Formation Of Extended Defects Research Articles

Defects in highly nonstoichiometric oxides

A number of important physical and chemical properties of nonstoichiometric transition metal oxides are strongly dependent on the kind and concentration of point defects in the crystalline lattice of these materials. If the concentration of these defects is sufficiently small they do not interact and the defecteed crystal can be treated as ideal solid solution of defects in its crystalline lattice. However, in many cases the concentration of defects in transition metal oxides is high enough for them to interact, what can result in formation of extended defects, i.e. of three-dimensional complexes and defect clusters, or of two-dimensional planar defects. For these cases the point defect model is not applicable and transport processes cannot be described in terms of solid state diffusion theory. An attempt has been made to systematize the current knowledge of extended defects and to formulate some conclusions concerning transport phenomena in crystals containing these defects.

Superconductivity and structural disorder in ion-irradiated rhenium films

Single- and polycrystalline Re films were irradiated at room temperature and liquid nitrogen temperature with 350-keV N ions and 700-keV doubly charged Ar ions. With increasing ion fluence ф, the ion-induced residual resistivity Δρ0 and the superconducting transition temperatureT c were observed to increase. The functional behavior of Δρ0(ф) and the recovery spectra are found to depend on ion species and ф. Annealing stages II and III are seen after low-dose N- and Ne-ion irradiation, whereas at high ion fluences stages II, IV, and V are most pronounced. Thus the increase of ρ0 at low fluences is attributed to vacancies mainly, and at high fluences to the formation of extended defects. TheT c increase at low fluences is caused by inhomogeneously distributed vacancies, and at high fluences by vacancies pinned to dislocations. Extended defects alone do not seem to have any influence onT c . Ion-induced recrystallization processes have also been observed.

Extended defect formation in oxides with the ReO 3 structure, I

We present results of a detailed atomistic computer simulation study of extended defect formation in ReO 3-structured nonstoichiometric oxides. Our results show, in accordance with experiment, that {102} shear planes are the most energetically favored isolated shear planes in such oxides. However, we show that lattice relaxations play an essential role in stabilizing these defects over {001} and higher-index planes. The latter are, however, sufficiently close in energy to permit the difference in the energies of the isolated defects to be outweighed by the defect interaction term considered in Part II of this study. We also establish that the energies of point defect modes of reduction for these oxides are sufficiently close to allow dissociation of shear planes into vacancies at very low deviations from stoichiometry.

Etude gravimetrique des ecarts a la stoechiometrie de WO 3−x

The non-stoichiometry of tungsten trioxide WO 3−x has been studied by a gravimetric method at 750 and 850°C. In the range 0,0008 < x < 0.0240 the variation of x with oxygen partial pressure obeys the law: log 10 x = A − 1 4 log 10 p O 2 where A is a constant. These results can be explained by the formation and continuous growth of extended defects, leading to (120) shear planes. From experimental data, the enthalpy of the reaction: 2 x′− x WO 3− x → 2 3− x′ +O 2 was calculated as ΔH° = 130 ± 3 kcal.

Formation of epitaxial NiO by Oxygen implantation in [100] Ni

18O has been implanted at room temperature up to dosesof 4.4 × 10 17/cm 2 in a [100] Ni crystal. The implantation energy was 60 keV. Backscattering and channeling analyses at various implantation steps give evidence for oxygen migration towards the surface. After the overall implantation, X-ray analysis reveals the presence of NiO in epitaxy [100]//[100] with the substrate. Backscattering and channeling experiments tend to indicate that between the surface and R p the sample is formed of NiO epitaxial crystallites and of pure nickel leading to a mean stoichiometry NiO 0.75, constant in depth up to R p. The misfit between the Ni and NiO lattice parameters induces strains and extended defects formation. Between R p and R p + ΔR p the oxygen concentration decreases, and the channeling results show no preferential direction. This region corresponds probably to a highly disordered NiO alloy. This hypothesis is confirmed by annealing experiments: the oxygen present between R p and R p+ ΔR p migrates towards the surface at 400°C and a reordering of this region is observed. There is also an improvement of the structural quality of the NiO crystallites.

Degradation induced formation of extended defects in GaP:N LED's

The light output degradation of commercial VPE GaP:N LED's was studied by monitoring minority carrier lifetime and deep level spectra. It was found that the decrease of the quantum efficiency can be completely accounted for by the formation of a nonradiative recombination center T 6 . T 6 is identified as a vacancy cluster, a model suggested by the formation-annihilation properties of this deep level.

An electron microscope study on substitutional order and disorder in the system MnS Ln2S 3 ( Ln = Yb or Y)

The substitution of 2 Ln 3+ ( Ln is Yb or Y) for 3Mn 2+ at about 1873 K in the α-MnS structure (cubic close packing) was investigated by means of electron diffraction (at room temperature). Diffuse intensity contours suggest that clusters of Mn 2+ and Ln 3+ around a vacancy are formed. In the close-packed plane, the cluster is a hexagon of 4Mn 2+ and 2 Ln 3+ around a vacancy, a seven-point cluster. Clusters remain independent up to composition 4MnS · Ln 2S 3. With higher Yb 2S 3 content spinel domains in the short-range-order matrix are formed. Samples of MnSY 2S 3 heated at 1873 K showed formation of extended defects (in this case twin planes) when they contained more than 20 mole% Y 2S 3 (14% vacancies).

Thermal behavior of laser-annealed GaAs studied by helium backscattering spectroscopy

The thermal behavior of Te-implanted, laser-annealed GaAs was investigated by helium backscattering and channeling analysis in order to determine the role of structural changes on the two-stage reduction in carrier concentration observed with post-laser-anneal heating above 250 °C. Post-laser-anneal heating up to 450 °C caused no observable structural changes in the GaAs or in the substitutionality of the implanted Te. On the other hand, 850 °C post-laser-anneal heating induced the formation of extended defects in the GaAs, and the channeling half-angle of Te was narrowed by about 11%. From those observations, possible models to explain the reduction in carrier concentration are postulated.

Nonequilibrium solid solutions obtained by heavy ion implantation and laser annealing

Nonequilibrium solid solubility of P, As, and B in single-crystalline silicon annealed by Q-switched ruby laser pulse irradiation was experimentally investigated for residual defects, lattice strain, and electrical activation of implanted impurities. The maximum solubility obtained without any macroscopically extended defect formation was 2–4 times higher than the thermal equilibrium solubility limit. Above this solubility, precipitates, dislocations, and surface cracks were observed. The highest full activation was realized by P implantation, with carrier concentration up to ∼5×1021/cm3 showing no such defects. Formation mechanisms of the defects are discussed and shown to be attributable to the rapid solidification process of the heavily doped layer and to large impurity-induced misfit stress comparable to the fracture stress.

Channeling analysis of disorder structure in neon implanted silicon

Channeling effect measurements at different energies of a 4He analyzing beam (0.7–2.2 MeV) have been used to study the disorder structure produced in 〈111〉 Si samples by 60 keV Ne ion implantation. For doses less than 10 15 ions/cm 2 and subsequent annealing up to 720°C, only a small step in the channeling spectra corresponding to a disordered region at a depth around the maximum of the deposited energy has been observed. For a higher dose (2×10 15 Ne ions/cm 2), the presence of the direct backscattering peak, even after annealing at 800°C, indicates the formation of a damaged layer of complex structure. The beam energy dependence of minimum yield and the direct backscattering peak show the important influence on dechanneling of strains due to the formation of extended defects during annealing.

Voids in ion-implanted silicon

Abstract The vacancy defect subsystem is studied by means of electron microscopy in ion-implanted silicon. It has been discovered that, unlike the interstitial atoms which form rod-like defects and two-dimensional defects (dislocation loops, stacking faults), vacancies condense during annealing into three-dimensional associations—voids. The formation temperature of a void consisting of ∼103 vacancies in 400–500°C. Voids have the tendency to associate into more complicated complexes; as a result of void interaction, disk-like clusters are formed in P+-implanted silicon. At temperatures 700–750°C, disk interaction is likely to take place which is accompanied by extended defect formation—chains. At annealing temperatures 800–850°C voids do not collapse in vacancy dislocation loops and chains do not rearrange in dislocations; all the defects dissolve in matrix. It has been shown that the postannealing defect distribution is heterogeneous. The experimental data are discussed in detail.

Improved polycrystalline ceramic lasers

Improved polycrystalline ceramic laser rods, composed of cubic solid solutions of 89–96.5 mole% Y2O3, 10–2.5% ThO2, and 1% Nd2O3, were synthesized by a conventional sintering process. This material, called Nd-doped Yttralox (NDY) ceramic, was produced with laser threshold energies lower than that of the best commercially available Nd:glass laser rod and with a lasing efficiency ∼94% that of laser glass at 40 J of input energy under pulsed mode conditions. In a similar operating mode a NDY rod, containing 5 mole% ThO2 and having dimensions 7.6×0.46 cm, delivered 0.41 J of optical energy when using an input energy of 162 J, a pump pulse of 150 μsec, and output mirror reflectivity of 70%. The lasing efficiencies depended strongly on the method of powder preparation and processing, composition, and the cooling rate from the sintering temperature. The dependence of the fluorescent linewidth on the NDY composition provides a means of appreciably varying the material gain coefficient. Active attenuation coefficients for AR - coated NDY laser rods were about 2% per cm as compared to 0.76% per cm for an OI ED-2 laser glass rod measured in the same optical cavity. The absorption component of the optical attenuation was measured to be 0.38% per cm at λ = 1.06 μ, indicating that the scattering component is the major contribution to the attenuation coefficient. Considerable evidence is presented which shows that submicroscopic scattering centers exist in the solid - solution matrix and are related to composition fluctuations arising from (i) chemical segregation in the starting powder which is not entirely eliminated during the high - temperature sintering process and (ii) the formation of extended defects or ordered zones in the solid - solution phase during specimen cooling from the sintering temperature.