Submolecular imaging by atomic force microscopy (AFM) has recently been established as a stunning technique to reveal the chemical structure of unknown molecules, to characterize intramolecular charge distributions and bond ordering, as well as to study chemical transformations and intermolecular interactions. So far, most of these feats were achieved on planar molecular systems because high-resolution imaging of three-dimensional (3D) surface structures with AFM remains challenging. Here we present a method for high-resolution imaging of nonplanar molecules and 3D surface systems using AFM with silicon cantilevers as force sensors. We demonstrate this method by resolving the step-edges of the (101) anatase surface at the atomic scale by simultaneously visualizing the structure of a pentacene molecule together with the atomic positions of the substrate and by resolving the contour and probe-surface force field on a C60 molecule with intramolecular resolution. The method reported here holds substantial promise for the study of 3D surface systems such as nanotubes, clusters, nanoparticles, polymers, and biomolecules using AFM with high resolution.

• Klíčová slova
• Noncontact atomic force microscopy (NC-AFM), high-resolution imaging, submolecular resolution, three-dimensional dynamic force spectroscopy,
• MeSH
• analýza selhání vybavení MeSH
• design vybavení MeSH
• fullereny chemie   MeSH
• krystalografie metody   MeSH
• mikroskopie atomárních sil přístrojové vybavení   MeSH
• molekulární konformace MeSH
• molekulární sondy - techniky přístrojové vybavení   MeSH
• molekulární zobrazování přístrojové vybavení   MeSH
• reprodukovatelnost výsledků MeSH
• senzitivita a specificita MeSH
• vylepšení obrazu přístrojové vybavení   MeSH
• zobrazování trojrozměrné přístrojové vybavení   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fullerene C60 MeSH Prohlížeč
• fullereny MeSH

Scanning probe microscopy has been extensively applied to probe interfacial water in many interdisciplinary fields but the disturbance of the probes on the hydrogen-bonding structure of water has remained an intractable problem. Here, we report submolecular-resolution imaging of the water clusters on a NaCl(001) surface within the nearly noninvasive region by a qPlus-based noncontact atomic force microscopy. Comparison with theoretical simulations reveals that the key lies in probing the weak high-order electrostatic force between the quadrupole-like CO-terminated tip and the polar water molecules at large tip-water distances. This interaction allows the imaging and structural determination of the weakly bonded water clusters and even of their metastable states with negligible disturbance. This work may open an avenue for studying the intrinsic structure and dynamics of ice or water on surfaces, ion hydration, and biological water with atomic precision.

• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The forces governing the contrast in submolecular resolution imaging of molecules with atomic force microscopy (AFM) have recently become a topic of intense debate. Here, we show that the electrostatic force is essential to understand the contrast in atomically resolved AFM images of polar molecules. Specifically, we image strongly polarized molecules with negatively and positively charged tips. A contrast inversion is observed above the polar groups. By taking into account the electrostatic forces between tip and molecule, the observed contrast differences can be reproduced using a molecular mechanics model. In addition, we analyze the height dependence of the various force components contributing to the high-resolution AFM contrast.

• Publikační typ
• časopisecké články MeSH

Here we show scanning tunneling microscopy (STM), noncontact atomic force microscopy (AFM), and inelastic electron tunneling spectroscopy (IETS) measurements on an organic molecule with a CO-terminated tip at 5 K. The high-resolution contrast observed simultaneously in all channels unambiguously demonstrates the common imaging mechanism in STM/AFM/IETS, related to the lateral bending of the CO-functionalized tip. The IETS spectroscopy reveals that the submolecular contrast at 5 K consists of both renormalization of vibrational frequency and variation of the amplitude of the IETS signal. This finding is also corroborated by first principles simulations. We extend accordingly the probe-particle AFM/STM/IETS model to include these two main ingredients necessary to reproduce the high-resolution IETS contrast. We also employ the first principles simulations to get more insight into a different response of frustrated translation and rotational modes of the CO tip during imaging.

• Publikační typ
• časopisecké články MeSH

We investigate the possibility of functionalizing Au tips by N2O molecules deposited on a Au(111) surface and their further use for imaging with submolecular resolution. First, we characterize the adsorption of the N2O species on Au(111) by means of atomic force microscopy with CO-functionalized tips and density functional theory (DFT) simulations. Subsequently we devise a method of attaching a single N2O to a metal tip apex and benchmark its high-resolution imaging and spectroscopic capabilities using FePc molecules. Our results demonstrate the feasibility of high-resolution imaging. However, we find an inherent asymmetry of the N2O probe-particle adsorption on the tip apex, in contrast to a CO tip reference. These findings are consistent with DFT calculations of the N2O- and CO tip apexes.

• Klíčová slova
• Au(111), atomic force microscopy, carbon monoxide, functionalization, high resolution, nitrous oxide, submolecular resolution,
• Publikační typ
• časopisecké články MeSH

How electronic charge is distributed over a molecule determines to a large extent its chemical properties. Here, we demonstrate how the electrostatic force field, originating from the inhomogeneous charge distribution in a molecule, can be measured with submolecular resolution. We exploit the fact that distortions typically observed in high-resolution atomic force microscopy images are for a significant part caused by the electrostatic force acting between charges of the tip and the molecule of interest. By finding a geometrical transformation between two high-resolution AFM images acquired with two different tips, the electrostatic force field or potential over individual molecules and self-assemblies thereof can be reconstructed with submolecular resolution.

• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Submolecular charge distribution significantly affects the physical-chemical properties of molecules and their mutual interaction. One example is the presence of a π-electron-deficient cavity in halogen-substituted polyaromatic hydrocarbon compounds, the so-called π-holes, the existence of which was predicted theoretically, but the direct experimental observation is still missing. Here we present the resolution of the π-hole on a single molecule using the Kelvin probe force microscopy, which supports the theoretical prediction of its existence. In addition, experimental measurements supported by theoretical calculations show the importance of π-holes in the process of adsorption of molecules on solid-state surfaces. This study expands our understanding of the π-hole systems and, at the same time, opens up possibilities for studying the influence of submolecular charge distribution on the chemical properties of molecules and their mutual interaction.

• Publikační typ
• časopisecké články MeSH

Resolution of enantiomers of chiral compounds via crystallization is the dominant method in chemical industry, but chiral recognition at the molecular level during this process is still poorly understood. Using single metal surfaces in ultrahigh vacuum as model system, the enantio-related transition from the monolayer structure into a double layer of the racemic mixture of heptahelicene has been studied with scanning tunneling microscopy. Submolecular resolution reveals enantiopure second layers on Ag(111) and almost enantiopure second layers on Au(111). In analogy to previous results on Cu(111), it is concluded that transition from the 2D first layer racemate into a layered racemate occurs.

• Klíčová slova
• chiral crystallization, heptahelicene, scanning tunneling microscopy, surface science,
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force, and light detection capabilities. The role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), using metal and CO-metal tips. CO-functionalization is found to have an impact on the resolution and contrast of the photon maps due to the localized overlap of the p-orbitals on the tip with the molecular orbitals of the emitter. The possibility of using the same CO-functionalized tip for tip-enhanced photon detection and high resolution atomic force is demonstrated. We study the electroluminescence of ZnPc, induced by charge carrier injection at sufficiently high bias voltages. We propose that the distinct level alignment of the ZnPc frontier orbitals with the Au(111) and Ag(111) Fermi levels governs the primary excitation mechanisms as the injection of electrons and holes from the tip into the molecule, respectively. These findings put forward the importance of the tip status in the photon maps and contribute to a better understanding of the photophysics of organic molecules on surfaces.

• Klíčová slova
• CO functionalization, Electroluminescence, atomic force microscopy, scanning tunneling microscopy, scanning tunneling microscopy-induced luminescence, zinc phthalocyanine,
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Scanning tunneling microscopy and atomic force microscopy can provide detailed information about the geometric and electronic structure of molecules with submolecular spatial resolution. However, an essential capability to realize the full potential of these techniques for chemical applications is missing from the scanning probe toolbox: chemical recognition of organic molecules. Here, we show that maps of the minima of frequency shift-distance curves extracted from 3D data cubes contain characteristic contrast. A detailed theoretical analysis based on density functional theory and molecular mechanics shows that these features are characteristic for the investigated species. Structurally similar but chemically distinct molecules yield significantly different features. We find that the van der Waals and Pauli interaction, together with the specific adsorption geometry of a given molecule on the surface, accounts for the observed contrast.

• Klíčová slova
• AFM, CO tip, DFT, Xe tip, molecular mechanics, single molecule,
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH