Search

To lower the charge leakage of a floating gate device and improve the operation performance of memory devices toward a smaller structure size and a higher component capability, two new types of floating gates composed of pn-type polysilicon or np-type polysilicon were developed in this study. Their microstructure and elemental compositions were investigated, and the sheet resistance, threshold voltages and erasing voltages were measured. The experimental results and charge simulation indicated that, by forming an n-p junction in the floating gate, the sheet resistance was increased, and the charge leakage was reduced because of the formation of a carrier depletion zone at the junction interface serving as an intrinsic potential barrier. Additionally, the threshold voltage and erasing voltage of the np-type floating gate were elevated, suggesting that the performance of the floating gate in the operation of memory devices can be effectively improved without the application of new materials or changes to the physical structure.

This study reports a thermodynamic route for self-forming an ultrathin V-Nb-Mo-Ta-W high-entropy alloy layer for potential use as a promising diffusion barrier. In Cu alloy films minor-doped with 1.2 at.% of one-to-five metallic elements (V, Nb, Mo, Ta and W), the alloying elements spontaneously segregated. Under the competition of enthalpy and mixing entropy that determines the delta Gibbs free energy, one and, in particular, five alloying element(s) formed an alloy solution layer at the Cu/Si interface, whereas three alloying elements differently formed intermetallic compound clusters at the grain boundaries of Cu. Dominant factors for the final states of the alloying elements include the large positive enthalpy between Cu and the alloying elements, the negative enthalpy among the alloying elements, and the low-to-high mixing entropy among the alloying elements. The self-forming quinary alloy layer of only 1.5 nm thick provided excellent resistance to the interdiffusion of Cu and Si up to 700°C, better than practical and other newly developed barrier materials.

Cr and Mn play intriguing roles in determining the magnetic properties of CoFeNi-based high-entropy alloys (HEA). In this study, we tune the stoichiometric Mn composition to systematically explore the magnetic properties of (CoCrFeNi)1−xMnx HEAs. We observe a change from ferro-to ferrimagnetism due to the incorporation of Mn atoms into the CoCrFeNi HEA. In addition, we measure an 81% reduction in magnetization with the incorporation of 7.6 (2)% Mn atoms. Such a significant reduction in magnetization cannot be solely explained by the effect of the inversed moments on the Mn atoms. Hence, we propose a mechanism whereby the Mn atoms flip the moments of neighboring atoms, which results in the magnetization reduction observed in the CoFeNi-based HEAs.

Diamond/Ag/Cu–Ti composites were fabricated by low-cost pressureless sintering with Ti addition to improve the diamond–metal matrix wettability and the effects of Ag/Cu matrix variation on the composites were investigated. Transmission electron microscopy identified the interfacial structure on the diamond (1 0 0) plane of the diamond/Ag/Cu–Ti composite with the 80 at.% Cu matrix as Cu–Ag/TiC/Ag–C/TiC/diamond. The thermal conductivity of the diamond/Ag/Cu–Ti composites was significantly enhanced upon increasing the Ag contents of the Ag/Cu matrix. The 60 vol% diamond/Ag/Cu–2 at.% Ti composite with 40 at.% Cu matrix content exhibited the maximum thermal conductivity of 826 W/m·K and the compatible coefficient of thermal expansion of 6.0 ppm/K. The diamond/Ag/Cu-Ti composites are promising low-cost thermal management materials for electronic device integration.

The authors would like to make corrections to a recently published paper [...]

Diamond/Ag-Ti composites were fabricated by pressureless sintering. The minor addition of Ti effectively ameliorated the wettability between diamond and the silver matrix. Transmission electron microscopy indicated that the interface structure of the diamond (100) plane of the diamond/Ag-Ti composites was Ag/TiC/TiC-Ag/diamond. The thermal conductivity of the 300 μm 60 vol% diamond/Ag-1.5 at% Ti composite reached 953 W/m·K – approximately 98% of the theoretical thermal conductivity calculated by the differential effective medium model in conjunction with the diffuse mismatch model. The composites possessed compatible coefficients of thermal expansion, and excellent thermal cycling performance under long-term operation and stringent joining packages condition. The excellent thermal properties and low cost of the diamond/Ag-Ti composites make them promising as thermal management materials in integrated electronic devices.

High hardness, high toughness, high oxidation resistance, and low friction coefficient are key properties of protective coatings. High-entropy alloy (HEA) films have considerable potential as protective hard coatings for tools used for surface milling, turning, and drilling. However, to date, despite their promise, high-entropy alloy carbonitride films (HEACN) have not been studied extensively. Therefore, in this study, we deposited (CrNbSiTiZr)CxNy on Si(100), SiO2, and WC-Co substrates via radio frequency magnetron sputtering and investigated their microstructures, oxidation behavior, and properties. The (CrNbSiTiZr)CxNy film having a carbon content of 71 at% displayed the lowest friction coefficient (0.13) and wear rate (0.4 × 10−7 mm3/N⋅m). Further, as the nitrogen content was increased, the hardness values, oxidation resistances, friction coefficients, and wear rates of the films also increased, reaching their maximum values at 48.2 at%. X-ray diffraction analysis revealed that all the films exhibited a single face-centered cubic (NaCl-type) structure, and the diffraction peaks shifted to higher angles with increase in the nitrogen content, suggesting an increase in the crystalline nitride phase.

This article presents detailed microstructure characterization of cemented carbide fabricated by selective laser melting process. Nickel-coated tungsten carbide powders were used for this study; the selective laser melting process induced complex microstructure consisting of partially-melted carbide, carbide precipitates and dendritic microstructure. Four phases were identified, i.e. MC, M2C, FCC and η in the as-built specimen. CALPHAD phase diagram was utilized to describe possible phase formation sequence during selective laser melting process, which involved melting, solidification and repeated heating. Although the composition of initial powder was very simple (spherical W2C-WC and Ni-coating), selective laser melting allowed the decomposition of initial carbides, subsequent formation of dendritic structure and precipitation of additional carbides. To the best of authors' knowledge, for the first time, detailed microstructure characterization of cemented carbide fabricated by selective laser melting is presented.

High-entropy (CrNbSiTiZr)Cx coatings were successfully fabricated by reactive radio-frequency magnetron sputtering using an equimolar CrNbSiTiZr alloy target under CH4-containing Ar flow. The effect of the CH4 flow ratio on the chemical composition, microstructure, mechanical and tribological properties of (CrNbSiTiZr)Cx coatings was investigated. The carbon content in the coatings varied from 36.7 at% to 87.8 at% with an increasing CH4 flow ratio from 3% to 20%. The (CrNbSiTiZr)Cx coatings revealed a simple NaCl-type FCC (face-centered cubic) structure. The maximum hardness of 32 GPa was obtained at the carbon content of 36.7 at% by applying substrate bias of −100 V. On the other hand, the coating with high carbon content of 87.8 at% possessed superior wear resistance, which friction coefficient and wear rate were, respectively, 0.07 and 2.0 × 10−7 mm3/N·m.

The lattice distortion of a solute primarily occurs because its atomic size and chemical bonding are different from those of neighboring atoms. The lattice distortion effects in conventional and high-entropy alloys are different; however, a detailed investigation on these effects has yet to be conducted. To fill this research gap, this study produced face-centered cubic-structured dilute solutions (Ni, Ni–2 at.% W, and Ni–4 at.% W) and concentrated solutions (equiatomic CrFeNi and CoCrFeMnNi) and compared their tensile properties. For the two W-containing alloys, lattice distortion occurred only around the large and strong W atoms. However, for the two concentrated solutions, which had a similar interelement atomic size and shear modulus to the aforementioned alloys, lattice distortion occurred at all lattice sites. These two types of lattice distortion had significantly different effects on tensile properties. The strength and ductility of the alloys with a high concentration of distorted lattice points were higher than those of the alloys with a low concentration of distorted lattice points, although the alloys with a low concentration of distorted lattice points had a larger nominal atomic size difference and shear modulus difference. The mechanisms underlying the evolution of different mechanical properties under different types of lattice distortion were examined for the dilute and concentrated alloys. Moreover, the universal solid solution strengthening mechanism was observed.

The HfNbTaTiZr refractory high-entropy alloy was investigated on the grain growth kinetics and tensile properties. Grain growth at 1200–1350 °C is rather slow. The activation energy is 389 kJ/mol and the growth exponent is 3.5. The HfNbTaTiZr alloy has high strength, small work hardening and high ductility. Grain refining is found to enhance the tensile strength and ductility simultaneously.

The crystal structure, microstructure, and mechanical properties of HfMoxNbTaTiZr (x≤1) alloys were investigated by X-ray diffraction, scanning electron microscopy, and compression testing. All the as-solidified HfMoxNbTaTiZr alloys possess a simple body-centered cubic structure. Lattice parameters of the HfMoxNbTaTiZr alloys decrease with an increase in Mo concentration, but the corresponding densities show an opposite trend. The yield strength of the HfMoxNbTaTiZr alloys increases from 1015 MPa to 1512 MPa as x increases from 0 to 1. The solid solution strengthening is linearly proportional to a Mo concentration suggesting that the strengthening effect from each Mo atom is additive. Except for the HfMoNbTaTiZr alloy, HfMoxNbTaTiZr (x 50%). The material with x=0.75 is a new ductile refractory high-entropy alloy with promising mechanical properties.

The superior mechanical properties of high-entropy alloys (HEAs) have made an outstanding success in materials science and engineering. Studies to date have been devoted to what the severe lattice distortion induces. However, most researchers focus on its stimulation to plastic deformation instead of scrutinizing the variations on elasticity. Compared with conventional alloys, HEAs may perform disproportionate elasticity with uneven local lattice strain resulting from the severe lattice distortion. Therefore, it is necessary to survey its influence on the mechanical properties of HEAs systematically. In this study, the Lennard-Jones (LJ) potential, the embedded atom method (EAM) potential, and the modified embedded atom method (MEAM), are respectively conducted to investigate the lattice distortion effect on Young’s modulus E (hkl) and Poisson’s ratio ν (hkl, θ) along [100], [110], and [111] loading directions for several fcc metals composed of 1 ∼ 5 atomic types, including Ni, Ni98W2, Ni96W4, FeCrNi, and CoNiCrFeMn HEAs. Also, a method is used to analyze the performance of the individual element on the elastic properties in the HEA environment. As a result, it can be unveiled that the effect of electron density inconsistency is more dominant than the effect of lattice distortion associated with the atomic size difference. The electronic configuration in the HEA environment plays a major role in elastic anisotropy while the difference of the atomic radii does the minor one. The anisotropy of CoNiCrFeMn HEA analyzed by this work is also consistent with in-situ neutron diffraction measurements.

Texture evolution during tension test was investigated on three face-centered cubic (FCC) metals, namely, Ni (unary), equiatomic CrFeNi (ternary), and equiatomic CoCrFeMnNi (quinary) with small and large grain sizes of ~20 and ~100 μm, respectively. The microtextures for 18%, 36% and 54% engineering strains of a tension-interrupted specimen were characterized on the same area. The three metals exhibited a similar texture evolution, which the fraction of {001}//ND remains constant. However, the fraction of {011}//ND decreases, whereas that of {111}//ND increases. On the other hand, the fraction of //RD also remains constant, that of //RD decreases, and that of //RD increases. However, the several differences still were found during plastic deformation. Fine-grained Ni initiated a significantly crystallographic rotation (CRo) at the lower strain, increased with strain and then remained nearly unchanged as strain was higher than 18%. Coarse-grained Ni delayed this rotation and slowly developed the trend at large strains. As for CrFeNi, the comparison between fine-grained and coarse-grained structure does not have obvious difference. As for fine-grained CoCrFeMnNi, it can be seen that an obvious CRo develops under 36% strain, and maintains constant over 36% strain. But the coarse-grained CoCrFeMnNi reveals that the significant CRo develops continuously from 0% to 54% strain. The mechanisms for the effects of number of element and grain size in the present study are elucidated.

Although refractory high-entropy alloys have exceptional strength at high temperatures, they are often brittle at room temperature. One exception is the HfNbTaTiZr alloy, which has a plasticity of over 50% at room temperature. However, the strength of HfNbTaTiZr at high temperature is insufficient. In this study, the composition of HfNbTaTiZr is modified with an aim to improve its strength at high temperature, while retaining reasonable toughness at room temperature. Two new alloys with simple BCC structure, HfMoTaTiZr and HfMoNbTaTiZr, were designed and synthesized. The results show that the yield strengths of the new alloys are apparently higher than that of HfNbTaTiZr. Moreover, a fracture strain of 12% is successfully retained in the HfMoNbTaTiZr alloy at room temperature.

Stress-induced ZnO·xH2O and TiO2·xH2O nanocrystals were spontaneously grown on ZnO and TiO2 films in an ambient atmosphere based on a bond breaking–hydrolysis–reconstruction mechanism, without the use of any other precursors. The development of their phase and structure towards ZnO and TiO2 was in situ and ex situ studied. The formation of unstable near-amorphous belt-like orthorhombic ZnO·1.5H2O nanowires and partially crystalline column-like (pyramid top) monoclinic TiO2·2.5H2O nanorods was initiated in a high relative humidity of 98%, whereas more stable polycrystalline faceted orthorhombic ZnO·H2O nanowires and bamboo leaf-shaped monoclinic TiO2·0.4H2O nanoflakes were formed in 70% humidity. Upon receiving energy through in situ exposure to an electron beam or ex situ thermal annealing, the ZnO·xH2O and TiO2·xH2O transformed into hexagonal (wurtzite) ZnO and orthorhombic (brookite) TiO2, respectively. Exposure of non-polar TiO2 to an electron beam or annealing generated a polycrystalline structure. Exposure of polar ZnO to a low-energy electron beam caused the formation of aligned subgrains, while high-energy annealing yielded a single-crystalline structure, both with a longitudinal [100] orientation, via a self-assembly process that involved nanocrystallite agglomeration, subgrain tilting and boundary elimination.

Diamond/Cu composites fabricated via the traditional powder metallurgy method show low thermal conductivities due to the poor wettability between diamond and Cu matrix. The fabrication method adopted in this study provides a simple and low-cost method for producing diamond/metal composites. Thermal properties of the diamond/Cu–Ti composites fabricated by pressureless sintering at 1373 K for 30 min with variation in diamond particle sizes and volume fractions were thoroughly investigated. The composites produced in this study exhibited thermal conductivity as high as 608 W/m K for 60 vol.% bimodal diamond/Cu-2 at.% Ti composite comprised of 50 vol.% diamond particles with the size of 300 μm and 10 vol.% diamond particles with the size of 150 μm. A suitable coefficient of thermal expansion of 5.4 × 10 −6 1/K was obtained. This thermal conductivity value comes up to 92% of the thermal conductivity calculated by Hasselman and Johnson model combining with diffuse mismatch model. The predicted value from this model is in good agreement with the experimental value. Furthermore, the pressureless sintering is a simple technique that requires only low-cost equipment, making this cost-effective method attractive for metal matrix composite fabrication.

Diamond/Ag–Ti composites were fabricated by a low-cost liquid sintering technique. The Ti addition can effectively improve wetting and promote penetration in composite pores during liquid sintering. The interface structure of the diamond/Ag–Ti composite was identified as Ag/TiC/Ag–Ti/diamond. A high thermal conductivity of 719 W/mK was obtained for the 50 vol.% diamond/Ag-1 at.% Ti composite. Using a bimodal mixture (60 vol.% 150 μm + 10 vol.% 50 μm diamond/Ag-2 at.% Ti composite), a low coefficient of thermal expansion of 6.3 × 10 − 6 /K still with high thermal conductivity of 687 W/mK was achieved. These composites have potential applications for thermal management of high integration electronic devices.

Degenerately Sn-doped In2O3 (ITO) nanowires were synthesized via an Au-catalyzed vapor–liquid–solid (VLS) method at 750 °C. The Au seed layer provided sites with a high surface energy for the selected-area growth of ITO nanowires. Morphology and crystal structures confirmed by field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) was employed to obtain the chemical compositions of the ITO nanowires as well as the ratio of Sn/In and oxygen concentrations. Under the photo-excitation the ITO nanowires emit ultraviolet light, which can be ascribed to transitions related to donor levels. Moreover, photoluminescence (PL) spectrophotometer and UV–VIS spectrum analysis revealed a blue shift peaks in the degenerately ITO nanowires. This phenomenon can be explained by Burstein–Moss effect.

Enhanced field emission properties of Sn-doped In2O3 (ITO) nanowires (NWs) after the formation of a heterostructure core–shell configuration, namely ZnO nanoparticle-decorated HfO2/Sn-doped ITO NWs, by the atomic layer deposition (ALD) process were reported and investigated in detail. Island growth of a ZnO layer on the ITO NWs, with a low density, after the ALD process was observed while for the growth of the ZnO layer on the HfO2/ITO core–shell NWs, a ZnO layer with very tiny nanoparticles (NPs) can be achieved along the axial direction throughout the whole nanowire. A turn-on field of ∼10.8 eV with a field enhancement factor (β) of 409 can be found for the ITO NWs while the turn-on field decreases from 10.8 to 6 V μm−1 with an increase in the field enhancement factor (β) from 409 to 753 after the ZnO nanoparticle growth on the ITO NW. By combining the two materials utilizing surface modification engineering, a highly dense ZnO NP decorated on HfO2/ITO core–shell NWs can be achieved, resulting in a significant reduction of the turn-on field to 3.7 V μm−1 with an excellent field enhancement factor of 1677. The findings provide an effective way of improving the field emission properties for nanodevice applications.

Resistive random access memory (ReRAM) has been considered the most promising next-generation nonvolatile memory. In recent years, the switching behavior has been widely reported, and understanding the switching mechanism can improve the stability and scalability of devices. We designed an innovative sample structure for in situ transmission electron microscopy (TEM) to observe the formation of conductive filaments in the Pt/ZnO/Pt structure in real time. The corresponding current-voltage measurements help us to understand the switching mechanism of ZnO film. In addition, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) have been used to identify the atomic structure and components of the filament/disrupted region, determining that the conducting paths are caused by the conglomeration of zinc atoms. The behavior of resistive switching is due to the migration of oxygen ions, leading to transformation between Zn-dominated ZnO(1-x) and ZnO.

Multicomponent high-entropy nitrides have been attempted as robust diffusion barrier materials to inhibit the severe interdiffusion of Cu and Si; however, the improvement in their diffusion resistance relative to the abilities of few-component nitrides has actually not been verified. Thus, in this study, nitride barriers with different numbers of components (metallic elements), from unitary TiN to senary high-entropy (TiTaCrZrAlRu)N (with the same face-centered cubic structure and a thickness of 5 nm), were prepared. The failure of these nitride barriers in resisting the interdiffusion of Cu and Si was examined, and the activation energy of Cu diffusion through the nitrides was determined. With more components incorporated, the failure temperature of the nitrides was found to markedly increase from 550°C to 900°C, and the activation energy of Cu diffusion was effectively raised from 107 kJ/mol to 161 kJ/mol. Severe lattice distortions and random cohesions are suggested as the dominant factors for the improved diffusion-resistant ability of the multicomponent high-entropy nitrides.

A ZnO-based transparent resistance random access memory (TRRAM) employs atomic layered graphene exhibiting not only excellent transparency (less than 2% absorptance by graphene) but also reversible resistive switching characteristics. The statistical analysis including cycle-to-cycle and cell-to-cell tests for almost 100 cells shows that graphene plays a significant role to suppress the surface effect, giving rise to the notable increase in the switching yield and the insensitivity to the environmental atmosphere. The resistance variation of high-resistance state of ZnO is greatly suppressed by covering graphene as well. The device reliability investigation, such as the endurance more than 102 cycles and the retention time longer than 104 s, reveals the robust passivation of graphene for TRRAM applications. The obtained insights show guidelines not only for TRRAM device design and optimization against the undesired switching parameter variations but also for developing practically useful applications of graphene.

A bias polarity-manipulated transformation from filamentary to homogeneous resistive switching was demonstrated on a Pt/ZnO thin film/Pt device. Two types of switching behaviors, exhibiting different resistive switching characteristics and memory performances were investigated in detail. The detailed transformation mechanisms are systematically proposed. By controlling different compliance currents and RESET-stop voltages, controllable multistate resistances in low resistance states and a high resistance states in the ZnO thin film metal-insulator-metal structure under the homogeneous resistive switching were demonstrated. We believe that findings would open up opportunities to explore the resistive switching mechanisms and performance memristor with multistate storage.

The hardening in Al 0.3 CrFe 1.5 MnNi 0.5 high-entropy alloy not only nearly triples the hardness of the alloy, but also shows a quick hardening response and the absence of overaging. However, the crystal structure, morphology, and composition of the hardening phase have not yet been confirmed. Here, such information regarding the hardening phase is investigated. It was found that the hardening phase is a Cr–Mn–Fe ternary sigma phase. Unlike in conventional engineering alloys, the sigma phase is not precipitated from the matrix, instead, the whole BCC matrix transforms to sigma phase almost without changing its composition. Therefore, the hardening phenomenon is not a precipitation hardening reaction as suggested before.

An Al 0.3 CrFe 1.5 MnNi 0.5 multi-component alloy with a very effective surface hardening ability attributed to intrinsic ρ phase precipitation and applicable to complex tool components was developed. Under a conventional aging treatment in a normal atmosphere at 550 °C for 2 h, the alloy with the surface precipitation hardening layer of 74 μm thick exhibited markedly enhanced surface hardness from HV 338 to HV 840 and efficiently improved wear resistance to 1.4 times the values of SUJ2 and SKD61 steels, while high fracture toughness close to that of ductile SKD61 steel was effectively retained. Precipitation thermodynamics and growth kinetics of the surface hardening layer were also investigated. The growth of the surface hardening layer was much faster than that of the precipitation in the bulk matrix; it did not follow typical long-distance diffusion kinetics but behaves more similar to a self-induced or reaction-accelerated short-range decomposition with a thickness increase proportional to the cube of aging time. On the surface, a lower heterogeneous nucleation energy and a reduced strain energy (total 55 kJ/mol) than the regular nucleation energy in the bulk matrix (78 kJ/mol) dominated the rapid formation and growth of the intrinsic surface precipitation with significant strain relaxations.

High-entropy alloys (HEAs) can be deposited on substrates as thick or thin alloy films for protection against wear, corrosion, and heat, and for function enhancement and decorative purposes. In addition, various HEA nitride coatings based on HEAs can be easily deposited using reactive coating technology by allowing the atoms or ions from the targets to react with N2-containing Ar flow during deposition. Similarly, HEA carbides, oxides, and carbonitrides could be deposited under CH4-containing, O2-containing, and CH4 + N2-containing Ar flow, respectively. Such HEA ceramic coatings also show the four core effects observed in HEAs: high-entropy, sluggish diffusion, severe lattice distortion, and cocktail effects. The structure is, in general, much simpler than expected. Amorphous, nanocrystalline, and nanocomposite films are often obtained. The properties of HEA coatings or HEA ceramic coatings can be outstanding, and these coatings have great potential for various applications if proper compositions and deposition parameters are used.

Plasmonic structures of FTO/TiO 2 /NPs-Ag and FTO/NPs-Ag/TiO 2 electrodes were fabricated by sputter technology and the sol–gel & spin coating procedure. These electrodes with similar optical absorptions in the visible region enhanced by the surface plasmon resonance of silver nanoparticles have different photovoltaic properties, revealing that the significant design can be used to identify the favorably enhanced direction of plasmonic structure resulting from plasmonic scattering to trap light which confines light within the active TiO 2 layer to promote dye absorption in dye-sensitized solar cells (DSSCs). In the FTO/TiO 2 /NPs-Ag, a 60% enhancement in photocurrent and an improvement in photovoltage were observed and the increased incident photon-to-photocurrent efficiency (IPCE) was consistent with the enhanced absorption spectrum. However, the photovoltaic properties of the FTO/NPs-Ag/TiO 2 were similar to those of the standard electrode. This concept is potentially applicable to new kinds of solar cells.

Self-assembled vertical nanostructures take advantage of high interface-to-volume ratio and can be used to design new functionalities by the choice of a proper combination of constituents. However, most of the studies to date have emphasized the functional controllability of the nanostructures using external electric or magnetic fields. In this study, to introduce light (or photons) as an external control parameter in a self-assembled nanostructure system, we have successfully synthesized oxide nanostructures with CoFe(2)O(4) nanopillars embedded in a SrRuO(3) matrix. The combination of photostrictive SrRuO(3) and magnetostrictive CoFe(2)O(4) in the intimately assembled nanostructures leads to a light-induced, ultrafast change in magnetization of the CoFe(2)O(4) nanopillars. Our work demonstrates a novel concept on oxide nanostructure design and opens an alternative pathway for the explorations of diverse functionalities in heteroepitaxial self-assembled oxide nanostructures.

This study investigates the effect of plasma nitriding at 798 K (525 °C) on microstructures and the mechanical performance of Al0.3CrFe1.5MnNi0.5 high-entropy alloys (HEAs) obtained using different cast and wrought processing. All the alloys can be well nitride, with a thickness of around 80 μm, and attain a peak hardness level around Hv 1300 near the surface. The main nitride phases are CrN, AlN, and (Mn, Fe)4N. Those of the substrates are bcc, fcc, Al-, and Ni-rich B2 precipitates, and ρ phase. Their relative amounts depend on the prior processing and also change under the heat treatment during nitriding. The formation of ρ phase during nitriding could in-situ harden the substrate to attain the suitable level required for wear applications. This gives the advantage in simplifying the processing for making a wear-resistance component or a mold since austenitizing, quench hardening, and tempering required for steels such as SACM and SKD steels are no longer required and final finishing can be accomplished before nitriding. Nitrided Al0.3CrFe1.5MnNi0.5 samples have much better wear resistance than un-nitrided ones by 49 to 80 times and also exhibit superior adhesive wear resistance to conventional nitrided alloys: nitriding steel SACM-645 (AISI 7140), 316 stainless steel, and hot-mold steel SKD-61 (AISI H13) by 22 to 55 times depending on prior processing. The superiority is due to the fact that the present nitrided alloys possess a much thicker highly hardened layer than the conventional alloys.

In this study, single-crystalline γ-Al2O3 nanowires were synthesized by simple evaporation of Al–Si alloy source powder at 1070 °C under different working pressures. The structures and growth mechanisms of the nanowires were examined. Under a low working pressure of 0.5 torr, uniform nanowires with a catalyst particle were synthesized by a vapor–liquid–solid mechanism and grew along a [2-20] direction. Twinning occurred parallel to nanowire growth direction and a twin angle of 15.5°/164.5° was identified. As the pressure increased, zigzag nanowires without a catalyst grew along a [−1−11] direction alternatively via a vapor–solid route. Twinning also formed with an angle of 15.5°/164.5°. Perpendicular twinning planes to the growth direction induced the deflected feature of the nanowires.

A series of AlxCo1.5CrFeNi1.5Tiy high-entropy alloys with different Al and Ti contents were designed, and their phase and microstructure were investigated. The adhesive wear behavior and mechanism were also studied and compared with the conventional wear-resistant steels SUJ2 and SKH51. The amounts of Al and Ti strongly affect the phase and microstructure, particularly the amount and morphology of the hard g-(Ni, Co)3Ti phase. It was found that the wear resistance of the Co1.5CrFeNi1.5Ti and Al0.2Co1.5CrFeNi1.5Ti alloys is at least two times better than that of conventional wear-resistant steels with similar hardness. The excellent anti-oxidation property and resistance to thermal softening in these high-entropy alloys are proposed to be the main reasons for the outstanding wear resistance. 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Single-ZnO-nanowire (NW) memory based on resistive switching is demonstrated for the first time. The NW memory is stable, rewritable, and nonvolatile with on/off ratio up to 7.7 × 105. The O vacancies at the surfaces of ZnO NWs and around the interface of Ti/ZnO NWs observed using X-ray phototelectron spectroscopy, transmission electron microscopy (TEM), selected-area electron diffraction, and high-resolution TEM might play a role in the resistive switching behavior. The endurance of resistive switching can be enhanced by further increasing the sweeping voltage. This paper brings an exciting possibility of building next-generation memory devices based on NWs.

(AlCrMoTaTiZr)Nx high-entropy films were deposited on silicon wafer and cemented carbide substrates from a single alloy target by reactive RF magnetron sputtering under a mixed atmosphere of Ar and N2. The effect of nitrogen flow ratio RN on chemical composition, morphology, microstructure, and mechanical properties of the (AlCrMoTaTiZr)Nx films was investigated. Nitrogen-free alloy film had an amorphous structure, while nitride films with at least 37 at.% N exhibited a simple NaCl-type FCC (face-centered cubic) structure. Mixed structures occurred in films with lower nitrogen contents. Films with the FCC structure were thermally stable without phase decomposition at 1000 °C after 10 h. The (AlCrMoTaTiZr)N film deposited at RN = 40% exhibited the highest hardness of 40.2 GPa which attains the superhard grade. The main strengthening mechanisms for this film were grain-size and solid-solution strengthening. A residual compressive stress of 1.04 GPa was small to account for the observed hardness. The nitride film was wear resistant, with a wear rate of 2.8 × 10− 6 mm3/N m against a loaded 100Cr6 steel ball in the sliding wear test. These high-entropy films have potential in hard coating applications.

Thermal management in microelectronic technology has become an important issue due to the increase of device power and integration levels. Diamond and silver were selected for the fabrication of composites with high thermal conductivity and low coefficient of thermal expansion (CTE). Diamond reinforcement powders with varied types, shapes and sizes were electroless plated by silver. Then these powders were hot-pressed in air at 600 °C, 500 MPa for 30 min to produce bulk silver matrix composites. The thermal conductivity and the CTEs of the composite at 20 vol.% are 420 W/m K and 12 ppm/K, respectively. These diamond/Ag composites have potential applications for the high integration electronic devices.

Diamond/Ag–Ti composites were fabricated by a low-cost vacuum liquid sintering technique and the effects of Ti addition on the thermal properties of the composites were studied. The results indicate that the optimal quantity of added Ti is 3 at%. Adding less than 3 at% Ti resulted in poor wettability, while adding more than 3 at% Ti resulted in excessive formation of TiC. Both reduced thermal conductivity. A composite comprising 60 vol% diamond/Ag–3at%Ti resulted in a maximum thermal conductivity of 836 W m −1 K −1 with a coefficient of thermal expansion of 5.6×10 −6 K −1 . These composites are excellent candidates for the thermal management of integrated electronic devices.

This study presents an innovative multi-principal-element CoFeMnTiVZr alloy system for the absorption and desorption of hydrogen. Pressure-composition-isotherms (PCIs) demonstrate that CoFeMnTi x VZr, CoFeMnTiV y Zr, and CoFeMnTiVZr z can absorb and desorb hydrogen for x , y, and z that satisfy 0.5 ≤ x ≤ 2.5, 0.4 ≤ y ≤ 3.0, and 0.4 ≤ z ≤ 3.0, respectively. X-ray diffraction (XRD) reveals that CoFeMnTi x V y Zr z alloys have a simple C14 Laves phase with a single set of lattice parameters before and after PCI tests. The distributions of each element in CoFeMnTi x V y Zr z alloys are roughly equal, as revealed by SEM/EDS mapping. The effects of values x , y , and z on the hydrogen storage properties are elucidated in terms of lattice constant, element segregation, hydride formation enthalpies of the alloy components and hydrogen, and the averaged formation enthalpy. The high-entropy effect promotes the formation of a single C14 Laves phase, and the maximum hydrogen storage capacity is strongly related to the hydride formation enthalpy of the alloy and hydrogen.

The photothermolysis of living EMT-6 breast tumor cells triggered by gold nanorods (AuNRs) with two-photon irradiation was conducted in situ and under real-time observation. The morphology and plasma membrane permeability of the cells were key indicators to the phenomena. AuNRs with an aspect ratio of 3.92, and a longitudinal absorption peak at 800 nm were synthesized with a seed-mediated method. The nanorods surfaces were further modified with polystyrenesulfonate (PSS) for biocompatibility. The prepared nanorods displayed excellent two-photon photoluminescence imaging. In situ real-time results revealed cavities internal to the cells were created from thermal explosions triggered by AuNRs localized photothermal effect. The cavitation dynamic is energy dependent and responsible for the perforation or sudden rupture of the plasma membrane. The energy threshold for cell therapy depended significantly on the number of nanorods taken up per cell. For an ingested AuNR cluster quantity N approximately 10-30 per cell, it is found that energy fluences E larger-than 93 mJ/cm(2) led to effective cell destruction in the crumbled form within a very short period. As for a lower energy level E = 18 mJ/cm(2) with N approximately 60-100, a non-instant, but progressive cell deterioration, is observed.

To elucidate low-dimensional effects on thermoelectric materials, bismuth telluride film and nanowires array were fabricated by potentiostatically electrodeposition. Both materials are slightly Te-rich, n-type Bi2Te3, exhibiting preferred orientation in rhombohedral strcture. For both the Seebeck coefficient S ≈ −70 μV/K at 300 K decreases linearly with decreasing temperature, showing a diffusive nature of current flow. The temperature dependence of resistivity (=1/σ) of nanowires obtained from the data of a nanowires array and a single-nanowire reveals a better electric conductivity than that of the bulk. By coupling temperature-dependent thermal diffusivity and heat capacity data with a modified effective medium theory, a thermal conductivity κ of 0.75 W/(m K) was obtained at 300 K. The ZT was calculated to be 0.45 at 300 K and 0.9 at 350 K for Bi2Te3 nanowires.

Multi-element (AlCrTaTiZr)N films were deposited on cemented carbide and M2 steel substrates by reactive RF magnetron sputtering. Prior to nitride film deposition, an interlayer between the film and the substrate was introduced to improve adhesion property. The influence of interlayer materials (Ti, Cr, and AlCrTaTiZr alloy) and interlayer thickness (0–400 nm) on the adhesion and tribological properties of films was investigated. In this study, the nitride film deposited at RN = 20% exhibited the highest hardness (35.2 GPa) and the lowest residual compressive stress (− 1.52 GPa), and was prepared as the top layer for further testing. The interlayer materials can effectively improved the film adhesion onto the cemented carbide substrates, and the adhesive failure was not observed even under the normal load of 100 N. For M2 steel substrates, only the Cr interlayer can slightly improve the film adhesion, and the cohesive and adhesive failure can be found at relatively lower applied load. The optimal interlayer thickness was 100–200 nm for the 1 µm-thick (AlCrTaTiZr)N film and can be related to the stress evolution. The friction coefficient and wear rate for the (AlCrTaTiZr)N film were 0.82 and 4.9 × 10− 6 mm3/Nm, respectively, and almost kept constant under different interlayer materials and thickness. The worn-through event of the nitride film during tribological test occurred easily owing to its poor adhesion behavior, and can be improved by interlayer additions.

This work studies the effect of the sized silver (Ag) nanoparticles on the optical property of SPR. Nanoparticles were prepared on fluorine-doped-tin-oxide (FTO) coated glass substrates by RF magnetron sputtering with various deposition times and the subsequent rapid thermal annealing (RTA) to control the particle size. To make the Ag films, Ag films of different thicknesses were first deposited on either glass or FTO substrate by a vacuum sputtering technique. Some of the samples founded nanoparticles by rapid thermal annealing. The substrates with and without nanoparticles were then sensitized by immersing them in a 0.2 mM N719 dye solution. Finally, the effect of the absorption coefficient was investigated by adsorbing it on fine silver Ag islands. The surface plasmon resonance enhanced the absorption by the sample with Ag nanoparticles above that of the sample without nanoparticles. In this study, the peak position of the surface plasmon characteristic absorption increased with the grain size of the nanoparticles in a red-shift. The structure and the quantity of Ag particles were very critical to the surface plasmon resonance effect.