Eiji Aoyagi

Strong flux pinning centers in Y‐Ba‐Cu‐O films prepared by chemical vapor deposition

The Y‐Ba‐Cu‐O film prepared by chemical vapor deposition showed Tc=91.5 K and Bc2 (77.3 K)=60 T defined by zero resistance. The Jc values measured at 77.3 K were 7.8×105 A/cm2 at B=0 and 1.0×105 A/cm2 at 16 T, magnetic fields perpendicular to the c axis. Small disk‐shaped precipitates possibly regarded as strong flux pinning centers in the Y‐Ba‐Cu‐O films were observed using transmission electron microscopy. The evaluation of Jc related to the concentration and configuration of the precipitates was in reasonable agreement with the measured Jc values.

Effect of Co Substitution on Tc in YBa2Cu3-xCoxO7-y,(x=0-1)

The crystal structure of YBa2Cu3-xCoxO7-y(x=0~1) was investigated by X-ray and electron diffraction and the crystallographic site of Co atoms was directly determined by electron-channelling-enhanced microanalysis. It was shown that the structure is tetragonal based on the tripled perovskite structure, and that Co atoms occupy the Cu atom sites. Electric resistivity was measured with changing Co atom content and it was shown that Tc did not decrease monotonically with increasing Co atom concentration.

Formation and atomic structure of a tetrahedral carbon onion

A carbon onion with a tetrahedral structure was produced by electron-beam irradiation of amorphous carbon, and structure models of C84 and C276 were optimized by molecular mechanics and semi-empirical molecular orbital calculation.

Effects of BaMO3 (M = Zr, Sn) Nanorods on Critical Temperature of ErBa2Cu3Oy Films

In order to study the degradation of critical temperature Tc for a coated conductor using nanorods, the relationship between Tc and nanorod shape was investigated by transmission electron microscopy for ErBa2Cu3Oy (Er123) films with BaZrO3 (BZO) and BaSnO3 (BSO) nanorods. The dependence of Tc on the BZO or BSO content was different, however, the nanorods interface density dependence of Tc was the same for both. Thus, the interface density of the nanorods controls Tc of the nanorod-added films. The different degradation in Tc between the BZO and BSO nanorod-added films originated in differences in the nanorod diameter and density.

Transmission electron microscopy of the sequence of phase formation in the interfacial solid-phase reactions in Ta/Si systems

The interfacial reaction of Ta thin films on (100) Si was investigated by high-resolution transmission electron microscopy. An amorphous layer was observed at the as-deposited Ta/Si interface. A phase of Ta5Si3 was first found to form at the interface between a Ta overlayer and the amorphous layer after annealing at 560 °C for 1 h. Annealing at 630 °C for 1 h led to the formation of another interlayer due to the outdiffusion of Si between the amorphous layer and Si. The phase in this interlayer transformed from a metastable one to TaSi2 due to annealing at 680 °C for 1 h. The first nucleation of Ta5Si3 at the interface between Ta and the amorphous layer implies that the initially formed amorphous layer has a metal-rich composition close to Ta5Si3. The formation of the interlayer between the amorphous layer and Si prior to the nucleation of TaSi2 was considered as a result of a kinetic constraint to favor the nucleation of TaSi2.

Synthesis and superconductivity of oxycarbonates of the Tl-1201 phase

Abstract TlBa x Sr 4- x Cu 2 (CO 3 )O y oxycarbonates with the Tl-1201 structure were synthesized over a wide range of x (1.0≤ x ≤3.2) and examined by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy and magnetometry methods. New phases with the Tl-1201 structure having 6 and 7 times periodicities along the b -axis were isolated. The former was stable for a wide Ba-rich range (1.8≤ x ≤3.2), and the latter was observed for a smaller Ba content range (1.2≤ x ≤1.6). The phase stability was found to depend on the synthesis condition. The maximum T c of the as-synthesized specimen in this series occurred at about 70 K around x =2.0. The Meissner volume fraction of the as-synthesized specimen ( x =2.4) was 30% at 5 K.

Application of Extremely Thin ZrN Film as Diffusion Barrier between Cu and SiOC

As an extremely thin diffusion barrier applicable to Cu interconnects for the 45 nm technology nodes, we propose a barrier material without interface layers that can become a cause of barrier consumption owing to solid-phase reaction and/or intermixing. We examine the barrier properties of a reactively sputtered ZrN barrier as thin as 5 nm between Cu and SiOC. The ZrN barrier with a slightly N-rich composition tolerates annealing at 500 °C for 30 min. Transmission electron microscopy indicates the absence of interface layers adjoining the barrier. Using the ZrN barrier, we can demonstrate the effectiveness of the interface-layer-free characteristics for an extremely thin barrier of high performance.

Transmission Electron Microscopy Study on Microstructure of Tungsten/Carbon Multilayer Films

Microstructure changes of tungsten/carbon (W/C) multilayer films with heat treatments were investigated by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction. When the W/C amorphous multilayer films were annealed in vacuum at 800 or 900°C, the X-ray reflectivity became 30% higher than that of as-prepared ones in association with a slight increase of the periodic spacing of the multilayers. HRTEM images of the annealed specimens revealed the existence of randomly distributed microcrystallites of W2C in the W layers. The increase of X-ray reflectivity was interpreted well with a simple structural model assuming the decrease of the C-atom-number density in the C layers.

Microstructure and Magnetic Properties of Sputter-Deposited Ho–Co Alloy Thin Films with Perpendicular Magnetic Anisotropy

The structures of Ho19Co81 thin films fabricated by r.f. sputtering in Ar atmosphere are discussed. Electron microscopic observation shows that a columnar structure is developed along the direction of the film thickness. Each column is largely amorphous but contains locally-microcrystalline regions 30–50 A in size. A high-resolution photograph of the lattice image indicates that these microcrystalline regions very likely consist of HoCo5 in a short range, and that the hexagonal c-axis is nearly directed along the thickness direction. It is suggested that the presence of such microcrystalline regions may need to be taken into account in discussing the origin of the observed perpendicular magnetic anisotropy in rare-earth transition metal amorphous films.

Atomic Layer Deposition of Thin VNx Film from Tetrakis(diethylamido)vanadium Precursor

Thin vanadium nitride (VNx) films were grown by atomic layer deposition using tetrakis(diethylamido)vanadium as a precursor and NH3 as a reactant. A growth rate of 0.1 nm/cycle without incubation time is obtained. Transmission electron microscopy reveals that a nanocrystalline texture in random orientation is characteristic of the VNx film, which is favorable as an extremely thin barrier application. A low carbon impurity level (~6 at.%) is achieved owing to acceleration of the transamination between the V(NR2)4 precursor and NH3. The lowest resistivity of 120 µΩ cm is successfully achieved for the VNx film prepared under optimized conditions.