A review. Ultrafast x-ray techniques using diffraction and absorption are discussed with an emphasis on the absorption techniques. Ultrafast x-ray sources and detectors for use in x-ray absorption spectroscopy are also reviewed. [on SciFinder (R)]

Ultrafast X-ray absorption spectroscopy

The study focused on the in-situ synthesis of titanium (Ti)-titanium boride (TiB) composites with β phase in the matrix by reaction sintering of TiB2 with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds of powder mixtures: (1) β-Ti alloy powders and TiB2; (2) α-Ti powder, a master alloy (Fe-Mo) powder containing the β-stabilizing elements, and TiB2; and (3) α-Ti powder, a β-stabilizing elemental powder (Mo or Nb), and TiB2. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at processing temperatures ranging from 1100°C to 1300°C. The morphology, size, and distribution of whiskers were found to be influenced by the powder-packing conditions. A large particle-size ratio in bimodally packed mixtures led to the formation of a TiB monolithic layer around β grains. With a relatively finer starting powder, smaller size ratio, and trimodal packing arrangement, the TiB whiskers were found to be distributed more homogeneously in the matrix. The study also used the X-ray direct comparison method and the structure factor for the β phase to determine the volume fraction of TiB phase from X-ray data. Tensile tests and fractographic investigations were carried out on selected composites. The evolution of the composite microstructure, the influence of powder-packing variables, and the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.

Synthesis of ductile titanium-titanium boride (Ti-TiB) composites with a beta-titanium matrix: The nature of TiB formation and composite properties

A kinetic analysis of residual stress evolution in polycrystalline thin films

http://www.rosakis.caltech.edu/downloads/pubs/1998/81%20Full%20Field%20measurements%20of%20curvature%20-Thin%20Solid%20Films.pdf

Full field measurements of curvature using coherent gradient sensing: application to thin film characterization

Aerosol deposition method (ADM) for shock-consolidation of fine ceramics powder to form dense and hard layers is reported. Submicron ceramic particles were accelerated by gas flow in the nozzle up to velocity of several hundred m/s. During interaction with substrate, these particles formed thick (10 ~ 100 µm), dense, uniform and hard ceramics layers. Depositions were fulfilled at room temperature. Every layer has polycrystalline structure with nano-meter order scale.􀀂 The results of fabrications, microstructure, mechanical and electrical properties of oxides (α-Al2O3; Pb(Zr0.52,Ti0.48)O3 etc.) and non-oxides materials are presented.

Aerosol Deposition Method for Fabrication of Nano Crystal Ceramic Layer

A dynamical model for the general case of Bragg x-ray diffraction from arbitrarily thick nonuniform crystalline films is presented. The model incorporates depth-dependent strain and a spherically symmetric Gaussian distribution of randomly displaced atoms and can be applied to the rocking curve analysis of ion-damaged single crystals and strained layer superlattices. The analysis of x-ray rocking curves using this model provides detailed strain and damage depth distributions for ion-implanted or MeV-ion-bombarded crystals and layer thickness, and lattice strain distributions for epitaxial layers and superlattices. The computation time using the dynamical model is comparable to that using a kinematical model. We also present detailed strain and damage depth distributions in MeV-ion-bombarded GaAs(100) crystals. The perpendicular strain at the sample surface, measured as a function of ion-beam dose (D), nuclear stopping power (Sn), and electronic stopping power (Se) is shown to vary according to (1–kSe)DSn and saturate at high doses.

/pdf/dynamical-x-ray-diffraction-from-nonuniform-crystalline-4vptj2kjms.pdf

Dynamical x‐ray diffraction from nonuniform crystalline films: Application to x‐ray rocking curve analysis

We have reported previously that the perpendicular strain produced in the surface layer (several μm thick) of GaAs(100) crystals under MeV ion irradiation saturates at ∼04% regardless of the doping of the specimen, and that the parallel strain is zero within the experimental error In this paper, the perpendicular strain in GaAs(111) and GaAs(110) crystals is reported to saturate at ∼03% The ionization-induced spontaneous defect recovery is discussed in terms of the activation-energy lowering of the higher-charge-state interstitials We suggest that inner-shell vacancies which decay by an Auger process may induce most effective self-annealing of defects created by nuclear collisions We present an ion-lattice single-collision model which describes the production and saturation of the primary defects (interstitial, vacancy, and antisite defect) in GaAs under MeV ion or MeV electron irradiation The model also shows that at low beam dose the concentration of interstitials and vacancies increases linearly with the product of stopping power and beam dose and is independent of the electronic stopping power The antisite defect concentration increases initially as the square of the nuclear stopping power times the beam dose, and depends upon the electronic stopping power The strain measured as a function of beam dose and stopping powers suggests that the strain in the room-temperature irradiated GaAs is controlled by the antisite defects

/pdf/mev-ion-damage-in-gaas-single-crystals-strain-saturation-and-4nbxqxm8b9.pdf

MeV ION DAMAGE IN GaAs SINGLE CRYSTALS: STRAIN SATURATION AND ROLE OF NUCLEAR AND ELECTRONIC COLLISIONS IN DEFECT PRODUCTION*

This paper presents the methodology employed in the determination of the stress tensor for thin crystalline films using x-ray rocking curves. Use of the same equipment for the determination of the average stress in poly- or non-crystalline thin films attached to a crystalline substrate is also discussed. In this case the lattice curvature of the substrate is determined by measurement of the shift In the Bragg peak with lateral position in the substrate.
Strains in single crystal layers may be measured using Bragg diffraction from the layers and from the substrate or a reference crystal, with the highest strain sensitivity of any known technique. The difference in Bragg angles for a strained and an unstrained crystal is related to the change in d spacing of the Bragg planes, and the elastic strain is related to this angular difference. The separation of two peaks on an x-ray rocking curve is generally not equal to the difference in Bragg angles of two diffracting crystals, so diffractometer measurements must be carefully Interpreted in order to obtain x-ray strains in crystalline films (x-ray strains are strains relative to the reference crystal). The unstrained d spacings of the film and the d spacings of the reference crystal must be known to obtain the elastic strains in the film, from which the stress tensor is determined.

/pdf/x-ray-diffraction-determination-of-stresses-in-thin-films-3igw00kqmp.pdf

X-Ray Diffraction Determination of Stresses in Thin Films

We have observed large changes in Ge and SixGe1−x layer strain during concurrent molecular beam epitaxial growth and low‐energy bombardment. Layers are uniformly strained, coherent with the substrate, and contain no dislocations, suggesting that misfit strain is accommodated by free volume changes associated with injection of ion bombardment induced point defects. The dependence of layer strain on ion energy, ion‐atom flux ratio, and temperature is consistent with the presence of a uniform dispersion of point defects at high concentration. Implications for distinguishing ion‐surface interactions from ion‐bulk interactions are discussed.

/pdf/strain-modification-in-coherent-ge-and-sixge1-x-epitaxial-njpih0eq1w.pdf

Strain modification in coherent Ge and SixGe1–x epitaxial films by ion-assisted molecular beam epitaxy

Results of a determination of strain perpendicular to the surface and of the damage in (100) Si single crystals irradiated by 250-keV Ar+ ions at 77 K are presented. Double-crystal x-ray diffraction and dynamical x-ray diffraction theory are used. Trial strain and damage distributions were guided by transmission electron microscope observations and Monte Carlo simulation of ion energy deposition. The perpendicular strain and damage profiles, determined after sequentially removing thin layers of Ar+-implanted Si, were shown to be self-consistent, proving the uniqueness of the deconvolution. Agreement between calculated and experimental rocking curves is obtained with strain and damage distributions which closely follow the shape of the trim simulations from the maximum damage to the end of the ion range but fall off more rapidly than the simulation curve near the surface. Comparison of the trim simulation and the strain profile of Ar+-implanted Si reveals the importance of annealing during and after implantation and the role of complex defects in the final residual strain distribution.

https://authors.library.caltech.edu/11745/1/TSAjap91.pdf

T. Vreeland

Papers

Dynamical x‐ray diffraction from nonuniform crystalline films: Application to x‐ray rocking curve analysis

MeV ION DAMAGE IN GaAs SINGLE CRYSTALS: STRAIN SATURATION AND ROLE OF NUCLEAR AND ELECTRONIC COLLISIONS IN DEFECT PRODUCTION*

X-Ray Diffraction Determination of Stresses in Thin Films

Strain modification in coherent Ge and SixGe1–x epitaxial films by ion-assisted molecular beam epitaxy

Self‐consistent determination of the perpendicular strain profile of implanted Si by analysis of x‐ray rocking curves