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Recent strong demands to fabricate novel nanoscopic devices and functional materials have led to the development of new multi-functional tools for nanofabrication and nano-characterization with unconventional environments. Conventional analytical tools need to be totally updated to match the new technological trend of nanotechnology and nanoscience. With an ever increasing need for a new guiding principle for advanced nano-characterization, the idea of active nano-characterization technology has been proposed, which can change a nano-characterization tool not only into an in-situ nanofabrication apparatus but also into a powerful explorer of unknown physics hidden in artificial nanostructures in extreme physical fields. Active nano-characterization means a nanometre-scale characterization with active operations, which are defined as multiple applications of special environments or operations on the sample probed. Applications of extreme physical environments such as low or high temperatures, variable magnetic and/or electric fields, ultrahigh vacuum, ultrahigh pressure, mechanical stress and strain, and irradiation of particle and/or photon beams are typical active operations.

With an obvious demand for a scientific meeting focused on the development of the advanced nano-characterization technology and its application to nanostructures and nanomaterials such as quantum dots, nanotubes, ultra-thin films, surfaces and interfaces, the First International Symposium on Active Nano-Characterization and Technology (ANCT2003) was held on 12-14 of November 2003 at the National Institute for Materials Science (NIMS) in Tsukuba, Japan. The intention of the organizers was to provide a forum, not only for researchers in the field of nano-characterization technology, but also for practitioners of the new techniques in the nanotechnology and nanoscience fields.

This special issue of Nanotechnology consists of selected papers presented at the ANCT2003 symposium. Over 200 scientific delegates attended the symposium and more than 100 valuable papers were presented as oral and poster contributions. I hope that the present issue can offer the readers of Nanotechnology a good opportunity to access state-of-the-art developments and future directions of the advanced nano-characterization technology.

Finally we would like to gratefully acknowledge the large number of people supporting the editorial processes, and the generous support from NIMS and the Special Coordination Fund of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), which made this symposium possible.

Microcapsules made of hard carbon films were fabricated for electron microscopic observations of liquid-like samples such as biological cells/molecules in water solution and liquid crystals. 4-(1-methylheptyloxycarbonyl) phenyl--octyloxybiphenyl-4-carboxylate (MHPOBC) liquid crystals housed in the capsule were observed by transmission electron microscopy at 120 kV accelerating voltage. From the series of electron diffraction patterns, the rate of electron irradiation damage was estimated for the cases of changing sample temperature, beam current density and accelerating voltage. Phase transitions from a crystalline phase to liquid crystalline phases such as an isotropic-A phase of a smectic state (Sm-I_A) and a chiral-A phase of a smectic state (Sm-C_A^*) were successfully observed and the rotation fluctuation of the molecules in the phase was measured by using the electron diffraction patterns.

Four-probe fine electrodes were fabricated on a Si(100)-2 × 1-H surface using conventional lithographic and scanning-probe nano-fabrication techniques followed by standard cleaning and hydrogenation processes of the surface. It was confirmed by scanning tunnelling microscopy that a Si(100)-2 × 1-H surface is formed in the area except for the fine electrodes. Tunnelling spectroscopy of the electrode surface and electrical conduction measurements of nanoscale wires were performed for evaluating the fabricated electrodes. The results showed that the fabricated fine electrodes are capable of measuring the electrical properties of nanoscale surface objects.

Supramolecular assemblies of lander molecules (C₉₀H₉₈) on Cu(100) are investigated with low-temperature scanning tunnelling microscopy. The energetically most favourable conformation of the adsorbed molecule is found to exist in two mirror symmetric enantiomers or conformers. At low coverage the molecules align in enantiomerically pure chains along the chiral directions and [021]. The arrangement is proposed to be mainly governed by intermolecular van der Waals interaction. At higher coverages, the molecular chains arrange into chiral domains, for which a structural model is presented.

Using a low temperature scanning tunnelling microscope with normal metal tungsten tips and superconducting niobium tips, we have observed in real space the formation of electron standing waves by the scattering of surface state electrons at surface defects on Au(111) surfaces. In the constant-current STM images of Au(111) observed at low temperature with both tips, standing waves are clearly seen emanating from step edges and point defects. From the observed structure of the standing waves, the wavenumber of the surface electrons can be obtained as a function of the electron energy. In comparison with the cross-sectional profiles (height versus distance) measured across the standing waves, it can be seen that the amplitude of the standing waves obtained with the niobium tip at 4.2 K is about three times larger than that with the tungsten tip. We have also proposed a simple model to explain these observed effects.

We describe near-field photoluminescence microscopy of an n-type GaAs/AlGaAs modulation-doped quantum well with a square mesh gate structure. The optical near-field image changed from a square array to an isolated dot array as the negative bias voltage between the mesh gate and back electrode was tuned. The correlation between the image and the calculated electron density distribution indicated that the photoluminescence signal was due to the recombination of electrons defined by the tunable field-induced potential and slowly diffusing holes.

Ultraviolet light was used to irradiate hydrocarbons on TiO₂ thin film in high-resolution transmission electron microscopy (TEM). The hydrocarbon was decomposed by photocatalysis of titanium oxide. Reaction processes were studied by using an in situ TEM observation system which was newly constructed for the present study. For measuring photocatalytic activities, electron energy loss spectroscopy (EELS) was used. We developed a new TEM method for observing crystal structures of TiO₂ and quantifying photocatalytic activities concurrently. We succeeded in measuring the photodecomposition activity of hydrocarbons on TiO₂ films in a submicron area. The spatial resolutions of the present method were compared with those of other methods for measuring photocatalytic activity.

An ultrahigh-vacuum low-temperature scanning tunnelling microscope with a near-field optical detection system using conductive and optically transparent probes was used to study tunnelling-electron-induced photon emission from a cleaved p-type GaAs(110) surface. Photons generated in a nanometre-scale area just under the probe were collected within the optical near-field region into the core of the optical fibre tip. We observed a strong photon emission at positive sample biases by injecting electrons into the surface, where radiative recombination of electron–hole pairs is a reasonable explanation for the STM-induced photon emission. A drop in photon intensity at the Zn dopant regions was observed, which can be explained by the local band potential change around the Zn acceptor atoms located at sub-surface layers.

We demonstrated the use of a polarization near-field scanning optical microscope (NSOM) with an aperture probe in illumination–collection (internal reflection) mode operation to obtain high-contrast images of very shallow NiO nano-channels. This was accomplished by measuring the polarization change (depolarization) due to the near-field interaction between the probe aperture and the nano-channel. The polarization NSOM is a promising tool for high-resolution optical detection of nanostructures.

A simple, direct synthesis method is used to grow core–shell Si–SiO_x and amorphous SiO₂ nanowires by heating a NiO-catalyzed silicon substrate. The morphology of the nanowires was controlled by carbothermal reduction of WO₃, which provides a reductive environment to synthesize crystalline Si nanowires covered with a SiO_x sheath at the growth temperature of 1000–1100 °C. Only amorphous SiO₂ nanowires were produced when the substrate was annealed without using WO₃/C. Transmission electron microscopy shows that the Si core is 20–50 nm in diameter and the SiO_x shell layer is 40–60 nm thick. After hydrofluoric acid (HF) treatment of core–shell Si–SiO_x, the single-crystalline silicon nanowires (SiNWs) were obtained in large quantities. The HF-treated SiNWs were 20–50 nm in diameter. The main crystal growth direction of the SiNWs was [111]. The nanowires grown were highly pure (no metal catalyst contamination) and very long (hundreds of micrometres). A solid–liquid–solid (SLS) mechanism is proposed for the growth of both core–shell Si–SiO_x and amorphous SiO₂ nanowires.

We present the performance of our newly developed very-low-temperature scanning tunnelling microscope (VLT-STM). This system can operate with high spatial and energy resolution at temperatures down to 350 mK, and in a magnetic field up to 11 T. The uniqueness of our VLT-STM is that the system possesses extreme-high-vacuum chambers (XHV) ( Pa). System operation ranges from sample preparation, such as cleaning and deposition, to observations in an extremely clean environment. XHV will have a significant impact within material sciences, particularly when treating a semiconductor surface. Test results have revealed STM images obtained below 1 K and with atomic resolution of highly oriented pyrolytic graphite (HOPG), Si(100) dimers, and Au(111) surfaces. Our Si(100) experiments are the first atomically-resolved STM images of the semiconductor surface obtained below 1 K. The results of those tests have conclusively determined its true ground state structure—a subject under debate for many years. Some of the STM images acquired in a high magnetic field are included in this paper. The XHV-VLT-STM system is state-of-the-art and a very powerful instrument for exploration of the nano-sciences.

In situ TEM straining experiments were performed for MgO ceramics in order to investigate the crack propagation behaviour. Using a micro-indenter driven accurately by a piezo actuator, cracks were introduced into MgO single crystals and polycrystals. In MgO single crystals, cleavage fracture along the (010) plane occurred, and the atomic structure of the crack walls were found to contain a number of square-shaped atomic steps. In contrast, cracks in polycrystalline MgO propagated along the grain boundaries, and crack deflection was observed at the triple grain junctions. It was found that a number of dislocations were generated around the triple junctions where the crack was deflected. The above results indicate that dislocation nucleation and/or emission play an important role in the crack propagation processes, even in brittle MgO.

ZnO nanorods were epitaxially grown by metalorganic chemical vapour deposition (MOCVD) on sapphire (0001) and substrates. The nanorods were elongated along the ZnO c-axis which was parallel to the substrate normal. Good alignment among the rods was achieved both in the length direction and in the in-plane orientations. The line width of bound exciton emissions was  meV at low temperatures. Emissions due to free excitons were observed from low to room temperature. Biexciton emissions were observed up to  K. The band edge emission at room temperature was found to be a mixture of emissions due to free excitons and other impurity-related emissions, indicating that care must be taken when assigning the emission peak at higher temperatures.

Magnetic nanostructures are attracting tremendous interest as regards application in high-density data storage devices and magnetic fluids. We have prepared magnetic nanoparticles ( nm) by x-ray irradiation of electroless solutions and furthermore have investigated their structural and magnetic properties. Interestingly, we find that the formation of these Ni nanoparticles occurs spontaneously, during the room temperature process, dominantly at electrolyte pH of 8.2. The hydrated electrons produced during the irradiation of electroless solution seem to play a decisive role in the spontaneous formation and growth of nanoparticles. The possible surface alloying and/or coating over these pure Ni cores occurs only upon longer irradiation of high-P-content solutions. This suggests a possible catalytic behaviour of these nano-Ni surfaces in relation to P counter-ions in the irradiated solutions. The magnetic properties of these 'as-received' particles have been studied using a vibrating sample magnetometer. The saturation magnetic moment per gram for the Ni particles is 9.38 emu g⁻¹, which is 17% of the saturation moment of bulk ferromagnetic Ni at room temperature; this can be attributed due to the size effect of these magnetic domains. The symmetric hysteresis loop about the zero-field axis showing negligible loop shift (–10 Oe) suggests that Ni particles are free from oxide layers.

We have studied in situ direct observations of depositing Au onto InSb{111}A,B -(2 × 2) surfaces up to monolayer (ML) thickness and their reaction processes by using high-resolution transmission electron microscopy in the profile-imaging geometry. During Au deposition up to  ML coverage, the In-vacancy and Sb-trimer outermost layers of the surfaces change their (2 × 2) structures to (1 × 1) periods, and the deposited Au atoms form the regions which agglutinate in the vicinity of their surfaces. Further, Au deposition (e.g.  ML) leads to a partial disruption of the substrate and to an infiltration of the substrates inside. The difference between the (111)A and the (111)B substrates is that the infiltration in the latter slowly progresses in comparison with the former. The difference in growth of gold in these systems is probably due to the polarity and the surface structures of their substrates.

Processes of reaction between Ag–Cu–Ti molten alloy and silicon, carbon and SiC substrates were directly observed by in situ heating high-resolution electron microscopy. It was found that TiC grew in a layer by layer mode at the spreading front, and that a double layer consisting of an outer Ti₅Si₃ and an inner TiC layers was formed by the reaction between the SiC substrate and the molten alloy. The morphology of the spreading front was also found to depend on the chemical composition of the dissociated substrate in the molten alloy.

Molecular fluorescence from the surface of ZnTBP porphyrin (ZnTBPP) molecular layers on Cu(100) is induced with nanoprobe excitation in the tunnelling regime. The observed well-defined molecular fluorescence is a perfect match with the standard photoluminescence data of ZnTBPP molecules. The decoupling of the electronic state of the top layer ZnTBPP is controlled by the thickness of the molecular layers. The excitation mechanism of molecular luminescence may be attributed to the hot electron injection into the molecules in proximity to the tip apex of a scanning tunnelling microscope. This approach features simplicity, bipolar operation and good reproducibility. The research provides a new way for the integration of molecular fluorescence with a nanoprobe and the development of a nanoscale molecular light source.

At the initial stage of 3C-SiC growth on Si(001) using a organosilicon compound such as monomethylsilane (MMS), Si(001)-c(4 × 4) was formed before the nucleation of SiC islands. From observation of the c(4 × 4) structure by scanning tunnelling microscopy (STM), it was found that both c(4 × 4) domains and (2 × 1) domains coexisted. From the estimation of the lattice size for these structures by line profile measurement, the lattice size of the c(4 × 4) domain was contracted and that of the (2 × 1) domain was expanded. Therefore, the c(4 × 4) domain was considered to be the preferential nucleation site of SiC. The STM observation for the c(4 × 4) structure formed using MMS also revealed that the c(4 × 4) domain consisted of both the α-cell and the β-cell, similar to that formed by silicon deposition and subsequent sample annealing. An STM image of an α-cell, however, did not show a central spot in the empty state. So, the top dimer of the α-cell is not an Si–Si dimer but another dimer.

A unique variable temperature scanning Hall probe system (VT-SHPM) has been developed for large area, nanometre scale lateral resolution imaging of ferromagnetic domains, in which piezoelectric actuators are maintained at ambient temperature and only the semiconducting micro-Hall probe and sample are cooled. Its design overcomes the limitations of conventional cryogenic SHPM systems, where the piezoelectric actuators are cooled thus reducing the maximum scan area to about 10 µm × 10 µm due to a reduction of the piezoelectric constant at cryogenic temperatures. The VT-SHPM operates between 300 and 77 K and consists of a liquid nitrogen glass Dewar housing the sample and the semiconducting micro-Hall probe (active area = 900 nm × 900 nm; magnetic sensitivity at 300 K 6 mG Hz^−1/2) used to detect surface magnetic fields. The VT-SHPM was used to image perpendicularly magnetized domains at the surfaces of 5.5 µm thick single crystal bismuth substituted garnet thin films between 300 and 77 K. Areas of about 120 µm × 130 µm were readily imaged by synchronizing the action of x–y piezoelectric actuators and corresponding stepper motors to move and scan the sample at a constant height of 0.25 µm over the surface of the micro-Hall probe. The average width of magnetic domains in the garnet thin films was found to increase as the measurement temperature decreased.

The effects of focus change on the electron-beam-induced deposition (EBID) of tungsten nanowire in a scanning transmission electron microscope (STEM), were systematically investigated. By focusing the electron beam on the surface of carbon film, smooth tungsten nanowires were fabricated. The lateral size of the nanowire first decreased with the increase of beam scan speed, then became constant at about 7 nm when the scan speed was higher than 10 nm s⁻¹. During the deposition of nanowire on carbon film, both overfocus and underfocus changes resulted in a conical profile with a central core line, whose deposition strongly depends on the electron dose. Broken wires can be fabricated by controlling the focus. For the deposition of self-supporting wire out of carbon film, the influence of focus change depended on the morphology of the deposited wire. Overfocus change can be used to keep the upward feature of the wire, while underfocus change is useful for the downward feature.

Vanadium clusters with a size of several nanometres can be dispersively distributed in ZnO films by using co-deposition. EELS mapping of V-L_2,3, HRTEM images, SAD patterns and EELS are a good combination for characterizing nanometre-sized V clusters embedded in a ZnO system. There is no obvious orientation relationship between V and ZnO lattices due to a less good match between ZnO and V atomic planes. The ratio of the vanadium L-white lines of vanadium clusters embedded in ZnO becomes bigger than that of the bulk. The samples were observed in situ from 298 to 923 K with a heating holder so as to study the aggregation process of vanadium clusters in the ZnO crystalline matrix. First, the size of the ZnO crystal grains becomes bigger after the sample is heated at 623 K for an hour; second, the size of ZnO and vanadium particles grows bigger after the sample is heated at 723 K for half an hour, and another orientation relationship between ZnO and vanadium appears; third, after the sample is heated at 873 K for half an hour, the size of vanadium becomes smaller, while V particles and ZnO begin to react and form another phase; finally, Zn₂V O₇ phase is formed after the sample is heated at 923 K for half an hour.

The present paper describes a new imaging method for obtaining information on the atomic-scale structure around specific elements covering quite a wide area of up to several cm² in a reasonable measuring time. Although the x-ray absorption fine structure (XAFS) technique is a popular method for analysing 'average' atomic-scale structures, recent rapid progress in materials research demands more information on inhomogeneous systems. In order to obtain an image of the heterogeneity of the structure, scanning by means of a microbeam has been employed in a wide variety of fields. However, this method has become rather impractical from the standpoint of measuring time once the pixel count is increased in order to obtain a high-quality image. The present research proposes the use of a new instrument: an x-ray fluorescence (XRF) projection-type microscope, which is a powerful new tool recently developed for rapid imaging. XAFS imaging was carried out by repeating the exposure of XRF images during the energy scan of the primary x-rays. The present research demonstrated the feasibility of the new instrument with respect to the imaging of the chemical-state as well as the atomic-scale structure.