surface chemical mapping, high-resolution spectral analysis, and confirmation of crystal structure without relocating the sample between instruments.

Methodology

A copper substrate bearing chemically vapor-deposited BN flakes was analyzed in three stages:

• SnapMap Imaging: A 30 µm X-ray spot scanned across the sample to generate an N 1s intensity map, distinguishing regions rich in nitride versus organic nitrogen.
• High-Resolution XPS: Targeted spectra of B 1s and N 1s were acquired at selected map coordinates to deconvolute chemical states including boron nitride, boron oxynitride, and chloride contamination.
• Raman Spectroscopy: A 532 nm laser was applied at the same coordinates to record the E2g phonon mode, confirming the hexagonal phase of BN.

Instrumentation Used

The analysis employed the Thermo Scientific™ Nexsa™ Surface Analysis System with co-incident Raman capability and Thermo Scientific™ Avantage™ software for data processing. The system’s integrated optical camera guided region selection and ensured precise alignment between XPS and Raman measurements.

Key Results and Discussion

• SnapMap imaging revealed two distinct chemical regions: red areas corresponding to inorganic nitride and green areas indicating organic nitrogen impurities.
• High-resolution B 1s spectra identified boron nitride, boron oxynitride, and residual chloride species. N 1s spectra confirmed the presence of nitride and oxidized nitrogen states.
• Raman spectra exhibited a prominent E2g peak at 1366 cm⁻¹, signature of hexagonal BN, with no detectable cubic phonon modes, verifying the desired sp² lattice structure.
These findings illustrate how coincident XPS and Raman data yield comprehensive insights on both chemical composition and crystalline phase at micron-scale resolution.

Benefits and Practical Applications of the Method

• Non-destructive and rapid mapping over large areas accelerates identification of nanoscale features.
• Combined chemical and structural analysis in one instrument eliminates sample transfer errors and enhances throughput.
• High spatial resolution supports process development for uniform 2D material growth and defect evaluation.

Future Trends and Potential Applications

Integration of additional analytical techniques such as atomic force microscopy or time-of-flight secondary ion mass spectrometry could further enrich surface characterization. Advances in automated mapping, machine learning–driven data interpretation, and in situ monitoring during growth processes will propel the development of tailored 2D heterostructures and device-grade materials.

Conclusion

The combined use of XPS SnapMap and Raman spectroscopy on the Nexsa system provides a powerful, efficient, and accurate workflow for locating and characterizing boron nitride flakes on copper substrates. This approach supports comprehensive chemical state analysis alongside crystal phase confirmation, meeting the stringent requirements of 2D materials research and production.

Reference

1. Novoselov KS, Jiang D, Schedin F, et al. Two-dimensional atomic crystals. Proc Natl Acad Sci U S A. 2005;102(30):10451-10453.
2. Novoselov KS, Neto AC. Two-dimensional crystals-based heterostructures: materials with tailored properties. Physica Scripta. 2012;T146:014006.
3. Reich S, Ferrari AC, Arenal R, Loiseau A, Bello I, Robertson J. Resonant Raman scattering in cubic and hexagonal boron nitride. Phys Rev B. 2005;71(20):205201.