Search

The evolution of roughness in the Cu6Sn5 intermetallic compound during the soldering reaction of PbSn on Cu and its effects on wettability has been studied. Results indicate that the root mean square roughness and the average distance between asperites have a parabolic dependence on the soldering time. However the ratio of the root mean square roughness with the average distance was observed to increase gradually for the range of soldering periods examined.

A-plane InxGa1-xN/GaN (x=0.09, 0.14, 0.24, and 0.3) multiple-quantum-wells (MQWs) samples, with a well width of about 4.5 nm, were achieved by utilizing r-plane sapphire substrates. Optical quality was investigated by means of photoluminescence (PL), cathodoluminescence, and time resolved PL measurements (TRPL). Two distinguishable emission peaks were examined from the low temperature PL spectra, where the high- and low-energy peaks were ascribed to quantum wells and localized states, respectively. Due to an increase in the localized energy states and absence of quantum confined Stark effect, the quantum efficiency was increased with increasing indium composition up to 24%. As the indium composition reached 30%, however, pronounced deterioration in luminescence efficiency was observed. The phenomenon could be attributed to the high defect densities in the MQWs resulted from the increased accumulation of strain between the InGaN well and GaN barrier. This argument was verified from the much shorter carrier lifetime at 15 K and smaller activation energy for In0.3Ga0.7N/GaN MQWs. In addition, the polarization-dependent PL revealed that the degree of polarization decreased with increasing indium compositions because of the enhancement of zero-dimensional nature of the localizing centers. Our detailed investigations indicate that the indium content in a-plane InGaN/GaN MQWs not only has an influence on optical performance, but is also important for further application of nitride semiconductors. [ABSTRACT FROM AUTHOR]

Pressure-induced resonant Raman scattering is adopted to analyze the zone-center optical phonon modes and crystal characteristics of Zn1-xMnxTe (0≤x≤0.26) thin films. The pressure (Pt) at which the semiconducting undergoes a transition to the metallic phase declines as a function of Mn concentration (x) according to the formula Pt(x)=15.7-25.4x+19.0x2 (GPa). Pressure-dependent longitudinal and transverse optical phonon frequencies and the calculated mode Grüneisen parameters were adopted to investigate the influence of Mn2+ ions on the iconicity. The experimental results indicate that the manganese ions tend to increase the iconicity of ZnTe under ambient conditions, whereas an external hydrostatic pressure tends to reduce the iconicity and the bond length of Zn1-xMnxTe. [ABSTRACT FROM AUTHOR]

The vibrational, electronic, and crystalline properties of n-type chlorine-doped ZnSe (ZnSe:Cl) layers with a carrier concentration from 8.2×1015 to 1.8×1018 cm-3 are studied by Raman spectroscopy. The spectral line shapes of the longitudinal-optical-phonon and plasmon coupling mode are analyzed using the Raman scattering efficiency and the dielectric function to obtain the electron densities and mobility. The splitting of the transverse-optical (TO) phonon and the redshift of the chlorine-related impurity vibration mode are clearly observed when pressure is applied. The semiconductor-to-metal phase transition pressure of ZnSe:Cl layers declines as the carrier concentration increases, indicating that n-type doping reduces crystal stability. Additionally, the pressure-induced weakening of the longitudinal-optical-phonon-plasmon coupling efficiency suggests that pressure tends to degrade the n-type characteristic of ZnSe:Cl because of the emergence of the new deep donorlike state. [ABSTRACT FROM AUTHOR]

The nanostructure formation of the Stranski–Krastanow (SK) systems is investigated by simulating the surface undulation of the systems driven by the surface diffusion mechanism. Of particular interest is how the surface undulation leads to the development of faceted nanostructures and wetting layers. The results reveal that the development exhibits three common features in the coarsening SK systems, while the development also results in distinct film morphologies, controlled by the maximum surface coverage of faceted islands. The maximum surface coverage depends on the film thickness, the ratio between the two characteristic lengths of the SK system, and the effective surface energy density of flat film. [ABSTRACT FROM AUTHOR]

Raman and photoluminescence spectra of cubic Zn1-xCdxSe (0≦x≦0.32) epilayers were obtained at high pressure. The impurity mode I observed in the phonon Raman spectra at low temperature confirms the intermediate phonon mode behavior. A split transverse optical phonon mode was found in the down-stroke high-pressure Raman scattering. Additionally, the pressure-dependent longitudinal optical (LO) phonon frequencies and the Grüneisen parameter (γLO) were obtained by quadratic polynomial fitting. Pressure-driven resonant Raman scattering effect was observed in samples with a high Cd concentration (x≧0.18). The critical pressure of semiconductor-to-metal phase transition (Pt) decreases as the Cd content increases. As the Cd concentration increases from 0 to 0.32, Pt falls from 13.6 to 9.4 GPa, according to Pt (GPa)=13.6-6.8x-20.3x2. [ABSTRACT FROM AUTHOR]

The paper presents the first-order perturbation solutions to the two-dimensional elasticity problems of strained wires embedded in a multilayered film-substrate system with homogeneous elastic properties. The solutions are accurate to the first order of the characteristic slope of the wires; the expressions of the solutions are concise for wires containing multiple facets; and the solutions are valid for single wire, multiple wires with different shapes, and a periodic array of identical wires. The perturbation solutions provide an efficient scheme for studying the effects of embedded wires on the stresses in the multilayered system. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of Pr9+xFe73-x-yTiyCo10B4C4 (x=0,0.5,1,1.5; y=0,2) melt-spun ribbons have been investigated. All these ribbons consist mainly of three phases, namely, 2:14:1, α-(Fe,Co), and 2:17 phases. It was found that the grain size of these phases decreases with increasing Pr content. A small substitution of Ti for Fe suppresses the grain growth of α-(Fe,Co) phase. The intergranular exchange coupling remarkably increases with increasing Pr and Ti substitution. For Ti-free Pr9+xFe73-xCo10B4C4 ribbons, the iHc increases, and Br decreases, but (BH)max nearly keeps invariable up to x=1.0, then slightly increases, with increasing x. A Br of 9.1 kG, iHc of 10.0 kOe, and (BH)max of 12.5 MG Oe were obtained in Pr10.5Fe71.5Co10B4C4. The coercivity and demagnetization-curve shape are substantially improved with Ti substitution, without a sacrifice of remanence (except for x=0). The (BH)max increases by a large amount (∼5 MG Oe) with a small substitution (2 at. %) of titanium. A Br of 9.6 kG, iHc of 10.2 kOe, and (BH)max of 17.4 MG Oe have been achieved in Pr10.5Fe69.5Ti2Co10B4C4 ribbon. [ABSTRACT FROM AUTHOR]

The phase evolution, microstructure, and magnetic properties of PrxFe80-xTi2Co10B4C4 (x=9,10.5) melt-spun ribbons were studied. All these ribbons consist mainly of three phases, namely, 2:14:1, α-(Fe,Co), and 2:17 phases. The iHc significantly increases and Br slightly decreases with increasing Pr content. It was found that increasing Pr content from 9 to 10.5 at. % leads to marked grain refinement in the ribbons. Increasing Pr content also helps suppress the formation of metastable 2:17 phase and the grain growth of the α-(Fe,Co) phase during the annealing treatment, thus avoiding the formation of extensive soft magnetic regions. The refined and uniform structure tends to enhance the exchange-coupling interaction between magnetic grains, which results in a significant improvement of the demagnetization-curve shape and magnetic properties accordingly. High coercivity iHc of 10.2 kOe, remanence Br of 9.6 kG, and maximum energy product (BH)max of 17.4 MG Oe have been achieved in Pr10.5Fe69.5Ti2Co10B4C4 ribbons after optimal annealing. [ABSTRACT FROM AUTHOR]

Effects of Co content on the magnetic properties and microstructure of melt-spun [(Fe1-xCox)0.675Pt0.325]84B16 (x=0–0.5) and [(Fe1-yCoy)0.725Pt0.275]85B15 (y=0 and 0.3) nanocomposite ribbons have been investigated. The substitution of Co for Fe in [(Fe1-xCox)0.675Pt0.325]84B16 ribbons enhances the coercivity (iHc) from 7.5 kOe for x=0 to 10 kOe for x=0.3, due to the formation of ordered L10-(Fe,Co)Pt phase with higher anisotropy field. The effect of Co substitution for Fe in [(Fe1-yCoy)0.725Pt0.275]85B15 series ribbons is similar to that in [(Fe1-xCox)0.675Pt0.325]84B16 system. Interestingly, larger magnetization could be obtained by decreasing the boron and Pt content simultaneously. Moreover, L10-(Fe,Co)Pt phase provides [(Fe0.7Co0.3)0.725Pt0.275]85B15 ribbons sufficient high coercivity iHc=5.4 kOe, resulting in a remarkable enhancement of energy product from 10.0 MG Oe for Co-free ribbons to 15.7 MG Oe for ribbons with y=0.3. [ABSTRACT FROM AUTHOR]

Magnetic properties, phase evolution, and microstructure of melt spun SmCo7-xHfxCy (x=0–0.5; y=0–0.14) ribbons via direct quenching have been investigated. For SmCo7-xHfx series ribbons, proper volume fraction of Hf is effective to stabilize and increase the magnetocrystalline anisotropy field of the TbCu7-type structure. Accordingly, the optimal magnetic properties of Br=6.4 kG, iHc=7.3 kOe, and (BH)max=8.7 MG Oe could be obtained for x=0.1. Furthermore, a slight C addition to above alloys is helpful in refining the grain size of the ribbons from 100–400 nm for C-free to 10–80 nm for C-containing samples. As a result, the magnetic properties are further improved to Br=6.9 kG, iHc=11.8 kOe, and (BH)max=10.6 MG Oe for SmCo6.8Hf0.2C0.12 nanocomposite ribbons. [ABSTRACT FROM AUTHOR]

The effect of Au content on the magnetic properties and microstructure of melt spun (FePt)100-xAux (x=0–40) ribbons have been investigated. X-ray diffraction and thermal magnetic analysis results indicate that Au-rich phase coexists with ordered L10-FePt(Au) phase in ternary FePtAu ribbons after an isothermal annealing. Meanwhile, the Curie temperature of L10-FePt(Au) phase in annealed (FePt)100-xAux (x=0–40) ribbons is almost unchanged, revealing that higher volume fraction of Au addition does not modify the composition of the L10-FePt(Au) phase. All the Au containing ribbons exhibit a completely isolated L10-FePt(Au) granular structure, and the grain size is effectively decreased with the increase of Au content. As a result, the intrinsic coercivity (iHc) of the ribbons increases substantially from 2.1 kOe for binary FePt to 19.5 kOe for (FePt)60Au40. [ABSTRACT FROM AUTHOR]

Phase evolution, microstructure, and magnetic properties of melt-spun Pr9FebalTixB11-yCy (x=0, 2.5, and 4, y=0–11) ribbons have been investigated. For Pr9FebalTixB11-yCy series ribbons, addition of Ti suppresses the formation of metastable Pr2Fe23B3 phase and ensures the existence of a large amount of magnetically hard Pr2Fe14B phase in the ribbons. However, the increase of C substitution in the Pr9FebalTi2.5B11-yCy (y=0–5.5) ribbons diminishes the Br, iHc, and (BH)max monotonically, which comes from the increase of volume fraction of Pr2Fe17Cz and α-Fe phases and the rapid decrease of the 2:14:1 phase. Only in the higher Ti content Pr9FebalTi4B11-yCy ribbons, a slight C addition cannot only form the Pr2Fe14(B,C) phase but also refine the grain size, giving rise to the improvement of magnetic properties. The optimal properties of Br=9.4 kG, iHc=11.1 kOe, (BH)max=18.0 MGOe, α=-0.207%/°C, and β=-0.612%/°C are achieved in Pr9FebalTi4B10.5C0.5 nanocomposites. [ABSTRACT FROM AUTHOR]

Magnetic properties, microstructure, and phase evolution of (Ce1-xPrx)9.5Febal.CoyTi2B10 (x=0–1 and y=0, 2.5) nanocomposites have been investigated. A progressive substitution of Pr for Ce enhances the remanence (Br), intrinsic coercivity (iHc), and maximum energy product [(BH)max] of the ribbons effectively. In addition, the Curie temperature of 2:14:1 phase also increases with increasing Pr concentration. For Co-free (Ce1-xPrx)9.5Febal.Ti2B10 ribbons, magnetically hard 2:14:1 phase and two soft phases, α-Fe and Fe3B, are found in the ribbons with x=0, 0.3, 0.4, and 0.7, while Fe3B phase disappears in the ribbons with x=1. On the other hand, the value of Br, (BH)max, temperature coefficient α, and Curie temperature of 2:14:1 and α-Fe are improved with a slight substitution of 2.5 at. % Co for Fe. The magnetic properties of Br=8.5 kG, iHc=7.5 kOe, (BH)max=13.5 MGOe, α=-0.185%/°C, and β=-0.54%/°C can be achieved in (Ce0.5Pr0.5)9.5Febal.Co2.5Ti2B10 nanocomposites. [ABSTRACT FROM AUTHOR]

Magnetic aftereffect and surface magnetic domain structure of (Fe0.675Pt0.325)100-xBx(x=12–20) nanocomposites have been investigated for correlating with their corresponding phases and magnetic properties. Exchange-coupling effect between grains is present for all the studied ribbons as evidenced by Henkel plot. The volume fraction of magnetically soft phases decreases with increasing B concentration from x=12 to x=18. It leads to the reduction in the activation volume of the reverse domain. Among all samples, the (Fe0.675Pt0.325)82B18 ribbon having the highest intrinsic coercivity (iHc) exhibits minimum value in activation volume V=1.1×10-18 cm3, because it possesses the least volume fraction of the magnetic soft phases, i.e., Fe2B or Fe3B phases. Magnetic force microscopy studies reveal the magnetic domain structures of the ribbons, confirming the existence of strong exchange coupling between magnetic grains. [ABSTRACT FROM AUTHOR]

The phase evolution, microstructure, and magnetic properties of melt-spun Pr11Febal.B8-xCx (x =0-8d and Pr11Febal.Co10B6C2 nanocomposites have been investigated. Summarizing the results of x-ray diffraction and thermal magnetic analysis for Pr11Febal.B8-xCx series ribbons, magnetically soft Fe3B and α-Fe phases are found to coexist with magnetically hard 2:14:1 phase for carbon-free (x=0) ribbons; three phases, namely, 2:14:1, Pr2Fe17Cy, and α-Fe, appear for x=2-6, while 2:14:1 phase is almost not formed in Pr11Febal.C8 ribbons. The optimal magnetic properties of Br =9.4 kG, iHc=9.3 kOe, and (BH)max=17.3 MGOe are obtained in Pr11Febal.B6C2. Substitution of 10 at. % Co for Fe in Pr11Febal.B6C2 ribbons refines the grain size of the existing 2:14:1, Pr2Fe17Cy, and α-(Fe,Co) phases and enhances the magnetic properties of the ribbons to Br=9.8 kG, iHc =10.4 kOe, (BH)max=19.0 MGOe. [ABSTRACT FROM AUTHOR]

Phase evolution and magnetic properties of melt-spun (Fe0.675Pt0.325)100-xBx (x=12-20) nanocomposite ribbons are investigated. For those ribbons spun at 45 m/s, followed with a 500 °C isothermal annealing for 1-6 h, the boron addition not only promotes disorder to order (γ!γ1) transformation but also leads to the formation of different kinds of Fe-borides. Pt exhibits a strong affinity to Fe during thermal processes in forming magnetically hard γ1(FePt) phase, leaving excess Fe to interact with B in forming Fe2B, Fe3B, or FeB. For x=12-18, all ribbons are composed of one hard phase, γ1-FePt, and three soft phases, γ-FePt, Fe2B, and Fe3B. But FeB also coexists for x =20. Through the exchange-coupling interaction between nanoscale γ1-FePt and multiple soft phases, record of magnetic properties of Br=9.4 kG, iHc=7.5 kOe, and (BH)max=14.0 MGOe has been successfully developed in isotropic (Fe0.675Pt0.325)84B16 ribbons, where the reduced remanence ratio (σr/σ12 kOe) is as high as 0.86. [ABSTRACT FROM AUTHOR]

Magnetic properties, phase evolution, and coercivity mechanism of melt-spun CoxZr98-xB2 (74⩽x⩽86) nanocomposites were studied systematically. From x-ray diffraction analysis, nearly single magnetic phase, Co23Zr6, is found in Co74Zr24B2 ribbon (x=74). With increasing Co content x, an additional phase, Co5Zr, is found for x=76; two phases, namely, fcc Co and Co5Zr, are found for x=78-84, but fcc Co is the only phase that can be detected in ribbon with x=86. The optimal magnetic properties of Br=5.13 kG (sr=49 emu/g), iHc=4.1 kOe, and (BH)max=5.1 MG Oe are obtained in Co80Zr18B2 ribbons quenched at Vs=45 m/s, which possesses Co5Zr and minor fcc-Co phases with nanoscale grain size (~50 and ~20 nm, respectively). Strong exchange-coupling effect occurred between grains as evidenced by the Henkel plot, giving rise to the improvement of remanence and magnetic energy product. The coercivity of CoxZr98-xB2 nanocomposites is mainly governed by reverse domain nucleation mechanism. [ABSTRACT FROM AUTHOR]