First-principles studies of gas molecule adsorption on a LaB₆(100) surface

Area of Science:

• Materials Science
• Surface Science
• Computational Chemistry

Background:

• Lanthanum hexaboride (LaB₆) is a key material in electron emission applications.
• Understanding gas adsorption on LaB₆(100) is crucial for predicting its performance and longevity.
• Surface poisoning by adsorbed molecules can degrade material properties.

Purpose of the Study:

• To investigate the adsorption behavior of common gas molecules (CO₂, H₂O, O₂, N₂) on the LaB₆(100) surface.
• To elucidate the mechanisms behind LaB₆(100) surface poisoning.
• To analyze the nature of chemical bonding during adsorption.

Main Methods:

• First-principles calculations (Density Functional Theory).
• Adsorption energy calculations.
• Bader charge analysis.
• Electronic density of states (DOS) and electron localization function (ELF) analyses.

Main Results:

• Thermodynamically stable molecular and dissociative adsorption structures were identified for CO₂, H₂O, O₂, and N₂.
• Dissociative adsorption involves greater electron transfer than molecular adsorption.
• Adsorption leads to electron transfer from LaB₆(100) to adsorbates, increasing the work function and causing poisoning.
• Lanthanum (La) forms non-covalent bonds, while Boron (B) forms covalent bonds with adsorbates, with B 2p orbitals being critical.

Conclusions:

• The observed poisoning effect on LaB₆(100) is attributed to electron transfer and work function increase.
• Partial resistance to poisoning can occur due to localized negative charging on the surface.
• The bonding characteristics reveal distinct roles for La and B in adsorbate interactions.