High Degree Of Preferred Orientation Research Articles

Effect of crystallographic orientation of Co2MnGe Heusler-alloy film on its surface roughness and ordered structure

The effects of direction and degree of preferred orientation of Co2MnGe film on the surface roughness and the ordered structure were investigated by utilizing various buffer layers and underlayers. Degrees of preferred orientation of Co2MnGe film were estimated by measuring the full width at half maximum (FWHM) of the x-ray diffraction rocking curve for Co2MnGe(400) or Co2MnGe(220) reflections. A high B2 ordered structure and a high saturation magnetization, which is almost the same value as in the case of epitaxial Co2MnGe films, were obtained regardless of the direction and degree of preferred orientation, except in the case of the Co2MnGe films without both buffer layers and underlayers. Also, surface roughness decreased when decreasing the FWHM of x-ray diffraction rocking curve, and the small surface roughness (that is almost the same value as in the case of epitaxial Co2MnGe films) was obtained for Co2MnGe films with the high degree of preferred orientation. A smaller surface roughness was obtained in the case of Co2MnGe films with (110) preferred orientation compared with the Co2MnGe(100) case. The tendencies of change of the surface roughness were explained from the viewpoint of surface energy.

A study of direct- and pulse-current chromium electroplating on rotating cylinder electrode (RCE)

Direct- and pulse-current (DC and PC) chromium electroplating on Cr–Mo steel were performed in a sulfate-catalyzed chromic acid solution at 50°C using a rotating cylinder electrode (RCE). The electroplating cathodic current densities were at 30, 40, 50 and 60Adm−2, respectively. The relationship between electroplating current efficiency and the rotating speed of the RCE was studied. The cross-sectional microstructure of Cr-deposit was examined by transmission electron microscope (TEM). Results showed that DC-plating exhibited higher current efficiency than the PC-plating under the same conditions of electroplating current density and the rotating speed. We found the critical rotating speed of RCE used in the chromium electroplating, above this rotating speed the chromium deposition is prohibited. At the same plating current density, the critical rotating speed for DC-plating was higher than that for PC-plating. The higher plating current density is, the larger difference in critical rotating speeds appears between DC- and PC-electroplating. Equiaxed grains, in a nanoscale size with lower dislocation density, nucleate on the cathodic surface in both DC- and PC-electroplating. Adjacent to the equiaxed grains, textured grains were found in other portion of chromium deposit. Fine columnar grains were observed in the DC-electroplated deposit. On the other hand, very long slender grains with high degree of preferred orientation were detected in PC-electroplated deposit.

The structure of sputter-deposited Co2MnSi thin films deposited on GaAs(001)

The structure of Co2MnSi thin films on GaAs(001) has been characterized by transmission electron microscopy in order to evaluate the feasibility of achieving spin injection into GaAs from such electrodes. The films were dc-magnetron sputtered and varied in thickness between 15 and 260 nm with substrate temperatures during growth of 250, 300, and 374 °C. All films exhibited a polycrystalline structure with mainly an L21 type crystallographic symmetry, and a high degree of preferred orientation with the GaAs. A reaction with the GaAs substrate, rich in Mn and As, occurs for deposition even of the 15 nm thick film, creating zones that exhibit an epitaxial relation with the substrate. Between this reaction zone and the film, a continuous interlayer forms, which is rich in Ga, and several nanometers thick. Films thicker than 35 nm were found to be stoichiometric in chemical composition, while thinner films were deficient in Mn and richer in Si. Decreasing the substrate temperature resulted in reduction of the extent of the reaction with the substrate, but also reduced the crystallographic ordering of the Co2MnSi layer. Finally, both kinematic and dynamic simulations of selected-area electron diffraction patterns demonstrate that this technique may not be a sensitive methodology to detect Co-Mn antisite defects and off-stoichiometry compositions. These defects may be responsible for the approximately 55% spin polarization measured in these films, rather than the full spin polarization expected from this theoretically predicted half-metal.

Effects of post-heat treatment on the characteristics of chalcopyrite CuInSe 2 film deposited by successive ionic layer absorption and reaction method

The influence of annealing effects in CuInSe 2 ternary films prepared by successive ionic layer absorption and reaction method has been investigated. The films have firstly been deposited on glass substrates at room temperature and then heat-treated under Ar atmosphere at various annealing temperatures. CuInSe 2 films were characterized using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectra, optical absorption spectrum and Hall system. XRD results showed that the proper post-annealing process can lead to a complete formation of chalcopyrite structure CuInSe 2 with high degree of preferred orientation towards (112) reflection. After annealing process, the composition of annealed films was close to the standard stoichiometry and O, Cl impurities decreased. The direct band gap increased from 0.94 to 0.98 eV and resistivity showed a big decrease with the increase of annealing temperature.

Anisotropy of expansion coefficient and slag resistance of spinel carbon bricks

Effects of the pressure direction on the thermal expansion and slag corrosion resistance were investigated and anisotropic microstructures of flaky graphite in spinel carbon bricks were examined. The experimental results show that slag corrosion velocities in the direction parallel to the pressure direction display a decrease of 34% compared to those in the vertical direction. Meantime, the linear expansion coefficient in the direction parallel to the pressure direction is 2.45 times as large as that in the vertical pressure direction. Slag corrosion velocities of spinel carbon bricks soaked in the AOD melting slag display a 46%–47% decrease compared to those of magnesia carbon bricks. The microstructure observation shows that spinel carbon bricks have a high degree of preferred orientation.

Characterization of CdTe thin films grown on glass by hot wall epitaxy

In this work we have investigated the properties of CdTe thin films grown on glass substrates by Hot Wall Epitaxy. Its most important feature is the growth at very low temperatures, which would allow the growth even on polymer substrates. Our samples were grown at temperatures between 150 and 250 oC at a growth rate between 0.2 and 2 µm/h. The CdTe films were characterized by x-ray diffraction, scanning electron microscopy and optical transmission. The x-ray teta-2teta scans revealed films with cubic structure and a very high degree of preferential orientation. In fact, for films thicker than 1 µm, no other reflections have been observed on the spectra besides the (111), (333) and (444). The scanning electron micrographs showed a grain size about 0.3 µm and the optical transmission indicated a very good optical quality of the interfaces, showing pronounced interference fringes.

Synthesis and characterization of type-II textured tungsten disulfide thin films by vdWR process with Pb interfacial layer as texture promoter

The growth of type-II textured tungsten disulfide (WS 2) thin films by solid state reaction between the spray deposited WO 3 and gaseous sulfur vapors with Pb interfacial layer has been studied. X-ray diffraction (XRD) technique is used to measure the degree of preferred orientation ‘ S’ and texture of WS 2 films. Scanning electron microscopy (SEM) and transmission electron microscopy techniques have been used to examine the microstructure and morphology. The electronic structure and chemical composition were studied using X-ray photoelectron spectroscopy (XPS). The use of Pb interfacial layer for the promotion of type-II texture in WS 2 thin films is successfully demonstrated. The presence of (0 0 3 l), (where l=1, 2, 3, …) family of planes in the XRD pattern indicates the strong type-II texture of WS 2 thin films. The crystallites exhibit rhombohedral (3R) structure. The large value of ‘ S’ (1086) prompts the high degree of preferred orientation as well. The stratum of crystallites with their basal plane parallel to the substrate surface is seen in the SEM image. The EDS and XPS analyses confirm the tungsten to sulfur atomic ratio as 1:1.75. We purport that Pb interfacial layer enhances type-II texture of WS 2 thin films greatly.

The effect of Ag diffusion on properties of YBa 2Cu 3O 7− x thin films produced by electron beam deposition techniques

Superconducting YBa 2Cu 3O 7− x thin films were prepared on pure MgO and Ag/MgO substrates (without and with Ag buffer layer) using an electron beam evaporation technique. The effects of isothermal annealing temperature and Ag diffusion on the crystalline structure and some superconducting properties were investigated by X-ray diffraction, scanning electron microscopy, critical temperature, critical current density and room temperature resistivity measurements. The optimum annealing conditions causing a high degree of preferential orientation with the c-axis perpendicular to the substrates were found to be the isothermal annealing at 930 °C for 5 h. Annealing of films on Ag/MgO substrates is accompanied by Ag diffusion from the buffer layer into YBCO films. The higher rate of crystallization of the YBCO films, the higher degree of c-axis orientation, the higher dense surface morphology, the increased lattice parameter c (by ≈0.1%), the reduced room temperature resistivity (2–3 times), the slightly enchanced critical temperature ( T c = 92 K at R = 0) and the critical current density ( J c = 4.2 × 10 5 A/cm 2 at 77 K) were observed for the Ag-doped films (on Ag/MgO substrates) in comparison with those for the undoped films (on MgO substrates). The temperature dependence of the Ag diffusion coefficient in YBCO films in the range 600–800 °C was described by the relation D = 1.9 × 10 −6 exp(−0.73 eV/kT).

Thin films of SmCo5 with very high perpendicular magnetic anisotropy

Thin films of SmCo5 with extraordinarily high perpendicular magnetic anisotropy were prepared by introducing a Cu∕Ti dual underlayer and controlling the substrate temperature during the sputter deposition. Under optimized conditions, the magnetic anisotropy constant reached 4.0×107erg∕cm3, and the coercivity and the remanence ratio in the direction perpendicular to the film surface were 12.0kOe and unity, respectively. The high perpendicular magnetic anisotropy is attributed to the high degree of preferred orientation of the c axis; the full width at half maximum in the rocking curve of SmCo5(002) reflection was 3.1°.

Self-organization in nanoscopic poly(alkylthiophene) films on water

Ultra-thin layers (10 - 50nm) of poly(alkyl)thiophenes (PATs) spread on water from diluted chloroform solutions were studied by means of synchrotron radiation. The molecular orientation in the films was obtained using grazing incidence diffraction (GID) and reflectometry, for both doped and pristine samples. Despite alkanes being hydrophobic, the side chains tend to orient perpendicularly to the water subphase. The study reveals the presence of crystalline order with a high degree of preferred orientation. A smectic model for the polymeric layers is in good agreement with the experimental data.

Characterization of tungsten oxide films of different crystallinity prepared by RF sputtering

Thin films of tungsten oxide have been prepared onto heated and un-heated substrates to get different degrees of crystallinity. The structure study has been characterized by X-ray diffraction, scanning electron microscope and scanning force microscope. Films deposited onto un-heated substrates proved to be amorphous, while those prepared onto heated substrates, 473⩽ T s⩽573 K showed orthorhombic structure. Monoclinic order was formed at T s>573 K. Due to the high degree of preferred orientation, Voigt analysis of a single reflection has been used to determine the microstructure parameters. The investigations lead to a two-phase-model characterized by nanocrystallites ∼12 nm dispersed in an amorphous matrix even for films deposited onto unheated substrates. The substrate temperature increases the number of crystallites rather than the size even for films sputtered onto unheated substrate. The microstrain was found to increase markedly with the sputtering power. The dark resistivity measurements at room temperature showed values of 1.58×10 7 Ω cm for amorphous tungsten oxide with one order of magnitudes lower for crystalline films. It shows linear dependence with oxygen concentration during sputtering. Conductivity versus temperature measurements revealed thermal activation energy of 0.77 and 0.84 eV for amorphous and crystalline tungsten oxide, respectively.

Production of BiPbSrCaCuO Thin Films on MgO and Ag/MgO Substrates by Electron Beam Deposition Techniques

Superconducting BiPbSrCaCuO thin films were prepared on MgO(001) and Ag/MgO substrates using an electron beam (e-beam) evaporation technique. The effects of annealing temperature and Ag diffusion on the crystalline structure and some superconducting properties, respectively, were investigated by X-ray diffraction, atomic force microscopy, and by measurements of the critical temperature and the critical current density. It was shown that an annealing of both types of films at 845 or 860 °C resulted in the formation of mixed Bi-2223 and Bi-2212 phases with a high degree of preferential orientation with the c-axis perpendicular to the substrates. The slight increase of the critical temperature from 103 K to 105 K, the enhancement of the critical current density from 2 x 10 3 to 6 x 10 4 A/cm 2 , and the improved surface smoothness are due to a possible silver doping from the substrate.

Opto-structural, electrical and electrochromic properties of crystalline nickel oxide thin films prepared by spray pyrolysis

Polycrystalline nickel oxide films with preferential growth along (1 1 1) plane were deposited onto glass substrates, maintained at 350°C, by the spray pyrolysis technique using nickel chloride as starting solution. The effect of solution concentration on their structural, electrical, and optical properties was studied. Using X-ray diffraction, the structural characteristics have been studied and due to the high degree of preferred orientation, Voigt analysis of single reflection was used to determine the microstructural properties (crystallite size and microstrain). The refractive index n and the extinction coefficient k have been computed from the corrected transmittance and reflectance measurements over the spectral range 300–2400 nm. Analysis of the absorption versus photon energy curves revealed a direct transition with optical band gap, E g, of 3.6 eV and indirect transition within the range 3.97–3.75 eV as solution molarity increases from 0.05 to 0.3 M. The electrochromic behaviour of polycrystalline nickel oxide film were investigated by means of cyclic voltametry in 1 M KOH aqueous solution. Cycling showed significant increase in solar optical modulation reaching a value of 0.23 after 150 cycles.

Comparison of the temperature dependence of the properties of ion beam and magnetron sputtered Fe films on (100) GaAs

The effects of substrate temperature on the crystallographic, electrical, and mechanical properties of ion beam (IBS) and magnetron sputtered (MS) Fe films on (100) GaAs were studied and compared. Films were deposited at substrate temperatures ranging from 100 to 500 °C. Given the large differences between the two deposition techniques, the film properties were remarkably similar. A higher deposition rate was achieved for magnetron sputtering, and the deposition rate increased with increasing temperature for both techniques. For both deposition techniques, as the substrate temperature was increased the films changed from random or (110) oriented to a preferred (200) orientation, with IBS films having a higher degree of preferred orientation. The full-width at half-maximum of the (200) rocking curves are comparable for both techniques and varied from 0.5° to 0.9°. Both techniques show an initial decrease in resistivity with increasing temperature, reaching a minimum resistivity approaching that of bulk Fe at about 200 °C. With further increases in temperature, the resistivity increases. Resistivity of IBS films was lower than that of MS films. The stress of MS films was tensile (0.5–1.5 GPa) at all deposition temperatures while the stress for IBS films was compressive (−1 GPa) at low temperatures and became tensile (0.5 GPa) at high temperatures.

The Study of a Naturally Fractured Gas Reservoir Using Seismic Techniques

The upper Green River Formation at the Bluebell-Altamont field, Utah (Figure 1) is a tight gas sand reservoir where economic production can be sustained only in regions of high natural fracturing. In 1994, a demonstration seismic project was conducted at the field to show how exploration for, and the characterization of, naturally fractured gas reservoirs can be more effective through the integrated use of seismic techniques. Study of field exposures, well logs, and regional stress indicators prior to the seismic survey indicated a high degree of preferential orientation to the dominant fracture trend at the field. The seismic survey consisted of two crossing, nine-component surface seismic lines and a nine-component vertical seismic profile. The compression, and shear-wave surface seismic both recorded anisotropies that were related to the presence and azimuth of the natural fracturing. The surface seismic results were supported by results from the nine-component vertical seismic profile. This program demonstrates the potential offered by the use of integrated seismic and geological techniques for the analysis of both land and marine naturally fractured reservoirs; furthermore, it demonstrates the possibilities of reviewing existing databases containing compression-wave surface seismic data for fracture information.

As-spun orientation as an indication of graphitized properties of mesophase-based carbon fiber

A 100% mesophase produced by supercritical fluid extraction was melt-spun into roundshaped fibers. The spinning temperature was allowed to vary while all other spinning conditions were held constant. The as-spun preferred orientation of the graphene basal planes with respect to the fiber axis was found to change as a result of a change in the spinning temperature. As-spun fibers that had developed a high degree of preferred orientation after spinning were found to have a high degree of preferred orientation, low d (0002)-spacing, and large crystallite size after graphitization. Also, as-spun fibers with a high degree of preferred orientation were found to have high modulus and low electrical resistivity after heat treatment. Scanning electron microscopy results indicate that, regardless of spinning temperature, all fiber sets exhibit a radial-folded transverse texture.

Effects of substrate temperature on the microstructure and photocatalytic reactivity of TiO2 films

Transmission electronic microscopy is used to study the structure, morphology and orientation of thin TiO2 films prepared by reactive magnetron sputtering on glass slides at different substrate temperatures (100 to 400 °C). The TiO2 films are used to purify a dye in waste water. The microstructure and photocatalytic reactivity of TiO2 films have been shown to be functions of deposition temperature. In the temperature range examined, all film samples have a porous nanostructure and the dimension of particles grown with increasing deposition temperature. Films are amorphous at temperatures of 100 °C and only anatase phase forms at 200 °C and above. Films deposited between 200 to 300 °C show a preferred orientation, while films at 400 °C change into complete random orientation. Deposition at 250 °C yields high efficiency in photocatalytic degradation owing to the high degree of preferred orientation and nanocrystalline/nanoporous anatase phase. © 1998 Kluwer Academic Publishers

Chemical Vapor Infiltration of Carbon into Graphite Block with Uniform Bore Capillary Tubes

Chemical Vapor Infiltration with carbon was studied in uniform bore capillary tubes using CH4 as a source gasat 1300°C and 2 to 20 Torr. The relation between CVI parameters and the resultant deposition profile, rate andmicrostructure were examined.Higher CH4 flow rate produces higher deposition rate and higher degree of preferred orientation, but lessdeposition uniformity along the capillary. The contact time of 0.1 to 0.3 seconds is suggested to be a preferred numberwithin the condition studied, in terms of densification rate and uniformity.From the CVI using C2H2 and C6H6 as source gases, it is suggested that these two hydrocarbons are thedecomposition products in the early stage, and produce acetylenic and aromatic species. The aromatic species give highdeposition rate and deposit with high degree of preferred orientation. The acetylenic species give better penetration ina capillary.The CVI penetration depends on the diameter of the capillary, but in the capillarywith the diameter smaller thanmean free path of gases, deposition profile is also determined by the surface to volume ratio of the capillary.Finally, the effect of wall-block spacing was studied. Better uniformity along the flow and higher conversionrate of feed gas to deposit can be achieved by controlling the wall-block spacing.

Soil Fabric Changes During Consolidation

Abstract A method for characterizing the directional distribution of voids in soils at the microstructural level is presented. A scanning electron microscope (SEM) was used to obtain high-resolution, high-magnification images of the soil microstructure. These images were analyzed using an image analysis program to obtain parameters of the directional void ratio distribution function. Useful indices based on both solid and void phases for describing the changes of fabric in soils are proposed, and their evolution under one-dimensional compression of soils is studied. The analyses showed a high degree of preferred orientation attained by soil particles during consolidation.

Thin Film Rechargeable Lithium Batteries for Implantable Devices

Thin films of LiCoO2 have been synthesized in which the strongest x-ray reflection is either weak or missing, indicating a high degree of preferred orientation. Thin film solid state batteries with these textured cathode films can deliver practical capacities at high current densities. For example, for one of the cells, 70% of the maximum capacity between 4.2 and 3 V (∼0.2 mAh/cm2) was delivered at a current of 2 mA/cm2. When cycled at rates of 0.1 mA/cm2, the capacity loss was 0.001%/cycle. The reliability and performance of LiLiCoO2 thin film batteries make them attractive for application in implantable devices such as neural stimulators, pacemakers, and defibrillators.