Although silicon is the material of choice in the semiconductor industry, it has one serious disadvantage: it is an extremely poor optoelectronic material. This is because it is an indirect gap semiconductor, in which radiative transition results in extremely weak light emission in the infrared part of the spectrum. Thus, the discovery of strong visible luminescence from a silicon-based material (porous silicon) has been quite surprising and has generated significant interest, both scientific and technological. This material differs from bulk silicon in one important way, in that it consists of interconnected silicon nanostructures with very large surface to volume ratios. Although the first mechanism proposed to explain this emission process involved carrier recombination within quantum size silicon particles, more recent work has shown that the surface chemistry appears to be the controlling factor in this light emission process. Thus, the aim of this work is to outline the data and arguments that have been presented to support the quantum confinement model, along with the shortcomings of such a model, and to examine more recent models in which the chemical and structural properties of the surface regions of the nanostructures have been incorporated.

Changing the film deposition rate is shown to be one way to influence the meandering configurations of grain boundaries (GB's) formed in YBa2Cu3Oy (YBCO) bicrystal thin films. The magnitude and wavelength of the meander in YBCO films deposited at two different rates have been characterized by transmission electron microscopy (TEM) and statistically quantified. It has been found that the meander becomes more uniform and considerably less rough in films deposited at lower rates compared to that observed in films deposited at higher rates. A mechanism for the formation of the meandering GB is proposed based on heterogeneous nucleation and three-dimensional (3D) island growth together with overgrowth of the YBCO films across the substrate grain boundary. The different island sizes and tendency for overgrowth induced by changing the film deposition rate are believed to play important roles in controlling the meandering GB configuration. The possible effects of meandering configurations on transport properties are discussed.

High-resolution electron microscopy was used to examine the structural features of grain boundaries in Al–1.5% Mg and Al–3% Mg solid solution alloys produced with submicrometer grain sizes using an intense plastic straining technique. The grain boundaries were mostly curved or wavy along their length, and some portions were corrugated with regular or irregular arrangements of facets and steps. During exposure to high-energy electrons, grain boundary migration occurred to reduce the number of facets and thus to reduce the total boundary energy. The observed features demonstrate conclusively that the grain boundaries in these submicrometer-grained materials are in a high-energy nonequilibrium configuration.

Single crystal GaN films with a wurtzite structure were grown on the basal plane of sapphire. A high density of threading dislocations parallel to the c-axis crossed the film from the interface to the film surface. They were found to have a predominantly edge character with a Burgers vector. In addition, dislocation hal-loops, elongated along the c-axis of GaN, were also found on the prism planes. These dislocations had a mostly screw character with a [0001] Burgers vector. Substrate surface steps with a height of were found to be accommodated by localized elastic bending of GaN (0001)GaN planes in the vicinity of the film/substrate interface. Observations show that the region of the film, with a thickness of ∼100 nm, adjacent to the interface is highly defective. This region is thought to correspond to the low-temperature GaN “buffer” layer which is initially grown on the sapphire substrate. Based on the experimental observations, a model for the formation of the majority threading dislocations in the film is proposed. The analysis of the results leads us to conclude that the film is under residual biaxial compression.

YBa2Cu3O7−δ precursor powder suitable for the fabrication of melt-processed ceramic has been prepared by spray drying and subsequent calcination. The dehydration and decomposition processes in the nitrate-based spray-dried powder and the formation processes of the YBa2Cu3O7−δ and Y2BaCuO5 phases have been studied in detail using thermal analysis and powder x-ray diffractometry. The morphology, microstructure, and size distribution of the particles in the calcined powder have been investigated using high resolution scanning electron microscopy and particle size analysis and found to contain a significant proportion of submicron sized particles of Y2BaCuO5. Melt-processed samples prepared using the spray-dried powder have been observed to exhibit a significantly finer distribution of the 211 phase than is typically obtained in similar specimens prepared via a mixed oxide route. This provides direct evidence of the suitability of spray-dried precursor powder for the fabrication of large grain, high Jc melt-processed YBCO ceramics.

A process has been developed for the fabrication of nearly single phase superconducting Tl2Ba2Ca2Cu3O10 thin films on (100) LaAlO3 substrates with a superconducting transition temperature Tc of 120 K and low microwave surface resistance at temperatures up to 110 K. Amorphous BaCaCuO precursor films were first deposited by rf magnetron sputtering and then thallinated at elevated temperatures. The double TlO layer phases (Tl2Ba2Ca2Cu3O10 + Tl2Ba2CaCu2O8) formed preferentially over the single TlO layer phases (TlBa2Ca2Cu3O9 + TlBa2CaCu2O7) at high Tl2O partial pressures. Thin films containing Tl2Ba2Ca2Cu3O10 and a small amount of CuO were prepared from Cu-rich precursor films (Cu/Ba > 1.7), while lower Cu content led to the formation of Tl2Ba2CaCu2O8 as a secondary phase. Tl2Ba2Ca2Cu3O10 film epitaxy was enhanced by carrying out the thallination in reduced oxygen partial pressures of 0.01–0.05 atm. Following the thallination step, the Tl2Ba2Ca2Cu3O10 thin films had a superconducting transition temperature Tc of only 106 ± 4 K. An additional 62 h anneal at 800 °C or an 8 h anneal at 850 °C in a Tl2O/O2 atmosphere increased the Tc to 120 K. The increase in Tc was accompanied by a decrease in the c-axis lattice constant, an enhancement in the long-range order in the c-direction, and the formation of a small amount of Tl2Ba2CaCu2O8 as a secondary phase. Minimization of surface resistance at high temperature (95–110 K) requires that the fraction of Tl2Ba2CaCu2O8 secondary phase in the films be kept low. Process routes are also described for the formation of nearly single phase TlBa2Ca2Cu3O9 and TlBa2CaCu2O7 thin films and the formation of a new ordered intergrowth phase, Tl4Ba4Ca3Cu5O18, which consists of alternating Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 layers.

By means of dc-reactive sputtering, it is possible to vary the stoichiometry of deposited zirconium nitrides, by varying the molar fraction of N2 in an Ar–N2 gas mixture. In order to understand the origin of this effect, a theoretical model of reactive sputtering is devised. It is based on the study of reaction kinetics taking place at the surfaces of the cathode and the chamber walls. In fitting the model with experimental data, it turns out that one has to introduce the roles of Ar, N2, and N species. For reactive sputtering of ZrNz films, a good fit is obtained when it is assumed that the molar fraction of N is constant when the molar fraction of N2 increases up to about 75% (under our experimental conditions). Above this concentration of N2, the concentration of N has to increase. By the analysis of the theoretical model, general scaling laws between experimental parameters (current, pressure, and areas of the cathode and the chamber walls) are easily obtained.

The phases present around the (Bi, Pb)2Sr2Ca2Cu3Ox (2223) phase between 830–880 °C have been studied by x-ray diffraction (XRD) and electron probe microanalysis (EPMA) methods. The decomposition and melting temperatures of the 2223 phase in these samples have been measured by the differential thermal analysis (DTA) method. Partial substitution of Bi with Pb (Pb: Bi = 3: 22) does not change the 850 °C phase relations around 2223 phase. 2223 decomposes to liquid, Sr7Ca7Cu24O41 (7724), and Ca2CuO3 at 875 °C. The invariant reactions (degree of freedom is zero) among 2223, 7724, Ca2CuO3, CuO, Bi2Sr2CaCu2O8 (2212), and liquid were proposed to be L + 7724 + Ca2CuO3 → 2223 + 2212, L + 7724 + Ca2CuO3 → 2223 + CuO, L + 7724 → 2223 + 2212 + CuO. The reaction temperatures were estimated to be 860 °C, 860 °C, and 854 °C, respectively. An invariant reaction scheme and a tentative liquidus projection were sketched out.

The feasibility of synthesizing silicon nitride-silicon carbide-titanium carbonitride composites by combustion reactions is demonstrated. With titanium carbonitride taken to be an ideal solid solution, its composition is determined as TiC0.36N0.64. Thermodynamic analysis supports the experimental results.

The ytrrium solubility in Ba–Cu–O solvent with a Ba to Cu ratio of 3 to 5 was investigated under different oxygen partial pressure [P(O2) = 2, 21, 100%]. A small amount of the solution was taken out by dipping thermally equilibrated MgO single crystals, and compositions of these specimens were analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The measurements were performed for the samples prepared in the temperature range from approximately 950 °C up to 1100 °C. The peritectic temperature of YBa2Cu3O72x (Y123) decreased with decreasing oxygen partial pressure. On the other hand, the Y123 liquidus lines do not show remarkable oxygen partial pressure dependency. Accordingly, the yttrium solubility at the peritectic temperature of Y123 under P(O2) = 100% was larger than those for the other conditions [P(O2) = 2% and 21%]. Assuming a regular solution, expressions for the solubility and the enthalpy of dissolution of Y123 and Y2BaCuO5 (Y211) were derived from classical thermodynamic calculations and found to be 289 kJ/mol at P(O2) = 0.02, 239 kJ/mol at P(O2) = 0.21 atm, 206 kJ/mol at P(O2) = 1 atm for Y123, and 105 kJ/mol at P(O2) = 0.02 atm, 88.0 kJ/mol at P(O2) = 0.21 atm, and 88.4 kJ/mol at P(O2) = 1 atm for Y211. Furthermore, the Jackson α factor of Y123 was estimated to be about 20, confirming a faceted growth nature of this crystal.

The thermal expansion coefficient of Bi-based 2223 and 2212 ceramics has been measured using dilatometric apparatus. Different typologies of bulk superconducting samples have been tested, in particular (2223) phase fully dense hot-pressed samples both parallel and perpendicular to the direction of applied pressure, pressureless sintered samples, and finally hot-pressed (2212) phase specimen, in order to gather information on the contribution of secondary phase to thermal expansion behavior. From the observed α (thermal expansion coefficient) values, accounting for the sample orientation degree, it was possible to distinguish the contributions along the basic crystallographic directions and to determine the following for (2223) phase: αa = 12.2 × 10-6 °C-1, and αc = 20.8 × 10-6 °C-1 for temperatures 200–600 °C. Theoretical α values were then calculated for the different samples and successfully compared with the measured ones. As regards (2212) phase, thermal expansion coefficient was evaluated for the oriented sample, and a value for random one extrapolated; the results are very similar to that of (2223), but lower with respect to previously reported data in air atmosphere.

Superconducting oxide films of YBa2Cu3O7−δ (YBCO) were produced on magnesia (MgO) single crystalline substrates (100) by laser-assisted metal-organic chemical vapor deposition. The highly volatile Ba(hfa)2 · tetraglyme was used as a Ba source metal-organic material. Smoother surface YBCO film was obtained with KrF laser irradiation than without. However, KrF laser irradiation does not lower the temperature for formation of YBCO(123) phase. YBCO film prepared at 750 °C on the MgO substrate showed a Tc(R = 0) of 69 K, and that prepared with KrF laser irradiation was 85 K. When water was added to the reaction chamber, barium fluoride was reduced and the YBCO formation was detected at a temperature of 650 °C and higher. YBCO film prepared at the temperature of 700 °C for 40 min without KrF laser irradiation behaves as a semiconductor, and one prepared with laser irradiation showed a Tc(R = 0) of 78 K.

This work deals with the influence of the starting Y-123 grain size on the growth mechanism and final microstructure of the melt-textured YBa2Cu3O7−x ceramics. Observations of the growth front morphology and stability for the different precursors using several decomposition temperatures are correlated with the theoretical equations. It is found that the final 211 inclusion size increases as the starting 123 grain size increases. However, using a small-grained 123 precursor disrupts the growth front and makes the control of grain alignment difficult. An appropriate morphology of the 123 precursor should be chosen prior to the MTG process in order to obtain the best properties.

Spatially isolated amorphous regions in Si and Ge have been regrown at room temperature by using an electron beam with an energy less than that required to cause displacement damage in crystalline material. The rate at which the zones regrow is a function of the energy of the electron beam. As the electron energy is increased from 25 keV (lowest energy employed), the regrowth rate decreases and reaches a minimum below the threshold displacement voltage. With further increases in the electron energy, the rate again increases. It is suggested that at the lower electron energies this room temperature regrowth process is stimulated by electronic excitation rather than by displacive-type processes.

Epitaxial TiN films were grown on cubic (3C)-SiC(001) and hexagonal (6H)-SiC(0001) substrates by ultrahigh vacuum reactive magnetron sputtering from a Ti target in a mixed Ar and N2 discharge at a substrate temperature of 700 °C. Cross-sectional transmission electron microscopy, including high-resolution imaging, showed orientational relationships TiN(001)‖3C-SiC(001), and TiN[110]‖3C-SiC[110], and TiN(111)‖6H-SiC(0001) and . In the latter case, twin-related TiN domains formed as the result of nucleation on SiC terraces with an inequivalent stacking sequence of Si and C. The TiN/SiC interface was locally atomically sharp for both SiC polytypes. Defects in the TiN layers consisted of threading double positioning domain boundaries in TiN(111) on 6H-SiC. Stacking faults in 3C-SiC did not propagate upon growth of TiN. Room-temperature resistivity of TiN films was ρ = 14 μΩ cm for 6H-SiC(0001) and ρ = 17 μΩ cm for 3C-SiC(001) substrates. Specific contact resistance of TiN to 6H-SiC(0001) was 1.3 3 10−3 Ω cm2 for a 6H-SiC substrate with an n-type doping of 5 × 1017 cm−3.

A two-dimensional quasicrystal with fivefold symmetry and two large-unit-cell crystalline approximants in an Al–Co–Ni–Tb alloy, which were observed in previous studies, are suggested to be composed of the same kind of atom cluster. Some characteristics of the atom cluster can be deduced from a high-resolution electron microscopy image of the Al–Co–Ni–Tb quasicrystal when the image is associated with a fivefold aperiodic tiling. By using the cut-and-projection method, a quasiperiodic tiling generated by an irrational projection is proposed as an ideal quasilattice of the Al–Co–Ni–Tb quasicrystal; in the meantime, periodic tilings generated by a rational projection present the lattices of the crystalline approximants.

Extruded eutectoid Zn–Al alloy was welded by a melt of the same eutectoid alloy. Two different microstructures were observed in the joint part and in the bulk of the welded alloy. Typical dendritic structure of as-cast Zn–Al alloy was observed in the joint part of the welded alloy. The bulk of the welded Zn–Al alloy appeared as fine grain structure. Two different metastable phases, η′T decomposed from η′s of the chilled as-cast state and η′E of the extruded state, were found to be unstable during the early stages of aging. A four-phase transformation occurred after the decompositions of these two metastable phases of η′T. Microstructures of both the joint part and bulk of the welded alloy were investigated simultaneously during the aging processes.

Pb-substituted Hg-based superconductor of Hg0.66Pb0.33Ba2Ca2Cu3Oy has been fabricated using the sealed quartz tube technique. R- and x-ray diffraction pattern (XDP) measurements show that the specimen has a Tc of 135 K and contains mainly the Hg-1223 phase. Scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDX) and transmission electron microscopy/energy dispersive x-ray analysis (TEM/EDX) were employed to study the texture and chemical composition of the specimen. It is found that the specimen contains round-shaped grains with a mixture of Hg-1223, BaCuO2, and Ca0.85CuO2 phases, square-shaped grains with a formula of PbBa2O3, small single crystals with single Hg-1223 phase, and crystal-like layers with a mixture of Hg-1223 and BaCuO2 phase. We consider that though the doping of Pb can benefit the stabilization of the Hg-1223 phase, it introduces other impurity phases and textures in the specimen at the same time.

The magnetic anisotropy of rare-earth substituted 2212 materials (Bi2Sr2Ca0.8RE0.2Cu2Ox with RE = Gd, Dy, Ho, Er) is put into evidence. Superconducting powder dispersed in epoxy resin is oriented under an external magnetic field (4 T) in a direction that depends on the nature of the rare-earth used in the substitution. Both directions of observation (parallel or perpendicular to the field) were investigated. Splitting of (00l) peaks is neatly observed and discussed.

The growth process of a YBCO/LaAlO3/YBCO trilayered film made by pulsed laser deposition has been studied by high resolution transmission electron microscopy (HRTEM). The high resolution images of the cross-section samples have shown that a 7 nm layer of LaAlO3 has been grown epitaxially between c-axis oriented YBCO layers having the nominal thickness of 250 nm. A stacking fault in the LaAlO3 layer may introduce a stacking fault into the YBCO layer, which may form nucleation sites for α-axis oriented grains. A second phase had been formed at the interface between the LaAlO3 layer and the lower YBCO layer, which has been identified by image simulation and energy dispersive x-ray (EDX) analysis as a new tetragonal La–Al–Cu–O phase based on LaAlO3 in which some of Al atoms have been replaced by Cu. The approximate lattice parameters of the new phase are a = 0.38 nm and c = 0.76 nm. However, no second phase was found at the interface between the lower YBCO layer and the LaAlO3 substrate.