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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.

This work investigates the corrosion mechanism of annealed equiatomic AlCoCrFeNi tri-phase alloy in 0.5 M H2SO4 aerated aqueous solution. Experimental results indicate that the B2 matrix is preferentially corroded away while grain-boundary FCC and labyrinth-like BCC endure, consistent with the tendency of formation energy for monolayer hydroxide on the (001) plane of three phases calculated by the first principle based on density function theory. Furthermore, the stable passive current density is related to lower ksp values of Co(OH)3, Fe(OH)3, and Cr(OH)3, while the annealing effect on enhancing corrosion resistance is owing to the more uniformity of passive hydroxide film.

Herein, we aim to develop a facile method for the fabrication of mechanical metamaterials from templated polymerization of thermosets including phenolic and epoxy resins using self-assembled block copolymer, polystyrene-polydimethylsiloxane with tripod network (gyroid), and tetrapod network (diamond) structures, as templates. Nanoindentation studies on the nanonetwork thermosets fabricated reveal enhanced energy dissipation from intrinsic brittle thermosets due to the deliberate structuring; the calculated energy dissipation for gyroid phenolic resins is 0.23 nJ whereas the one with diamond structure gives a value of 0.33 nJ. Consistently, the gyroid-structured epoxy gives a high energy dissipation value of 0.57 nJ, and the one with diamond structure could reach 0.78 nJ. These enhanced properties are attributed to the isotropic periodicity of the nanonetwork texture with plastic deformation, and the higher number of struts in the tetrapod diamond network in contrast to tripod gyroid, as confirmed by the finite element analysis.

We demonstrate the fabrication of free-standing inverse opals with gradient pores via a combination of electrophoresis and electroplating techniques. Our processing scheme starts with the preparation of multilayer colloidal crystals by conducting sequential electrophoresis with polystyrene (PS) microspheres in different sizes (300, 600, and 1000 nm). The critical factors affecting the stacking of individual colloidal crystals are discussed and relevant electrophoresis parameters are identified so the larger PS microspheres are assembled successively atop of smaller ones in an orderly manner. In total, we construct multilayer colloidal crystals with vertical stacking of microspheres in 300/600, 300/1000, and 300/600/1000 nm sequences. The inverse opals with gradient pores are produced by galvanostatic plating of Ni, followed by the selective removal of colloidal template. Images from scanning electron microscopy exhibit ideal multilayer close-packed structures with well-defined boundaries among different layers. Results from porometer analysis reveal the size of bottlenecks consistent with those of interconnected pore channels from inverse opals of smallest PS microspheres. Mechanical properties determined by nanoindentation tests indicate significant improvements for multilayer inverse opals as compared to those of conventional single-layer inverse opals.

To understand the dominance of lattice distortion and cocktail effect for an appropriate element selection and optimistic design of multicomponent protective hard coatings, in this study, four groups of Ta-based high-entropy nitride coatings, including (AlCrTa2TiZr)Nx, (HfNbTaTiZr)Nx, (MoNbTaTiZr)Nx and (Al2Cr2HfMoNbTa)Nx, were deposited by sputtering in an N2 + Ar mixed atmosphere. The structures, mechanical properties, wear resistance and oxidation resistance of the coatings were investigated, and the roles of different constituent metallic elements in their performance were examined. Experimental results indicated that, similar to conventional nitride coatings, the sputtering yield and resputtering loss of metallic elements determined the chemical composition. While the high mixing entropy of multiple metallic elements yielded a solid-solution structure, the N2-to-total flow ratio dominated the film structure and growth orientation. A certain level of lattice distortion generated similarly high mechanical properties no matter which metallic elements were added, but the cocktail effect of the constituents decided the tribological and oxidation resistance of the coatings.

The thermodynamic parameters for a series of Fe(100−x)/2Co(100−x)/2Cux (x from 10 to 90, at. pct) alloys including their characteristic temperatures, the enthalpy and entropy changes of three phase transformations were determined systematically using differential scanning calorimetry (DSC). The corresponding vertical section of ternary Fe-Co-Cu phase diagram was predicted, and the relationships of the enthalpy and entropy changes vs Cu content were described by polynomial expressions. Metastable phase separation took place in those liquid Fe-Co-Cu alloys with the Cu content 30 ≤ x ≤ 70. The liquid phase separation temperatures were determined to outline the metastable miscibility gap, and the critical undercoolings to initiate phase separation were measured as a range of 57 K to 98 K. After such a phase separation, the liquid phase (to γ(Fe, Co)) exhibited the strongest undercooling ability in the Fe-Co-Cu alloys with x ≤ 70, whereas the solid-state undercooling for the eutectoid transformation is comparatively higher in the alloys with x > 70. The nanomechanical properties of α(Fe, Co) and (Cu) phases were measured by nanoindentation technique. In the Fe20Co20Cu60 alloy, both phases had the lowest nanohardness and reduced elastic modulus, and displayed severe creep behaviors, resulting mainly from its conspicuous liquid phase separation.

Ductile vanadium layers were alternately deposited with brittle aluminum-copper-iron-based quasicrystal-alloy layers to form multilayered coatings. The in-situ transmission electron microscopic observations of nanopillar compression revealed that the as-deposited single-layered amorphous aluminum-copper-iron alloy slightly deformed via shear banding. After annealing at 800 °C, brittle quasicrystal and intermetallic compounds were formed, so the single-layered coating cracked and peeled. In comparison, the multilayered coatings were effectively toughened. The multilayered nanopillars plastically deformed via dislocation activities and were work hardened owing to confined dislocation gliding. The as-deposited multilayered structure (amorphous alloy/crystalline vanadium) had a low 10% flow stress of 1.72 GPa, while the annealed multilayered structure (quasicrystal/vanadium) presented a high flow stress of 2.58 GPa owing to quasicrystal strengthening. Dislocation clusters were in-situ observed to glide laterally in the crystalline vanadium layers and move vertically through the vanadium and quasicrystal layers, yielding an improved plasticity.

We employ a sequential electrophoresis and electrodeposition approach to fabricate a large-area ordered macroporous Ni foam in 5 × 5 cm 2 via a template route. Images from scanning electron microscope exhibit hierarchical structures with hexagonally-arranged pores and interconnected pore channels. For as-prepared and annealed ordered macroporous Ni foams, the loading-depth profiles from nano indentation show typical elastic and plastic deformation. Upon annealing, moderate growth in grain size is observed, resulting in lower hardness and Young’s modulus. In contrast, for disordered macroporous Ni foam and solid Ni film, nano indentation results reveal larger hardness and undetermined Young’s modulus. The ordered macroporous foam reveals hardness that is 22% of that of solid Ni film, a value close to its theoretic packing density of 24%.

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.

Microanode-guided electroplating (MAGE) was performed to prepare cobalt-iron-nickel alloying micropillars. The electrolyte was prepared by fixing [Fe2+] at 0.040 M and varying [Co2+] in 0.040–0.100 M and [Ni2+] in 0.30–0.60 M. The effect of bath composition on the compositional, mechanical, and magnetic properties of the alloying micropillars was investigated. Resulting from FE-SEM and EDS, all the micropillars demonstrated a smooth morphology but in different compositions depending on the bath composition. Through XRD analysis, the micropillars were characterized in nanocrystals of Co-Ni and Co7Fe3. After nano-indentation testing, the reduced Young’s modulus of the pillars was estimated at 103.1–185 GPa and the hardness at 5.70–6.38 GPa. Investigation of all the specimens with VSM, Co61Fe27Ni12 and Co63Fe25Ni12 displayed the notable saturation magnetization (Ms = 180 and 175 emu/g) and the lowest coercive magnetic field (Hc = 2.1 and 1.4 Oe) among them. The mechanism of anomalous Co-Fe-Ni electrodeposition is proposed.

We show quasicrystal formation by annealing multilayers of Al, Cu and Fe. The mechanical and surface properties of quasicrystals are affected by the parameters of annealing process. Here, multilayer Al-Cu-Fe thin film samples with different compositions were sputtered on Si/SiO2 substrates and subjected to a two-step annealing process for different durations (5, 10 and 15 h). X-ray diffraction analyses indicated that the 15-h annealed sample had a sharper quasicrystal peak, which was more stable than any other phases. From the XRD data, the amount of each phase was calculated; the sample with longer annealing duration revealed a high amount of ψ-phase (84.3% crystallinity of quasicrystal) with a small amount of cubic Al50 (CuFe) 50 phase. Nanoindentation tests and contact angle measurements showed that this sample also had the greatest hardness (∼11 GPa) and the highest contact angle (127°), respectively.

Microgravity solidification provides a particular opportunity to produce an extraordinary microstructure and optimized mechanical properties. To shed further light on the influence of rapid solidification mechanism on mechanical properties, both the microgravity solidification mechanism and resultant micromechanical properties of ternary Al 57 Ag 12 Ge 31 alloy were analyzed by means of drop tube, nanoindentation and frictional sliding techniques, which was compared with equilibrium solidification condition. The solidification pathways changed with the decrease of droplet size, owing to a larger cooling rate and a higher undercooling. Consequently, the microstructure transformed from dendrites plus two-phase eutectic to two-phase eutectics, eventually to anomalous ternary eutectic, while the thickness of surface (Ge) layer decreased. The micromechanical properties of rapidly solidified alloy droplets were evidently improved with the decrease of droplet size, which is mainly ascribed to the microstructure refinement and the homogenous distribution especially of hardening (Ge) phase. The measured microhardness, yield strength, strain hardening exponent, pile-up resistance and friction coefficient were analyzed as a function of droplet size.

TiO2 nanotube-based heterostructures grafted with ZnO nanorods, Ag nanoparticles, or Pd nanodendrites were synthesized for photocatalytic H2O/CH3OH splitting and H2 generation. Compared with P25 TiO2 nanoparticles and bare TiO2 nanotubes, these heterostructures, in particular, the one grafted with Pd nanodendrites, were found to present a markedly enhanced photocatalytic H2 generation efficiency (net H2 generation rate ∼143 μmol/h). Rather than the surface area of the photocatalysts, the lifetime (separation) of photogenerated carriers and, in particular, the surface plasmon resonance-stimulated carrier excitation dominated the number of total effective carriers. A power relationship with an exponent of 0.2 between the H2 generation rate and the number of total photogenerated carriers was determined, which suggests that the number of effective carriers or the efficiency in H2O/CH3OH splitting might decay in an exponential way.

Band structure by design in 2D layered semiconductors is highly desirable, with the goal to acquire the electronic properties of interest through the engineering of chemical composition, structure, defect, stacking, or doping. For atomically thin transition metal dichalcogenides, substitutional doping with more than one single type of transition metals is the task for which no feasible approach is proposed. Here, the growth of WS2 monolayer is shown codoped with multiple kinds of transition metal impurities via chemical vapor deposition controlled in a diffusion-limited mode. Multielement embedment of Cr, Fe, Nb, and Mo into the host lattice is exemplified. Abundant impurity states thus generate in the bandgap of the resultant WS2 and provide a robust switch of charging/discharging states upon sweep of an electric filed. A profound memory window exists in the transfer curves of doped WS2 field-effect transistors, forming the basis of binary states for robust nonvolatile memory. The doping technique presented in this work brings one step closer to the rational design of 2D semiconductors with desired electronic properties.

Self-assembly of amphiphilic polymers in water is of fundamental and practical importance. Significant amounts of free unimers and associated micellar aggregates often coexist over a wide range of phase regions. The thermodynamic and kinetic properties of the microphase separation are closely related to the relative population density of unimers and micelles. Although the scattering technique has been employed to identify the structure of micellar aggregates as well as their time-evolution, the determination of the population ratio of micelles to unimers remains a challenging problem due to their difference in scattering power. Here, using small-angle neutron scattering (SANS), we present a comprehensive structural study of amphiphilic n-dodecyl-PNIPAm polymers, which shows a bimodal size distribution in water. By adjusting the deuterium/hydrogen ratio of water, the intra-micellar polymer and water distributions are obtained from the SANS spectra. The micellar size and number density are further determined, and the population densities of micelles and unimers are calculated to quantitatively address the degree of micellization at different temperatures. Our method can be used to provide an in-depth insight into the solution properties of microphase separation, which are present in many amphiphilic systems.

In this study, AlCrSiNbZr nitride thin films were deposited on Si substrate by reactive radio frequency magnetron sputtering under the substrate bias from 0 V to −100 V at room temperature. The effect of substrate bias on structure, morphology, hardness and resistivity of the films was investigated. The results show that (111) preferred orientation was dominant phases for samples under bias of 0 V, −25 V, −50 V and − 75 V whereas amorphous-like feature was observed for samples under the bias of −100 V. In addition, crystallinity of film was enhanced when the substrate bias increased from 0 V to −50 V, but decreased when substrate bias further increased from −50 V to −100 V, suggesting that the optimized crystallinity of films was achieved under the substrate bias of −50 V. The oxygen contents of the thin films decreased significantly when the substrate bias was higher than −25 V. The hardness of the films was divided into two regions and samples under bias of −75 V and −100 V possessed higher hardness than those under bias of 0 V, −25 V and −50 V, which was mainly attributed to less oxynitride phases for samples under bias of −75 V and −100 V. The resistivity of thin films decreased as the substrate bias increased, which was mainly affected by the concentration of oxygen in films. The optimized substrate bias was −75 V with the maximum hardness and lowest resistivity.

Al-Cu-Fe based quasicrystal thin films exhibit unique surface and mechanical properties. To better understand the formation of the quasicrystal thin films, we observe direct growth of quasicrystals, prepared in a multilayer Al-Cu-Fe thin films with subsequent heat treatment, by in-situ synchrotron x-ray diffraction and in-situ transmission electron microscopy during heating and cooling. Using these two methods, we show that the ternary phase is more thermodynamically stable compared to the binary phases at temperature higher than 470 °C during the heating process, and quasicrystal formation occurs during the cooling process, specifically at 660 °C, after the sample has reached a liquid state. To distinguish quasicrystal from approximant crystals in the obtained thin film samples, we use high resolution x-ray diffraction to analyze the sample at room temperature. We reveal that the peak broadening increases monotonically along the twofold, threefold, and fivefold high-symmetry directions with the physical scattering vector but does not have systematic dependence on the phason momentum, which suggests that the thin film sample is indeed a quasicrystal instead of approximant crystals and it is almost free of phason strain. Our study provides a complete understanding of the growth mechanism for thin film Al-Cu-Fe quasicrystals, which is of particular importance for developing versatile applications of quasicrystal thin films.

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.

Herein, we adopted alloying and rapid-dendrite-growth methods to improve the mechanical properties of Fe-based alloys. Three molten alloys including Fe-5Ni-5Mo-5Ge, Fe-5Ni-5Mo-5Ge-5Co, and Fe-5Ni-5Mo-5Ge-5Co-5Si were undercooled, during which (αFe) dendrites grew rapidly with the decrease of temperature (i.e., increase of undercooling). The rapid growth of (αFe) dendrites in the Fe-5Ni-5Mo-5Ge-5Co alloy at a high rate of 31.8 ms–1 caused by a large undercooling more effectively enhanced the microhardness than a Co addition did. In comparison, because of the great disparity of atom size and valence electron number between Fe and Si, a further Si addition suppressed the (αFe) dendrite growth while dramatically increasing the Vickers microhardness of the Fe-5Ni-5Mo-5Ge-5Co-5Si alloy to HV 622.

To minimize the room-temperature brittleness of AZ magnesium alloys (Mg–Al–Zn) and to inhibit grain growth at elevated temperatures for superplasticity optimization, AZ91−xSn alloys (x=0, 1, 2 and 3 wt%) were developed, processed by high-ratio hot extrusion for microstructure refinement. The mechanistic correlations of their superplasticity, from the perspectives of grain growth and boundary sliding, with the Sn content and the testing parameters were examined. With a higher Sn content, the activation energy of grain growth and diffusion-mediated boundary sliding, QG and QS, increased from 29.7 to 35.2 kJ/mol and from 114.1 to 126.5 kJ/mol, respectively. With an adequate Sn addition (2 wt%) and at a relevant strain rate and temperature, a compromise between competitive grain growth and boundary sliding was reached, and the superplasticity was optimized (elongation >1000%), following a proposed superplasticity parameter ( p Q G − Q S ) / 2.3 n G p R T + ( n G p − 1 ) log e .

Various (AlCrMoTaTi)-Six-N coatings were prepared on Si substrates through a reactive magnetron sputtering system to methodically investigate the effects of Si contents and free Si on oxidation behavior. The as-deposited Si-containing coating presented a relatively dense and compact structure compared with the Si-free coating. An oxide layer was formed on the coating surface and continued to thicken when the coatings were exposed to ambient air at elevated temperatures. At 1073 K, a two-layer structure, which consists of an amorphous Al2O3 layer with traces of other target elements followed by a rutile TiO2 + oxide of the target element mixed zone, was developed in the oxide layer. Oxidation resistance was gradually enhanced with the continued increase in Si concentration in the coatings. At 1173 K, the coatings with Si content of as low as 7.51 at.% exhibited a single order of magnitude lower oxidation rate than that of the Si-free coating. Nanohardness measurement of the coatings further confirmed the oxidation behavior. The significantly enhanced oxidation resistance may be attributed to the presence of Al and Si in the coatings.

To improve the mechanical properties, including the ductility, of cast AZ91 magnesium alloy (Mg–9Al–Zn) to provide high workability, small amounts of Sn were added to AZ91, forming AZ91−xSn (x = 1–3) alloys; following homogenization/aging treatments, high-ratio extrusion was conducted on the alloys. The correlation between the microstructural refinement and the improvement in mechanical performance was studied. In the as-cast AZ91−xSn alloys, small Mg2Sn precipitates formed in an Al-enriched α-Mg matrix, and the formation of detrimental, large eutectic β-Mg17Al12 was suppressed, resulting in an increase in hardness from Hv 68 to 77. The high-ratio extrusion greatly refined the microstructure and increased the hardness further to Hv 101. A higher Sn content resulted in the formation of more small Mg2Sn precipitates, and reduced the size of the coarse grains to 5 μm. The wrought AZ91−xSn alloys with added 2–3 wt.% Sn and extrusion had a markedly better tensile strength, 380 MPa, than that of a cast AZ91 alloy, and exhibited an elongations of 8–9%.

Both microstructure sizes and phase distributions influence the mechanical performance of multi-phase alloys. Herein, we investigated the microhardness enhancements of two Al–Cu–Ge alloys with enlarged undercoolings, corresponding to their microstructural evolutions. The similar-range undercoolings for the two alloys were obtained by a glass fluxing method, and comparatively minimum undercoolings were achieved by differential scanning calorimetry. For an Al70Cu10Ge20 alloy, the microstructure refinements of primary CuAl2 dendrite and (Al) + (Ge) pseudobinary eutectic, especially the former, dominate its large microhardness increase with high-level undercoolings. By comparison, for an Al80Cu10Ge10 alloy with a slight composition difference, a hardness drop and a limited refinement hardening effect are observed due to the early formation of primary (Al) dendrite. As undercooling increases, an alternative hardening owing to the reduced amount of (Al) dendrite as well as the larger amount and more homogenous distribution of (Al) + CuAl2 pseudobinary eutectic phases is presented. The mechanical performance of the two alloys well matches the combined values of their composing structures, following the rule of mixtures and according to their microstructure evolutions.

This study demonstrates that simply by rolling at ambient temperature, FCC type high entropy alloy Al0.5CoCrCuFeNi can be refined to have nanocrystalline structure and exhibits outstanding combination of strength and ductility. The yield strength and ultimate tensile strength are 1284 and 1344 MPa, respectively, in combination with an elongation of 7.6%. After a short annealing at 900°C for 10 min, the elongation is doubled to 15.3% with a trade-off around 20% in strength. This excellent combination of strength and ductility is attributable to the activation of quasi-dynamic recrystallisation during cold work and the limited grain growth during 900°C annealing.

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.

This study reports a mechanical stress-based technique that involves scratching or imprinting to write textured graphite conducting wires/patterns in an insulating amorphous carbon matrix for potential use as interconnects in future carbonaceous circuits. With low-energy post-annealing below the temperature that is required for the thermal graphitization of amorphous carbon, the amorphous carbon phase only in the mechanically stressed regions transforms into a well aligned crystalline graphite structure with a low electrical resistivity of 420 μΩ-cm, while the surrounding amorphous carbon matrix remains insulating. Micro-Raman spectra with obvious graphitic peaks and high-resolution transmission electron microscopic observations of clear graphitic lattice verified the localized phase transformation of amorphous carbon into textured graphite exactly in the stressed regions. The stress-induced reconstruction of carbon bonds to generate oriented graphitic nuclei is believed to assist in the pseudo-self-formation of textured graphite during low-temperature post annealing.

Three-dimensional ordered macroporous Ni films, known as Ni inverse opals, are fabricated via a template approach in which polystyrene (PS) microspheres (820 nm in diameter) are assembled in closely-packed colloidal crystals via a vertical electrophoresis process, followed by electroplating of Ni into the interstitial voids within the colloidal crystals and the selective removal of PS microspheres. To improve its mechanical strength, a conformal Ni-Co layer (45 ∼ 64 nm) is electrodeposited on the skeletons of the Ni inverse opals by cyclic voltammetry. After coating, from nano-indentation tests, the hardness and reduced elastic modulus are enhanced considerably (172 ∼ 220% for hardness; 72 ∼ 79% for reduced elastic modulus), as compared to those of pristine inverse opals. After an annealing treatment for the interdiffusion of Ni and Co, the sample reveals an even stronger hardness. X-ray diffraction patterns indicate that the finite thickness of the inverse opals skeletons induces preferential growth of the (111) plane. In short, a combined effect of solid solution alloying, thickening of inverse opals skeletons for greater load bearing, and a predominant (111) plane is responsible for the improved mechanical strength of the Ni inverse opals.

The formation of graphitic nanocrystallites at the surface of amorphous carbon under large mechanical stresses was examined by using micro-Raman spectrometry, transmission electron microscopy and in-situ compressions. In the Raman analyses of severely deformed (above a strain energy density criterion of 5.9 J/m2) surface regions of nanoscratched and nanoindented amorphous carbon films, two additional sharp and narrow peaks, DGr and GGr at 1330 and 1580 cm−1, appeared from the main unchanged broad spectra, revealing the transformation of some small-range amorphous carbon to nanocrystalline graphite. Transmission electron microscopic images presented the formation of surface shear layer within which dispersed graphitic nanocrystallites (a size of about 3 nm) were formed in the remaining amorphous matrix. The in-situ nanoscopic observation of amorphous carbon nanopillars under compressions confirmed the formation of graphitic nanocrystallites at pillar edge surfaces. The formed graphite (0 0 1) and (1 0 0) lattices were well oriented along maximum resolved shear stresses, being an evidence of lattice reconstruction and suggesting a possibility of stress-induced graphitization of amorphous carbon in the absence of heat.

By using sacrificial ZnO nanorods, a self non-uniform electric field was established to yield the aqueous growth of 〈111〉 oriented, single-crystalline (Zn,Sn)-doped Pd nanodendrites on TiO2 nanotubes for synthesizing three-dimensional hydrophobic heterostructures. Structural analyses revealed that primary dendrite arms grew along a 〈111〉 direction group; symmetric branches were built on the basal plane of the arms but sprouted in another [111] direction, similar to a twin structure. Sequential growth processes different from a diffusion-limited aggregation model were suggested, including the dissolution of ZnO nanorods for forming a self non-uniform electric field, the protruding of primary arms towards a Zn2+ concentrated zone, and then the development of branches through a cation depletion zone. A strong surface enhanced Raman scattering and high photocatalytic activity, owing to the strong surface plasmon resonance on the large-surface symmetric structures and the inhibited recombination of photogenerated electron–hole pairs, suggested the high potential of the heterostructures for applications in self-cleaning photocatalysts and nano-optoelectronic devices.

In this study multi-component (AlCrTaTiZr)NxSiy high-entropy coatings were developed by co-sputtering of AlCrTaTiZr alloy and Si in an Ar/N2 mixed atmosphere with the application of different substrate biases and Si-target powers. Their nanomechanical properties and deformation behaviors were characterized by nanoindentation tests. Because of the effect of high mixing entropies, all the deposited multi-component (AlCrTaTiZr)NxSiy high-entropy coatings exhibited a simple face-centered cubic solid-solution structure. With an increased substrate bias and Si-target power, their microstructures changed from large columns with a [111] preferred orientation to a nanocomposite form with ultrafine grains. The hardness, H/E ratio and H3/E2 ratio of (AlCrTaTiZr)N1.07Si0.15 coating reached 30.2 GPa, 0.12 and 0.41 GPa, respectively, suggesting markedly suppressed dislocation activities and a very high resistance to wear and plastic deformation, attributable to grain refinements and film densification by the application of substrate bias, a nanocomposite structure by the introduction of silicon nitrides, and a strengthening effect induced by severe lattice distortions. In the deformed regions under indents, stacking faults or partial dislocations were formed, while in the stress-released regions, near-perfect lattices recovered.

In situ nanoscopic observations of healthy and osteoporotic bone nanopillars under compression were performed. The structural-mechanical property relationship at the atomic scale suggests that cortical bone performance is correlated to the feature, arrangement, movement, distortion, and fracture of hydroxyapatite nanocrystals. Healthy bone comprising tightly bound mineral nanocrystals shows high structural stability with nanoscopic lattice distortions and dislocation activities. On the other hand, osteoporotic bone exhibits brittleness owing to the movements of dispersed minerals in and intergranular fracture along a weak organic matrix.

This paper reviews the past and possible future development of anti-bacteria and anti-wear TaN-(Ag,Cu) nanocomposite thin films. The review starts with the development of TaN-Cu and TaN-Ag nanocomposite thin films which are prepared with co-sputtering followed by rapid thermal annealing (RTA). The incorporation of Ag–Cu atoms simultaneously into TaN film has later shown some advantages over TaN-Ag or TaN-Cu, such as wider bactericidal spectrum, lower annealing temperature, and equally low friction coefficient. Besides describing these advantages, this paper addresses some of the un-solved problems with TaN-(Ag-Cu) thin films, which include a short life time due to fast diffusion of Ag and Cu atoms out on the film surface as well as the adaptive behavior. The paper also discusses about the importance of controlled-releasing the soft metal ions in antibacterial applications. The last part of this paper also discusses briefly the adaptive behavior of these composite films. While the out-diffusion of soft metals from the composite matrix to the surface is essential for the chameleon adaptive behavior to be realized, the controlled diffusion of soft metals is definitely required. In sum, this paper addresses the developing process of anti-bacterial and anti-wear TaN-(Ag,Cu) films, along with some current problems, and provides some possible solutions.

(AlCrMoTaTi)N coatings were deposited on Si substrates via reactive magnetron sputtering. The effects of N 2 -to-total (N 2 + Ar) flow ratio ( R N ) on the coating structure and properties were examined. Alloy coatings have composite equiaxed grain structures consisting of amorphous and body-centered cubic crystal phases, whereas nitride coatings have columnar structures with single face-centered cubic crystal phase. Distinct lattice expansion and grain refinement were observed in nitride coatings as R N increased. Typical V-shaped columnar structures with faceted tops and open column boundaries transformed into denser and smaller columnar structures with domed surfaces. Increasing R N to 30% caused the hardness and modulus to reach maximum values of 30.6 and 291.6 GPa, respectively. Electrical resistivity increased from 536 μΩ cm to 8212 μΩ cm when R N increased from 10% to 50%.

(TiVCrZrY)N coatings were deposited onto Si substrate by the radio-frequency (RF) magnetron sputtering of a TiVCrZrY alloy target in an N2/Ar atmosphere. The crystal, microstructural, mechanical, and electrical properties at different N2-to-total (N2+Ar) flow-rate ratio (R N) values were investigated. The coating produced in pure Ar had an equiaxed structure with a hexagonal-close-packed phase. With increased R N, the crystallinity and grain size markedly decreased. The microstructure of (TiVCrZrY)N coatings transformed from V-shaped columnar with a rough-domed surface into fine fibrous with a smooth surface. The amorphous transition layer above the substrate was also significantly thickened. The hardness of (TiVCrZrY)N decreased from 20.9 GPa to 18.9 GPa, and the electrical resistivity increased from 398.2 μΩ⋅cm to 21870 μΩ⋅cm.

TaN–(Cu,Ag) nanocomposite films were deposited by reactive co-sputtering on Si(001) and M2 tool steels. The films were then annealed using RTA (Rapid Thermal Annealing) at 200 °C–400 °C to induce the nucleation and growth of metal particles in TaN matrix and on film surface. After deposition, structures, surface morphologies, and mechanical properties were analyzed, the samples were tested for their anti-wear and anti-bacterial behaviors against Gram-negative Escherichia coli. It is found that the antibacterial efficiency against E. coli can be much improved for TaN–(Cu,Ag), comparing with that of TaN–Ag or TaN–Cu films. This could be attributed to large number of surfaced Ag and Cu particles. The tribological properties could also be improved, and are similar to TaN–Ag under a normal load of 5 N. In general, the annealing temperature for TaN–(Cu,Ag) can be as low as 200 °C. Being annealed at this temperature, the film still shows good antibacterial and anti-wear behaviors.

Cu-doped TaN films were known to have good anti-bacterial and anti-wear behaviors. However, in some of the practical applications, the depletion of surfaced Cu might eventually cause the films to lose their effectiveness against wear and bacteria. This study hence was aimed at understanding the rejuvenation process for these films. The structures, morphologies, antibacterial and mechanical properties of TaN–Cu nanocomposite thin films after multi-rejuvenating processes were the focus of this study. The results revealed that the Cu particles would re-appear on the film surface after each rejuvenation cycle, which can recover the anti-wear and anti-bacterial properties. The particle size and density appeared to decrease with the increase of rejuvenation cycle. The hardness of the samples would also decrease with the number of cycles. This was due to the slow depletion of Cu atoms, which might cause the increase of porosity and the decrease of hardness. The wear rates and friction coefficients of these rejuvenated samples depend mainly on the possibility of forming lubricious Cu films, although film hardness also played a certain role. In sum, the present study confirms that the anti-bacterial and anti-wear behaviors can be rejuvenated twice or more, under the experimental conditions adopted.

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.

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.

In this study, attempts were made to prepare and characterize TaN–(Cu,Ag) nanocomposite films by using a hybrid approach combining reactive co-sputtering and rapid thermal annealing at various temperatures to induce the formation of soft metal particles in the matrix or on the surface. The films’ properties and their antiwear and antibacteria behaviors were compared with those previously studied TaN–Cu and TaN–Ag films. All three types of TaN–(soft metal) films showed good tribological properties due to the lubricious Ag and/or Cu layers. It was also found that the antibacteria efficiency of TaN–(Ag,Cu) film against either Escherichia coli or Staphylococcus aureus could be much improved, comparing with that of TaN–Ag or TaN–Cu film. The synergistic effect due to the coexistence of Ag and Cu is obvious. The annealing temperature used to develop TaN–(Cu,Ag) films with good antibacterial and antiwear behaviors could be as low as 250 °C. The lowering of the annealing temperature made these films applicable onto low-melting-point materials, such as polymers.

This work develops (AlCrTaTiZr)NC y multi-component coatings by co-sputtering of AlCrTaTiZr alloy and graphite in an Ar/N 2 mixed atmosphere with the application of different substrate biases. All the (AlCrTaTiZr)NC y coatings deposited in different conditions exhibited a simple face-centered cubic structure. As the applied substrate bias and graphite-target power increased, the (AlCrTaTiZr)NC y coatings transformed from a large columnar structure with a [111] preferred orientation to a dense, ultrafine nanocomposite structure. With increasing substrate bias and graphite-target power, the hardness, H/E ratio and H 3 /E 2 ratio of the coatings increased from 20 to 35 GPa, from 0.07 to 0.12 and from 0.10 to 0.43 GPa, respectively, attributed to the densification of the coatings, the refinement of grains, the introduction of covalent-like carbide bonds, the formation of nanocomposite structure and the existence of large lattice distortions. Because of the severe distortions in the multi-component coatings caused by the addition of differently-sized atoms, the deformation mechanism was dominated by the activity of low-angle dislocations and/or stacking faults.

Direct current electropulsing was used to improve the plasticity of (Zr53Cu30Ni9Al8)99.5Si0.5 bulk metallic glasses. After the electropulsing treatment, the specimen showed reductions in both the glass transition and the crystallization temperatures while retaining its amorphous structure, and both Young's modulus and the hardness decreased while the nanoindentation loading curve became more serrated. Using the bond-interface method and Vickers indentation, the treated specimen showed more branching of semi-circular shear bands and less radial shear bands compared to its as-cast counterpart. The possible plasticity enhancement mechanism of the electropulsing treatment was also discussed.

This work develops a multilayer structure of alternating (AlCrRuTaTiZr)N 0.5 senary nitride and AlCrRuTaTiZr senary alloy with a total thickness of only 4 nm as a diffusion barrier layer for application to Cu interconnects. Under annealing at a high temperature of 800 °C, the interdiffusion of Cu and Si through the multilayer structure was effectively retarded without the formation of any Cu silicides. Interdiffusion occurred only at 900 °C, and compounds that included Cu 3 Si were thus formed. This finding suggests that the high endurance temperature of the diffusion barrier is probably attributable to the stable amorphous solid-solution structure, the high packing factor, the severe lattice distortions that are caused by the incorporation of multiple components and the elongated diffusion path through the multilayer stacking structure.

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.

To fulfill the strict demands for Cu interconnects below 65 nm, a 10 nm-thick (TiVCr)N film with ternary metallic elements was developed in this study as a candidate diffusion barrier by reactive sputtering in an N2/Ar mixed atmosphere. Barrier properties were examined by annealing over a temperature range of 700–900 °C for 30 min. From the analyses of diffusion behaviors after thermal annealing at 700 °C, the electrical resistance of the Si/(TiVCr)N/Cu film stack remained as low as the as-deposited value. No interdiffusion between the Si substrate and the Cu metallization was found through the (TiVCr)N film at temperatures as high as 700 °C. After annealing at 800 °C, the penetration of a partial number of Cu atoms through the (TiVCr)N barrier occurred and thus some Cu silicides were formed. With temperature further increased to 900 °C, severe interdiffusion of Si and Cu through the layer occurred and induced the formation of a large amount of Cu silicides. This demonstrates that TiVCr ternary refractory metal nitrides have potential use as effective diffusion barriers for copper metallization.

Multi-component (AlCrTaTiZr)N x C y coatings with the incorporation of quinary metallic elements and different N and C contents were deposited by AlCrTaTiZr/C co-sputtering in an N 2 /Ar mixed atmosphere under an AlCrTaTiZr-alloy-target power of 150 W and different C-target powers (0–200 W). At a C-target power of 0 W, an (AlCrTaTiZr)N 0.6 coating with a face-centered cubic solid-solution structure was deposited and exhibited a large columnar structure; its hardness and steady-stage creep strain rate were measured as about 20 GPa and 1.5 × 10 −4 1/s, respectively. By applying a C-target power of 100 W, an (AlCrTaTiZr)N 0.6 C 0.2 coating was formed with a fine columnar structure. Owing to the incorporated C atoms, the (111) interplanar spacing of the face-centered cubic structure was increased from 0.249 to 0.253 nm. The hardness increased to 32 GPa and the creep strain rate was lowered to 1.1 × 10 −4 1/s attributed to the introduction of covalent-like bonds, grain refinement and the formation of an amorphous-like and nanocomposite structure. Furthermore, under a C-target power of 200 W, excess C atoms agglomerated to form clusters in the deposited (AlCrTaTiZr)N 0.6 C 0.4 coating. Consequently, the hardness slightly decreased to 30 GPa and the creep strain rate increased to 2.4 × 10 −4 1/s.