The transient supersaturation in a system undergoing Ostwald ripening is related to the cluster formation energy E fc as a function of cluster size n. We use this relation to study the energetics of self-interstitial clusters in Si. Measurements of transient enhanced diffusion of B in Si-implanted Si are used to determine S͑t͒, and inverse modeling is used to derive E fc ͑n͒. For clusters with n . 15, E fc ഠ 0.8 eV, close to the fault energy of ͕113͖ defects. For clusters with n , 10, E fc is typically 0.5 eV higher, but stabler clusters exist at n ഠ 4 (E fc ഠ 1.0 eV) and n ഠ 8 (E fc ഠ 0.6 eV). [S0031-9007(99)09311-4]

The validities of the Warren-Averbach analysis and of an alternative analysis for separation of size and strain contributions to diffraction line broadening are investigated. The analyses are applied to simulated and experimental line profiles. The Fourier coefficients of the simulated line profiles are derived from expressions for the distortion field around specific lattice defects: misfitting inclusions and small-angle grain boundaries. Applicability tests are also performed on experimental powder diffraction line profiles taken from plastically deformed specimens: thin aluminium layers and ball-milled molybdenum powders. It is concluded that for both methods finite but different classes of specimen exist for which they give meaningful results. In practice, each time an analysis is performed the results must be tested against common (physical) sense and all information available on the specimens.

Broadening of (X-ray) diffraction lines is often due to the distortion fields associated with lattice defects as dislocations. A generally applicable flexible model for distributions of lattice defects and their distortion fields is presented. The model allows a straightforward calculation of diffraction-line profiles. Parameters of the model are the average distance between the defects, the extent of the distortion fields and the mean-squared strain. The order dependence of the shape and width of line profiles is studied as a function of these model parameters. The adequacy for practical application of two methods frequently used to analyse X-ray diffraction-line broadening (the Warren-Averbach analysis and the Williamson-Hall analysis) is investigated by applying them to calculating line profiles. The 'size' and 'strain' parameters deduced by the methods mentioned are discussed with reference to the strain-field model parameters. It is concluded that only in limiting cases can the results be related directly to the microstructure. Experimental line profiles taken from a ball-milled tungsten powder are used to show that the line profiles calculated on the basis of the strain-field model pertain to realistic situations. It is shown that, in principle, an interpretation of measured line broadening is possible directly in terms of strain-field parameters. § The limited coherency of the incident radiation in the directions parallel and perpendicular to the direction of wave propagation [usually --~ llam and a few tens of nm, respectively, for X-rays (Cowley, 1981)] is ignored in this paper.

A perfect general purpose standard specimen for high accuracy line-profile analysis is shown to be an illusion. Balancing the partly contradictory requirements, an optimum standard specimen for a parafocusing diffractometer is developed. To obtain the optimum standard specimen, a 5–10 μm particle size fraction is taken from the NIST certified Si powder SRM640a, about 1.5 mg/cm2 of this powder is uniformly deposited on a (510) oriented Si single-crystal wafer and the assembly is heat treated for 2 h at 1273 K to remove lattice imperfections. All procedures necessary are precisely given, easily applicable, and reproducing. For the present standard specimens, the random errors due to crystal statistics are quantified and shown to be acceptable for spinning specimens; the systematic errors due to residual size and transparency broadening are determined semi-empirically and can be eliminated, if desired. Thus the proposed optimum standard specimen allows the determination of instrumental line profiles free from systematic errors and with random errors in the line width of the order of 0.001 °2θ, allowing a full use of the capacities of modern diffractometers and data evaluation procedures.

This article presents results of a study initiated to characterize the plasma-oxidation process of very thin Al films, a technology commonly used to produce good barrier layers for magnetic spin-tunnel junctions. The behavior of oxygen in the oxidizing Al layer is determined using both quantitative (Rutherford backscattering spectrometry, transmission electron microscopy) and qualitative (x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry) analytical techniques. We have applied in situ XPS and experimented with O218 to unravel details of the oxidation mechanism. In addition, the influence of the oxygen pressure on the oxidation rate was established, both with and without a plasma being present. From optical emission spectra it is concluded that this pressure has a minor effect on the relative abundance of excited species in the oxygen plasma. When combined, these data constitute the basis of a model that distinguishes several steps in the plasma oxidation of Al. At the start, oxygen penetrates rapidly throughout the total Al layer, followed by a period of increasing oxygen concentration but constant oxide thickness. Finally, the Co underlayer becomes involved in the oxidation process, which marks the deterioration of the spin-tunnel junction. Evidence is obtained that for the thicker initial Al layers the Co electrode layer starts to oxidize before completion of the Al oxidation. This explains why for 0.8-nm-thick Al films the highest tunnel-magnetoresistance effect is obtained for stoichiometric Al2O3, whereas for 1.5 nm Al this occurs while the oxide is still substoichiometric.