Self-assembly of organic molecules at metal surfaces

Kühnle A. Self-assembly of organic molecules at metal surfaces. Current Opinion in Colloid & Interface Science. 2009;14(2):157-168.Self-assembly represents a promising strategy for surface functionalisation as well as creating nanostructures with well-controlled, tailor-made properties and functionality. Molecular self-assembly at solid surfaces is governed by the subtle interplay between molecule-molecule and molecule-substrate interactions that can be tuned by varying molecular building blocks, surface chemistry and structure as well as Substrate temperature. In this review, basic principles behind molecular self-assembly of organic molecules on metal surfaces will be discussed. Controlling these formation principles allows for creating a wide variety of different molecular surface structures ranging from well-defined clusters, quasi one-dimensional rows to ordered, two-dimensional overlayers. An impressive number of studies exist, demonstrating the ability of molecular self-assembly to create these different structural motifs in a predictable manner by tuning the molecular building blocks as well as the metallic substrate. Here, the multitude of different surface structures of the natural amino acid cysteine on two different gold surfaces observed with scanning tunnelling microscopy will be reviewed. Cysteine on Au(110)-(1x2) represents a model system illustrating the formation of all the above mentioned structural motifs without changing the molecular building blocks or the substrate surface. The only parameters in this system are substrate temperature and molecular coverage, controlling both the molecular adsorption state (physisorption versus chemisorption) and molecular surface mobility. By tuning the adsorption state and the molecular mobility, distinctly different molecular structures are formed, exemplifying the Variety of structural motifs that can be achieved by molecular self-assembly. (C) 2008 Elsevier Ltd. All rights reserved

On-Surface Reactions

Lindner R, Kühnle A. On-Surface Reactions. ChemPhysChem. 2015;16(8):1582-1592.On-surface synthesis constitutes a rapidly growing field of research due to its promising application for creating stable molecular structures on surfaces. While self-assembled structures rely on reversible interactions, on-surface synthesis provides the potential for creating long-term stable structures with well-controlled properties, for example superior electron transport for future molecular electronic devices. On-surface synthesis holds the promise for preparing insoluble compounds that cannot be produced in solution. Another highly exciting aspect of on-surface synthesis is the chance to discover new reaction pathways due to the two-dimensional confinement of the reaction educts. In this review, we discuss the current state-of-the-art and classify the reactions that have been successfully performed so far. Special emphasis is put on electrically insulating surfaces, as these substrates pose particular challenges for on-surface synthesis while at the same time bearing high potential for future use, for example, in molecular electronics

Manipulation of C-60 islands on the rutile TiO2 (110) surface using noncontact atomic force microscopy

Loske F, Kühnle A. Manipulation of C-60 islands on the rutile TiO2 (110) surface using noncontact atomic force microscopy. Applied Physics Letters. 2009;95(4):043110.Regular, almost quadratic pits were created in an island of C-60 molecules on a rutile TiO2 (110) surface using noncontact atomic force microscopy at room temperature. Upon gradually approaching the scanning tip toward the surface, the interaction between the tip and the C-60 island was increased until manipulation was achieved. Analyzing the manipulation process unambiguously revealed that the manipulation was performed in the repulsive regime. Retracting the tip allowed for reproducible imaging the C-60 island after the manipulation process. Moreover, whole islands could be reshaped or even removed when scanning with appropriate scanning parameters

Origin of Ubiquitous Stripes at the Graphite–Water Interface

Seibert S, Klassen S, Latus A, Bechstein R, Kühnle A. Origin of Ubiquitous Stripes at the Graphite–Water Interface. Langmuir. 2020;36(27):7789-7794

Molecular self-assembly on an insulating surface: interplay between substrate templating and intermolecular interactions

Kittelmann M, Rahe P, Kühnle A. Molecular self-assembly on an insulating surface: interplay between substrate templating and intermolecular interactions. Journal of Physics : Condensed Matter. 2012;24(35): 354007.We report on molecular self-assembly of biphenyl-4,4'-dicarboxylic acid (BPDCA) on CaCO3(10 (1) over bar4) under ultra-high vacuum conditions. Two-dimensional, ordered islands are obtained upon deposition at room temperature, coexisting with a streaky structure that is ascribed to individual, mobile molecules forming a two-dimensional gas-like phase. High-resolution non-contact atomic force microscopy (NC-AFM) images of the molecular islands reveal an ordered inner structure that is dominated by rows of molecules aligned side by side running along the [(42) over bar 61] crystallographic direction. A detailed analysis of these rows exhibits inter-row distances that are multiples of the calcite unit cell dimension along the [01 (1) over bar0] direction, clearly demonstrating the templating effect of the substrate. Our results indicate that an excellent size match of the molecular structure with respect to the underlying substrate results in an increased binding of the BPDCA molecules to the surface. In between the rows, a different molecular structure is coexisting with the molecules aligning head to tail. This structure is explained by intermolecular hydrogen bond formation very similar to the BPDCA bulk structure. The coexistence of the bulk-like structure with the row structure suggests a close balance of intermolecular and molecule-surface interactions to be responsible for the observed structure formation

NC-AFM contrast formation on the calcite (1014) surface

Rahe P, Schütte J, Kühnle A. NC-AFM contrast formation on the calcite (1014) surface. Journal of Physics : Condensed Matter. 2012;24(8): 84006.Calcite, the most stable polymorph of calcium carbonate, is one of the most abundant simple salts in the geological environment. Consequently, its natural (10 (1) over bar4) cleavage plane has been studied extensively by a wide range of surface-sensitive techniques, giving indications for two reconstructions, namely a (2 x 1) and a so-called 'row-pairing' reconstruction. The existence of the (2 x 1) reconstruction has been discussed controversially in the literature, but is now confirmed as a true surface property. In contrast, a comprehensive discussion on the existence of the row-pairing reconstruction is lacking so far. Here, we present a non-contact atomic force microscopy (NC-AFM) study of the (10 (1) over bar4) calcite surface performed in an ultra-high vacuum. We discuss a broad variety of different NC-AFM contrasts and present a comprehensive classification scheme. This scheme encompasses a total of 12 different contrast modes. Atomically resolved NC-AFM images are shown, giving experimental evidence for 10 of these contrast modes. In particular, some of these modes allow for identification of the two surface reconstructions while others do not. This variety in appearances provides an explanation for the seemingly contradicting observations in the literature. Based on a detailed investigation of the influence of tip termination and interaction regime, we further analyse the existence of the row-pairing reconstruction

Steering molecular island morphology on an insulator surface by exploiting sequential deposition

Loske F, Reichling M, Kühnle A. Steering molecular island morphology on an insulator surface by exploiting sequential deposition. Chemical Communications. 2011;47(37):10386-10388.Depending on the deposition order in coadsorption of C(60) and SubPc molecules on CaF(2) (111), distinctly different island morphologies can be obtained. We demonstrate that non-equilibrium processes can play a significant role in molecular structure formation and constitute a new route for complex molecular patterning of an insulating surface

Contrast inversion in non-contact atomic force microscopy imaging of C-60 molecules

Loske F, Rahe P, Kühnle A. Contrast inversion in non-contact atomic force microscopy imaging of C-60 molecules. Nanotechnology. 2009;20(26):264010.Non-contact atomic force microscopy (NC-AFM) was applied to study C-60 molecules on rutile TiO2(110). Depending on the tip-sample distance, distinctly different molecular contrasts are observed. Systematically decreasing the tip-sample distance results in contrast inversion that is obtained reproducibly on the C-60 islands. This change in contrast can be related to frequency shift versus distance (d f (z)) curves at different sample sites, unraveling crossing points in the d f (z) curves in the attractive regime. We have performed simulations based on a simple Morse potential, which reproduce the experimental results. This combined experimental and simulation study provides insight into the mechanisms responsible for molecular contrast in NC-AFM imaging. Moreover, this work demonstrates the importance of distance-dependent measurements for unambiguously identifying molecular positions within a molecular island using NC-AFM

Vertical and lateral drift corrections of scanning probe microscopy images

Rahe P, Bechstein R, Kühnle A. Vertical and lateral drift corrections of scanning probe microscopy images. Journal of Vacuum Science & Technology B. 2010;28(3):C4E31.A procedure is presented for image correction of scanning probe microscopy data that is distorted by linear thermal drift. The procedure is based on common ideas for drift correction, which the authors combine to a comprehensive step-by-step description of how to measure drift velocities in all three dimensions and how to correct the images using these velocities. The presented method does not require any knowledge about size or shape of the imaged structures. Thus, it is applicable to any type of scanning probe microscopy image, including images lacking periodic structures. Besides providing a simple, ready-to-use description of lateral and vertical drift correction, they derive all formulas needed from the model of linear drift. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3360909

Deposition Sequence Determines Morphology of C-60 and 3,4,9,10-Perylenetetracarboxylic Diimide Islands on CaF2(111)

Loske F, Reichling M, Kühnle A. Deposition Sequence Determines Morphology of C-60 and 3,4,9,10-Perylenetetracarboxylic Diimide Islands on CaF2(111). Japanese Journal of Applied Physics. 2011;50(8): 08LB07.The coadsorption of C-60 and 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) molecules on atomically flat terraces of the CaF2(111) surface is studied under ultra-high vacuum conditions using non-contact atomic force microscopy (NC-AFM). Deposition of PTCDI molecules on CaF2(111) yields needle-shaped, molecularly well-ordered crystals. Upon following deposition of C-60 molecules, the PTCDI islands are completely covered by C-60. For the opposite deposition order, the initially grown C-60 islands are not covered by PTCDI molecules, instead, most of the PTCDI molecules condense in pure islands, while only few PTCDI molecules nucleate at the edges of previously grown C-60 islands. Simultaneous deposition of both molecules results in an intermixed phase with yet another island morphology. The observed fundamental differences in island morphology suggest that different dewetting barriers are involved in the formation process. (C) 2011 The Japan Society of Applied Physic