Masao Komatsu

Spontaneous alloying of copper into gold atom clusters

Abstract A double-source evaporator which can be set in the specimen chamber of a high voltage electron microscope has been constructed, With the use of the evaporator, isolated gold clusters of 5 ~ 10 nm in size were first prepared on a supporting film of amorphous carbon, and then copper atoms were deposited onto the film (and of course onto the gold clusters as well), which was kept at room temperature. Upon the deposition of copper, the gold clusters changed into highly concentrated, homogeneously mixed Au—Cu alloy clusters. The copper atom diffusivity in gold clusters deduced from the present observations is at least 9 orders of magnitude faster than the copper solute diffusion in bulk gold.

Spontaneous alloying of copper atoms into gold clusters at reduced temperatures

The alloying behavior of copper atoms into gold clusters at temperatures lower than 300 K was examined using a 200 kV transmission electron microscope equipped with a double source evaporator in the specimen chamber. Isolated gold clusters of about 4 nm in mean diameter were prepared on a supporting film and were cooled down to 245, 215, 165, or 125 K. Copper atoms were then deposited onto the same film. Upon the deposition of copper, the gold clusters quickly changed into completely or partially alloyed clusters, depending upon the substrate temperature. The copper diffusivity estimated from such spontaneous alloying was many orders of magnitude faster than that in bulk gold. A possible mechanism behind the spontaneous alloying is discussed.

Behavior of electromigration‐induced gaps in a layered Al line observed by in situ sideview transmission electron microscopy

We observed the detailed behavior of electromigration‐induced gaps (voids that cause an open circuit) in a submicron‐wide Al line layered on a Ti/TiN conductor by in situ sideview transmission electron microscopy. Two types of gaps were observed. The first type is characterized by extensive growth, which may make the Ti/TiN shunt ineffective under use conditions. The gap causes a decrease in the Al drift velocity upstream in the electron flow. This decrease probably results from mass transport through the exposed TiN surface into the gap. The second type of gap did not grow and later healed; therefore, the shunt seems to be effective. The gap had little influence on the drift velocity. Mass was transported directly from the cathode‐side Al segment through the gap to the anode‐side segment. These mass transport processes may be the causes of resistance oscillation in layered lines.

Alloying behavior of gold atoms into nm‐sized copper clusters

Alloying behavior of gold atoms into copper clusters has been studied using a 200 kV transmission electron microscope (TEM) equipped with a double source evaporator in the specimen chamber. Isolated copper clusters of approximately 4 nm in diameter were first prepared on a supporting film of amorphous carbon, and then gold atoms were deposited onto the same film kept at room temperature. Upon the deposition of gold, the copper clusters quickly changed into homogeneously mixed Cu‐Au alloy clusters. The gold diffusivities in the clusters estimated from the experimental results are at least 19 orders of magnitude faster than those in the bulk copper.

Electromigration in layered Al lines studied by in-situ ultra-high voltage electron microscopy

Abstract In-situ side-view transmission electron microscopy (TEM) observations of electromigration in Al-on-TiN lines with a drift velocity measurement structure have been carried out using an ultrahigh voltage (2 MV) electron microscope. Thick chips as-diced from silicon substrates served as TEM samples. The observations revealed the dynamic behavior of electromigration-induced voids and hillocks during forward and reverse current feeding through the Al lines. The results include vertical growth of voids bounded by faceted Al, refilling of voids, void growth in a hillock upon current reversal, and whisker growth.

A New Type of Very-High Temperature Heating Stage and In Situ Experiments on α-Al 2 O 3 Crystals

A new type of very-high temperature stage for a 3 MV electron microscope has been developed, with which the specimens can be tilted up to ±8° around any axis in a wide temperature range up to 2300 K. In-situ heating experiments on Al2O3 powder have been carried out with this stage, and the detailed processes of sintering, void disappearance and boundary migration were observed.

Depth-Resolved In - Situ TEM Observation of Electromigration in a Submicron-Wide Layered Al–0.5%Cu Line

We studied electromigration (probably at ~350°C) in a submicron-wide Al–0.5 wt%Cu-on-TiN line with a drift-velocity measurement structure by using depth-resolved (side-view) in-situ transmission electron microscopy. Voiding at the cathode was characterized by uniform thinning of a grain and by mass transport from no-current flow ledges with a (111) faceted plane. The adjacent grain began to void when the grain upstream in the electron flow was almost depleted. The voiding proceeded in a manner similar to that in the upstream grain. Voiding between the cathode and the anode began mostly at the intersection of the Al top surface with grain boundaries. It proceeded mainly downward along the anode side of the grain boundary until it reached the Al bottom surface causing a gap in the Al. Then it grew laterally toward the anode. The cathode side surface of the void remained stationary during the void evolution.

Topics in in-situ experiments in the HVEM

Abstract Current topics in in-situ experiments with HVEM are presented, with emphasis on the work that has been carried out with a 2 MV (routine) HVEM at Osaka University. A hot stage capable of operation at temperatures of up to 2300 K has been developed, exhibiting its performance when applied to the study of various annealing phenomena in refractory materials. With the use of a window-type environmental cell, the nucleation and growth process of transition metal hydrides, which resulted from a gas (hydrogen)-solid (transition metals) reaction, have successfully been observed. Through systematic experiments it is revealed that the electron-irradiation-induced C-A transition is a phenomenon of wide generality and occurs not only in metallic compounds but also in non-metallic compounds and that the amorphization tendency is closely related with the position of the compounds in the T-C phase diagram. A unique foreign atom implantation technique, in which irradiation effects of MeV electrons are utilized, has been developed. It is confirmed that with the use of this technique such foreign atoms as lead and gold can successfully be implanted into the substrate material on an extensive scale.

In-situ side-view observation of electromigration in layered Al lines by ultrahigh voltage transmission electron microscopy

Depth-resolved observation of formation and evolution of electromigration-induced voids was made for an Al (0.7 μm wide)-on-TiN line with a drift-velocity-measurement structure by using ultrahigh voltage (2 MV) transmission electron microscopy from the side of the line. Voiding at the cathode did not necessarily begin at the Al-TiN interface. Voiding between the cathode and the anode started on the Al surface, and grew initially downward until reaching the Al-TiN interface and then grew laterally toward the anode. Vertical growth of voids sometimes accompanied formation of faceted planes at the top or bottom of the voids. Even after Al separation, mass transport continued from the cathode-side segment of the separated line through the exposed TiN surface to islands in the separation or to the anode-side segment. The drift velocity measured at the cathode decreased to the value determined by the mass transport through the TiN surface at Al-separation.

A Universal Environmental Cell for a 3MV-Class Electron Microscope and Its Applications to Metallurgical Subjects

A universal closed-type environmental cell, which can be used in the temperature range -100°~1000°C, has been developed for a 3 MV-class electron microscope. The pressure of the atmosphere in the cell can be increased up to about 2 kg/cm2. The cell has been used in the voltage range 1~2 MV to investigate some of the fundamental metallurgical problems with the following results. 1) Image contrast of a specimen in the cell whose gas layer is about 100 µm in thickness increases remarkably at 2MV. 2) The specimen damage of metal powders during observation, which is due to evaporation and melting, decreases with increasing convection of the atmosphere and increasing heat-conductivity of supporting films. 3) The specimen damage of surface-active powders, such as carbon black, is most sensitive to the partial pressure of oxygen in the atmosphere. 4) Pressurized atmosphere is effectively used for the suppression of evaporation of metal specimens at high temperatures and for studying chemical reactions between wet H2-gas and metals.