Electromigration void nucleation and growth is a failure mechanism of integrated circuit (IC) metallization. The time-to-failure of interconnect lines depends on the void nucleation time and the void growth time. While much work has been done to model the void nucleation stage, the current understanding of the void growth stage is minimal. The importance of characterizing the void growth and motion dynamics is essential to further explain electromigration performance of IC metal interconnections.

Electromigration-induced voids previously studied have been observed to grow, coalesce, and even heal, but quantitative information on these dynamics is lacking. This work uses high-resolution electron-beam lithography to define sub-micrometer voids of various sizes and shapes into gold lines in order to observe void growth and movement with respect to initial void size and shape. The electromigration-induced dynamic behavior of pre-defined voids was measured in a field-emission scanning electron microscope in-situ. Results showed these prepatterned voids can re-fill or grow, and can yield quantitative results on dynamic void behavior.

An in-situ straining experiment was performed in a transmission electron microscope (TEM) on the polycrystalline Ti49Ni51 alloy with full R-phase at room temperature. The reorientation of Rphase variants to a single, favorable one was observed under small stress at the beginning of straining, corresponding to the deformation mode of the first yielding stage. During further straining, the observation showed that the reoriented R-phase undergoes a stress-induced martensite transformation, and this dynamic process was considered to contribute to the second stage deformation in the R-phase stress-strain curve. The orientation relationship between the R-phase and stress-induced martensite has been determined and the internal (001)M twins were found in the stressinduced martensite plates.

Recrystallization and grain growth studies of Al-Mg-Mn-Zr alloys have been carried out in-situ in the transmission electron microscope. Nucleation sites were primarily on large (>I μm diameter) eutectic constituent particles. The sub-micron A16Mn dispersoids were observed to be effective as nuclei if present in clusters, and were effective at retarding grain boundary migration and dislocation motion. The smaller A13Zr precipitates seemed to have little effect on nucleation and growth, but were effective in pinning dislocations. These results have been analyzed in terms of precipitate size and shape in both the as-cold-worked microstructure and during recrystallization. The implications on the microstructural refinement of these alloys for improved superplastic properties will be discussed.

Environmental-cell dynamic high-resolution transmission electron microscopy (DHRTEM) has been used to provide atomic-level insight into lamellar reaction processes for the model weak- charge-transfer intercalation reaction of NH3 with 2H-TaS2. In situ intercalation was induced by exposing 2H-TaS2 crystallites to controlled pressures of NH3(g) and recorded on videotape with 0.03 second time resolution. The intercalation processes observed possess a strong similarity to nucleation and growth processes. Onset occurs in either outermost or internal guest galleries, with further intercalation of the galleries progressing away from the onset layers. Randomly staged regions, containing occasional packages of short-range order, were observed to form during the growth process.

The formation of vacancy clusters in various Si crystals covered with SiO2 and Si3N4 films has been studied by means of high-voltage and high-resolution electron microscopy using electron beam energies of 1000 and 400 keV, respectively, and at temperatures between 20 and 250°C. Small vacancy clusters of about 2-5 nm in the form of Frank dislocation loops and stacking fault tetrahedra were observed by irradiating the thinnest areas (< 20 nm) of the investigated silicon specimens. Vacancy clustering seems to be more complicated in the thicker parts (> 20 nm) of irradiated crystals. We assume that in these areas vacancy clusters may be formed only in Si layers near the interfaces Si-SiO2 or Si-Si3N4 and they may interact with interstitials without full recombination of the defects. This leads to the appearance of a new form of interstitial clusters such as {111}-defects as well as the usual interstitial {113}-defects associated with vacancy clusters during prolonged irradiation in the HVEM.

We studied by high resolution transmission electron microscopy (HRTEM) unsupported bismuth-molybdenum-oxide catalysts. The microscope utilized was a JEOL 4000 EX electron microscope with a resolution better than 0.19 nm (point to point). The image simulation were performed on a personal computer with the aid of a commercial program. With the aid of image simulation it is possible to identify γ-Bi2MoO6 and X-Mo4O11 phases, among several other possibilities that fit the interplanar spacings and angles.

A very important aspect, thermal instability, was proved indirectly in the microscope, by the changes of the particles under the electron beam irradiation at 400 kV. After several minutes of irradiation, the amorphous surface layer was totally reconstructed to crystalline phases.

The fact that we observe many phases in this sample, is certainly deleterious to the catalytic properties, since not all of them are active. Also the sensitivity to the beam indicates that minimum exposure microscopy has to be applied in order to prevent unecessary complications for phase identification.

The unique capability of the scanning tunneling microscope, STM, for in situ nanoscale electronic measurements has been utilized to establish the nature of the oxide film on 304 stainless steel under HCI, distilled water, and in air. New insights were obtained concerning the kinetics and electronic surface states of the oxide film as a function of exposure time to these environments: quantitative measurements of the corrosion behavior and the stability of the oxide film, as related to observed defects, have been obtained. These findings have resulted in a model which incorporates these new insights with previously established theories concerning oxidized surfaces.

The initial oxidation of Si(111)-7×7 surface has been investigated by taking the STM images of samples dosed with oxygen at room temperature and high temperatures between 500°C and 750 °C. In particular, different site selectivities between two oxygen-induced features, bright and dark sites, were observed and explained in terms of the difference in potential energy curves. In addition to such a strong site selectivity under low oxygen partial pressure (l×10-9 torr), heavy surface etching by oxygen was observed at higher O2 partial pressures and temperatures resulting in the high density of monolayer-deep etch marks on terraces.

Two phase titanium aluminides with a lamellar microstructure of the intermetallic phases α2(Ti3Al) and γ (TiAl) are being developed for high temperature structural applications. Due to differences in lattice parameters and crystal structure, coherency stresses and mismatch structures occur at various types of semicoherent interfaces present in the material. The implications of these structural features on the stability of lamellar microstructures were studied by TEM in situ heating experiments. The investigations revealed that the lamellar interfaces serve as sources for perfect and twinning dislocations. The results will be discussed with respect to the observed degradation of the strength properties of the two phase alloys in the intended service temperature range of 900- 1000 K.

Amorphous d.c. sputtered SbOx films (0.19< x<2.0) have been found to be fast crystallising materials sensitive to nano- and pico-second laser pulses, and have potential applications as optical data-storage media. They were crystallised in-situ in a JEOL 4000EX TEM, and the crystallisation recorded onto video tape. The crystallisation of the SbO0.37 films occurred by random nucleation followed by growth until coalescence. In contrast the crystallisation of the SbO0.533 films occurred by surface crystallisation across the whole film followed by bulk crystallisation through the film, during which contrast in the TEM increased steadily. Analysing the video frames in an image processing package enabled kinetic parameters such as transformation index and activation energy to be extracted. High resolution transmission electron microscopy showed the crystalline phase to contain nano-crystallites approximately 10 nm in size in a less-ordered matrix.