Lorentz-mikroskopie von Bloch- und Néelwänden in Ni-Fe-kristallen

We prepared thin single crystal foils of 50 Ni 50 Fe for observation in a 100 kV electron microscope. Due to its high saturation induction and low anisotropy, magnetic domain walls can be easily observed in this material. The effective anisotropy which governs the wall angles consists of crystal anisotropy and superimposed random stress anistropies so that wall angles of any magnitude are found.In accordance with theory three distinct wall types are identified for film thickness between 500 Å and 2000 Å as a function of wall angle θ: (i) the asymmetric Bloch wall for 180° θ #62; 140°, (ii) the asymmetric Néel wall for 140° #62; θ #62; θ_s, and (iii) the symmetric Néel wall for θ_s #62; θ, where θ_s is an angle which decreases with increasing film thickness.     

Optical inhomogeneity of ZnS films deposited by thermal evaporation

Zinc sulfide (ZnS) films with optical thickness (reference wavelength is 620 nm) ranging from 310 to 1240 nm were deposited on quartz substrates at room temperature by a thermal evaporation system. The structure and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, respectively. The optical properties of the films were determined by in situ transmittance measurements and wideband spectra photometric measurements, respectively. The experimental results show that the films exhibit cubic structure, and the intensity of the (2 2 0) diffraction peak enhances with the increase of optical thickness. Surface grain size and surface roughness increase monotonously with increasing film thickness. Refractive indices and extinction coefficients calculated by in situ transmittance measurements are well consistent with those calculated by wideband spectra photometric measurements. Both the refractive index and packing density of the film increase as the increase of film thickness, which confirms the film is positive inhomogeneous and has an expanding columnar structure. Extinction coefficients of the films increase with increasing film thickness, which results from the increase of surface roughness.     

Preparation and characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes

Preparation conditions of single-phase SiC nanotubes and C-SiC coaxial nanotubes were investigated. The characterization of single-phase SiC nanotubes and C-SiC coaxial nanotubes were carried out. The SiC nanowires, which were made of the catenated SiC grains of 50–200 nm in diameter, were obtained in carbon nanotubes reacted at 1450 °C. The only C-SiC coaxial nanotubes were formed at 1300 °C. A few single-phase SiC nantoubes were synthesized at 1200 °C for 100 h. More than half number of nanotubes reacted at 1200 °C for 100 h were altered to single-phase SiC nantoubes by heat treatment of 600 °C for 1 h in air since the remained carbon was removed. The energy dispersive X-ray spectroscopy analysis revealed that the atomic ratio of Si to C in single-phase SiC nanotubes was almost 1; these single-phase SiC nanotubes consisted of near-stoichiometric SiC grains.     

Synthesis and microstructure observation of titanium carbonitride nanostructured coatings using reactive plasma spraying in atmosphere

In the present study, nanostructured titanium carbonitride (TiCN) coatings were successfully deposited by reactive plasma spraying (RPS) technology using a self-designed gas tunnel mounted on a normal plasma spray torch. The phase composition and microstructure of the TiCN coatings were characterised by XRD, SEM and TEM. The results indicated that the main phase of the coatings was FCC TiC_0.2N_0.8 with a small amount of Ti₃O. The coating that was deposited using 35 kW displayed better microstructure and properties. The coating exhibited a typical nanostructure including 90 nm diamertrical equiaxed grains and 400 nm long columnar grains by TEM images. The SEM observation further revealed that the equiaxed grains in parallel direction to the substrate surface in TEM images were actually the columnar grains perpendicular to the substrate surface. The formation mechanism of the nanostructured coatings was also discussed. The measured microhardness value of the coating was approximately 1659 Hv_100 g, and the calculated crack extension force was about 34.9 J/m².     

Electron beam physical vapor deposition of YSZ electrolyte coatings for SOFCs

YSZ electrolyte coatings were prepared by electron beam physical vapor deposition (EB-PVD) at a high deposition rate of up to 1 μm/min. The YSZ coating consisted of a single cubic phase and no phase transformation occurred after annealing treatment at 1000 °C. A typical columnar structure was observed in this coating by SEM and feather-like characteristics appeared in every columnar grain. In columnar grain boundaries there were many micron-sized gaps and pores. In TEM image, many white lines were found, originating from the alignment of nanopores existing within feather-like columnar grains. The element distribution along the cross-section of the coating was homogeneous except Zr with a slight gradient. The coating exhibited a characteristic anisotropic behavior in electrical conductivity. In the direction perpendicular to coating surface the electrical conductivity was remarkably higher than that in the direction parallel to coating surface. This mainly attributed to the typical columnar structure for EB-PVD coating and the existence of many grain boundaries along the direction parallel to coating surface. For as-deposited coating, the gas permeability coefficient of 9.78 × 10⁻⁵ cm⁴ N⁻¹ s⁻¹ was obtained and this value was close to the critical value of YSZ electrolyte layer required for solid oxide fuel cell (SOFC) operation.     

Structure and mechanical properties of Al/AlN multilayer with different AlN layer thickness

Nanometer scale Al/AlN multilayers have been prepared by dc magnetron sputtering technique with a columnar target. A set of Al/AlN multilayers with the Al layer thickness of 2.9 nm and the AlN layer thickness variation from 1.13 to 6.81 nm were determined. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the coatings was investigated with grazing angle XRD (GAXRD). Mechanical properties of these multilayers were thoroughly studied using a nanoindentation and ball-on-disk micro-tribometer. It was found that the multilayer hardness and reduced modulus showed no strong dependence on the AlN layer thickness. Al2.9 nm/AlN1.13 nm multilayer had more excellent tribological properties than single layers and other proportion multilayers with a lowest friction coefficient of 0.15. And the tribological properties of all the multilayers are superior to the AlN single layer.     

Morphology of open films of discotic hexagonal columnar liquid crystals as probed by grazing incidence X-ray diffraction

The structure and the orientation of thermotropic hexagonal columnar liquid crystals are studied by grazing incidence X-ray diffraction (GIXD) for different discotic compounds in the geometry of open supported thin films. Whatever the film deposition mode (either spin-coating or vacuum evaporation) and the film thickness, a degenerate planar alignment with the liquid crystalline columns parallel to the substrate is found. However, if a specific thermal process is applied to the liquid crystal film, homeotropic anchoring (columns normal to the interface) can be stabilized in a metastable state.     

Efficient blue laser generation at 473 nm by a BIBO crystal

It is reported that efficient blue laser generation at 473 nm in a BIBO crystal at type-I phase matching direction of (θ,)=(18.3°,90°) performed with a diode-pumped Nd:YAG laser. With incident pump power of 1.6 W, output power of 183 mW at 473 nm has been obtained using a 5.0 mm-long BIBO crystal. The optical conversion efficiency was up to 11.4%. It was found that the intracavity frequency doubling efficiency is about 50% greater than that obtained with a 10 mm-long type-I phase-matching LBO crystal.     

Effects of Cr dopant on the microstructure and electromigration performance of Cu interconnects

Cu and Cu(Cr) alloy films were deposited on SiO₂ substrates by magnetron sputtering. The microstructure and electromigration performance of films were investigated. A small amount of Cr refines the Cu grains and improves the surface morphology of Cu films. After annealing at 450 °C, in contrast to the Cu film with large lateral grown grains, the Cu(Cr) alloy film exhibits fine columnar grains with a 1 1 1 preferred orientation. Most of Cr in the annealed Cu(Cr) film has segregated at the film surface and the film/substrate interface. The grain boundary grooving at the film/substrate interface is completely prohibited for Cu(Cr) films. As a result, the electromigration lifetimes of annealed Cu(Cr) lines are 10–100 times longer than those of annealed Cu lines. The final resistivity of the annealed Cu(Cr) film is 2.55 μΩ cm which is close to that of the annealed Cu film. With the improved surface morphology and high electromigration resistance, the dilute Cu(Cr) alloy film can be a viable interconnect material or a seed layer in the Cu-damascene technology.     

AlF3 film deposited by IAD with end-Hall ion source using SF6 as working gas

A novel and effective process to fabricate high quality fluoride thin films was presented. Aluminum fluoride films deposited by a conventional thermal evaporation with an ion-assisted deposition (IAD) using SF₆ as a working gas at around room temperature were investigated. In this study, the optimal voltage and current, 50 V and 0.25 A, were found according to the optical properties of the films: high refractive index (1.489 at 193 nm), low optical absorption and extinction coefficient (<10⁻⁴ at 193 nm) in the UV range. The physical properties of the film are high packing density and amorphous without columnar structure. It was proved that using SF₆ working gas in IAD process is a good choice and significantly improves the quality of AlF₃ films.     

Microstructure and microwave permeability of FeCo thin films with Co underlayer

Microstructure, static magnetic properties and microwave permeability of sputtered FeCo films were examined. Fe₆₀Co₄₀ films (100 nm in thickness) deposited on glass substrates exhibited in-plane isotropy and a large coercivity of 161.1 Oe. When same thickness films were deposited on 2.5 nm Co underlayer, well-defined in-plane anisotropy was formed with an anisotropy field of 65 Oe. The sample had a static initial permeability of about 285, maximum imaginary permeability of 1255 and ferromagnetic resonance frequency of 2.71 GHz. Cross-sectional TEM image revealed that the Co underlayer had induced a columnar grain structure with grain diameter of 10 nm in the FeCo films. In comparison, FeCo films without Co underlayer showed larger grains of 70 nm in diameter with fewer distinct vertical grain boundaries. In addition, the Co underlayer changed the preferred orientation of the FeCo from (1 0 0) to (1 1 0). The improvement in soft magnetic properties and microwave behavior originates from the modification of the film microstructure, which can be well understood by the random anisotropy theory.     

Effects of deposition temperature and thickness on the structural properties of thermal evaporated bismuth thin films

Bismuth (Bi) thin films of different thicknesses were deposited onto Si(1 0 0) substrate at various substrate temperatures by thermal evaporation technique. Influences of thickness and deposition temperature on the film morphologies, microstructure, and topographies were investigated. A columnar growth of hexahedron-like grains with bimodal particle size distribution was observed at high deposition temperature. The columnar growth and the presence of large grains induce the Bi films to have large surface roughness as evidenced by atomic force microscopy (AFM). The dependence of the crystalline orientation on the substrate temperature was analyzed by X-ray diffraction (XRD), which shows that the Bi films have completely randomly oriented polycrystalline structure with a rhombohedral phase at high deposition temperature (200 °C) and were strongly textured with preferred orientation at low deposition temperatures (30 and 100 °C).     

Sputter damage in Si surface by low energy Ar+ ion bombardment

The damage distributions in Si(1 0 0) surface after 1.0 and 0.5 keV Ar⁺ ion bombardment were studied using MEIS and Molecular dynamic (MD) simulation. The primary Ar⁺ ion beam direction was varied from surface normal to glancing angle. The MEIS results show that the damage thickness in 1.0 keV Ar ion bombardment is reduced from about 7.7 nm at surface normal incidence to 1.3 nm at the incident angle of 80°. However, the damage thickness in 0.5 keV Ar ion bombardment is reduced from 5.1 nm at surface normal incidence to 0.5 nm at the incident angle of 80°. The maximum atomic concentration of implanted Ar atoms after 1 keV ion bombardment is about 10.5 at% at the depth of 2.5 nm at surface normal incidence and about 2.0 at% at the depth of 1.2 nm at the incident angle of 80°. However, after 0.5 keV ion bombardments, it is 8.0 at% at the depth of 2.0 nm for surface normal incidence and the in-depth Ar distribution cannot be observable at the incident angle of 80°. MD simulation reproduced the damage distribution quantitatively.     

Investigation of induced parallel magnetic anisotropy at low deposition temperature in Ba-hexaferrites thin films

In this paper we present the effect of low substrate temperature on structural, morphological, magnetic and optical properties of Ba-hexaferrite thin films. Films were deposited on single crystal Silicon (1 0 0) substrate employing the Pulsed Laser Deposition (PLD) technique. The structural, morphological, magnetic and optical properties are found to be strongly dependent on substrate temperature. The low substrate temperatures (room temperature to 200 °C) restrict the formation of larger grains. For the higher substrate temperature i.e., 400 °C, the grain size of the deposited thin film are much larger. The film grown at low substrate temperature do not show any anisotropy. As the substrate temperature is increased, the easy axis of the films alinged itself in the direction parallel to the film plane whereas the hard axis remained in the perpendicular direction. The higher substrate temperature caused the uniaxial magnetic anisotropy, which is very important in magnetic recording devices. The saturation magnetization and optical band gap energy values of 62 emu/cc and 1.75 eV, respectively, were achieved for the film of thickness 500 nm deposited at 400 °C. Higher values of coercivity, squareness and films thickness are associated with the growth of larger grains at higher substrate temperature.     

Abnormal residual stress in nanostructured Al thin films grown on Ti/glass substrates

The residual stress and micro-structural properties of nanostructured Al thin films prepared by electron beam evaporator are studied. The films were grown on Ti/glass substrates at normal and oblique angles of inclination. The average aspect ratio of Al nanorods produced at an oblique angle of incidence of 85°, increased from 2.2 to 6.0, as the thickness of the films increased from 100 nm to 600 nm. The column tilt angle of Al nanorods was observed to be in close agreement with the theoretical value. The XRD pattern of nanostructured Al thin films showed (111) planes oriented parallel to the substrate surface. The crystallite size was observed to be ～9 nm for all the films produced at oblique angle deposition (OAD). Abnormal residual stresses were determined in the films produced at OAD. The nanocrystalline films produced at normal angle, exhibited tensile residual stress, while, the residual stresses in the films produced at oblique angles of inclination (α = 65°, 75°), were observed to be compressive. Residual stress-free nanocolumnar Al films (Al nanorod films) were observed, when they were grown at an oblique angle of inclination of 85°.     

Angular dependence of coercivity in Pr---Fe---B sintered magnets

Hysteresis loops were measured for varying angles of the applied field at different temperatures in oriented sintered magnets of compositions Fe₇₅Pr₁₇B₈ and Fe₅₃Pr₁₇B₃₀. While at elevated temperatures the coercive field increases monotonically with the angle of the applied field, a minimum in the angular dependence is found below room temperature. The temperature dependence of coercivity for the field applied parallel and with an angle of 45° to the alignment direction is well described by a nucleation model in the whole temperature range. The results are compared to Fe---Nd---B magnets, showing that the occurrence of a minimum in the angular dependence is related to the ratio of the experimental to the theoretical coercive fields.     

Thickness dependence of magnetic anisotropic properties of FeCoNd films

The magnetic FeCoNd films with thickness (t) from 50 to 166 nm were fabricated by RF magnetron co-sputtering at ambient condition. The amorphous structures of all of the films were investigated by X-ray diffraction and transmission electron microscopy. A spin reorientation transition from in-plane single domain state to out-of-plane stripe domain state was observed as a function of t. When t is below a critical thickness, magnetic moments lie in the film plane corresponding to in-plane single domain state because of the strong demagnetization energy. However, when t is increased, out-of-plane stripe domain structure was developed due to a dominated perpendicular magnetic anisotropy. Scanning electron microscopy data indicate that the perpendicular anisotropy, which is responsible for the formation of stripe domains, may result from the shape effect of the columnar growth of the FeCo grains.     

Theoretical investigations of the effect of vacancies on the geometric and electronic structures of zinc sulfide

The effects of S-vacancy and Zn-vacancy on the geometric and electronic structures of zinc blende ZnS are investigated by the first-principles calculation of the plane wave ultrasoft pseudopotential method based on the density functional theory. The results demonstrate that both S-vacancy and Zn-vacancy decrease the cell volume and induce slight deformation of the perfect ZnS. Furthermore, this change of geometric structure caused by Zn-vacancy is more obvious than the one due to the S-vacancy. The formation energy of S-vacancy is higher than that of Zn-vacancy, indicating that Zn-vacancy is easier to form than S-vacancy in ZnS crystal. Electronic structure analysis shows that Zn-vacancy increases the band-gap of ZnS from 2.03 eV to 2.15 eV, while the S-vacancy has almost no effect on the band-gap of ZnS. Bond population analysis shows that Zn-vacancy increases covalence character of the Zn–S bonds around Zn-vacancy, while S-vacancy shows a relatively weak effect on the covalence character of Zn–S bonds.     

Texture change through film thickness and off-axis accommodation of (0 0 2) planes

We present our recent experimental results on the formation of off-axis texture and crystallographic tilting of crystallites that take place in thin film of transition metal nitrides. For this purpose, the microstructural development of TiAlN film was studied, specially the change in texture with film thickness. Fiber texture was measured using θ-2θ and pole figure X-ray diffraction (XRD), while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microstructure and changes in texture with thickness. The sin²ψ method was applied to determine the stresses on (1 1 1) and (0 0 2) plane. With deposition parameters chosen, the growth texture mechanism is discussed in three different stages of film growth. Surface energy minimization at low thickness leads to the development of (0 0 2) orientation. On the other hand, the competitive growth promotes the growth of (1 1 1) planes parallel to film surface at higher thickness. However, contrary to the prediction of growth models, the (0 0 2) grains are not completely overlapped by (1 1 1) grains at higher thickness. Rather the (0 0 2) grains still constitute the surface, but are tilted away from the substrate normal showing substantial in-plane alignment to allow the (1 1 1) planes remain parallel to film surface. Intrinsic stress along (1 1 1) and (0 0 2) shows a strong dependence with preferred orientation. The stress level in (0 0 2) grains which was compressive at low thickness changes to tensile at higher thickness. This change in the nature of stress allows the (0 0 2) planes to tilt away in order to promote the growth of 〈1 1 1〉 parallel to film normal and to minimize the overall energy of system due to high compressive stress stored in the (1 1 1) grains. The change in surface morphology with thickness was observed using SEM. An increase in surface roughness with film thickness was observed which indicates the development of (1 1 1) texture parallel to film surface. TEM observations support the XRD results regarding texture change. Film hardness was measured by nanoindentation and a correlation between (1 1 1) texture, stress and hardness is obtained. The results indicate that texture development is a complex interplay between thermodynamic and kinetic forces. An attempt is made to understand this phenomenon of off-axis accommodation of (0 0 2) at higher thicknesses, which is a new result not reported previously.     

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 60 A dm⁻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.