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Developing approaches to effectively manipulate the magnetic states and phase transition is critical to the application of transition metal dichalcogenides (TMDs) in spintronic or phase-switching d...

Free volume gradient was introduced using intermittent magnetron sputtering processes to fabricate two different series of CuZr/CuZr metallic glass multilayers, forming heterogeneous atomic structure in glass/glass interfaces. Multilayers in series 1 have identical bi-layer thickness but different modulation ratios, while those in series 2 have the modulation ratio of 1/1 but different bi-layer thicknesses. Nanoindentation was subsequently carried out to evaluate the shear banding deformation of the fabricated multilayers. Despite that all the multilayers were only consisted of a single monophase (i.e., CuZr metallic glass), their shear banding deformation behaviors were dependent upon both the modulation ratio and bi-layer thickness. Upon annealing treatment, such dependence nearly vanished in both series of the multilayers. It was proposed that free volume gradient plays a crucial role in the observed unusual shear banding deformation behaviors. Specifically, asymmetric and symmetric free volume gradients in series 1 and 2, respectively, induce different stress states in glass/glass interfacial regions, which may alter the initiation and propagation processes of shear bands in CuZr/CuZr multilayers.

The creep behavior of nanocrystalline body-centered cubic Mo thin films was evaluated using nanoindentation testing. The creep rate and the corresponding strain rate sensitivity (m) were found to be strongly dependent upon indentation size and loading strain rate (LSR). Other than the mechanism of diffusion along indenter tip-sample interface previously proposed for face-centered cubic metals and metallic glasses, alternative mechanisms involving surface effect enhanced screw dislocation activities, inverse indentation size effect of hardness and LSR dependent microstructural and stress states, were proposed to interpret the observed dependence of penetration depth and LSR of m.

Heterointerface in a nanoscale metallic layered composite could improve its crack resistance. However, the influence of metallic interface structures on crack propagation has not been well understood at atomic scale. By using the method of molecular dynamics (MD) simulation, the crack propagation behavior in Cu-Nb bilayer is compared with that in Cu-Ni bilayer. We find that the weak Cu-Nb interface plays an important role in hindering crack propagation in two ways: (i) dislocation nucleation at the interface releases stress concentration for the crack to propagate; (ii) the easily sheared weak incoherent interface blunts the crack tip. The results are helpful for understanding the interface structure dependent crack resistance of nanoscale bicrystal interfaces.

The dependence of microstructure, hardness (H) and strain rate sensitivity (m) of nanocrystalline (NC) body-centered cubic Nb thin films at various annealed temperature were experimentally evaluated. The annealed temperatures ranged from 100 to 400 °C, and kept for 30 min respectively. Despite nearly unchanged grain sizes upon annealing, the strengthening effect was observed in nanoindentation hardness testing as annealing temperature was increased above 200 °C. In particular, the strain rate sensitivity of NC Nb increased significantly after annealing at 100 °C and slightly decreased at higher annealing temperatures. Competitive mechanisms underlying the different variation trends of hardness and strain rate sensitivity of NC Nb annealed in the two different temperature regimes were proposed.

The adhesion of coating to substrate is an important factor governing the performance and durability of coated engineering components. Existing evaluation methods cannot produce quantitative measurement of bonding strength for strong adherent coating. This paper proposes a novel evaluation method based on the cyclic spherical indentation (CSI) test, which uses successive indentations of a spherical ball onto a coated specimen to induce the detachment of the coatings along the interface. Compared with earlier methods, this method creates only adhesive failures, which only occur during elastic deformation of the substrate, yet it is applicable to coating with strong bonding. The evaluation method creates a curve of shear stress range versus failure cycles for each coating/substrate system. These curves can be used directly to compare the bonding strength of hard coatings.

Metal oxides with high-energy facets usually have more active surface sites to facilitate gas adsorption. In this work, the ZnO/graphene composites are synthesized hydrothermally and the morphology of ZnO nanoparticles can be changed from nanorods to nanoplates with the high-energy {0001} polar surface exposed by changing the density of sodium citrate in the reaction. The ZnO{0001}/graphene composites have better sensing properties to NO2 at room temperature (RT). Based on first-principles calculation, the adsorption energy of NO2 on the ZnO{0001} facet is more negative than that on the {01 1 ¯ 0} surface indicating stronger interactions between the former and NO2. Furthermore, the ZnO{01 1 ¯ 0} surface shows semiconducting characteristics, whereas the ZnO{0001} polar surface is metallic. The metallic characteristics promote charge transfer at the interface between ZnO and graphene and enhance the NO2 detection sensitivity.

Fatigue failure of hard coatings usually occurs at much lower loads than failure under static loading. Hence one way to evaluate coating adhesion should be cyclic loading close to service conditions. In this study, a new method of adhesion measurement for hard coatings is introduced based on interfacial fatigue under repeated indentation. Mono- and multi-layered coatings with different interfacial states are evaluated by a repeated-indentation test. Detachment of the coatings occurs initially at the rim of the indenter imprint, apparently as a result of adhesive failure. In contrast to monolayer coatings, peeling of multilayer coatings depends on the lowest strength of the interfaces. This study also demonstrates that the adhesion determined by the repeated-indentation test is sensitive to the interfacial state, allowing an optimised or weakened interface to be clearly revealed.

Ti-Si-N coatings are deposited on titanium alloy by arc-enhanced magnetron sputtering at different negative bias voltages and their corrosion resistance in blood, effects on platelet activation, endothelial cell functions are studied. The Ti-Si-N coatings are made up of crystalline TiN and amorphous Si 3 N 4 phases and show better corrosion resistance compared with titanium alloy. Reduced platelet receptor activation is observed on the Ti-Si-N coatings and that deposited at −100 V shows the longest clotting time and smallest platelet activation. Ti-Si-N coatings also enhance the endothelial cell proliferation and spreading as well as the endothelial nitric oxide synthase (eNOS) expression.

For the bulk and (001) surface of Ti2CoSn Heusler alloy, the electronic and magnetic properties in bulk and the surface effect on the structural, electronic and magnetic properties of the alloy for different terminations of (001) surface have been studied by using first-principles calculations. The spin-gapless semiconductor (SGS) ferromagnetism with the magnetic moment of 3.00 μB/f.u. is confirmed in the bulk Ti2CoSn alloy with Hg2CuTi-type structure. For two ideal terminations (TiCo, TiSn) and three modified terminations (CoCo*, TiTi*, SnSn*), the density of states (DOS) indicates that all terminations destroy the SGS character. Furthermore, we find that the atomic magnetic moments (AMM) decrease for the most atoms on the outmost three layers due to structural relaxation of these atoms inward. Both the DOS and AMM of the central layer L9 are similar to the corresponding bulk characters because surface effects fade out at the position of the inner layer, 12 A below the surface.

The structural, electronic, and magnetic properties of the stoichiometric (001) surface of double perovskite Sr2FeMoO6 have been studied by using a 10-layer FeMoO4 and SrO terminated (001)-oriented slab model and the first-principles projector augmented wave potential within the generalized gradient approximation as well as taking into account the on-site Coulomb repulsive (U = 2.0 eV for Fe and 1.0 eV for Mo). An outwards relaxation is observed for several layers near surface, and the accompanying layer rumpling has a decrease tend from surface layer to inner layer. Along Fe–O–Mo–O–Fe or Mo–O–Fe–O–Mo chains, the oxygen atom is closer to the adjacent Mo atom than to the adjacent Fe atom. In FeO6 or MoO6 octahedra, the two axial TM−O bonds are not equal, and especially, the surface dangling bond makes the remaining one axial TM−O bond slightly shorter than four equally equatorial TM−O bonds. The half-metallic nature and a complete (100%) spin polarization character ensure the FeMoO4 and SrO terminated (001)-oriented slab of double perovskite Sr2FeMoO6 a potential application in spintronics devices. The Fe+3 and Mo+5 ions are still in the (3d5, S = 5/2) and (4d1, S = 1/2) states with positive and negative magnetic moments respectively and thus antiferromagnetic coupling via oxygen between them. There is no direct interaction between two nearest Fe–Fe or Mo–Mo pairs, whereas the hybridizations between Fe 3d and 4s, O 2s and 2p, as well as Mo 4d, 5s and 5p orbitals are fairly significant. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper, we use the first-principles calculations based on the density functional theory to investigate the structural, electronic and magnetic properties of a symmetry Ti 2 CoSn (110) surface. The relaxations of the atoms are mainly occurred on the outmost three layers and the layer rumpling has a decrease tend from surface to inner layers. Unfortunately, the half-metallic character confirmed in bulk Ti 2 CoSn is destroyed on the (110) surface. The surface effects are mainly occurred on the outmost three layers, leading to not only a shift toward higher energy region in both channels of the DOS, a small surface state produced around the Fermi level in spin-down channel, but also a reduction in atomic magnetic moments with respect to those in the inner layers which are extremely close to the corresponding bulk values.

Controllable degradation behavior of hydroxyapatite (HA) plays a crucial role in successful long-term implantation of a bone tissue substitute. In this study, electron beam irradiation (EBI) was carried out as an efficient strategy to modify HA structure. The degradation characteristics, bioactivity and cell response of the irradiated HA were comprehensively evaluated. The results showed that EBI with absorbed dose of 3.42, 10.27 and 20.54 Gy did not introduce newly-formed phase or impurity, but created crystal defects and nanovoids, which were formed from oxygen deficiencies, into HA lattice with irradiation dose-dependence. The dissolution rate of the irradiated HA enhanced continuously with increasing irradiation dose, as a result of constantly increasing crystal defects and enlarging voids, where the main reactive sites for the degradation of HA formed. The Ca2+ and PO43- releasing of HA with the highest irradiation dose enhanced by 92.75% and 138.85% respectively compared to that of the pristine HA after 28 days’ immersion. SBF immersion results suggested the irradiated HA with raising EBI doses exhibited preferable performance in bioactivity as well. Moreover, the results from CCK-8 assay and SEM observation showed that the irradiated HA were beneficial to the proliferation and attachment of osteoblasts.

Amorphous Zr-B-N thin films were prepared on Si substrates by DC reactive magnetron sputtering as diffusion barriers for advanced Cu interconnection. To evaluate its thermal stability and barrier performance, Cu/Zr-B-N/Si stacked structures were annealed in high vacuum at temperatures varying from 500 °C to 700 °C for 30 min. The Zr-B-N films remained amorphous after annealing at 600 °C and crystalized at 650 °C, effectively block the intermixing of Cu and Si atoms. However, the thin films became invalid after annealing at 700 °C and high-resistivity Cu3Si compounds formed, revealing the significant atomic diffusion between Cu and Si. The excellent barrier performance and high thermal stability of Zr-B-N is attributed to the stable amorphous structure. Therefore, the amorphous Zr-B-N thin film can be exploited as a promising diffusion barrier for Cu interconnect technology.

Ternary nickel cobalt phosphide (NiCoP) is believed to be a promising water-splitting electrocatalyst owing to the synergistic effect between different transition metals. Herein, nitrogen doping NiCoP (N-NiCoP) nanowire arrays on carbon fiber paper skeleton (CFP) are synthesized by a facile hydrothermal reaction and subsequent phosphorization-nigtrogenization method. Structural characterizations and density functional theory (DFT) calculations demonstrate that N dopant prefer to replace O defects rather than P atoms in NiCoP lattice. It is illustrated that the Gibbs free energy of H (ΔGH*) in Ni-Co bridge sites is lowered from −0.35 eV of NiCoP to −0.26 eV of N-NiCoP by 25.7%, moreover, the increased d-orbital electronic density of Co and Ni promotes the charge transfer of hydrogen evolution reaction (HER). Consequently, the HER performance of N-NiCoP is substantially enhanced as compared to NiCoP. For N-NiCoP, the overpotentials to reach a current density of 100 mA·cm−2 are 149 and 162.5 mV in 0.5 M H2SO4 and 1 M KOH, respectively, and their Tafel slopes are 40.1 and 59.8 mV·dec−1, respectively. N doping offers an effective and promising route for improved HER performance of NiCoP catalyst in acid and alkaline electrolytes.

To exploit the potential application of nitride nanotube (BNNT), the adsorption of sulfur dioxide (SO 2 ) on pristine and Mn-doped BNNT was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are discussed. SO 2 molecule is weakly adsorbed on the pristine BNNT. The Mn-doped BNNT show high reactivity toward SO 2 regardless of the Mn B site or Mn N site adsorption. The larger formation energies and analysis of density of states show the SO 2 molecules are chemically bonded to Mn-doped BNNT and the covalent interaction between the SO 2 molecule and Mn atom can be formed. Therefore, the Mn-doped BNNT can be used as SO 2 gas sensor manufacturing raw materials, and it may be a potential material for nanodevice applications.

While hillock has so far been only observed in crystalline metals, here we show that hillock appeared on the surface of CuZr metallic glass film after annealing treatment. Other than compressive stresses generated upon annealing, surface selective oxidation processes, i.e., preferential oxidation of zirconium arouses the formation of surface ZrO2 layer and Cu-enriched area in the subsurface, were proposed to play a crucial role in hillock formation in metallic glasses. Cu atoms diffused faster than Zr from the Cu-enriched area towards the film surface, promoting the formation of Cu or Cu-enriched hillocks. Different from the diffusion mechanism in crystal films, the mechanism of atom diffusion to surface with vacancy to relieve compressive thermal stresses dominated the formation of hillocks in CuZr metallic glass films.

Sensitivity of pristine graphene (PG) and Pd-doped graphene (Pd-G) toward a series of small gas molecules (CO, NH 3 , O 2 and NO 2 ) has been investigated by first-principles based on density functional theory (DFT). The most stable adsorption configuration, adsorption energy, charge transfer, density of states and magnetic moment of these molecules on PG and Pd-G are thoroughly discussed. It is found that four gas molecules are weakly adsorbed on PG with low adsorption energy of 0.08–0.24 eV, and the electronic properties of PG are only sensitive to the presence of O 2 and NO 2 molecules. In contrast, doping graphene with Pd dopants significantly enhances the strength of interaction between adsorbed molecules and the modified substrate. The dramatically increased adsorption energy and charge transfer of these systems are expected to induce significant changes in the electrical conductivity of the Pd-G sheet. The results reveals that the sensitivity of graphene-based chemical gas sensors could be drastically improved by introducing the Pd dopants, so Pd-G is more suitable for gas molecules detection compared with PG.

Praseodymium (Pr) is implanted into TiN coatings to improve the corrosion resistance and cytocompatibility in blood plasma. The corrosion resistance of the Pr-doped TiN coatings in blood plasma is improved based on electrochemical measurements. Pr ion implantation dramatically decreases the hemolysis rate of the TiN coatings suggesting their suitability in cardiovascular applications. The viability of vascular endothelial cells seeded on the untreated TiN coatings and two Pr implanted TiN coatings implanted for different time is assessed. The vascular endothelial cell attach and grow to confluence on the Pr implanted TiN coatings and a network composed of vascular tissues is observed from the 0.5 h Pr implanted coatings. The results suggest that Pr ion implantation can effectively improve the corrosion resistance as well as cytocompatibility of TiN coatings in blood plasma.

Built upon recent findings that nanocrystalline–amorphous multilayers could possess both high strength and ductility due to nano-layer-limited structures, depth-sensing nanoindentation was employed to evaluate the hardness and shear band deformation behavior of nanoscale crystalline–Cu / amorphous–CuZr (C/A) multilayers among a wide range of amorphous layer thickness with constant crystalline Cu layer thickness. By varying individual layer thickness of amorphous layers, both weakening and strengthening effects on the hardness of C/A multilayers were observed, comparing with that derived from the rule of mixture, for which discontinuity of dislocation motion played a crucial role. A critical amorphous layer thickness of 20 nm was identified, above which interface–dislocation–absorption dominated plastic deformation, causing the weakening effect, below which, continuous-dislocation-impediment took over and was responsible for the strengthening effect. Mechanisms underlying the observed shear band morphologies under indentation were also extendedly discussed.

Ti–Si–N coatings are synthesized on titanium alloy (Ti6Al4V) by arc-enhanced magnetron sputtering and the microstructure and tribological properties are determined. The friction coefficient of the Ti–Si–N coatings, which is smaller in human serum than ambient air, decreases gradually with Si contents. Protein gel electrophoresis shows that the small friction coefficient is due to adsorbed proteins from the human serum under sliding conditions. The cytocompatibility of the coatings is assessed in vitro by a relative nitrite assay. The Ti–Si–N coatings have a positive effect on nitric oxide synthesis on the endothelial cells. The cell morphology and spreading on the coatings are examined by fluorescence staining. The Ti–Si–N coating with 12 at% Si exhibits the best effects in promoting actin cytoskeleton formation and cell spreading compared to coatings with different Si contents and titanium alloy.

Nanoscale metallic multilayers are a promising structural material for fabricating the next generation of nanoscale devices. Even though the mechanical properties of the multilayers have been extensively studied, the interpretation for the strain rate sensitivity of the multilayers is still lacking. In present study, the hardness and strain rate sensitivity of Ag/W multilayers with a wide range of modulation period Λ and modulation ratio η deposited by d.c. sputtering deposition were evaluated by nanoindentation testing. X-ray diffraction and transmission electron microscopy were carried out to investigate the texture and microstructure of the multilayers. Experimental results indicated that a mechanism transition occurred as the plastic deformation of the Ag/W multilayers was accommodated by the two constituent layers together at Λ ≤ 50 nm, while the plastic deformation localized mainly in Ag layers when Λ > 50 nm. A modified rule of mixture and plastic deformation localization model was proposed to describe the variation of strain rate sensitivity for the multilayers with smaller and larger Λ, respectively.

Micro-arc oxidation films are fabricated on the surface of AZ31B magnesium alloy in the Na 2 SiO 3 electrolyte. The mechanical performance of magnesium alloy bonding with the adhesive is examined by single lap-shear test, and the morphology and composition of the oxidation film are characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The data indicate that the increase of Na 2 SiO 3 solution concentration results in the decrease of bonding strength of magnesium alloy joints, while the porosity has no directly relation with the variation of the lap-shear strength. The results also show that Na 2 SiO 3 participates into the film formation and the fabricated film is mainly composed of MgO and Mg 2 SiO 4 . In particular, with the increase of Na 2 SiO 3 solution concentration, the content of MgO decreased while that of Mg 2 SiO 4 increased. Moreover, MgO could initiate the formation of the hydroxyl group, which potentially enhances surface wettability and hydrogen bonding with the adhesive. This rationale is strongly supported by the results of Fourier Transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle measuring.

Adsorption of sulfur dioxide (SO2) on intrinsic and modified graphene, including Stone–Wales (SW) defect, Al doping and a combination of these two, was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are thoroughly discussed. It was found that SO2 molecule is weakly adsorbed on the intrinsic and SW defected graphenes and their electronic properties were slightly changed. The Al-doped graphene and the defect–dopant combination show high reactivity toward SO2. Compared with Al-doped adsorption system, the adsorption energy for Al-doped SW defect adsorption system can be enhanced by the introduction of a SW defect. This work reveals that the sensitivity of graphene-based chemical gas sensors for SO2 can be drastically improved by introducing dopant and defect, and the Al-doped SW graphene is more suitable for SO2 gas detection.

Superhard ternary Ti–Si–N coatings with different Si atomic concentrations are deposited on titanium alloy substrates by arc-enhanced magnetron sputtering (AEMS) and the vascular endothelial cell compatibility is studied. In vitro studies show that the surface hydrophilicity and hemolysis are about the same as those of the titanium alloy control and platelet adhesion and protein adsorption tests suggest a close relationship between the surface energy and blood compatibility. Endothelial cells cultures reveal better proliferation and anti-platelet adhesion on the coatings compared to the titanium alloy control and the Ti–Si–N coating with 20 at% Si exhibits excellent endothelialization.

Using the first-principles projector augmented wave potential within the generalized gradient approximation, we investigate the magnetic and electronic properties in the bulk and (001) surface of the Heusler alloy Ti2MnAl with Hg2CuTi-type. For the bulk, our calculations indicate that the Heusler alloy Ti2MnAl exhibits antiferromagnetic half-metallicity at the equilibrium lattice constant. Owing to the surface effects, the half-metallicity which can be observed in bulk is destroyed in five terminations. The high spin polarization only maintains in TiMn-termination. Through further studies on the atomic magnetic moments, we find that the moment of surface Ti1 is enhanced obviously, as well as the absolute value of surface Mn atomic moment.

Nano-layered films of Cu/Cu(Zr)/Zr(Ge) and Cu/Cu(Zr) were deposited on the p-SiOC:H/Si substrates by RF magnetron sputtering in Ar. Samples were subsequently annealed at temperatures ranging from 350-500^oC in vacuum, and characterized by four-point probe technique (FPPT), glancing incident angle X-ray diffraction (GIXRD), Auger electron spectroscopy (AES) and transmission electron microscopy (TEM), respectively. Results indicated that these samples have a high thermal stability and favorable electrical property when the Ge content in the Zr(Ge) nano-interlayer ranged from 26% to 79%. The fundamental relationship between the alloy content of the Zr(Ge) nano-interlayer and the property of the Cu/Cu(Zr)/Zr(Ge)/SiOC:H/Si film stacks was established, and the critical temperature of the self-formed ZrO"x/ZrSi"yO"x barrier formation was also revealed.

The structure and hydrogen storage behavior of Pd-decorated nitrogen-doped graphene are investigated using the first principals based on density functional theory (DFT) calculations. Among the three types of defective structures, it is found that Pd-decorated graphene with pyridinic and pyrrolic N-doped defects are more stable and exhibit hydrogen uptake ability up to three H2 per Pd atom. A single H2 or two H2 are molecularly chemisorbed on the Pd atom, where the stretched H H bond is relaxed but not dissociated. The binding mechanism of H2 molecule is attributed to hybridization of the 4d orbitals of Pd with the σ orbitals of H2 (so-called Kubas interaction). Out of two adsorbed H2, the first and second H2 are still chemisorbed molecularly, the nature of bonding is very weak physisorption for the third adsorbed H2. Double-side Pd-decorated graphene with pyridinic and pyrrolic N defects can theoretically reach a gravimetric capacity of 1.99 wt.% hydrogen, which is very close to the recent experimental finding.

In this study, a series of nanoscale Al/W multilayers with different individual layer thicknesses were prepared by d.c. magnetron sputtering. Shear banding behavior was studied using the depth-sensing nanoindentation test at room temperature. By evaluating both deformation behavior and the morphology of the residual indentation, interestingly, contrary trends of the dependence of the shear banding behavior on the individual layer thickness were observed. A new parameter, which could represent the width of the pileup in residual indentation, was proposed; and the number of shear bands generated during deformation is strongly dependent on the parameter. To interpret the unique shear banding behavior in the Al/W multilayer, a physical model was proposed and the possible dominant mechanisms were suggested and extendedly discussed.

The diffusion barrier properties of Zr–Ge–N thin films are reported, focusing on issues relevant to their application as diffusion barriers for Cu interconnections in Si devices. The Zr–Ge–N films were prepared by reactive r.f. magnetron sputtering with different bias voltage. The analyses of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate that the final structure and composition of Zr–Ge–N film are very sensitive to the sputtering bias voltage. The N content in Zr–Ge–N film changes very little, and only decreases from 51.6 to 48.4 at.% when sputtering bias voltage increases from 0 V to − 150 V. However, the correlation between bias voltage change and the atomic ratio of Zr and Ge is very remarkable. These results clearly show that the Ge atoms are preferentially resputtered with increasing substrate bias voltage. The high sputtering bias appears to be in favor of the growth of ZrN grains. The copper diffusion barrier properties of Zr–Ge–N on Si have been examined and compared to ZrN. XRD and four-point probe method (FPP) both showed the onset of formation of copper silicide crystallites for ZrN barriers annealed at 650 °C. In contrast, TEM on a Zr–Ge–N barriers annealed even at high annealing temperatures of 800 °C revealed sharp interfaces and the energy dispersive X-ray spectroscopy (EDS) line scan showed no Cu diffusion through the barrier into Si substrate. The results suggest that Zr–Ge–N is superior to ZrN as a copper diffusion barrier on Si.

Magnetoelectric effect at Fe 3 Si/BaTiO 3 (001) interfaces is investigated by using the first-principles calculations. Interfacial separation works reveal that the FeSi/TiO 2 and modified FeFe/TiO 2 and SiSi/TiO 2 interfaces are more stable than the Fe/TiO 2 interface. While for the modified SiSi/TiO 2 interface, the paraelectric phase is recovered in BaTiO 3 slab due to its symmetrical structure in the central TiO 2 layer. Compared with the original Fe/TiO 2 and FeSi/TiO 2 interfaces, more net change magnetizations are achieved at modified FeFe/TiO 2 interface. The predicted magnetoelectric effect opens a direction to control magnetic properties of thin-film layered structure by electric fields.

Graphical abstractAn ultrathin α-Ta (5nm)/graded Ta(N) (1.5nm)/TaN (2.5nm) multilayer film covered by Cu film was deposited on the Si substrate using reactive magnetron sputtering in N2/Ar ambient. The film stacks of Cu/α-Ta/graded Ta(N)/TaN/Si were then annealed in a vacuum chamber at 400-700?C for 1h. X-ray diffraction (XRD), scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and energy-dispersive spectrometer (EDS) line scans were employed to investigate the microstructure evolution and the diffusion behavior of the film stacks. The results show that the α-Ta/graded Ta(N)/TaN multilayer film as a diffusion barrier had sufficient interface stability, which was attributed to a relative stable amorphous layer forming at the interface of Cu and α-Ta layer, to prevent Cu atom diffusion at elevated temperatures up to 700?C. The relationship between the interface stability and the microstructure of the multilayer barrier were also constructed.Display Omitted Highlights? An ultrathin α-Ta/graded Ta(N)/TaN multilayer film was prepared. ? The reliability of Ta/TaN film is sensitive to variation of Ta phase structure. ? An amorphous interlayer can improve the properties of the diffusion barrier. ? The α-Ta/graded Ta(N)/TaN multilayer could block Cu diffusion at 700?C. An ultrathin α-Ta (5nm)/graded Ta(N) (1.5nm)/TaN (2.5nm) multilayer film coated with Cu film was deposited on the Si substrate using reactive magnetron sputtering in N2/Ar ambient. The film stacks of Cu/α-Ta/graded Ta(N)/TaN/Si were then annealed in a vacuum chamber at 400-700?C for 1h. X-ray diffraction (XRD), scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and energy-dispersive spectrometer (EDS) line scans were employed to investigate the microstructure evolution and the diffusion behavior of the film stacks, respectively. The results show that the α-Ta/graded Ta(N)/TaN multilayer film as a diffusion barrier had sufficient interface stability, which could be attributed to a relative stable amorphous layer forming at the interface of Cu and α-Ta layer, to prevent Cu atom diffusion at elevated temperatures up to 700?C. The relationship between the interface stability and the microstructure of the multilayer barrier were also investigated.

The structural, electronic and magnetic properties of a 9-layer symmetrical FeMoO terminated (001)-oriented slab of double perovskite Sr 2 FeMoO 6 have been studied by using the first-principle projector augmented wave potential within the generalized gradient approximation taking into account the on-site Coulomb repulsive (U = 2.0 eV for Fe and 1.0 eV for Mo). An outward relaxation is observed for each layer of the first four layers and the accompanying layer's rumpling has a decreasing trend from layer 1 to layer 4. Along Fe–O–Mo–O–Fe or Mo–O–Fe–O–Mo chain, the oxygen atom is closer to the adjacent Mo atom than to the adjacent Fe atom. The half-metallic nature ensures the symmetrical FeMoO terminated (001)-oriented slab of double perovskite Sr 2 FeMoO 6 to be a potential application in spintronic devices. The Jahn–Teller structural distortions and the outward relaxations lead to the differences between p z state and similar p x and p y states, between d xy state and similar d yz and d xz states as well as between d z 2 and d x 2 − y 2 . The reduction in the restrictions from the reduction in the number of the near neighbors, especially the vanishing of the nearest neighbor oxygen atom just above the transition-metal (TM) atoms on the first layer makes not only the remaining axial TM–O distances slightly shorter than the four equatorial TM–O distances but also shifts toward higher energy region the occupied up-spin and down-spin states with respect to the cases of the TM atoms on the third and fifth layers.

Quaternary Ti–B–C–N coatings with different carbon concentrations are deposited on high-speed steel substrates by reactive magnetron sputtering. The oxidation behavior between 300 and 800 °C under ambient conditions is studied by scanning electron microscopy, high-resolution transmission electron microscopy, Vickers micro-hardness, and X-ray diffraction. The Ti–B–C–N coatings with smaller carbon contents have better oxidation resistance and the oxidation process can be divided into two stages: low-speed oxidation below 700 °C and high-speed oxidation above 700 °C. An oxidation mechanism is proposed to explain the relationship between the reaction with oxygen and observed oxidation behavior.

In the experiment, nano-structured and amorphous ultrathin Ru–Ge interlayers (∼15 nm in thickness) were deposited between Cu(Ru) alloy film and Si substrate via co-sputtering functioning as preventive diffusion barrier layers. After annealing at different temperatures, X-ray diffraction and four-point probe method revealed that the amorphous Ru–Ge layer effectively suppressed the Cu diffusion into Si substrate up to a temperature of at least 873 K; however, it is less than 773 K for the nano-structured Ru–Ge layer. A self-formed amorphous multilayer of Ru(RuO x )/RuGe x Cu y could be attained by annealing Cu/Cu(Ru)/Ru–Ge(amorphous)/Si system at a very low temperature (even 473 K). The results proved that the amorphous Ru–Ge system could self-form the multilayer diffusion barrier before the diffusion reaction between Cu and Si and improved the thermal stability of the Cu interconnection significantly.

A systematic density functional theoretical study of the single-walled LiF nanotubes (NTs) in armchair (n,n) and zigzag (n,0) (2 < n < 11) configurations is presented. Full geometry and spin optimizations with unrestricted symmetry have been performed. Both zigzag and armchair LiF NTs can exist stably because of their large binding energies that are slightly smaller than the bulk’s. Furthermore, the insulating character is observed for them. Given single transition-metal (TM) atom adsorbed stable (8,0) LiF NT, it is found that TM atom almost locates on the top site of the nearest F atom, regardless of the initial site. Dramatically, the half-metallic character is obtained for V-, Cr-, and Mn-adsorbed (8,0) LiF NTs. The results suggest that these systems could be used in the field of quasi-1D spintronics devices for producing nearly 100% spin polarized currents.

Au/NiCr/Ta multi-layered metallic films were deposited on Si substrate by magnetron sputtering at different substrate temperatures. The residual stress, hardness and resistivity were investigated as a function of substrate temperature by laser polarization phase shift technique, nanoindentation technique and four point probe method, respectively. The residual stress in as-deposited films at different substrate temperatures was tension with 385 MPa–606 MPa. Nanoindentation tests at shallow indentation depths (h ≤ t/4) where the hardness is reliable for metal films on hard substrate. Au film at deposition temperature 200 °C has the highest hardness 4.2 GPa. The resistivity in the deposited films reached the lowest value 3.1 μΩ.cm at substrate temperature 200 °C. The most interesting facts are that the hardness decreases with increasing residual stress and resistivity increases with increasing residual stress. The relationship of residual stress and resistivity may hint that there is a definite correlation between the mechanical properties and electrical properties in the metallic films.

Within density function theory under the generalized gradient approximation, for ideal Co2MnSi/GaAs (001) and (110) multilayer structures, the CoSi–AsGa interfaces are found to be half-metallic. While the most stable (110) CoSi–GeGe interface, for the ideal Co2MnSi/Ge multilayer systems, is near half-metallic. Given the atomic disorder in the Co2MnSi/GaAs (001) ((110)) multilayer systems with the CoSi–AsGa interface, Co anti-site defect is more readily presented at the (001) ((110)) interface. These results show that the low tunneling magnetoresistance ratio or spin injection measured in Co2MnSi/GaAs (001) (or (110)) tunnel junction in some experiments may be relevant to the interfaced Co anti-site defect as well as interfacial structure.

The structural properties, the formation and migration energies of a single vacancy migrating intralayer and interlayer in the CuAu-terminated (110) surface of Cu3Au ordered alloy have been calculated and discussed by using the modified analytical embedded-atom method (MAEAM) and molecular dynamics (MD) methods. The surface layer exhibits rippling that the Au atoms are raised above Cu atoms about 0.117 A in the topmost layer. The displacements of the topmost two layers are comparatively larger, while the third layer relaxes slightly and there are no changes in the nether layers. From energy minimization, the vacancy is most likely to be formed in the first layer (1L), especially on the Au site. The surface vacancy shows the smallest formation energy compared to the interlayer and bulk vacancies, while the corresponding value converges after the fifth layer (5L). For Cu vacancy originally sited in the second layer (2L) and migrated intralayer and interlayer, the diffusion without causing the local disorder is the most favorable, and the vacancy tends to migrate to the topmost layer. In the topmost layer of the CuAu-terminated (110) surface, the circularity path is preferred over the beeline path. Copyright © 2011 John Wiley & Sons, Ltd.

By using the density-functional theory, we have systematically investigated the adsorption of oxygen on Pt(1 1 1) surface for a wide range of coverages (from 0.11 ML to 1.00 ML) and adsorption sites. In the view of adsorption energy maximization, we found that the fcc site is the most stable site for oxygen adsorption, which is always slightly energetically favorable than the hcp site, and for these two sites, the adsorption energies decrease as the increasing oxygen coverage due to the increasing repulsive lateral interactions in the overlayer O adatoms. Except for coverage of 1.00 ML, the oxygen-induced lateral relaxations and bucklings are found in the outermost substrate Pt layers. Taking into account the effects of the chemical environment as a function of the relative richness in oxygen, we obtained that oxygen can form two stable configurations in the fcc site adsorption: the 0.25 ML configuration in oxygen-poor conditions, and the 0.50 ML case in oxygen-rich environments. The work function and the surface dipole moment are also studied and analyzed. Electron transfer between the first layer Pt and the O adatoms indicates the O–Pt chemical bond shows some degree of ionic character. In addition, the hybridization between O 2p and Pt 5d orbitals, especially at oxygen coverage of 1.00 ML, implies the O–Pt bond also shows some degree of covalence character. Moreover, with the increasing oxygen coverage, more Pt 5d states are empty thus weakening the binding of O/Pt(1 1 1) systems at higher coverage, and the density of states at the Fermi level for the O/Pt(1 1 1) system decreases thereby the metallic character is weakened.

The structural, electronic, and magnetic properties of Fe nanowire encapsulated in zigzag CNTs have been investigated systematically using the first-principles PAW potential within DFT under GGA. Among the seven Fe-encapsulated C cables, only the (8,0) nanocable is formed endothermically, the other larger cables are formed exothermically. Therefore, it is expected that thicker Fe nanowires would be pulled spontaneously into larger CNTs by forces amounting to a fraction of a nanonewton. The high spin polarization and magnetic moments of the Fe-encapsulated C cables coming solely from the Fe nanowire imply the Fe-encapsulated C cables can be appropriate to various applications such as spintronics, high-density magnetic storage, and magnetically guided drug-delivery systems.

Mg–Zr–O protective films for plasma display panels were deposited on soda-lime glass substrates by magnetron sputtering. The effects of oxygen partial pressure on both the discharge properties (i.e., firing voltage Vf, minimum sustaining voltage Vs, and memory coefficient MC) and the microstructure of the Mg–Zr–O films were investigated. The results show that the deposited Mg–Zr–O films retain the NaCl-type structure as the pure MgO crystal and the doped Zr exists in the form of Zr4+ substitutional solid solution in MgO crystal lattice. The grain of the films is very fine and the mean grain size is about 7nm. As the oxygen partial pressure increases from 0.06to0.12Pa, the Zr content increases and surface roughness of the films decreases. However, when oxygen partial pressure further increases, the film shows a decrease in Zr content and an increase in surface roughness. At oxygen partial pressure of 0.12Pa, the Mg–Zr–O film has the lowest Vf and Vs and the largest MC, exhibiting the best discharge propert...

We performed first-principle calculations, by employing the ultrasoft pseudopotential plane-wave (UPPW) method, for the multilayer relaxation and the local density of states (LDOS) of Cu(430) and its corresponding flat Cu(110) surfaces. The shift directions of the atoms in the terrace (layers 1–4), sub-terrace (layers 5–7) and third-terrace (layers 8–11) of the Cu(430) surface are similar to the layers 1, 2 and 3 of the Cu(110) surface, respectively. And the stepped surface changes to a flatter version with a thin compacted layer, including the topmost seven atomic layers and separating slightly from the underneath atomic layers. Because of a reduction in the coordination numbers (CNs),there is a sharp rise in the higher energy region and a slight reduction in the lower energy region of the LDOSfor the topmost three layer atoms of the Cu(430) surface and the first layer atom of the Cu(110) surface. The shape of the LDOS of the corresponding layer with the same CN is similar for both the surfaces. Copyright © 2009 John Wiley & Sons, Ltd.

With static relaxation, the surface diffusion activation energies of a single Cu adatom migrated by both atomic exchange and hopping mechanisms and the forces acted on the diffusing adatom from other atoms of Cu (0 0 1) or (1 1 0) surface are calculated by using the MAEAM. When adatom migrated on Cu (0 0 1) or (1 1 0) surface, the increment curves of the system energy by hopping mechanism are symmetrical and the saddle points are in the midpoints of the migration path, but the ones by the exchange mechanism are dissymmetrical and the saddle points are always close to the initial hole positions of the adatom and away from the initial equilibrium positions of the exchanged atom. From minimization of both the diffusion activation energy and the force acted on the diffusing adatom from other atoms, we found that, on Cu (0 0 1) surface the favorable diffusion mechanism is hopping mechanism, however, on Cu (1 1 0) surface, hopping via long bridge is easier than the exchange mechanism but the hopping via short bridge is more difficult than the exchange mechanism.

Mg–Zr–O protective films for plasma display panels (PDPs) were deposited on soda-lime glass substrates by magnetron sputtering method. The effects of Zr doping on both the discharge properties (firing voltage, V f and the minimum sustaining voltage, V s ) and the microstructure of the Mg–Zr–O films were investigated. The results show that the deposited Mg–Zr–O films retain the NaCl-type structure as the pure MgO crystal. The doped Zr exists in the form of Zr 4+ substitution solution in MgO crystal and an appropriate amount of Zr can improve the surface characteristics of the Mg–Zr–O films effectively. When the Zr atomic concentration is about 2%, the Mg–Zr–O films have the strongest (2 0 0) preferred orientation and the minimum surface roughness. The firing voltage and the minimum sustaining voltage of Mg–Zr–O protective layer are reduced at most by about 25 V and 15 V, respectively, compared with those of the pure MgO film. Mg–Zr–O protective layers with an appropriate amount of Zr are promising to meet the demands of advanced high-vision PDPs.

The structural and electronic properties of Pt monolayer adsorption on both PbO and TiO 2 terminations of PbTiO 3 (100) surface have been investigated by first-principles projector-augmented wave calculations with slab models. It is found that Pt monolayer prefers to bind on PbO site of PbO termination and on O site of TiO 2 termination. The main impetus for the stability of these preferred binding sites is the close proximity of Pt atoms to O atoms. In addition, strong interaction between Pt atom and the first layer O atom is observed and the hybridization between Pt 5 d orbital and the O 2 p orbital is found. Moreover, the coordination number dominates the position of the DOS curve while the hybridization mainly influences the shape of the DOS and results in new peaks.

Under the generalized gradient approximation, the relaxed structures and electronic properties have been investigated for Au nanowires with cross sections of 3 x 3, 5 x 5, 7 x 7, 9 x 9, and 11 x 11 atom layers using the first-principles projector-augmented wave potential within the density functional theory. For all five-sized nanowires, the relaxed structures still have tetragonal symmetry and show a "round corner" phenomenon. The vanishing of the neighbor atoms outside the nanowire after being cleaved from bulk crystal not only causes the structure relaxation above but also affects the electronic properties in the following three aspects. (1) The total charges of the surface and near surface atoms are reduced. (2) The enhanced interactions appear between the surface atoms as well as the surface atoms and their first nearest neighbor atoms; we term this phenomenon the "skin effect", which enhances the mechanical and the electronic transport properties of the nanowire compared to bulk. (3) The farther the atoms are from the central axis of the nanowires, the more the electrons fall in the higher energy region of the occupancy state due to the lower coordination number and thus fewer restrictions. In fact, the conclusions drawn here are applicable to not only the nanowires but also the other surface cases, such as nanobelts, nanotubes, nanocables, clusters, thin films, and so on.

The electronic and magnetic properties of the three types of ferromagnetic nanowires (FN4’s), Fe4, Co4, and Ni4, encapsulated in boron nitride nanotubes (BNNTs) have been investigated systematically using the first-principles projector-augmented wave potential within the density functional theory under the generalized gradient approximation. We find that all three types of the FN4 encapsulated into the narrower (6,6) BNNT are endothermic, whereas if they are encapsulated into the broader (8,8) BNNT, they are exothermic. Both the spin polarization and the magnetic moment of the FN4@(8,8) systems are larger than those of the FN4@(6,6) systems due to weaker restriction of the broader (8,8) BNNT, but those of these two combined systems are smaller than those of the corresponding freestanding FN4. The spin polarization of the Co4@(8,8) system is larger than that of either the Fe4@(8,8) system or the Ni4@(8,8) system, which means that the Co4@(8,8) system can be used as a spin valve in spin-dependent transport ...

MAEAM. When the adatom is very close to the surface, the maximum (minimum) values of the energy and repulsive force appear above the top (hollow) of the first layer atoms of the Pt (111) surface. With increasing the distance of the adatom from the surface, energy and force become negative, and their maps are more complicated than those obtained by using pair-potential because of dominant effects of the many body interaction and nonspherical distribution of the electrons of the atoms in the crystal. The stable position of the Pt adatom is found to be 0.19 nm above the hollow of thefirst layer atoms of the Pt (111) surface, but the energy corresponding fcc hollow is a little smaller than the hcp hollow. There are no relevant available experimental and calculational data about the energy and force of a Pt adatom on a Pt (111) surface for comparison. Our calculational results could give some guidance for experimental study. MAEAM

The formation and diffusion of a single Mo or Ta vacancy in the (0 0 1) surface of the B2-type MoTa alloy have been investigated by using modified analytical embedded-atom method (MAEAM). The results show that the effect of the surface on the vacancy is only down to the sixth layer. It is easier for the vacancy to form in the first layer. Comparing the migration energy of the vacancy migrating in the intra-layer, to the upper layer and to the nether layer via 2NN jump, we find that the vacancy in the first or second layer is preferred to migrate in intra-layer, and that in the third or fourth layer is favorable to migrate to the upper layer. Although 1NN jump will result in an anti-site so that a disorder in the order alloy, it may also occur due to the much lower migration energy especially for the vacancy in the second and third layer to migrate to the first and second layer, respectively.