Development Of Nanostructures Research Articles

Strain-modulated initial oxidation of Al(1-x)Nix alloy surface

Despite of extensive studies about surface oxidation of metals and alloys, the impact of external loadings on nanoscale initial oxidation remains relatively unclear. Here, we demonstrate that surface prestrains and dynamic loadings can effectively modulate the initial oxidation of Al(1-x)Nix alloys. We find that prestrains can not only suppress or promote outward and inward ionic diffusions, but change the oxygen Ehrlich-Schwöbel (ES) barrier across oxide islands. The former affects the oxidation kinetics while the latter leads to a oxide growth mode transtion, which comprehensively determines the evolution of oxide nanostructure. In addition, we propose a theoretical chemo-mechanical coupling model to predict the internal stress evolution and the stress relaxation in Al0.7Ni0.3 oxidation. Finally, the study of Al and Al0.7Ni0.3 oxidations under dynamic strains shows that alloying nickel in aluminum effectively enhances the oxidation resistance under cyclic loadings by intensifying the chemo-mechanical coupling effect. Findings in this work may shed the light on the modulation of surface oxidation through applying mechanical loadings, and is helpful to the materials design and protection.

MoSe2-WS2 Nanostructure for an Efficient Hydrogen Generation under White Light LED Irradiation.

In this work, MoSe2-WS2 nanocomposites consisting of WS2 nanoparticles covered with few MoSe2 nanosheets were successfully developed via an easy hydrothermal synthesis method. Their nanostructure and photocatalytic hydrogen evolution (PHE) performance are investigated by a series of characterization techniques. The PHE rate of MoSe2-WS2 is evaluated under the white light LED irradiation. Under LED illumination, the highest PHE of MoSe2-WS2 nanocomposite is 1600.2 µmol g−1 h−1. When compared with pristine WS2, the MoSe2-WS2 nanostructures demonstrated improved PHE rate, which is 10-fold higher than that of the pristine one. This work suggests that MoSe2-WS2 could be a promising photocatalyst candidate and might stimulate the further studies of other layered materials for energy conversion and storage.

Kinetic Reconstruction of DNA-Programed Plasmonic Metal Nanostructures with Predictable Shapes and Optical Properties.

It is desirable to rationally engineer plasmonic metal nanostructures with sets of structural parameters that lead to specific functions. However, it is still challenging to predict the nanostructured outcome of a synthesis reaction by design because not only the exact kinetic path for the structural evolution is very complicated but also the relationships among various functional and structural parameters are often tangled. It is necessary to deconvolute the structure-function relationships and understand the co-evolution of structural and functional parameters as the nanostructures grow. DNA is a programable biomolecular capping ligand that was shown to be capable of precisely controlling the evolution of metal nanostructures. In this study, we systematically analyzed the evolution of two structural parameters and several functional parameters in the growth of Au-Ag nanostructures controlled by two DNA sequences. We deconvoluted the contributions from the two structural parameters in affecting the plasmonic properties in different kinetic and geometric domains. We further designed new nanostructures by exchanging DNA sequences in the growth environment, which also changed their evolution pathways. The resulting structural and functional parameters could be predictively tuned by the timing of the exchange. This study demonstrates the powerful toolbox provided by programable biomolecules in producing novel nanostructures in a predictable manner. It also shows that by understanding the kinetic evolution of the structural parameters and their relationships with the function parameters, it is possible to design the precise combinations of structural and functional parameters in the nanostructured products.

Deformation behavior of heterogeneous nanostructured austenitic stainless steel at cryogenic temperature

Herein, systematic investigations were conducted to elucidate the deformation behavior and the microstructure evolution of the heterogeneous nanostructured (HNed) SUS316LN austenitic stainless steel during tensile tests at cryogenic temperature (77 K). The HNed steel exhibited an excellent strength/ductility balance of 2200 MPa in the ultimate tensile strength and 0.55 in the total elongation, ascribed to the high inherent strength of the heterogeneous nanostructure (HN), and the significant work hardening caused by the transformation-induced plasticity (TRIP). At the non-necked region, deformation-induced martensitic transformation (DIMT) of γ → ε → α′ occurred with the orientation relationship of (111¯)γ || (0002)ε || (011¯)α′, <011>γ || <211¯0>ε || <1¯11¯>α'. The HN reserved its morphology. However, ∼80% of the γ austenite transformed into α’ martensite at the necked region, leading to the significant deformation of the HN. Finally, preparing the ultrafine HN improved the yield and ultimate strength at cryogenic temperature. Therefore, the high flow stress promoted the DIMT in enhancing the ductility owing to the TRIP effect.

Nontrivial nanostructure, stress relaxation mechanisms, and crystallography for pressure-induced Si-I\u2009\u2192\u2009Si-II phase transformation

Crystallographic theory based on energy minimization suggests austenite-twinned martensite interfaces with specific orientation, which are confirmed experimentally for various materials. Pressure-induced phase transformation (PT) from semiconducting Si-I to metallic Si-II, due to very large and anisotropic transformation strain, may challenge this theory. Here, unexpected nanostructure evolution during Si-I → Si-II PT is revealed by combining molecular dynamics (MD), crystallographic theory, generalized for strained crystals, and in situ real-time Laue X-ray diffraction (XRD). Twinned Si-II, consisting of two martensitic variants, and unexpected nanobands, consisting of alternating strongly deformed and rotated residual Si-I and third variant of Si-II, form {111} interface with Si-I and produce almost self-accommodated nanostructure despite the large transformation volumetric strain of -0.237. The interfacial bands arrest the {111} interfaces, leading to repeating nucleation-growth-arrest process and to growth by propagating {110} interface, which (as well as {111} interface) do not appear in traditional crystallographic theory.

Tailoring the magnetic properties and microstructure of Alnico 8 magnets by various Ti contents and processing conditions

Shape anisotropy, developed as a result of spinodal decomposition (SD) is the basis for the hysteresis behavior of Alnico magnets. The SD process is sensitive to processing conditions and constituent elements. In this paper, the development of spinodal structure and its effects on magnetic properties and serviceability of Alnico 8 alloys are investigated. The Ti-content is varied between 2.5 and 7.5 wt%. The magnets are fabricated by conventional casting, homogenization, magnetic field annealing and tempering treatments. The magnetic properties of intrinsic coercivity, Hcj = 30 kA/m, remanence, Br = 0.53 T and maximum energy density, (BH)max = 6.03 kJ/m3 for 2.5 wt% Ti are increased to Hcj = 150 kA/m, Br = 0.0.88 T and (BH)max = 29.3 kJ/m3 for 6.5 wt% Ti alloy. These magnetic properties are 100% reversible up to 800 K. Furthermore, an alloy with 5.5 wt% Ti is directionally solidified and magnetic properties of Br = 1.01 T and (BH)max = 58.9 kJ/m3 are obtained. The evolution of mosaic nano structure, the mechanism of magnetic hardening and the interactions of various phases have been investigated.

Synergistic Effect of Mixing Ethylene with Propane on the Morphology and Nanostructure of Soot in Laminar Coflow Diffusion Flames

AbstractThe synergistic effect of mixing ethylene with propane on the nanostructure and morphology evolution of soot in laminar coflow diffusion flames was investigated via combining thermophoresis...

Understanding the nanostructure evolution and the mechanical strengthening of the M50 bearing steel during ultrasonic shot peening

Ultrasonic shot peening (USP) is a surface engineering technology used to enhance the mechanical properties of the components during manufacturing. M50 steel is one of the commonly used materials for aerospace bearings. In this study, surface nanocrystallization of the high-strength M50 bearing steel is performed at room temperature via USP technology. The materials characterizations show that the thickness of the lath martensite in the M50 bearing steel has been refined down to 10 nm. The extremely fine nanostructured M50 martensite increases the mechanical strength significantly at the nanoscale. Nanoindentation tests show that the nanohardness of the nanostructured M50 is 12.43 GPa, which is 38% higher than that of the as-received matrix materials with a value of 9.03 GPa. Additionally, the microstructure evolution of the M50 during the USP process is investigated and the grain refinement mechanism for M50 is revealed. EBSD characterization results confirm the transformation of the low angle grain boundaries to high angle grain boundaries and the formation of the equiaxed ultrafine grains. The decomposition of the carbides in the M50 during grain refinement is observed. This indicates that in addition to the diffusion of C, the decomposition of the carbides is also influenced by carbide-forming elements. This work deepens the current understanding of the grain refinement of the M50 bearing steel during the USP process and its mechanical strengthening at the nanoscale.

Correction to: Quantitative Nanostructure and Hardness Evolution in Duplex Stainless Steels: Under Real Low-Temperature Service Conditions

Correction to: Quantitative Nanostructure and Hardness Evolution in Duplex Stainless Steels: Under Real Low-Temperature Service Conditions

A galvanic replacement reaction and the Kirkendall effect in the room-temperature synthesis of tubular NiSe2: a nanozyme catalyst with peroxidase-like activity.

The synthesis of nickel selenide nanostructures under ambient conditions remains fascinating, aesthetically beautiful, and energy efficient, as most reported methods involve high-temperature techniques. In this work, we have reported the wet chemical synthesis of NiSe2 nanostructures at room temperature. The approach starts with nickel nanowires (NiNW) and selenous acid as active ingredients. Upon the incubation of NiNW in selenous acid, zero-valent metallic nickel gradually oxidised with the successive deposition of nano-selenium, a reductive product, over the pristine NiNW surface. This thermodynamically controlled galvanic replacement reaction (GRR) is favourably governed by the reduction potential values of the Ni2+/Ni and SeO32-/Se redox couples. Moreover, the selenium nanoparticles over the NiNW surface and the oxidized Ni2+ underneath then interplay during inward and outward diffusion. The different diffusivities of the elements/ions cause the generation of void interiors, thus resulting in tubular nanostructures. Therefore, both the GRR and nanoscale Kirkendall effect jointly remain engaged, resulting in the formation of hollow NiSe2 nanotubular structures. Then, we ably exploit this heterogeneous chalcogenide nanostructure material as an artificial enzyme for peroxidase mimics. This provides a method for the naked-eye detection of peroxide in solution. The peroxidase activity was selectively restrained in the presence of glutathione. Hence, a colourimetric assay was simultaneously developed for the selective detection of this biothiol. The intrinsic nanozyme activity of the substrate is hitherto unknown and can, hence, be explored further with other nanostructured nickel selenide materials.

Insight into soot formed in coal combustion flame: Evolution of physiochemical structure, oxidation reactivity

Combustion experiments of a bituminous coal were performed on a flat-flame burner that provided a realistic low-O2 combustion atmosphere. Soot samplings were performed via both thermophoresis and dilution-filtering sampling methods along the flame centerline. The morphology, size, fractional- and nanostructure evolution, and especially the detailed oxidation characteristics of soot of different maturities in flame were comprehensively characterized. Results showed that liquidus tar was formed in the flame bottom which acted as soot precursor, and a direct evidence was obtained that the solid soot particles in the coal flame were mostly derived from the liquidous tar via carbonization. In the nanostructure of the mature soot particles, both of fullerenic, amorphous and diamond phases were detected, indicating a multiple nucleation process during the soot formation in coal flame. Furthermore, it was found that soot in the bright flame core was more difficult to be oxidized than the soot upstream and downstream it. And finally based on the Raman spectrum and particle micromorphology analysis, the non-linear change of the oxidation reactivity of the soot along the flame centerline was revealed to be controlled firstly by the gradual graphitization with increasing of the flame temperature and then by the change of soot aggregate size.

Bottom-Up Evolution of Diamond-Graphite Hybrid Two-Dimensional Nanostructure: Underlying Picture and Electrochemical Activity.

The diamond-graphite hybrid thin film with low-dimensional nanostructure (e.g., nitrogen-included ultrananocrystalline diamond (N-UNCD) or the alike), has been employed in many impactful breakthrough applications. However, the detailed picture behind the bottom-up evolution of such intriguing carbon nanostructure is far from clarified yet. Here, the authors clarify it, through the concerted efforts of microscopic, physical, and electrochemical analyses for a series of samples synthesized by hot-filament chemical vapor deposition using methane-hydrogen precursor gas, based on the hydrogen-dependent surface reconstruction of nanodiamond and on the substrate-temperature-dependent variation of the growth species (atomic hydrogen and methyl radical) concentration near substrate. The clarified picture provides insights for a drastic enhancement in the electrochemical activities of the hybrid thin film, concerning the detection of important biomolecule, that is, ascorbic acid, uric acid, and dopamine: their limits of detections are 490, 35, and 25nm, respectively, which are among the best of the all-carbon thin film electrodes in the literature. This work also enables a simple and effective way of strongly enhancing AA detection.

Micro‐/nanostructure evolution of C/SiFeO(N,C) polymer‐derived ceramic papers pyrolyzed in a reactive ammonia atmosphere

AbstractSiFeO(N,C)‐based ceramic papers were prepared via a one‐pot synthesis approach by dip‐coating a cellulose‐based paper template with a polymeric perhydropolysilazane precursor modified with iron(III)acetylacetonate. The preceramic composites were subsequently pyrolyzed in ammonia atmosphere at 500, 700, and 1000°C, respectively, and the characteristics of the three resulting ceramic papers were comparatively investigated.Scanning electron microscopy revealed that in each sample, the morphology of the template is successfully transferred on the ceramic system, with the cellulose‐derived fibers being converted to elemental carbon encased by a SiFeO(N,C) coating. Electron transparent cross‐sectional samples for transmission electron microscopy (TEM) were prepared from the ceramic papers, employing a standard ultramicrotomy slice cutting procedure, allowing for a detailed characterization of their in situ generated micro‐/nanostructure as well as occurring crystalline phases.TEM imaging and diffraction revealed that depending on pyrolysis temperature a different microstructure with a distinct phase assemblage is generated in the polymer‐derived ceramic papers. Crystallization from the polymer precursor starts with the precipitation of wüstite (Fe(1‐x)O) nanoparticles at 700°C inside the ceramic coating and secondary ε‐FexN at the fiber‐coating interface. Upon pyrolysis at 1000°C however, the sample primarily accommodates metallic α‐iron nanocrystals that impart ferromagnetic characteristics to the ceramic paper.The results show that the template‐assisted polymer‐derived ceramic route is a feasible approach in the production of complex ceramic compounds with fibrous paper‐like morphology. By adjusting the pyrolysis temperature, microstructure and phase composition of the ceramic paper can be conveniently tailored to the needs of its respective application.

Imaging nanostructure phase transition through ultrafast far-field optical ultramicroscopy

Imaging photo-induced ultrafast dynamics of nanostructure phase transition is of great interest to the fields of laser-matter interactions and nanotechnology. However, conventional ultrafast far-field optical imaging methods cannot image nanostructures as their scattering scales as D 6 , with D being the diamater, leading to a vanishing signal-to-noise ratio. Here, we use ultrafast ultramicroscopy to capture the spatiotemporal evolution of surface nanostructures as they undergo melting, spallation, and re-solidification processes. Our experimental observations, combined with finite difference time domain (FDTD) simulations, show agreement with molecular dynamic simulations on ultrashort laser pulse-irradiated metallic nanoparticles and suggest the occurrence of melting of nanostructures followed by photomechanical spallation within a few picoseconds. At longer timescales, we image the re-solidification dynamics of the melted nanostructures occurring within nanoseconds. The re-solidification time for nanostructured surface occurs an order of magnitude faster than for an initially flat surface. Our study demonstrates a simple but powerful far-field optical approach for studying ultrafast dynamics of nanostructures. • Introducing an optical far-field ultrafast imaging method for nanostructures • Imaging photomechanical spallation of nanostructures within picoseconds • Imaging the re-solidification dynamics of nanostructures Ultrafast imaging of nanostructures is challenging due to their low signal-to-noise-ratio. ElKabbash et al. use ultrafast ultramicroscopy to image light-matter interactions at the nanoscale, spatial, and femtosecond scale temporally. The results show that irradiating surface nanostructures with an intense femtosecond laser pulse undergo photomechanical spallation within a few picoseconds.

Shape evolution and optical response of ZnO nanostructures grown on thermally evaporated ZnO and Au thin films

ZnO thin films of 100–400 nm thickness and 100 nm thickness Au thin films were deposited on glass substrates by thermal evaporation. Shape control of ZnO nanostructures on these films is achieved by microwave assisted hydrothermal synthesis at 90 °C for 30 min using zinc nitrate and zinc acetate as the precursors. There is a hierarchy of shapes comprising star shaped tetrapods and ball-shapes at the microscale made up of rice grains at the nanoscale on the ZnO and Au thin films respectively, when the precursor is zinc nitrate. The typical dimensions of the nano rice grains are 1 μm length, 100 nm width and tips of the order of 10 nm. In contrast, when the precursor is zinc acetate the nanostructures grow as hexagonal rods on the ZnO films and hexagonal tetrapods on the Au films with dimensions of 1–3 μm length and hexagon side of the order of 100–150 nm. Raman spectroscopy studies indicate the presence of defect related peaks in the nanostructures that are suppressed with increase in thickness of the ZnO films. The intensity of the defect peaks is much higher in the nanostructures grown on the Au films and is dependent on the precursor used to produce the nanostructures. Photoluminescence studies indicate that the ultraviolet-near band edge emission is the strongest on ZnO while defect related emission is prominent on the Au films. Shape control by microwave assisted hydrothermal synthesis is, thus, a facile low temperature method to produce nanostructures with different properties by simply changing the precursor and substrate on which they are grown.

Strain driven phase transition and mechanism for Fe/Ir(111) films

By way of introducing heterogeneous interfaces, the stabilization of crystallographic phases is critical to a viable strategy for developing materials with novel characteristics, such as occurrence of new structure phase, anomalous enhancement in magnetic moment, enhancement of efficiency as nanoportals. Because of the different lattice structures at the interface, heterogeneous interfaces serve as a platform for controlling pseudomorphic growth, nanostructure evolution and formation of strained clusters. However, our knowledge related to the strain accumulation phenomenon in ultrathin Fe layers on face-centered cubic (fcc) substrates remains limited. For Fe deposited on Ir(111), here we found the existence of strain accumulation at the interface and demonstrate a strain driven phase transition in which fcc-Fe is transformed to a bcc phase. By substituting the bulk modulus and the shear modulus and the experimental results of lattice parameters in cubic geometry, we obtain the strain energy density for different Fe thicknesses. A limited distortion mechanism is proposed for correlating the increasing interfacial strain energy, the surface energy, and a critical thickness. The calculation shows that the strained layers undergo a phase transition to the bulk structure above the critical thickness. The results are well consistent with experimental measurements. The strain driven phase transition and mechanism presented herein provide a fundamental understanding of strain accumulation at the bcc/fcc interface.

Controlling Equilibrium Morphologies of Bimetallic Nanostructures Using Thermal Dewetting via Phase-Field Modeling.

Herein, we report a computational model for the morphological evolution of bimetallic nanostructures in a thermal dewetting process, with a phase-field framework and superior optical, physical, and chemical properties compared to those of conventional nanostructures. The quantitative analysis of the simulation results revealed nano-cap, nano-ring, and nano-island equilibrium morphologies of the deposited material in thermal dewetting, and the morphologies depended on the gap between the spherical patterns on the substrate, size of the substrate, and deposition thickness. We studied the variations in the equilibrium morphologies of the nanostructures with the changes in the shape of the substrate pattern and the thickness of the deposited material. The method described herein can be used to control the properties of bimetallic nanostructures by altering their equilibrium morphologies using thermal dewetting.

Effect of Stress on Spinodal Decomposition in Binary Alloys: Atomistic Modeling and Atom Probe Tomography

Self-organizing nanostructure evolution through spinodal decomposition is a critical phenomenon determining the properties of many materials. Here, we study the influence of stress on the morphology of the nanostructure in binary alloys using atomistic modeling and atom probe tomography. The atomistic modeling is based on the quasi-particle approach, and it is compared to quantitative three-dimensional (3-D) atom mapping results. It is found that the magnitude of the stress and the crystallographic direction of the applied stress directly affect the development of spinodal decomposition and the nanostructure morphology. The modulated nanostructure of the binary bcc alloy system is quantified by a characteristic wavelength, lambda . From modeling the tensile stress effect on the A-35 at. pct B system, we find that lambda _{001}< , lambda _{111}< , lambda _{101}< , lambda _{112} and the same trend are observed in the experimental measurements on an Fe-35 at. pct Cr alloy. Furthermore, the effect of applied compressive and shear stress states differs from the effect of the applied tensile stress regarding morphological anisotropy.

Precursor concentration induced nanostructural evolution of electrodeposited ZnO thin films and its effect on their optical and photocatalytic properties

Precursor concentration induced nanostructural evolution of electrodeposited ZnO thin films and its effect on their optical and photocatalytic properties

Nanostructural evolution of Al(OH)3 gel formed by the cubic and orthorhombic ye'elimite clinkers of calcium sulfoaluminate cements in an ultra-wide hydration temperature range

This paper investigated the influence of hydration temperature on the nanostructure of the AH3 phase formed in calcium sulfoaluminate cements. Orthorhombic ye'elimite (st-ye'elimite) and cubic ye'elimite (ss-ye'elimite) were hydrated in an ultra-wide temperature range (5–220 °C). Results showed that the AH3 phase formed by ss-ye'elimite was always microcrystalline in nature at various curing temperatures (5–130 °C), and transformed into the AlOOH phase at 150 °C and above. However, the AH3 phase formed by st-ye'elimite grew from a microcrystal to a favorable crystal as the temperature increased, and transformed into the AlOOH phase at 170 °C and above. The nanostructure of hydration products was further investigated using TEM/SAED analysis together with FE-SEM images, directly evidencing that the formed AFm-12 phase was single-crystal in nature, and the formed AH3 phase was microcrystalline at low temperatures and grew into single-crystal hexagonal prisms with the preferred growth direction along [001] direction at high temperatures.