Nanoscale Alloy Research Articles

Structural defects and magnetic properties of gadolinium silicide nanoparticles synthesized by laser ablation technique in liquid

Magnetic nanoscale compounds and alloys of gadolinium are promising materials for technological and medical applications. In this paper the influence of structural defects on the properties of the binary GdSi nanopowders formed in laser ablation and post-irradiation processes have been investigated. To obtain compound GdSi nanoparticles (NPs) we used laser ablation of a combined target consisting of Gd and Si plates tightly pressed to each other with focusing a laser beam onto the gadolinium–silicon interface. The crystalline structure, phase composition of the NPs formed were examined by SEM and X-ray diffraction (XRD). Magnetic measurements showed that the resulting NPs did not exhibit hysteresis at low temperature (6 K), which is typical to nanosized magnetic materials demonstrating superparamagnetic behavior. Magnetization increased after laser processing of the samples due to ordering in the grain structure and in the magnetic moments at the surface.

A nanoscale co-precipitation approach for property enhancement of Fe-base alloys

Precipitate size and number density are two key factors for tailoring the mechanical behavior of nanoscale precipitate-hardened alloys. However, during thermal aging, the precipitate size and number density change, leading to either poor strength or high strength but significantly reduced ductility. Here we demonstrate, by producing nanoscale co-precipitates in composition-optimized multicomponent precipitation-hardened alloys, a unique approach to improve the stability of the alloy against thermal aging and hence the mechanical properties. Our study provides compelling experimental evidence that these nanoscale co-precipitates consist of a Cu-enriched bcc core partially encased by a B2-ordered Ni(Mn, Al) phase. This co-precipitate provides a more complex obstacle for dislocation movement due to atomic ordering together with interphases, resulting in a high yield strength alloy without sacrificing alloy ductility.

Nanoscale alloying: A study in free Cu–Ag bimetallic clusters

Abundance measurements of bimetallic clusters synthesized in gas phase could address the issues of alloying between two metals at nanometer scale. In fact, these studies might be able to answer why some metals do not form good alloy in bulk phase, from an atomic point of view. We report one such investigation between Cu and Ag atoms. Formation of free bimetallic clusters between these two coin metals is investigated up to 7100amu by synthesizing them in gas phase under completely unperturbed conditions. The results produce evidence of magic combination as proposed in several theoretical calculations. A total of 1465 binary CumAgn nanoclusters could be identified in which many magic compositions appear with higher abundances. Overall, it is observed that Cu and Ag atoms do not mix randomly but preferably surface segregate. The findings validate the structure motif reported in theoretical studies and thereby, depict a natural selectivity in the formation of these nanoscale alloys. Thus, the study contributes in the understanding of fundamental issues involved in alloying between two noble metals.

Synthesis and Characterization of Nanoscale Fe/Ni Alloy Particles by Hydrothermal Method

Nanoscale Fe/Ni alloy particles have been synthesized by hydrothermal method in this study. The influences of various reaction temperatures on the properties and morphologies were studied. The structure of Fe/Ni alloy nanoparticles were characterized by SEM, XRD and FTIR. Additional, the magnetic and electrical properties were also studied to obtain the optimum reaction condition. It would provide the foundation to the study about the synthesis and performance of iron-based nanoscale alloy powder.

Gold–Copper Nanoparticles: Nanostructural Evolution and Bifunctional Catalytic Sites

Understanding of the atomic-scale structure is essential for exploiting the unique catalytic properties of any nanoalloy catalyst. This report describes novel findings of an investigation of the nanoscale alloying of gold–copper (AuCu) nanoparticles and its impact on the surface catalytic functions. Two pathways have been explored for the formation of AuCu nanoparticles of different compositions, including wet chemical synthesis from mixed Au- and Cu-precursor molecules, and nanoscale alloying via an evolution of mixed Au- and Cu-precursor nanoparticles near the nanoscale melting temperatures. For the evolution of mixed precursor nanoparticles, synchrotron X-ray-based in situ real-time XRD was used to monitor the structural changes, revealing nanoscale alloying and reshaping toward an fcc-type nanoalloy (particle or cube) via a partial melting–resolidification mechanism. The nanoalloys supported on carbon or silica were characterized by in situ high-energy XRD/atomic pair disributoin function (PDF) analyses, revealing an intriguing lattice “expanding–shrinking” phenomenon depending on whether the catalyst is thermochemically processed under an oxidative or reductive atmosphere. This type of controllable structural changes is found to play an important role in determining the catalytic activity of the catalysts for carbon monoxide oxidation reaction. The tunable catalytic activities of the nanoalloys under thermochemically oxidative and reductive atmospheres are also discussed in terms of the bifunctional sites and the surface oxygenated metal species for carbon monoxide and oxygen activation.

Design of Ternary Nanoalloy Catalysts: Effect of Nanoscale Alloying and Structural Perfection on Electrocatalytic Enhancement

The ability to tune the atomic-scale structural and chemical ordering in nanoalloy catalysts is essential for achieving the ultimate goal of high activity and stability of catalyst by design. This article demonstrates this ability with a ternary nanoalloy of platinum with vanadium and cobalt for oxygen reduction reaction in fuel cells. The strategy is to enable nanoscale alloying and structural perfection through oxidative–reductive thermochemical treatments. The structural manipulation is shown to produce a significant enhancement in the electrocatalytic activity of the ternary nanoalloy catalysts for oxygen reduction reaction. Mass activities as high as 1 A/mg of Pt have been achieved by this strategy based on direct measurements of the kinetic currents from rotating disk electrode data. Using a synchrotron high-energy X-ray diffraction technique coupled with atomic pair function analysis and X-ray absorption fine structure spectroscopy as well as X-ray photoelectron spectroscopy, the atomic-scale structural and chemical ordering in nanoalloy catalysts prepared by the oxidative–reductive thermochemical treatments were examined. A phase transition has been observed, showing an fcc-type structure of the as-prepared and the lower-temperature-treated particles into an fct-type structure for the particles treated at the higher temperature. The results reveal a thermochemically driven evolution of the nanoalloys from a chemically disordered state into chemically ordered state with an enhanced degree of alloying. The increase in the chemical ordering and shrinking of interatomic distances as a result of thermochemical treatment at increased temperature is shown to increase the catalytic activity for oxygen reduction reaction, exhibiting an optimal activity at 600 °C. It is the alloying and structural perfection that allows the optimization of the catalytic performance in a controllable way, highlighting the significant role of atomic-scale structural and chemical ordering in the design of nanoalloy catalysts.

Nanoscale alloying effect of gold–platinum nanoparticles as cathode catalysts on the performance of a rechargeable lithium–oxygen battery

The understanding of nanoscale alloying or the phase segregation effect of alloy nanoparticles on the catalytic properties is important for a rational design of the desired catalysts for a specific reaction. This paper describes findings of an investigation into this type of structural effect for carbon-supported bimetallic gold–platinum nanoparticles as cathode catalysts in a rechargeable lithium–oxygen battery. The nanoscale structural characteristics in terms of size, alloying and phase segregation were shown to affect the catalytic properties of the catalysts in the Li–O2 battery. In addition to the composition effect, the catalysts with a fully alloyed phase structure were found to exhibit a smaller discharge–charge voltage difference and a higher discharge capacity than those with a partial phase segregation structure. This finding is significant for the design of alloy nanoparticles as air cathode catalysts in rechargeable lithium–air batteries, demonstrating the importance of the control of the nanoscale composition and phase properties.

Thickness-dependence of the B2–B19 martensitic transformation in nanoscale shape memory alloy thin films: Zero-hysteresis in 75 nm thick Ti 51Ni 38Cu 11 thin films

The influence of film thickness on the B2–B19 martensitic transformation properties of nanoscale Ti 51Ni 38Cu 11 thin films with thicknesses ranging from 750 to 50 nm is reported. For these films an unexpected behavior of the phase transformation temperatures was observed: A f and O s initially decrease with decreasing film thickness but increase sharply again for thicknesses <100 nm. The phase transformation temperatures and thermal hysteresis width range from 58 to 35 °C ( A f ) and 14 to ∼0 K, respectively. For the first time we can show that substrate-attached Ti–Ni–Cu thin films as thin as 50 nm show reversible B2–B19 phase transformations. Furthermore, it is shown that with decreasing film thickness a change in the tetragonality of the B19 martensite phase occurs. This leads to fulfilling the so-called λ 2 criterion, causing a vanishing hysteresis for a film thickness of 75 nm.

Patchy Multishell Segregation in Pd−Pt Alloy Nanoparticles

Chemical ordering in face-centered-cubic-like PdPt nanoparticles consisting of 38-201 atoms is studied via density-functional calculations combined with a symmetry orbit approach. It is found that for larger particles in the Pd-rich regime, Pt atoms can segregate at the center of the nanoparticle (111) surface facets, in contrast with extended systems in which Pd is known to segregate at the surface of alloy planar surfaces. In a range of compositions around 1:1, a novel multishell chemical ordering pattern was favored, in which each shell is a patchwork of islands of atoms of the two elements, but the order of the patchwork is reversed in the alternating shells. These findings are rationalized in terms of coordination-dependent bond-energy variations in the metal-metal interactions, and their implications in terms of properties and applications of nanoscale alloy particles are discussed.

Gold-platinum nanoparticles: alloying and phase segregation

The ability to control nanoscale alloying and phase segregation properties is important for the exploration of multimetallic nanoparticles for the design of advanced functional materials and catalysts. This report highlights recent insights into the nanoscale phase properties of gold-platinum (AuPt) nanoparticles, which serves as an example to shine a light on the importance of changes in physical and chemical properties in which nanoscale multimetallic materials may differ from their bulk counterparts. In contrast to the wide miscibility gap well known for the bulk gold-platinum system, the bimetallic nanoparticles have been demonstrated to exist in phases ranging from alloy, partial alloy, to phase segregation depending on the preparation conditions, the bimetallic composition, and the supporting materials. For AuPt nanoparticles supported on carbon materials, the nanoscale alloying or phase segregation is shown to be controllable by thermal treatment temperatures, which is not only evidenced by detailed analysis of the phase and surface properties, but also supported by theoretical modeling based on thermodynamic and density function theory. The understanding of the nanoscale phase properties can be correlated with the electrocatalytic activities for fuel cell reactions such as methanol oxidation reaction and oxygen reduction reaction. Implications of the new insights to designing and nanoengineering the phase properties of multimetallic nanoparticles and catalysts are also briefly discussed.

Quantum dot laser

Discovery of self-organized epitaxial quantum dots (QDs) resulted in multiple breakthroughs in the field of physics of zero-dimensional heterostructures and allowed the advancement of optoelectronic devices, most remarkably, lasers. The most advanced and well-understood results are obtained for lasers based on Stranski–Krastanow InGaAs–GaAs three-dimensional QDs; even significant progress in the understanding of basic lasing properties is also achieved for QDs made of II–VI materials and ‘native’ QDs formed by nanoscale alloy phase separation in the InGaN–AlGaN material system.

A facile co-gelation route to synthesize FeCo/carbon nanocomposites and their application as magnetically separable adsorber

A new kind of magnetic porous FeCo/carbon nanocomposites was successfully synthesized by using a facile co-gelation sol–gel route. The sol–gel process of this route started from an ethanol solution containing teraethylorthosilicate (TEOS), furfuryl alcohol (FA), and metal nitrates. With the evaporation of solvent, the weak acidity produced from hydrolysis of metal nitrates simultaneously catalyzed the polymerization of FA and the hydrolysis of TEOS, which led to the inorganic/organic hybrid xerogel, accompanying metal salts spontaneously captured in the xerogel. The composites obtained have high surface areas, pore volumes and strong magnetic strengths, which make them exhibit excellent performance of adsorption for bulk dyes and easily separated from solution by external field after adsorption. Compared to the previous methods, this route is very simple and operable for the preparation of magnetic porous carbon composites. Such facile co-gelation route also provides a common path to the synthesis of nanoscale metal or alloy embedded in the porous carbon materials.

Annealing induced nanostructure and photoluminescence property evolution in solution-processed Mg-alloyed ZnO nanowires

Solution-processed Mg-alloyed ZnO nanowire arrays have been achieved recently without using high temperature annealing process. By introducing thermal annealing processes in oxygen-rich ambient condition, the UV near-band-edge (NBE) emission was surprisingly mitigated until disappeared with annealing temperature increasing from 400 to 900 °C. As the annealing temperature increased, intensity of UV peak decreased while intensity of visible peak (490–520 nm) increased. The structure evolution upon thermal annealing was revealed to be responsible for these abnormal photoluminescence property variations, where unusual (Zn,Mg)1.7SiO4 epitaxially evolved on ZnMgO nanowires surface and contributed to the quenching of UV NBE emission. The structure evolution induced UV-NBE quenching and nanoscale localized alloying in semiconductor ZnMgO nanowires could bring up opportunities in catalysis, optoelectronics, spintronics, and sensors.

Degradation of metronidazole by nanoscale zero-valent metal prepared from steel pickling waste liquor

In this study, steel pickling waste liquor was employed to obtain reactive nanoscale zero-valent metal (nZVM) with the purpose of engineering application. The degradation of metronidazole reacted with as-prepared nZVM in water was investigated to explore the feasibility of using the nZVM to treat antibiotics in wastewater. The synthesized nZVM was characterized by Brunauer–Emmett–Teller (BET) surface analyzer, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectrometer (EDS). The results showed that the nZVM (20–40nm) with crystalline structure had a BET surface area of 35m2/g. XPS and EDS only detected Fe, C and O on the surface, suggesting Ni and Zn distributed inside the core of nanoscale alloy. Degradation of metronidazole followed the pseudo-first-order kinetics, and the observed reaction rate constant (kobs) could be improved with increasing nZVM dosage, as well as with diminishing initial metronidazole concentration and pH. A high reaction rate was observed at reduction potential, indicating that electrons and hydrogen species produced by nZVM were driving forces of reaction. The surface area-normalized rate coefficient (kSA) for nZVM (0.254Lmin−1m−2) was 375.2 times larger than that for commercial iron powder (6.67×10−4Lmin−1m−2). Several possible pathways of degradation of metronidazole were proposed according to the results of UV–vis spectra and HPLC chromatograms.

Nanoscale Alloying, Phase-Segregation, and Core−Shell Evolution of Gold−Platinum Nanoparticles and Their Electrocatalytic Effect on Oxygen Reduction Reaction

The design of active and robust bimetallic nanoparticle catalysts requires the control of the nanoscale alloying and phase-segregation structures and the correlation between the nanoscale phase structures and the catalytic properties. Here we describe new findings of a detailed investigation of such nanoscale phase structures and their structure−catalytic activity correlation for gold−platinum nanoparticles prepared with controllable sizes and compositions. The nanoscale alloying and phase-segregation were probed as a function of composition, size, and thermal treatment conditions using X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, electrochemical characterization, and density functional theory modeling. The results have provided the experimental evidence in support of the theoretically simulated dependence of alloying and phase segregation on particle size and temperature. More importantly, new insights have been gained into the control of the nano...

Establishing relationships between bath chemistry, electrodeposition and microstructure of Co–W alloy coatings produced from a gluconate bath

Electrodeposited Fe group: W and Mo alloys have the potential to replace hard Cr coatings for use in engineering applications where wear and corrosion resistance are needed. Electrochemical studies have concentrated in the past on Ni–W alloy deposition, but now interest in Co–W alloys has developed as they possess lower coefficients of friction when in contact with another metal. The most attractive coating composition is in the range 14–20 at.% W, if controlled deposition promotes crystalline alloys of high hardness, rather than softer amorphous alloys containing >20 at.% W. This paper employs ammonia free baths with low concentrations of cobalt and sodium tungstate and varying additions of sodium gluconate to produce alloys at close to 50% efficiency. Voltammetry, UV and visible spectrometry, and potentiostatic deposition have been performed on such baths, whilst XRD, SEM and TEM observations have been made on the deposits. This aims to optimise the process and to understanding the relationships between bath contents, electrochemical kinetics and alloy composition. Efficient deposition of coatings with hardness values up to 1000 kgf mm −2 occurred from a bath containing a high concentration of gluconate. Such deposits arise from concentrations of Co–W–gluconate complexes which promote the formation of nanoscale alloy grains. Current densities up to 2.75 A dm −2 in the agitated bath promoted deposition kinetics to form these highly orientated structures. These kinetics produced nano-segregation of W which may be assisted by the migration of Co–W clusters to boundary sites during the growth of the deposit.

Facile Synthesis of Porous Fe7Co3/Carbon Nanocomposites and Their Applications as Magnetically Separable Adsorber and Catalyst Support

A facile co-gelation route has been developed to synthesize novel porous Fe(7)Co(3)/carbon composites with Fe(7)Co(3) nanoparticles embedded in the porous carbon matrix. The sol-gel process of this route simultaneously involves the hydrolysis of tetraethylorthosilicate (TEOS) and the polymerization of furfuryl alcohol (FA) within an ethanol solution containing TEOS, FA, and metal nitrates, which led to the inorganic/organic hybrid xerogel, accompanying metal salts spontaneously captured in the xerogel, mostly in the framework of poly(furfuryl alcohol) (PFA). Compared to the nanocasting route, the advantage of this method is that the formation of silica template and the impregnation of carbon precursor and metal salts were simultaneously carried out in one co-gelation process, which makes the synthesis very simple and eliminates the time-consuming synthesis of the silica template and multistep impregnation process. Different amounts of Fe(7)Co(3) can be introduced into the composites, which led to different pore structures and magnetic properties. The composites have large surface areas (as high as 651.4 m(2)/g) and high saturation magnetizations (as high as 31.2 emu/g). The Fe(7)Co(3)/carbon composites prepared were successfully applied to the removal of dyes from water and catalysis of hydrogenation as efficient magnetically separable adsober and catalyst support. The facile co-gelation route makes the scalable synthesis of magnetic porous carbon possible for application, and it also provides a promising path to the synthesis of nanoscale metal or alloy embedded in the porous carbon materials.

Preparation and growth of Ni–Cu alloy nanoparticles prepared by arc plasma evaporation

Nano-scale alloy powders, with the average particle size of 50 nm and face-centered cubic structure, were prepared from Ni x Cu 1 − x (20% < x < 80 at.%) bulk alloys by arc plasma evaporation. Because of the difference in evaporation rates for both nickel and copper in the alloy melt, the composition of the prepared powders is found to be different from that of raw bulk alloys in most of the cases. Thus the composition relationship between the powders and raw alloys are constructed in the present work. In order to control the size distribution of the powders, the aggregation and growth process of the nanoparticles are analyzed.

Nanostructure development during devitrification and deformation

The devitrification of amorphous phases can be controlled to yield a nanoscale microstructure based upon either a high density of nanocrystals dispersed in an amorphous matrix or a completely nanocrystalline solid. For both rapidly solidified marginal glass forming alloys and slowly cooled bulk glass forming alloys, the high nanocrystal densities are related to nucleation reactions that are sensitive to the initial as-prepared state of the amorphous phase. For example, nucleation densities of 10 21 m −3 can be enhanced to 10 23 m −3 by selective doping of Al-based glasses and the glass forming ability of bulk amorphous alloys is known to be sensitive to minor impurities. The addition of only 1 at.% of Cu to amorphous Al–Sm–Ni or Al–Y–Fe alloys is an effective microstructure control by narrowing the size distribution of Al nanocrystals and reducing the average size of the nanocrystals from 10 nm to about 7.5 nm while increasing the particle number density. Calorimetry and microstructural analyses of the primary Al crystallization reaction suggest that the addition of Cu modifies the atomic arrangement and induces structural heterogeneities based upon medium range order (MRO) that can act as nucleation sites. The strong composition dependence of the crystallization reactions and resulting microstructures reflect not only underlying thermodynamic constraints, but also indicates a strong composition dependence of the amorphous phase atomic arrangement. These features point to a central role for heterogeneities in the evolution of nanoscale microstructures. During nanostructure synthesis by deformation of multilayers the thermodynamic constraints are also important, but the co-deformation of layers governs the generation of interfacial area that allows for the nanoscale alloying reaction. Moreover, kinetics studies have also revealed that the governing reactions often proceed under transient conditions and can lead to relatively stable and robust nanoscale microstructures.

Nanoscale shape-memory alloys for ultrahigh mechanical damping

Shape memory alloys undergo reversible transformations between two distinct phases in response to changes in temperature or applied stress. The creation and motion of the internal interfaces between these phases during such transformations dissipates energy, making these alloys effective mechanical damping materials. Although it has been shown that reversible phase transformations can occur in nanoscale volumes, it is not known whether these transformations have a sample size dependence. Here, we demonstrate that the two phases responsible for shape memory in Cu-Al-Ni alloys are more stable in nanoscale pillars than they are in the bulk. As a result, the pillars show a damping figure of merit that is substantially higher than any previously reported value for a bulk material, making them attractive for damping applications in nanoscale and microscale devices.