Self-assembled diacetylene molecular wire polymerization on an insulating hexagonal boron nitride (0001) surface

Area of Science:

• Surface Science
• Materials Science
• Nanotechnology

Background:

• Fabricating single-polymer chains on surfaces is crucial for molecular electronics.
• A key challenge is the absence of atomically flat insulating substrates.
• Hexagonal boron nitride (h-BN) is an atomically flat insulating material with potential for surface-based fabrication.

Purpose of the Study:

• To investigate the potential of hexagonal boron nitride (h-BN) as a substrate for on-surface polymerization of diacetylene compounds.
• To demonstrate the formation of long polydiacetylene chains on h-BN surfaces.
• To compare the polymerization efficiency on h-BN with other substrates like graphite.

Main Methods:

• Atomic force microscopy (AFM) was used to characterize the self-assembled monolayer and polymerized chains.
• On-surface polymerization was initiated via thermal annealing or ultraviolet (UV) irradiation.
• The frequency of polymerization events was quantified and compared between h-BN and graphite substrates.

Main Results:

• A flat-lying self-assembled monolayer of diacetylene compounds was successfully formed on the h-BN(0001) surface.
• On-surface polymerization, forming long polydiacetylene chains, was achieved through heating or UV irradiation.
• The photo-polymerization frequency on h-BN(0001) was found to be two orders of magnitude higher than on graphite(0001).
• This enhanced efficiency is attributed to the suppressed relaxation pathways in h-BN due to its large band gap, leading to an increased molecular excited-state lifetime.

Conclusions:

• Hexagonal boron nitride (h-BN) is a highly effective substrate for on-surface polymerization of diacetylene compounds.
• The unique electronic properties of h-BN enhance polymerization efficiency, offering a significant advantage over graphite.
• On-surface polymerization on h-BN remains feasible even after lithography, paving the way for subsequent electrical characterization and molecular device development.