Nanoscale Area Research Articles

High temperature desulfurization over nano-scale high surface area ceria for application in SOFC

In the present work, suitable absorbent material for high temperature desulfurization was investigated in order to apply internally in solid oxide fuel cells (SOFC). It was found that nano-scale high surface area CeO2 has useful desulfurization activity and enables efficient removal of H2S from feed gas between 500 to 850°C. In this range of temperature, compared to the conventional low surface area CeO2, 80–85% of H2S was removed by nano-scale high surface area CeO2, whereas only 30–32% of H2S was removed by conventional low surface area CeO2. According to the XRD studies, the product formed after desulfurization over nano-scale high surface area CeO2 was Ce2O2S. EDS mapping also suggested the uniform distribution of sulfur on the surface of CeO2. Regeneration experiments were then conducted by temperature programmed oxidation (TPO) experiment. Ce2O2S can be recovered to CeO2 after exposure in the oxidation condition at temperature above 600°C. It should be noted that SO2 is the product from this regeneration process. According to the SEM/EDS and XRD measurements, all Ce2O2S forming is converted to CeO2 after oxidative regeneration. As the final step, a deactivation model considering the concentration and temperature dependencies on the desulfurization activity of CeO2 was applied and the experimental results were fitted in this model for later application in the SOFC model.

Nano-processing Utilizing Plasmon on Glass Surface by Femtosecond Laser Pulse with Template of Dielectric Particle Array

Nano-processing using a near-field generated by laser irradiation onto the nano-particle is becoming a new emerging nanofabrication technology, because it can fabricate nano-sale structures even with near-infrared laser. Nano-scale area near the contact point with the dielectric particle on the material surface can be ablated by lens effects and/or Mie scattering depending on the particle size. We report on new phenomena, leading to a new nano-processing technique via surface plasmons, even by the use of dielectric particles.

Nanotechnology in dentistry

Technology has continuously improved along with the complexity of devices. Nowadays, it is widely accepted that micro-technology, which is defined as a further reduction in the size of interconnections and components, is achieved by a conventional “top-down” method. We have now moved to a new concept and approach for fabrication from small to bigger building-block elements, which is called nanotechnology. Nanotechnology is the fabrication technology of tiny parts that is achieved by a “bottom-up” method. Nanotechnology has been developed in many areas of life sciences, such as in dentistry. This presentation provides some examples that illustrate the progress in technological growth, especially in the nanoscale. In the developments of nanotechnology, we are also concerned in many ways about its ethics and the laws of physics. The expansion in nanotechnology shows that much multidisciplinary research is being done in the nanoscale area. In dentistry, one of the examples is research in dental materials such as nanoleakage types in the use of various adhesives with resin composition. Nanodiagnostics are nanotechnology in applied molecular diagnostics. All these fields have applications in diagnostics and in point-of-care hand-held devices.

Transmission Electron Microscopy on Magnetic Phase Transformations in Functional Materials

This article reports our recent studies on the magnetic imaging by electron holography or Lorentz microscopy, which is combined with other supplementary techniques related to transmission electron microscopy (TEM). By combining with dark-field imaging, the “one-to-one correspondence” between the magnetic domain walls and antiphase boundaries (APBs) in a ferromagnetic shape memory alloy (SMA) Ni2Mn(Al,Ga) was revealed. In order to examine both magnetism and conductivity in a nanoscale area, we have developed a double probe piezodriving holder, by which microprobes can be brought in contact with the portion of interest. The conductivity measurement can be simultaneously performed with Lorentz microscopy or electron holography.

Nanoscale Evaluation of Strength and Deformation Properties of Ultrahigh-Purity Aluminum

In order to investigate the strength and the deformation properties of metals in nearly perfect crystals, the nanoindentation test is performed on aluminum samples with various purities: 99.9999% (6 N), 99.99% (4 N) and 99% (2 N). It is widely known that the strength decreases with increasing purity of metals. On the nanoscale, however, the strength has been revealed to be close to the ideal shear strength, because a nanoscale area is expected to behave as a perfect crystal. In this study, a nanoindentation system that is able to provide indentation load vs penetration depth curves is employed. The experiment is performed on ultrahigh-purity aluminum (99.9999%), and high-purity aluminum (99.99%) and commercial-purity aluminum (99%) so as to discuss the relationship between the purity level and the mechanical properties at room temperature. It is revealed that the penetration depth decreases with increasing purity, and the critical shear stress estimated from the experimental results is close to the ideal shear strength. These results suggest that a perfect crystal is harder than an imperfect crystal. Furthermore, the indentation load vs penetration depth curves indicate a discontinuous deformation of the metals. It is considered that these discontinuities are caused by the existence of impurities or the initiation and the multiplication of dislocations in these samples. [doi:10.2320/matertrans.48.1]

Light scattering by a thin wire with a surface-plasmon resonance: Bifurcations of the Poynting vector field

We analyze the energy flow during the scattering of a plane wave by a small homogeneous cylinder in the vicinity of surface-plasmon resonance, where ${\ensuremath{\epsilon}}^{\ensuremath{'}}=\mathrm{Re}\phantom{\rule{0.2em}{0ex}}\ensuremath{\epsilon}=\ensuremath{-}1$ ($\ensuremath{\epsilon}$ stands for permittivity). For the case of small dissipation, ${\ensuremath{\epsilon}}^{\ensuremath{''}}=\mathrm{Im}\phantom{\rule{0.2em}{0ex}}\ensuremath{\epsilon}ll1$, this scattering can strongly deviate from the classical dipole approximation (Rayleigh scattering). In certain specified cases, the Rayleigh scattering is replaced with an anomalous light scattering regardless the wire smallness. The phenomenon is based on interplay of the usual dissipative and radiative damping, where the latter is related to inverse transformation of localized resonant plasmons into scattered light. The anomalous light scattering possesses a variety of unusual features, such as an inverse hierarchy of optical resonances and a complicated near-field structure, which may include optical vortexes, optical whirlpools, and other peculiarities in nanoscale area.

Simultaneous measurements of conductivity and magnetism by using microprobes and electron holography

This study demonstrates a transmission electron microscopy based system that enables simultaneous measurements of conductivity and magnetism in a nanoscale area. A double-probe piezodriving holder is developed in order to determine the conductivity in any part of a thin-foil specimen. The conductivity measurement can be combined with electron holography, which can be used to obtain a magnetic flux map of the same area. This system can be applied extensively for the research and development of electronic and/or magnetic materials.

Nanoscale selective area epitaxy of C60 crystals on GaAs by molecular beam epitaxy

Fabrications of nanoscale structures of C60 crystals on GaAs substrates are successfully achieved by selective area molecular beam epitaxy. The grown structures are examined by scanning electron and atomic force microscopies. The {100} and {110} facets appear at the side boundaries of the C60 crystals. The surface morphology of C60 crystals grown on GaAs (111)B is much smoother than that grown on GaAs (001). Good crystalline properties of C60 films grown on GaAs (111)B are also confirmed by x-ray diffraction φ (phi) scan measurement. During C60 deposition, C60 molecules landing on SiO2 mask either evaporate or migrate to the open area enhancing the growth rate at the edges of the area. The mean diffusion length of C60 molecules on SiO2 mask at 200°C is evaluated to be 200–300nm. The C60 crystals grown on GaAs (001) with narrow open area (100–200nm) have a fourfold symmetry, indicating that the epitaxial orientation of these C60 crystals is [001]. This result should be compared with the [111] orientation observed in planar or wide area growth.

超高純度アルミニウムの強度および変形特性の微視的評価

In order to investigate the strength and the deformation properties of metals in nearly perfect crystals, the nanoindentation test is performed on aluminum samples with various purities: 99.9999% (6 N), 99.99% (4 N) and 99% (2 N). It is widely known that the strength decreases with increasing purity of metals. On the nanoscale, however, the strength has been revealed to be close to the ideal shear strength, because a nanoscale area is expected to behave as a perfect crystal. In this study, a nanoindentation system that is able to provide indentation load vs penetration depth curves is employed. The experiment is performed on ultrahigh-purity aluminum (99.9999%), and high-purity aluminum (99.99%) and commercial-purity aluminum (99%) so as to discuss the relationship between the purity level and the mechanical properties at room temperature. It is revealed that the penetration depth decreases with increasing purity, and the critical shear stress estimated from the experimental results is close to the ideal shear strength. These results suggest that a perfect crystal is harder than an imperfect crystal. Furthermore, the indentation load vs penetration depth curves indicate a discontinuous deformation of the metals. It is considered that these discontinuities are caused by the existence of impurities or the initiation and the multiplication of dislocations in these samples. [doi:10.2320/matertrans.48.1]

High Temperature Plasticity and Chemical Bonding State of Grain Boundary Nano-scale Area in Ceramics

High Temperature Plasticity and Chemical Bonding State of Grain Boundary Nano-scale Area in Ceramics

Enhanced Raman scattering for temperature measurement of a laser-heated atomic force microscope tip

Illuminating a silicon cantilever of an atomic force microscope with a focused laser beam creates heat that can be funneled into a nanoscale area at the apex of its tip. To characterize the heating dynamics and measure the temperature of the tip, a Raman scattering pump-and-probe method is used. It is found that at the apex of the tip the intensity of the Raman Stokes and anti-Stokes components are significantly enhanced relative to those obtained on a bulk silicon sample. Modeling the temperature rise at the tip of the cantilever by a closed-form analytical expression gives good agreement with the Raman measurements. This model can be used to design the structure of the cantilever so that the heat delivery to its tip is optimized. Such an optimized cantilever can potentially be used in high-density, heat-assisted magnetic recording, optical data storage using phase-change media and thermomechanical recording systems, for example, where nanoscale heated regions are of importance.

Equilibrium crystal shape of GaAs in nanoscale patterned growth

The equilibrium crystal shape (ECS) of GaAs homoepitaxially grown on a nanoscale SiO2-patterned (001) plane by molecular beam epitaxy is investigated. A GaAs epilayer selectively grown on a nanoscale area bounded by a circular SiO2 mask undergoes faceting, resulting in a pyramidal shape with {110} sidewalls. Growth is slowed or terminated with the generation of these {110} facets even with a continuing supply of Ga atoms. This implies that the pyramidal shape is energetically very stable. Based on experimental results and the Wulff construction, a {110}-type sidewall pyramid is proposed as an ECS of GaAs on (001) in nanoscale patterned growth.

Nanoheteroepitaxy for the integration of highly mismatched semiconductor materials

We describe an ongoing study of nanoheteroepitaxy (NHE), the use of nanoscale growth-initiation areas for the integration of highly mismatched semiconductor materials. The concept and theory of NHE is briefly described and is followed by a discussion of the design and fabrication by interferometric lithography of practical sample structures that satisfy the requirements of NHE. Results of NHE growth of GaAs-on-Si and GaN-on-Si are described, following the NHE process from nucleation through to coalescence. Micro-Raman measurements indicate that the strain in partially coalesced NHE GaN-on-Si films is <0.1 GPa.

From molecular biology to nanotechnology and nanomedicine

Great progress in the development of molecular biology techniques has been seen since the discovery of the structure of deoxyribonucleic acid (DNA) and the implementation of a polymerase chain reaction (PCR) method. This started a new era of research on the structure of nucleic acids molecules, the development of new analytical tools, and DNA-based analyses. The latter included not only diagnostic procedures but also, for example, DNA-based computational approaches. On the other hand, people have started to be more interested in mimicking real life, and modeling the structures and organisms that already exist in nature for the further evaluation and insight into their behavior and evolution. These factors, among others, have led to the description of artificial organelles or cells, and the construction of nanoscale devices. These nanomachines and nanoobjects might soon find a practical implementation, especially in the field of medical research and diagnostics. The paper presents some examples, illustrating the progress in multidisciplinary research in the nanoscale area. It is focused especially on immunogenetics-related aspects and the wide usage of DNA molecules in various fields of science. In addition, some proposals for nanoparticles and nanoscale tools and their applications in medicine are reviewed and discussed.

Studies on Surface and Interface with X-ray Absorption Fine Structure (XAFS). Analysis of Local Structures in Light-Element Materials by Core-Excitation Spectra in Transmission Electron Energy-Loss Spectroscopy.

Analysis of core-loss spectra in electron energy-loss spectroscopy associated with transmission electron microscopy (TEM-EELS) is introduced as a tool giving information equivalent to X-ray absorption fine structure (XAFS) on nano-scale areas. After briefly describing the principle of TEM-EELS, including extended energy-loss fine structure (EX-ELFS) and energy-loss near edge structure (ELNES), merits and demerits of TEM-EELS are compared to those of XAFS analysis. A new analysis method applying the ‘wavelet transformation’ is introduced. This method is effective particularly to isolate the signals from the original EXELFS spectrum containing noises and artifacts. Furthermore, information on higher-order coordination shells and many-body correlations can be extracted from the EXELFS interference function, using the wavelet transformation. As an application example of this method, we show characterization of local structural relaxation of amorphous silicon by intense X-ray illumination. Finally some future prospects of TEM-EELS are briefly mentioned.

The Electrical Measurement of Molecular Junctions

ABSTRACT: We present the investigation of the electrical transport of metal/(organic molecule or monolayer)/metal junctions. Utilizing a novel mechanically controllable break junction to form a statically stable system, we have self‐assembled molecules of benzene‐ 1,4‐dithiol onto two facing gold electrodes allowing for direct observation of charge transport through the molecules. Current‐voltage I(V) measurements provides a quantitative measure of the conductance of a junction containing a single molecule. We have also created a technique to form well‐defined, stable, and reproducible metallic contacts to a self‐assembled monolayer of 4‐thioacetylbiphenyl with nanoscale area. Electronic transport measurements show a prominent rectifying behavior arising from the asymmetry of the molecular heterostructure. Variable‐temperature measurements reveal the dominant transport mechanisms, such as thermionic emission for the Ti‐organic system. These techniques demonstrate the capability of electrically characterizing and engineering conductive molecular systems for future potential device applications.

Nanoscale Si selective homoepitaxial growth observed by scanning tunneling microscopy

Nanometer-scale Si selective epitaxial growth on oxide-passivated Si(0 0 1) and Si(1 1 0) surfaces was dynamically monitored by scanning tunneling microscopy combined with chemical beam epitaxy. The precursor used was disilane Si 2H 6 and the oxide thickness was 0.3 nm. Nanoscale window areas were produced in oxide layers by oxide thermal decomposition. The thin oxide layers were found to be useful for the selective growth of nanoscale Si crystals. The crystals grown on Si(0 0 1) showed quadrangular pyramids consisting of double-atomic-layer stepped structures. The crystals on Si(1 1 0) were pyramids surrounded by {17 15 1} facets. The growth mechanism of the crystals is discussed.

Nanoscale metal/self-assembled monolayer/metal heterostructures

We present the investigation of novel metal/organic monolayer/metal heterostructure diodes. Our technique provides well-defined, stable, and reproducible metallic contacts to a self-assembled monolayer of 4-thioacetylbiphenyl with nanoscale area. Electronic transport measurements show a prominent rectifying behavior arising from the asymmetry of the molecular heterostructure. Variable-temperature measurements reveal that thermal emission of electrons over a barrier of 0.22 eV dominates for electron injection from Ti into the organic layer while the transport for electron injection from Au into the organic layer satisfies the formula for hopping conduction.

Surface Molecular Rearrangements on the (0001) Face of C70 Single Crystals

Surface molecular rearrangements on the (0001) face of C70 single crystals were investigated using atomic force microscopy (AFM). On the surface of a freshly prepared crystal, the molecules are arranged in a slightly distorted hexagonal close-packed (hcp) structure, with an average nearest-neighbor distance of 10.5±0.3 Å. After the samples were stored for two weeks in dry air, the surfaces of the crystals became relatively rough. A quasi-two-dimensional molecular rearrangement from a purely hexagonal structure to a mixture of hexagonal, cubic, and rhombic structures was observed over a several-nanometer region. For different crystal growth conditions, a superstructure resulting from a quasi-three-dimensional surface molecular rearrangement was grown and observed on the surface of the crystals. The superstructure appears as an ordered array of domain boundaries between surfaces regions with face-centered cubic (fcc)-type stacking (CBA) and hcp-type stacking (ABA) regions. The coexistence of the different phases in a nano-scale area is probably due to the similarity of the cohesive energies of the phases. The AFM images represent the direct observation of a transient state in a surface phase transformation on the C70 single crystals.

A Cbed Procedure for Determining Local Residual Stresses from Nanoscale Areas in Cermets

ABSTRACTA convergent beam electron diffraction method was used in a transmission electron microscope to determine residual thermal stresses from nanometer-scale areas in a ceramic-metal (cermet) composite material. It is demonstrated that the method is simple, but requires a standard sample for each of the phases in the composite. The principle of the technique is that the stresses are determined by comparing higher order Laue zone line shifts, due to lattice strain, in high-symmetry zone-axis electron diffraction patterns recorded under the same experimental conditions from the unknown phases and the standards. The application of the method to composite systems containing dissimilar phases, such as ceramic-metal composite systems, demonstrates the universality of the technique in obtaining local structural information of anisotropic strain unambiguously with a high accuracy. The procedure involved is described in detail with application to B4C-AI, a three-dimensional intertwined ceramic-metal composite.