Lock-and-key effect in the surface diffusion of large organic molecules probed by STM

Abstract

Violet Lander (VL) (C108H104) is a large organic molecule that when deposited on Cu (110) exhibited lock-and-key like behavior (Otero et al., Nature Mater. 3, 779 (2004)). In this work we report on a detailed fully atomistic molecular dynamics study of this phenomenon. Our results show that it has its physical basis in the interplay of the molecular hydrogens and the Cu(110) atomic spacing, which is a direct consequence of an accidental commensurability between molecule and surface dimensions. This knowledge could be used to engineer new molecules capable of displaying lock-and-key behavior with new potential applications in nanotechology.PACS numbers: 61.46.+w, 68.37.Lp, With the advent of nanoscience and nanotechnology and the perspective of molecular electronics [1,2,3,4,5,6,7], significant theoretical and experimental efforts have been devoted to the study of the complex interactions involving organic molecular structures and metallic surfaces [8,9,10,11,12,13,14,15]. One essential aspect of these phenomena is to understand how these interactions alter the properties of both molecule and surface. Recent progress has been achieved through the use of UHV-STM (ultrahigh vacuum-scanning transmission microscopy) [10,16] that allowed the identification of important structural and dynamical features related to the behavior of molecular wires adsorved on metallic surfaces.One important family of molecular wires is the socalled "Lander molecules" (because of its resemblance to a Mars surface rover) [17]. These large organic molecules are composed of a rigid polyaromatic π central board and four spacers (legs) of up to eight 3,5-di-tert-butylphenyl σ-bonded to the central board (Fig. 1). These spacers generate a configuration where the phenyl groups are nearly perpendicular to the main board plane by steric crowding. When deposited onto a metallic surface, these conformations allow an electronic decoupling (π-bonded from the metallic surface) to occur. Also, the presence of the tert-butyl groups, which increases the board-surface distance, permits some rotation of the "legs" without significantly reducing this distance. When adsorbed on Cu(100) or Cu(110) surfaces, the Lander molecule can act as a template for selfaccomodating metal atoms at the step edges of the copper substrate, spontaneously generating metallic nanostructures dimensionally commensurable with the Lander

Azobenzene on Cu(110): Adsorption Site-Dependent Diffusion

“…A similar result was recently demonstrated by manipulating a large organic molecule into a metastable state using the STM tip. 17 In the present system, however, the molecules spontaneously assume the metastable state of higher mobility by deposition onto a cold surface.Although azobenzene may exist in either a trans-or a cisconformation, we only appear to observe the former after deposition. (Since the cis-isomer has a nonplanar conformation in the gas phase, we expect it to adsorb with only one phenyl ring attached to the surface, appearing slightly larger than a single phenyl ring.)…”

“…A similar result was recently demonstrated by manipulating a large organic molecule into a metastable state using the STM tip. 17 In the present system, however, the molecules spontaneously assume the metastable state of higher mobility by deposition onto a cold surface.…”

Bicomponent Supramolecular Architectures at the Vacuum–Solid Interface

“…12, 244 In contrast, when the bonding energy is of the same order of magnitude as the diffusion energy, the adsorbate behavior on the surface is more sensitive to temperature effects, and an equilibrium exists between a 2D gas phase on the surface and the gas phase itself. Although surface diffusion of atoms and of small molecules, such as carbon monoxide, is well understood (and often follows a simple single particle hopping model), the problem is significantly more complex in the case of larger molecules 245 because they span several surface adsorption sites, 246 deform during diffusion, 247 interact with surface defects, 248 can induce local surface reconstruction (see below), 249 can diffuse only in specific directions, 250 and can be immobilized or highly mobile depending on the orientation with respect to the surface atomic lattice, 251 among other effects.…”

Origins of Twinned Microstructures in B12As2 Epilayers Grown on (0001) 6H-SiC and Their Influence on Physical Properties

“…Note that the interface in both samples exhibits steps of opposite sign as expected for these "on-axis" substrates. the surface diffusion of large organic molecules on metal substrates [14]. For such systems only those molecules adsorbed onto the surface that are not oriented correctly to form bonds to the surface have the opportunity to become mobile and diffuse.…”