Molecular Identification, Bond Order Discrimination, and Apparent Intermolecular Features in Atomic Force Microscopy Studied with a Charge Density Based Method.

We introduce an efficient method to simulate high-resolution atomic force microscopy (HR-AFM) images with CO probes. Our model explicitly takes into account the charge densities of the sample and the probe for the calculation of the short-range (SR) interaction and retains ab initio accuracy with only two parameters, that are essentially universal, independent of the number of chemical species and the complexity of the bonding topology. The application to molecular images shows a strong dependence on the stoichiometry and bonding configuration that precludes the chemical identification of individual atoms based on local force-distance curves.

Atomic-Scale Variations of the Mechanical Response of 2D Materials Detected by Noncontact Atomic Force Microscopy.

We show that noncontact atomic force microscopy (AFM) is sensitive to the local stiffness in the atomic-scale limit on weakly coupled 2D materials, as graphene on metals. Our large amplitude AFM topography and dissipation images under ultrahigh vacuum and low temperature resolve the atomic and moiré patterns in graphene on Pt(111), despite its extremely low geometric corrugation. The imaging mechanisms are identified with a multiscale model based on density-functional theory calculations, where the energy cost of global and local deformations of graphene competes with short-range chemical and long-range van der Waals interactions.

The Electric Field of CO Tips and Its Relevance for Atomic Force Microscopy.

Metal tips decorated with CO molecules have paved the way for an impressively high resolution in atomic force microscopy (AFM). Although Pauli repulsion and the associated CO tilting play a dominant role at short distances, experiments on polar and metallic systems show that electrostatic interactions are necessary to understand the complex contrast observed and its distance evolution. Attempts to describe those interactions in terms of a single electrostatic dipole replacing the tip have led to contradictory statements about its nature and strength.

Effect of classroom modification on attention and engagement of students with autism or dyspraxia.

Students with autism display sensory sensitivities to environmental stimuli that affect their attending and engagement in classroom learning activities. The purpose of the study was to determine whether attending of 4 male students, ages 13-20, increased after the installation of sound-absorbing walls and halogen lighting. The multiple single-subject, mixed-method design, AB(B+C), included a 2-wk baseline and two intervention phases: 2 wk after sound-absorbing wall installation using the Owens Corning Basement Finishing System™ (Owens Corning, Toledo, OH) and 2 wk after halogen light installation.