Molecular Order Induced Charge Transfer in a C₆₀-Topological Insulator Moiré Heterostructure.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Topological insulators (TIs) like Bi4Te3 exhibit unique electronic properties.
• Fullerenes (C60) are molecules with significant electron affinity.
• Heterostructures combining TIs and molecular layers offer tunable electronic behavior.

Purpose of the Study:

• To synthesize and characterize monolayer C60 on Bi4Te3.
• To investigate the electronic interaction and charge transfer between C60 and Bi4Te3.
• To understand the temperature-dependent behavior of the C60/Bi4Te3 heterostructure.

Main Methods:

• Synthesis of monolayer C60 on Bi4Te3.
• Spectroscopic investigations including Angle-Resolved Photoemission Spectroscopy (ARPES), Raman spectroscopy, and Photoluminescence (PL).
• Theoretical calculations to explain observed phenomena.

Main Results:

• A well-ordered (4x4) C60 superstructure on a (9x9) Bi4Te3 cell was observed.
• Temperature-dependent charge transfer was detected: electron donation from Bi4Te3 to C60 at room temperature, ceasing at low temperatures.
• A transition to a rotationally ordered state of C60 at low temperatures, accompanied by increased Raman and PL signals, was observed.

Conclusions:

• The charge transfer is primarily driven by C60 adsorption to surface defects on Bi4Te3.
• The temperature dependence of charge transfer is attributed to the orientational ordering of C60 molecules.
• Freezing of C60 rotational motion at low temperatures enhances electron affinity, influencing doping levels.