Application of the symbolic regression program AI-Feynman to psychology.

The discovery of hidden laws in data is the core challenge in many fields, from the natural sciences to the social sciences. However, this task has historically relied on human intuition and experience in many areas, including psychology. Therefore, discovering laws using artificial intelligence (AI) has two significant advantages.

Hybrid mode atomic force microscopy of phase modulation and frequency modulation.

We propose hybrid phase modulation (PM)/frequency modulation (FM) atomic force microscopy (AFM) to increase the imaging speed of AFM in high-Q environments. We derive the relationship between the phase shift, the frequency shift and the tip-sample interaction force from the equation of motion for the cantilever in high-Q environments. The tip-sample conservative force is approximately given by the sum of the conservative force with respect to the phase shift in the PM mode and that with respect to the frequency shift in the FM mode.

Direct measurement of surface photovoltage by AC bias Kelvin probe force microscopy.

Surface photovoltage (SPV) measurements are a crucial way of investigating optoelectronic and photocatalytic semiconductors. The local SPV is generally measured consecutively by Kelvin probe force microscopy (KPFM) in darkness and under illumination, in which thermal drift degrades spatial and energy resolutions. In this study, we propose the method of AC bias Kelvin probe force microscopy (AC-KPFM), which controls the AC bias to nullify the modulated signal.

Charge Behavior of Terminal Hydroxyl on Rutile TiO(110).

Titanium dioxide (TiO) is of considerable interest as a photocatalyst and a catalyst support. Surface hydroxyl groups (OH) are the most common adsorbates on the TiO surface and are believed to play crucial roles in their applications. Although the characteristics of bridging hydroxyl (OH) have been well understood, the adsorption structure and charged states of terminal hydroxyl (OH) have not yet been experimentally elucidated at an atomic scale.

Elucidating the charge state of an Au nanocluster on the oxidized/reduced rutile TiO (110) surface using non-contact atomic force microscopy and Kelvin probe force microscopy.

The charge state of Au nanoclusters on oxidized/reduced rutile TiO (110) surfaces were investigated by a combination of non-contact atomic force microscopy and Kelvin probe force microscopy at 78 K under ultra-high vacuum. We found that the Au nanoclusters supported on oxidized/reduced surfaces had a relatively positive/negative charge state, respectively, compared with the substrate. In addition, the distance dependence of LCPD verified the contrast observed in the KPFM images.

Imaging the surface potential at the steps on the rutile TiO(110) surface by Kelvin probe force microscopy.

Although step structures have generally been considered to be active sites, their role on a TiO surface in catalytic reactions is poorly understood. In this study, we measured the contact potential difference around the steps on a rutile TiO(110)-(1 × 1) surface with O exposure using Kelvin probe force microscopy. A drop in contact potential difference was observed at the steps, indicating that the work function locally decreased.

Tip-Induced Control of Charge and Molecular Bonding of Oxygen Atoms on the Rutile TiO (110) Surface with Atomic Force Microscopy.

We study a low-temperature on-surface reversible chemical reaction of oxygen atoms to molecules in ultrahigh vacuum on the semiconducting rutile TiO(110)-(1 × 1) surface. The reaction is activated by charge transfer from two sources, natural surface/subsurface polarons and experimental Kelvin probe force spectroscopy as a tool for electronic charge manipulation with single electron precision. We demonstrate a complete control over the oxygen species not attainable previously, allowing us to deliberately discriminate in favor of charge or bond manipulation, using either direct charge injection/removal through the tip-oxygen adatom junction or indirectly via polarons.

Measurement and Manipulation of the Charge State of an Adsorbed Oxygen Adatom on the Rutile TiO(110)-1×1 Surface by nc-AFM and KPFM.

For the first time, the charge states of adsorbed oxygen adatoms on the rutile TiO(110)-1×1 surface are successfully measured and deliberately manipulated by a combination of noncontact atomic force microscopy and Kelvin probe force microscopy at 78 K under ultrahigh vacuum and interpreted by extensive density functional theory modeling. Several kinds of single and double oxygen adatom species are clearly distinguished and assigned to three different charge states: O/2O, O/2O, and O-O, i.e.

Direct observation of atomic step edges on the rutile TiO(110)-(1 × 1) surface using atomic force microscopy.

Clarifying the atomic configuration of step edges on a rutile TiO2 surface is crucial for understanding its fundamental reactivity, and the direct observation of atomic step edges is still a challenge. AFM is a powerful tool for investigating surface structures with true atomic resolution, and it provides the opportunity to resolve the real structure of step edges with improved techniques. In this work, we successfully imaged the atomic configuration of 001 and 1-11 step edges on the surface of rutile TiO2(110)-(1 × 1), and we present the direct observation of oxygen vacancies along the 1-11 step edges, indicating that one 1-11 step edge site corresponds to one oxygen vacancy using AFM.