The results of an x-ray photoelectron loss spectroscopy (XPLS) study of several wide band gap aluminum compounds are presented here. XPLS is a new application of x-ray photoelectron spectroscopy involving the determination of the energy separation, ΔE, between a particular core photoelectron peak and its principal loss peak. The materials investigated here are sputter deposited thin film Al-nitride and oxide, and bulk single crystal α-alumina. It is not possible to distinguish between these materials on the basis of the chemical shift in the binding energy of the A12p and A12s photoelectrons (Siegbahn shift). The results show that XPLS can be used to distinguish between these materials. ΔE in Al-oxides and nitride differs by several eV and is independent of sample charging. Comparison with ΔE calculated using a free electron gas model is made and related to the plasmon nature of ΔE.

The critical dose for formation of an amorphous layer of Al2O3 by ion irradiation at 77 K has been determined. It is found to lie between 2 and 3 × 1015/cm2 if the sample is irradiated near the <0001> axis of the substrate and is found to lie in the neighborhood of 2 × 1016/cm2 if the irradiation is near the <1210> axis. The amorphous layers are found to recrystallize epitaxially if annealed at 1190 degrees C and to form a metastable microstructure upon annealing at 800 degrees C.

Problems associated with nonrandom distributions of active ions in solid state insulator laser materials are discussed. A12O3:Ti3+ and BeAl2O4:Cr3+ crystals are used to show typical examples of some of these problems. In addition some problems of this type observed in new materials with potential for solid state laser applications are discussed.

Ion exchanged ß“-aluminas display a number of interesting optical properties which suggest that the material is well suited for application as a solid state laser host. Small platelets of Nd3+ Ion exchanged β“-alumina exhibit laser action with gain coefficients many times greater than YAG. The versatility of the ion exchange process enables one to form a wide variety of compounds with different active ions and concentrations, thereby allowing the study of many different effects within a single host crystal.

The electrical and optical properties of single crystals of Ni, Ni + Zr, and Fe doped Y3Al5O12(YAG) were studied as a function of temperature, atmosphere and composition. The often dramatic changes in properties observed for these materials are interpreted in terms of the underlying defect structure of these materials. Defect formation and migration energies are derived as well as the position of energy states within the gap.

Transmission electron microscope studies of Ti-doped, congruent lithium niobate (LiNbO3) have shown that extended structural faults are only present within the Ti diffused layer (i.e. the wave guiding region). Structural faults have not been observed in undoped control crystals of congruent and stoichiometric LiNbO3. Therefore, it appears that the introduction of Ti is responsible for the formation of these defects. The chemical driving forces which may be controlling the formation of structural faults are discussed.

Diffraction contrast experiments, which have been interpreted in terms of two-beam dynamical theory for a centrosymmetric crystal, indicate that the faults are tensile in nature (i.e. formed by removing a plane of atoms – so-called intrinsic faults) and have a displacement vector of the type c/12/001] when indexed in the hexagonal coordinate system. That is, the displacement vector is along the c-axis. The detailed crystallographic character of the fault planes is not clear; both (118) and (1 1 12) planes have been confirmed from trace analyses and therefore the fault has a shear component. Additional contrast experiments will be required in order to clarify this feature of structural faults in Ti-doped LiNbO3.

Since the extent of these structural faults is tens of microns, they are clearly potential scattering sites for photons. In this regard, a systematic understanding of their origin and thermal stability is crucial to integrated optical device technologies based on LiNbO3 and on the Ti-doped waveguide fabrication technique.

An attempt is made to fabricate positive-index waveguides by ion implantation of metal ions into crystals of LiNb03. The observed structural, chemical, and optical damage is summarized and possible solutions are discussed.

Recent advances of glass materials and fabrication processes will be reviewed in the field of guided-wave technology. A variety of optical fibers and guided-wave devices are in development by using high-silica and non-silica glasses. Following the successful development of silica fiber, a new family of optical fibers is being investigated by using non-silica glasses such as fluoride and chalcogenide glasses, which operate at mid-infrared wavelength range and offer the potential of ultra-low loss. High-silica channel waveguides are fabricated by processing a SiO2TiO2 planer waveguide on a silicon substrate. These are applied to various guided wave optical circuits such as switch and wavelength-division multi/demultiplexer, which would be used for the construction of optical communication systems. The materials and processing techniques influencing optical guided-wave performance are described.

A study is made of irradiation effects on α-quartz crystals using the techniques of electrical conductivity and dielectric loss measurements. The initial radiation-induced conductivity (RIC) induced by X-ray irradiation over the temperature range from 94 to 250 K is found to have a nearly constant activation energy of 0.29 ± 0.02 eV. Since a large RIC still results from irradiation at temperatures too low for alkalis to be liberated, it is proposed that the RIC is due to holes (as small polarons) rather than to alkalis. The dielectric loss measurements in Na-swept quartz are used to follow the changes in the relaxation peaks due to the Al-Na defect as a function of radiation dose and annealing. At the same time a low-temperature “irradiation peak” is studied. Restoration of the main Al-Na peak during annealing occurs in two stages: one near 500 K and the other above 600 K. From the observed behavior of the irradiation peak in various crystals, it is concluded that this peak is probably due to alkali centers. Finally, a defect model interpreting the two annealing stages is presented.

Electrodiffusion (sweeping) is a post-growth treatment which allows the selective exchange of charge compensating intersititial ions in quartz. This technique is employed commercially to enhance the radiation hardness of the material used for precision oscillator crystals. Most as-grown quartz contains substitutional Al3+ with an interstitial alkali providing the charge compensation. Additional unidentified sites also trap protons to form the OH--growth defects responsible for several IR absorption bands. When thermally released from their trapping sites, the intersitials can migrate along the large c-axis channels. Therefore, if the sample is heated with an electric field applied along the c-axis, the ions can be swept out and replaced either by protons from the surrounding atmoshpere or by the desired alkal i from a salt electrode. In order to better understand the electrodiffusion, we are systematically investigating various aspects of the process. The apparent ionic conductivity data taken as the swept sample is cooled usually shows a curved log( T) vs 1000/T plot. The conductivity of H+ in is much less than that of the lithium or sodium. The activation energies at high temperatures tend to be lower than those found from the low temperature data. The exponential prefactors are considerably larger than the values predicted for a given aluminum content and reasonable estimates of the attack frequency and jump distance. It seems likely that an additional source of mobile ions is present. The peak or plateau observed during the warm-up period for air or hydrogen sweeping appears to be caused by the transition from conduction primari1y by a1ka1i s to conduction by protons.

Predominantly 6H <0001> SiC single crystals have been implanted with nitrogen and aluminum at 300°K. The effects of implantation and post-implantation annealing at 573–1173°K have been characterized by Rutherford backscattering/channeling, microhardness measurements and transmission electron microscopy. Even at 1173°K, defect annealing was inhibited in amorphized regions. Progressive damage recovery as the anneal temperature was increased was otherwise generally observed. Fluences predicted by the critical damage energy of 2 × 1021 keV/cm3 did not quite produce amorphization to x = 0. In the as-implanted specimens, decreasing hardness was observed with increasing fluence. Significant surface softening (∼ 33% hardness reduction) was achieved at the highest aluminum fluence (5 × 1015 Al/cm2) and was stable at temperatures < 893°K.

Current understanding of R-curve behaviour and the strength-toughness relationship of transformation-toughened ZrO2-containing ceramics is reviewed. If the toughness increases with crack, extension along an R-curve, a maximum in strength versus toughness is observed, which is related to the crack instability criterion for R-curves. An analytical expression from a well-known “wake” theory of crack tip shielding due to McMeeking and Evans is used to compute R-curves and strength/toughness relations, which are compared with experiment.

The properties of yttria stabilized tetragonal zirconia polycrystalline ceramic fabricated from commercial powders are described. The fracture strength, fracture toughness, density, and low temperature aging effects, are studied for sintered and hot isostatically pressed ceramics. The role of alumina as an additive to the material and its influence on properties is also discussed.

The grain boundary chemistry of reaction bonded silicon nitride (RBSN) and the effects of iron species and content on this chemistry are investigated using X-ray photoelectron spectroscopy (XPS). Data are reported for semiconductor grade RBSN, Fe-doped semiconductor grade RBSN, and metallurgical grade RBSN specimens. Results indicate that the grain boundaries have an elemental composition of Si, N, O, and C, with important chemical differences depending on the purity of the starting material. In the RBSN made from metallurgical grade silicon, the grain boundaries have a distinct “oxide-like” layer, with a subregion of Si3N4. No distinct oxide layer was observed in the RBSN made from semiconductor-grade silicon, where the O appears to be uniformly incorporated into the Si3N4.

The effect of an applied, time varying voltage on the plastic behavior of (Hg,Cd)Te has been investigated. We observe that both positive and negative voltages suppress plasticity, with the negative voltage being more effective. The influence of this voltage polarity is strain dependent and provides information on the charge of the mobile dislocations. From these results we present a model of the strain dependence of the voltage dependent plasticity.

The steady-state flow stress τs in nonstoichiometric NiO single crystals has been measured in the temperature range of 1428 to 1653 K with oxygen partial pressures p(O2) between 6 and 1×105 Pa. Strain rates were varied from 1×10−5 to 2×10−3 s−1. Transmission electron microscopy indicates that dislocation climb is the primary mechanism of recovery. Because dislocation climb is diffusion controlled, the data may be described at fixed temperature by = Aτns (O2)1/m, where n is the stress exponent and m is a parameter that is determined by the dominant atomic defects on each sublattice. At high temperatures and p(O2) > 2×104 Pa, n was found to be in agreement with dislocation-climb models; however, n increased at low p(O2) owing to effects of impurities. The values of m are consistent with control of climb rate by diffusion of singly charged oxygen vacancies for low p(O2) and by diffusion of neutral oxygen interstitials for high p(O2). At lower temperatures, the values of n are strongly affected by dislocation/impurity interactions for all p(O2).

It has been established that the wear behavior of ceramic materials can be modified through ion implantation. Studies have been done to characterize the effect of implantation on the structure and composition of ceramic surfaces. To understand how these changes affect the wear properties of the ceramic, other mechanical properties must be measured. To accomplish this, a commercially available ultra low load hardness tester has been used to characterize Al 2O3 with different implanted species and doses. The hardness of the base material is compared with the highly damaged crystalline state as well as the amorphous material.