Surface-induced spin state locking of the [Fe(H2B(pz)2)2(bipy)] spin crossover complex

Area of Science:

• Surface Science
• Materials Chemistry
• Condensed Matter Physics

Background:

• Spin crossover (SCO) Fe(II) complexes exhibit distinct high-spin and low-spin states.
• Understanding SCO behavior on surfaces is crucial for molecular electronics and spintronics.
• Substrate interactions can significantly alter molecular properties.

Purpose of the Study:

• To investigate the temperature and coverage-dependent behavior of [Fe(H2B(pz)2)2(bipy)] SCO complex on an Au(111) surface.
• To determine how the gold substrate influences the spin crossover transition.
• To elucidate the structural and electronic properties of the SCO film.

Main Methods:

• Surface-sensitive spectroscopy
• Scanning tunneling microscopy (STM)
• Temperature-dependent electronic structure analysis

Main Results:

• The Au(111) substrate inhibits thermally induced spin transitions, preserving spin states beyond the free molecule transition temperature.
• [Fe(H2B(pz)2)2(bipy)] forms ordered molecular bilayer islands at sub-monolayer coverage and disordered films at higher coverage.
• SCO films exhibit a mixture of spin states at room temperature, with a constant ratio of high-spin to low-spin states upon cooling below the transition.

Conclusions:

• Substrate-induced conformational changes in interfacial molecules are the primary cause of spin state locking.
• Intra-atomic electron-electron Coulomb correlation energy (Hubbard U) may also contribute to the observed spin state locking.
• The findings offer insights into designing surface-supported molecular switches with enhanced stability.