Atomic‐Level Studies of Molecular Self‐Assembly on Metallic Surfaces

Abstract

Shrinking devices to the nanoscale, while still maintaining accurate control on their structure and functionality is one of the major technological challenges of our era. The use of purposely directed self‐assembly processes provides a smart alternative to the troublesome manipulation and positioning of nanometer‐sized objects piece by piece. Here, we report on a series of recent works where the in‐depth study of appropriately chosen model systems addresses the two key‐points in self‐assembly: building blocks selection and control of bonding. We focus in particular on hydrogen bonding because of the stability, precision and yet flexibility of nanostructures based on this interaction. Complementing experimental information with advanced atomistic modeling techniques based on quantum formalisms is a key feature of most investigations. We thus highlight the role of theoretical modeling while we follow the progression in the use of more and more complex molecular building blocks, or “tectons”. In particular, we will see that the use of three‐dimensional, flexible tectons promises to be a powerful way to achieve highly sophisticated functional nanostructures. However, the increasing complexity of the assembly units used makes it generally more difficult to control the supramolecular organization and predict the assembling mechanisms. This creates a case for developing novel analysis methods and ever more advanced modeling techniques.

Modeling the Electronic Properties of π‐Conjugated Self‐Assembled Monolayers

“…Instead, electrons are transferred from the upper (i.e., right) region of the SAM to the lower (i.e., left) region of the 2P layer and, additionally, the SAM backbone is polarized without significant long-range charge transfer along the backbone. These findings are best visible in the plot of the integrated net charge transfer Q(z) as defined in Equation (3).…”

“…Integrating Dr in the plane of the surface (the x,y-plane) over the unit cell again reduces the dimensionality of the problem and yields Dr(z). As before, the net charge transfer between regions at different z-values, e.g., between substrate and SAM, can then be accessed through Q(z) calculated via Equation (3). Moreover, the change in the electron potential energy, DE(z), due to the interfacial chargerearrangements, i.e., the difference to the mere sum of the potential wells of clean gold slab and free-standing SAM, can be evaluated by integrating Q(z) over z (with A being the area of the unit cell in the x,y-plane):…”

“…Such 2D crystalline structures can be classified on the basis of the interaction amongst the individual building blocks as well as the interaction between adsorbate and substrate. They comprise, for example, hydrogen bonded systems, [2,3] extended grid-type structures resulting from the assembly of transition metal atoms with suitably chosen ligands, [4,5] quasi-epitaxially growing layers, [6] chemisorbed organic molecules experiencing strong charge transfer to the metal-where long-range order arises from the electrostatic interaction of the charge-transfer dipoles, [7] and strongly (often covalently) bonded layers of essentially upright-standing molecules usually referred to as SAMs (i.e., selfassembled monolayers). [8][9][10][11][12] As far as the latter are concerned, it is useful to distinguish between SAMs on noble metals, [13][14][15] on semiconductors, [16,17] and on conducting [18,19] or insulating oxides.…”

Valence band photoemission from the Zn-phthalocyanine/Ag(110) interface: Charge transfer and scattering of substrate photoelectrons

“…Moreover, at room temperature ͑RT͒, the molecules may diffuse on the substrate surface and nanostructuration is possible via intermolecular interactions. 5,6 Electron spectroscopies are fundamental tools to explore the electronic properties of interfaces. For instance, the modification of frontier molecular orbitals and the appearance of hybrid states at the interface can be detected by valence-band ͑VB͒ ultraviolet photoelectron spectroscopy ͑UPS͒ probing, to a first approximation, the density of states ͑DOS͒ of the first surface atomic layers.…”

Modeling and simulation of protein–surface interactions: achievements and challenges

“…Several of these provide a general overview of the adsorption of proteins at solid surfaces (Cohavi et al 2010;Costa et al 2013;Horbett & Brash, 1995;Rabe et al 2011;Qu et al 2013), whereas others focus on more specific aspects such as the determination of the adsorption kinetics of protein-surface binding by weakly bound mobile precursor states (Garland et al 2012), and adsorption on various different surface types, such as metallic surfaces (Tomba et al 2009;Vallee et al 2010), polymer surfaces (Hahm, 2014;Wei et al 2014) and protein repellent surfaces (Szott & Horbett, 2011). The physicochemical properties of nanomaterials, and their applications in medicine, biology and biotechnology, have also been reviewed in several papers (see, e.g.…”