Effect of grain boundary character on sink efficiency

The dependence of the width of void-denuded zones (VDZs) on grain boundary (GB) characters was investigated in Cu irradiated with He ions at elevated temperature. Dislocation loops and voids formed near GBs during irradiation were characterized by transmission electron microscopy, and GB misorientations and normal planes were determined by electron back-scatter diffraction. The VDZ widths at Σ3〈1 1 0〉 tilt GBs ranged from 0 to 24 nm and increased with the GB plane inclination angle. For non-Σ3 GBs, VDZ widths ranged from 40 to 70 nm and generally increased with misorientation angle. Nevertheless, there is considerable scatter about this general trend, indicating that the remaining crystallographic parameters also play a role in determining the sink efficiencies of these GBs. In addition, the VDZ widths at two sides of a GB show different values for certain asymmetrical GBs. Voids were also observed within GB planes and their density and radius also appeared to depend on GB character. We conclude that GB sink efficiencies depend on the overall GB character, including both misorientation and GB plane orientation.     

Investigation of electrical properties of nanostructured carbon films derived from block copolymers

Electrical properties of nanostructured carbon (ns-C) films fabricated by pyrolysis of PAN–b–PBA copolymers were investigated. Films having cylindrical morphology and pyrolyzed at 400, 500 and 600 °C were investigated. Both carbide forming (Zr, Ti) and non-carbide forming (Cu, Pt) metals spanning a wide range of electron work functions (4.1–5.5 eV) formed ohmic contacts to the ns-C films in the as-deposited state. The conductivity of the ns-C films increased roughly three orders of magnitude for every 100 °C increase in the pyrolysis temperature. Hall-effect measurements showed that the films pyrolyzed at 600 °C were n-type with a majority carrier concentration and mobility of 5.8 × 10¹⁸ cm^?3 and 0.97 cm²/V s, respectively. Current–voltage measurements as a function of temperature (I–V–T) were performed on films pyrolyzed at 600 °C, whereas films pyrolyzed at 400 and 500 °C were too resistive for reliable resistivity–temperature and Hall-effect measurements. The resistivity as a function of temperature was analyzed by using the reduced activation energy method and was determined to follow variable-range hopping (VRH) mechanisms at and below room temperature. The data indicates a crossover from Efros–Shklovskii VRH [J. Phys. C 8, (1975) L49] to Mott VRH [J. Non-Cryst. Solids 1, (1968) 1] at temperatures above 100 K.     

Comparative study of grain-boundary migration and grain-boundary self-diffusion of [0 0 1] twist-grain boundaries in copper by atomistic simulations

Molecular-dynamics simulations were used to study grain-boundary migration as well as grain-boundary self-diffusion of low-angle and high-angle [0 0 1] planar twist grain boundaries (GBs) in copper. Elastic strain was imposed to drive the planar [0 0 1] twist GBs. The temperature dependence of the GB mobility was determined over a wide misorientation range. Additionally grain-boundary self-diffusion was studied for all investigated [0 0 1] planar twist GBs. A comparison of the activation energies determined shows that grain-boundary migration and self-diffusion are distinctly different processes. The behavior of atoms during grain-boundary migration was analyzed for all studied GBs. The analysis reveals that usually in absolute pure materials high-angle planar [0 0 1] twist GBs move by a collective shuffle mechanism while low-angle GBs move by a dislocation based mechanism. The obtained activation parameters were analyzed with respect to the compensation effect.     

Relation between precipitate-free zone width and grain boundary type in 7075-T7 Al alloy

The effect of grain boundary (GB) type on precipitate-free zone (PFZ) width in friction stir-processed 7075-T7 Al alloy is investigated by transmission electron microscopy (TEM) and stereology. The average half width of PFZs at random GBs is 70.4 ± 0.7 nm. For low-angle GBs, an apparent transition of PFZ half width is observed at a misorientation of 11°. For coincidence site lattice (Σ) GBs, only Σ1, Σ3 and Σ5 have smaller PFZ width than that of random GBs. Crystal-frame stereology is used to recover the GB plane distribution. It is found that the GB plane distribution is relatively isotropic for most Σ GBs. Low/high index plane combinations are observed for most Σ GBs; furthermore, most Σ GBs have both tilt and twist components. The combined results of TEM and stereology suggest that smaller PFZ width is associated only with low Σ GBs since the formation and growth of PFZs at GBs depends closely on the core structure, in addition to the geometric structure of GBs.     

Tracer diffusion of Au and Cu in a series of near Σ=5 (310)[001] symmetrical Cu tilt grain boundaries

Grain boundary diffusion of Au and Cu was measured in a series of Cu bicrystals with symmetrical near Σ=5, Θ=36.9° (310)[001] CSL tilt grain boundaries (GBs) using the radiotracer and the serial sectioning technique. The orientations of the bicrystals were very precisely determined with the Kossel technique where all three macroscopic parameters describing the orientations of the grains in the bicrystal were evaluated. The tilt angles ranged from 33.21° to 39.26°. The GB diffusion of the radiotracers ¹⁹⁵Au and ⁶⁴Cu was measured as a function of tilt angle and temperature. In the investigated temperature range 1030–661 K the orientation dependence of both radiotracers shows a characteristic cusp not exactly at but slightly below the ideal Σ=5 CSL GB. The Arrhenius parameters, activation enthalpy and frequency factor, determined from lower temperature data adopt a maximum, again slightly before the ideal Σ=5 CSL GB. These features are discussed with respect to the accidental small twist and second tilt orientations and the corresponding dislocation network inherent in the investigated real GBs. With increasing temperature a negative deviation from a straight Arrhenius behaviour is observed. This result indicates a certain change in the GB structure in the temperature range above 800 K.     

2-Mercaptobenzoxazole as a copper corrosion inhibitor in chloride solution: Electrochemistry, 3D-profilometry,and XPS surface analysis

2-Mercaptobenzoxazole (MBOH) was studied as a corrosion inhibitor for Cu in 3 wt.% NaCl solution using EIS, a potentiodynamic curve, 3D-profilometry, and XPS measurements. It was shown that Cu corrosion in solution containing MBOH follows kinetic-controlled and diffusion-controlled processes and that MBOH is a mixed-type inhibitor. The diffusion coefficient of the Cu ions travelling through the solid surface layers was estimated to be on the order of 10⁻¹⁵–10⁻¹⁴ cm² s⁻¹. It was also demonstrated that the Cu(I)–MBOH complex is formed on the Cu surface and that the thickness of this surface layer is 1.4 ± 0.4 nm.     

The interdependence of structural and electrical properties in TiO2/TiO/Ti periodic multilayers

Multilayered structures with 14–50 nm periods composed of titanium and two different titanium oxides, TiO and TiO₂, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. The structure and composition of these periodic TiO₂/TiO/Ti stacks were investigated by X-ray diffraction and transmission electronic microscopy techniques. Two crystalline phases, hexagonal close packed Ti and face centred cubic TiO, were identified in the metallic-rich sub-layers, whereas the oxygen-rich ones comprised a mixture of amorphous TiO₂ and rutile phase. DC electrical resistivity ρ measured for temperatures ranging from 300 to 500 K exhibited a metallic-like behaviour (ρ_473K = 1.05 × 10^?5 to 1.45 × 10^?6 Ω m) with a temperature coefficient of resistance ranging from 1.20 × 10^?3 K^?1 for the highest period (Λ = 50.0 nm) down to negative values close to ?4.97 × 10^?4 K^?1 for the smallest one (Λ = 14.0 nm). A relationship between the dimensions of periodic layers and their collective electrical resistivity is proposed where the resistivity does not solely depend on the total thickness of the film, but also depends on the chemical composition and thickness of each sub-layer. Charge carrier mobility and concentration measured by the Hall effect were both influenced by the dimension of TiO₂/TiO/Ti periods and the density of ionized scattering centres connected to the titanium concentration in the metallic sub-layers.     

Magnetic,electronic and thermodynamic properties of the heavy fermion compound CeNiAl4

We have carried out the magnetic susceptibility, electrical resistivity, specific heat, thermoelectric power and X-ray photoemission spectroscopy (XPS) measurements for CeNiAl₄. The magnetic susceptibilities have revealed a Curie–Weiss behavior above 30 K with a large negative paramagnetic Curie temperature θ_P = ?66 K and an effective moment of 2.45μ_B. The f-occupancy and the coupling between the f level and the conduction states are derived from XPS to be about 0.83 and ～40–64 meV, respectively. The valence state of the Ce ion is close to 3+. Extrapolation of the lowest temperatures range of C/T(T²) yields the electronic specific heat coefficient γ = 0.5 J mol^?1 K^?2. In combination with the thermoelectric power and resistivity data, a heavy fermion state is confirmed in CeNiAl₄.     

Grain boundary diffusion and segregation of Ni in Cu

Grain boundary (GB) diffusion of ⁶³Ni in polycrystalline Cu was investigated by the radiotracer technique in an extended temperature interval from 476 to 1156 K. The independent measurements in Harrison’s C and B kinetic regimes resulted in direct data of the GB diffusivity D_gb and of the so-called triple product P = s · δ · D_gb (s and δ are the segregation factor and the diffusional GB width, respectively). Arrhenius-type temperature dependencies for both the D_gb and P values were measured, resulting in the pre-exponential factors $D_{\mathrm{gb}}^0=6.93\times {10}^{-7}$ m² s⁻¹ and P₀ = 1.89 × 10⁻¹⁶ m³ s⁻¹ and the activation enthalpies of 90.4 and 73.8 kJ mol⁻¹, respectively. Although Ni is completely soluble in Cu, it reveals a distinct but still moderate ability to segregate copper GBs with a segregation enthalpy of about −17 kJ mol⁻¹.     

Effect of particle/matrix interfacial character on the high-temperature deformation and recrystallization behavior of Cu with dispersed Fe particles

The effect of particle/matrix interfacial character on the high-temperature deformation and recrystallization behavior of Cu was systematically investigated at various temperatures from 723 to 973 K and at true strain rates between 4.1 × 10⁻⁴ and 3.2 × 10⁻² s⁻¹. Cu with dispersed coherent γ-Fe precipitates (Cu–γ-Fe alloy) displayed lower yield stresses and higher flow stresses than Cu containing incoherent α-Fe precipitates (Cu–α-Fe alloy) under all testing conditions. Dynamic recrystallization (DRX) took place more easily in the Cu–α-Fe alloy than in the Cu–γ-Fe alloy. Although DRX was strongly impeded by the presence of the coherent precipitates at low to medium strains, the recrystallized regions gradually spread, accompanied by transformation of the coherent precipitates into incoherent ones. Such a large difference in the deformation and DRX behaviors depending on the particle/matrix interfacial character is attributed to the stronger interaction between dislocations and the coherent particles.     

Texture development in Bi1.5Pb0.5Sr1.7Y0.5Co2O9−δ layered cobaltite by high-temperature compression deformation and its effect on thermoelectric properties

Texture development in Bi_1.5Pb_0.5Sr_1.7Y_0.5Co₂O_9−δ (BPSYO) layered cobaltite by plastic deformation is examined experimentally by high-temperature uniaxial compression, in order to develop a method to reduce the resistivity of thermoelectric cobaltite by controlling the spatial arrangement of the (0 0 1) conductive CoO₂ layers. It is found that the present oxide can be plastically deformed up to a true strain of −2.2 at 1113 K with strain rates in the order of 10⁻⁵ s⁻¹. It is concluded that high-temperature compression is effective both for densification and texture development. Evolution of (0 0 1) (compression plane) texture is experimentally confirmed as expected from the crystal structure, where a dislocation that has a small Burgers vector may move in the (0 0 1) plane. The formation of a sharp (0 0 1) texture results in a reduction in resistivity to about one-tenth of that of the specimen without texture. The estimated value of the dimensionless thermoelectric figure of merit is 0.11 at 973 K, which is close to the practical level of a thermoelectric material.     

Very rapid growth of aligned carbon nanotubes on metallic substrates

Aligned carbon nanotubes were grown on metallic substrates using a microwave plasma-enhanced chemical vapor deposition system. The substrates were Ni and Cu, and the catalyst was an Fe–Si alloy thin film. The effects of substrate and catalyst characteristics and growth temperature were studied. We show, via the use of a microwave shield, and with optimized catalyst thickness and growth temperature, that carbon nanotubes (CNTs) with a length of up to 2.15 mm and an unprecedently high growth rate of 177 μm min^?1 can obtained. Non-isothermal growth was performed to investigate the growth kinetics and therefore to obtain the activation energies of CNTs grown on Ni and Cu. Very similar activation energies for the growth of CNTs on Ni and Cu substrates were determined to be 101.5 (1.05 eV) kJ mol^?1 and 102.3 (1.06 eV) kJ mol^?1, respectively.     

MoOx interlayer to enhance performance of pentacene-TFTs with low-cost copper electrodes

We demonstrated that the electrical properties of pentacene-thin film transistors with low-cost Cu electrodes can be enhanced by inserting a thin MoO_x interlayer layer between pentacene and Cu source/drain (S/D) electrodes. In comparison with the device having Cu-only electrodes, the performance of the device with MoO_x/Cu electrodes was significantly improved. The saturation mobility increased from 0.13 to 0.61 cm²/V s, threshold voltage reduced from ?14.5 to ?7.3 V, on/off ratio shifted from 8.9 × 10⁵ to 1.6 × 10⁶ and threshold swing varied from 1.92 to 1.33 V/decade. The improvement was attributed to the reduction of contact resistance and the enhancement of hole-injection efficiency. The results suggest modification of Cu S/D electrodes is a simple and effective way to improve device performance and reduce the fabrication cost.     

Mechanical behavior of Σ tilt grain boundaries in nanoscale Cu and Al: A quasicontinuum study

Molecular simulations using the quasicontinuum method are performed to understand the mechanical response at the nanoscale of grain boundaries (GBs) under simple shear. The energetics and mechanical strength of 18 Σ 〈1 1 0〉 symmetric tilt GBs and two Σ 〈1 1 0〉 asymmetric tilt GBs are investigated in Cu and Al. Special emphasis is placed on the evolution of far-field shear stresses under applied strain and related deformation mechanisms at zero temperature. The deformation of the boundaries is found to operate by three modes depending on the GB equilibrium configuration: GB sliding by uncorrelated atomic shuffling, nucleation of partial dislocations from the interface to the grains, and GB migration. This investigation shows that (1) the GB energy alone cannot be used as a relevant parameter to predict the sliding of nanoscale high-angle boundaries when no thermally activated mechanisms are involved; (2) the E structural unit present in the period of Σ tilt GBs is found to be responsible for the onset of sliding by atomic shuffling; (3) GB sliding strength in the athermal limit shows slight variations between the different interface configurations, but has no apparent correlation with the GB structure; (4) the metal potential plays a determinant role in the relaxation of stress after sliding, but does not influence the GB sliding strength; here it is suggested that the metal potential has a stronger impact on crystal slip than on the intrinsic interface behavior. These findings provide additional insights on the role of GB structure in the deformation processes of nanocrystalline metals.     

CuO nanowire synthesis catalyzed by a CoWP nanofilter

This paper presents a new approach to synthesizing self-aligned, uniform single-crystal cupric oxide (CuO) nanowires on a Cu-based multilayer on SiO₂/Si. The key is to introduce CoWP as a nanofilter to catalyze CuO-nanowire synthesis simply by calcination at 400 °C in air. The CuO nanowires (diameter: 10–50 nm, length: 7 μm) exhibit low resistivity (10–60 Ω cm), a low turn-on field (4.5 V μm^?1) and a high field-enhancement factor (～1400).     

Ultrafine-grained copper produced by machining and its unusual electrochemical corrosion resistance in acidic chloride pickling solutions

Ultrafine-grained (UFG) copper was prepared by facile machining procedure. High resolution transmission electron microscopy images revealed that, in UFG Cu, minimum grain size of 80 nm could be formed when a small machining rake angle was applied. The electrochemical corrosion behavior of UFG Cu in 0.5 M HCl was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. Comparing with coarse-grained Cu, UFG Cu exhibited notably declined corrosion current density. Particularly, when the size of Cu grains were reduced from 500 μm to 80 nm, the charge transfer resistance of anodic dissolution step dramatically increased from 200 to 621 Ω cm².     

Thermoelectric properties of Sb-doped Mg2Si semiconductors

The thermoelectric properties of Sb-doped Mg₂Si (Mg₂Si:Sb = 1:x(0.001 ≦ x ≦ 0.02)) fabricated by spark plasma sintering have been characterized by Hall effect measurements at 300 K and by measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) between 300 and 900 K. Sb-doped Mg₂Si samples are n-type in the measured temperature range. The electron concentration of Sb-doped Mg₂Si at 300 K ranges from 2.2 × 10¹⁹ for the Sb concentration, where x = 0.001, to 1.5 × 10²⁰ cm⁻³ for x = 0.02. First-principles calculation revealed that Sb atoms are expected to be primarily located at the Si sites in Mg₂Si. The electrical resistivity, Seebeck coefficient, and thermal conductivity are strongly affected by the Sb concentration. The sample x = 0.02 shows a maximum value of the figure of merit ZT, which is 0.56 at 862 K.     

Synthesis and spectroscopic properties of a series of octacationic water-soluble phthalocyanines

The synthesis, characterization of newly synthesized metal-free 2 and metallophthalocyanine complexes 3–5 (MPcs, M = Ni, Co, Cu) and quaternized metallophthalocyanine derivatives 3a, 5a (MPcs, M = Ni, Cu) containing 4,5-bis(quinolin-6-yloxy) substituents have been presented in this work. The new compounds have been characterized by using elemental analysis, UV–vis, IR, ¹H NMR, ¹³C NMR and MS spectroscopic data. Also, aggregation properties of Pcs were investigated at different concentrations in chloroform, dimethylformamide and water. The effect of the concentration on the aggregation properties of complexes 2–5 was studied in chloroform. No aggregation was demonstrated in chloroform from concentration between 1 × 10^?5 and 0.4 × 10^?5 M.     

The characteristics of organic light emitting diodes with Al doped zinc oxide grown by atomic layer deposition as a transparent conductive anode

Al doped zinc oxide (AZO) films, deposited by atomic layer deposition (ALD) were investigated for applying a transparent conductive oxide (TCO) layer as an anode for organic light emitting diode (OLED) devices. AZO films with a thickness of 100 nm were deposited at various Al atomic ratios ranging from 0 to 5% at a deposition temperature (250 °C). The optimum electrical properties: the carrier mobility, the resistivity, and the sheet resistance for the 2% AZO film were found to be 16.2 cm² V^?1 s^?1, 1.5 × 10^?3 cm^?3, and 217 Ω/sq, respectively. The red OLED devices were fabricated using AZO anodes utilizing the various Al atomic ratios; the electrical and optical characteristics were then investigated. The best luminance, quantum efficiency, and current efficiency were found in the OLED device using the 2% AZO TCO; the results were 16599 cd/m², 8.2%, and 7.5 cd/A, respectively.     

Investigation of diffusion and electromigration parameters for Cu–Sn intermetallic compounds in Pb-free solders using simulated annealing

An efficient numerical method was developed to extract the diffusion and electromigration parameters for multi-phase intermetallic compounds (IMC) formed as a result of material reactions between under bump metallization (UBM) and solder joints. This method was based on the simulated annealing (SA) method and applied to the growth of Cu–Sn IMC during thermal aging and under current stressing in Pb-free solder joints with Cu-UBM. At 150 °C, the diffusion coefficients of Cu were found to be 3.67 × 10¹⁷ m² s⁻¹ for Cu₃Sn and 7.04 × 10¹⁶ m² s⁻¹ for Cu₆Sn₅, while the diffusion coefficients of Sn were found to be 2.35 × 10¹⁶ m² s⁻¹ for Cu₃Sn and 6.49 × 10¹⁶ m² s⁻¹ for Cu₆Sn₅. The effective charges of Cu were found to be 26.5 for Cu₃Sn and 26.0 for Cu₆Sn₅, and for Sn, the effective charges were found to be 23.6 for Cu₃Sn and 36.0 for Cu₆Sn₅. The SA approach provided substantially superior efficiency and accuracy over the conventional grid heuristics and is particularly suitable for analyzing many-parameter, multi-phase intermetallic formation for solder systems where quantitative deduction for such parameters has seldom been reported.