Two-Dimensional Crystals as a Buffer Layer for High Work Function Applications: The Case of Monolayer MoO₃.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Work function (WF) modification is critical for advanced electronic devices.
• Two-dimensional (2D) materials offer unique properties for surface engineering.
• Achieving high and tunable WF is essential for organic electronics and energy storage.

Purpose of the Study:

• To investigate the impact of crystallinity on the work function of 2D MoO₃.
• To explore the potential of 2D MoO₃ for enhancing substrate work function.
• To understand the role of growth conditions and defects on the electronic properties of 2D MoO₃.

Main Methods:

• Kelvin probe force microscopy (KPFM) for nanoscale WF mapping.
• Ultraviolet photoemission spectroscopy (UPS) for electronic structure analysis.
• Density functional theory (DFT) calculations for electronic potential and defect analysis.

Main Results:

• Crystalline 2D α-MoO₃ monolayers enhance substrate WF to 6.4 eV at 0.7 nm thickness.
• UPS is effective for high WF determination on lower WF substrates with sufficient 2D island coverage.
• KPFM is the preferred method for nanoscale WF investigations, especially under ultrahigh vacuum.
• DFT calculations reveal WF anisotropy due to oxygen vacancies in MoO₃.

Conclusions:

• Crystallinity of 2D materials is key for effective WF modification.
• 2D MoO₃ is a promising material for high WF applications in organic electronics.
• Controlled growth environments are crucial for achieving desired WF properties in MoO₃ films.