The issue of Vacuum and Surface Science presents you a collection of review articles that focus on recent activities in scanning probe microscopy. This article briefly explains the intention and purpose of the special issue.

Frequency modulation atomic force microscopy (FM-AFM) can simultaneously detect the conservative and non-conservative force interactions between a tip and a sample, based on the resonance frequency shift (Δf) and the mechanical energy dissipation of an oscillating cantilever, respectively. Here, we outline the energy dissipation measured by FM-AFM and introduce our recent results obtained through measurement of the energy dissipation. First, surface resistances can be evaluated in non-contact using the proportional relationship between the energy dissipation due to Joule heat and Δf due to the electrostatic attractive force. Second, Si adatoms on a Si(111)-(7×7) surface, which are observed to be static by FM-AFM, can move back and force between their stable sites and their neighboring quasi-stable sites, detected by measuring of the energy dissipation.

The catalytic mechanism of TiO₂ surface fascinated us for long time because of the unrevealing reaction mechanism in ambient condition. A key challenge is to reveal these mechanisms at atomic scale under specific gas phase. However, direct experimental insights into this mechanism have not been investigated yet. Here, we investigate the charge state of oxygen atoms on rutile TiO₂ (110) surface using Kelvin probe force microscopy and spectroscopy. We successfully manipulate the charge state of oxygen atoms. This work provides a novel route for the investigation of the charge state of the adsorbates and opens up a prospect for the studies of transition metal oxide based catalytic reactions.

We present an experimental technique for probing the charge state and electronic level structure of individual quantum dots (QD) which is based on the sensitive electric force detection using atomic force microscopy (AFM). An oscillating AFM tip positioned above a QD modulates the energy of the QD with respect to the back electrode and causes single electrons to tunnel back and forth between the QD and back electrode. The resulting periodically oscillating electric force changes the resonance frequency and damping of an AFM cantilever, enabling electric charge sensing with single-electron charge sensitivity. The technique enables quantitative energy level spectroscopy of individual QD and spatial mapping of the charge state of coupled QDs from which the interaction between QD can be extracted.

Combination of scanning tunneling microscope with inelastic electron tunneling spectroscopy (STM-IETS) enables us to investigate the vibration of a molecule on a surface at the atomic scale spatial resolution. However it was known that the intensity of IETS strongly depends on each tip. Here we have further incorporated atomic force microscopy (AFM) to characterize the geometrical structure of a tip apex and investigated the tip apex geometry dependent IETS for a CO molecule on a Cu(111) surface. We demonstrate for a metallic tip that the ratio of the current passing through a CO molecule to the bypass current is a critical factor to determine the intensity of IETS.

The buried interface structure was found to cause faint 3×3 periodic ripples in scanning tunneling microscope (STM) at the surface of ultra-thin Ag films on the Si(111)√3×√3-B substrate. The ripples were purely geometric, since they showed no bias voltage dependence. X-ray diffraction revealed that the Ag/Si lattice commensuration introduces the 3×3 periodic displacement to the bottom layer of the Ag film. The displacement was also found to be transferred to upper layers in the Ag film while damping. It manifests itself as the 3×3 faint ripples on top of the Ag film in STM.

Hydrogen(H)-bonding and H-transfer dynamics are involved in many important processes in physics, chemistry, and biology. I review our recent progress on direct observation of intramolecular double H-atom transfer reactions (tautomerization) in a single porphycene molecule on metal surfaces using low-temperature scanning probe microscopy. We have elucidated the reaction mechanisms occurring by quantum tunneling of H atoms and induced by various external stimuli such as heat, electron attachment, photo irradiation, and chemical interaction.

Weyl semimetals host topologically protected surface states, with arced Fermi surface contours that are predicted to penetrate through the bulk when their momentum matches that of the surface projections of the bulk's Weyl nodes. Here, we describe our experiment in which we used spectroscopic mapping with a scanning tunneling microscope (STM) to visualize quasi-particle interference at the surface of the Weyl semimetal TaAs. Our measurements revealed multitude of scattering wavevectors, which can be reproduced by taking into account the shape and spin texture of the Fermi arc surface states and their momentum-dependent penetration into the bulk. Our result exemplifies an atomic-scale manifestation of surface-bulk connectivity of Weyl semimetal.

We have developed chromium oxide layer segregated on electrolytic polished stainless steel (SS316L) surface as inner coat of the ultra-high vacuum chamber. In order to investigate the superiority of the surface of chromium oxide on electrolytic polished surface compared with the only electrolytic polished surface, the thermal desorption characteristics and the initial exhaust characteristics after the air exposure were investigated. We found that the initial evacuation such as mass number m/z＝14 (mixture of N and CH₂) and 18 (H₂O) as well as reduction of hydrogen release amount in temperature raising desorption is faster than electrolytic polished surface. It was found to be suitable for surface treatment when quick exhaust of high vacuum region such as a load lock chamber is desired.