Low temperature photoluminescence measurements were carried out on pseudomorphically strained InxGa1−xAs-Al0.28Ga0.72As ternary-on-ternary heterostructures grown by molecular beam epitaxy to investigate the change in the transition energy, linewidth, and intensity as a function of InGaAs well thickness at two different indium compositions, x = 0.10 and x = 0.15, respectively. Sharp exciton peaks as narrow as 4-6 meV were observed from the InGaAs wells grown at 530 °C with 1 min of growth interruption at the top and bottom heterointerfaces. The linewidth decreases as the well thickness is increased up to 300 Å. In addition, there are signs of linewidth broadening and sharp decrease in the photoluminescence intensity at higher well thicknesses that may indicate the onset of plastic relaxation. Relatively small variations in the transition energy were observed at well thicknesses that are up to ≍3 times the theoretical critical layer thickness calculated by the Matthews-Blakeslee model,10 suggesting that the small density of dislocations that may be present may not have a significant effect on the band structure of the well.

Dislocations in MgO introduced by ion irradiation and by plastic deformation are observed by HREM. Depending on the Burgers vector and the dislocation character, various types of lattice images are obtained. Image simulations are performed for the inclination of dislocations, as well as for dissociated dislocations. A comparison of observed and simulated images shows that inclination of nondissociated dislocations makes them appear as if they were dissociated; in reality a/2(110) dislocations in MgO are not dissociated.

The upconversion of infrared radiation into visible light has been studied in heavy metal oxyfluoride glass-ceramics co-doped with Yb3+ and Tm3+ ions at 300 K. The general composition of the compounds is 69.9PbF2 + 7.5WO3 + 7.5MO2 + 15YbF3 + 0.1TmF3 (M = Si, Ge, Zr, Te, and Th). Two main upconversion emissions were observed. They are centered at 477 and 775 nm, corresponding to the 1G4 → 3H6 and 3F4 → 3H6 transitions, respectively. Slopes of the emission intensity versus excitation power measurements indicate that the blue emission is due to three-photon absorption, while two-photon absorption processes are responsible for the red emission. A comparative method was used to measure the upconversion efficiencies under 16.5 mW/cm2 excitation power. Measurements were made after the compounds were annealed at 450 °C for 4 h. The best conversion efficiencies were obtained for the compound having silicon (Si). They are 28 × 10−6 for the blue and 18 × 10−2 for the red emission.

High strength can be achieved in high alumina cement (HAC) through the incorporation of phosphate-based additions at levels of 10 and 20 wt. %. In order to establish the mechanism that results in higher strength, the effects of a variety of condensed sodium phosphates (NaPO3)n, (NaPO3)n · Na2O, Na5P3O10, and (NaPO3)3 were studied. The influence of these additions on the kinetics of hydration was studied using isothermal calorimetry. The phosphatic additions enhanced reactivity, but x-ray diffraction analyses did not reveal evidence of new crystalline phosphate-containing hydration products. Microstructural evolution was examined in real time using environmental SEM, and hydration products exhibiting distinct morphologies were observed. The features exhibited ranged from amorphic to polygonal shapes, plates, and fibers. These frequently formed between crystalline calcium aluminate hydrate grains and by doing so appear to provide a means to enhance the strengths of these cements. In spite of the morphological variations, companion energy dispersive x-ray analysis showed that the compositions of these products did not vary widely. Their ranges of compositions are 52-60 wt. % Al2O3, 20-26 wt. % P2O5, and 20-24 wt. % CaO.

A novel technique to enhance the nucleation of low-pressure diamond on silicon (100) was discussed in this study. It was found that coating the silicon with ballpoint pen ink can greatly increase the diamond nucleation density when the coating was followed by heat treatment at 100 °C–400 °C. Moreover, the optimum enhancement effect was reached when the ink coating was pre-heat-treated at 300 °C × 30 min. Further SEM observation showed that heat treatment at 200 °C-400 °C produced many tiny carbonaceous particles on ballpoint pen ink-coated silicon. Particularly, the nucleation density of diamond on differently treated silicon, such as ink-coated, diamond paste scratched and polished silicon wafers, was compared using the SEM technique. The diamond structure was also characterized by Raman spectroscopy.

Aluminum oxide films have been prepared by ion assisted deposition using argon ions with energy in the range 300 to 1000 eV and current density in the range 50 to 220 μA/cm2. The influence of ion energy and current density on the optical and structural properties has been investigated. The refractive index, packing density, and extinction coefficient are found to be very sensitive to the ion beam parameters and substrate temperatures. The as-deposited films were found to be amorphous and could be transformed into crystalline phase on annealing. However, the crystalline phases were different in films prepared at ambient and elevated substrate temperatures.

Epitaxial Grain Growth (EGG) is an orientation-selective process that can occur in polycrystalline thin films on single crystal substrates. EGG is driven by minimization of crystallographically anisotropic free energies. One common driving force for EGG is the reduction of the film/substrate interfacial energy. We have carried out experiments on polycrystalline Ag films on Ni(001) substrates. The orientation dependence of the Ag/Ni interfacial energy has been previously calculated using the embedded atom method. Under some conditions, EGG experiments lead to the (111) orientations calculated to be interface- and surface-energy-minimizing. However, when Ag films are deposited on Ni(001) at low temperature, EGG experiments consistently find that (111) oriented grains are consumed by grains with (001) orientations predicted to have much higher interface and surface energy. The large elastic anisotropy of Ag can account for this discrepancy. Strain energy minimization favors growth of (001) grains and can supersede minimization of interfacial energy if sufficient strain is present and if the film is initially unable to relieve the strain by plastic deformation.

The microstructures of sputtered thin films of lead-lanthanum zirconate-titanate (PLZT) on (0001) sapphire substrate have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thin films of polycrystalline PLZT (9/65/35), Pb0.91La0.09Zr0.65Ti0.35O3, were prepared on a (0001) sapphire substrate by reactive sputtering, using the dc-magnetron system with a multitarget, Pb, La, Zr, and Ti at the substrate temperature of 700 °C. The PLZT thin films comprised (111) oriented small crystallites of PLZT. Although the average direction of the crystal orientation corresponded to the ideal epitaxial relationship (111) PLZT ‖ (0001) sapphire, the individual crystallites showed misalignment in both the growth direction and the film plane. The thin films could not be considered epitaxially grown films. From analysis of the TEM images, there exists an interfacial region between the PLZT thin film and the substrate. The interfacial region comprises ordered clusters of (111), disordered (101), and/or (110) PLZT crystallites. The presence of the interfacial region will suppress ideal epitaxial growth with uniform crystal orientation. It is confirmed that the addition of the buffer layer of graded composition of PLT-PLZT, between the substrate and the PLZT thin film, will suppress the formation of the disordered interfacial region and will enhance the epitaxial growth of the (111) PLZT on (0001) sapphire with three-dimensional crystal orientations.

A combined experimental and theoretical investigation of the sedimentation of unstable colloidal ceramic suspensions has been performed. Suspensions containing submicron-sized α-Al2O3 particles were prepared at various pH values in order to modify suspension stability. Particle volume fraction during sedimentation was determined as a function of position and time by gamma-ray densitometry. A population balance model was developed to account for various coagulation and decoagulation mechanisms that affect sedimentation behavior in flocculating suspensions. Model predictions were then compared with experimental measurements, in order to establish the validity of the theoretical model.

Polycrystalline diamond films may be produced by chemical vapor deposition (CVD) with morphologies ranging from multimicron crystallites with well-defined facets and texture to nanocrystalline “cauliflower” nodules. While previous efforts to connect diamond film “quality” to growth conditions focus on competitive growth of non-diamond phases, we propose that twinning is a major controlling factor. We use geometric arguments to define the conditions under which a given twin can outgrow and bury the “parent” face on which it originated. We then show how the full spectrum of diamond crystallite shapes and film morphologies can be explained in terms of penetration twins without reference to the actual mechanistics of diamond growth.

Lithium titanium orthophosphate LiTi2(PO4)3 (LTP) has attracted attention as a chemically stable fast Li+-conductor in ambient atmosphere. It was reported in our previous paper7 that monolithic microporous glass-ceramics with a skeleton of this crystal were successfully prepared from glasses in the pseudobinary system of LTP and Ca3(PO4)2. Here we report that these porous glass-ceramics (mean pore diameter: ∼40 nm; total specific surface area: ∼30 m2; porosity: ∼45 vol.%) show excellent cation exchange properties. Approximately 50% of Li+ ions in the materials are exchanged with monovalent ions with ionic radii smaller than 130 ppm in 1 h at room temperature. In particular, Li+ ions are selectively exchanged with Ag+ ions even in the presence of Na+ ions. The exchange rate in the porous glass-ceramics is larger by two orders of magnitude than that of sintered LTP. The ratio of these exchange rates is close to that of the total surface areas, indicating that most of the pores in porous LTP glass-ceramics are available for ion exchange reactions. These are the first porous glass-ceramics having excellent cation exchange properties.

The anisotropies and mechanical properties of hot-pressed Al2O3 and SiC-whisker/Al2O3 composites were investigated. The c-axis of Al2O3 crystals in monolithic Al2O3 was oriented in the direction of hot-pressing. The same tendency was observed in Al2O3 matrices of composites, but orientation of Al2O3 crystals was smaller than that of monolithic Al2O3. SiC-whiskers obstructed plastic deformation and mass transfer of Al2O3 matrices. The twist mode crack deflection was remarkable on fractured surfaces of polycrystalline Al2O3 in which the main crack propagated perpendicular to hot-pressing direction. This was caused by the orientation of Al2O3 crystals. This anisotropy resulted in a small difference in fracture toughness; however, other mechanicl properties didn't change. The fracture mode of SiC-whisker/Al2O3 composites was obviously changed, depending on the direction of crack extension as compared with the changes observed in monolithic Al2O3. However, there was no difference in mechanical properties among the composites. Macroscopic fracture mode seemed to have less effect than microscopic fracture mechanism, such as whisker bridging and pull-out.

Brominated, anodically oxidized, and pristine p-100 carbon fiber reinforced tin-lead alloy composites were fabricated by squeeze casting. The fibers were brominated by bromine vapor for 48 h and then desorbed at 200 °C in air for 12 h. The anodic oxidation treatment of fibers involved electrochemical etching in a dilute sodium hydroxide electrolyte for 3 min, or immersing in nitric acid for 72 h. The composites containing surface-treated carbon fibers had higher tensile and interlaminar shear strength than the ones containing pristine carbon fibers. The composite containing brominated carbon fibers had better tensile strength than the other two surface treatments.

The Hertzian indentation response of a machinable mica-containing glass-ceramic is studied. Relative to the highly brittle base glass from which it is formed, the glass-ceramic shows evidence of considerable “ductility” in its indentation stress-strain response. Section views through the indentation sites reveal a transition from classical cone fracture outside the contact area in the base glass to accumulated subsurface deformation-microfracture in the glass-ceramic. The deformation is attributed to shear-driven sliding at the weak interfaces between the mica flakes and glass matrix. Extensile microcracks initiate at the shear-fault interfaces and propagate into the matrix, ultimately coalescing with neighbors at adjacent mica flakes to effect easy material removal. The faults are subject to strong compressive stresses in the Hertzian field, suggesting that frictional tractions are an important element in the micromechanics. Bend-test measurements on indented specimens show that the glass-ceramic, although weaker than its base glass counterpart, has superior resistance to strength degradation at high contact loads. Implications of the results in relation to microstructural design of glass-ceramics for optimal toughness, strength, and wear and fatigue properties are discussed.

Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitors have been fabricated with four electrode combinations: Pt/PZT/Pt/SiO2Si, RuO2/PZT/Pt/SiO2/Si, RuO2/PZT/RuO2/SiO2/Si, and Pt/PZT/RuO2/SiO2/Si. It is shown that polarization fatigue is determined largely by the electrode type (Pt vs RuO2), and microstructure has only a second-order effect on fatigue. If either the top or bottom electrode is platinum, significant polarization fatigue occurs. Fatigue-free capacitors are obtained only when both electrodes are RuO2. In contrast, the bottom electrode is found to have a major effect on the leakage characteristics of the PZT capacitors, presumably via microstructural modifications. Capacitors with bottom RuO2 electrodes show high leakage currents (J = 10−3-10−5 A/cm2 at 1 V) irrespective of the top electrode material. Capacitors with Pt bottom electrodes have much lower leakage currents (J = 10−8 A/cm2 at 1 V) irrespective of the top electrode material. At low voltage, the I-V curves show ohmic behavior and negligible polarity dependence for all capacitor types. At higher voltages, the leakage current is probably Schottky emission controlled for the capacitors with Pt bottom electrodes.

A high resolution electron microscopic (HREM) study of interface structure between diamond film and its silicon substrate is presented. The HREM images reveal that there is an amorphous intermediate layer between the diamond film and its substrate for samples grown by hot filament chemical vapor deposition (HF-CVD). In some cases, β-SiC crystallites and a few graphite microcrystallites may be embedded in this amorphous layer. The HREM images obtained from cross-sectional specimens reveal that the diamond crystallites nucleate directly either on the amorphous intermediate layer, at diamond seed crystallites that were left during pretreatment of Si substrate by diamond paste,β-SiC particles, or at some scratches of the Si substrate. HREM images also reveal that the quantity, distribution, and the size of β-SiC particles in the intermediate layer are different for different processes. Some β-SiC crystallites have certain orientation relationships with the Si substrate. A HREM study of cross-sectional specimens indicates that twins and microtwins in the HF-CVD diamond film are formed during nucleation of the film either from diamond seeds, β-SiC crystallites, or the amorphous intermediate layer. Multiple twins formed from different β-SiC crystallites have also been observed. High densities of “V” shaped microtwins formed during the initial growth of the diamonds and the formation mechanism of these twins are discussed.

Diamond nucleation on unscratched silicon substrates coated with thin films of hard carbon was investigated experimentally with a microwave plasma-assisted chemical vapor deposition system. A new pretreatment process was used to enhance the nucleation of diamond. Relatively high diamond nucleation densities of ∼108 cm−2 were achieved by pretreating the carbon-coated silicon substrates with a methane-rich hydrogen plasma at a relatively low temperature for an hour. Scanning electron microscopy and laser Raman spectroscopy studies revealed that diamond nucleation occurred from nanometer-sized spherical particles of amorphous carbon produced during the pretreatment. The nanoparticles possessed a structure different from that of the original hard carbon film, with a broad non-diamond Raman peak centered at ∼1500 cm−1, and a high etching resistance in pure hydrogen plasma. The high diamond nucleation density is attributed to the significant percentage of tetrahedrally bonded (sp3) atomic carbon configurations in the nanoparticles and the presence of sufficient high-surface free-energy sites on the pretreated surfaces.

Precursor glass and glass-ceramics with molar composition 2Na2O · ICaO · 3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm−1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm−1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm−1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.

The measured room temperature magnetic susceptibility of a bulk sample of buckytubes (buckybundle) is −10.75 × 10−6 emu/g for the magnetic field parallel to the buckybundle axis, which is approximately 1.1 times the perpendicular value and 30 times larger than that of C60. The experimental results are discussed in terms of a graphite-like electronic structure model.