An Atomistic Analysis of the Carpet Growth of KCl Across Step Edges on the Ag(111) Surface.

The carpet growth of alkali halide (AH) layers across step edges of substrates enables the growth of seamless and continuous large domains. Yet, information about how the AH layer adapts continuously to the height difference between the terraces on the two sides of a step is only described by continuum models, which do not give details of the ionic displacements. Here, we present a first study of thin epitaxial KCl(100) layers grown on the Ag(111) surface by scanning tunneling microscopy that provides atomistic details for the first time.

Automated Scanning Probe Tip State Classification without Machine Learning.

The manual identification and in situ correction of the state of the scanning probe tip is one of the most time-consuming and tedious processes in atomic-resolution scanning probe microscopy. This is due to the random nature of the probe tip on the atomic level, and the requirement for a human operator to compare the probe quality via manual inspection of the topographical images after any change in the probe. Previous attempts to automate the classification of the scanning probe state have focused on the use of machine learning techniques, but the training of these models relies on large, labeled data sets for each surface being studied.

Precise determination of molecular adsorption geometries by room temperature non-contact atomic force microscopy.

High resolution force measurements of molecules on surfaces, in non-contact atomic force microscopy, are often only performed at cryogenic temperatures, due to needing a highly stable system, and a passivated probe tip (typically via CO-functionalisation). Here we show a reliable protocol for acquiring three-dimensional force map data over both single organic molecules and assembled islands of molecules, at room temperature. Isolated cobalt phthalocyanine and islands of C are characterised with submolecular resolution, on a passivated silicon substrate (B:Si(111)-[Formula: see text]).

Intramolecular Force Mapping at Room Temperature.

Acquisition of dense, three-dimensional, force fields with intramolecular resolution via noncontact atomic force microscopy (NC-AFM) has yielded enormous progress in our ability to characterize molecular and two-dimensional materials at the atomic scale. To date, intramolecular force mapping has been performed exclusively at cryogenic temperatures, due to the stability afforded by low temperature operation, and as the carbon monoxide functionalization of the metallic scanning probe tip, normally required for submolecular resolution, is only stable at low temperature. In this paper we show that high-resolution, three-dimensional force mapping of a single organic molecule is possible even at room temperature.

Cyclic Single Atom Vertical Manipulation on a Nonmetallic Surface.

Motivated by the quest for experimental procedures capable of controlled manipulation of single atoms on surfaces, we set up a computational strategy that explores the cyclical vertical manipulation of a broad set of single atoms on the GaAs(110) surface. First-principles simulations of atomic force microscope tip-sample interactions were performed considering families of GaAs and Au-terminated tip apexes with varying crystalline termination. We identified a subset of tips capable of both picking up and depositing an adatom (Ga, As, Al, and Au) any number of times via a modify-restore cycle that "resets" the apex of the scanning probe to its original structure at the end of each cycle.

Chemical shielding of HO and HF encapsulated inside a C cage.

Molecular surgery provides the opportunity to study relatively large molecules encapsulated within a fullerene cage. Here we determine the location of an HO molecule isolated within an adsorbed buckminsterfullerene cage, and compare this to the intrafullerene position of HF. Using normal incidence X-ray standing wave (NIXSW) analysis, coupled with density functional theory and molecular dynamics simulations, we show that both HO and HF are located at an off-centre position within the fullerene cage, caused by substantial intra-cage electrostatic fields generated by surface adsorption of the fullerene.

On-surface chemical reactions characterised by ultra-high resolution scanning probe microscopy.

In the last decade it has become possible to resolve the geometric structure of organic molecules with intramolecular resolution using high resolution scanning probe microscopy (SPM), and specifically using the subset of SPM known as noncontact atomic force microscopy (ncAFM). In world leading groups it has become routine not only to perform sub-molecular imaging of the chemical, electronic, and electrostatic properties of single molecules, but also to use this technique to track complex on-surface chemical reactions, investigate novel reaction products, and even synthesise new molecular structures one bond at a time. These developments represent the cutting edge of characterisation at the single chemical bond level, and have revolutionised our understanding of surface-based chemical processes.

Modelling of 'sub-atomic' contrast resulting from back-bonding on Si(111)-7×7.

It has recently been shown that 'sub-atomic' contrast can be observed during NC-AFM imaging of the Si(111)-7×7 substrate with a passivated tip, resulting in triangular shaped atoms [Sweetman et al. Nano Lett. 2014, 14, 2265].

Visualizing the orientational dependence of an intermolecular potential.

Scanning probe microscopy can now be used to map the properties of single molecules with intramolecular precision by functionalization of the apex of the scanning probe tip with a single atom or molecule. Here we report on the mapping of the three-dimensional potential between fullerene (C60) molecules in different relative orientations, with sub-Angstrom resolution, using dynamic force microscopy (DFM). We introduce a visualization method which is capable of directly imaging the variation in equilibrium binding energy of different molecular orientations.

Nano-contact microscopy of supracrystals.

Background: Highly ordered three-dimensional colloidal crystals (supracrystals) comprised of 7.4 nm diameter Au nanocrystals (with a 5% size dispersion) have been imaged and analysed using a combination of scanning tunnelling microscopy and dynamic force microscopy.

Results: By exploring the evolution of both the force and tunnel current with respect to tip-sample separation, we arrive at the surprising finding that single nanocrystal resolution is readily obtained in tunnelling microscopy images acquired more than 1 nm into the repulsive (i.

Critical assessment of the evidence for striped nanoparticles.

There is now a significant body of literature which reports that stripes form in the ligand shell of suitably functionalised Au nanoparticles. This stripe morphology has been proposed to strongly affect the physicochemical and biochemical properties of the particles. We critique the published evidence for striped nanoparticles in detail, with a particular focus on the interpretation of scanning tunnelling microscopy (STM) data (as this is the only technique which ostensibly provides direct evidence for the presence of stripes).

Uncertainties in forces extracted from non-contact atomic force microscopy measurements by fitting of long-range background forces.

In principle, non-contact atomic force microscopy (NC-AFM) now readily allows for the measurement of forces with sub-nanonewton precision on the atomic scale. In practice, however, the extraction of the often desired 'short-range' force from the experimental observable (frequency shift) is often far from trivial. In most cases there is a significant contribution to the total tip-sample force due to non-site-specific van der Waals and electrostatic forces.

Unique determination of "subatomic" contrast by imaging covalent backbonding.

The origin of so-called "subatomic" resolution in dynamic force microscopy has remained controversial since its first observation in 2000. A number of detailed experimental and theoretical studies have identified different possible physicochemical mechanisms potentially giving rise to subatomic contrast. In this study, for the first time we are able to assign the origin of a specific instance of subatomic contrast as being due to the back bonding of a surface atom in the tip-sample junction.

Effect of the tip state during qPlus noncontact atomic force microscopy of Si(100) at 5 K: Probing the probe.

Background: Noncontact atomic force microscopy (NC-AFM) now regularly produces atomic-resolution images on a wide range of surfaces, and has demonstrated the capability for atomic manipulation solely using chemical forces. Nonetheless, the role of the tip apex in both imaging and manipulation remains poorly understood and is an active area of research both experimentally and theoretically. Recent work employing specially functionalised tips has provided additional impetus to elucidating the role of the tip apex in the observed contrast.

Measuring Si-C60 chemical forces via single molecule spectroscopy.

We measure the short-range chemical force between a silicon-terminated tip and individual adsorbed C(60) molecules using frequency modulation atomic force microscopy. The interaction with an adsorbed fullerene is sufficiently strong to drive significant atomic rearrangement of tip structures.

Toggling bistable atoms via mechanical switching of bond angle.

We reversibly switch the state of a bistable atom by direct mechanical manipulation of bond angle using a dynamic force microscope. Individual buckled dimers at the Si(100) surface are flipped via the formation of a single covalent bond, actuating the smallest conceivable in-plane toggle switch (two atoms) via chemical force alone. The response of a given dimer to a flip event depends critically on both the local and nonlocal environment of the target atom-an important consideration for future atomic scale fabrication strategies.