Dear Colleagues: Please take a moment to read the new Aims and Scope statement found on page 188. This statement has recently been revised in response to comments indicating that the previous statement could be interpreted as not encouraging submission of manuscripts that describe mainly applications, particularly in the biological fields. That is clearly not the case, and the Aims and Scope statement has been revised in this issue to correct that misperception.

This issue of Microscopy and Microanalysis contains invited and contributed papers from the 1998 Arizona State University (ASU) Workshop on In Situ Electron Microscopy, held January 7-10 at the Embassy Suites in Scottsdale, Arizona. This was the eighteenth in a series of Workshops organized annually by the Facility for High Resolution Electron Microscopy in the Center for Solid State Science at ASU. The Workshops are part of an educational program, and are intended to foster interaction and collaboration between researchers in electron microscopy. The workshop was attended by over 80 participants from universities, industries, and government laboratories around the world. Many of the contributions to the workshop are included in this issue.

A focused ion beam (FIB) interface attached to a column of 200 keV transmission electron microscope (TEM) was developed for in situ micropatterning to semiconductors. TEM specimens of Si and GaAs, and those of a thin Ni2Si layer on a Si substrate were micromilled in the TEM during observation. A set of 6 x 6-um squares and alphabet letters were patterned with a 25 keV Ga+-FIB of 0.2-μm beam diameter at room temperature. The effect of FIB irradiation on the structural evolution was observed simultaneously by a TV-rate video camera and sequentially by regular film. FIB micropatterning to semiconductor specimens caused amorphization and Ga injection. The excess Ga in the specimens precipitated as metastable solid γ-phase for Si and as liquid phase for GaAs. Ni2Si/Si specimens lost silicide crystallinity after FIB patterning. Annealing of these bilayer specimens at 673K resulted in the precipitation of Ni-rich silicide.

Time-resolved high-resolution transmission electron microscopy at a spatial resolution of 0.2 nm and a time resolution of 1/60 sec using a piezo-driving specimen holder is reported here. Various types of atomic processes in mechanical interaction, such as contact, bonding, deformation, and fracture, in nanometer-sized gold crystallites and carbon nanotubes are demonstrated.

Design rules are described here for high-temperature straining stages for transmission electron microscopy. Temperatures above 1000°C can be attained by electron bombardment of the specimen grips. Thermal equilibrium can be reached in a short time by carrying off the heat by water cooling. Some applications of this stage are described. Ferroelastic deformation was observed at 1150°C in t′ and partially stabilized zirconia, which changes the microstructure for successive dislocation plasticity. In the oxide-dispersion-strengthened alloy INCOLOY MA 956, dislocations are impeded by oxide particles and move smoothly between the particles. At high temperatures, both the resting and traveling times control the average dislocation velocity. In MoSi2 single crystals of a soft orientation, dislocations with 1/2〈111〉 Burgers vectors are created in localized sources and move on {110} planes in a viscous manner. The dislocations in Al-Pd-Mn single quasicrystals are oriented in preferred crystallographic directions and move in a viscous way as well. On the basis of in situ observations, conclusions are drawn for interpreting macroscopic deformation behavior at high temperatures.

This study discusses the use of in situ high-resolution transmission electron microscropy (HRTEM) techniques to determine the structure, composition, and interphase boundary dynamics during phase transformations at the atomic level. Three main in situ HRTEM techniques are described: (1) in situ HRTEM dynamic studies that are performed on the same precipitate plates from different viewing directions to determine the three-dimensional structure of the interfaces; (2) in situ compositional mapping of precipitate interfaces obtained by energy-filtering TEM experiments at temperature in a HRTEM, and (3) real-time HRTEM image simulations that are being created for comparison with and interpretation of experimental in situ HRTEM dynamic observations. The results from these studies demonstrate that it is possible to understand the mechanisms and kinetics of interphase boundary motion at the atomic level.

We discuss various techniques for the characterization of supported nanoparticles by in situ plan-view transmission electron microscopy. In particular, we discuss here mechanisms of image contrast formation by particles undergoing reorientation on the surface of a single crystal substrate. We consider reorientation by a variety of mechanisms including rotation, sintering and grain growth, and surface diffusion. Experimental observations are presented and the data compared with theoretical predictions.

We describe here real-time, in situ observations of the formation of nanosize germanium (Ge) islands on silicon (Si). The deposition of Ge onto electron-transparent Si(100) takes place in a UHV transmission electron microscope that has been modified to allow chemical vapor deposition to be carried out in the polepiece. We recorded the growth process at video rate and were therefore able to follow the evolution of individual islands. As the islands grew, we observed a coarsening process similar to classical Ostwald ripening, but which leads at certain times to a bimodal distribution of island sizes. We show that this phenomenon can be understood using a model in which a conventional coarsening process is modified by a transition between two different island shapes.

The processes of melting and freezing of aluminum (Al) particles have been observed directly in a transmission electron microscope. The liquid phase nucleated preferentially at the surface of an Al particle, surrounding the crystalline solid at the onset of melting. The liquid phase then propagated inside the Al particle at the expense of the solid.

In this work, the high-temperature behavior of nanocrystalline TiO2 is studied using in situ transmission electron microscopy (TEM). These nanoparticles are made using wet chemical techniques that generate the anatase phase of TiO2 with average grain sizes of 6 nm. X-ray diffraction studies of nanophase TiO2 indicate the material undergoes a solid-solid phase transformation to the stable rutile phase between 600° and 900°C. This phase transition is not observed in the TEM samples, which remain anatase up to temperatures as high as 1000°C. Above 1000°C, nanoparticles become mobile on the amorphous carbon grid and by 1300°C, all anatase diffraction is lost and larger (50 nm) single crystals of a new phase are present. This new phase is identified as TiC both from high-resolution electron microscopy after heat treatment and electron diffraction collected during in situ heating experiments. Video images of the particle motion in situ show the nanoparticles diffusing and interacting with the underlying grid material as the reaction from TiO2 to TiC proceeds.

We have used the technique of in situ electron microscopy to study the oxidation and reduction of the palladium (Pd) catalysts. In this study, we have subjected a Pd catalyst to oxidation and reduction cycles and studied the changes in particle structure and morphology with in situ electron diffraction and imaging. The PdO particles can be reduced to Pd metal in situ at temperatures as low as 200°C in an atmosphere of a few Torr of both H2 and O2. We also found that essentially the same reduction occurred in the vacuums of 10−6 to 10−7 Torr in two different electron microscopes. Our in situ reduction studies show that many of the oxide particles form voids when reduced to Pd metal. The decrease in volume that occurs during reduction is often accommodated by a combination of particle shrinkage and void formation. The production of voids does not seem to depend on either the reducing atmosphere or the rate of reduction, although the voids appear to be unstable above 500°C.

The evolution of liquid lead (Pb) inclusions at grain boundaries in aluminum (Al) was investigated by direct in situ TEM observation in the temperature range from 330°–643°C, In agreement with earlier reports on quenched alloys, the characteristic contact angle of the lens-shaped grain boundary inclusions was found to be near 120°. This angle remained approximately constant over the entire temperature range, ruling out the possibility of a wetting transition. Coarsening of grain boundary inclusions was observed to proceed mainly by Ostwald ripening, although coalescence could also be observed. Inclusions at grain boundaries, at triple junctions, and at the intersection of grain boundaries with the foil surfaces adopted characteristic shapes that were shown to be equilibrium forms. At the highest temperatures, the grain boundaries were observed to detach from the inclusions and the interaction of a migrating grain boundary with inclusions could be observed.

Strained layer heterostructures provide ideal systems with which to study the dynamics of dislocation motion via in situ transmission electron microscopy, as the geometry, strain state, and kinetics can be characterized and directly controlled. We discuss how these structures are used to study dislocation-point defect interactions, emphasizing the experimental requirements necessary for quantification of dislocation motion. Following ion implantation, different concentrations and types of point defects are introduced within the SiGe epilayer depending on the implantation species, energy, and current density. By annealing samples in situ in the transmission electron microscope (TEM) following implantation, we can directly observe dislocation motion and quantify the effect of dislocation-point defect interactions on dislocation velocities. We find that dislocation motion is impeded if the implantation dose peak lies within the epilayer, as dislocations pin at point defect atmospheres. Shallow BF2 implantation into the sample capping layer results in more complicated behavior. For low current density implants, dislocation velocities may be dramatically increased; at higher current densities the magnitude of this increase is significantly smaller. Implantation of different ions separately implicates fluorine as the species responsible for the observed increases in dislocation velocities, presumably due to an electrical effect on the rate of dislocation kink nucleation.

We discuss the application of ion microscopy and in situ electron microscopy to the study of electronic and optical materials and devices. We demonstrate how the combination of in situ transmission electron microscopy and focused ion beam microscopy provides new avenues for the study for such structures, enabling extension of these techniques to the study of dopant distributions, nanoscale stresses, three-dimensional structural and chemical reconstruction, and real-time evolution of defect microstructure. We also discuss in situ applications of thermal, mechanical, electrical, and optical stresses during transmission electron microscopy imaging.

Morphological evolution associated with silicidation of Co thin films deposited on (100) and (111) Si substrates has been followed using transmission electron microscopy with in situ thermal annealing from ambient temperature up to 850°C. Noticeable structural changes associated with the formation of CoSi2 occur at temperatures as low as 400°C and the reaction is essentially complete at about 500°C. Prolonged heating above 500°C leads to CoSi2 grain growth and coalescence and, finally, to pinholes formation. Silicidation of Co films on (100) and (111) Si substrates follows the same pattern. The morphology of films annealed in situ is similar to those annealed ex situ except that the Si/CoSi2 interface appears to be much rougher. This behavior is associated with the specific geometry of cross-sectional TEM specimens, where surface diffusion dominates bulk diffusion. Very thin Co films, which have less contribution from surface diffusion than thicker films, are ideal for studying dynamic phenomena at Co/Si reactive interfaces.

The Foucault and Fresnel modes of Lorentz microscopy, together with a quantitative magnetization mapping technique, summed image differential phase-contrast imaging, were used to study the magnetization reversal mechanism of the sense layer in spin-valve structures exhibiting the giant magnetoresistance effect. In addition to studies of sheet film, lithographically defined spin-valve elements were investigated. A current can be passed through the element during magnetizing so that the effect of the applied current on the giant magnetoresistance and magnetization reversal mechanism can be studied. Results are presented for a number of different spin-valve structures.

Reconstruction of the Cu(001) surface due to oxygen gas impingement on a clean copper surface was directly observed by in situ UHV-TEM. Strain contrast between differently oriented surface reconstruction domains, assumed to be √2 × 2√2 R45, were clearly visible by this method. The reconstruction precedes the nucleation of Cu2O islands. When Cu2O islands were partially reduced and then re-oxidized, a dwell time before formation of Cu2O was noted, demonstrating that a reconstructed Cu-O surface monolayer is necessary before oxide formation.

Microscopic Explorations, Microscopy Society of America's microscopy-based middle school manual, has just been published by the Lawrence Hall of Science (LHS), one of the leading institutions in U.S. precollege science education. This is an appropriate time to give some thanks and present some history. Let's begin with the description of the manual that appears in the MICRO bibliography (MSA Bulletin [Special Issue] 23:1–16 [1997], and www.MSA.microsco-py.com/Project MICRO/Books.html).

1998 Microbeam Analysis Society (MAS) award winners.

1998 Microscopy Society of America (MSA) award winners.