Hiroyasu Saka

Melting temperature of In particles embedded in an Al matrix

Abstract The melting and freezing temperatures of small In particles with a radius r of less than 20 nm embedded in an Al matrix have been measured as a function of particle size using in situ heating in an electron microscope. The melting temperature of In particles whose radii are smaller than 15 nm is higher than that of bulk material and increases with decreasing r. The freezing temperature is lower than the melting temperature of bulk material for all radii studied and has a minimum at around r = 13 nm. The behaviour of the melting of embedded particles contrasts sharply with that of free particles, for which the melting temperature decreases with decreasing r. The difference is discussed in terms of the interfacial energies between the Al matrix and liquid or solid In.

Characteristics of Indium-Tin-Oxide/Silver/Indium-Tin-Oxide Sandwich Films and Their Application to Simple-Matrix Liquid-Crystal Displays

We developed low-resistivity transparent conductive films having the structure of indium-tin-oxide/silver/indium-tin-oxide (ITO/Ag/ITO). The thin silver film was sandwiched by ITO films. Our goal was to study the characteristics of the sandwich films and the display characteristics of simple-matrix liquid-crystal displays (LCDs) fabricated using the sandwich film. The electrical and optical characteristics of the sandwich films depended greatly on the thickness of the ITO and silver layers. Low resistivity and high transmittance were obtained when the film structure had a thickness of ITO/Ag/ITO: 40 nm/15 nm/40 nm. The simple-matrix LCD fabricated using a sandwich of ITO/Ag/ITO exhibited 27%–48% reduction in the level of crosstalk compared to the conventionally available simple-matrix LCDs fabricated using a single-layer ITO film; thus, the display performance was improved.

Improvement of hydrogen storage properties of melt-spun Mg–Ni–RE alloys by nanocrystallization

The hydrogen absorbing rates and pressure–composition isotherms (PCT) are measured on Mg–Ni and Mg–Ni–RE (RE=La, Nd) alloys which have been amorphized by melt-spinning and crystallized to form nanocrystalline structures. The microstructures of these alloys as examined by X-ray diffraction and transmission electron microscopy consist of mixtures of crystalline grains of major Mg and Mg2Ni phases, together with a minor La2Mg17 or NdMg12 phase, of 50–100 nm in diameter. These nanocrystallized alloys, particularly of the Mg–Ni–RE systems, exhibit excellent hydrogen absorbing kinetics and PCT characteristics in comparison with those of the corresponding as-cast alloys with coarse eutectic structures.

TEM observation of interfaces in a solder joint in a semiconductor device

Abstract Microstructure of a joint between a Pb–Sn eutectic solder and an electroless Ni–8 mass% P has beenexamined using transmission electron microscopy. Four layers, i.e. Ni3Sn4, Ni48Sn52, Ni2SnP and Ni–20 mass% P, are formed between the solder and the electroless Ni–8 mass% P. Among them, Ni48Sn52 and Ni2SnP were found for the first time in a solder joint. Spherical voids are formed at the interface between Ni48Sn52 and Ni2SnP, and columnar voids are formed at the interface between Ni2SnP and Ni–20 maas% P. From the analysis of the migration of the respective interfaces observed during in situ heatingexperiments, it is concluded that these voids are Kirkendall voids formed due to the difference in diffusivity of Ni across the interfaces. Fracture takes place at either of those interfaces during a dropping test.

Dislocation structures of β-CuZn deformed in compression between 25 and 300°C

Abstract Dislocation structures of β-CuZn single crystals with two different orientations deformed in compression between room temperature and 300°C, where the anomalous strength peak occurs, have been examined by the high-order reflection imaging technique in a HVEM; Burgers vectors of the dislocations have been determined without ambiguity by the g·b = 0 invisibility criterion. In crystals deformed below T p (the temperature at which the strength shows the peak in the stress versus temperature curve), superlattice dislocations, consisting of two 1/2 superpartials, are predominant, while in crystals deformed at or above T p, and dislocations are predominant. Mechanisms so far proposed to explain the anomalous strength peak are criticized on the basis of the present observations.

Climb dissociation of 〈111〉 superdislocations in β-CuZn

Abstract The core structure of 〈111〉 superdislocations in β-CuZn deformed at high temperatures has been studied in detail by weak-beam electron microscopy. It has been found that the two superpartials of the 〈111〉 superdislocations, both in edge and near-screw orientations, do not lie on the same glide plane. That is, the 〈111〉 superdislocations are climb-dissociated. The climb dissociation most likely takes place during glide motion, presumably as a result of interactions with vacancies. The transition of slip direction and the strength anomaly observed at around 200°C in β-CuZn can be explained by this mechanism.

Electron holographic characterization of electrostatic potential distributions in a transistor sample fabricated by focused ion beam

A cross-sectional sample of a silicon-metal-oxide semiconductor field-effect transistor, which was directly cut from an integrated circuit wafer, has been prepared carefully using a focused-ion-beam technique and examined by means of off-axis electron holography. In the reconstructed phase image, heavily doped source, and drain regions are revealed clearly as bright contrast, from which an n-channel transistor is identified. In addition, two-dimensional phase distributions around both source and drain regions show a core area with relatively high phase in the heavily doped region, which may be attributed to the effect of doping atoms and residual defects and strains remaining after implantation. The electrostatic potentials across the core area and depletion layer are estimated and discussed. This work demonstrates the feasibility of using a focused-ion-beam technique to prepare electron holographic sections of a wide range of semiconductor devices.

In situ high-resolution electron microscopy observation of the melting process of In particles embedded in an Al matrix

Abstract The melting process of In particles embedded in an Al matrix has been observed continuously using an in situ heating experiment in a high-resolution high-voltage electron microscope. The crystalline In particles are cubo-octahedral in shape, bounded by eight {111}Al,ln and six {100}Al,ln facets. Cavities are attached to most of the In particles. Melting started either at the cavity or at one of the {100} facets and proceeded into the interior of the In particle. The process took place in six stages, in each of which one {100} facet became covered by the liquid phase. In particular, at the very beginning of the melting process, the liquid droplet, nucleated at a {100} facet, assumed two configurations alternately before the liquid reached the next {100} facet. The time spent in this stage was much longer than that spent in the rest of the process, and it is concluded that this stage is the rate-controlling process.

Transmission electron microscopy of amorphization and phase transformation beneath indents in Si

Abstract The microstructure beneath indents, with three different tip shapes (spherical, Vickers and Berkovich), in Si was examined using transmission electron microscopy. The focused-ion beam technique was applied to the preparation of specimens for cross-sectional observation. Activation of dislocations, cracking, phase transformation and amorphization were observed.

Direct Measurement of Mobility of Edge and Screw Dislocations in 3% Silicon-Iron by High Voltage Transmission Electron Microscopy

A new method to investigate directly the dynamical properties of dislocations was developed by means of HVEM. The motions of edge and screw dislocations were observed in thick foil specimens of Fe-Si being stretched in a HVEM operated at 500 kV. The dislocation motions were recorded continuously on a video tape recorder (VTR) with the aid of an image intensifier and the corresponding stress-strain curve was also recorded simultaneously. Edge dislocations moved well below the yield stress and the frequency of their motions increased with increasing applied stress. Luders band nucleated at upper yield point and propagated in transition from upper to lower yield points. The motions of screws were observed immediately after upper yield point, accompanying dislocation multiplication. Edge dislocations had much higher mobility than screws but both of them moved much faster in comparison with the observation by etch-pitting technique.