Abstract
Self-assembly of organic molecules is a mechanism crucial for design of molecular nanodevices. We demonstrate unprecedented control over the self-assembly, which could allow switching and patterning at scales accessible by lithography techniques. We use the scanning tunneling microscope (STM) to induce a reversible 2D-gas-solid phase transition of copper phthalocyanine molecules on technologically important silicon surface functionalized by a metal monolayer. By means of ab-initio calculations we show that the charge transfer in the system results in a dipole moment carried by the molecules. The dipole moment interacts with a non-uniform electric field of the STM tip and the interaction changes the local density of molecules. To model the transition, we perform kinetic Monte Carlo simulations which reveal that the ordered molecular structures can form even without any attractive intermolecular interaction.
Highlights
The process of molecular self-assembly, using organic molecules as building blocks of spontaneously grown molecular structures, became one of the leading topics important for development of molecular devices[1, 2]
The controlled room-temperature switching of the copper phthalocyanine (CuPc) molecule belongs to the family of planar macrocycles, phtalocyanines
scanning tunneling microscopy (STM) images of approximately 0.8 monolayer (ML) of the CuPc molecules deposited on the Si(111)/Tl - (1 × 1) surface reveal the similar long-range ordering (Figs 1a,b and 2a,b)
Summary
The process of molecular self-assembly, using organic molecules as building blocks of spontaneously grown molecular structures, became one of the leading topics important for development of molecular devices[1, 2]. In recent applications, such as organic field-effect transistors[3], tunnel diodes[4], solar cells[5], light-emitting diodes[6] etc., static ordered layers are utilized. We demonstrate the electric-field-controlled room-temperature switching of the copper phthalocyanine (CuPc) self-assembled arrays on the Si(111)/Tl - (1 × 1) surface, evidenced experimentally by the scanning tunneling microscopy (STM) and explained with help of ab-initio calculations. We expect that a similar electric-field control over surface assembly can be achieved for a wide range of systems containing a weakly interacting mobile adsorbate carrying sufficiently strong permanent dipoles
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