RESUMEN

Despite the compositional analogue to Fe71B17(NbYZr)12 metallic glass, the Fe71B17Y12 metallic glass has a saturated magnetization of Ca 108 emu g-1, more than 5 times of that in Fe71B17(NbYZr)12 (20 emu g-1). The structural origin for such significant difference in magnetic performance was investigated by x-ray absorption fine structure spectra and ab initio molecular dynamics (AIMD) simulations including simulated pair-correlation function (PCF) and Voronoi tessellation. Based on the Heisenberg model of magnetism, the narrow distribution of Fe-Fe bonds with larger distances accounts for a large Fe moment of 2.0 µ B in Fe71B17Y12, while the broad distribution of Fe-Fe bonds leads to ferrimagnetic couplings which result in the small net Fe moment of 0.45 µ B in Fe71B17(NbYZr)12. This work emphasizes how the substitution of analogous 4d transition metals induces a significantly different magnetism, which sheds lights on the development of new magnetic metallic glasses with both a promising magnetic performance and larger glass forming ability.

RESUMEN

Current fabrication methods of nanoporous gold (NPG) mainly rely on dealloying Ag-Au binary crystalline precursors, typically Ag65Au35, with the "dealloying threshold" or "parting limit" above 55 at%. Here we report a simple chemical dealloying process, through selective dissolution of one element from a Au55Cu25Si20 metallic glass ribbon with low 'parting limit', and a novel peculiar three-dimensional 'cone shaped protrusion' nanoporous structure which has never been reported before. In this structure, a metastable gold silicide formed in the initial dealloying stage was decomposed into gold nanoparticles and amorphous SiOx in the later coarsening stage. Our finding provides insights into the underlying relationship between 'parting limit' and atomic level structure of metallic glass. Comprehensive discussions on the porosity evolution stages as well as the correlation between the porous 'cone shaped protrusion' development and potential energy landscape are made in this report. The fabricated 3D NPG also exhibited excellent electro-oxidation catalytic ability attributed to the high density of low-coordinated atomic sites provided by the gold particle inside of 'cone shaped protrusion'.

RESUMEN

A new method to fabricate an Au-rich interconnected ligament substrate by dealloying the Au-based metallic glass ribbon for surface-enhanced Raman scattering (SERS) applications was investigated in this study. Specifically, three substrates, Au film, Au-based metallic glass ribbon, and dealloyed Au-based metallic glass ribbon, were studied. The dealloyed surface showed ligament nanostructure with protruding micro-islands. Based on the field emission scanning electron microscopy, reflection and scattering measurements, the dealloyed Au-based metallic glass provided a large surface area, multiple reflections, and numerous fine interstices to produce hot spots for SERS enhancements. The SERS signal of analyte, p-aminothiophenol, in the micro-island region of dealloyed Au-based metallic glass was about 2 orders of magnitude larger than the flat Au film. Our work provides a new method to fabricate the inexpensive and high SERS enhancements substrates.

RESUMEN

A series of ternary rare-earth metal aluminum germanides with the general formula REAl1-xGe3 (RE = Nd, Sm, Gd, Tb, Dy, and Ho; 0.6 < x < 0.9) have been synthesized by direct fusion of the corresponding elements. Their structures have been characterized by single-crystal X-ray diffraction and selected area electron diffraction methods. The average structure for all members is a representative of the orthorhombic SmNiGe3-type structure (Pearson symbol oS20, space group Cmmm), where the Al atoms occupy the Ni site, and the deep off-stoichiometry is due to statistical vacancies at this position. Considering long-range ordering of the vacancies, a monoclinic and a different orthorhombic structure, which represent idealized ordered variants, are possible, and the structural evolution depending on the nature of the rare-earth metals and the amount of vacancies at the aluminum site are discussed. Commensurate and incommensurate structural modulations based on these parent structures are also observed by electron diffraction, attesting to the great structural complexity in these systems. Magnetic susceptibility measurements are presented and discussed, along with the results from electronic band-structure calculations.

RESUMEN

The development of novel materials with excellent performance depends not only on the constituents but also on their remarkable micro/nanostructures. In this work, manganese oxide (Mn3O4) hausmannite structures with a uniform three-dimensional (3D) flower-like hierarchical architecture have been successfully synthesized by a novel chemical route using surfactants as structure-directing agents. Microstructure analysis indicates that the obtained 3D flower-like Mn3O4 superstructure consists of a large number of two-dimensional (2D) Mn3O4 nanosheets, which is different from the reported 3D Mn3O4 hierarchical structures based on zero-dimensional nanoparticles or one-dimensional nanowires and nanorods. This 3D Mn3O4 hierarchical architecture provides us with another type of manganese oxide with different superstructural characteristics, which may have potential practical applications in the catalytic degradation of organic pollutants. The catalytic performance of this hierarchical Mn3O4 superstructure, which was prepared by three different types of structure-directing agents, including cetyltrimethylammonium bromide (CTAB), poly(vinylpyrrolidone) (PVP), and poly(ethylene oxide)-poly(propylene oxide) (P123), was evaluated for the catalytic degradation of organic pollutants, e.g. methylene blue. Interestingly, the hierarchical Mn3O4 superstructure prepared using CTAB as a template showed efficient catalytic degradation. The formation processes and possible growth mechanism of this novel 3D Mn3O4 hierarchical superstructure assembled by 2D Mn3O4 nanosheets are discussed in detail.

RESUMEN

Tin dioxide (SnO2) and graphene are unique strategic functional materials with widespread technological applications, particularly in the areas of solar batteries, optoelectronic devices, and solid-state gas sensors owing to advances in optical and electronic properties. Versatile strategies for microstructural evolution and related performance of SnO2 and graphene composites are of fundamental importance in the development of electrode materials. Here we report that a novel composite, SnO2 quantum dots (QDs) supported by graphene nanosheets (GNSs), has been prepared successfully by a simple hydrothermal method and electron-beam irradiation (EBI) strategies. Microstructure analysis indicates that the EBI technique can induce the exfoliation of GNSs and increase their interlayer spacing, resulting in the increase of GNS amorphization, disorder, and defects and the removal of partial oxygen-containing functional groups on the surface of GNSs. The investigation of SnO2 nanoparticles supported by GNSs (SnO2/GNSs) reveals that the GNSs are loaded with SnO2 QDs, which are dispersed uniformly on both sides of GNSs. Interestingly, the electrochemical performance of SnO2/GNSs indicates that SnO2 QDs supported by a 210 kGy irradiated GNS shows excellent cycle response, high specific capacity, and high reversible capacity. This novel SnO2/GNS composite has potential practical applications in SnO2 electrode materials during Li(+) insertion/extraction.

RESUMEN

Tin dioxide (SnO2) is a unique strategic functional material with widespread technological applications, particularly in fields such as solar batteries, optoelectronic devices, and solid-state gas sensors owing to advances in its optical and electronic properties. In this review, we introduce the recent progress of tin dioxide and its composites, including the synthesis strategies, microstructural evolution, related formation mechanism, and performance evaluation of SnO2 quantum dots (QDs), thin films, and composites prepared by electron-beam irradiation, pulsed laser ablation, and SnO2 planted graphene strategies, highlighting contributions from our laboratory. First, we present the electron-beam irradiation strategies for the growth behavior of SnO2 nanocrystals. This method is a potentially powerful technique to achieve the nucleation and growth of SnO2 QDs. In addition, the fractal assessment strategies and gas sensing behavior of SnO2 thin films with interesting micro/nanostructures induced by pulsed delivery will be discussed experimentally and theoretically. Finally, we emphasize the fabrication process and formation mechanism of SnO2 QD planted graphene nanosheets. This review may provide a new insight that the versatile strategies for microstructural evolution and related performance of SnO2-based functional materials are of fundamental importance in the development of new materials.

RESUMEN

In this work, a novel catalyst, Fe-species-loaded mesoporous manganese dioxide (Fe/M-MnO2) urchinlike superstructures, has been fabricated successfully in a two-step technique. First, mesoporous manganese dioxide (M-MnO2) urchinlike superstructures have been synthesized by a facile method on a soft interface between CH2Cl2 and H2O without templates. Then the M-MnO2-immobilized iron oxide catalyst was obtained through wetness impregnation and calcination. Microstructural analysis indicated that the M-MnO2 was composed of urchinlike hollow submicrospheres assembled by nanorod building blocks with rich mesoporosity. The Fe/M-MnO2 retained the hollow submicrospheres, which were covered by hybridized composites with broken and shortened MnO2 nanorods. Energy-dispersive X-ray microanalysis was used to determine the availability of Fe loading processes and the homogeneity of Fe in Fe/M-MnO2. Catalytic performances of the M-MnO2 and Fe/M-MnO2 were evaluated in catalytic wet hydrogen peroxide oxidation of methylene blue (MB), a typical organic pollutant in dyeing wastewater. The catalytic degradation displayed highly efficient discoloration of MB when using the Fe/M-MnO2 catalyst, e.g., ca. 94.8% of MB was decomposed when the reaction was conducted for 120 min. The remarkable stability of this Fe/M-MnO2 catalyst in the reaction medium was confirmed by an iron leaching test and reuse experiments. Mechanism analysis revealed that the hydroxyl free radical was responsible for the removal of MB and catalyzed by M-MnO2 and Fe/M-MnO2. MB was transformed into small organic compounds and then further degraded into CO2 and H2O. The new insights obtained in this study will be beneficial for the practical applications of heterogeneous catalysts in wastewater treatments.

RESUMEN

Tin oxide materials are a class of unique semiconductor materials with widespread technological applications because of their valuable semiconducting, gas sensing, electrical and optical properties in the fields of macro/mesoscopic materials and micro/nanodevices. In this review, we describe the efforts toward understanding the synthetic strategies and formation mechanisms of the micro/nanostructures of various tin dioxide thin films prepared by pulsed laser ablation, highlighting contributions from our laboratory. First, we present the preparation and formation processes of tetragonal-phase tin dioxide thin films with interesting fractal clusters. In addition, the quantum-dot formation and dynamic scaling behavior in tetragonal-phase tin dioxide thin films induced by pulsed delivery will be discussed experimentally and theoretically. Finally, we emphasize the fabrication, properties and formation mechanism of orthorhombic-phase tin dioxide thin films by using pulsed laser deposition. This research may provide a novel approach to modulate their competent performance and promote rational design of micro/nanodevices. Once mastered, tin dioxide thin films with a variety of fascinating micro/nanostructures will offer vast and unforeseen opportunities in the semiconductor industry as well as in other fields of science and technology.

RESUMEN

To obtain a highly efficient and stable heterogeneous catalyst in catalytic wet hydrogen peroxide oxidation, we have successfully synthesized hierarchical mesoporous manganese dioxide (MnO2) superstructures by a facile and environmental friendly method on a soft-interface between CH2Cl2 and H2O without templates. The main crystal phase of as-prepared MnO2 was proved to be ε-MnO2 by X-ray diffraction techniques. The structure characterizations indicated that the hierarchical MnO2 superstructures were composed of urchin-like MnO2 hollow submicrospheres assembled by one-dimension nanorods building blocks with rich mesoporosity. The nitrogen sorption analysis confirmed that the as-synthesized MnO2 has an average pore diameter of 5.87 nm, mesoporous volume of 0.451 cm(3) g(-1), and specific surface area of 219.3 m(2) g(-1). Further investigations revealed that a possible formation mechanism of this unique hierarchical superstructure depended upon the synthesis conditions. The catalytic performances of the hierarchical mesoporous MnO2 superstructures were evaluated in catalytic degradation of methylene blue in the presence of H2O2 at neutral pH, which demonstrated highly efficient catalytic degradation of the organic pollutant methylene blue using hierarchical mesoporous MnO2 superstructures as catalyst at room temperature.

RESUMEN

Germanium materials are a class of unique semiconductor materials with widespread technological applications because of their valuable semiconducting, electrical, optical, and thermoelectric power properties in the fields of macro/mesoscopic materials and micro/nanodevices. In this review, we describe the efforts toward understanding the microstructures and various properties of the fractal germanium micro/nanoclusters induced by gold prepared by high vacuum thermal evaporation techniques, highlighting contributions from our laboratory. First, we present the integer and non-integer dimensional germanium micro/nanoclusters such as nanoparticles, nanorings, and nanofractals induced by gold and annealing. In particular, the nonlinear electrical behavior of a gold/germanium bilayer film with the interesting nanofractal is discussed in detail. In addition, the third-order optical nonlinearities of the fractal germanium nanocrystals embedded in gold matrix will be summarized by using the sensitive and reliable Z-scan techniques aimed to determine the nonlinear absorption coefficient and nonlinear refractive index. Finally, we emphasize the thermoelectric power properties of the gold/germanium bilayer films. The thermoelectric power measurement is considered to be a more effective method than the conductivity for investigating superlocalization in a percolating system. This research may provide a novel insight to modulate their competent performance and promote rational design of micro/nanodevices. Once mastered, germanium thin films with a variety of fascinating micro/nanoclusters will offer vast and unforeseen opportunities in the semiconductor industry as well as in other fields of science and technology.

Asunto(s)

RESUMEN

Transition metal oxides belong to a class of versatile materials that are vitally important for developing new materials with functionality and smartness. Research on manganese oxides has been a key topic among studies on transition metal oxides. This is due to their potential applications in diverse areas, including rechargeable lithium ion batteries, catalysis, molecular adsorption, gas sensors, energy storage, and magnetics. In this review, we will elucidate in detail various characterization strategies, including temperature-dependent growth, micro/nanostructures, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and electron spin resonance, for Mn2O3 nanocrystals, highlighting contributions from our laboratory. This review article mainly focuses on the wide-ranging research effort on the development of preparation methodologies and the assessment of various characterization strategies in Mn2O3 nanomaterials. The main purpose is to provide the readers a comprehensive understanding of the research progress of manganese oxides. This is an interdisciplinary work that integrates the areas of physics, chemistry, materials science, and nanotechnology.

Asunto(s)

RESUMEN

In this article, an amorphous Fe rich amorphous structure designed based on a competitive atomic cluster model was synthesized and characterized successfully. The constituent zero-valent iron (ZVI) has excellent activity and efficiency for decolorization of Orange G (OG) solution at room temperature. The decolorization is characterized by UV-vis spectrum and pseudo-first-order kinetics. The X-ray Micro fluorescence spectrometer, Inductively Coupled Plasma Optical Emission Spectrometry, and Scanning Electron Microscope were employed to trace the ZVI. The consumption of ZVI destabilizes the local atomic arrangement and yields the phase separation of Fe at the surface and responds to the high activity and the catalysis for decolorization. This observation is in accordance with the change of k1 0.011 min(-1) to k2 0.047 min(-1), which is supported by the cyclic decolorization test. This work provides a new strategy to design multifunctional metal materials and indicates their brilliant future in practical applications.

RESUMEN

Nanocomposites have significant potential in the development of advanced materials for numerous applications. Tin dioxide (SnO2) is a functional material with wide-ranging prospects because of its high electronic mobility and wide band gap. Graphene as the basic plane of graphite is a single atomic layer two-dimensional sp(2) hybridized carbon material. Both have excellent physical and chemical properties. Here, SnO2 quantum dots/graphene composites have been successfully fabricated by a facile ultrasonic method. The experimental investigations indicated that the graphene was exfoliated and decorated with SnO2 quantum dots, which was dispersed uniformly on both sides of the graphene. The size distribution of SnO2 quantum dots was estimated to be ranging from 4 to 6 nm and their average size was calculated to be about 4.8 ± 0.2 nm. This facile ultrasonic route demonstrated that the loading of SnO2 quantum dots was an effective way to prevent graphene nanosheets from being restacked during the reduction. During the calcination process, the graphene nanosheets distributed between SnO2 nanoparticles have also prevented the agglomeration of SnO2 nanoparticles, which were beneficial to the formation of SnO2 quantum dots.

RESUMEN

Results on Al-induced crystallization of amorphous Ge (a-Ge) deposited by vacuum thermal evaporation techniques under thermal annealing in N(2) atmosphere are presented in detail. The a-Ge crystallization and fractal Ge pattern formation on the free surface of annealed Al/Ge bilayer films deposited on single-crystal Si (100) substrates were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive X-ray spectrometry (EDS), and Raman spectra. It is found that the temperature field effects play an extremely crucial role in a-Ge crystallization and fractal Ge formation process. The open branched structure of fractal Ge clusters in Al/Ge bilayer films was effectively prepared by Al-induced crystallization when they were annealed at 400 °C for 60 min. These films with fractal Ge clusters exhibit charming noninteger dimensional nanostructures, which differ from those of conventional integer dimensional materials such as one-dimensional nanowires/nanorods, nanotubes, nanobelts/nanoribbons, two-dimensional heterojunctions, thin films, and zero-dimensional nanoparticles. The SEM image shows that a big Al grain was found located near the center of a fractal Ge cluster after the films were annealed at 400 and 500 °C for 60 min. This suggests that the grain boundaries of polycrystalline Al films are the initial nucleation sites of a-Ge. It also validates the preferred nucleation theory of a-Ge at triple-point grain boundaries of polycrystalline Al at the interface. This discovery may be explained by the metal-induced nucleation (MIN) mechanism.

RESUMEN

Metal/semiconductor thin films are a class of unique materials that are widespread technological applications, particularly in the field of microelectronic devices. Assessment strategies of fractal and tures are of fundamental importance in the development of nano/microdevices. This review presents the preparation methodologies and nano/microstructural evaluation of metal/semiconductor thin films including Au/Ge bilayer films and Pd-Ge alloy thin films, which show in the form of fractals and nanocrystals. Firstly, the extended version of Au/Ge thin films for the fractal crystallization of amorphous Ge and the formation of nanocrystals developed with improved micro- and nanostructured features are described in Section 2. Secondly, the nano/microstructural characteristics of Pd/Ge alloy thin films during annealing have been investigated in detail and described in Section 3. Finally, we will draw the conclusions from the present work as shown in Section 4. It is expected that the preparation methodologies developed and the knowledge of nano/microstructural evolution gained in metal/semiconductor thin films, including Au/Ge bilayer films and Pd-Ge alloy thin films, will provide an important fundamental basis underpinning further interdisciplinary research in these fields such as physics, chemistry, materials science, and nanoscience and nanotechnology, leading to promising exciting opportunities for future technological applications involving these thin films.

Asunto(s)

Asunto(s)

RESUMEN

Mn(3)O(4) morphologies with tetragonal single-crystal nanostructures including nanoparticles, nanorods and nanofractals were successfully prepared by a widely applicable chemical reaction route. The morphologies were synthesized using the reactants MnCl(2)·4H(2)O, H(2)O(2), and NaOH in a suitable surfactant and alkaline solution. The dripping speed of the NaOH solution plays an important role in the microstructure evolution of Mn(3)O(4) morphologies. The difference in the dripping speed of NaOH solutions leads to different Mn(3)O(4) nanomorphologies, which are called nanoparticles, nanorods and nanofractals. The average grain size of the Mn(3)O(4) nanoparticles ranged from a few to several tens of nanometers. The Mn(3)O(4) nanorods were smooth, straight, and the geometrical shape was structurally perfect. Their lengths ranged from several hundred nanometers to a few micrometers, and their diameters ranged from 10 nm to 30 nm. The fractal branches of the Mn(3)O(4) nanofractals were a few micrometers in length and several hundred nanometers in width. The catalytic properties of these Mn(3)O(4) nanomorphologies for the degradation of phenol were evaluated in detail. The results indicated that the Mn(3)O(4) nanofractals possess remarkable catalytic activity for the degradation of phenol in water treatment.

RESUMEN

Metal/semiconductor thin films are a class of unique materials that have widespread technological applications, particularly in the field of microelectronic devices. New strategies of fractal assessment for Pd/Ge bilayer films formed at various annealing temperatures are of fundamental importance in the development of micro/nanodevices. Herein, Pd/Ge bilayer films with interesting fractal nanoclusters were successfully prepared by evaporation techniques. Temperature-dependent properties of resistance and fractal dimensions in Pd/Ge bilayer films with self-similar Ge fractal nanoclusters were investigated in detail. Experimental results indicated that the fractal crystallization behavior and film resistance in Pd/Ge bilayer films are influenced significantly by annealing temperatures and fractal dimensions. The measurements of film resistance confirmed that there is an evident relationship between the film resistance and the fractal dimension. These phenomena were reasonably explained by the random tunneling junction network mechanism.