•A systematical study has been employed on 2D TiO2 nanosheets with the donor-acceptor codoping.•The (2Nb/2Ta + C) codoping in TiO2 nanosheets creates the delocalized midgap states.•The C-related systems are desirable visible and UV-light-driven photocatalysts.•The water splitting power of (Mo/W + 2N) codoped systems is improved with enhanced UV light response.•The high doping concentration means the stronger absorption ability of the solar energy.Here we explore the effect of charge-compensated donor-acceptor pairs (2Nb + C), (2Ta + C), (Mo + 2N) and (W + 2N) codoping on the electronic and optical properties of TiO2 nanosheets. The results demonstrate that the (2Nb + C) and (2Ta + C) codoping create the delocalized midgap states in TiO2 nanosheets. The appearance of impurity states extends the absorption edge of nanosheets to the visible light region. The interaction of the host and the foreign chiefly occurs at the band edges of the N-related systems, which reduces the band-gap by 0.5 eV. Although this large band-gap still renders the visible light inefficient, the enhanced UV light absorption has been observed. Besides, the position of absorption edge is independent on the doping concentration, but the higher codoping concentration yields stronger light absorption. Moreover, the band edge alignment verifies that the C-related systems are desirable visible and UV-light-driven photocatalysts for overall water splitting.

•The S vacancy defect is most likely to form under the Sn-rich conditions.•The S-on-Sn anti-site defect is most likely to form under the S-rich conditions.•The S-on-Sn anti-site in monolayer SnS2 can realize p-type semiconductor behavior.•The Sn vacancy, Sn-on-S anti-site and S adsorption defects can induce magnetism.•The room temperature ferromagnetism is available in S adsorption structure.The effect of intrinsic defects on the structural, electronic and magnetic properties of monolayer SnS2 has been studied using density functional theory. Among the possible intrinsic defects, S vacancy is the most energetically favorable intrinsic defect under the Sn-rich condition, while S-on-Sn anti-site defect is most likely to form under the S-rich condition. Besides, S-on-Sn anti-site defect can realize p-type semiconductor behavior. Additionally, Sn vacancy, Sn-on-S anti-site and S adsorption on the top of S atom from the upper triple layer defects can induce magnetism, which originates mainly from the nearest-neighbor S atoms close to the Sn vacancy, Sn substitutional atom and S adatom, respectively. Moreover, the room temperature ferromagnetism is possible to be realized in monolayer SnS2 with S adsorption on the top of S atom from the upper triple layer defects. These predictions give a new path to explore monolayer SnS2-based magnetic nanomaterials.

•Microstructures of solder alloys are refined and reach the best with 0.03 wt.% addition of graphene nanosheets (GNSs).•The ductility of Sn58Bi shows 49% enhancement with 0.01 wt.% GNSs addition.•The tensile strength influenced by the variation of microstructures is enhanced by 14% with 0.1 wt.% GNSs addition.•Addition of GNSs improves the wettability, corrosion resistance and hardness effectively.In this study, graphene nanosheets (GNSs) with various percentages (0, 0.01, 0.03, 0.05 and 0.1 wt.%) were successfully incorporated into Sn58Bi lead-free solder. The effects of GNSs on the microstructure, tensile properties, wettability, corrosion resistance, hardness and creep behavior were subsequently investigated. The results show that GNSs refine the microstructure with different features and enhance the wettability efficiently. Tensile and nanoindentation tests reveal that the composite solder with 0.1 wt.% GNSs exhibits about 14% and 38% enhancement in tensile strength and hardness, respectively. With 0.01 wt.% GNSs addition, the elongation is 49% greater than that of the pure Sn58Bi solder alloy. The creep performance and the corrosion resistance are all enhanced by addition of GNSs. The enhancing mechanism of GNSs on the performance of composite solder alloy is also analyzed in this work.Download high-res image (168KB)Download full-size image

In this work, graphene nanosheets (GNSs) functionalized SnBi solder alloys were synthesized and the effects of GNSs addition on the microstructure evolution and mechanical properties of SnBi alloys during solid-state aging were investigated. The results show that the microstructure and mechanical properties of solders enhanced by 0.03 wt% GNSs addition possess the best performance during solid-state aging. After 360 h aging at 100 °C, the coarse microstructure and growing grains in pure SnBi are effectively inhibited in the GNSs reinforced solders, meanwhile the ultimate tensile strength and elastic modulus of pure samples are improved by 15% and 24% in SnBi-0.03GNSs samples. The failure features after aging show that GNSs can restrain the formation and propagation of micro-cracks at the fracture surface of SnBi alloys. The hardness of solders is also enhanced by GNSs and varies with tensile strength following a linear relationship. Moreover, the strengthening mechanism of GNSs in the composite solders during aging treatment is also analyzed.

•Na-doped SnO2 nanoparticles were prepared by hydrothermal growth method.•All the nanoparticles show ferromagnetism and the ferromagnetism is enhanced due to Na doping.•The origin of ferromagnetism is analyzed by the first-principles calculation.•Holes are responsible for the mediating ferromagnetism of Na-doped SnO2 NPs.Sn1−xNaxO2 nanoparticles (about 5 nm) have been successfully synthesized by a template-free hydrothermal growth method. XRD and XPS analyses reveal that the incorporated Na atoms substitute for Sn atoms in SnO2 lattice. The absorption spectra data show the band-gap decreases at low doping concentration (x ≤ 4%). With further doping, a transformation of Na atoms from substitutional sites to interstitial sites occurs. Magnetic measurements at room temperature showed a weak ferromagnetic behavior characterized by an open hysteresis loop. Their saturation magnetization MS increases initially with increasing Na concentrations and the largest saturation magnetization of 1.1 memu/g appears in Sn0.96Na0.04O2; however for x > 0.04, MS decreases. With the combination of defect analysis based on experimental results and first-principle calculations of the possible magnetic defect centers in Na-doped SnO2, the effect of defects on the nature and origin of ferromagnetism was investigated. The results suggest in Na-doped SnO2 nanoparticles the holes created by Na substituted incorporation may be the origin of the ferromagnetism in Na-doped SnO2 nanoparticles.

The effects of substitution of Cu and Au for Ni on the mechanical, thermodynamic and electronic properties of two different Ni3Sn2 structures are investigated by first-principles calculations. Cu atom at Ni2 site and Au atom at Ni1 site of the η phase lead to the thermodynamic stable structure. For the λ phase, Au atom can only replace the Ni1 site. Substitution causes the decrease of the polycrystalline elastic modulus and the Debye temperature. The degree of anisotropy along Z axis decreases dramatically for η phase, but it increases along Y axis for λ phase after substitution. The Ni3Sn2-based intermetallics are all ductile; the η phase is more ductile than the λ phase. The electronic density of states manifest an energy gap appearing in η phase and the effective mass of the η phase is lower than λ phase.

In this work, Cu6Sn5 nanoparticles in dimension of 10 nm are synthesized and first applied to improve the SnBi solder alloys. The microstructure, tensile properties, creep behavior and corrosion resistance of the composite solder are all investigated. Furthermore, solder with 0.05 wt% Cu6Sn5 nanoparticles presents the best performance among all the samples. Addition of Cu6Sn5 nanoparticles refines the microstructure of SnBi solder. Comparing with the pure sample, tensile properties of the composite one perform a brittle to ductile change. The nanoindentation test reveals that the creep resistance of SnBi-Cu6Sn5 samples is enhanced through the creep mechanism transformation. In corrosion experiments, samples with nanoparticles exhibit a lower corrosion rate. This reinforcement from nanoparticles of intermetallic compounds will provide us a new cognition in solder micro-alloying.

•A systematical study has been employed on SrTiO3 with the donor-acceptor codoping.•The donor-acceptor pair codoping yields the absorption edge extend to visible light.•The formation energy implies that the codoped systems are favorable under the O-rich condition.•The Nb@Ti/N@O system is desirable for the spontaneous water splitting under visible light.•The Nb@Sr/B@O system can split water into hydrogen in presence of sacrificial agent.In this study, the extensive density functional theory calculations are performed to modify the electronic structure of perovskite SrTiO3 by doping with Nb and N/B. The unoccupied states induced by the Nb monodoping at the Sr or Ti site, which were passivated in the codoped systems (the substitution of Nb at Ti site with the replacement of N at O site: Nb@Ti/N@O and the substitution of Nb at Sr site with the replacement of B at O site: Nb@Sr/B@O). The charge-compensated donor-acceptor pair codoping creates the new occupied states within the band gap, which yields the absorption edge extend to visible light. And the calculated defect formation energy implies that the codoped systems are energetically favorable under the O-rich condition. Moreover, the band-edge alignment confirmed that the Nb@Ti/N@O system is desirable for the spontaneous water splitting under visible light and the Nb@Sr/B@O system can split water into hydrogen in presence of sacrificial agent.

The structural, elastic and electronic properties of quaternary intermetallic compounds η-Cu4.5Ni1Au0.5Sn5 and η-Cu5Ni1Sn4.5In0.5 are investigated by an ab initio method. The calculated heat of formation determines preferential occupancy sites for Ni, Au and In atoms which lead to thermodynamically stable compounds. Variation of lattice constants reveals that the change of atomic bonding has a directional discrepancy in η-Cu4.5Ni1Au0.5Sn5; the polycrystalline moduli obtained from single-crystal elastic stiffness show an increase after both Ni/Au and Ni/In additions. Also, the anisotropy of Young’s modulus and shear modulus is significantly weakened in η-Cu4.5Ni1Au0.5Sn5. The density of states and maps of charge density distribution suggest that the atomic bonding in the quaternary intermetallic compounds is strengthened by the addition of Ni and Au but weakened by the addition of In.

•Novel Ni-doped SnO microflowers have been synthesized by hydrothermal growth method.•The low doping narrows the Eg while the high doping has the opposite effect.•The analysis of PL spectra reveals that surface defects are present in all samples.•The ferromagnetism originated from tin vacancies is discovered firstly in SnO.Sn1-xNixO microflowers self-assembled with nanopetals have been synthesized successfully with template-free hydrothermal growth method. Field-emission scanning electron microscopy results exhibit the flower-like architecture consist of nanopetals, which have lateral dimensions of 1–2 μm with a thickness of ∼100 nm. X-ray diffraction results show that all the samples possess typical tetragonal structure and Ni would occupy different positions (NiSn and Nii) with various concentrations. The bandgap of SnO tends to shrink firstly then widen after Ni-doping, which is caused by the sp-d exchange interactions and the Burstein-Moss effect. Meanwhile, PL and XPS measurements illustrate that tin vacancies (VSn) and oxygen vacancies (VO) were generated during the process of preparation and the VSn as the origin of the ferromagnetism in pure SnO was verified by air-anneal experiment. In addition, Ni-doping can improve the ferromagnetism via enhancing the content of VSn. This literature studies the ferromagnetism of novel SnO flower-like structure firstly and reasonably reveals the desired ferromagnetism originated from the VSn.Download high-res image (281KB)Download full-size image

•AlH3 doped with 3d transition metals were studied from first principles.•Single V, Cr, Mn, and Fe dopants can produce high spin polarization.•Single Co and Ni dopants show low spin polarization.•The long-range ferromagnetic coupling is observed upon doping V, Mn, and Fe.•3d dopants tailor AlH3 into either a half-metal or n-type magnetic semiconductor.The effects of 3d transition metals doping on the structural, electronic, and magnetic properties of aluminum hydride were investigated based on spin-polarized first-principles calculations. The studies indicated that V, Cr, Mn, and Fe doping could produce polarization of high-spin state, while Co and Ni doping would induce polarization of low-spin state. It was found that the magnetic ground state depended on the distance between two substitutions and the long-range ferromagnetic coupling was achieved upon doping V, Mn, and Fe. The present work indicated that the introduced 3d-block dopants could tailor aluminum hydride into either a potential half-metallic or n-type magnetic semiconductor by tuning the valence electrons of the impurities. The main findings of this work pointed out the possibilities of the applications of hydrides in future hydride electronics and spintronics.Download high-res image (390KB)Download full-size image

Nanostructured CuO/ZnO heterojunctions were fabricated via a template-free hydrothermal reaction. The prepared CuO/ZnO nanocomposites are composed of one dimensional (1D) hexagonal ZnO nanorods and two-dimensional (2D) monoclinic CuO nanosheets. The single crystal nature of both ZnO and CuO was confirmed. Optical spectra show the widened absorption range from UV to visible light, which suggests the potential of the obtained CuO/ZnO composites for visible-light-driven photocatalyst. The point defects at the interface play the leading role in triggering ferromagnetism of CuO/ZnO composites. Fundamentally, the ferromagnetism can be understood by the charge-transfer mechanism according to Stoner theory. The findings can give a further insight into the ferromagnetic origin of nonmagnetic composites and the integration of ferromagnetic and photocatalytic properties into an identical sample.Download high-res image (242KB)Download full-size image

•CuO/ZnO nanocomposites have been synthesized by a one-step hydrothermal method.•The interaction between ZnO and CuO causes a modification of electronic structure.•The abnormal RTFM is discovered at the interface of CuO/ZnO.•The MS can be tuned by changing the phase ratios of the CuO and ZnO.•The indirect double-exchange model was employed to explain the origin of magnetism.CuO/ZnO nanocomposites have been successfully synthesized by a one-step hydrothermal method with different phase ratios. Field emission scanning electron microscopy and transmission electron microscopy results show that the obtained products of nanosheets are composed of small primary particles with an average size of about 20 nm. With the increasing proportion of CuO phase, nanosheets have significant collapse and the amount of small sheets increases obviously. The abnormal room temperature ferromagnetism was discovered at the interface between diamagnetic ZnO and antiferromagnetic CuO, which can be tuned by changing the phase ratios. Optical spectra indicate that the interaction between ZnO and CuO modifies the electronic structure of nanocomposites. XPS results verify the valence change of Cu ions and the presence of oxygen vacancies, which are ultimately responsible for the observed ferromagnetism. The indirect double-exchange model was employed to explain the origin of magnetism. Our study suggests that magnetically functional interfaces exhibit very appealing properties for novel devices.Download high-res image (211KB)Download full-size image

•Novel Sn1-xCoxO particles have been synthesized by hydrothermal growth method.•Co ions tend to occupy different positions with the concentration increasing.•The low doping narrows the Eg while the high doping has the opposite effect.•The room temperature ferromagnetism is discovered firstly in the Sn1-xCoxO particles.Novel plate-like Sn1-xCoxO particles have been successfully synthesized by a template-free hydrothermal growth method. Field emission scanning microscopy and transmission electron microscopy results show that the obtained particles are consist of nanosheets with a thickness of ∼10 nm. X-ray diffraction results show that the Sn1-xCoxO possesses typical tetragonal structure, Co-doping has certain influence on the host lattice structure and Co would occupy different positions (CoSn and Coi) with different doping concentrations. And the optical band gap of the samples firstly narrows and then widens as the positions of Co changing from substituted sites to interstitial sites. Meanwhile, room-temperature ferromagnetism originated from the double exchange interactions between the O 2p and Co 3d states is discovered as well, and the ferromagnetism firstly increases and then decreases with Co concentration increasing.

•Effect of GNSs on properties of Sn58Bi0.7ZnxGNS composite solder joint has been investigated.•GNSs addition refined the solder microstructure and enhanced the mechanical properties.•The best mechanical properties improvement came from the 0.076 wt.% GNS-doped Sn58Bi0.7Zn solder joint.•The time exponent and thickness of the total IMC layer were effectively reduced in the 0.114 wt.% GNS-doped sample.•The strengthening mechanism of GNSs was analyzed and proposed in detail.The effects of graphene nanosheets (GNSs) on the microstructure and mechanical properties of Sn58Bi0.7Zn solder joint were investigated. Experimental results and finite element (FE) simulations showed that the best mechanical properties improvement came from the 0.076 wt.% GNS-doped Sn58Bi0.7Zn sample. It exhibited the highest creep resistant in all the as-prepared solder joints, and the average interphase spacing in solders was reduced by 32.52%, the stress exponent was increased by 13.70%. For the thermal aging samples, the ultimate tensile strength (UTS) of the solder joint was also increased by 2.04%. Moreover, the 0.114 wt.% GNS-doping significantly reduced the time exponent from 0.403 to 0.362 and decreased the thickness of total IMC layers by 56.31%. Based on the theories related to material performance and the restacking behavior of GNSs, the strengthening mechanism of GNSs in composite solder joint was analyzed and an optimum concentration of GNSs in Sn58Bi0.7Zn solder alloy was proposed.

•The substitutional doping of Fe would not result in large structural deformation.•The magnetic moment of Fe-doped SnS2 is mainly from the 3d orbitals of Fe atom.•The two Fe atoms doped SnS2 systems show magnetic anisotropy.•The room temperature ferromagnetism is available in Fe-doped SnS2 materials.•Sulfur vacancy has a strong influence on the magnetic properties of Fe-doped SnS2.The structural and magnetic properties of Fe-doped SnS2 have been systematically investigated using the density functional theory calculations. The results show that Fe-doped SnS2 is half-metal with magnetic ground states. The total induced magnetic moment is about 2.0 μB, which is mainly from the 3d orbitals of Fe atom. Besides, the systems with two Fe dopants show magnetic anisotropy. Namely, the magnetic coupling between magnetic moments induced by two Fe atoms is long-range ferromagnetic with Fe atoms fixed at the intralayer sites but paramagnetic at the interlayer sites. The room temperature ferromagnetism is available in Fe-doped SnS2 with the Curie temperature TC = 629 K. Moreover, sulfur vacancy has a strong influence on the magnetic properties of Fe-doped SnS2.

The nature of adsorbates (water and ethanol) on the anatase TiO2 (1 0 1) surface has been investigated with first-principles calculations. Our results reveal that the band gap narrows by 0.2 and 0.7 eV for the water and ethanol respectively adsorbed on the perfect surface. The O3 molecule in the system with one Ti vacancy on the surface will disappear after adsorbing. On the basis of the Bader charge analysis, water and ethanol would donate electrons to the 2p of twofold coordinated O atoms, which leads to the valence band maximum up. In addition, the disappearance of the O3 molecule also affects the distribution of the impurity states in the band gap. Although the adsorbates affect the electronic structures and local structures of the TiO2 (1 0 1) surface, the magnitude of magnetic moments induced by the Ti vacancy hardly changes.

In this study, Ni functionalized Sn58Bi solder alloys were successfully synthesized. Composite solders up to 1 wt% Ni reinforcement were prepared. Microstructures and mechanical properties of composite solders after sintering and solid-state aging for 120 h and 240 h were compared with those of the pure Sn58Bi solder. The results indicate that the elastic modulus, tensile and yield strength increase with the increasing Ni content during the solid-state aging, which is because Ni can decrease the CTE and refine the microstructure of SnBi solder. The ductility of composite solders presents a non monotonic trend with the increasing Ni content and aging time because the concentrated Ni3Sn4 grains form at the solder matrix. The hardness can reflect the tensile and yield strength transformation veritably. Besides, the hardness varies with tensile and yield strength following the linear relationships.

With the addition of 0.075 wt% graphene nanosheets (GNSs), the mechanical properties of coupled and aged solder joint were respectively investigated in this study. During the tensile tests, the weakening of the anode interface between intermetallic compounds (IMCs) and Bi layer significantly affected the ultimate tensile strength (UTS) of electromigration (EM) and thermal aging coupled solder joint. The formation of vacancies and stress concentration at the Cu–Sn–Zn/Cu–Zn interface in the aged solder joint was ascribed to the Bi segregation and GNSs. Nanoindentation results showed that the creep resistance of coupled solder joint was higher than that of the aged solder joint, which was because that the Bi layer, GNSs and cracks played a role of load transfer at the solder joint interface in coupled sample.

•(100)-orientated SnO2:K films were grown on buffered c-sapphire.•The residual strain could be modified through adding a buffer layer.•K+ doping site changes from Ki to KSn as increasing the tensile strain.•The band gap related to carrier concentration is narrowed by tensile strain.•The biaxial tensile strain could enhance the d0 ferromagnetism induced by holes.The strain sensitivity in epitaxial Sn0.94K0.06O2 thin films grown on buffered c-plane sapphire was systematically investigated. Both XRD and Raman results demonstrate the biaxial tensile strain induced by the lattice mismatch between substrate and film could be altered by a SnO2 buffer layer. When the tensile strain in the bc plane becomes larger, more K ions tend to occupy substitutional sites, with more holes being created. By enlarging the strain, the hole carrier concentration is increased while the optical band gap is narrowed. Besides, the saturation magnetization of the films increases when the biaxial tensile strain becomes larger, indicating the increased strain could enhance the ferromagnetism. This proves that the properties of Sn0.94K0.06O2 films are sensitive to the residual strain.

The massive spalling of CuZn IMC was mainly affected by the Zn concentration. Only when the Zn concentration was about 0.67 wt% in the solder sample during liquid-state aging, this behavior could occur. Comparing with the Sn–58Bi–0.7Zn bulk solder sample, the massive spalling phenomenon was more likely to appear in small solder ball sample. The related IMCs transformation was explained by the Cu–Sn–Zn isotherm with the diffusion path concept for the different addition of Zn in the solder sample during liquid-state aging. The average concentration distribution of Sn between the CuZn and Cu6(Sn, Zn)5 IMC layer also affected this behavior. When the aging temperature was just higher than the liquidus temperature of Sn–58Bi–0.7Zn bulk solder, the massive spalling phenomenon appeared. Trace amounts of Bi atoms in the Sn-rich layer between the CuZn and Cu6(Sn, Zn)5 could lead to lattice distortion, which delayed the occurrence of this behavior. Thermodynamic analysis showed that this kind of spalling behavior was partly attributed to the reduction of free energy at the CuZn/Cu6(Sn, Zn)5 interface due to the change of Sn concentration.

Ni-coated Carbon Nanotubes (Ni-CNTs) with weight percentages of 0%, 0.05%, 0.1% and 0.2% were incorporated into Sn58Bi solder alloy. The microstructure and mechanical properties of composite solders were investigated. Experimental results and finite-element simulation show that the tensile strength of solder slabs and joints is improved by the CNT bridging effect and load transfer. The fracture modes of solder joints and slabs change from ductile to brittle fracture. The creep behaviors of solders are improved significantly compared to those of the pristine samples because of the strengthening effect of Ni-CNTs. Hardness transformation is ascribed to the creep, which makes a large contribution to the plastic deformation during indentation process. Finite-element simulation indicates that the Ni3Sn4 and CNTs play the main role in the process of nanoindentation deformation. Besides, the mechanical properties and microstructure are declined when the content of Ni-CNTs exceeds 0.05%.

Doping with foreign element is an effective method to narrow the band gap of TiO2. Here, the S doping and (S, Mg) codoping effects on the electronic structure and optical properties of the anatase TiO2 were investigated at the HSE06 hybrid functional level. The hybridization of the O 2p, Ti-t2g, and S 3p states creates the intermediate band for the doped TiO2, which makes the absorption onset extend into the visible-light region. The introduction of Mg promotes the corporation of S into TiO2. The heavy doping with S further improves the absorption efficiency and eliminates the unoccupied intermediate band. The band alignment confirms that the (S, Mg) codoping with two O atoms substituted by S atoms in TiO2 is desirable for the overall water splitting.

The effects of isovalent doping on electronic and magnetic properties in sputtered polycrystalline Ce1−xSnxO2 films were investigated. All the samples have a fluorite structure with [100] preferred orientation. The Sn doping helps to boost the magnetism in CeO2, but has no significant impact when the doping content exceeds 6% (x > 0.06). Experimental analysis indicates that the magnetism may be directly associated with the structure distortion as well as the concentration of Ce3+ and oxygen vacancies. Theoretical calculations based on the density-functional theory suggest that the redox process of CeO2 can be influenced by the presence of dopant. The superexchange mechanism through Ce–O–Ce interaction and F+ centers lying deep in the gap can ease the mediation of ferromagnetic coupling in the system. Meanwhile, there is a competition mechanism in electronic modification, causing the spin-polarization to have a maximum stability at a critical doping concentration.

•Epitaxial K-doped ZnO films were deposited on c-Al2O3 substrates by RF-magnetron sputtering system.•A conversion of conductivity from n-type to p-type was observed with increasing the K concentration.•The effect of K-doping and annealing on the ferromagnetism of ZnO films were examined.•The origin of the ferromagnetism was discussed using first-principle calculations.Room-temperature ferromagnetism with p-type conductivity was observed in epitaxial K-doped ZnO films prepared by RF-magnetron sputtering. The coincident changes in the electrical, optical and magnetic properties indicate that the cation holes play important roles in mediating the ferromagnetism in K-doped ZnO films. The maximum saturation magnetization of 8 emu/cm3 was obtained in the 8% K-doped film and the thermal annealing in air could stabilize the ferromagnetic signature. Finally, first-principle calculations reveal that the magnetic properties in K-doped ZnO films are attributed to the strong p–p interaction between the unpaired 2p electrons at O sites.

•The magnetic behavior of rock-salt sulfide superlattices in the (001) direction is investigated.•All these superlattices maintain the half metallicity.•The p–p hybridization is shown to be essential for the formation of spin polarization.•S atoms in different layers of the superlattices show distinct polarized directions.•Discussion of volume-conserving deformations further demonstrates the magnetic stability.Density functional calculations were performed to study the structural, electronic, and magnetic properties of sp-electron half-metallic superlattices (KS)1/(CaS)1, (RbS)1/(SrS)1, and (CsS)1/(BaS)1 (001) in rock-salt structure. All the superlattices are found to be spin polarized, and the calculated band structure suggests a 100% polarization of the conduction carriers. The p–p hybridization is shown to be essential for the formations of localized orbitals and spin-splitting. The half-metallic electronic structure will be destroyed upon an excessive lattice compression, accompanying with a metallic transition. Moreover, the analysis of the orbital-decomposed partial density of states and spin density reveal that S atoms in different layers of the superlattice show distinct polarization directions. Discussion of volume-conserving deformations further demonstrates the stability of half metallicity in sp-electron superlattices.

The effect of mis-match strain on the structural, electronic, and optical properties in SnO2 epitaxial thin films has been systematically investigated by the experimental and theoretical methods. Our results indicate that the tensile strain exists in the thin film and decreases with the thickness of epitaxial samples. Besides, the optical band gap significantly reduces with increasing the tensile strain in the bc plane. Our hybrid functional calculations present that the narrowing of band gap of SnO2 under tensile strain is due to the weakening of bonding and antibonding split, which results from the disorder of SnO6 octahedra, and the biaxial strain is found to be more efficient than the uniaxial strain for tuning the band gap of SnO2.

The correlated room temperature ferromagnetism and photoluminescence were investigated in Al-doped SnO2 nanoparticles (about 50 nm) synthesized by the sol-gel method. X-ray diffraction and selected area electron diffraction results show that the Sn1−xAlxO2 samples possess typical rutile structure and have no other impurity phases with Al fractions of up to 8 at.%. The optical bandgap energies decrease, while the Urbach energies increase with Al concentration. The ferromagnetic signature was found to be significantly enhanced after Al doping, with the saturation magnetization reaching a maximum of 7.3 × 10−3 emu/g in Sn0.92Al0.08O2 sample. The photoluminescence studies clearly indicated the presence of a large concentration of singly ionized oxygen vacancies in the pure and Al-doped SnO2 nanoparticles. An interesting correlation between the saturation magnetization and green–yellow luminescence intensity with the increase of Al doping has suggested that the observed ferromagnetic ordering of the Sn1−xAlxO2 nanoparticles is related to the singly ionized oxygen vacancies.

•We have systematically investigated the properties of η-Cu6−xNixSn5 compounds.•A stress–strain approach is employed to calculate polycrystalline elastic properties.•The unit cell volume and lattice parameter of ‘a’ axis decrease with increasing Ni content.•Ni increases the stability, brittleness, modulus and Debye temperatures of η-Cu6Sn5.•The electronic structure and charge density distribution are also analyzed.Based on first-principles calculations, the effects of various Ni concentrations on the structural, elastic, electronic and thermodynamic properties of hexagonal η-Cu6Sn5 compound have been systematically investigated. The results demonstrate that higher Ni concentration in the η-Cu6−xNixSn5 (x = 0, 0.5, 1, 1.5 and 2) leads to thermodynamically stable compounds, and Ni atoms preferentially occupy Cu2 + Cu1c sites forming the η-Cu4Ni2Sn5 compound. It is also found that the unit cell volume and lattice parameter of the ‘a’ axis decrease with increasing Ni concentration, which are consistent with the other experimental results. Furthermore, the polycrystalline elastic properties are obtained from single-crystal elastic constants. Our results indicate that the addition of Ni enhances the mechanical stability, brittleness, modulus and Debye temperatures of η-Cu6Sn5 compound. Analyzing the electronic structure and charge density distribution provides the explanation that Ni develops distinct bonding energy to Cu and Sn in the structure.

The electronic and optical properties of W-doped SnO2 are investigated by first-principles calculations in this work. The results show that the Fermi level shifts into the conduction band and the compound exhibits n-type metallic characters with high conductivity when W atoms substitute Sn atoms. As for defect cases, oxygen vacancies increase the density of states near the Fermi level resulting in a possible increase in the conductivity of W-doped SnO2, while the Sn vacancies make the Fermi level shift into the valence band and narrow the band gap. And the formation energy analysis indicates the possibility of W dopant and related defects forming in SnO2 crystal. The W-doped SnO2 shows high optical anisotropy, and the blue-shift of optical spectra can be observed. Additionally, the increased absorption in the visible region can be expected with the presence of oxygen vacancies in the crystal.Highlights► The electronic and optical properties of W-doped SnO2 were calculated. ► The W doing increases the electrical conductivity and the visible absorption. ► The formation possibility and the effects of defects were discussed. ► The high optical anisotropy in W-doped SnO2 was observed and analyzed.

A Cu/Sn-8Zn-3Bi/Cu structure was used to investigate the intermetallic compound (IMC) growth behavior during discontinuous electromigration under current density of 104 A/cm2 at 70°C. Cu5Zn8 IMC formed at both the anode and the cathode interfaces, and the thickness increased with the stressing time. With prolonging the current stressing time, a bulged Cu5Zn8 layer was squeezed out between the former Cu5Zn8 layer and Cu substrate in the samples to relax the excess compressive stress. Additionally, due to the back stress gradient built up by the Sn diffusion, the Zn atomic flux reacted with Cu to form Cu5Zn8 at the cathode side when the power was turned off. Finally, the total IMC thickness of the anode and the cathode under discontinuous current stressing showed a “reversion” in the 69 h and 310 h samples.

The effects of Zn (1 wt.%, 3 wt.%, and 7 wt.%) additions to Sn-3.5Ag solder and various reaction times on the interfacial reactions between Sn-3.5Ag-xZn solders and Cu substrates a during liquid-state aging were investigated in this study. The composition and morphological evolution of interfacial intermetallic compounds (IMCs) changed significantly with the Zn concentration and reaction time. For the Sn-3.5Ag-1Zn/Cu couple, CuZn and Cu6Sn5 phases formed at the interface. With increasing aging time, the Cu6Sn5 IMC layer grew thicker, while the CuZn IMC layer drifted into the solder and decomposed gradually. Cu5Zn8 and Ag5Zn8 phases formed at the interfaces of Sn-3.5Ag-3Zn/Cu and Sn-3.5Ag-7Zn/Cu couples. With increasing reaction time, the Cu5Zn8 layer grew and Cu atoms diffused from the substrate to the solder, which transformed the Ag5Zn8 to (Cu,Ag)5Zn8. The Cu6Sn5 layer that formed between the Cu5Zn8 layer and Cu was much thinner at the Sn-3.5Ag-7Zn/Cu interface than at the Sn-3.5Ag-3Zn/Cu interface. Additionally, we measured the thickness of interfacial IMC layers and found that 3 wt.% Zn addition to the solder was the most effective for suppressing IMC growth at the interfaces.

In this work, interfacial reactions of Sn–8Zn–3Bi–xNi (x = 0, 1) lead-free solders with Cu substrate and the growth of intermetallic compounds (IMCs) during isothermal aging were investigated. After soldering at 250 °C for 90 s, the Cu5Zn8 and CuZn5 phases formed at the Sn–8Zn–3Bi/Cu interface and only the Cu5Zn8 phase was found at the interface of the solder with addition of Ni. During aging treatment at 150 °C for 100, 400 and 900 h, the CuZn5 IMC at the Sn–8Zn–3Bi/Cu interface transformed to the Cu5Zn8 due to Cu atoms diffusing from Cu substrate. The Cu5Zn8 IMC layer at solder/Cu interfaces grew thicker with increasing the aging time and the growth was diffusion controlled. Moreover, the thickness of the IMC layer at the Sn–8Zn–3Bi/Cu interface was thicker than that at the Sn–8Zn–3Bi–1Ni/Cu interface. The reduction effect of Ni addition to the solder on the interfacial reaction might be attributed to the formation of the Ni5Zn21 IMC in the solder bulk, which effectively suppressed the diffusion of Zn atoms to the interface to react with Cu.

Electromigration behavior in a one-dimensional Cu/Sn–8Zn–3Bi/Cu solder joint structure was investigated in ambient with a current density of 3.5 × 104 A/cm2 at 60 °C. Due to the compressive stress induced by volume expansion resulting from Cu–Zn intermetallic compound (IMC) growth, Cu5Zn8 IMC layers were squeezed out continuously along IMC/Cu interfaces at both the anode and the cathode with increasing the current stressing time, which was not only driven by the concentration gradient, but also accelerated by the electromigration. And a few voids propagated and formed at the anode and the cathode solder/IMC interfaces during electromigration. Additionally, Sn hillocks occurred in the bulk solder, and Sn hillocks formed at the anode side were larger than those at the cathode side.

Electromigration in SnBi thin film was investigated experimentally and analyzed with the finite element simulation and the first-principles method. After current stressing, both Sn and Bi atoms migrated from the cathode to the anode and a higher migration rate of Bi than Sn was observed due to its lower diffusion activation energy, which resulted in forming the layer-like structure in the film. At the anode, besides Sn and Bi hillocks, unexpected voids were found which were associated with the current density distribution there. It was also interesting to find a much faster diffusion of Bi in the SnBi thin film than in the bulk sample. And this enhanced mass migration was considered to result from the small grain size in the thin film which could provide more fast diffusion paths for Bi atomic diffusion.

The structural, elastic and thermodynamic properties of two important intermetallic compounds, Cu6Sn5 and Cu5Zn8, have been deeply investigated by performing the first-principles calculations based on density functional theory and using the quasi-harmonic approximation for the non-equilibrium Gibbs free energy. Key physical parameters, such as lattice constants, bulk modulus, heat capacity, Debye temperature and volume thermal expansion coefficients were calculated, and their dependences on temperature and pressure were also obtained. Our calculated results are in good agreement with the available experimental data. It is found that Cu6Sn5 is elastic anisotropy with relatively low bulk modulus, while Cu5Zn8 shows elastic isotropy with high bulk modulus. And the electronic origin of elastic properties was also analyzed in this paper.

The formation and the growth of the intermetallic compounds (IMCs) at the interface between the Sn–8Zn–3Bi–xAg (x = 0, 0.5, and 1 wt.%) lead-free solder alloys and Cu substrate soldered at 250 °C for different durations from 5 to 60 min were investigated. It was found that Cu5Zn8 and CuZn5 formed at Sn–8Zn–3Bi/Cu interface, and Cu5Zn8 and AgZn3 formed at the solder/Cu interface when the solder was added with Ag. The thickness of IMC layers in different solder/Cu systems increased with increasing the soldering time. And the growth of the IMCs was found to be mainly controlled by a diffusion mechanism. Additionally, the growth of the IMC layers decreased with increasing content of Ag in the soldering process.

The structural, elastic and electronic properties of intermetallics in the Pt–Sn binary system are investigated using first-principles calculations based on density functional theory (DFT). The polycrystalline elastic properties are deduced from the calculated single-crystal elastic constants. The elastic anisotropy of these intermetallics is analyzed based on the directional dependence of the Young’s modulus and its origin explained based on the electronic nature of the crystals. All the Pt–Sn intermetallics investigated are found to be mechanically stable, ductile and metallic, and some of them show high elastic anisotropy.

The structural, elastic, and electronic properties of Al-Cu intermetallics were investigated using first-principles calculations. The polycrystalline elastic modulus and Poisson’s ratio were deduced from calculated single-crystal elastic constants, and the calculated structural properties agreed well with previous experimental results. Meanwhile, the elastic anisotropy of Al-Cu intermetallics was analyzed based on the directional dependence of the Young’s modulus and its origin explained based on the electronic nature of the crystals.

•Sodium chloride bulk and (0 0 1) surface doped with B, C, N, and O were studied.•Magnetic moments of 2.00, 3.00, 2.00, and 1.00 μB were induced by doping B, C, N, and O into NaCl bulk.•Magnetic moments of 2.00, 1.00, 2.00, and 1.00 μB were created by doping B, C, N, and O onto NaCl(0 0 1) surface.•The similarities and differences between bulk and surface doping were indentified and characterized.Based on density functional calculations, we studied the structural, electronic, and magnetic properties of sodium chloride bulk and (0 0 1) surface doped with the light non-metallic elements boron, carbon, nitrogen, and oxygen. The results indicated that doping such an isolated foreign atom can produce considerable spin polarization, mainly due to highly localized and partially filled 2p states of the dopants. From simple GGA computation, all these diluted magnetic chlorides exhibit nearly half-metallic characteristic with weak conductivity, and thereby they could be used as spin filter materials for improving spin-specific magnetic tunnel junctions. Especially, substitution onto the surface removes the degeneration of 2p impurity states, leading to anisotropic spin and electron atmosphere with specific orientation. The differences between bulk doping and surface doping were further explained by spin-resolved energy spectrums. In addition, compared with standard GGA approach, applied Ueff of 2p orbitals of C, N, and O atoms can correct the error and improve the description of the electronic structures and magnetic properties in some extent. N and O-doped NaCl bulks transform from approximate half metals to magnetic semiconductors, owning to the enhancement of electronic localization and correlation. And the total magnetic moment increases from 1 μB to 3 μB for C-doped NaCl (0 0 1), accompanying with a transformation from intermediate-spin state to high-spin state. In particular, O-substituted system is energetically more favorable than other doped systems, i.e., the negative value of the predicted formation energy, demonstrating that O-doped NaCl should be a candidate material for potential spintronic applications.

The electronic structural, magnetic and optical properties of pure and V-doped ZnO are investigated by first-principles calculations based on the density functional theory. With the introduction of V atoms, the spin-splitting near the Fermi level leads to a net magnetic moment of the system. A significant possibility of room temperature ferromagnetism (RTFM) originated from the Ruderman–Kittel–Kassuya–Yosida (RKKY) exchange is predicted. Oxygen vacancy is positive to enhance the ferromagnetism while zinc vacancy is negative. With respect to the optical properties, the presence of V atoms was found to have an obvious influence on the transmittivity, especially in the low energy region. A slight V-doping can keep a high optical transmission and smoothly modulate the optical bandgap.Highlights► A systematical investigation has been made on pure and V-doped ZnO system. ► The influences of intrinsic defects on V-doped ZnO are taken into consideration. ► A reasonable origin of RTFM and possible Tc are given. ► The V doping can manipulate the optical bandgap and visible light transmittance. ► Our results give significant referents for potential TCO and DMS applications.

•The shift of PL emission due to lattice distortion is observed in Sn1−xAlxO2 films.•The band gap is narrowed by holes induced by AlSn while widened by electrons.•Air-annealing makes Al ions transformed from AlSn to Ali.•The localized holes introduced by AlSn are responsible for the d0 ferromagnetism.The role of acceptor and donor defects in epitaxial Al-doped SnO2 films were systematically investigated. Al doping introduces acceptor defects (AlSn) at low doping concentration while donor ones (Ali) in a concentration range from 8 to 10 at%. The band gap is firstly narrowed by hole-doping and then widened by electrons introduced by oxygen vacancies and Ali. Air-annealing absorbs oxygen and makes Al ions transformed from AlSn to Ali, corresponding to a decrease (increase) in the band gap when most Al ions occupy the substitutional (interstitial) sites. The saturation magnetization of the films is enhanced by AlSn doping, with the maximum value in the Sn0.98Al0.02O2 film. The magnetic moment is contributed by the localized holes introduced by AlSn. The existence of the ferromagnetism induced by holes in the film with oxygen vacancy gives a new insight into the behavior of defects in SnO2.

We extend Galenko's nonequilibrium kinetic model of planar interface migration during solidification to non-dilute solution with non-straight liquidus and solidus curves. Using this more complex thermodynamic model for silicon–arsenic we show that the model with significant solute drag is consistent with the available experimental data for Si–9at%As alloy. Comparison with the typical kinetic models shows that the present model provides a better description of the data and the linear phase boundary assumption may lead to a relatively large deviation from reality.