Craig L. Barnes

Preparation of silver behenate coatings to provide low- to mid-angle diffraction calibration

A method for the preparation of a well aligned silver behenate sample is described. Multiple (0 0 l) diffraction peaks, (0 0 1) to (0 0 48), are easily observed using a conventional laboratory X-ray diffraction instrument.

The effect of X-ray penetration depth on structural characterization of multiphase Bi-Sr-Ca-Cu-O thin films by X-ray diffraction techniques

Abstract X-ray diffraction has been used extensively to assess the crystalline phase composition of superconducting ceramics. In instances where randomly oriented powders are available, X-ray diffraction provides a means of identifying not only the phases present but also the volume fraction of each phase. In instances where ultrathin films ( 0.2 μm) the ability to measure phase composition by X-ray diffraction is hampered by the fact that due to the limited effective X-ray penetration depth the X-ray beam may not sample all depths of the film equally. This phenomenon could result in a lessening of the contribution to the final diffraction pattern by phases concentrated near the substrate-film interface. This paper describes the characterization of Bi-Sr-Ca-Cu-O superconducting films by X-ray diffraction. Reactive beam ion etching experiments made it possible to observe the change in the relative volume fraction of three superconducting phases as a function of etch depth.

Influence of processing conditions on hillock formation in electron-beam evaporated platinum/titanium films

Abstract Hillock formation during annealing of Pt/Ti electrodes has been an obstacle in the development of ferroelectric memories. In order to minimize hillock formation, a factorial experiment was carried out to investigate the effects of deposition temperature, and oxide, titanium, and platinum thicknesses. The appropriate metal thicknesses for minimizing hillock formation was found to depend on deposition temperature. The developed model predicted best results for a deposition temperature of 200–250°C, Pt thickness of 2000–2500 A, and Ti thickness of ≤500A. Without substrate heating, both thin Ti (≤500A) and Pt (≤1000A) were required for reduced hillock formation. Pt strain levels and crystallite size distributions were also determined for the films. Strain level correlated with the occurrence of hillocks. In addition, a broad crystallite size distribution appeared to give smoother films.

The use of X-ray diffraction rocking curve methodology for assessment of the c-axis orientation in BiSrCaCuO superconducting thin films

Abstract An X-ray diffraction theta scan rocking curve analysis method has been developed which allows one to assess the relative degree of c -axis preferred orientation of BiSrCaCuO superconducting ceramic thin films deposited on (100) MgO and Ag foil substrates. The full width at half maximum (FWHM) of the rocking curve peak is taken as a relative measure of c -axis orientation. Precision measurements of the data collection parameters, sample holder mounting, and instrument loading of the sample were performed. Defocusing of the X-ray beam was characterized using random α-Al 2 O 3 powder and a (100) Si wafer. Rocking curves of the BiSrCaCuO 37 A-110 K superconducting phase (00 14 ) peak for a random powder, thin film on Ag substrate, and thin film on (100) MgO were obtained with FWHM values of > 20° ∼ 5° and ∼0.3°θ, respectively.

D-75 Quantitative Analysis of Calcium Oxide Desiccant Conversion to Calcium Hydroxide Using X-ray Diffraction

Calcium oxide (calcia, CaO) can be used as a desiccant in electronic displays. When exposed to water, CaO converts to Ca(OH)2. X-ray diffraction techniques have been developed to study the conversion process and quantify the amount of CaO/Ca(OH)2 in powder and dispersed samples using the reference intensity ratio (RIR) method. To incorporate CaO in an electronic device the powder is dispersed in a polymeric binder. X-ray diffraction was also used to conduct in situ humidity studies to evaluate the water uptake of calcia dispersed in different polymeric binders. The time required to convert 50 percent of the CaO to Ca(OH)2 was selected as the criteria for rating the best polymers to be used in this application. INTRODUCTION The interest in organic materials for use in organic light-emitting diodes (OLEDs) began with the pioneering report of efficient green electroluminescence from Alq3, tris(8hydroxyquinoline)aluminum, by Tang and Van Slyke [1]. A typical OLED device is comprised of a cathode and anode along with four organic layers (Figure 1). These organic layers allow for electroluminescence when voltage is passed through the device. The resulting visible light emission can be tailored by using dopants in the emissive layer, creating a display that is brighter, uses less energy, and has a wider viewing angle than current liquid crystal displays. Figure 1. Schematic of an organic light-emitting diode Some of the organic components in an OLED device will degrade when exposed to water. To protect the OLED layers, displays are encapsulated with a glass front and a glass or metal back, joined together with an appropriate sealant. Over time , however, water vapor in air will permeate the encapsulation components resulting in a degradation of device performance. One method of extending the life of an OLED display is to place a desiccant inside the display, so Copyright ©JCPDS International Centre for Diffraction Data 2005, Advances in X-ray Analysis, Volume 48. 45

MATERIALS CHARACTERIZATION USING A NOVEL SIMULTANEOUS NEAR-INFRARED/X-RAY DIFFRACTION INSTRUMENT

X-ray powder diffraction (XRD) is utilized for the determination of polymorphism in crystalline organic materials. Though convenient to use in a laboratory setting, XRD is not easily adapted to in situ monitoring of synthetic chemical production applications or thin film depositions. Near-infrared spectroscopy (NIR) can be adapted to in situ manufacturing schemes by use of a source/detector probe. Conversely, NIR is unable to conclusively define the existence of polymorphism in crystalline materials. By combining the two techniques, a novel simultaneous NIR/XRD instrument has been developed. During material’s analysis, results from XRD allowed for the determination of the existence of polymorphic phases, and NIR data were collected as a fingerprint for each of the observed polymorphs. These NIR fingerprints allowed for the development of a library, which can be referenced during the use of a NIR probe in manufacturing settings. The NIR/XRD instrument was also used to monitor materials during exposure to ambient air. XRD can detect crystalline phase changes and NIR can monitor solvent loss and/or water uptake.

Semiquantitative assessment of 2223/2212 phase homogeneity in Bi(Pb)SrCaCuO superconducting thin films using XRD techniques

Abstract Phase segregation in multiphasic Bi(Pb)SrCaCuO (BSCCO) films deposited on a silver foil substrate by m metallo-organic decomposition (MOD) has been observed using X-ray diffraction (XRD) techniques. The concept of a phase inhomogeneity factor (PIHF), developed in this work, has been applied to a semiquantitative assessment of the distribution of the 2223 and 2212 phases in the bulk versus film-substrate interface region. On the basis of the XRD-PIHF analyses, we conclude that the silver substrate tends to promote the 2212 to 2223 phase transformation with 2223-rich compositions being formed at the film-substrate interface. This phase transformation was shown to occur at lower temperatures for thinner films. These films contain higher volume-fractions of the 2223 phase and exhibit a higher degree of phase homogeneity. Moreover, the film-substrate interactions seem to induce the lowering of the melting point of the system in the interfacial region and lead to an increase in the degree of c -axis orientation by promoting partial melt textured grain growth.

X-RAY DIFFRACTION CHARACTERIZATION OF MOVPE ZnSe FILMS DEPOSITED ON (100) GaAs USING CONVENTIONAL AND HIGH- RESOLUTION DIFFRACTOMETERS

ZnSe-based heterostructures grown on GaAs substrates have been investigated for use in pindiode LED applications. ZnSe has a large band gap, 2.76 eV, as well as a near lattice match to GaAs, 5.6688 A vs. 5.6538 A, respectively. In this study a metallorganic vapor phase epitaxy (MOVPE) deposition technique is used to produce doped and undoped thin films of ZnSe on (100) GaAs. Understanding the effect of deposition parameters on the crystallographic quality of the ZnSe films is important for optimizing the performance of these devices. X-ray diffraction is well suited for analyzing epitaxial thin films deposited on single-crystal substrates. In this study, a conventional Bragg-Brentano diffractometer (BBD) has been used to screen samples for phase identification, crystallite size, presence of polycrystalline ZnSe, and initial rocking curve (RC) analysis. A limitation of the conventional diffractometer is that the smallest RC full width at half maximum (FWHM) that can be achieved is 500–600 arc seconds. As deposition parameters are optimized and the RC limit of the conventional diffractometer is reached, analysis is moved to a 4-bounce high-resolution diffractometer (HRD). Although more time for analysis is required, using the HRD has a RC resolution advantage, where RCs of <20 arc seconds are obtained for neat GaAs wafers. Combining the BBD and HRD instruments for analysis of ZnSe films grown on GaAs substrates allows for an efficient means of high sample throughput combined with an accurate measurement of film alignment.

Effects of cold rolling and thermal annealing on superconducting properties of 2212 Bi-Sr-Ca-Cu-O/Ag tapes

Abstract High-temperature superconducting (HTS) tapes were fabricated by doctor-blade coating of a BSCCO 2212 dispersion in Butvar-B76 binder, and thermal processing in a three-zone belt furnace. The crystalline properties of these HTS layers were studied by X-ray diffraction techniques. The superconducting properties of HTS tape conductors were examined using AC susceptometry. The effects of sintering, cold rolling, and thermal annealing were monitored by following the temperature dependence of the AC susceptibility and process-induced changes in the crystalline microstructure. A significant degradation of the superconducting properties due to cold rolling has been observed. This degradation is attributed to inferior intergranular coupling and appears to be reversible. Thermal annealing of the cold-rolled samples leads to the full recovery of the AC susceptibility versus temperature response.