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Switches are omnipresent in all electronic devices. Miniaturization reduced the size of switches down to atomic dimensions. While on-surface tip-tuned molecular switches have recently been widely s...

Probing CO at a specific site on a metal oxide surface is essential for characterizing various applications such as CO oxidation, hydrogenation, and water-gas shift reaction. Herein, we use atomic force microscopy and Kelvin probe force microscopy to probe the CO on a rutile TiO2(110) surface. Our results indicate that CO can be manipulated along the Ti row by the repulsive lateral force of “pushing” mode. Furthermore, the joint combination of precise manipulation and the distance dependence of local contact potential difference allow us to resolve the interatomic dipole moment and charge state of CO at atomic resolution. Therefore, we found that the negatively charged CO with the dipole moment of negative pole down on the rutile TiO2(110) surface. Our results suppose that both the charge state as well as the on-surface dipole interaction are very effective for CO reaction on rutile TiO2(110) surface.

Titanium dioxide (TiO2) is of considerable interest as a photocatalyst and a catalyst support. Surface hydroxyl groups (OH) are the most common adsorbates on the TiO2 surface and are believed to play crucial roles in their applications. Although the characteristics of bridging hydroxyl (OHbr) have been well understood, the adsorption structure and charged states of terminal hydroxyl (OHt) have not yet been experimentally elucidated at an atomic scale. In this study, we have investigated an isolated OHt on the rutile TiO2(110) surface by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We found that OHt is in a negatively charged state. The unique characteristic of OHt is different from that of OHbr and involves the amphoterism and diversity of catalytic reactions of TiO2.

The redox states of oxygen species on the surface of TiO2 can be altered by electron tunneling by varying the applied bias voltage of an atomic force microscope tip. However, tunneling is stochastic in nature and typically requires ultra-low temperatures to obtain statistically significant data. Here, we use a highly sensitive fast atomic force microscopy setup to study redox transitions of oxygen atoms on a TiO2 surface, in the form of reactive oxygen species and single-atom quantum dots, at 78 K. The fast and highly sensitive nature of our experimental setup enables a statistically necessary amount of data to be collected without having to resort to ultra-low temperatures. This enabled us to study multiple dots and provide insight into the electronic structure and correlation between the oxygen species, which are inaccessible by standard atomic force microscopy. We show that single-atom quantum dots exist in two charge states with drastically different conductance, with one being conducting and the other non-conducting. Oxygen species on a TiO2 surface exist in different redox states, which can be switched between by electron tunneling with an atomic force tip. Here, a fast experimental setup enables statistically significant tunneling rates to be determined, revealing changes in electronic structure.

The discovery of hydrogen atoms on the TiO2 surface is crucial for many practical applications, including photocatalytic water splitting. Electronically activating interfacial hydrogen atoms on the TiO2 surface is a common way to control their reactivity. Modulating the potential landscape is another way, but dedicated studies for such an activation are limited. Here we show the single hydrogen atom manipulation, and on-surface facilitated water deprotonation process on a rutile TiO2 (110) surface using low temperature atomic force microscopy and Kelvin probe force spectroscopy. The configuration of the hydrogen atom is manipulated on this surface step by step using the local field. Furthermore, we quantify the force needed to relocate the hydrogen atom on this surface using force spectroscopy and density functional theory. Reliable control of hydrogen atoms provides a new mechanistic insight of the water molecules on a metal oxide surface. Rutile TiO2 is a prominent photocatalyst for overall water splitting, but the on-surface activation of hydrogen atoms is still not fully understood. Here, the authors use atomic force and kelvin probe force microscopy to study the lateral manipulation of hydrogen on a rutile (110) surface.

Noble metal nanoclusters supported on a transition metal oxide surface are always regarded as the prototypical catalysts, and the controllable manipulation of the metal catalysts provides an effici...

The charge state of palladium nanocatalysts can alter the catalytic conversion process and is required for understanding the important catalytic reactions in applications. However, the charge state...

The atomic structure of a three-dimensional Au nanocluster on a TiO2 surface is important for various studies such as photocatalysis and chemical reactions on metal oxide surfaces. However, accessing the atomic structure of a metal nanocluster supported on a metal oxide surface is still challenging possibly because of its small size, complexity, and flexible structure. Here, we report a detuning imaging mode combined with an atomically sharp tip to address these challenges. Using this method, for the first time, we resolve a three-dimensional Au nanocluster on a rutile TiO2 (110) surface. We found that the Au nanocluster was continuously adsorbed at the upper and lower terraces. Our results open up a new methodology for studying subnanometer clusters at various surfaces at an atomic scale.

Remotely controlling the charge state plays a key role in oxidized rutile TiO2 (110) surface which determines the nanoscale properties of photooxidation reactions. However, the remote charging mech...

The charge state of Au nanoclusters on oxidized/reduced rutile TiO2 (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. The physical background of charge transfer observation can be explained by the model of charge attachment/detachment from multiple oxygen vacancies/adatoms surrounding Au nanoclusters. These results suggest that the electronic properties of the Au nanoclusters are dramatically influenced by the condition of the support used.

Understanding oxygen adsorption and dissociation on the five-fold coordinated titanium (Ti5c) site of the rutile TiO2 surface is important in clarifying chemical reaction processes. Accordingly, three different configurations of molecularly adsorbed O2, including parallel side-on, inclined side-on and end-on configurations, and their dissociation were directly observed with atomic resolution at 78 K by atomic force microscopy. Our results experimentally demonstrated that the three adsorbed O2 configurations could be changed by electric field stimulation. The initial configurations of the adsorbed O2 and transition of O2 configurations were related to their coverage. On the other hand, the tunneling current stimulation could dissociate these O2 species, indicating that they are precursors for the O adatom (Oad). It is proposed that the effect of electric field stimulation contributes to the transition of these three adsorbed O2 configurations, and the effect of the tunneling current is the main factor for the dissociation of the adsorbed O2. In addition, based on the atomic contrast and height histograms of Oad, different charge states of Oad were observed, which could coexist on the surface region. The present study demonstrates an intuitional observation of O2 adsorption and dissociation on the Ti5c site, and thus is expected to be useful to understand the surface reactions on the oxide surface.

Controllable manipulation of the chemisorbed adsorbates and surface defects on transition metal oxides may provide an efficient means of improving the efficiency of catalytic reactions. Electricall...

In this study, we have systematically characterized and reversibly manipulated the subsurface hydrogen (Hsub) on rutile TiO2(110)-(1 × 1) by a combination of noncontact atomic force microscopy, sca...

Although step structures have generally been considered to be active sites, their role on a TiO2 surface in catalytic reactions is poorly understood. In this study, we measured the contact potential difference around the steps on a rutile TiO2(110)-(1 × 1) surface with O2 exposure using Kelvin probe force microscopy. A drop in contact potential difference was observed at the steps, indicating that the work function locally decreased. Moreover, for the first time, we found that the drop in contact potential difference at a step was larger than that at a step. We propose a model for interpreting the surface potential at the steps by combining the upward dipole moment, in analogy to the Smoluchowski effect, and the local dipole moment of surface atoms. This local change in surface potential provides insight into the important role of the steps in the catalytic reaction.

For the first time, the charge states of adsorbed oxygen adatoms on the rutile TiO2(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: Oad-/2Oad-, Oad2-/2Oad2-, and Oad--Oad2-, i.e., formal charges of either one or two electrons per atom. Because of the strong atomic-scale image contrast, these states are clearly resolved. The observations are supported by measurements of the short-range force and local contact potential difference as a function of the tip-sample distance as well as simulations. Comparison with the simulations suggests subatomic resolution by allowing us to resolve the rotated oxygen p orbitals. In addition, we manage to reversibly switch the charge states of the oxygen adatoms between the Oad- and Oad2- states, both individually and next to another oxygen, by modulating the frequency shift at constant positive voltage during both charging and discharging processes, i.e., by the tip-induced electric field of one orientation. This work provides a novel route for the investigation of the charge state of the adsorbates and opens up novel prospects for studying transition-metal-oxide-based catalytic reactions.

The hydroxyl defects on rutile TiO2 surface play an important role in surface chemical reactions and understanding the catalytic reactions due to its excess electrons. In this work, the reaction be...

The hydrogen on the surface or in the subsurface of rutile TiO2 play an important role in the surface chemical reactions and understanding the catalytic reactions due to its excess electrons. In this work, we have systematically explored the nature of hydrogen atom by atomic force microscopy (AFM)/scanning tunneling microscopy (STM) and investigated the behaviors and mechanism of hydrogen atom desorption and transfer between the surface and subsurface by Kelvin probe force spectroscopy (KPFS). The atomic contrast of surface hydrogen (Hsurf) and subsurface hydrogen (Hsub) are clearly identified by dynamic and static STM. The Hsub-Hsub interactions are systematically investigated, demonstrating the unusual no-repulsive effect of species with the same polarity. Importantly, the reversible hydrogen atom transfer between the sample surface and subsurface was successfully manipulated by KPFS performance, and mechanism of hydrogen transfer proceeds was proposed that force field together with electric field between the tip-sample space reduce the height and width of barrier resulting in the hydrogen atom transfer. The present study is expected to provide some new insights into the nature and manipulation of hydrogen atom and is useful to design the new catalyst of metal oxide.

The strain has been employed for controlled modification of electronical and mechanical properties of two-dimensional (2D) materials. However, the thermal strain-engineered behaviors of the CVD-grown MoS2have not been systematically explored. Here, we investigated the strain-induced structure and properties of CVD-grown triangular MoS2flakes by several advanced atomic force microscopy. Two different kinds of flakes with sharp-corner or vein-like nanostructures are experimentally discovered due to the size-dependent strain behaviors. The critical size of these two kinds of flakes can be roughly estimated at ∼17μm. Within the small flakes, the sharp-corner regions show specific strain-modified properties due to the suffering of large tensile strain. While in the large MoS2flakes, the complicated vein-like nanoripple structures were formed due to the interface slipping process under the larger tensile strain. Our work not only demonstrates the size-specific strain behaviors of MoS2flakes but also sheds light on the artificial design and preparation of strain-engineered nanostructures for the devices based on the 2D materials.

We developed a versatile Quasi-finite-element scanning method to analyse the concentration and homogeneity of the ensembles of nitrogen-vacancy (NV−) centres in block diamonds. In this method, 13 μ m × 13 μ m area of the bulk diamond with high-density NV− centres was divided into small pieces at the nanoscale by using a focused light beam. The concentration of NV− centres was obtained and imaged through the fluorescence intensity of each pixel by employing a home-built spectrometer. In addition, global and local homogeneities were introduced to evaluate the NV− centre distribution. NV− centres in a specific pixel exhibited preferred direction growth peaks attributed to the diamond crystal orientation. Moreover, the uniformity of NV− centres was not proportional to the electron irradiation duration, but an optimal time was observed. This study can be beneficial for enhancing the sensitivities of bulk magnetometry based on confocal systems.

Recently, we achieved atomic-resolution optical imaging with near-field scanning optical microscopy using photon-induced force detection. In this technique, the surface photovoltage of the silicon-tip apex induced by the optical near field on the surface is measured as the electrostatic force. We demonstrated atomicresolution imaging of the near field on the α-Al2O3 (0001) surface of a prism. We investigated the spatial distribution of the near field by scanning at different tip-sample distances and found that the atomic corrugation of the near-field signal was observed at greater distances than that of the atomic force microscopy signal. As the tip-sample distance increased, the normalized signal-to-noise ratio of the near field is in a gradual decline almost twice that of the frequency shift (Δf).

We experimentally observed the dynamic behavior of OH on the Ti site (OHt) of TiO2(110) at 78 K in detail by atomic force microscopy (AFM). OHt was imaged as a dimer shape or a fuzzy round shape corresponding to the motion of OHt that OHt swings along the [1–10] direction. The frequency of swing positively responds to the applied bias voltage between the tip and the sample, and it is proposed that the applied bias voltage decreases the barrier of the OHt transition between two or more equilibrium states. Such specific response of OHt to the applied bias voltage can be used as the fingerprint. In addition, the atomic contrast of O adatom (Oad) and OHt is compared with the contrast of other surface species by AFM, and it is demonstrated that the contrast of Oad and OHt is similar to the contrast of the surface defects due to the effect of tip apex polarity. H atom desorption of OHt is performed by Kelvin probe force spectroscopy, and it is resulted from the reduction of barrier width together with the tunneling electron excitation. The present study is expected to be useful to explore the property of H-involved species and the surface reactions on the oxide surface by AFM.

Oxygen adatom on rutile TiO2(1 1 0)-(1 × 1) surface was imaged by atomic force microscopy (AFM) with atomic resolution. The atomic contrast inversion of oxygen adatom is dependent on tip-sample distance and can be obtained in both constant frequency shift and constant height mode. The origin of contrast inversion was analyzed, combining the effect of adsorbed species, feedback loop and tip apex structure. Experimental frequency shift versus distance curves around O adatom show that there is a turning-point in the constant frequency shift mode and a cross-point in the constant height mode. The repulsive force is thought to contribute to the contrast inversion of oxygen adatom. The present results show the origin of contrast inversion of oxygen adatom on rutile TiO2(1 1 0)-(1 × 1) surface and illustrate the importance of tip-height for the atomic contrast inversion of the surface adsorbate on the metal oxide surface.

Transition-metal-oxide as a typical model surface for investigating the catalytic mechanism has been widely studied. Over the past years, the TiO2 properties have been reported. It is commonly accepted that the catalytic activity of reduced TiO2 is related to its defects, with the accompanying excess electrons leading to n-type conductivity. It is realized that subsurface charge is of key importance for the redox chemistry of TiO2 (110).Subsurface charge is explored by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). Subsurface charge exerts an additional attractive force on the scanning AFM tip, resulting in the relative retraction of tip motion in order to keep a constant frequency shift. As a result, the subsurface charged region is imaged as protrusion in an AFM topographic image. The height of bright hillock is mainly distributed in three different ranges, which means that the subsurface charges are at three different subsurface layers. The AFM results show such subsurface charges repel the electropositive oxygen vacancy, hydrogen atoms and step edges. It is obvious that there is not only an Ov depletion zone but also the subsurface charge free region in the proximity of the \begin{document}$\left\langle {001} \right\rangle $\end{document} and \begin{document}$\left\langle {1\bar 11} \right\rangle$\end{document} step edge.The KPFM image indicates that the subsurface charges are the positive charges. which is consistent with common sense. After oxygen exposure, it is found that the oxygen adatom is electronegative, but it is absent in the vicinity of positive subsurface charges. Irrespective of adsorbate being electropositive or electronegative, an adsorbate-free zone generally exists in the proximity of the charged region. Obviously, the present study is expected to provide some insights into clarifying the nature of subsurface charge and improving catalytic design.

Interfacial engineering, such as molecule intercalation, can modify properties and optimize performance of van der Waals heterostructures and their devices. Here, we investigated the pristine and water molecule intercalated heterointerface of niobium disulphide (NbS2) on hexagonal boron nitride (h-BN) (NbS2/BN) using advanced atomic force microscopy (AFM), and observed the metal-insulator transition (MIT) of first layer (1L-) of NbS2 induced by water molecule intercalation. In pristine sample, interfacial charge transfers were confirmed by the direct detection of trapped static charges at the post-exposed h-BN surface, produced by mechanically peeling off the 1L-NbS2 from the substrate. The interfacial charge transfers facilitate the intercalation of water molecules at the heterointerface. The intercalated water layers make a MIT of 1L-NbS2, while the pristine metallic state of the following NbS2 layers remains preserved. This work is of great significance to help understand the interfacial properties of 2D metal/insulator heterostructures and can pave the way for further preparation of an ultrathin transistor.

We present an experimental study of coexisting p(2 × 1) and c(6 × 2) phases on an oxygen-terminated Cu(110) surface by noncontact atomic force microscopy (NC-AFM) at 78 K. Ball models of the growth processes of coexisting p(2 × 1)/c(6 × 2) phases on a terrace and near a step are proposed. We found that the p(2 × 1) and c(6 × 2) phases are grown from the super Cu atoms on both sides of O-Cu-O rows of an atomic spacing. In this paper, we summarize our investigations of an oxygen-terminated Cu(110) surface by NC-AFM employing O- and Cu-terminated tips. Also, we state several problems and issues for future investigation.

The authors integrated the frequency modulation (FM) technique into multifrequency atomic force microscopy (AFM). Based on theoretical considerations, simultaneous excitation of the cantilever oscillation at the first and second flexural modes allows us to acquire the surface topography and surface elasticity simultaneously. The authors performed multifrequency FM-AFM observation using a tungsten-coated silicon cantilever on a Ge(001) surface exhibiting a dimer structure at room temperature. The topography and the elasticity of the surface were successfully obtained at the atomic scale. The authors found that the dimer atoms around a missing dimer defect have higher elasticity than the other dimer atoms. This suggests that stiffer atomic bonding of the dimer atoms occurred as a result of the additional tensile strain field from the defect. Therefore, the multifrequency FM-AFM described in the present study is expected to be useful for the investigation of the surface elasticity at the atomic scale.

Extension of AFM-based viscoelasticity measurement into a frequency-resolved analysis is attempted. A cantilever immersed into and interacting with distilled water was employed for the trial system. Using a home-built wideband magnetic excitation AFM, a step force with a transient time less than 1 μs is applied to the AFM cantilever and its deflection is measured. The 1st and 2nd mode resonance ringing of the cantilever was suppressed using quality-factor-control technique, so that the measurement system becomes equivalent to driving a resonance-free virtual cantilever within the bandwidth limited by the surviving 3rd mode resonance. From the obtained response of the cantilever deflection, a frequency-dependent complex compliance of the cantilever-water system was derived in a frequency range of 1–100 kHz. Effect of water confining between the tip and a mica substrate is discussed.

The characterization of mobile charge carriers of semiconductor materials has spurred the development of numerous 2D carrier profiling tools. Here, we investigate the mobile charge carriers of several samples by multi-harmonic electrostatic force microscopy (MH-EFM) and scanning microwave impedance microscopy (sMIM). We present the basic principles and experiment setups of these two methods. And then several typical samples, i.e. a standard n-type doped Si sample, mechanical exfoliation and chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) layers are systemically investigated by sMIM and MH-EFM. The difference and (dis)advantages of these two modes are discussed. Both modes can provide carrier concentration profiles and have sub-surface sensitivity. They also have advantages in sample preparation in which contact electrodes are not required and insulating or electrically isolated samples can readily be studied. The basic mode, physics quantities extracted, dielectric response form and parasitic charges in scanning environment result in difference experiment results of these two kinds of methods. The techniques described in this study will effectively promote research on basic science and semiconductor applications.

Formation of an oxidized overlayer onto Cu(1 1 0) surface was examined by means of noncontact atomic force microscopy at oxidation temperature ranging from RT to 610 °C and an O 2 exposure from 10 4 to 10 5 L. Atomic resolution images of an c(6 × 2) reconstruction exhibited different contrasts from those obtained in STM studies and coincided well with the presented structural model. The surface oxidized at RT in the present exposure range exhibited a rough morphology, and was observed to undergo a partial transition to the c(6 × 2) structure at 25,000 L. At an oxidation temperature of 360 °C an well-ordered c(6 × 2) reconstruction was observed to cover the entire terrace irrespective of the exposure amount. Characteristic point defect was also imaged on this surface in detail. At an oxidation temperature of 610 °C a (2 × 1) reconstruction was observed to coexist on the same terrace with c(6 × 2). Formation mechanism of this coexistence phase in this high temperature regime is discussed.

Noncontact atomic force microscopy (NC-AFM) using frequency modulation detection method has been widely used to investigate the various surfaces with atomic resolution. In this paper, we introduce the measurement technique of NC-AFM operating at low temperatures (LTs). First, we theoretically discuss the enhancement of the force sensitivity in NC-AFM operating at LTs. Then, we present the design and performance of LT-NC-AFM using fiber optic interferometer with quick sample and cantilever exchange mechanism. We also show the present status of the LT-NC-AFM imaging. In detail, we show the experimental results to investigate the influence of the surface stress around an SA step of Si(001) surface onto the buckled dimer at 5 K. We demonstrate that the LT-NC-AFM has a capability to detect the surface stress with atomic resolution.

Recently we have found that phase modulation atomic force microscopy (PM-AFM) has higher force sensitivity than amplitude modulation AFM (AM-AFM). The Q-control technique which is often utilized in AM-AFM allows to increase the effective Q-factor of the cantilever. In this study, we utilize the technique to PM-AFM and investigate the force sensitivity with and without the technique theoretically as well as experimentally. We show that the force sensitivity in PM-AFM is highly improved by the Q-control technique.

Ultrathin alumina film formed by oxidation of NiAl(110) was studied by non-contact atomic force microscopy in an ultra high vacuum at room temperature with the quest to provide the ultimate understanding of structure and bonding of this complicated interface. Using a very stiff Si cantilever with significantly improved resolution, we have obtained images of this system with unprecedented resolution, surpassing all the previous results. In particular, we were able to unambiguously resolve all the differently coordinated aluminum atoms. This is of importance as the previous images provide very different image patterns, which cannot easily be reconciled with the existing structural models. Experiments are supported by extensive density functional theory modeling. We find that the system is strongly ionic and the atomic force microscopy images can reliably be understood from the electrostatic potential which provides an image model in excellent agreement with the experiments. However, in order to resolve the finer contrast features we have proposed a more sophisticated model based on more realistic approximants to the incommensurable alumina interface.

We succeeded in distinguishing between oxygen and silicon atoms on an oxygen-adsorbed Si(111)7 x 7 surface, and also distinguished between silicon and tin atoms on Si(111)7 x 7-Sn intermixed and Si(111) square root(3) x square root(3)-Sn mosaic-phase surfaces using non-contact atomic force microscopy (NC-AFM) at room temperature. Atom species of individual atoms are specified from the number of each atom in NC-AFM images, the tip-sample distance dependence of NC-AFM images and/or the surface distribution of each atom. Further, based on the NC-AFM method but using soft nanoindentation, we achieved two kinds of mechanical vertical manipulation of individual atoms: removal of a selected Si adatom and deposition of a Si atom into a selected Si adatom vacancy on the Si(111)7 x 7 surface at 78 K. Here, we carefully and slowly indented a Si atom on top of a clean Si tip apex onto a predetermined Si adatom to remove the targeted Si adatom and onto a predetermined Si adatom vacancy to deposit a Si atom, i.e. to repair the targeted Si adatom vacancy. By combining the atom-selective imaging method with two kinds of mechanical atom manipulation, i.e. by picking up a selected atom species and by depositing that atom one by one at the assigned site, we hope to construct nanomaterials and nanodevices made from more than two kinds of atom species in the near future.

Kelvin probe force microscopy (KPFM) using noncontact atomic force microscopy (NC-AFM) has been utilized for years and has achieved true atomic-scale resolution in the measurement of contact potential difference (CPD). However, the meaning of atomic-scale CPD images has not been clearly explained. In this paper, we propose a novel model which explains the imaging mechanism of atomic-scale KPFM. Our model shows that the cantilever oscillation induced by an AC electric field, which is applied for KPFM measurement, brings about the atomic resolution in CPD images. We show experimental evidence of our model by measuring the dependence of the cantilever oscillation and the frequency-shift signal on the tip-sample distance. We conclude that the CPD images reflect the interaction strength between the tip and the sample surface rather than the electrostatic force. Finally, we propose a novel method for force mapping based on our model.

We investigate the possibility of distinction of individual atom species using noncontact atomic force microscopy (NC-AFM) combined with the electrostatic force (ESF) measurement. We simultaneously measured the topography and the surface potential on the Si(1 1 1) 5 3 ×5 3 -Sb surface by Kelvin probe force microscopy (KPFM). The surface potential image indicates the existence of two kinds of adatoms while the difference is not clear in topography. Atom species of each adatom are specified from other NC-AFM images with different experimental conditions and therefore spots with a lower surface potential are specified as Si adatoms. It is found that, in addition to adatoms, Si rest atoms can be specified from the surface potential image. The result indicate that KPFM has the ability to distinguish the individual atom species on intermixing surfaces.

We investigated performances and functions of the noncontact atomic force microscope (NC-AFM) method. As a result, we found that the NC-AFM functions not only as the atomic resolution microscope but also novel atomic tools based on a mechanical method as follows; a three-dimensional mapping tool of atomic force between the tip and sample atoms, a discrimination tool of atomic force mechanisms and atom species of the sample surface, a control tool of atomic force and atom position on the sample surface, and an atom manipulation tool. [DOI: 10.1380/ejssnt.2003.158]

Atomically resolved imaging of Si(100)2×1-clean, Si(100)2×1:H-monohydride and Si(100)1×1:2H-dihydride surfaces using a noncontact atomic force microscope (NC-AFM) is reviewed. These experimental results clarify that our original NC-AFM had lateral resolution of about 0.01 nm and could image tilted dangling bonds of the Si(100)2×1-clean surface, individual hydrogen atoms of the Si(100)2×1:H-monohydride surface, and atomic strain around missing dimers of the Si(100)2×1-clean surface. In addition, the NC-AFM image pattern of the Si(100)1×1:2H-dihydride surface can be changed from 1×1 through 2×1 to 1×1 by decreasing the tip-sample distance. From these results, it was concluded that the NC-AFM could mechanically induce phase transition of surface reconstruction from the Si(100)1×1:2H to Si(100)2×1:2H-dihydride surface due to self-organization, and could also pull up the nearest hydrogen atoms one by one by increasing the attractive force between the tip apex atom and sample surface atom.

We demonstrated the possibility of measuring the three-dimensional force-related map with true atomic resolution between an Si tip and Si(1 1 1)√3×√3–Ag sample surface by measuring the tip–sample distance dependence of noncontact atomic force microscope (NC-AFM) image, i.e. atomically resolved atomic force spectroscopy. Furthermore, we demonstrated the possibility of controlling the interaction force between the atom on the tip apex and a sample atom of Si(1 1 1)√3×√3–Ag surface on an atomic scale by placing an Ag atom on the Si tip apex instead of Si atom.

We investigate the ‘artifact’ included in Kelvin probe force microscopy (KPFM). We theoretically show that the artifact due to the applied AC field cannot be canceled by conventional KPFM and that the artifact signal can be detected from the force signal through the second harmonic component of AC field. We made an experiment to simultaneously obtain the topography, the spatial distribution of the surface potential and the artifact signal on Si(1 1 1) surface using our noncontact atomic force microscope (NC-AFM). The result indicates that topography includes the artifact signal and that the surface potential image reflects the charge density of Si adatoms. We propose the novel method to completely eliminate the artifact due to the electrostatic force.

We investigate the capability of single atom manipulation using the noncontact AFM operating low temperatures. Here, for the first step of atom manipulation, we try to perform the vertical manipulation. By applying the bias voltage between Si (1 1 1)7×7 surface and the tip of the conductive AFM cantilever, we succeed in removing the adatoms from the surface for the first time. This experimental result opens a new research field with the noncontact AFM. Furthermore, by analyzing the noncontact AFM images measured on Si (1 1 1)7×7 surfaces, we propose a model for the atomic arrangement of the Si tip apex with an asymmetric ad-dimer.

We observed atomic resolution images of the Si(1 0 0) surface at 5 K using low-temperature noncontact atomic force microscope (LT-NC-AFM). Si(1 0 0) surface shows almost the asymmetric dimers structure, except for the symmetric dimers structure near the defects. The asymmetric dimers are mainly c(4×2) structure with antiparallel zigzag pattern and partly p(2×2) structure with parallel zigzag pattern.

We investigated the Si (1 0 0)1×1 :2H dihydride surface using the noncontact atomic force microscopy (NC-AFM). NC-AFM images showed that the pattern of the dihydride surface changed depending on the distance between the tip and the sample surface. The image with 1×1 structure appeared when the tip was a little far from the sample surface. When the tip became close to the surface, 2×1 structure where the bright lines and the dark lines were alternately located appeared. This 2×1 image was stable for retracting the tip from the surface. Furthermore, when the tip became close to the surface, 1×1 structure reappeared. It turned out that the structures of the dihydride surface changed due to the attractive force between the tip and the sample under NC-AFM measurement.

In this review article, we clarified what we can image on semiconductor surfaces using noncontact atomic force microscopy (NC-AFM): 1. We can image covalent bonding force on Si(111)7×7 surface. 2. We can discriminate Si adatoms from Sb adatoms on Si(111)5√3×5√3-Sb surface with a Si tip and a Sb adsorbed tip. 3. We can image tilted dangling bond on Si(100)2×1 surface. 4. We can image individual hydrogen atom on Si(100)2×1:H monohydride surface. 5. We can measure atomic strain around missing dimer. 6. We can image a potential map on Si(111)√3×√3-Ag surface by measuring NC-AFM image as a function of tip-sample distance. 7. We can selectively control atomic force by placing an adequate atom on the tip apex. 8. We can pull up lower Si atoms constituting buckled Si dimer by increasing attractive force between tip and sample surface.

Manipulation is the most exciting feature of the non-contact atomic force microscopy technique as it allows building nanostructures on surfaces. Usually vertical manipulations are accompanied by an abrupt tip modification leading to a change of contrast. Here we report on low-temperature experiments demonstrating vertical manipulations of 'super'-Cu atoms on the p(2 × 1) Cu(110):O surface, both extractions to and depositions from the tip, when the imaging contrast remains the same. These results are rationalized employing a novel and completely general method that combines density functional theory calculations for obtaining energy barriers as a function of tip height and a Kinetic Monte Carlo algorithm for studying the tip dynamics and extraction of manipulation statistics. The model reveals a novel multi-step manipulation mechanism combining activated jumps of 'super'-Cu atoms to/from the tip with their drag by and diffusion on the tip.

We investigated elementary processes of microscopic contact charging and charge dissipation on and in thin silicon oxide using a reproducible and controllable contact charging method. As a result, we found that negative charges have three stages of contact charging and charge dissipation, while positive charges have only one stage. By continuing with the contact charging, negative charges became high density, i.e. a solid phase of charges, on the silicon oxide surface at room temperature in air. Furthermore, we succeeded in imaging point charges on n+-GaAs(110) cleaved surfaces with atomic resolution using a modified non-contact atomic force microscope.