One of the critical issues for development of the nuclear fusion demonstration reactor (DEMO) is the high heat flux on heat-resistant equipments, especially the blanket and divertor. Materials of such equipments require relatively high thermal conductivities. In this study, we developed iron-based composite materials with carbon nanotube (CNT) and copper, which have high thermal diffusivities, by means of Hot Pressing (HP) and Spark Plasma Sintering (SPS).

The thermal diffusivity in the iron/CNT composites was not high enough compared with that of pure iron, while iron/copper composite showed a relatively high thermal diffusivity in the joining conditions. One of the reasons not to be improved thermal diffusivity could be non-mono-dispersion of CNT by the formation of carbides in the matrix.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

An In0.25Ga0.75Sb/InAs strained-layer superlattice, grown by molecular-beam epitaxy (MBE) on a GaSb[001] substrate, has been characterized by four-circle x-ray diffractometry. This system, proposed by Maliot and Smith for ir detection application, is challenging because of the two group V species and the likelihood of cross-incorporation of the different elements during growth, leading possibly to interdiffusion and thus, to a more diffuse interface. High-resolution x-ray diffraction (XRD) profiles were obtained about several reciprocal lattice points in order to extract a reliable set of structural parameters. The profiles were then successfully modeled by computer simulation. The presence of many sharp higher-order satellite reflections in the XRD profiles is a measure of the high quality of the superlattices. The normal and lateral structural coherence was also measured and will be discussed.

We have confirmed that grain boundaries are related to leakage problems in Ta2O5/SiON capacitors for high dielectric DRAMs. XRD studies using an intensity ratio of (200) to (001) showed that the crystallographic structure of Ta2O5 film was strongly dependent on preparation conditions. As the (200) oriented grains grew faster than the other grains, it became important to control its grain growth in forming uniform grain boundaries. TEM observation has shown that Ta2O5 film with a high intensity ratio of (200) to (001) was made up of large size grains and had SION interface intruding into grain boundaries. By using the current-mode AFM, we could monitor leakage current directly through grain boundaries on Ta2O5 film.

We describe three different aspects of the self-organization of steps and domain boundaries of a 7×7 reconstruction on SI(111) surfaces. The first is the formation of a triangular-tiled pattern of “1×1’ and 7×7 domains during the phase transition. ‘1÷1’ and 7×7 domains have different surface stresses. The triangular-tiled pattern is stabilized through stress relaxation. The second is the step arrangement inside a hole, which was fabricated by a standard lithographic technique. The step arrangement in the hole depends on the temperature. Below the ‘1×1’-to-7×7 phase transition, the hole has a three-fold symmetry consisting of step-bunched and non-bunched regions. This is because the step arrangement on the vicinal Si(111) surfaces depends on the direction of the steps. The third aspect is the formation of a pattern of steps and domain boundaries induced by Si growth. During the step-flow growth on Si(111), steps preferentially protrude along the domain boundaries on the lower terrace. The resulting changes in step shape induce a unique rearrangement of the domain boundaries, the number of which decreases during growth. However, when a periodic pattern is formed in the initial stages, it remains stable during growth.

Effects of an excitation frequency on on-axis rf magnetron sputtering have been studied for fabrication of YBa2Cu3O7−δ thin films on MgO (100). The excitation frequencies examined are 13.56, 40.68, 67.80, and 94.92 MHz. Sputtering was performed in a pure argon gas in order to distinguish excitation frequency effects of oxygen emitted from a target from those of oxygen in a mixture atmosphere. Excitation frequencies higher than 40.68 MHz result in both a low self-bias voltage and a narrow distribution of the energy of sputtering ions, which reduce resputtering of a film surface caused by negatively charged oxygen from the target. Thin films of a-axis oriented YBa2Cu3O7−δ deposited at 94.92 MHz have shown better morphology and crystallinity than those at lower excitation frequencies under the same conditions. Furthermore, a-axis oriented superconductive YBa2Cu3O7−δ films have successfully sputtered in 200 mTorr atmosphere of argon and oxygen on SrTiO3 (100) by using an excitation frequency of 94.92 MHz, showing a full width at half maximum of 0.1° in the rocking curve through the (100) peak and a very smooth surface. The zero resistance temperature is, at most, 33 K.

The results of specular and diffuse x-ray scattering studies of multilayers are discussed. We show here that such studies can yield detailed statistical information about the interfacial roughness and morphology. Results on a GaAs/AlAs multilayer are presented and the data is analyzed within the Born approximation.

The microstructure of the electroless-plated CoNiReP/NiMoP doublelayered media was examined with various methods and the origin of the inplane anisotropy initial regions of the CoNiReP recording layers was discussed. It was confirmed that the initial region consists of randomly oriented fcc phase with Ni-rich composition, showing the granular condition, while the perpendicular anisotropy region at the top consists of <002> perpendicularly oriented hcp phase, showing the columnar structure. It is considered that the formation of the initial region is due to a preferential deposition of Ni onto the underlayers, and that the thickness of the initial region changes due to a change in the condition of the underlayers, especially that of deposition activity and/or morphology at their surfaces.

The nuclear scattering of 3 MeV protons on oxygen is applied to determine the oxygen stoichiometry in high Tc superconducting (HTS) thin films. Their oxide substrates are used as reference standards. This is a nondestructive, absolute method, which is as simple as the traditional Rutherford Backscattering Spectrometry (RBS). However, the relative sensitivity to oxygen has been enhanced. To obtain the stoichiometry, one only needs the data on atomic stopping powers and the chemical composition of the substates.When the measurements on the thin film and on the substate are carried out simultaneously, the inaccuracy in charge integration can be avoided and the accuracy of the oxygen stoichiometry can be further improved.

We present the possibilities that metallic superlattices offer for the study of materials at length scales ranging from a few to hundreds of angstroms. The materials problems being studied span practically all interesting solid-state phenomena, including superconductivity, magnetism, elastic behavior, development of novel materials, diffusion, ion beam mixing, crystallization, and amorphization. Several applications are also being pursued. We present a few examples of problems that can be studied at different length scales. Emphasis is made that for a proper study of materials properties, extensive structural characterization is imperative.

We have generalised our x-ray diffraction results from amorphous/crystalline multilayers, to include random interfacial disorder of a gaussian type. A general relation is obtained which can be applied to both crystalline/crystalline and crystalline/amorphous multilayers. This gaussian fluctuation or “roughness” can strongly reduce the long-range atomic order along the growth direction of the multilayer. Using classical structure factor calculations, we simulate the evolution of x-ray patterns as a function of the fluctuation amplitude, the superlattice wavelength, and the interatomic distances. Applying this model to the crystalline/crystalline case we fit the experimental Nb/Cu data, deduce a fluctuation amplitude of about 0.4 Å, and relate it to the lattice mismatch between Nb and Cu. For crystalline/amorphous systems (Pb/Ge) this amplitude can be significantly larger (2 Å).

The stability of Pb/Ge and Pb/C multilayers has been studied over a broad temperature range by x-ray diffraction experiments. In the Pb/Ge system an amorphous to microcrystalline phase transformation of the Ge-layers was already observed at ≃ 100 °C. This transition destroys the modulation structure and improves the Pb(111) texture. In the Pb/C multilayers, the layered structure was still present at temperatures higher than the melting temperature of Pb. Contrary to recent publications, no depression of the melting temperature of the two-dimensional Pb layers could be observed.