Imaging prototypical aromatic molecules on insulating surfaces: a review

Abstract

Insulating substrates allow for in-plane contacted molecular electronics devices where the molecule is in contact with the insulator. For the development of such devices it is important to understand the interaction of molecules with insulating surfaces. As substrates, ionic crystals such as KBr, KCl, NaCl and CaF are discussed. The surface energies of these substrates are small and as a consequence intrinsic properties of the molecules, such as molecule-molecule interaction, become more important relative to interactions with the substrates. As prototypical molecules, three variants of graphene-related molecules are used, pentacene, [Formula: see text] and PTCDA. Pentacene is a good candidate for molecular electronics applications due to its high charge carrier mobility. It shows mainly an upright standing growth mode and the morphology of the islands is strongly influenced by dewetting. A new second flat-lying phase of the molecule has been observed. Studying the local work function using the Kelvin method reveals details such as line defects in the center of islands. The local work function differences between the upright-standing and flat-lying phase can only be explained by charge transfer that is unusual on ionic crystalline surfaces. [Formula: see text] nucleation and growth is explained by loosely bound molecules at kink sites as nucleation sites. The stability of [Formula: see text] islands as a function of magic numbers is investigated. Peculiar island shapes are obtained from unusual dewetting processes already at work during growth, where molecules 'climb' to the second molecular layer. PTCDA is a prototypical semiconducting molecule with strong quadrupole moment. It grows in the form of elongated islands where the top and the facets can be molecularly resolved. In this way the precise molecular arrangement in the islands is revealed.

Electrostatic forces above graphene nanoribbons and edges interpreted as partly hydrogen-free

“…Scanning force microscopy dynamic measurement modes can determine the internal atomic structure of a molecule [13,14,15,16]. Interconnected graphene nanoribbons [15], graphene nanoribbons with internal doping and edge functionalization [17,18] have been investigated using tuning fork sensors.…”

Protruding hydrogen atoms as markers for the molecular orientation of a metallocene

“…It is still a challenge to determine the precise adsorption geometry of three-dimensional (3D) molecules on surfaces. While spectroscopic methods, such as X-ray standing waves [1] or photoelectron diffraction [2], can precisely determine the location of atomic species in ordered molecular systems on surfaces [3], scanning probe methods are commonly employed for the investigation of both ordered and unordered molecular systems as well as of individual and isolated species [4][5][6]. For example, two different non-planar isomers of dibenzo[a,h]thianthrene molecules could be identified by high-resolution non-contact atomic force microscopy (NC-AFM) [7,8].…”

Self-Assembled Composite Langmuir Films via Fluorine-Containing Bola-Type Derivative with Metal Ions

“…In addition, the air/water interface can provide a good environment for many molecules/building blocks to construct supramolecular assemblies in a controlled manner [19][20][21][22]. To date, Langmuir and Langmuir-Blodgett (LB) techniques are considered well-known methods to fabricate organized ultrathin films at the air/water interface [23][24][25][26][27][28][29][30][31][32]. Moreover, in comparison to other self-assembly techniques [33,34], special two-dimensional (2D) and three-dimensional (3D) nanostructures can also be fabricated by the LB technique [35][36][37].…”