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Thecrystal structure of a γ-Ga2O3layergrown epitaxially on an MgO substrate by a vapor phase transport methodwas investigated by transmission electron microscopy, electron diffraction,and scanning transmission electron microscopy with aberration correctors.Some forbidden reflections were excited in electron diffraction patternsby double reflection from the vicinity of the substrate interface.Phase boundaries are observed in atomic column images using high-angleannular dark field images. A structure model is proposed to explainthe experimental results. Cation vacancy ordering is introduced inthe structure model to distort the γ-Ga2O3crystal lattice along one axis and reduce the lattice mismatch withthe substrate. Some grains are formed and alter the directions toreduce the distortion for the other axis. The grains are stacked with{110} phase boundaries and form a rhombic dodecahedral honeycomb.The rhombic dodecahedral honeycomb structure model with cation vacancyordering is stabilized by the lattice mismatch between the γ-Ga2O3crystal and the MgO substrate, and it disappearsat a depth of 170 nm from the interface. [ABSTRACT FROM AUTHOR]

The low-energy Ar-ion milling method was used to prepare ultrathin specimens for transmission electron microscope observation. The samples were thinned initially by a usual focused ion beam technique or typical Ar-ion milling with a high energy of 2–10 keV and were thinned additionally by an Ar-ion beam with an energy less than 1 keV, typically 500–900 eV. This low-energy ion beam was scanned over the specimen, and secondary electrons induced by the ion beam could be detected to form secondary electron images with a resolution of a few micrometre. Because a desired area can be selected and thinned by the low-energy ion beam, redeposition or cross contamination from irradiation of a metal grid that supports the sample can be prevented. It was shown that the low-energy Ar-ion beam thins a surface amorphous damage layer preferentially and effectively rather than a crystal specimen. Images from ultrathin specimens of two different materials revealed a detailed structure. [ABSTRACT FROM PUBLISHER]

Solid solutions (Ho xIn1− x)1.9Sn0.1O3 with x = 0-0.3 were synthesized to employ as dispersion matrix for oleic acid coated Fe3O4 nanocrystals (NCs). The x = 0.05 matrix exhibited a resistance minimum at a non-zero temperature in each temperature dependent resistivity with magnetic fields of 0 and 1 T, and a negative magnetoresistance. The sample of oleic acid coated Fe3O4 NCs dispersed in the x = 0.05 matrix showed enhanced spontaneous magnetization as the factor of ≈1.3 relative to as-synthesized oleic acid coated Fe3O4 NCs. [ABSTRACT FROM AUTHOR]

Based on the transport of intensity equation (TIE), a phase map can be readily retrieved from only three images of a focal series. The retrieval procedure does not require an iterative calculation and it is performed very fast with the use of the fast Fourier transform. However, it must be noted that sensitivity depends on the spatial frequency components and difficulties are encountered when phase information is retrieved to be of the same quality for all frequency components. Since the retrieved phase is influenced by conditions in which the focal series was taken, it is important to select the appropriate conditions and parameters used in this process. Optimal conditions to preserve the quantitativeness of phase maps measured by the TIE method are discussed theoretically and they are demonstrated by measuring phase shifts in silver particles. It was found that the high quantitativeness can be obtained by selecting appropriately a defocus difference and a high pass filter constant according to the frequency components for the objects. [ABSTRACT FROM PUBLISHER]

The visibility of a Si crystalline nanoparticle of diameter 2 nm embedded in an amorphous SiO2 layer is evaluated quantitatively by multislice calculation. The visibility depends on the crystal orientation of the Si nanoparticle, the thickness of the amorphous SiO2 layer and the defocus. Scherzer defocus always gives the highest visibility at any crystal orientation. The visibility is higher when the incident beam is parallel to the (111) planes and the (111) fringes are most visible. The image of a Si nanoparticle is obscured by random images from the amorphous SiO2 layer and the Si nanoparticle becomes invisible when it is misoriented or the amorphous layer is thicker than 60 nm. The probability that a Si nanoparticle can be distinguished from the random noise of amorphous images is 89% when the thickness of the amorphous SiO2 layer is 12 nm, but this is reduced to 21% when the layer is 48 nm thick. These quantitative results are useful when estimating the density of Si nanoparticles including invisible nanoparticles. [ABSTRACT FROM PUBLISHER]

Abstract: Crystal structure of Ga2O3 nanocolumns grown on MgO substrate is analyzed by electron microscopy and electron diffraction study. The nanocolumns have β-Ga2O3 structure and the growth direction is [001] directions. A thin γ-Ga2O3 layer grows on the substrate to relax the lattice misfit between MgO and β-Ga2O3. The bottom layer of the γ form layer is disordered by {110} stacking faults. Poly crystalline structure that consists of β-Ga2O3 and γ-Ga2O3 nanocrystals exists between the β form nanocolumns and the γ form layer. The γ form changes gradually to the β form growing up to the nanocolumn. Though various crystal forms appear in a specimen, oxygen cubic close-packed lattice in crystal structures has always the same orientation in all layers including the MgO substrate. [Copyright &y& Elsevier]

The basic structure of α-LiFeO2, lithium iron oxide, is a cubic NaCl-type structure with a lattice constant of 0.42 nm; some short-range ordering characterized by octahedral clusters exists. The local structure of the short-range ordering was investigated by transmission electron microscopy and electron diffraction. A new short-range ordering structure was found in local areas. The local structure has a cubic lattice with a doubled lattice constant. The occupation factors of cations on Wyckoff sites 4(a) and 4(b) are different from those on 24(d) sites, but the stoichiometric composition in cubic clusters is the same as the macroscopic composition. The number of pairs in which iron cations exist in nearest-neighbor sites and next nearest-neighbor sites is reduced in the structure. This means that a magnetic interaction between the iron cations is reduced by cation ordering even without spin ordering at room temperature. [ABSTRACT FROM AUTHOR]

The basic structure of α-LiFeO2, lithium iron oxide, is a cubic NaCl-type structure with a lattice constant of 0.42 nm; some short-range ordering characterized by octahedral clusters exists. The local structure of the short-range ordering was investigated by transmission electron microscopy and electron diffraction. A new short-range ordering structure was found in local areas. The local structure has a cubic lattice with a doubled lattice constant. The occupation factors of cations on Wyckoff sites 4(a) and 4(b) are different from those on 24(d) sites, but the stoichiometric composition in cubic clusters is the same as the macroscopic composition. The number of pairs in which iron cations exist in nearest-neighbor sites and next nearest-neighbor sites is reduced in the structure. This means that a magnetic interaction between the iron cations is reduced by cation ordering even without spin ordering at room temperature. [ABSTRACT FROM AUTHOR]

We have developed a robust method for fabricating Si nanoregions in silica glass using femtosecond laser processing. We attained a vivid formation of silicon-rich nanoregions site-selectively generated in SiO2 by irradiation of femtosecond laser pulses to the interface of a SiO2 substrate and deposited aluminum (Al) thin film, where the Al element acts as a gettering site for O atoms. Growth of high-density Si nanocrystals and amorphous Si was observed by transmission electron microscopy in the region that was multiply irradiated with the femtosecond laser. Furthermore, local annealing with a cw laser enhances the Si nanocrystal growth, which was determined by micro-Raman measurements. [ABSTRACT FROM AUTHOR]

Presents a letter to the editor about the crystal structure of the nanorods.

Splitting between the field-cooled dielectric constant and the zero-field-cooled dielectric constant was observed for a diluted system of LiTaO3 nanoparticles (diameter ≈30 Å) embedded in amorphous SiO2. At the applied field frequency of 100 kHz, the real part of the field-cooled dielectric constant diverged from that of the zero-field-cooled one at ≈380 °C. The bifurcation point of the history-dependent dielectric constant rose from ≈310 to ≈540 °C upon increasing the field frequency from 10 to 1000 kHz. Bulk LiTaO3 powders showed no splitting in the history-dependent dielectric constant and the maximum at 645 °C in the real part of the dielectric constant, despite the variation of frequency. Both the splitting of the history-dependent dielectric constant and the frequency dependence of the bifurcation point suggest that the LiTaO3 nanoparticles with a single-domain structure were in the superparaelectric state as a consequence of insignificant cooperative interactions among the nanoparticles in the diluted system. The energy barrier of ≈0.9 eV separating two (+p and -p) polarization states corroborated the potential of the LiTaO3 nanoparticle for ultrahigh-density recording media applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A large frequency dependence of the maximum dielectric constant temperature was observed for LiTaO[SUB3] nanocrystals (the diameter ≈ 20 Å) dispersed in mesoporous silicate. At the applied field frequency of 100 kHz, the maximum temperatures in the real and imaginary parts were 365 and 345 °C, respectively. The maximum temperature in the real part is apparently lower than the paraelectric-ferroelectric transition temperature (645 °C) of bulk LiTaO[SUB3]. The maximum temperature in the imaginary part rose from 285 to 420 °C with increasing frequency from 10 to 1000 kHz. Since the bulk LiTaO[SUB3] shows no relaxor behavior, such superparaelectric behavior is obviously a consequence of nanominiaturization of LiTaO[SUB3] crystal and insignificant cooperative interactions between the nanoparticles. [ABSTRACT FROM AUTHOR]

In this reply, the authors show that the argument by Scott regarding the band gap of bulk SrBi[sub 2]Ta[sub 2]O[sub 9] (SBT) is not based on concrete evidence. The authors will also show additional data from a Raman study of a powdered SBT sample to prove that the surface of the specimen was not covered by Bi[sub 2]O[sub 3]. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Heterostructures provide a great chance to tune the properties and functions of a nanomaterial, e.g., its mechanical and electrical properties, and thus allowing for the design and realization of novel nanoelectromechanical devices. Boron nitride and carbon nanotubes, with similar structure and mechanical properties but dramatically different electrical properties, are ideal candidates for investigating nanoscale heterostructured materials. In this work, graphitic C‐coated BN nanotubes (BN‐C NTs) were synthesized and their mechanical and electrical properties were simultaneously measured using in situ high‐resolution transmission electron microscopy (TEM). As a function of the coated carbon content, the elastic modulus obtained from second order harmonic resonance of heterostructured nanotubes could be tuned from ∼140 to ∼700 GPa, and their electrical resistivity could be adjusted within three orders of magnitude from ∼0.16 to ∼2.5×10−4 Ω · m. This work opens the way for making custom‐designed heterostructures for the requirements of specific applications. Coaxial BN‐C heterostructured nanotubes are synthesized in a large scale and in situ. Transmission electron microscopy (TEM) experimental results showed that their mechanical and electrical properties can be tuned over a wide range of values as a function of the wrapped C content. [ABSTRACT FROM AUTHOR]

We propose a new theoretical kinetic model of strength recovery by oxidation-induced self-healing of surface cracks in composites containing a healing agent (HA). The kinetics is a key parameter in the design of structural components that can self-heal the damage done in service. Based on three-dimensional (3D) observations of crack-gap filling, two crack-gap filling models, i.e., a bridging model and a tip-to-mouth filling model, are incorporated in the proposed kinetic model. These crack-gap filling models account for the microstructural features of the fracture surfaces, crack geometry, and oxidation kinetics of the healing-agent. Hence, the minimum and maximum remaining flaw sizes in the healed crack gaps are estimated for various healing temperatures, times, and oxygen partial pressure conditions. Further, the nonlinear elastic fracture mechanics suitable for small-sized remaining flaws, together with a statistical analysis of the original Weibull-type strength distribution, enables the prediction of upper and lower strength limits of the healed composites. Three sintered alumina matrix composites containing silicon carbide (SiC)-type HAs with various volume fractions and shapes, together with monolithic SiC ceramics, are considered. The strength of the healed-composite predicted by our model agrees well with the experimental values. This theoretical approach can be applied to HAs other than SiC and enables the design of self-healing ceramic components for various applications. [ABSTRACT FROM AUTHOR]