Electronic Processes at the Carbon-Covered (100) Collector Tungsten Surface

Area of Science:

• Surface Science
• Quantum Mechanics
• Materials Science

Background:

• Electron penetrability in nanometric tunnel diodes is influenced by surface properties.
• The work function (Φ) is a critical parameter determining electron emission and transport.
• Carbon-covered surfaces may exhibit unique electronic behaviors compared to pure metals.

Purpose of the Study:

• To investigate the effect of an electric field (E) on the work function of carbon-covered tungsten (C-W).
• To understand the quantum mechanical basis for enhanced electron penetrability in carbon-covered surfaces.
• To correlate work function changes with electronic density variations under an electric field.

Main Methods:

• Density functional theory (DFT) calculations using the VASP code.
• Simulation of pure and (100) carbon-covered tungsten surfaces.
• Application of an external electric field (E) directed away from the surface.
• Extrapolation of potential energy to determine work function at non-zero electric fields.

Main Results:

• The work function of pure tungsten (100) showed minor dependence on the electric field.
• The work function of carbon-covered tungsten (100) exhibited a stronger dependence on the electric field.
• A continuous decrease in work function was observed for C-W surfaces with increasing electric field (ΔΦ = 0.08 eV at E = 1 V/nm).
• Calculated changes in electronic density explained the observed work function reduction.

Conclusions:

• Carbon-covered tungsten surfaces demonstrate a significant field-dependent work function reduction.
• This phenomenon enhances electron penetrability, relevant for nanometric tunnel diodes.
• Findings may explain collector current dependencies observed in Scanning Field Emission Microscopy.