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Quantification of Surface Reactivity and Step-Selective Etching Chemistry on Single-Crystal BiOI(001)
Julia L Martin1, Roy Stoflet1, Alexander D Carl1
1Department of Chemistry and Biochemistry; Life Science and Bioengineering Center; Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts 01609, United States.
Surface treatments for 2D bismuth oxyiodide (BiOI) were explored to achieve clean surfaces. Hydrofluoric acid (HF) etching created interfacial bismuth iodide (BiI3) that acetone sonication removed, revealing n-type BiOI for energy applications.
Area of Science:
- Materials Science
- Surface Chemistry
- Solid-State Physics
Background:
- Achieving pristine surfaces on 2D materials like bismuth oxyiodide (BiOI) is crucial for electronic applications.
- Existing chemical etching methods often leave residual contaminants, hindering performance.
Purpose of the Study:
- To investigate various surface treatments for single-crystal BiOI.
- To quantify the chemical states and electronic properties of treated BiOI surfaces.
- To understand the impact of treatments on surface termination and electronic behavior.
Main Methods:
- Vapor transport synthesis of BiOI using single-source, Bi2O3 + BiI3, and Bi + I2 + Bi2O3 precursors.
- Surface treatments including tape cleaving, water rinsing, acetone sonication, aqueous HF etching, and sequential HF etching with acetone sonication.
- Characterization using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Ultraviolet Photoelectron Spectroscopy (UPS).
Main Results:
- Angle-resolved XPS revealed surface terminations dependent on the treatment method.
- UPS data confirmed n-type behavior for vapor-transport-synthesized BiOI.
- HF etching introduced interfacial BiI3 at BiOI steps, which was subsequently removed by acetone sonication.
- Surface work function and Fermi level shifts were observed for each chemical treatment.
Conclusions:
- Acetone sonication effectively removes HF-induced BiI3, yielding cleaner BiOI surfaces.
- Surface treatments significantly alter the electronic properties (work function, Fermi level) of BiOI.
- Optimized surface processing of BiOI is critical for enhancing its performance in energy-conversion applications.
