Showing papers on "Texture (crystalline) published in 1999"

Mechanisms for microstructure evolution in electroplated copper thin films near room temperature

Abstract: We present a model which accounts for the dramatic evolution in the microstructure of electroplated copper thin films near room temperature. Microstructure evolution occurs during a transient period of hours following deposition, and includes an increase in grain size, changes in preferred crystallographic texture, and decreases in resistivity, hardness, and compressive stress. The model is based on grain boundary energy in the fine-grained as-deposited films providing the underlying energy density which drives abnormal grain growth. As the grain size increases from the as-deposited value of 0.05–0.1 μm up to several microns, the model predicts a decreasing grain boundary contribution to electron scattering which allows the resistivity to decrease by tens of a percent to near-bulk values, as is observed. Concurrently, as the volume of the dilute grain boundary regions decreases, the stress is shown to change in the tensile direction by tens of a mega pascal, consistent with the measured values. The small ...

Automated indexing for texture and strain measurement with broad-bandpass x-ray microbeams

Abstract: Methods are derived for measuring local strain, stress, and crystallographic texture (orientation) in polycrystalline samples when 1–10 grains are simultaneously illuminated by an energy scanable or broad-bandpass x-ray beam. The orientation and unit-cell shape for each illuminated grain can be determined from the diffracted directions of four Bragg reflections. The unit-cell volume is determined by measuring the energy (wavelength) of one reflection. The methods derived include an algorithm for simultaneously indexing the reflections from overlapping crystal Laue patterns and for determining the average strain and stress tensor of each grain. This approach allows measurements of the local strain and stress tensors which are impractical with traditional techniques.

Structure and magnetization of arrays of electrodeposited Co wires in anodic alumina

Abstract: We have produced arrays of Co nanowires in anodic porous alumina filters by means of electrodeposition. The structure and magnetization behavior of the wires was investigated with nuclear magnetic resonance (NMR) and magnetization measurements. NMR shows that the wires consist of a mixture of fcc and hcp texture with the (0001) texture of the hcp fraction oriented preferentially perpendicular to the wires. The magnetization direction is determined by a competition of demagnetizing fields and dipole–dipole fields and can be tuned parallel or perpendicular to the wires by changing the length of the wires.

Single crystal superconductor nanowires by electrodeposition

Abstract: Superconducting Pb wires (diameter∼50 nm) have been prepared by pulse electrodeposition in nanoporous membranes. Single crystal or polycrystalline nanowires may be grown selectively and reproducibly depending on the pulse parameters. Unexpectedly, the growth of single crystal wires requires a greater departure from equilibrium conditions (greater overpotential) than the growth of polycrystalline ones. The importance of controlling the crystal texture is demonstrated by measurements of the superconducting transition temperature Tc which give significantly different results for polycrystalline and single crystal nanowires.

Dense fully 111-textured TiN diffusion barriers: Enhanced lifetime through microstructure control during layer growth

Abstract: Low-temperature deposition of TiN by reactive evaporation or sputter deposition onto amorphous substrates leads to highly underdense layers which develop mixed 111/002 orientations through competitive growth. In contrast, we demonstrate here the growth of low-temperature (450 °C) fully dense polycrystalline TiN layers with complete 111 texture. This was achieved by reactive magnetron sputter deposition using a combination of: (1) highly oriented 25-nm-thick 0002 Ti underlayers to provide 111 TiN orientation through texture inheritance (local epitaxy) and (2) high flux (JN2+/JTi=14), low-energy (EN2+≃20 eV), N2+ ion irradiation in a magnetically unbalanced mode to provide enhanced adatom diffusion leading to densification during TiN deposition. The Ti underlayers were also grown in a magnetically unbalanced mode, in this case with an incident Ar+/Ti flux ratio of 2 and EAr+≃11 eV. All TiN films were slightly overstoichiometric with a N/Ti ratio of 1.02±0.03. In order to assess the diffusion-barrier propert...

Self-assembling ferroelectric Na0.5K0.5NbO3 thin films by pulsed-laser deposition

Abstract: Highly [100]-axis oriented single-phase Na0.5K0.5NbO3 (NKN) thin films have been grown on polycrystalline Pt80Ir20 (Pt) and SiO2 (native oxide)/Si (111) substrates using KrF excimer laser ablation of a stoichiometric ceramic target. X-ray diffraction θ–2θ scan and rocking curve data are evidence of the strong effect of film self-assembling along the [100] direction regardless of the substrate texture. Furthermore, multiple-cell structuring along the polar axis has been observed in NKN films grown onto the Pt substrate. Ferroelectric measurements yield remnant polarization Pr of 10 μC/cm2 and spontaneous polarization Ps of 17.5 μC/cm2 at 80 kV/cm. The electrical resistivity of the Na0.5K0.5NbO3 film was in the order of 1010 Ω cm at 10 kV/cm. Dielectric permittivity e′ and dissipation factor tan δ have been found to vary 480–440 and 0.028–0.024, respectively, in the frequency range 0.4–100 kHz.

Relationship between texture and corrosion resistance in hot-dip galvanized steel sheets

Abstract: The addition of lead or antimony to the zinc bath promotes both excessive growth of the zinc crystals and a dendritic solidification in the form of spangles. This phenomenon affects not only the zinc coating texture but also its surface appearance and corrosion resistance. Therefore, the effects of the zinc bath chemical composition (changed by the addition of lead or antimony) on the texture and corrosion behaviour of hot-dip galvanized steel sheets were evaluated. Standardized salt spray tests as well as exposure to a 0.5 M NaClO4 solution test were employed. The surface texture was analyzed using X-ray diffraction (XRD). In order to study the corrosion performance, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques were employed. From the experimental results it was concluded that the characteristic texture of zinc coatings was not modified by an increase in the antimony content, but an increment in the lead content produced a crystallographic preferential orientation with the pyramidal family planes parallel to the coating surface. This last effect deteriorates not only the surface appearance but also the corrosion resistance of the galvanized steel sheets.

Effect of three-dimensional strain states on magnetic anisotropy of La0.8Ca0.2MnO3 epitaxial thin films

Abstract: Magnetic anisotropy of La0.8Ca0.2MnO3 (LCMO) epitaxial thin films grown on (001) SrTiO3 and LaAlO3 a substrates exhibits strong correlation with substrate-induced strain states as determined by normal and grazing incidence x-ray diffraction. In a 250 A thick LCMO (001)T film grown on SrTiO3 substrate, an in-plane biaxial magnetic anisotropy is observed, and it is accompanied by a substrate-induced in-plane biaxial tensile strain. In contrast, the observed magnetic easy axis for a 250 A (110)T film grown on LaAlO3 substrate is perpendicular to the film plane, and the corresponding in-plane strain is biaxial compressive. In both cases the magnetic easy axes are along the crystallographic directions under tensile strain, indicating the presence of a positive magnetostriction. In thicker films (∼4000 A) grown on both substrates that are nearly strain relaxed, the magnetic easy axis lies in the film plane along the [110] direction of the (001) substrate.

Characterization of surface structure in sputtered Al films: Correlation to microstructure evolution

Abstract: Quantitative roughness and microstructural analysis of as-deposited Al films, 0.1–1.0 μm thick, were performed by atomic force microscopy (AFM), one-dimensional power spectral density analysis (1DPSD), transmission electron microscopy, and x-ray pole figure methods. The variation of grain size (d) with thickness (h) in the columnar grained film was d∝h0.9. The initial crystallographic texture was nearly random, with a strong Al (111) fiber texture evolving by ≈0.2 μm in deposited thickness. AFM imaging revealed a surface structure with hillocks, grains, and grain boundary grooves, and periodic within-grain ridges extending over entire grains. The root-mean-square surface height variation (RRMS) initially decreased during deposition but increased as RRMS∝h0.55 from 0.3 to 1.0 μm thickness. The 1DPSD analysis revealed three spatially resolved regimes of roughness evolution; a frequency independent regime at low frequency attributed to hillock growth, an intermediate frequency self-similar regime attributed ...

The crucial role of particle morphology in the magnetic properties of haematite

Abstract: Haematite particles of four different morphologies (polyhedral, platelike, needlelike and disk shaped) were synthesized by the hydrothermal method. The morphology and average particle diameter (1.4, 7.4, 0.2, and 0.12 μm, respectively) were determined by transmission electron microscopy combined with electron diffraction. The haematite samples were studied by transmission Mossbauer spectroscopy in the temperature range 4.2–300 K. In all cases, a weak ferromagnetic (WF) phase was present above the Morin temperature of 230 K and found to coexist with an antiferromagnetic (AF) phase below this temperature. However, the populations of the two phases at 230 K were demonstrated to depend on the morphology of the particles. Moreover, the WF and AF phases exhibit a different dependence of the magnetic texture on temperature and particle morphology.

The influence of rolling practice on notch toughness and texture development in high-strength linepipe

Abstract: The mechanical properties and notch toughnesses of an X80 linepipe steel were determined for various test directions in the plane of sheet that had been finish rolled in the γ and in the intercritical (α+γ) regions The anisotropies of yield strength (YS) and of impact energy are correlated to the presence of various texture components, as detected by the use of an orientation distribution function (ODF) analysis The final microstructures were similar and consisted of polygonal and acicular ferrite The textures were also similar; however, after rolling in the (α+γ) region, the intensity of the texture was significantly higher These textures were mainly comprised of two fibers, the rolling direction (RD), 〈110〉//RD, and the normal direction (ND), 〈111〉//ND, fibers The observations show that the RD fiber centered at {112}〈110〉 and the {110}〈001〉 orientation were responsible for the YS anisotropy The relationships between notch toughness and texture were considered for the brittle or cleavage (−196 °C), mixed brittle-ductile (−60 °C), and ductile (room temperature (RT)) modes of fracture This work shows that the anisotropy of impact energy associated with ductile fracture at the higher temperatures is caused by the {112}〈110〉 component, and that the {001}〈110〉 and {110}〈001〉 components (if present) are responsible for the anisotropy of the impact energy associated with cleavage at low temperatures The lack of anisotropy of the impact energy observed at −196 °C and the increase in toughness at higher temperatures are interpreted in terms of the volume fractions of textured grains present in the sheet and the intensities of specific texture components

Lithium ion transport in Li2SO4-Li2O-B2O3 glasses

Abstract: Electrical conductivity and dielectric relaxation studies with a wide range of compositions of lithium ion conducting glasses belonging to the ternary glass system Li2SO4-Li2O-B2-O3- have been carried out over the temperature range 150-450 K and between 10 - 10(7) Hz. DC conductivities exhibit two different activation regions. This seems to suggest the presence of a cluster tissue texture in these glasses with weakly ordered clusters of Li2SO4 and lithium berates being held together by a truly amorphous tissue of the same average composition as clusters. AC conductivity behaviour of these glasses has been analysed using both power law and stretched exponential relaxation functions. The variation of the power law exponent s and the stretched exponent beta with temperature seems to be consistent with the presence of a cluster tissue texture in these glasses.

A microtexture based analysis of the surface roughening behaviour of an aluminium alloy during tensile deformation

Abstract: The development of surface roughening during uniaxial tensile deformation, with particular attention to the development of parallel ridges and valleys (ribbed profile), has been investigated for a commercial aluminium alloy. A comparison has been made between two samples which exhibit different propensities for roughening and a detailed microstructural characterisation of these samples has been performed in order to explain the differences. Microstructural characterisation techniques included polarised light microscopy, bulk texture and microtexture. In addition, yield properties were calculated from the microtexture data using polycrystal plasticity analysis. The results show that the differences in the roughening behaviour can be attributed to spatial differences in texture at the specimen surface whereby R-component colonies in a cube matrix produce differential straining, which eventually leads to strain localisation through the specimen thickness to produce a ribbed profile.

Preparation and characterization of sno2 and moox-sno2 nanosized powders for thick film gas sensors

Abstract: This work gives results about the characterization of SnO 2 materials, prepared via the sol–gel route, pure and Mo 6+ -added. The materials were characterized as powders or thick films using a variety of techniques. The morphology of the powders was analyzed by XRD, SEM, TEM and HRTEM, their texture by volumetric measurements. The morphology of the thick films was analyzed by SEM. The goal of obtaining powders and films made by regularly shaped and nanosized (30÷50 nm) particles, even after thermal treatments at 850°C is attained. FT-IR spectroscopic and electrical measurements were employed on powders and films, respectively, to obtain information on the electronic effect due to the molybdenum addition. FT-IR results show that Mo lowers the intensity of the light scattered by free electrons and the intensity of a broad absorption, previously assigned to the photoionization of V O + [V O + + hν →V O 2+ +e − (c.b.)]. Accordingly, electrical data show that molybdenum markedly lowers (of about 2 orders of magnitude) the conductance of the films in air. Electrical measurements show that Mo lowers the response of tin oxide towards CO, but leaves almost unaltered or enhances its ability to sense NO 2 , depending on the thermal pretreatments. Both pure and Mo-added materials treated at 650°C show the same response to NO 2 . However, for the pure material treated at 850°C the response to NO 2 is halved, while it is almost unaffected by the thermal treatment on the Mo-added materials. The sensing temperature of maximum response is in any case 150°C. FT-IR spectroscopy was also employed to obtain information on the Mo species present on the surface of the materials after treatments in oxygen and on how they are affected in the presence of the different testing gases. Furthermore surface species formed by NO 2 interaction were carefully investigated.

Effects of film thickness and lattice mismatch on strain states and magnetic properties of La0.8Ca0.2MnO3 thin films

Abstract: The effects of strain relaxation on the crystallographic domain structure and on the magnetic and transport properties of epitaxial colossal magnetoresistive La0.8Ca0.2MnO3 (LCMO) thin films have been studied. LCMO films in the thickness range of 100–4000 A were grown on (001) SrTiO3 and (001) LaAlO3 substrates, which impose an in-plane tensile and an in-plane compressive biaxial stress in the films, respectively. On (001) SrTiO3 substrates, the films can be grown coherently up to a thickness ∼250 A, then strain relaxation occurs at a thickness of ∼500 A. In contrast, even the 100 A film grown on (001) LaAlO3 is partially relaxed, and the critical thickness for complete strain relaxation is ∼750 A. The very thin films (<250 A) show a pure (001)T normal orientation for growth on SrTiO3 and a pure (110)T texture for growth on LaAlO3. As thickness increases, the lattice strain relaxes, resulting in mixed (001)T and (110)T textures for growth on both substrates. Both the Curie and peak resistivity temperature...

10 Gbit/in.2 longitudinal media on a glass substrate (invited)

Abstract: This article reports on the properties of the media prepared on glass substrates which were used in IBM’s 10 Gbit/in.2 demonstration. In order to support a linear density of 315 kbpi and a track density of 33 ktpi, the remanant coercivity Hcr and remanant moment thickness product Mrt of the magnetic layer were 3450 Oe and 0.37 memu/cm2, respectively. The media used a NiAl seed layer, a CrV underlayer, a Co alloy magnetic layer, and a carbon overcoat protection layer. The magnetic film had a grain size of 12 nm as observed by transmission electron microscopy. The preferred orientation (PO) of the magnetic layer was (1010). This PO enables one to sustain high coercivities at low values of Mrt. It is observed that the c-axis in-plane texture of the magnetic layer is critical to achieve a low noise medium. Using a focused-ion-beam (FIB) trimmed giant magnetoresistance head and conventional partial response maximum likelihood channel, the on-track-error rates were measured at the 10−10 level.

Relationship among synthesis, microstructure and properties in sinter-forged Bi-2212 ceramics

Abstract: High quality Bi-2212 powders were prepared using three different synthetic methods (solid state, sol–gel and polymer matrix), showing that the polymer matrix method is very promising from the point of view of the synthesis time and grain size The Bi-2212 sintered pellets were then submitted to sinter-forging process to obtain textured ceramic discs The discs were characterized by XRD, pole figures and SEM to determine the phase purity, the texture degree and the microstructure, respectively Following characterization, the discs were cut into bars and annealed for 12 h at different temperatures ranging between 845 and 873°C to determine the best thermal treatment, whereafter they were characterized using resistivity and transport Jc measurements It has been found that most of the bars had a Tc around 92 K and that transport properties can be correlated to the samples' microstructure