Geometric imaging of borophene polymorphs with functionalized probes

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Borophene exhibits polymorphism due to varied hollow hexagon (HH) arrangements.
• Direct HH imaging is crucial for identifying borophene's atomic structure.
• Conventional scanning tunneling microscopy (STM) methods struggle with distinguishing topographic and electronic features.

Purpose of the Study:

• To develop and apply advanced imaging techniques for unambiguous borophene atomic structure determination.
• To confirm unifying structural models for observed borophene phases.
• To construct a borophene phase diagram and understand phase transitions.

Main Methods:

• Utilized CO-functionalized atomic force microscopy (AFM) for visualizing boron-boron covalent bonds.
• Employed CO-functionalized scanning tunneling microscopy (STM) as an accessible alternative for HH imaging.
• Developed a methodology for direct visualization of atomic structures in borophene polymorphs.

Main Results:

• Successfully visualized structures corresponding to boron-boron covalent bonds using CO-functionalized AFM.
• Confirmed CO-functionalized STM as an effective and accessible technique for HH imaging.
• Identified v1/5 and v1/6 borophene models as unifying structures across observed phases.
• Assembled a borophene phase diagram, revealing a transition to incommensurate phases at high temperatures.

Conclusions:

• CO-functionalized AFM and STM enable definitive imaging of borophene's atomic structure.
• The v1/5 and v1/6 models provide a unifying framework for borophene polymorphism.
• The observed phase transitions support the chemically discrete nature of borophene.