The growth of ferroelectric lead zirconate titanate (PZT) films by rf-sputtering using a facing targets geometry is described. This study focuses on the influence of the substrate on PZT thin film composition, structure, and electrical properties. The deposition temperatures ranged from room temperature to 700 °C and the process gas was a mixture of argon and oxygen. Effects of deposition conditions and post-deposition annealing on film composition, microstructure, and properties were evaluated using Rutherford backscattering spectroscopy (RBS), x-ray diffraction, electron microscopy, and measurements of the permittivity and polarization. The microstructure, composition, and permittivity of the films were found to be strongly dependent on the substrate temperature and on the preparation history of the films.

Transmission electron microscopy (TEM) techniques have been employed to study the room temperature solid state form of chromatographically purified C70. Tilting and electron diffraction experiments in three-dimensional reciprocal space, on samples prepared by crystallization from several different solvents, show that C70 crystallites adopt hexagonal close packed (hcp) structure with a = 1.01 ± 0.05 nm and c = 1.70 ± 0.08 nm. The extinctions and observed reflections conform to the P63/mmc space group. High resolution TEM images reveal the molecular order and periodicity associated with C70 crystallites in real space. The experimental results are in agreement with the preliminary computations of crystal structure within acceptable error limits.

Nanocrystalline materials have a grain size of only a few nanometers and are expected to possess very high hardness and strength values. Even though the hardness/strength is expected to increase with a decrease in grain size, recent observations have indicated that the hardness increases in some cases and decreases in other cases. A careful analysis of the available results on the basis of existing models suggests that there is a critical grain size below which the triple junction volume fraction increases considerably over the grain boundary volume fraction and this is suggested to be responsible for the observed softening at small grain sizes.

The lattice location of several transition metal (Hf, Ta) and rare-earth (Nd, Eu) impurities has been investigated in LiNbO3 by ion-beam channeling methods, including Rutherford backscattering and the 7Li(p, α)4 He nuclear reaction. From the detailed analysis of the angular scans near crystallographic axes and planes and the comparison between the two methods, it has been concluded that Hf lies at a Li site, but Ta at a Nb site, whereas Eu and Nd present double occupancy. By using additional results on other impurities, a wider picture of location behavior is described and possible physical mechanisms are discussed.

Amorphous spherical particles of magnesium and potassium niobates were produced by homogeneous precipitation in solutions of magnesium and potassium salts, respectively, in the presence of polymeric niobium oxo-hydroxide ions. At pH 9 solids of definitive compositions were achieved and converted to crystalline powders of MgNb2O6 and KNbO3 on calcination. Chemical mechanisms for the formation and transformation of such colloidal particles are offered.

Fe/AlOOH gels calcined and reduced at different temperatures have been investigated by a combined use of Mössbauer spectroscopy, x-ray diffraction, and electron microscopy in order to obtain information on the nature of the iron species formed as well as the various reduction processes. Calcination at or below 1070 K mainly gives reducible Fe3+ while calcination at higher temperatures gives substitutional Fe3+ in the form of Al2−xFexO3. The Fe3+ species in the calcined samples are, by and large, present in the form of small superparamagnetic particles. Crystallization of Al2O3 from the gels is catalyzed by Fe2O3 as well as FeAl2O4. Fe (20 wt. %)/AlOOH gels calcined at or below 870 K give FeAl2O4 when reduced in hydrogen at 1070 K or lower and a ferromagnetic Fe0–Al2O3 composite (with the metallic Fe particles >100 Å) when reduced at 1270 K. Samples calcined at 1220 K or higher give the Fe0–Al2O3 composite when reduced in the 870–1270 K range, but a substantial proportion of Fe3+ remains unreduced in the form of Al2−xFexO3, showing thereby the extraordinary stability of substitutional Fe3+ to reduction even at high temperatures. Besides the ferromagnetic Fe0–Al2O3 composite, high-temperature reduction of Al2−xFexO3 yields a small proportion of superparamagnetic Fe0–Al2O3 wherein small metallic particles (<100 Å) are embedded in the ceramic matrix. In order to preferentially obtain the Fe0–Al2O3 composite on reduction, Fe/AIOOH gels should be calcined at low temperatures (∼1100 K); high-temperature calcination results in Al2−xFexO3. Several modes of formation of FeAl2O4 are found possible during reduction of the gels, but a novel one is that involving the reaction, 2Fe3+ + Fe0 → 3Fe2+.

The properties of a variety of HNCC's supported on holey carbon films have been investigated by transmission and analytical electron microscopy; a review of how these techniques can be used to study these crystallographically well-characterized clusters is also presented. Images of the metallic skeleton corresponding to a single cluster unit have been observed for [Ni38Pt6(CO)48H]5−, [Ni34C4(CO)38H]5−, [Pt38(CO)44Hx]2−, [Rh17S2(CO)32]3−, [Ni12Sn(CO)22]2−, and [Ni22Ge(CO)22]2−, and analytical data at low electron beam intensities are consistent with their crystallographically established structures. At increasing current densities, agglomeration into larger particles occurs and these larger particles (2–5 nm) gradually lose the chemical identity of the precursor. Ultimately at current densities of the order of 107 A/m2 metal segregation and/or metal alloy particles having close-packed crystal structures are formed together with graphitic carbon from decomposition of the CO ligands. Possible mechanisms for this beam damage are discussed. There is evidence of cluster/substrate interaction resulting in increased stability compared to that observed in solution and in the normal crystalline state.

The mechanical behavior of intermetallic alloys is related to the mobility of the dislocations found in these compounds. Currently the effect of bonding on dislocation core structure and its influence on deformation behavior is not well understood. However, the unusual properties of these materials, such as the anomalous temperature dependence of flow stress observed in TiAl, are derived in part from the aspects of bonding that determine dislocation mobility. Several recent studies have suggested a particular relationship between directional bonding in TiAl and dislocation mobility. To understand better the flow behavior of high temperature intermetallics, and as a step toward bridging the gap between electronic structure and flow behavior, we have calculated the electronic structure of various planar faults in TiAl. The self consistent electronic structure has been determined using a layered Korringa Kohn Rostoker (LKKR) method which embeds the fault region between two semi-infinite perfect crystals. Calculated defect energies in stoichiometric TiAl agree reasonably well with other theoretical estimates, though overestimating the experimental (111) anti-phase boundary (APB) energy, found for Ti46Al54. We approximate the energy of the (111) APB for the Al-rich stoichiometry by calculating the energy of Al antisites near that defect plane. The calculated (111)APB energy decreases by 6% in going from stoichiometric TiAl to Ti46Al54. The overall hierarchy of fault energies is found to be associated with the number of crystal bond states that are disrupted by the introduction of the fault plane. However, the hierarchy of fault energies is inconsistent with the traditionally accepted ordering. Changes in bonding taking place in the vicinity of the planar defects are illustrated through the density of states and charge density plots. A three body atomistic model is introduced to parameterize the bonding observed in TiAl. The L10 lattice (c/a = 1.00), within a second nearest neighbor three body model, yields a (111)APB energy which is the sum of the complex and superlattice-intrinsic stacking fault energies.

The anatase → rutile transformation reaction of TiO2 prepared in contact with amorphous aluminum phosphate and with fume silica has been investigated as a function of temperature by x-ray diffraction methods. It is observed that the anatase → rutile transformation in such systems becomes greatly inhibited and the Raman spectra of titania on such surfaces exhibit features that indicate substrate-TiO2 interfacial reactions.

We have investigated the binding and diffusion pathways for atomic hydrogen in diamond using the semiempirical atom superposition and electron delocalization molecular orbital (ASED-MO) theory. The bond-centered site has been found to be more stable than the tetrahedral and hexagonal interstitial sites due to the formation of a low-lying band-gap orbital which takes the promoted electron. A second hydrogen binds even more stably to the nearby antibonding site with additional stabilization of the now doubly occupied band gap orbital. The bond-centered hydrogen is predicted to migrate along the high-density (110) planes in the diamond lattice with an activation barrier of 1.9 eV. A carbon atom vacancy is found to attract interstitial H which bind to dangling orbitals on the surrounding C atoms. These bond strengths decrease as up to a maximum of four H atoms enters the vacancy. A hydrogen atom in a vacancy is found to increase the activation energy for vacancy migration.

Morphological instabilities attending the high growth rate of diamond films are examined. Pertinent literature on morphological instabilities and microstructure evolution in vapor deposited films is reviewed and theoretical treatments related to the case of diamond growth are discussed. Diamond films of various thicknesses have been synthesized utilizing the combustion flame synthesis technique involving diamond growth rates of ∼1 μm/min. Films of thicknesses under 20 μm are found to be dense and the surface smoothness of such films is governed by facets on the individual crystallites that make up the film. Increasing film thicknesses, at high growth rates, results in extremely rough surfaces, the trapping of voids and discontinuities, and the incorporation of non-diamond phases in the growing film. These characteristics are typical of morphological instabilities when surface diffusion and re-evaporation processes are absent and instability is promoted by the high rate arrival of the appropriate species from the flame ambient to the surface. Factors contributing to morphological instabilities include competitive shadowing and nutrient starvation and growth anisotropy of the different crystallographic faces on individual diamond crystals. It is shown that surface temperature and the presence of oxidizing species in the flame ambient contribute to anisotropic growth of diamond crystals and hence to morphological instabilities in diamond films. An approach to avoiding these instabilities is briefly discussed.

Polycrystalline diamond films were produced in a microwave plasma assisted CVD reactor using CO as the carbon source gas. Reactor exhaust gas compositions were determined by mass spectrometry using 2–10% CO and 0–1.5% O2 in H2 feed gas mixtures. The chemistry involved in the gas phase is similar to that which occurs when diamond is grown using hydrocarbons as carbon source gases. A chemical mechanism for the oxidation of CH4 in flames appears to be applicable to this system. Addition of O2 to the reactor feed gas results in increased growth rates for low addition levels possibly due to activation of the diamond surface, while lower growth rates result at high addition levels due to oxidation of carbon from the surface and depletion of diamond growth precursors in the gas phase. The chemical reactions that take place in the plasma are similar to those that occur in flames and hot filament reactors, indicating that the plasma acts to induce reactions that are normally associated with high temperature combustion processes.

Nanocrystalline fcc metals have been synthesized by mechanical attrition. The crystal refinement and the development of the microstructure have been investigated in detail by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The deformation process causes a decrease of the grain size of the fcc metals to 6–22 nm for the different elements. The final grain size scales with the melting point and the bulk modulus of the respective metal: the higher the melting point and the bulk modulus, the smaller the final grain size of the powder. Thus, the ultimate grain size achievable by this technique is determined by the competition between the heavy mechanical deformation introduced during milling and the recovery behavior of the metal. X-ray diffraction and thermal analysis of the nanocrystalline powders reveal that the crystal size refinement is accompanied by an increase in atomic-level strain and in the mechanically stored enthalpy in comparison to the undeformed state. The excess stored enthalpies of 10–40% of the heat of fusion exceed by far the values known for conventional deformation processes. The contributions of the atomic-level strain and the excess enthalpy of the grain boundaries to the stored enthalpies are critically assessed. The kinetics of grain growth in the nanocrystalline fcc metals are investigated by thermal analysis. The activation energy for grain boundary migration is derived from a modified Kissinger analysis, and estimates of the grain boundary enthalpy are given.

We use molecular-dynamics simulations to study the growth of pure Si, Si0.5Ge0.5, and pure Ge on the 2 × 1 reconstructed surface of Si(100) in a way appropriate to the fabrication of thin films by the method of molecular-beam epitaxy (MBE), namely sequential deposition of energetic atoms. The atoms interact with one another via effective potentials of the Stillinger–Weber form, with parameters adjusted such as to describe all possible types of triplet interactions. Motivated by numerous experimental studies of MBE-grown films, we investigate in particular the structure of the deposits as a function of substrate temperature. We find in all three cases that at low substrate temperatures, poorly ordered structures form, while at high substrate temperatures, epitaxial growth takes place. The presence of Ge limits the number of crystalline overlayers that form, even though it appears to favor a more-ordered structure in the initial stages of growth. For pure Ge epitaxy, in particular, only the first three layers are crystalline, after which growth appears to proceed by the formation of islands, reminiscent of the Stranski–Krastanow growth scheme, and in qualitative agreement with recent experimental and theoretical work. In all samples, annealing improves the quality of the films—at least when grown at sufficiently high substrate temperatures. The interdiffusion of the species at the substrate-deposit interface is also examined.

Tungsten-containing amorphous hydrogenated carbon (W–C:H) films were prepared on silicon substrates by reactive rf sputtering (13.56 MHz). Elastic recoil detection (ERD) and Rutherford backscattering (RBS) of MeV He+ ions have been performed to determine the hydrogen concentration and mass density of the films, respectively. The mechanical properties, i.e., the microhardness, Young's modulus, and the adhesion on substrates, have been studied by depth-sensing indentation equipment (nanoindenter) and a scratch tester with an acoustic emission (AE) detector, respectively. The electric conductivity of the films was also measured. The results show that these properties depend mainly on the tungsten concentration. X-ray diffraction suggests that the W–C:H films consist of an a–C: H polymeric matrix with WC1−x(β) particles embedded. With increasing tungsten concentration the films change from polymeric a–C:H dominant to crystalline WC1−x(β) dominant W–C:H, resulting in different film properties.

The dynamic behavior of a novel chemical vapor infiltration (CVI) technique called pulsed-power volume-heating CVI is investigated using a diffusion-reaction model. In this technique, a volume-heating source (e.g., RF or microwave) is used to heat the preform. The source power is modulated in time (e.g., square-wave modulation) with a specific period and duty cycle. During the low-power part of the cycle, the temperature of the composite drops, reducing the reaction rate and thus allowing the precursor gas to diffuse into the composite, essentially “refilling” the composite. This alleviates reactant concentration gradients within the composite minimizing density nonuniformities. The high-power part of the cycle is used to achieve rapid reaction rates, thereby minimizing processing time. CVI of a carbon fiber preform with carbon resulting from methane decomposition is taken as an example to illustrate the technique. The results reveal the dependence of density uniformity and processing time on relevant variables such as pulse period, duty cycle, power density level, and methane mole fraction. It is shown that pulsed-power volume-heating CVI can provide a window of operating conditions leading to rapid and complete densification.

Measurements of the engineering constants E, G, and v are routinely made for polymeric materials. If these materials are isotropic, these measurements should satisfy the relationship G = E/2(1 + v). However, many past measurements have indicated that this relationship is not satisfied. This raises questions about the assumptions of material isotropy and the applicability of Hooke's law. The methods used to measure these engineering constants for a number of different polymers are first described. Then, new results obtained in the current investigation are presented, indicating that the elastic constants do in fact satisfy the isotropic relationship for strains up to 0.5%. However, it is shown that at strain levels above this level, the relationship between stress and strain is nonlinear.

Space resolved, on-line spontaneous and stimulated emission, and CARS diagnostics have been employed on CH4/H2 mixtures excited by rf-discharge in order to investigate the chemical processes and the gas phase kinetics in the plasma. CH4 and H2 concentration and temperature have been monitored during the process as a function of main reaction parameters (rf-power, total pressure, CH4/H2 ratio). Formation of CH,H2, and H in excited states has been observed. On the basis of present spectroscopic data, a model for the gas-phase reactions accompanying the carbon film deposition is proposed.

Twenty-five silicates were irradiated at ambient temperature conditions with 1.5 MeV Kr+. Critical doses of amorphization were monitored in situ with transmission electron microscopy. The doses required for amorphization are compared with the structures, bond-types, compositions, and physical properties of the silicates using simple correlation methods and more complex multivariate statistical analysis. These analyses were made in order to determine which properties most affect the critical amorphization dose. Simple two-variable correlations indicate that melting point, efficiency of atomic packing, the dimensionality of SiO4 polymerization (DOSP), and bond ionicity have a relationship with critical amorphization dose. However, these relationships are evident only in selected portions of the data set; that is, for silicate phases with a common structure type. A clearer relationship between the silicate properties and critical amorphization dose was determined for the entire data set with multiple linear regression. Several regression models are proposed which describe the variation in amorphization dose. All regression models contain the following properties: (i) melting point; (ii) a structural variable (DOSP, elastic modulus, and/or atomic packing); and (iii) the proportion of Si–O bonding (instead of bond ionicity). The regression models are equivalent, because they represent combinations of similar properties. Notably, density and atomic mass are not controlling properties for the critical amorphization dose. Melting and amorphization by ion irradiation are apparently related processes. Neither melting point nor critical amorphization dose can be predicted by considering only the structure, composition, or bonding of a particular phase. The Si–O bond is the most covalent bond in silicates, and is the “weak link” in the structure with respect to amorphization. Thus, DOSP is also an important property, as the topology of these “weak links” influences a structure's ability to accumulate amorphous regions. The efficiency of atomic packing is related to the process of defect self-recombination during amorphization. The bulk modulus and shear modulus are important variables within the regression models because of their direct relationship to atomic packing.

Si3N4 deposited by CVD on the surface of single crystal SiC was studied by SEM, x-ray diffraction, and TEM techniques. Characterization of the thick Si3N4 deposit was made by SEM and x-ray diffraction. The main emphasis, however, was on the analysis of the Si3N4/SiC interface and this analysis was carried out by electron diffraction studies in TEM. Both x-ray diffraction and TEM studies revealed that the CVD Si3N4 deposit has almost entirely the α-form except for occasional large β crystals. The structure of the SiC substrate in the interior was 6H but the surface structure close to the interface was always microtwinned β. Diffraction studies of the bulk Si3N4 deposit showed not only the presence of preferred growth directions but also different growth orientations near the substrate interface. TEM investigations at the interface also revealed that preferred growth orientations at the Si3N4/SiC interface are different from those in the bulk. The prominent orientation relationship at the interface is [0001]Si3N4//[101]SiC; Si3N4//SiC; a second one, namely Si3N4//[101]SiC; Si3N4//SiC relationship was also occasionally observed. Microindentation tests at the interface indicated that the Si3N4/SiC interface bonding is strong at ambient temperatures but weakens at high temperatures.