Bragg Peak Position Research Articles

Surface Roughness Effect on Pseudo-GIXRD Stress Analysis

Residual stresses levels and their distributions in thin films have an important effect on their mechanical properties. The non-destructive analysis by pseudo-grazing incidence X-ray diffraction (GIXRD) allows us to define residual stresses gradients as a function of thin film depth. In case of pseudo-GXRD, we must take into account the effects due to surface roughness on residual stress analysis. We have investigated firstly a set of carbon steel specimens with different surface roughness (RZ varies from 4.2µm to 9.5µm) obtained by grinding. All specimens were tempered to eliminate the residual stresses due to machining. With K radiation of Chromium, Bragg peak positions were determined with various incidence angles  (varies from 1° to 78°) for each specimen. Secondly, a carbon steel specimen containing 4 zones with different surface roughness was loaded elastically in tension, pseudo-GIXRD has used for stress analysis on the loaded specimen with various incidence angles. The peak shifts due to the surface roughness were studied as function of different roughness and different incidence angles. The stress relaxation due to surface roughness was then studied.

Optical Control of Coherent Lattice Motions Probed by Femtosecond Electron Diffraction

We report the study of laser-induced coherent lattice motions using femtosecond electron diffraction. The oscillations of Bragg peak positions associated with a damped lattice vibration along the surface normal were directly observed in real time and with sub-milli-angstrom spatial resolution. In addition, by using a pair of optical excitation pulses and varying their time delay and relative pulse intensities, we demonstrated the successful control of coherent lattice motions.

Structural and thermal investigation of gadolinium gallium mixed oxides obtained by coprecipitation: Observation of a new metastable phase

Polycrystalline gadolinium gallium mixed oxides were prepared by coprecipitation and annealing at various temperatures below 1000 °C. The oxide materials appear to be X-ray amorphous after a heat treatment at 500 °C for 30 h, but after 30 h at 800 and 900 °C a major, unreported, hexagonal phase, isostructural with TAlO 3 compounds (where T=Y, Eu, Gd, Tb, Dy, Ho, Er) appears to crystallize. On the other hand, a highly energetic mechanical treatment of the amorphous powder previously annealed at 500 °C changes considerably the shape and position of exothermal events occurring in the range from 700 up to 900 °C. Subsequent annealing at 900 °C of the mechanically treated powder gives rise to the complete formation of the Gd 3Ga 5O 12 garnet structure at the expense of the hexagonal phase and of the minor Gd 4Ga 2O 9 oxide phase. However, a 7.0 wt% contamination is found to be due to tetragonal zirconia coming from vials and balls colliding media. The garnet phase may have strong deviations from the nominal stoichiometry of the garnet, as suggested by the refined lattice parameter obtained from the powder diffraction patterns and by the remarkable absence of intensity relative to the (220) Bragg peak position.

Density resolution of proton computed tomography

Conformal proton radiation therapy requires accurate prediction of the Bragg peak position. Protons may be more suitable than conventional x-rays for this task since the relative electron density distribution can be measured directly with proton computed tomography (CT). However, proton CT has its own limitations, which need to be carefully studied before this technique can be introduced into routine clinical practice. In this work, we have used analytical relationships as well as the Monte Carlo simulation tool GEANT4 to study the principal resolution limits of proton CT. The noise level observed in proton CT images of a cylindrical water phantom with embedded tissue-equivalent density inhomogeneities, which were generated based on GEANT4 simulations, compared well with predictions based on Tschalar's theory of energy loss straggling. The relationship between phantom thickness, initial energy, and the relative electron density resolution was systematically investigated to estimate the proton dose needed to obtain a given density resolution. We show that a reasonable density resolution can be achieved with a relatively small dose, which is comparable to or even lower than that of x-ray CT.

Stress Characterization of Post-CMP Copper Films Planarized Using Novel Low-Shear and Surface-Engineered Pads

AbstractA family of novel low-shear and surface-engineered pads for copper chemical mechanical planarization (CMP) are designed and evaluated for polishing characteristics and process induced stress. Tribological studies are carried out on blanket copper films using these low-shear/surface-engineered pads and comparison is made with state of the art commercial pads (IC1000 and JSR). Results indicate that low-shear surface-engineered pads exhibit vastly improved tribological performance. These pads exhibit a 40% lower coefficient of friction (COF) over a larger range of Sommerfeld numbers (So) compared to commercial pads. A simplified XRD line profiling technique has been utilized to characterize stress within post-CMP copper films. The (222) Bragg peak position obtained from the XRD spectra of films polished using low-shear surface-engineered pads indicates virtually no shift compared to the peak position for the unpolished copper films. This result establishes that almost no stress is incorporated during bulk Copper removal using the newly designed pads.

744 poster Accuracy of the Bragg peak position in light ion therapy — Monte Carlo simulations using shield-hit

744 poster Accuracy of the Bragg peak position in light ion therapy — Monte Carlo simulations using shield-hit

Anomalous displacement of magnetic Bragg peaks in the presence of short rangeorder

An asymmetric shift in the position of the magnetic Bragg peak with respect to thefiducial lattice has been observed by resonant x-ray scattering in a diverse series ofantiferromagnetic compounds. A possible explanation is given in terms of a generalizedBerry phase correction.

Domain growth kinetics in the isosceles triangular Ising antiferromagnetCoNb2O6

We have studied the domain-growth kinetics of fourfold-degenerate antiferromagnetic (AF) and threefold-degenerate ferrimagnetic states in the isosceles triangular Ising antiferromagnet ${\mathrm{CoNb}}_{2}{\mathrm{O}}_{6}$ by ac susceptibility measurements and Monte Carlo simulations. In both magnetic phases ac susceptibility after the field quench is found to decrease with time according to the power-growth law with an universal growth exponent $n=0.21\ifmmode\pm\else\textpm\fi{}0.01.$ The prefactor in the power-growth law suggests that the zero-field growth of the AF state is strongly suppressed by the application of magnetic fields along the direction perpendicular to the frustrated isosceles-triangular lattice. Monte Carlo results show the unusual domain growth dominated by the reversal of the free magnetic spins near favorable domain walls where the exchange field is effectively canceled out due to the isosceles triangular geometry of spins. The obtained domain configuration strongly supports our neutron-diffraction results that revealed the temporal shift of the magnetic Bragg peak position during the growth.

The plumber's nightmare: a new morphology in block copolymer-ceramic nanocomposites and mesoporous aluminosilicates.

A novel cubic bicontinuous morphology is found in polymer-ceramic nanocomposites and mesoporous aluminosilicates that are derived by an amphiphilic diblock copolymer, poly(isoprene-b-ethylene oxide) (PI-b-PEO), used as a structure-directing agent for an inorganic aluminosilicate. Small-angle X-ray scattering (SAXS) was employed to unambiguously identify the Im(-)3m crystallographic symmetry of the materials by fitting individual Bragg peak positions in the two-dimensional X-ray images. Structure factor calculations, in conjunction with results from transmission electron microscopy, were used to narrow the range of possible structures consistent with the symmetry and showed the plumber's nightmare morphology to be consistent with the data. The samples are made by deposition onto a substrate that imposes a strain field, generating a lattice distortion. This distortion is quantitatively analyzed and shown to have resulted in shrinkage of the crystallites by approximately one-third in a direction perpendicular to the substrate, in both as-made composites and calcined ceramic materials. Finally, the observation of the bicontinuous block-copolymer-derived hybrid morphology is discussed in the context of a pseudo-ternary morphology diagram and compared to existing studies of ternary phase diagrams of amphiphiles in a mixture of two solvents. The calcined mesoporous materials have potential applications in the fields of catalysis, separation technology, and microelectronics.

Magnetic neutron scattering measurements on a single crystal of frustratedZnFe2O4

Single crystals of ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ are investigated with neutron scattering measurements from the viewpoint of geometrical frustration. Magnetic diffuse scattering was distributed along the first Brillouin zone boundary of the fcc structure. The results show that the frustration occurs between the antiferromagnetically coupled third-neighbor spins, rather than between the similarly coupled first-neighbor spins. In addition, another type of diffuse scattering was found around some nuclear Bragg peak positions. This indicates that the first-neighbor exchange interaction in the 90\ifmmode^\circ\else\textdegree\fi{} configuration is ferromagnetic rather than antiferromagnetic. Energy spectra were investigated at several points. The unusual magnetic behavior originates from the geometrical frustration and a unique property of the first-neighbor interaction.

Soft x-ray longitudinal magneto-optical Kerr effect measured from Co/Cu multilayers at the Co L2,3 edges

We report on x-ray magneto-optical reflectivity investigations of Co/Cu multilayers with circularly polarized synchrotron light. The individual layer thicknesses of the samples were tuned to the second maximum of the giant magnetoresistance. An external magnetic field was applied parallel to the sample surface and the scattering plane utilizing the longitudinal magneto-optical Kerr effect. The reflectometry curves measured at the Co L3 absorption edge clearly show antiferromagnetic (AFM) coupling of the Co layers by half-integer-order Bragg peaks of magnetic origin, which disappear for nonresonant excitation. Whereas the first-order magnetic peak overlaps with strong charge scattering contributions, the higher-order magnetic peaks are more pronounced and sensitive to magnetic effects. In an applied field, the magnetic peaks are suppressed due to a reduction of the AFM layer coupling, and an additional intensity modulation occurs due to asymmetry effects. Measurements of the photon energy dependence of the Bragg peak positions were employed close to the Co L2,3 edges to determine the dispersive part of the magneto-optical constants of the Co/Cu multilayer.

Stresses on two sets of Cu precipitates in Fe 95 Cu 5 alloy

The Cu (111) Bragg peak position and its broadening after different heat treatments have been investigated by neutron diffraction in the Fe95Cu5 alloy. Depending on the treatment, the Cu (111) peak shifts and broadens, showing quite big elastic stresses and indicating plastic deformations, respectively. In some cases the broadening even turns to splitting. It is shown that the separated peaks are connected to different sets of Cu precipitates. Stress calculations are carried out for both cases.

Polarised neutron reflectometry study of Co/CoO exchange-biased multilayers

We have investigated via SQUID magnetometry and polarised neutron reflectivity the exchange-bias effect in CoO/Co sputtered multilayers. In particular, we studied the magnetisation reversal and the time relaxation of the exchange-bias field close to the coercive field Hc1. Neutron intensities of all four cross sections (I++, I+-, I-+, I–) were recorded at the position of the first multilayer Bragg peak while scanning the magnetic field. From such scans we infer that the magnetisation reversal for the ascending as well as for the descending branch of the magnetic hysteresis occurs not by in-plane rotation but through domain-wall movements. The exchange-bias field, HEB, is strongly affected by thermal fluctuations. HEB decreases, following an exponential decay function with a half-life time of about 580 s at T=240 K.

Undulation Properties of the Lamellar Phase of a Diblock Copolymer: SAXS Experiments

We report on X-ray scattering results on an oriented lamellar single crystal of a diblock copolymer melt of poly(dimethylsiloxane)-b-poly(ethylene propylene). From the Bragg peak position, q0, we calculate the temperature dependence of the lamellar period and show that it is in agreement with the values obtained using literature values of the Flory−Huggins parameter, χ. We observe the predicted diffuse scattering affecting the profile of the Bragg peak, which is related to the layer splay and compressional elasticity. We show that extremely small misalignments of the lamellar planes prevent a quantitative calculation of the layer compressibility modulus, B̄, and we explain this effect qualitatively using the mosaicity theory.

The Influence of Surface Roughness on the Refraction Correction of Bragg Peak Positions

The influence of surface roughness on the refraction effect for X-rays at gracing incidence was investigated using a set of brass samples with different surface roughnesses. For each sample Bragg peak positions were measured varying the incidence angle. The refraction effect at the sample surface was calculated and compared with theoretical values derived from Snell's law of refraction. Peak shift due to residual stress was also taken into account.

Effect of the chemical state of the surface on the relaxation of the surface shell atoms in SiC and GaN nanocrystals

The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-surface layer was examined using the concept of the apparent lattice parameter (alp) determined for different diffraction vectors Q. The apparent lattice parameter is a lattice parameter determined either from an individual Bragg reflection, or from a selected region of the diffraction pattern. At low diffraction vectors the Bragg peak positions are affected mainly by the structure of the near-surface layer, while at high Q-values only the interior of the nano-grain contributes to the diffraction pattern. Following the measurements on raw (as prepared) powders we investigated powders cleaned by annealing at 400C under vacuum, and the same powders wetted with water. Theoretical alp-Q plots showed that the structure of the surface layer depends on the sample treatment. Semi-quantitative analysis based on the comparison of the experimental and theoretical alp-Q plots was performed. Theoretical alp-Q relations were obtained from the diffraction patterns calculated for models of nanocrystals with a strained surface layer using the Debye functions.

The successive phase transformation in a Co-rich Al–Ni–Co decagonal phase

Peak broadening and the peak positions of Bragg reflections were studied with the high-resolution X-ray diffraction method for decagonal Al 72.7Ni 8.5Co 18.8 quasicrystals. From the Q ⊥ dependences of the full-width at half-maximum (FWHM) of the Bragg reflections and the peak shifts from ideal Bragg peak positions along the longitudinal direction, these decagonal quasicrystals were classified into three groups with different phason strains. These three groups were identified as the random phason strain, the one-dimensional linear phason strain and the two-dimensional linear phason strain, respectively. This means that the Al 72.7Ni 8.5Co 18.8 decagonal phase undergoes a successive phase transformation from a decagonal quasicrystal through a one-dimensional quasicrystal to an approximant crystal.

Optimisation of Data Collection and Processing for Efficient Strain Scanning

A constraint to the academic and industrial exploitation of neutron strain scanning is its cost in relation to that of alternative techniques. Generally, a large proportion of the resource cost is that for beam-time. The efficient utilisation of beam-time can be enhanced by optimising data collection and processing. The selection of three principal related factors -- detector range, angular step size and the counting time -- determines the data quality and uncertainties in defining the Bragg peak parameters required to determine strain. Theoretical and numerical analysis of computed and experimental data are used to establish a general set of well-founded, semi-empirical but theoretically-based, practical of thumb to be used when making strain measurements to a specified statistical uncertainty. The rules apply mostly to constant wavelength techniques where the angular position and other profile parameters of a single symmetrical Bragg peak are required but have relevance for fixed angle time-of-flight methods.

Polygonization of single-wall carbon nanotube bundles under high pressure

The pressure-induced structural changes of single-wall carbon nanotubes organized into two-dimensional crystalline bundles are studied by neutron diffraction up to $\ensuremath{\sim}50 \mathrm{kbar}.$ The strong variation of the (10) Bragg peak position with pressure is interpreted as a progressive deformation of the tube section from circular to hexagonal, in addition to the van der Waals compression. Data at 50 kbar suggest that the tubes are closed to be fully polygonized at this pressure. The anisotropic behavior of the patterns with pressure is assigned to the presence of a uniaxial pressure component and to preferential orientations of the bundles.

Relationship between Phason Strain and Approximant Crystal Structure in Co-Rich Al-Ni-Co Decagonal Phase

Peak broadening and the peak positions of the Bragg reflections were studied with the high-resolution X-ray diffraction method for the decagonal Al72.7Ni8.5Co18.8 quasicrystal. The full-widths at half-maximum (FWHM) of the Bragg reflections along the longitudinal direction (L), which is perpendicular to the periodic axis, have no Q|| or Q⊥ dependences. On the other hand, notable peak shifts from ideal Bragg peak positions with linear Q⊥ dependence were observed. This means that the Al72.7Ni8.5Co18.8 decagonal phase has linear phason strains. According to the absolute values of the linear phason strains, the transformation from the decagonal phase to an approximant crystal is discussed.