This special issue focuses on recent development of scanning probe microscopy (SPM) after its invention in the 1980s. Novel and precise SPM measurements have further been devised and applied to the fields of physics, chemistry and bioscience, which open new world in science and technology. Six articles from various fields are selected and introduced.

Electric double layer (EDL) is formed at the electrolyte / electrode interface and provides a field of energy storage or accumulated career conduction in addition to that of electrochemical reaction i.e. electron transfer with chemical bond rearrangement. Electrochemical frequency modulation AFM (EC-FM-AFM) enables acquisition of the liquid side information from the highly sensitive force spectrum vertical to the interface as well as the atomic scale resolution imaging of the solid side at the electrode surface, both are often affected by the electrode potential. In this article, some examples of “operando analyses” of such electrochemical interfaces by using EC-FM-AFM are introduced.

We have systematically examined a large number of vortices in the topological superconductor Fe(Se,Te), using a dilution-refrigerator scanning tunneling microscope. We found that a certain number of vortices possess the zero energy vortex bound state (ZVBS) below 20 µeV suggesting its Majorana bound-state origin, but others do not. Interestingly, the emergence of the ZVBS is not related to the preexisting chemical and electronic disorders, and the fraction of vortices with the ZVBS systematically decreases with increasing magnetic field, suggesting the importance of the inter-vortex interaction. These results provide an important insight into a way to control Majorana quasiparticles for future applications.

We will review recent studies in atomic-resolution ultrahigh vacuum AFM over the last decade or so. After a brief description of AFM measurement principles, force sensitivity, instrumentation and performance, recent experimental results will be introduced, divided into three categories by the tip-sample distance.

In recent years, the rapid development of technology coupling optical light with Scanning Probe Microscopes has made it possible to investigate the quantum dynamics of materials and unravel the light-matter interaction on the atomic scale spatial resolution and ultrafast time resolution. This article introduces recent experimental results achieved by a novel time-resolved STM that utilizes a transient tunneling current driven by an electric field of the sub-cycle optical pulse. Finally, we provide a future perspective of the technology.

Frequency modulation atomic force microscopy (FM-AFM) allows atomic-scale imaging at the solid-liquid interface regardless of the conductivity of the sample. In addition, combined with a three-dimensional (3D) tip scanning technique, it allows direct visualization of 3D distributions of mobile water (i.e., hydration structures) and flexible molecular chains. These unique features open up various possibilities in the nanoscale or even subnanoscale studies on the biological interfaces and phenomena. Here, we present an overview of the basic principle of these in-liquid AFM techniques and their applications to the studies on biological systems such as lipid membranes, proteins, and exosomes.

Remarkable development of the machine learning has been reported in recent years, and its concept is spreading into the field of solid state physics. In the first part of this review, we explain the sparse modeling, which is a method analytically extracting information assuming sparsity of the data. In the latter part, we review the application of the sparse modeling method to quasi-particle interference probed by scanning tunneling microscopy, which provides us information on wavenumbers of surface electronic states. Our results indicate that the method works well for extracting useful information from data whose quantity is significantly reduced compared with the standard method, demonstrating promise for effective and time-saving measurements.

We successfully fabricated the high-performance transparent thin film heaters using ITO/AgPd/ITO laminated films with various thickness combinations and investigated their optical, electrical, structural and heating properties in detail. The surface temperature rise rate (TRR) from 0 to 7 seconds for the ITO (200 nm)/AgPd (10 nm)/ITO (200 nm) under the applied voltage of 6.0 V was 16℃/s, where the temperature reached over 300℃ within 20 sec. The transmittance at 550 nm of this heater was 81%, where the sheet resistance was 4.2 Ω/□. The cross-sectional HREM analyses revealed that the bottom and top ITO films showed quite different polycrystalline structures after the temperature rising tests, which can be explained by the solid-phase and vapor-phase crystallizations, respectively.