Novel pulsed electron deposition route to ZnO nanowire arrays

Well aligned ZnO nanowire arrays with uniform size are grown on Au-coated indium tin oxide substrates via a novel pulsed electron deposition (PED) technique. These nanowires have single-crystal hexagonal wurtzite structure and are grown along [0 0 0 1]. Au nanoparticles are found at the tip of the nanowires, indicating the growth process follows a typical vapor-liquid-solid mechanism. It is also found that the aligned ZnO nanowire arrays can be grown on Au-coated 6H-SiC and Si substrates, revealing that the PED technique is applicable for growth of ZnO nanowires on some common substrates. All the photoluminescence spectra of the ZnO nanowires reveal strong ultraviolet emission bands, indicating that the high-quality ZnO nanowires can be fabricated via the novel PED technique.     

Structural and optical properties of epitaxial ZnO thin films on 4H–SiC (0 0 0 1) substrates prepared by pulsed laser deposition

Epitaxially grown ZnO thin films on 4H–SiC (0 0 0 1) substrates were prepared by using a pulsed laser deposition (PLD) technique at various substrate temperatures from room temperature to 600 °C. The crystallinity, in-plane relationship, surface morphology and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements, respectively. XRD analysis showed that highly c-axis oriented ZnO films were grown epitaxially on 4H–SiC (0 0 0 1) with no lattice rotation at all substrate temperatures, unlike on other hexagonal-structured substrates, due to the very small lattice mismatch between ZnO and 4H–SiC of ～5.49%. Further characterization showed that the substrate temperature has a great influence on the properties of the ZnO films on 4H–SiC substrates. The crystalline quality of the films was improved, and surfaces became denser and smoother as the substrate temperature increased. The temperature-dependent PL measurements revealed the strong near-band-edge (NBE) ultraviolet (UV) emission and the weak deep-level (DL) blue-green band emission at a substrate temperature of 400 °C.     

Activity measurements of Al and Cu in Si–Al–Cu melt at 1273 and 1373 K by the equilibration with molten Pb

For the effective control of Al introduction to solidified Si during the solidification refining of Si with the Si–Al-based melt for the solar cell material or the LPE Si film growth processes from the Si–Cu–Al solvent, thermodynamic properties of the Si–Al–Cu melt were investigated at 1273 and 1373 K. Activities of Al and Cu in the Si–Al–Cu melt were measured by the equilibration with molten Pb. Also, the excess Gibbs energy of the melt was studied by the ternary regular solution model.

The evaluated thermodynamic properties of the Si–Al–Cu melt indicated that Cu addition to the Si–Al melt brings the smaller activity coefficient of Al and is effective for reducing the Al content of solidified Si from the melt more effectively than its dilution effect for Al.     

Microstructure and mechanical properties of Cr–Si–N coatings prepared by pulsed reactive dual magnetron sputtering

Cr–Si–N thin films were deposited by pulsed DC reactive dual-magnetron sputtering using Cr and Si targets, while various currents applied to the Si target allowed one to vary the Si content (C_Si) in the films. Microstructure, composition and mechanical properties were studied as a function of C_Si using XRD, ERD-TOF and depth-sensing indentation. Three regions of C_Si were distinguished: (i) C_Si < 2.3 at.%, where the grain size (D) does not significantly change with increasing C_Si; (ii) 2.3 < C_Si < 6.7 at.%, where D decreases as C_Si increases; and (iii) 6.7 ≤ C_Si ≤ 11.6 at.%, where a relatively rapid decrease of D is observed with increasing C_Si. We found that the hardness (H) and the reduced Young's modulus (E_r) of the films reached maximum values of H ~ 24 GPa and E_r ~ 240 GPa for C_Si ~ 2.3 at.%. Based on the evolution of the microstructural and mechanical properties of the Cr–Si–N films, we propose to explain the hardening observed for C_Si < 2.3 at.% in terms of the solid solution mechanism rather than the nanocomposite formation.     

Study on high-temperature oxidation behaviors of Cr–Si–N films

The high-temperature oxidation behavior of CrN and Cr–Si–N films was investigated. These films were deposited on STS 304 substrates by a hybrid deposition system with arc ion plating (AIP) and DC magnetron sputtering method using separate Cr (99.99%) and Si (99.99%) targets in a gaseous mixture of Ar and N₂. Good oxidation resistance of the CrN film was further improved by the incorporation of Si into the CrN film. The oxidation products of the Cr–Si–N film were Cr₂O₃ and amorphous SiO₂, which were gradually formed by the outward diffusion of Cr, Si, and N as well as the inward diffusion of oxygen. The oxidation kinetics of the specimen showed parabolic behavior, indicating that the diffusion process prevailed during oxidation. The oxidation activation energies for CrN, CrSi_0.10N, and CrSi_0.15N coatings are 303.8, 316.4, and 333.9 kJ/mol, respectively.     

Growth and Characterization of Pencil-Like ZnO Nanowires in the Presence of a Disturbance in Boundary Layer

Pencil-like zinc oxide(ZnO) nanowire was synthesized on Si(111) substrate through a simple vapor phase method using a mixture of zinc oxide and graphite as the source material. The source inside a quartz tube created a Zn-rich vapor that facilitated the formation and growth of ZnO nanowires. Field emission scanning electron microscopic studies indicated that pencil-like ZnO nanowires had a size of the range from 50 to 150 nm in diameter and several microns in length. X-ray diffraction was used to investigate the crystal structure of ZnO nanowires. Raman scattering and photoluminescence were applied to characterize the optical properties of the pencils. The growth mechanism of the nanopencils was discussed based on the growth conditions.     

Influence of Ti addition on the microstructure and hardness properties of near-eutectic Al–Si alloys

In this study, the influence of Ti addition on the microstructure and hardness of near-eutectic Al–Si has been investigated. Near-eutectic Al–Si alloys (13.1 wt.% Si) with 0.1, 1, 2, 3, 5, and 10% Ti have been utilized for this purpose. The melting operation was carried out in an electrical furnace, where the charge materials were placed in a graphite crucible. After melting, alloys have been cast in the metal mold at 1100 °C and solidified.     

Magnesium interlayered diamond coating on silicon

Diamond thin films have been deposited using hot filament chemical vapour deposition technique on manually scratched p-Si(1 0 0) substrate, with and without magnesium interlayer. In spite of magnesium melting point being lower (T_m = 649 °C) than the growth temperature of the substrate (T_s  750 °C) used in these experiments, it was found that high quality diamond films could be grown on Mg covered substrate. A liquid substrate is probably generated during the diamond film growth. Raman spectroscopy analysis exhibited only the triply degenerate, zone centre optical phonon peak at 1333 cm⁻¹ indicating that nearly stress free crystallites were present. Broadening of the Raman peak (11.76 cm⁻¹) indicates that some small crystallites also are present. Scanning electron and atomic force microscopy accompanied by X-ray diffraction analysis where used to compare the details of diamond film growth directly on scratched Si(1 0 0) and Mg interlayered scratched Si(1 0 0) substrates.     

The ternary system Na2O–ZnO–WO3: Compounds and phase relationships

The subsolidus phase relationships of ternary system Na₂O–ZnO–WO₃ have been investigated by X-ray diffraction (XRD) and differential thermal analyzer (DTA). All the samples were synthesized in the temperature range from 530 to 850 °C in air. There are one ternary compound and five binary compounds in the Na₂O–ZnO–WO₃ system, which can be divided into eight three-phase regions. The crystal structure of the ternary compound Na_3.6Zn_1.2(WO₄)₃ is determined by single-crystal structure analysis method. It belongs to triclinic system with space group and lattice constants a = 7.237 (5) Å, b = 9.172 (6) Å, c = 9.339 (6) Å and  = 94.920 (4)°, β = 105.772 (9)°, γ = 103.531 (8)°, Z = 2. DTA analyses indicate that the compound Na₂WO₄ is not suitable to be the flux for ZnO crystal growth below 1250 °C, since no liquidus was observed in the system before 1250 °C.     

Synthesis and characterization of LiGaxMn2−xO4 (0 ≤ x ≤ 0.05) by triethanolamine-assisted sol–gel method

Spinel LiGa_xMn_2−xO₄ (0 ≤ x ≤ 0.05) cathode materials with phase-pure particles and nano-sized distribution were synthesized by sol–gel method using triethanolamine as the chelating agent. The effects of heat treatment on the physicochemical properties of the spinel LiGa_xMn_2−xO₄ powders were examined with thermogravimetric and differential thermal analysis (TG/DTA), powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). The LiGa_xMn_2−xO₄ (0 ≤ x ≤ 0.05) electrodes were characterized electrochemically by charge/discharge experiments under a current rate of 0.5C at 55 °C. Although the Ga-doped spinel electrode showed smaller initial discharge capacity, it exhibited better cycling performance than the undoped-LiMn₂O₄ electrode. The dQ/dV versus potential plots at 55 °C revealed that the improvement in cycling performance of the Ga-doped spinel electrode is attributed to stabilization of the spinel structure by the presence of gallium ion.     

Structures and superparamagnetic properties of overaged Fe–Al–Mn–C alloys

Microstructures and superparamagnetic properties in aged-hardened Fe–9%Al–30%Mn– (x)C,Si alloys, resulting from overaging at a temperature of 823 K for 48 h to 313 days, have been investigated by transmission electron microscopy (TEM), X-ray diffraction patterns, and vibrating sample magnetometry (VSM). The results reveal that the precipitate κ-phase [(Fe,Mn)₃AlC] decomposition in this alloy, overaged at 823 K for one week, resulted from two separate mechanisms: (1) wetting of the antiphase boundary segment (APBs) of D0₃ [(Fe/Mn)₃Al] domains by the B2 [(Fe/Mn)Al] phase; and (2) precipitation of the B2 [(Fe/Mn)Al] phase within the domain. A superparamagnetic behaviour was discovered when the alloy was overaged at 823 K for ≈120–313 days. The super-soft magnetic property was mainly attributable to the ferromagnetic spinel-ordered (B2 [(Fe/Mn)Al]+D0₃ [(Fe/Mn)₃Al]) phases and ordered B2 with monoclinic ′Mn structures.     

An investigation of the Pd–Ag–Ru–Gd quaternary system phase diagram

On the basis of the Ag–Pd–Gd, Ag–Ru–Gd and Pd–Ru–Gd ternary systems, the partial phase diagram of Pd–Ag–Ru–Gd (Gd < 25 at.%) quaternary system has been studied by means of X-ray diffraction analysis, differential thermal analysis, electron probe microanalysis and optical microscopy. The 700 °C isothermal sections of the Ag–Pd–5Ru–Gd, Ag–Pd–20Ru–Gd and Ag–Pd–50Ru–Gd (Gd ≤ 25 at.%) phase diagrams were determined, respectively. And the 700 °C isothermal section of the Pd–Ag–Ru–Gd (Gd ≤ 25 at.%) quaternary system phase diagram was finally inferred. The section consists of four single-phase regions: solid solution Pd(Ag), (Ru), Pd₃Gd and Ag₅₁Gd₁₄; five two-phase regions: Pd(Ag) + (Ru), Pd(Ag) + Ag₅₁Gd₁₄, (Ru) + Ag₅₁Gd₁₄, Pd(Ag) + Pd₃Gd and (Ru) + Pd₃Gd; three three-phase regions: Pd(Ag) + Pd₃Gd + (Ru), Pd(Ag) + Ag₅₁Gd₁₄ + (Ru) and (Ru) + Ag₅₁Gd₁₄ + Pd₃Gd; one four-phase region Pd(Ag) + (Ru) + Ag₅₁Gd₁₄ + Pd₃Gd. No new quaternary intermetallic phase has been found.     

Effect of ZnO additive on sintering behavior and microwave dielectric properties of 0.95MgTiO3–0.05CaTiO3 ceramics

The effects of ZnO additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO₃–CaTiO₃ ceramics were investigated. The sintering temperature of ZnO-doped 0.95MgTiO₃–0.05CaTiO₃ ceramics can be lowered to 1300 °C due to the liquid phase effect. Formation of second phase MgTi₂O₅ can be effectively restrained through the addition of ZnO. The microwave dielectric properties are found strongly correlated with the sintering temperature as well as the amount of ZnO addition. At 1300 °C, 0.95MgTiO₃–0.05CaTiO₃ ceramics with 1 wt% ZnO addition possesses a dielectric constant _r of 20, a Q × f value of 65,000 (at 7 GHz) and a τ_f value of −5.8 ppm/°C. In comparison with pure 0.95MgTiO₃–0.05CaTiO₃ ceramics, the doped sample shows not only a 16% loss reduction but also a lower sintering temperature. That makes it a very promising material to replace the present one for GPS patch antennas.     

Subsolidus phase relations in the ZnO–MoO3–B2O3, ZnO–MoO3–WO3 and ZnO–WO3–B2O3 ternary systems

The subsolidus phase relations in the ZnO–MoO₃–B₂O₃, ZnO–MoO₃–WO₃ and ZnO–WO₃–B₂O₃ ternary systems have been investigated by the means of X-ray powder diffraction (XRD). There is no ternary compound in all the systems. There are five binary compounds and five tie lines in the ZnO–MoO₃–B₂O₃ system. This system can be divided into six 3-phase regions. There are three binary compounds and three tie lines in the ZnO–MoO₃–WO₃ system. This system can be divided into four 3-phase regions. There are four binary compounds and four tie lines in the ZnO–WO₃–B₂O₃ system. This system can be divided into five 3-phase regions. The possible component regions for ZnO single crystal flux growth were discussed. The phase diagram of Zn₃B₂O₆–ZnWO₄ pseudo-binary system has been constructed, and the result reveals this system is eutectic system. The eutectic temperature is 1007 °C and eutectic point component is 70 mol% Zn₃B₂O₆.     

The Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system

Following up on recent studies of the isothermal section of the Zn–Fe–Ni, Zn–Fe–Bi and Zn–Bi–Ni ternary systems at 450 °C, the Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system with the Zn being fixed at 93 at.% was determined experimentally using the equilibrated alloys approach. The specimens were investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). It was found there exist 4 two-phase regions, 5 three-phase regions and 2 four-phase regions. Two liquid L (Zn) and L (Bi) can coexist with T, ζ and δ-Ni in this isothermal section, no new phase was found in this study.     

The 260 °C phase equilibria of the Sn–Sb–Ag ternary system and interfacial reactions at the Sn–Sb/Ag joints

The isothermal section of the Sn–Sb–Ag ternary system at 260 °C has been determined in this study by experimental examination. Experimental results show no existence of ternary compounds in the Sn–Sb–Ag system. Two extensive regions of mutual solubility have been determined. The one located between the two binary isomorphous phases, Ag₃Sn and Ag₃Sb, is labeled as and the other one located between the two binary isomorphous phases, Ag₄Sn and Ag₄Sb, is labeled as ξ. The phase is a very stable phase and is in equilibrium with ξ, Sb, SbSn, Sb₂Sn₃, and liquid Sn phases. Each of the Sb and SbSn phases has a limited solubility of Ag. Only one stoichiometric compound, Sb₂Sn₃, exists. Besides phase equilibria determination, the interfacial reactions between the Sn–Sb alloys and the Ag substrate were investigated at 260 °C. It was found that the phase formations in the Sn–Sb/Ag couples are very similar to those in the Sn/Ag couples.     

Observations on the growth of Al–Ni–Co decagonal thin films by atomic force microscopy and transmission electron microscopy

Thin films of Al–Ni–Co alloy were produced by vacuum deposition technique using a substrate material of amorphous carbon thin-foil. Attempts were made to obtain a homogeneous decagonal quasicrystalline film, where the preparation technique was based on the direct evaporation of pre-alloyed ingot of Al₇₂Ni₁₅Co₁₃ onto the heated substrates. In order to explore early stages of the decagonal film growth, the Al–Ni–Co films with different thicknesses ranging from 2 nm to 30 nm were deposited on either substrates heated at 500 °C or non-heated substrates. The film samples so obtained were examined mainly by atomic force microscopy in combination with transmission electron diffraction and imaging techniques. On the basis of these observations, deposition conditions necessary for the growth of decagonal phase in the resulting films as well as the growth mechanism of the decagonal film will be discussed.     

The temporal evolution of the decomposition of a concentrated multicomponent Fe–Cu-based steel

The nucleation (to a limited extent), growth and coarsening behavior of Cu-rich precipitates in a concentrated multicomponent Fe–Cu-based steel aged at 500 °C from 0.25 to 1024 h is investigated. The temporal evolution of the precipitates, heterophase interfaces, matrix compositions and precipitate morphologies are presented. With increasing time, Cu partitions to the precipitates, Ni, Al and Mn partition to the interfacial region, whereas Fe and Si partition to the matrix. Coarsening time exponents are determined for the mean radius, R(t), number density, N_V(t), and supersaturations, which are compared to the Lifshitz–Slyzov–Wagner (LSW) model for coarsening, modified for concentrated multicomponent alloys by Umantsev and Olson (UO). The experimental results indicate that the alloy does not strictly follow UO model behavior. Additionally, we delineate the formation of a Ni–Al–Mn shell with a stoichiometric ratio of 0.51:0.41:0.08 at 1024 h, which reduces the interfacial free energy between the precipitates and the matrix.     

Ultrafine hardmetals prepared by WC–10 wt.%Co composite powder

Ultrafine tungsten carbide–cobalt (WC–10 wt.%Co) composite powder was synthesized via spray-drying and direct reduction and carburization process in vacuum, which includes precursor preparation by spray-drying of a suspension of ammonium metatungstate (AMT) and cobalt carbonate (CoCO₃), calcination to evaporate volatile components, formation of tungsten–cobalt mixed oxide powder (CoWO₄/WO₃), ball-milling with carbon black, and subsequent direct reduction and carburization reaction in vacuum. The synthesis temperature of WC–10 wt.%Co composite powder without η or graphite phases is lower than 1000 °C. The calculated particle size by BET test is 0.29 μm. Coarse WC powder (FSSS: 0.9 μm) and Co powder (FSSS: 1.0 μm) (WC:Co = 9:1 in mass) were added into the obtained WC–10 wt.%Co composite powder with addition of 30 wt.%, 50 wt.% and 70 wt.%, respectively. Results show that the hardmetal fabricated from 70 wt.% (WC–10 wt.%Co composite powder) + 30 wt.% (90 wt.%WC + 10 wt.%Co coarse powder) mixed powders exhibits a fine microstructure as well as optimum mechanical properties.     

Investigations of interfacial reactions of Sn–Zn based and Sn–Ag–Cu lead-free solder alloys as replacement for Sn–Pb solder

The interfacial reactions of Sn–Zn based solders and a Sn–Ag–Cu solder have been compared with a eutectic Sn–Pb solder. During reflow soldering different types of intermetallic compounds (IMCs) are found at the interface. The morphologies of these IMCs are quite different for different solder compositions. As-reflowed, the growth rates of IMCs in the Sn–Zn based solder are higher than in the Sn–Ag–Cu and Sn–Pb solders. Different types of IMCs such as γ-Cu₅Zn₈, β-CuZn and a thin unknown Cu–Zn layer are formed in the Sn–Zn based solder but in the cases of Cu/Sn–Pb and Cu/Sn–Ag–Cu solder systems Cu₆Sn₅ IMC layers are formed at the interface. Cu₆Sn₅ and Cu₃Sn interfacial IMCs are formed in the early stages of 10 min reflow due to the limited supply of Sn from the Sn–Pb solder. The spalling of Cu–Sn IMCs is observed only in the Sn–Ag–Cu solder. The size of Zn platelets is increased with an increase of reflow time for the Cu/Sn–Zn solder system. In the case of the Sn–Zn–Bi solder, there is no significant increase in the Zn-rich phases with extended reflow time. Also, Bi offers significant effects on the wetting, the growth rate of IMCs as well as on the size and distribution of Zn-rich phases in the β-Sn matrix. No Cu–Sn IMCs are found in the Sn–Zn based solder during 20 min reflow. The consumption of Cu by the solders are ranked as Sn–Zn–Bi > Sn–Ag–Cu > Sn–Zn > Sn–Pb. Despite the higher Cu-consumption rate, Bi-containing solder may be a promising candidate for a lead-free solder in modern electronic packaging taking into account its lower soldering temperature and material costs.