John P. Quintana

Defect structure studies of bulk and nano-indium-tin oxide

The defect structure of bulk and nano-indium-tin oxide was investigated by a combination of experimental techniques, including high-resolution synchrotron x-ray diffraction, extended x-ray absorption fine structure, and time-of-flight neutron diffraction on powder specimens. The structural results include atomic positions, cation distributions, and oxygen interstitial populations for oxidized and reduced materials. These structural parameters were correlated with theoretical calculations and in situ electrical conductivity and thermopower measurements as well as existing defect models, with special reference to the model of Frank and Kostlin [G. Frank and H. Kostlin, Appl. Phys. A 27, 197 (1982)].

Small angle x-ray scattering metrology for sidewall angle and cross section of nanometer scale line gratings

High-volume fabrication of nanostructures requires nondestructive metrologies capable of measuring not only the pattern size but also the pattern shape profile. Measurement tool requirements will become more stringent as the feature size approaches 50nm and tolerances of pattern shape will reach a few nanometers. A small angle x-ray scattering (SAXS) based technique has been demonstrated to have the capability of characterizing the average pitch size and pattern width to subnanometer precision. In this study, we report a simple, modeling-free protocol to extract cross-section information such as the average sidewall angle and the pattern height of line grating patterns from the SAXS data. Diffraction peak intensities and reciprocal space positions are measured while the sample is rotated around the axis perpendicular to the grating direction. Linear extrapolations of peak positions in reciprocal space allow a precise determination of both the sidewall angle and the pattern height.

On the structure of aragonite

High-resolution synchrotron powder diffraction measurements were carried out at the 32-ID beamline of the Advanced Photon Source of Argonne National Laboratory in order to clarify the structure of geological aragonite, a widely abundant polymorph of CaCO(3). The investigated crystals were practically free of impurity atoms, as measured by wavelength-dispersive X-ray spectroscopy in scanning electron microscopy. A superior quality of diffraction data was achieved by using the 11-channel 111 Si multi-analyzer of the diffracted beam. Applying the Rietveld refinement procedure to the high-resolution diffraction spectra, we were able to extract the aragonite lattice parameters with an accuracy of about 20 p.p.m. The data obtained unambiguously confirm that pure aragonite crystals have orthorhombic symmetry.

Non-destructive microstructural analysis with depth resolution: application to seashells

Energy-variable X-ray diffraction at a synchrotron beamline has been used to control the X-ray penetration depth and thus to study structural parameters in polycrystalline and textured materials with depth resolution. This approach was applied to the investigation of the depth evolution of microstructure in the nacre layer of bivalvia seashells. According to conventional X-ray diffraction and scanning electron microscopy, the nacre layer in the seashells of Acanthocardia tuberculata under investigation consists of large [001]-oriented lamellae packed nearly parallel to the inner shell surface. In this paper, attention is focused on the microstructural information that can be extracted from the shapes of diffraction profiles (line profile analysis) measured at X-ray energies that are varied by small steps. Depth dependences of the thickness of the lamellae and the average microstrain fluctuation are revealed.

Fast time-resolved x-ray diffraction in BaTiO3 films subjected to a strong high-frequency electric field

The pulsed synchrotron radiation from the Advanced Photon Source of Argonne National Laboratory was used to measure the dynamic structural response in 200-nm-thick BaTiO3 ferroelectric films, in situ, under the application of a high-frequency electric field. X-ray diffraction measurements were performed in the stroboscopic mode, i.e., by synchronizing the x-ray bursts with the electric-field periodicity. Time-dependent variations of lattice parameters were derived from the electric-field-induced distortions of the diffraction profiles. Drastic reduction of the relaxation time, from 6.9 ns at 71.69 MHz down to 0.7 ns at 521.36 MHz, was found with an increase of the electric-field frequency.

Simple on-line X-ray setup to monitor structural changes during fiber processing

We demonstrate that on-line X-ray characterization during fiber processing can be carried out using a low-power X-ray generator and an image plate detector. Two fiber processes using 66-nylon were chosen as examples : high-temperature drawing at different ratios (3.5-5.0 X) and melt spinning at moderate speeds (450 and 1,200 mpm). For the draw measurement, useful diffraction images were obtained in a reasonable time frame (30 min). These patterns were equal in quality to static in-laboratory images and sufficient for quantitative analysis. Results showed significant differences in structure between on-line and off-package samples. The crystal density was found to be lower but the crystal orientation was found to be higher as draw ratio increases. The on-line spinning image was found to be similar to those obtained by synchrotron X-ray measurements, which confirm the development of two-dimensional crystals having a hydrogen bonding characteristic distance during spinning. Finally, several ways to improve the demonstrated on-line setup design will be discussed.

A miniature X-ray emission spectrometer (miniXES) for high-pressure studies in a diamond anvil cell.

Core-shell X-ray emission spectroscopy (XES) is a valuable complement to X-ray absorption spectroscopy (XAS) techniques. However, XES in the hard X-ray regime is much less frequently employed than XAS, often as a consequence of the relative scarcity of XES instrumentation having energy resolutions comparable with the relevant core-hole lifetimes. To address this, a family of inexpensive and easily operated short-working-distance X-ray emission spectrometers has been developed. The use of computer-aided design and rapid prototype machining of plastics allows customization for various emission lines having energies from ∼3 keV to ∼10 keV. The specific instrument described here, based on a coarsely diced approximant of the Johansson optic, is intended to study volume collapse in Pr metal and compounds by observing the pressure dependence of the Pr Lα emission spectrum. The collection solid angle is ∼50 msr, roughly equivalent to that of six traditional spherically bent crystal analyzers. The miniature X-ray emission spectrometer (miniXES) methodology will help encourage the adoption and broad application of high-resolution XES capabilities at hard X-ray synchrotron facilities.

Non-destructive microstructural analysis with depth resolution

A depth-sensitive X-ray diffraction technique has been developed with the aim of studying microstructural modifications in inhomogeneous polycrystalline materials. In that method, diffraction profiles are measured at different X-ray energies varied by small steps. X-rays at higher energies probe deeper layers of material. Depth-resolved structural information is retrieved by comparing energy-dependent diffraction profiles. The method provides non-destructive depth profiling of the preferred orientation, grain size, microstrain fluctuations and residual strains. This technique is applied to the characterization of seashells. Similarly, energy-variable X-ray diffraction can be used for the non-destructive characterization of different laminated structures and composite materials.

Pattern fidelity in nanoimprinted films using critical dimension small angle x-ray scattering

The primary measure of process quality in nanoimprint lithography (NIL) is the fidelity of pattern transfer, comparing the dimensions of the imprinted pattern to those of the mold. Routine production of nanoscale patterns will require new metrologies capable of nondestructive dimensional measurements of both the mold and the pattern with subnanometer precision. In this work, a rapid, nondestructive technique termed critical dimension small angle x-ray scattering (CD-SAXS) is used to measure the cross sectional shape of both a pattern master, or mold, and the resulting imprinted films. CD-SAXS data are used to extract periodicity as well as pattern height, width, and sidewall angles. Films of varying materials are molded by thermal embossed NIL at temperatures both near and far from the bulk glass transition (TG). The polymer systems include a photoresist and two homopolymers. Our results indicate that molding at low temperatures (T-TG 30°C.

Depth‐resolved strain measurements in polycrystalline materials by energy‐variable X‐ray diffraction

An energy-variable synchrotron diffraction technique is being established as a novel method for the depth-resolved measurement of residual strains in polycrystalline structures. An analytic expression for the diffraction profile is obtained by taking into account the instrument misalignment, change of the height of an incident X-ray beam with energy, and penetration of X-rays into the sample depth. It is shown that the maximum diffraction intensity recorded in the detector is coming from a certain depth beneath the surface of the sample, the depth being energy-dependent. This finding opens a way for precise strain measurements with high depth resolution by changing the X-ray energy in small enough steps. An experimental example, residual strain measurements across an alumina/zirconia multilayer, demonstrates the capability of the method.