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The size tunability and chemical versatility of nanostructures enable electron sources of high brightness and temporal coherence, both of which are important characteristics for high-resolution electron microscopy1–3. Despite intensive research efforts in the field, so far, only conventional field emitters based on a bulk tungsten (W) needle have been able to yield atomic-resolution images. The absence of viable alternatives is in part caused by insufficient fabrication precision for nanostructured sources, which require an alignment precision of subdegree angular deviation of a nanometre-sized emission area with the macroscopic emitter axis4. To overcome this challenge, in this work we micro-engineered a LaB6 nanowire-based electron source that emitted a highly collimated electron beam with good lateral and angular alignment. We integrated a passive collimator structure into the support needle tip for the LaB6 nanowire emitter. The collimator formed an axially symmetric electric field around the emission tip of the nanowire. Furthermore, by means of micromanipulation, the support needle tip was bent to align the emitted electron beam with the emitter axis. After installation in an aberration-corrected transmission electron microscope, we characterized the performance of the electron source in a vacuum of 10−8 Pa and achieved atomic resolution in both broad-beam and probe-forming modes at 60 kV beam energy. The natural, unmonochromated 0.20 eV electron energy loss spectroscopy resolution, 20% probe-forming efficiency and 0.4% probe current peak-to-peak noise ratio paired with modest vacuum requirements make the LaB6 nanowire-based electron source an attractive alternative to the standard W-based sources for low-cost electron beam instruments. So far, only conventional field emitters based on a bulk W needle have achieved atomic resolution in electron microscopy. Here, through the integration of a passive collimator structure and micromanipulation-based alignment of the support needle, a LaB6 nanowire emitter yields stable emission under moderate vacuum conditions and allows for atomic-resolution images and high energy resolution.

Energy storage devices using electrochemical reactions have become an integral part of our daily lives, and further improvement of their performance is highly demanded. An important task for this purpose is to thoroughly understand the electrochemical processes governing their chemistry. Here we develop a method based on Kelvin probe force microscopy that enables dynamic visualization of changes in the internal potential distribution in an operating electrochemical device and use it to characterize an all-solid-state lithium ion battery. Observation of the cathode composite regions during a cyclic voltammetry operation reveals differences between the behavior of local electrochemical reactions in the charge and discharge processes. Based on careful inspection of the results, we show that the difference arises from a change in the state of an electronic conductive path network in the composite electrode. Our method provides new insights into the local electrochemical reactions during electrochemical operation of devices. Understanding the working mechanisms of electrochemical energy storage devices is crucial for the design of those with improved performances. Here the authors use Kelvin probe force microscopy to dynamically image the internal potential distribution in an operating all-solid-state Li ion battery.

The relationship between the properties and substrates of graphene is important to research the graphene synthesized by a bottom-up approach. Here, we synthesized graphene with a surface segregation method and demonstrated that a quadrilateral graphene was formed by using Ni(110) as a substrate. Most of the graphene edges were parallel to the [101] or [100] directions of Ni(110). We found that sulfur impurities in Ni that segregated to the surface with a C(2 × 2) surface reconstruction during the graphene growth played critical roles in the formation of the quadrilateral graphene flakes.

Graphene synthesis by chemical vapor deposition (CVD) on Cu foil involves a series of complex interplays between the atmosphere and Cu substrate. The large number of topographical irregularities and impure elements existing in the normal Cu foils inevitably result in heterogeneous graphene nucleation and uncontrolled growth. Thus, resolving the mutual entanglements between topographical irregularity, impure element, and carbon is fundamental for the understanding of graphene nucleation and growth. Here, two kinds of Cu surface features, topographical Cu hills and elemental oxygen, are deliberately introduced and their interaction is studied. The synergistic effects of Cu hills and oxygen on graphene nucleation and growth are further demonstrated. Molecular dynamics simulations are employed over the whole process to explain the experimental phenomena including Cu hill construction, oxygen distribution, and carbon adsorption. This work is crucial in revealing the microscopic mechanisms for graphene nucleation and growth, and can shed light on how to controll graphene synthesis via Cu surface engineering.

Synchronizing thousands of 100% efficient rotors in a macrodevice for harvesting noise is unapprehended. Thermodynamically, realizing a thermal gradient at the atomic scale is critical. Harvesting free thermal energy or noise by resonance has a hidden clause; either externally activating a directed self-powered motion or constructing a nanoscale power supply. To accomplish this, we combined two rotor concepts, Brownian rotor, BR, and power stroke, PS, rotors available in living systems in two planes of a single molecule. Quantum tunneling images reveal how a radio-wave guided synchronization of PS-BR combination tweaks rotational dynamics of a rotor to bypass the necessity of temperature gradient (Δ

Lithium ion batteries (LIBs) are the most important energy storage devices. Novel methods for directly characterizing the behavior of Li ions during battery operations are highly coveted for understanding the fundamental working principles of the batteries and improving their device performances. In this study, we developed a novel method to visualize the change in Li ion distribution in the electrodes of all-solid-state (ASS) LIBs based on the time-of-flight secondary ion mass spectrometry technique with an in situ electrical measurement system. We succeeded in directly visualizing the decrease/increase of Li concentration in the cathode composite electrode during the charging/discharging cycles. Our method paves the way to characterize the fundamental aspects of ASS LIBs for improving device performance, including the evaluation of Li-depleted regions, visualization of the conductive paths and analysis of the causes of device degradation.

The advanced confocal Raman microscopy provides a unique nondestructive, submicron feature resolving, and utility-convenient methodology for material stress analysis. Conventionally, only materials transparent to the excitation laser are allowed for depth-resolved 3D characterization. For opaque materials, the collected Raman scattering signal is inevitably an ensemble of contributions from multiple specimen layers. In this work, an informatics approach was adopted while considering both laser attenuation and confocal exclusivity to decompose true local stress components in three dimensions with submicron resolution. Such analytical power was demonstrated on a laser-opaque silicon wafer, where a depth-dependent study of stress dynamics was made possible. The technique extends to narrow band semiconductor-based microelectronic, solar cell, and battery materials, where stress plays a key role in the device performance and durability.

OBJECTIVE To evaluate outcome of limb fracture repair in rabbits. DESIGN Retrospective case series. ANIMALS 139 client-owned rabbits with limb fractures treated between 2007 and 2015. PROCEDURES Medical records were reviewed for information on fracture location, fracture treatment, and time to fracture healing. RESULTS 25 rabbits had fractures involving the distal aspects of the limbs (ie, metacarpal or metatarsal bones, phalanges, and calcaneus or talus). Fractures were treated in 23 of these 25 rabbits (external coaptation, n = 17; external skeletal fixation, 4; and intramedullary pinning, 2) and healed in all 23, with a median healing time of 28 days (range, 20 to 45 days). One hundred ten rabbits had long bone fractures, and fractures were treated in 100 of the 110 (external skeletal fixation, n = 89; bone plating, 1; intramedullary pinning, 3; and external coaptation, 7). The percentage of fractures that healed was significantly lower for open (14/18) than for closed (26/26) tibial fractures and was significantly lower for femoral (19/26) and treated humeral (4/6) fractures than for radial (23/24) or closed tibial (26/26) fractures. Micro-CT was used to assess fracture realignment during external skeletal fixator application and to evaluate fracture healing. CONCLUSIONS AND CLINICAL RELEVANCE The prognosis for rabbits with limb fractures was good, with fractures healing in most rabbits following fracture repair (109/123). Micro-CT was useful in assessing fracture realignment and evaluating fracture healing.

Solid-state-lithium ion batteries (SS-LIBs) are a promising candidate for next-generation energy storage devices. Novel methods for characterizing electrochemical reactions occurring during battery operation at the nanoscale are highly required for understanding the fundamental working principle and improving the performance of the devices. In this work, we combined Ar ion milling under non-atmospheric conditions with in situ cross-sectional Kelvin probe force microscopy (KPFM) for direct imaging of the internal electrical potential distribution of the SS-LIBs. We succeeded in the direct visualization of the change in the potential distribution of a cathode composite electrode (a mixture of the active materials, solid electrolytes, and conductive additives) arising from battery charging (electrochemical reaction). The observed results provided several insights into battery operation, such as the behavior of Li ions and inhomogeneity of electrochemical reactions in the electrode. Our method paves the way to characterize the fundamental aspects of SS-LIBs for the improvement of device performance, including the evaluation of the distribution of the Li ion depleted regions, visualization of the conductive paths, and analysis of the cause of degradation.

Looking beyond ionic communication in bio-systems that is limited to a narrow band of kHz frequency domain is our objective. Microtubule, a vital subcellular biomolecule found in almost all eukaryotic living systems, plays an important role in processing the cellular information. Therefore, here we introduce a microtubule analogue device, which wirelessly communicates with the neighboring microtubules and harvest energy from the noise present in the environment. The device is composed of spatially arranged lattice geometry with two different lattice parameters made of capacitors as tubulin protein analogue arranged on cylindrical shape structures. To demonstrate that the noise is harvested, both the devices are operated by noise, no ordered signal is applied in any measurement. Separation between both the devices is varied, while nearing the distance, the transmitted signal increases continuously and when they are taken further apart, the signal decreases gradually to null at ~140 cm. We image live, the generation and transmission of magnetic flux condensate between these two devices. This experiment is also repeated by inserting a magnetic shield 99.99% pure Ni sheet between two structures, which allows very less wireless transmission due to the shielding. The wireless communication frequency is in the range kHz–MHz.

Scanning helium ion microscope (SHIM) is based on the similar principle with field emission scanning electron microscope (FE-SEM) (Guo in Scanning Helium Ion Microscopy, Characterization of Materials. Wiley, pp. 1–9, 2012 [1]). The difference between them is that scanning beam of SHIM is a positively charged helium ion (He+) beam from a gas field ion source (GFIS), but not a negatively charged electron beam. An enlarged image of the sample surface is obtained like FE-SEM. Helium gas is field-ionized almost only from the top-most atoms by applying a high voltage to a sharp tip made of monocrystalline refractory metals in a diluted helium gas. Only the He+ beam emitted from a single atom is focused by the ion optical system and is scanned over the sample surfaces. If a backscattered ion detector is equipped, the secondary electrons (SE) and backscattered ions (BSI) can be acquired simultaneously. SHIM can observe the sample image with less current than FE-SEM. If the neutralizing flood gun is equipped, it is easier to observe insulating materials than FE-SEM. SHIM can also be used for direct nanofabrication like focused ion beam (FIB) systems. Since He+ beam does not have such a sputtering capability as a gallium ion beam, it cannot process on the micron-scale, but nanoscale ultrafine modification utilizing the nanoscale-focused He+ beam is possible. If a gas introduction system is installed, deposition of gas-decomposition microstructures by a precisely controlled He+ beam is possible

The interaction between nitrogen (N) impurity states in III-V compounds plays a key role in controlling optoelectronic properties of the host materials. Here, we use scanning tunneling microscopy to characterize the spatial distribution and electronic properties of N impurity states in dilute GaNAs. We demonstrated that the N impurity states can be directly visualized by taking empty state current images using the multipass scanning method. The N impurity states broadened over several nanometers and exhibited a highly anisotropic distribution with a bowtie-like shape on the GaAs(110) surface, which can be explained by anisotropic propagation of strain along the zigzag chains of Ga and As atoms in the {110} plane. Our experimental findings provide strong insights into a possible role of N impurity states in modifying properties of the host materials.

Microtubule nanotubes are found in every living eukaryotic cells; these are formed by reversible polymerization of the tubulin protein, and their hollow fibers are filled with uniquely arranged water molecules. Here we measure single tubulin molecule and single brain-neuron extracted microtubule nanowire with and without water channel inside to unravel their unique electronic and optical properties for the first time. We demonstrate that the energy levels of a single tubulin protein and single microtubule made of 40,000 tubulin dimers are identical unlike conventional materials. Moreover, the transmitted ac power and the transient fluorescence decay (single photon count) are independent of the microtubule length. Even more remarkable is the fact that the microtubule nanowire is more conducting than a single protein molecule that constitutes the nanowire. Microtubule's vibrational peaks condense to a single mode that controls the emergence of size independent electronic/optical properties, and automated noise alleviation, which disappear when the atomic water core is released from the inner cylinder. We have carried out several tricky state-of-the-art experiments and identified the electromagnetic resonance peaks of single microtubule reliably. The resonant vibrations established that the condensation of energy levels and periodic oscillation of unique energy fringes on the microtubule surface, emerge as the atomic water core resonantly integrates all proteins around it such that the nanotube irrespective of its size functions like a single protein molecule. Thus, a monomolecular water channel residing inside the protein-cylinder displays an unprecedented control in governing the tantalizing electronic and optical properties of microtubule.

The growth mode of small Ni clusters evaporated in UHV on HOPG has been investigated by scanning tunnelling microscopy. The size, the size distribution, and the shape of the clusters have been evaluated for different evaporation conditions and annealing temperatures. The total coverage of the surface strongly depends on the evaporation rate and time, whereas the influence of these parameters is low on the cluster size. Subsequent stepwise annealing has been performed. This results in a reduction of the total amount of the Ni clusters accompanied by a decreasing in the overall coverage of the surface. The diameter of the clusters appears to be less influenced by the annealing than is their height. Besides this, the cluster shape is strongly influenced, changing to a quasi-hexagonal geometry after the first annealing step, indicating single-crystal formation. Finally, a reproducible methodology for picking up individual clusters is reported Parts of this work have been presented as oral or poster presentations in several national and international conferences (Meeting of the Physical Society of Japan 2011 and 2012, 6th International Symposium on Surface Science 2012, and ImagineNano 2013)..

Dynamics of coherent G-mode and D-mode phonons in Ar + -ion implanted graphite has been investigated using transient reflectivity measurement. With an increase in the Ar + -ion dose, coherent D-mode phonon appears at which the dephasing rate of the coherent G-mode phonon begins to increase. The increase in the amplitude of the coherent D-mode phonon and those in dephasing rates of the coherent D-mode and G-mode phonons indicate effective carrier-defect scatterings in the defective graphite. The dephasing rate of the D-mode is larger than that of the G-mode, indicating an existence of an additional dephasing process for the D-mode. We attribute it to the broad spectral distribution of the D-mode phonon, which is understood as a coherent excitation of large wavevector phonons with different wavevectors through inter-Dirac-cone scattering. The frequency chirping of the D-mode and its defect density dependence are also discussed based on this scattering mechanism.

Silicon dioxide (SiO2) is one of the key materials in many modern technological applications such as in metal oxide semiconductor transistors, photovoltaic solar cells, pollution removal, and biomedicine. We report the accidental discovery of free-standing grassy silica nanoribbons directly grown on SiO2/Si platform which is commonly used for field-effect transistors fabrication without other precursor. We investigate the formation mechanism of this novel silica nanostructure that has not been previously documented. The silica nanoribbons are flexible and can be manipulated by electron-beam. The silica nanoribbons exhibit strong blue emission at about 467 nm, together with UV and red emissions as investigated by cathodoluminescence technique. The origins of the luminescence are attributed to various defects in the silica nanoribbons; and the intensity change of the blue emission and green emission at about 550 nm is discussed in the frame of the defect density. Our study may lead to rational design of the new silica-based materials for a wide range of applications.

We investigated the adsorption properties of Co-phthalocyanines (CoPc's) on the rutile TiO2(110) surface using scanning tunneling microscopy and spectroscopy. Analytical results showed that the adsorption properties strongly depend on the deposition conditions. Under specific deposition conditions (elevated substrate temperatures and low deposition rates), the molecules are immobilized on the surface without aggregation up to the full monolayer coverage. The substrate temperature plays a key role in determining the bonding nature between the molecules and the substrate. The immobilized molecules introduce gap states at the interface and locally decrease the surface band gap to an energy value that is lower than that of the absorption band of the CoPc thin film. Coverage dependence studies show that the adsorption structures are dominated by molecule–substrate interactions for the first monolayer growth and by a complex interaction between molecules in the first and second monolayers for the second monolay...

Using a surface segregation technique, single-layer graphene can be grown on a carbon-doped Pd(1 1 1) substrate. The growth was monitored and visualized using Auger electron spectroscopy, X-ray photoelectron spectroscopy, Raman microscopy, atomic force microscopy and scanning tunneling microscopy. Appropriate adjustment of annealing parameters enables controllable growth of single-layer graphene islands and homogeneous, wafer-scale, single-layer graphene. The chemical state of the C 1s peak from X-ray photoelectron spectroscopy indicates there is almost no charge transfer between graphene and the Pd(1 1 1) substrate, suggesting weak graphene–substrate interaction. These findings show surface segregation to be an effective method for synthesizing large-scale graphene for fundamental research as well as potential applications.

Scanning capacitance microscopy (SCM) is one of techniques imaging two-dimensional carrier distribution in semiconductor devices. We have demonstrated that quantitative analysis of carrier concentration can be performed using calibration curves, which are statistically prepared for respective materials like silicon, silicon carbide, etc. The procedure was circulated to research organizations in domestic round robin test, and this method was found to be available from the viewpoint of comparability among users for the industrial standardization. It was also applied to other microscopes, and their profiles of carrier concentration coincide with each other, suggesting compatible to next-generation microscopes which would come up in the future.

Graphene has attracted an enormous amount of interest recently because of its unique electronic, optical, mechanical, and other properties. We report a promising method for producing single-layer graphene fully covering an entire substrate at low temperature. Single-layer graphene sheets have been synthesized on a whole 2 cm ×2 cm nickel (Ni) film deposited on a highly oriented pyrolytic graphite (HOPG) substrate by heating the Ni/HOPG in a vacuum. The carbon atoms forming our graphene are diffused from the graphite substrate through the nickel template. Our results demonstrate how to control the amount of carbon atoms for graphene formation to yield graphene films with a fine controlled thickness and crystal structure. Our method represents a significant step toward the scalable synthesis of high-quality graphene films with predefined thickness and toward realizing the unique properties of graphene films.

We report the determination of the thickness of graphene layers by Auger electron spectroscopy (AES). We measure AES spectra of graphenes with different numbers of layers. The AES spectroscopy shows distinct spectrum shape, intensity, and energy characteristics with an increasing number of graphene layers. We also calculate electron inelastic mean free paths for graphene layers directly from these measurements. The method allows unambiguous and high-throughput determination of thickness up to six graphene layers and detection of defect and dopant in graphene films on almost any substrate. The availability of this reliable method will permit direct probing of graphene growth mechanisms and exploration of novel properties of graphenes with different thicknesses on diverse substrates.

The growth of Au on thin Pb films was studied by scanning tunneling microscopy and low energy electron diffraction. We found that the initial Au deposition resulted in a rough Au-Pb alloy interface on the thin Pb films. With further deposited Au, Moire patterns in a (root 3 x root 3)-Au layer was formed on top of a laterally contracted Au-Pb alloy surface. Finally, the Au deposition performed the Stranski-Krastanov type growth mode to form three-dimensional Au crystals. This structure information provided a possible explanation to the observed phase shift pi between the density of states near the Fermi energy and the superconducting transition temperature as a function of film thickness as reported recently [Guo et al., Science 306 (2004) 1915 and Zhang et al., Phys. Rev. Lett. 95 (2005) 096802]. (c) 2008 Elsevier B.V. All rights reserved.

The porphyrin-based molecules including H 2 TBPP, ZnTBPP and P t TBPP as well as the perinone derivatives (PD) molecules were deposited on Au(100), Au(1 11) and Cu(100) substrates in the form of single molecule, molecular line, submonolayer, monolayer and multilayer. The features of the performed molecular nanostructures were characterized by an ultrahigh vacuum scanning tunneling microscopy (STM) at room temperature. The observed molecular topographies matched very well with the molecule structures in spite of the fact that the molecular adsorption states were influenced by different metal surface. STM-induced photon emission was generated from the surface of H 2 TBPP multilayer structures on Au(100) in tunneling junction when the applied bias exceeds the "turn-on" voltages ∼-1.6 V or +1.3 V at 0.5 nA. © 2007 Elsevier B. V. All rights reserved.

Scanning tunneling microscopy luminescence (STML) was induced from the nanometer scale surfaces of cleaved n-type and p-type GaAs(1 10) wafers by using of an ITO-coated optical fiber probe in an ultrahigh-vacuum chamber. The STML from n-type GaAs(1 1 0) surface was induced under negative sample bias when the applied bias exceeds a threshold voltage around -1.5 V. Whereas the STML from p-type GaAs( 110) surface was induced under positive sample bias when the applied bias exceeds a threshold voltage around +1.5 V. The excitation energies at the threshold voltages are consistent with the band gap of GaAs (1.42 eV) at 295 K. The typical quantum efficiencies for n-type and p-type GaAs are about 3 x 10 -5 and 2 x 10 -4 photons/electron, respectively. The observed STML from are attributed to a radiative recombination of electron-hole pairs generated by a hole injection for n-type GaAs under negative sample bias and an electron injection for p-type GaAs under positive sample bias, respectively.

Carbon nanowires (CNWs) spontaneously formed on the surface of a freshly cleaved highly ordered pyrolytic graphite (HOPG) wafer have been observed for the first time by atomic force microscopy (AFM), an ultrahigh vacuum scanning tunneling microscopy (UHV-STM), and a scanning electron microscopy (SEM). The observed CNWs grow straight on the surface of one terrace or across the step edges with a diameter range from ~10 to 200 nm and have ametallic conductivity. The growth of such CNWs seems to originate from surface defects such as step edges and protrusions during the fabrication of the HOPG wafer, or by the rolling of graphene layers into cylinders during cleavage. This result has provided a new method of obtaining CNWs.

Graphene nucleation at oxygen-rich Cu sites instead of on the commonly assumed pure Cu surface is discovered using high-spatial-resolution scanning Auger electron microscopy, which reveals a strong O signal existing underneath the graphene seeds, along with density functional theory calculations.

Recent developments of fabrication, manipulation and characterization techniques at nanometer scale for low-dimensional nanostructures using scanning tunneling microscopy (STM) are reviewed. Firstly two reliable methods for metallic nanostructure formation using tip material transfer are introduced. Secondly STM-manipulation of Au nanoclusters grown on self-assembled monolayers is introduced, where single electron tunneling effect is clearly observable using tunneling spectroscopy. As a new type of STM manipulation, a reversible control method of surface periodic structures (phases) on Si(100) at low temperatures is introduced. Finally using a single atom deposition technique using a controlled point contact, fabrication of one-dimensional quantum well on a single dimer row of Si(100) surface is explained. Combining the fabrication and characterization capabilities of STM in various environments, STM can be a powerful tool for the exploration of nanotechnology and nanoscience.

Using scanning tunneling microscope, we have investigated the formation of Au nanoclusters on self-assembled monolayers of octanethiol (CH3(CH2)7SH) molecules modified with octanedithiol (HS(CH2)8SH). By changing the modification condition and the amount of Au deposition, it is found that the density and the size of the clusters can be controlled. The cluster-formation mechanism is discussed.

Scanning tunneling microscopy and spectroscopy (STM/STS) experiments on a high-density sintered MgB 2 surface were performed at 4.2 K, using a low temperature STM. The intrinsic superconducting density of states (DOS) was obtained in the tunneling spectra exhibiting the BCS-shaped characteristic with a metallic background. A double-gap structure, with the gap values of Δ L =9.5 meV and Δ S =4.0 meV, was clearly observed in the local tunneling spectra. The result supports the multiple-gap model in MgB 2 in the clean limit. The proximity effect was observed in the present conductance spectra and experimentally confirmed to be due to the Ar + ion sputtering. The origin of the varied energy gap values reported in surface-sensitive STS measurements on MgB 2 was also discussed in detail.

Scanning tunneling microscopy and spectroscopy (STM/STS) experiments on a high-density sintered MgB 2 surface were performed at 4.2 K, using a low-temperature STM. For a 20-min Ar + ion sputtered MgB 2 surface, a double-gap structure with gap values of Δ L =9.5 meV and Δ S =4.0 meV was clearly observed in the local tunneling spectra, exhibiting the BCS-shaped characteristic with a metallic background. But for a 2-h Ar + ion sputtered surface, the observed current–voltage characteristics of the MgB 2 surface show metallic electronic transport behavior. In an attempt to clarify the effect of Ar + ion sputtering on the electronic transport, the MgB 2 surface was characterized by Auger electron spectroscopy (AES). The compositional changes of the MgB 2 surface were investigated in real time during the course of Ar + ion sputtering. The detailed compositional analysis of the MgB 2 surface may help to elucidate the various electronic transport behavior observed in surface-sensitive STS measurements.

Previously, we have reported that it is possible to manipulate the Si(1 0 0) surface phases between c(4 × 2) and p(2 × 2) by precise sample bias control in scanning tunneling microscopy (STM). Electron injection into the surface from the STM tip is responsible for the phase manipulation. In the present study, the phase manipulation by STM is thoroughly studied in a wide range of temperature from 4.2 to 100 K. We have found that the manipulation is feasible below 40 K but not above 40 K. This temperature dependence is quite similar to the recent result observed by low-energy electron diffraction (LEED), which was viewed as an order–disorder phase transition of the Si(1 0 0) surface below 40 K. From the similarity of both phenomenon occurring at 40 K, we conclude that the order–disorder phase transition is induced by energetic electron irradiation onto the Si(1 0 0) surface during the LEED analysis.

Sprout-like growth of carbon nanowires on single-crystal graphite (0 0 0 1) terraces on a carbon-doped Ni(1 1 1) substrate has been observed for the first time using only a heat treatment in ultrahigh vacuum. Nanometer-scale morphology and chemistry have been clarified by low-energy electron diffraction, Auger electron spectroscopy and scanning tunneling microscopy (STM). The growth mechanism is based on a bulk-to-surface precipitation process of internal carbon atoms that were doped in a high-purity Ni(1 1 1) substrate in advance. The observed carbon nanowires are single wires and their bundles, which have a metallic conductivity. The structures have some similarity to those of single-wall and multi-wall carbon nanotubes. Simple manipulation of a single carbon nanowire is demonstrated by STM.

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.

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.

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.

Scanning tunneling microscopy and spectroscopy (STM/STS) experiments on a high-density sintered MgB 2 surface were performed at 4.2 K, using a low temperature STM. The intrinsic superconducting density of states (DOS) was obtained in the tunneling spectra exhibiting the BCS-shaped characteristic with a metallic background. A double-gap structure, with the gap values of Δ L =9.5 meV and Δ S =4.0 meV, was clearly observed in the local tunneling spectra. These values give a BCS ratio (2 Δ / k B T C ) of 5.6 and 2.4, respectively, well above and well below the BCS limit. The result supports the multiple-gap model in MgB 2 in the clean limit. The proximity effect observed in the conductance spectra and the origin of the varied reported energy gap values of MgB 2 were also discussed in this study.

We have discovered a synthesis method for carbon nanowires on a flat single-crystal graphite (0001) surface on a carbon-doped Ni(111) substrate using only heat treatment in ultrahigh vacuum. It should be noted that this new carbon nanowire synthesis method requires no external carbon-containing source. The growth mechanism utilizes a bulk-to-surface precipitation process of internal carbon atoms that were doped in a pure Ni(111) substrate in advance. Nanometer-scale morphology and chemistry of the carbon nanowires have been clarified by low-energy electron diffraction combined with Auger electron spectroscopy (LEED/AES), scanning tunneling microscopy (STM) and field-emission scanning Auger microcopy (FE-SAM).

New fabrication method for metal nanostructures on a Si(111) surface is presented. By applying voltage pulses to the Ag/W tip, nanometer-scale silver mounds have been fabricated with high yield on an n-type Si(111)-(7×7) surface in UHV. Although these silver nano-mounds were formed in both polarities, negative tip polarity was found to be more suitable to form smaller mounds. Main mechanism for tip-material transfer can be attributed to the spontaneous formation of a nanometer-scale point-contact. By this method we have succeeded in fabricating nanodots, nanowires and nano-characters, which can be used as parts for electric circuits of future quantum computation nanodevices.

An ultrahigh-vacuum scanning tunneling microscopy equipped with a conductive optical fiber tip and photon detector has been established to explore photon emission from a self-assembled monolayer (SAM) of Cu-tetra-[3,5-di-t-butylphenyl]porphyrin (Cu-TBPP) molecules on a Cu(100) surface. In a few nanometer scale areas, emitted photons from molecules induced by tunneling electrons were effectively collected within the near-field region through an apex of the conductive optical fiber tip. The photon emission can be attributed to the inelastic tunneling involving the optical fiber tip, the Cu-TBPP molecules, and the Cu(100) surface. We proposed two kinds of mechanisms in terms of the photon emission from a SAM of Cu-TBPP molecules on a Cu(100) surface. The quantum efficiency for molecular fluorescence induced by inelastic tunneling can be approximately estimated to be ∼3.0×10−6 photons per electron in the current experimental studies.

Positioning of a scanning tunneling microscope (STM) tip above Cu-tetra-(3,5-di-tertiary-butyl-phenyl)-porphyrin (Cu-TBPP) molecules on Cu(100) is found to induce plasmon-mediated emission and molecular luminescence when bias voltages are above ~ 2.3 V. Optical spectra acquired at a low current of 0.2 nA suggest not only the enhancement effect of the molecules on light emission but also new features associated with the molecules. The quantum efficiency of such light emission excited by inelastic tunneling is on the order of 10-6 photons per electron.

As widely known, the spatial resolution of a scanning near-field optical microscope (SNOM) is strongly limited by its aperture size (50–200 nm). However, as reported by the authors [Jpn. J. Appl. Phys. 38 (1999) 3949], a hybrid system of a SNOM with a scanning tunneling microscope (STM) using a "doubly metal-coated optical fiber probe" could be used to overcome this limitation, resulting in a high-resolution feature (λ/ 50 10 nm). However, the throughput of such a probe was extremely low because of the metal coating on the aperture. In this study, we developed a novel probe to overcome this disadvantage, where the metal coating on the aperture was replaced with an indium-tin-oxide (ITO) coating. The performance of this probe was evaluated by examining isolated CdSe nanoparticles on an ITO substrate. The fluorescence from each nanoparticle was observed as a bright spot with the full-width at half-maximum of about 20 nm, indicating high spatial resolution beyond the aperture size without sacrificing single-molecular-level high sensitivity.

Real graphene sheets show limited anti-permeation performance deviating from the ideally flat honeycomb carbon lattice that is impermeable to gases. Ripples in graphene are prevalent and they could significantly influence carrier transport. However, little attention has been paid to the role of ripples in the permeation properties of graphene. Here, we report that gases can permeate through graphene ripples at room temperature. The feasibility of gas permeation through graphene ripples is determined by detecting the initial oxidation sites of Cu surface covered with isolated graphene domain. Nudged elastic band (NEB) calculations demonstrate that the oxygen atom permeation occurs via the formation of C–O–C bond, in which process the energy barrier through the rippled graphene lattice is much smaller than that through a flat graphene lattice, rendering permeation through ripples more favorable. Combining with the recent advances in atoms intercalation between graphene and metal substrate for transfer-free and electrically insulated graphene, this discovery provides new perspectives regarding graphene's limited anti-permeation performance and evokes for rational design of graphene-based encapsulation for barrier and selective gas separation applications through ripple engineering.

Solar cells (SCs) that contain elaborate nanostructures, such as quantum dots and quantum wells, have been rigorously investigated as a way to harvest a wide range of the solar spectrum [1]. However, the energy conversion efficiency of those SCs still remains low. For the further improvement of the device performance, a much deeper understanding of the role of nanostructures in the photovoltaic conversion process is essential to gain the effective design criteria. To achieve this, local electronic properties including electrical potential, energy states, and charge distribution around the excitation centers have to be characterized under light irradiation since they govern the behavior of excited carriers. These properties have so far been indirectly deduced from macroscopic characterization such as current-voltage (I-V) measurement; however, it is not sufficient to clarify rather complicated roles of the nanostructures [2]. Thus, a direct measurement of those properties with high spatial resolution is required to understand the detailed mechanisms of the photovoltaic conversion process. To this end, we have been developing a platform for performing scanning tunneling microscopy/spectroscopy (STM/STS), atomic force microscopy (AFM), and Kelvin probe force microscopy (KPFM) working under light irradiation conditions.Here, we outline the characterization of a multiple quantum well (QW) SC based on III-V compounds that is expected to be a potential candidate of intermediate band type SC. First, we show the electrical potential measurements along the p-i-n junction of the SC using KPFM in air. Measurements were performed in open and short circuit configurations under light irradiation conditions [Fig.1]. We demonstrate that the dependence of the open circuit voltage on the intensity of light can be successfully measured by careful interpretation of the KPFM data. Second, we introduce some examples of the atomic scale characterization of the multiple QW using ultrahigh vacuum STM including the atomic arrangement, electronic states, and band profile. Also, charge accumulation at the QW is discussed based on the topographic measurement under light irradiation.jmicro;63/suppl_1/i12/DFU042F1F1DFU042F1Fig. 1.(a) Schematic illustration of measurement system of KPFM in air. (b) Effect of light irradiation on potential profile in open circuit configuration.

An ultrahigh-vacuum scanning tunneling microscope with an optically transparent tip was used to excite photon emission from a clean Cu(1 0 0) surface and a sub-monolayer of Cu-tetra-[3,5-di-t-butylphenyl]porphyrin (Cu-TBPP) molecules chemisorbed on a Cu(1 0 0) surface. Photons generated in a nanometer-scale area just under the tip were collected within the near-field region through the apex of the optical fiber tip. Two kinds of mechanisms for the photon emission from a Cu-TBPP/Cu(1 0 0) surface are proposed. The quantum efficiency for molecular fluorescence induced by inelastic tunneling was estimated to be ∼3×10−6 photons/electron.

Ag deposited self-assembled monolayers (SAMs) of octanethiol (CH 3 (CH 2 ) 7 SH) have been studied using scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS). At the initial stage of Ag deposition, monatomic height islands, ∼7 x 10 1 cm 2 in density, grow at the SAMs/Au(1 I I) interface and become larger as more Ag atoms are deposited up to a full monolayer coverage of Ag. The differences of the nucleation density and the growth property between Ag and Au islands can be attributed to the higher mobility of Ag atoms and the difference of the molecular packing on these islands. XPS analysis of this structure (SAMs/Ag monolayer/Au) shows that the Ag 3d 5.2 binding energy is shifted -0.3 eV with respect to bulk Ag, the C Is binding energy is ∼0.3 eV higher than that before Ag deposition, and the S 2p 3 2 binding energy exhibits little shift before and after deposition. The origin of the shift can be explained by the change of the dipole at the interface and the electrical isolation of alkyl chains from the surroundings.

Photon emission induced by tunneling electrons has been observed from a submonolayer of Cu-tetra-[3,5-di-t-butylphenyl]porphyrin (Cu-TBPP) molecules chemisorbed on a Cu(100) surface in ultrahigh vacuum. Near-field photons generated in a nanometer-scale region with Cu-TBPP molecules were collected effectively through the apex of a conductive optical fiber tip. The photon emission mechanism can be attributed to the inelastic tunneling events involving the tip, the Cu-TBPP molecules, and the Cu(100) substrate.