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In this article, two alternative experimental strategies for reaching light confinement at metallic nanotips are discussed. The first approach utilizes optical field enhancement to localize nonlinear optical signals at the tip end. The second approach employs surface plasmon polaritons propagating coherently along the tip shaft and converging at its apex.

Near-field optical microscopy enables spectroscopic and imaging measurements with a spatial resolution far beyond the diffraction limit of light. We show in this review that spatial structures of plasmonic wavefunctions and those of enhanced optical fields are visualized by near-field spectroscopic imaging for gold nanoparticles and their assemblies. A simple formulation for the optical observation of wavefunctions of oscillating polarization modes in nanomaterials is given. We will introduce experimental methods for near-field linear transmission and nonlinear two-photon excitation measurements. We will demonstrate that the wavefunctions of surface plasmons resonant with the incident wavelength are visualized by the near-field methods for gold nanorods. In addition, we will also show for aggregated gold nanospheres that an enhanced optical field is localized in the interstitial gaps between the particles by near-field two-photon excitation measurements.

Scanning tunneling microscopy (STM) has greatly contributed to the field of surface science over the past two decades. Today, the STM is a powerful instrument contributing to the study of emerging research directions in nanoscience. With a suitable choice of STM manipulations combined with tunneling spectroscopy and imaging, experiments can be tailored to investigate electronic, structural, and mechanical properties specific to atoms, molecules, and nanosystems. In this article, the basic STM manipulation schemes are explained and some examples of STM manipulation experiments related to the atomistic constructions and mono-molecular devices are described.

Modern functional materials and devices require thorough testing for safety and reliability. Here, we describe solutions to meet this requirement in the field of scanning probe microscopy, and the most practical approach among them; ultrasonic atomic force microscopy (UAFM). In this review, we focus on evaluation of subsurface defects with scientific and technological importance, such as domains of ferroelectric materials and subsurface delamination of metal electrodes on microdevices. In addition, we show the development and application of the lateral bending (LB) mode and lateral modulation atomic force microscopy (LM-AFM) with applications in nanomaterials including carbon nanotube composites and discuss their future development in combination with UAFM.

The present study reports for the first time the mapping of elastic stiffness of different phases in a structural metallic material with lateral resolution of less than 100 nm. The distribution of elastic stiffness across the α, β, and α' phases in Ti–6Al–4V alloy has been studied using atomic force acoustic microscopy. The experimentally obtained indentation modulus values for the various phases in the titanium alloy are compared with those estimated in literature. The effect of crystallographic orientation of phases on the indentation modulus is also discussed.

The structure of Fe films grown on Ni(111) with an Fe coverage of 3.2 monolayers and its conversions during heating in ultrahigh vacuum have been investigated by scanning tunneling microscopy (STM). The Fe films consist of elongated domains stacked with four to six monatomic layers of Fe, forming ridgelike structures. A phase transition from fcc(111) to bcc(110) with the Nishiyama–Wassermann orientation relationship occurs from at least the third monatomic layer. A triangular network structure and large accumulated bcc-Fe islands are formed on the surface after heating the Fe films at 550 K. The network is considered to be misfit dislocation loops caused by the lattice misfit between the fcc-Fe films and the Ni substrate. A surface structure consisting of two distinct randomly distributed spots and a well-ordered (5 ×5) superstructure are observed after further heating at 620 and 700 K, respectively, and they are caused by the formation of the Fe–Ni surface alloy on the Ni(111) surface.

The distance between bright spot in a dimer on the Si(100)-(2×1) surface imaged by noncontact atomic force microscopy (NC-AFM) is analyzed. We used in the analysis only high-spatial-resolution topographic NC-AFM images obtained using different tips at room temperature. Atoms in the dimer was clearly resolved, which enabled us to analyze the distance between two bright spots in the dimer statistically. The average distance was similar to that obtained in a previous study and the theoretical predition. The results indicated that dimer flipping was induced by the AFM tip during scanning and upper–upper atoms are imaged at room temperature.

A Ni₂P(0001) single crystal surface has been studied in the framework of model catalysis with a low temperature scanning tunneling microscope (STM) under ultrahigh vacuum (UHV). We observed a previously unreported (√3×√3) R30° reconstruction and successfully recorded its atomically-resolved STM images. Two types of atomic arrangements have been found for this (√3×√3) R30° structure depending on annealing conditions during preparation. One shows a filled and the other one an empty network of polygons. Upon annealing to 940 K, only the latter empty type of structure has been observed.

We have simulated noncontact atomic force microscopy on benzene-molecule-adsorbed Si(001) surfaces using the density-functional based tight-binding calculation. We show that three adsorption structures, namely, the standard butterfly, the tight bridge, and the twisted bridge, can be distinguished from topographic line profiles along directions perpendicular and parallel to the Si dimer row. The atomic configuration does not change markedly during the noncontact atomic force microscopy line scan even when the tip almost contacts the surface, which suggests that a stable adsorbed structure hardly changes to another stable structure at zero temperature.

Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM) are applied to investigate the composition and morphology of the Cu–9 at. % Al(111)-(√3×√3)R30° superstructure. We found that the Al concentration on the topmost layer is about 41 at. %. STM reveals that segregated Al atoms are partially consumed to form the (√3×√3)R30° structure and the excess Al atoms are randomly distributed on the surface. Moreover, STM resolves a superposition of the (√3×√3)R30° structure and standing waves. The surface Fermi wave number is obtained as 0.39 ±0.04 Å^-1 by analyzing the Fourier transform of STM images.

We investigate the electronic properties of c(3√2×√2)R45°-C-reconstructed Cr(001) thin-film surfaces by scanning tunneling microscopy and spectroscopy (STM/STS). We previously observed that c(3√2×√2)R45°-C/Cr(001) thin-film surfaces yield two types of STM image, line structures along the Cr<110> direction and an atomically resolved image, and discussed interpretations of the STM images in detail in a previous paper [Jpn. J. Appl. Phys. 46 (2007) 5602]. Here, STM measurements reveal that the top and bottom sites of the line structures correspond to the Cr atoms within and between C zig-zag chains in the atomically resolved STM image, respectively. An STS study indicates that dI/dV spectra taken on the top and bottom sites show a single peak at +0.15 eV and a main peak at +0.15 eV with a shoulder at +0.32 eV, respectively.

The structure of the Si(553) surface, tilted at -12.27° toward the (001) plane from the (111) plane, has been studied by scanning tunneling microscopy (STM). The STM images reveal that the Si(553) surface consists of (111) and (331) facets. The (111) facet is composed of a single unit cell of 7×7 (or 5×5) structure, while the (331) facet is composed of a 1×1 structure. As the results of high-temperature STM (HT-STM) observations at 600 °C show a noise-like glimmering pattern due to atomic migration is observed around the (331) facet.

We have demonstrated that chemical states on the anode-oxidized Si surfaces prepared by atomic force microscopy (AFM) can be controlled by selecting the appropriate applied voltage for the oxidation. The frictional force on the oxidized surface formed at relatively low voltages (4.5–9 V) was large, whereas that at relatively high voltages (9–10 V) was small. This is due to a difference in the hydrophilicity of the surfaces. Octadecyltrichlorosilane (OTS) films were formed only on the oxidized surface prepared at the low voltages. Since OTS molecules require OH groups to form a film, the hydrophilicity originates from OH group termination of the surfaces. Therefore, the oxide surface is terminated with OH groups when the applied voltage is relatively low. When the applied voltage is relatively high, it is speculated that the oxide surface is covered with Si–O–Si groups instead of OH groups.

We studied local optical properties of Si-doped GaAs(110) surface by scanning tunneling microscope cathodoluminescence (STM-CL) spectroscopy, where low-energy (∼100 eV) electrons field-emitted from STM tips were used as bright excitation sources. Each STM-CL spectrum of the GaAs surface showed a sharp GaAs band-edge emission peak and a broad peak at ∼1 eV related to Si clusters composed of Si impurities and vacancies. The intensity ratio of the sharp peak to the broad peak in the STM-CL spectrum depended on the measurement position under the same excitation density. This locality is considered to be originated from the local Si cluster concentration. We also observed the correlation between the redshifts of the band-edge emission peaks and high Si impurity concentrations. Our study demonstrated that STM-CL spectroscopy is a useful tool to evaluate the local Si cluster concentration with high spatial resolution.

We have investigated laser-induced light emission from Au film evaporated on the bottom of a hemispherical glass prism in the Kretschmann geometry. Picosecond laser pulses tuned at a photon energy of 1.35 eV were focused onto the Au film from the vacuum side of the prism, and the time- and photon-energy-resolved spectra of light emitted through the prism were measured in a photon energy range from 1.5 to 2.5 eV for a time span of 2 ns by a streak camera operated in synchronization with the laser pulses. The total intensity of emission was proportional to the square of incident laser power, suggesting that the emission is excited via a second order nonlinear optical process. The time-integrated spectrum of the emission was successfully reproduced by the dielectric theory of light emission that treats radiation by surface plasmon polaritons (SPP) confined in this sample structure. Hence we see that the emission is radiated by SPP being excited via the nonlinear optical process. This feature is not consistent with the temporal behavior of emission, i.e., the lifetime of the emission was as long as 240 ps.

Surface photovoltage (SPV) was visualized over the interface of a GaAs p–n junction using light modulated scanning tunneling spectroscopy. Spatially resolved SPV includes information about the built-in potential of the p–n junction as well as the photo-induced relaxation of tip-induced band bending. These two components were separately evaluated, and mapping of the built-in potential was accomplished on the nanoscale.

We have developed high-speed phase-modulation atomic force microscopy (PM-AFM) in a constant-amplitude (CA) mode. Using this imaging mode, we have theoretically demonstrated that energy dissipation due to tip–sample interaction can be obtained from the excitation amplitude of a cantilever. Moreover, we have found that the photothermal excitation method is better than the acoustic excitation method for cantilever oscillation in liquids. For the first time, we have demonstrated that a homebuilt high-speed PM-AFM in the CA mode has the capability to simultaneously measure the topography and energy dissipation with a material-specific contrast for a PS/PIB polymer-blend film.

In frequency modulation atomic force microscopy (FM-AFM), the average interaction force is detected as the frequency shift of the oscillating cantilever. Therefore, it is desirable to oscillate a cantilever with a small amplitude in order to achieve a high resolution. However, the oscillation may become unstable or the tip may jump into a static contact unless a cantilever with a high spring constant is used. In this study, we used a silicon cantilever with a spring constant as high as 700 N/m, which is far larger than those for conventional FM-AFM. We demonstrated molecular-resolution FM-AFM on lead phthalocyanine thin films with an oscillation amplitude of 2 nm.

An atomic force microscopy (AFM) probe tip characterizer with 14 line and space structures and two knife edges was fabricated by means of a superlattice technique. The shape of a probe tip both before and after AFM imaging was acquired by this tip characterizer with general variations <1.5 nm; depending on imaging conditions. The geometric structures of carbon nanotubes (CNTs) on a SiO₂ substrate were studied by dynamic mode AFM in conjunction with this tip characterizer. Contact points between the tip and the CNTs were detected by observing changes in the AFM phase images. A modified CNT width correction model was established to calculate the estimated and upper-limit widths of two CNTs. The experimental results showed that imaging under a weak attractive force was suitable for obtaining accurate CNT height measurements, whereas a weak repulsive force provided the most accurate widths. Differing heights and widths between the two CNTs suggested that one CNT was double-walled, whereas the other had more than two walls; these results agree with transmission electron microscopy (TEM) measurements of the CNTs.

In this paper, we describe the mechanical interaction between the vibrating tip of an atomic force microscope (AFM) and carbon nanotubes (CNTs) suspended over a trench on a Si wafer. The interaction was detected by recording the oscillation amplitudes of the cantilever tip above the suspended CNTs during both tip-down and tip-up processes. We refer to the oscillation amplitude versus tip vertical position as a force curve. In the force curve obtained in air, the mechanical response of a CNT bundle under a periodic external force applied by the tip is interpreted as a simple model that includes the attachment/detachment of the CNTs onto the tip surface and the oscillation of the CNTs fixed to the tip. The curve obtained in water has features similar to that obtained in air. The difference between the force curves obtained in air and in water suggests that the adhesion force between the AFM tip and CNTs is weaked in water than in air.

One-dimensional (1D) iron silicides prepared under various growth conditions have been studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS). The nanowires (NWs) are formed in an ultrahigh vacuum (UHV) of below 5.0×10^-8 Pa by solid-phase epitaxy (SPE) or reactive-deposition epitaxy (RDE). The sizes of the NWs obtained by SPE and RDE are 1.0–2.0 nm (height) × 6–15 nm (width) × 20–120 nm (length) and 2.0–4.0 nm (height) × 15–20 nm (width) × 100–1000 nm (length), respectively. The difference in shape is briefly discussed on the basis of the nucleation and growth theory. A similar chemical shift in XPS spectra is observed on both surfaces, corresponding to iron disilicide. NWs are also formed even in a high vacuum (HV) of below 4.0×10^-4 Pa at 600 °C, the morphology of which is characterized by cross-sectional TEM, which clearly shows endotaxial growth.

Using a time-averaged dielectrophoretic force from an applied electric field, we have observed the assembly of a chemically adsorbed monomolecular layer (CAM) on microwires and connections and the formation of an electric path between a lithographically patterned array of two platinum (Pt) electrodes. A Pt electrode/monolayer/Pt electrode junction was fabricated by the self-assembly of a rigid monomolecular layer, namely 3-{6-[11-(trichlorosilyl)undecanoyl]hexyl} thiophene (TEN) with thiophene groups in the lateral direction between the Pt electrodes. Conductive probe AFM (CP-AFM) was used to investigate the forward bias conduction properties of a TEN film grown by a wet deposition process on a glass substrate. The self-assembly depends on the ideal rigidity of the CAM and the strong affinity of the thiophene end groups of the CAM for the Pt electrode. The current–voltage (I–V) characteristics of the conjugated thiophene junction exhibited stepwise features at room temperature. The I–V characteristics can be explained by electron transport through the junction. From the results of experiments carried out under ambient conditions, the conductivity of the laterally conjugated polythiophene groups was calculated to be 5.0 ×10⁴ S/cm. Understanding and using these effects will allow the controlled fabrication and positioning of microwires or connections at densities much greater than those now achievable.

The surface forces between a polystyrene particle (negatively charged surface) of latex and a flat silica plate for several concentrations of aqueous solution of anionic amphipathic molecules (sodium dodecylsulfonate) were investigated using an atomic force microscope (AFM) colloidal probe method. In the lower concentration region approximately 1–2 mM, the surface force showed general repulsive profiles according to normal Derjaguin–Landau–Verwey–Overbeek (DLVO) theory between the surfaces having the same sign of surface charge under an electrolyte aqueous solution. While in the higher concentration region at less than the critical micelle concentration (cmc), the surface force showed attractive profiles. Findings suggest that the anionic amphipathic molecules adsorbed to the polystyrene particle in the higher concentration region and induced changes in the surface morphology and properties of the surface region. The change in the surface morphology is believed to be one of the origins of the attractive interaction.

The rutile titanium dioxide (TiO₂) (110) surface exposed to Cl₂ gas was examined using scanning probe microscopes. The Cl adatoms formed by Cl₂ dissociation were observed as bright spots in empty-state scanning tunneling microscope images. While 94% of the Cl adatoms were on the top of surface Ti atoms, the remaining 6% of the adatoms missed the on-top site. The Kelvin probe force microscope measurements revealed a local work function increase on the Cl adatoms. The electronegative Cl adatoms were proposed to accumulate electrons from the surface. The resultant dipole moments were directed from the vacuum to the surface, and hence the work function of the adatoms locally increased.

The chemical reaction of a glycine molecule on a Cu(100) surface from the neutral (NH₂CH₂COOH) to the glycinate (NH₂CH₂COO^-) form via deprotonation, which had been analyzed on the basis of the results obtained by, for example, vibrational spectroscopy and diffraction methods, was studied at the single-molecule level by scanning tunneling microscopy (STM) and spectroscopy. The chemical reaction was successfully reproduced by the inelastic tunneling process thorough deprotonation. The threshold bias voltage for the reaction process could be attributed to the energy of the O–H stretch vibrational mode, and the asymmetric STM image after the reaction was in good agreement with the structure based on the predicted model.

We have studied the self-assembled monolayers (SAMs) of adamantane-based trithiolate, which consists of a ferrocene derivative at the head (ferrocene adamantane trithiolate; ferrocene-ATT), on Au(111) using low temperature scanning tunneling microscopy (STM). It was found that the adsorption behavior of ferrocene-ATT is similar to that of bromine adamantane trithiolate (BATT) adsorbed on Au(111). This indicates that adsorption of adamantane-based trithiol is controlled by three legs (CH₂S) connected to bridgehead positions of the adamantane cage. Molecules, which form an ordered structure, are stable under low-bias-voltage scanning, i.e., a sample bias voltage lower than 1 V. STM tip-induced diffusion, however, was observed both for small clustered molecules and for molecules bound around the edge of an ordered molecular island. Furthermore, applying a high bias voltage (5 V) resulted in the destruction of SAMs structures.

We fabricated a Co (cobalt metal) core particle structure using a low-energy Ar⁺ ion beam. A monolayer of Co core ferritin molecules (CoO: cobalt oxide) was adsorbed on the silicon substrate. Bombardment energy was optimized using Ar gas after the protein of the monolayer was eliminated with UV/O₃. The Ar⁺ ion beam enabled the complete reduction, when the irradiation time of ion beam was 60 s. We reduced the core particles to conductive Co nanoparticles. X-ray photoelectron spectroscopy (XPS) measurements confirmed the reduction of the cores. As a result, the diameter of the Co–ferritin nanostructure became 7 nm, which was not identical to that of the cobalt core in the ferritin after the ion beam bombardment. In addition, the Kelvin probe force microscopy (KFM) profiles of the CoO and Co cores obtained. It is relatively easy to fabricate such a fine structure of Co cores using conventional low energy Ar⁺ beam processes. The results obtained here will open a new field that combines semicoductor technology and biotechnology.

Lipid vesicle fusion is an important reaction in the cell. Calcium ions (Ca²⁺) participate in various important biological events including the fusion of vesicles with cell membranes in cells. We studied the effect of Ca²⁺ on the fusion of egg yolk phosphatidylcholine/brain phosphatidylserine (eggPC/brainPS) lipid vesicles on a mica substrate with fast scanning atomic force microscopy (AFM). When unattached and unfused lipid vesicles on mica were rinsed away, discrete patches of fused vesicles were observed under high Ca²⁺ concentrations. At 0 mM Ca²⁺, lipid vesicles were fused on mica and formed continuous supported lipid bilayers (SLBs) covering almost the entire mica surface. The effect of Ca²⁺ on SLB formation was offset by a Ca²⁺ chelating agent. When lipid vesicles were added during AFM observation, vesicles fused on mica and covered almost all areas even under high Ca²⁺ concentrations. These results indicate that force between AFM tip and vesicles overcomes the Ca²⁺-reduced fusion of lipid vesicles.

Conventional atomic force microscopy (AFM) can visualize not only the specific binding between a DNA molecule and an enzyme directly, but also the resulting conformation of DNA that reacted with the enzyme. However, it is difficult to visualize the dynamic behavior of biomolecules by conventional AFM, which need a few minutes to image a sample, because the conformation of a biomolecule changes within seconds. In the present study, we successfully observed the dynamic behavior of the interaction between a DNA and an enzyme in a reaction buffer by high-speed AFM. Moreover, we successfully visualized the digestion of the DNA by the enzyme and the motions of the enzyme on a DNA strand. The dynamic observation by high-speed AFM enabled us the quantitative evaluation of what. The movement speed of the enzyme along the DNA strand was about 23 nm/100 ms.

Mechanical stimuli such as cyclic stretch and fluid stress affect various cellular physiologies, including proliferation, morphology, and differentiation. We investigated cellular response to shrinking stimuli by developing an isotropic deformation device and observing cellular elasticity with mechanical scanning probe microscopy (M-SPM). The isotropic deformation device consists of a steel ring and a deformable elastic culture dish made of transparent silicone rubber. The M-SPM can visualize topography and spatial distribution of local elasticity of biomaterials in solution. Fibroblasts became softer in response to 6% shrinkage. Cell elasticity did not increase for 1 h after the shrinking stimulus. Inhibitory studies using lysophosphatidic acid and calyculin-A revealed that myosin light chain phosphatase leading to dephospholylation of myosin II regulatory light chain is involved in cell softening.

The number distribution of the elastic modulus of fibroblast cells was successfully measured during the early stages of adhesion using an atomic force microscope (AFM) combined with a microarray as a substrate, which allowed us to arrange and culture cells so that a large number of cells could be measured in a short time period. We confirmed that the cells deposited in the wells of the microarray could be cultured for at least 12 h without any significant migration. Histograms of the Young's modulus, E, of the cells during the early stages of adhesion produced from force curve measurements of cells (n\cong300) cultured for 3–9 h were well fitted to a log-normal distribution function. With increasing incubation time, the average value of E increased significantly, while the standard deviation of the distribution remained almost constant. The results are discussed in terms of the cytoskeleton inside cells.

We describe a nanometer-scale manipulation and cutting method using ultrasonic oscillation scratching. The system is based on a modified atomic force microscope (AFM) coupled with a haptic device as a human interface. By handling the haptic device, the operator can directly move the AFM probe to manipulate nanometer scale objects and cut a surface while feeling the reaction from the surface in his or her fingers. As for manipulation using the system, nanometer-scale spheres were controllably moved by feeling the sensation of the AFM probe touching the spheres. As for cutting performance, the samples were prepared on an AT-cut quartz crystal resonator (QCR) set on an AFM sample holder. The QCR oscillates at its resonance frequency (9 MHz) with an amplitude of a few nanometers. Thus it is possible to cut the sample surface smoothly by the interaction between the AFM probe and the oscillating surface, even when the samples are viscoelastics such as polymers and biological samples. The ultrasonic nano-manipulation and cutting system would be a very useful and effective tool in the fields of nanometer-scale engineering and biological sciences.

We studied methods of estimating three-dimensional (3-D) tip structure using impulse response technique. We have proposed a 3-D tip estimation method using an infinite small diameter standard column as the impulse response technique. The standard column has been made by image processing of a finite-small-diameter-column standard sample by a software elimination technique. We demonstrated how to obtain the 3-D atomic force microscope (AFM) pyramidal tip shape using a commercial pyramidal tip and a 665-nm-diameter-column sample. The estimated tip radii are 10–15 nm in various profiles of the top. The results indicate that the method is effective to estimate a 3-D AFM tip structure in order to obtain an accurate AFM image.