XPS and LEED were used to study the adsorption and ordering of oxygen on Cu(11O) at 83±1 K and between 300 and 320 K and to follow changes in the oxygen coverage and surface structure produced by 5-min anneals at temperatures up to 880 K. The relationship between oxygen coverage and surface structure, as well as their mutual dependence upon exposure, surface temperature at exposure, and subsequent annealing treatment, is discussed.

Measurements of uv photoemission from evaporated aluminum films were made at photon energies 7.7–11 eV as a function of time after film deposition. Evidence of the initial stage of chemisorption of oxygen can be seen in the uv photoelectron spectra. The spectra taken immediately after film deposition showed a smooth energy distribution characteristic of clean aluminum. Structure in the spectra was found to appear at approximately 60 minutes after deposition at 10−9 Torr. Three noticeable features were observed at 1.0, 1.3, and 2.5 eV above the vacuum level. They appeared stationary with increasing photon energy. The structure can be attributed to inelastic scattering of photoelectrons into resonant states associated with oxygen ions on the metal surface. The energy levels of the calculated resonant states of a helium-like system are compared with the energy of the observed structure. The agreement suggests that there are adsorbed 0− ions to which photoelectrons can be scattered at the metal-vacuum interface.

Electron diffraction patterns with <111> incidence of f.c.c. plate-like crystals prepared by gas evaporation technique show forbidden spots such as the 1/3.422 spot. The origin of the spots has been explained in terms of planar defects such as (i) fractional unit cells on (111) surfaces, (ii) repeated thin twins and (iii) stacking faults or hexagonal layers. In the present study, the defect structures are examined by CBED and HRTEM techniques. The <111> CBED pattern of the platelet shows three-fold symmetry for the whole pattern. The dark field patterns of ± 1/3. 422 discs show symmetry of. These features prove that the platelet ha-s no center of symmetry for the three dimensional crystal (3m) and irregular arrangements of twins parallel to (111) planes. The electron micrographs taken along the <110> and <211> directions can give “cross-section” images of the platelet. The images show a few repeated twins with a thickness of several nm. The dark field images taken with the forbidden spots with <111> incidence show weak step contrast. The contrast may be due to fractional unit cells. Consequently, the forbidden spots of the platelet are mostly due to the fractional unit cells.

The role of x-ray diffraction in characterising defects in crystals is reviewed briefly. It is most sensitive to the presence of plane defects which destroy the long-range order. The same argument is shown to apply to line defects in surface structures. Two recent glancing incidence x-ray diffraction experiments provide contrasting examples: randomly distributed steps are found in the Au(110) reconstructed surface, while regular arrays of domain walls modify certain phases of krypton monolayers physisorbed on graphite substrates.

Low energy electron diffraction is a surface sensitive tool which is most widely used for the determination of surface symmetries and equilibrium atomic positions. Experimental and theoretical advances made in the past five years make it possible now to use LEED also for the characterization of a wide variety of surface defect structures. In this paper a variety of experimental results involving analysis of diffracted electron beam shapes as a function of primary electron beam energy, adsorbate coverage, crystal tem-perature and ordering time are presented. These experimental results coupled with kinematic theory, allow the determination of step density, size and shape of reconstruction domains and overlayer islands, island size distribution in an overlayer during growth, and the mode of growth.

Angular profiles of diffracted beams in surface-sensitive diffraction techniques can be used to establish the degree of order at the surface of crystals. Results are presented showing the sensitivity of such profiles to the growth mode of overlayer islands. A method is presented to incorporate the two-dimensional nature of the problem into the analysis and to extract finite-size effects from fundamental and superlattice beams.

The growth of thin Pb layers (<12 monolayers) was studied in ultrahigh vacuum by high energy ion scattering/channeling, low energy electron diffraction (LEED)), and Auger electron spectroscopy (AES). Deposition and analysis were performed at 300 K and 140 K. The Pb coverage was determined quantitatively by ion scattering. The results indicated a clear transition in the growth mode as a function of temperature. At 300 K, two-dimensional island growth was observed up to 1.0 monolayer, followed by three-dimensional epitaxial growth of strained islands. Two-dimensional island growth was observed up to 5 monolayers at 140 K. The relative positions of the overlayer atoms relative to the substrate was studied to understand two-dimensional phase transitions above room temperature.

The application of diffraction techniques to study the atomic structure of grain boundaries is reviewed. The determination of the projected structure of a large angle [001] twist boundary is described. The influence of f.c.c. metal type and bonding type on boundary structure is examined. Generalizations are made concerning the structure of large angle [001] twist boundaries based on the results of the diffraction studies.

The problem of solute segregation came to prominence with relation to studies of the temper embrittlement of low alloy steels. McLean and Northcott1(1948) first suggested that segregation of various elements to the grain boundaries was primarily responsible for the intergranular fracture observed in steels susceptible to this embrittlement. Direct evidence for segregation came much later with the development of surface sensitive analytical techniques, especially Auger electron spectroscopy (AES). Using AES, it was determined that impurity elements such as P, Sb and Sn, as well as alloying elements such as Ni and Cr, were highly concentrated at the fracture surfaces in embrittled steels2. It is not clear, however, why solute segregation changes the mechanical strength of the grain boundaries in these materials. Based on recent calculations, Messmer and Briant3 proposed that certain solute species at a grain boundary change the chemical bonding at the interface. However, other more dramatic structural rearrangements may be possible upon segregation. Such structural changes were first suggested by the observation of facetted fracture surfaces in tellurium-doped iron alloys4. In the study presented here, it is shown that low concentrations of solute can cause changes in grain boundary structure. In particular, small concentrations of Au solute were found to cause a major change in the dislocation structure of low angle [001] Fe twist boundaries. Preliminary observations on the str ucture of a Fe-0.18 at.% Au* twist boundary were presented elsewhere5. Additional results will be presented here on the effect of changes in solute concentration and misorientation angle, θ, on this structural transformation. It is believed that these observations are evidence for the occurrence of a two-dimensional phase transformation in the grain boundary, similar to that predicted by Hart6

Defocus-imaging and high-resolution electron microscopy (HREM) are used to study tilt grain boundaries (GB) in NiO near the <001> axis over the whole range of possible misorientation. Faceting and structural periodicities within facets are observed in high- and low-angle GBs. A reduced atomic density at high-angle GBs is suggested by the defocus behavior.

By recording the intensity of electron scattering along the reciprocal lattice direction normal to the interface plane of a grain boundary, diffraction data is obtained which is sensitive to the boundary structure along this direction. Kinematical calculations of the diffracted intensity profile normal to the interface show that such diffraction data can provide information on the local expansion at the interface and the rigid body translation between the two grains. Electron diffraction data obtained from a variety of different boundaries are presented and analyzed by comparison with intensity profiles calculated for various model boundary structures.

Frequently, the processing of dense, strong, and tough ceramics requires the addition of sintering aids. The materials are therefore composed of various components. For the understanding of the properties of the ceramics it is essential that the microstructure and the distribution of the different components within the material are known. The possibilities and limitations of microanalytical TEM studies will be described for different structural ceramics, e.g. ZrO2 , NiO, SiC, and SiAlON.

In situ high-voltage electron microscopy (HVEM) observations have shown that the highly-focused electron beams normally employed for HVEM irradiation experiments can cause large chemical composition changes in the irradiated zone of thin film alloys during elevated temperature irradiations. The driving force for the process comes primarily from the radial gradients in displacement rates generated by the beam. Hence, the rate of change in composition exhibits a strong dependence not only on the temperature and beam intensity, but also on the spatial characteristics of the beam profile. This dependence on beam shape and size poses previously unrecognized problems, particularly for HVEM studies of the effects of dose-rate on radiation-induced phenomena that are sensitive to alloy composition. Moreover, composition changes driven by radial gradients in the displacement- rate occur at increasingly rapid rates as the beam diameter is reduced. Hence, at higher voltages, beam-induced composition changes occurring during analysis may become a serious problem, even at relatively low temperatures, for microchemical analysis techniques, such as EDX and EELS, which employ far smaller diameter electron beams than those used for irradiation purposes in the HVEM.

The theoretical ideas for STEM probe spreading using spherical wave X-ray diffraction theory and expel imental results of diffractive probe spreading are briefly described. Clear evidence is found for two beam Bormann fan effects arising from nigh order diffracted beams.

A high resolution electron microscope study of grain boundary structures in Au thin films has been undertaken from both a theoretical and experimental point of view. The criteria necessary to interpret images of tilt boundaries at the atomic level, which include electron optical and specimen effects, have been considered for both 200kV and the newer 400kV medium voltage microscopes. So far, the theoretical work has concentrated on two different [001] tilt bounda-ries where a resolution of 2.03Å is required to visualize bulk lattice structures on either side of the interface. Both a high angle boundary, (210) σ=5, and a low angle boundary, (910) σ=41, have been considered. Computational results using multislice dynamical diffraction and image simulations of relaxed bounda-ries viewed edge-on and with small amounts of beam and/or specimen inclina-tion have been obtained. It will be shown that some structural information concerning grain boundary dislocations can be observed at 200kV. However, many difficulties occur in the exact identification of the interface structure viewed experimentally for both [001] and [011] boundaries since the resolution required is near the performance limit of a 200kV microscope. The simulated results at 400kV indicate a considerable improvement will be realized in obtain-ing atomic structure information at the interface.

The incorporation of lattice dislocations into a 16° [011] tilt bound-ary in Ge bicrystals has been analyzed with high-resolution and conventional transmission electron microscopy techniques. Dislocations in subgrain boundaries produced during high-temperature creep, knit into the high-angle grain boundary. As these lattice dislocations are absorbed, the structure changes along the grain boundary from one subgrain to the next. Analysis of the boundary structure by lattice-fringe imaging demonstrates that the secon-dary dislocations which accomodate the deviation from the coincidence orien-tation do not have primitive DSC Burgers vectors.

Channeling of fast, light ions in crystals has been widely used as a tool for studying crystal defects. This subject has been reviewed earlier at MRS-1980. During MRS-1980, principles of ion channeling, and examples of channeling analysis on bulk defects and surface structures, lattice location of impurities, and clustering phenomena were given. In this review, we give a brief overview of defect studies by the channeling technique and then elaborate on recent developments in channeling analysis of interfacial structure. The ion beam channeling technique permits characterization of heteroepitaxial growth starting at monolayer coverages and allows quantitative measurement of the lattice strain in heteroepitaxial layers. The strain analysis has been developed for multilayer structures and, for example, the tetragonal distortions of strained-layer superlattices can be determined for lattice mismatches as low as 0.2% corresponding to lattice distortions of 0.01Å.

We summarize the results of an extensive investigation on ion implanted arsenic in silicon after pulsed laser annealing and laser plus furnace annealing. The experiments are aimed at determining the structural and chemical environment around an arsenic impurity atom and relating that information to the electrical behavior of arsenic in silicon. We have implanted silicon with arsenic, 6×1016 As/cm2 at 100 KeV, followed by laser annealing, to obtain epitaxial regrowth with peak As concentrations of about 8 at.%. Subsequent furnace annealing at 800°C for 30 minutes reduces the apparent electrical activity of the arsenic atoms, increasing the electrical resistivity by a factor of three. We have used EXAFS, together with RBS and ion channeling, to investigate the structural and chemical origins of this deactivation. EXAFS measurements are consistent with As occupying tetrahedral sites in both laser ann-ealed and laser plus furnace annealed samples. Average As-As coordination numbers, found from fitting the EXAFS data, were 0.2 and 4.5 for nearest neighbors and for next nearest neighbors respectively. These coordination numbers suggest that there are regions with As concentrations much greater than the nominal maximum concentration mentioned above, and that the preferred local chemical order in regions of high As content resembles that in GaAs, with Si preferentially occupying Ga-sites. This short-range chemical order is unchanged by the furnace annealing. However, we find that furnace annealing does reduce the As-As second neighbor distance by approximately 0.1Å.

Magnetorefiection and preliminary Rutherford Backscattering channeling experiments indicate that point defects induced in the bismuth lattice by ion implantation are largely annealed out during the implantation process due to its low melting temperature of 271.3°C. These experiments also show that the implanted ions cause long range strains in the crystal. Single crystal bismuth samples have been implanted at low temperatures (from 273°K down to 77°K) with 75 As to a total fluence of 5 × 1016/cm2 at energies ranging from 50 keV to 200 keV to yield an approximately constant arsenic profile from the sample surface to a depth of 625 Å. To study the local environment of the implanted As ions, EXAFS measurements have been made at the Cornell High Energy Synchrotron Source (CHESS). From these data, we obtain a comparison of the As nearest neighbor distances in samples implanted at different temperatures. We discuss the effect of sample temperature during implantation on these properties. This work represents the first use of EXAFS to characterize annealing of implantation-induced lattice defects during the process of ion implantation.

Two new electron microscopy techniques have been developed which greatly extend the capabilities for the micro-characterization of semiconductors. The first is a technique for the direct imaging of dopants in semiconductors, whether or not they are in solution, using Z-contrast, and the second is a technique for determining the substitutional fraction of dopant. Both techniques are capable of nanometer spatial resolution and allow the detailed study of dopant segregation, precipitation, and clustering effects.