Control of tribological properties of diamond-like carbon films with femtosecond-laser-induced nanostructuring

This paper reports tribological properties of diamond-like carbon (DLC) films nanostructured by femtosecond (fs) laser ablation. The nanostructure was formed in an area of more than 15 mm × 15 mm on the DLC surface, using a precise target-scan system developed for the fs-laser processing. The frictional properties of the DLC film are greatly improved by coating a MoS₂ layer on the nanostructured surface, while the friction coefficient can be increased by surface texturing of the nanostructured zone in a net-like patterning. The results demonstrate that the tribological properties of a DLC surface can be controlled using fs-laser-induced nanostructuring.     

Development and properties of nanostructured thermal spray coatings

Nanostructured thermal spray coatings have been intensively studied because of their potential in a wide variety of industrial applications. In the present paper, current development status of nanostructured thermal spray coatings is presented, mainly based on the results of the authors. In the nanostructured WC–Co wear-resistant coatings, the influence of feedstock characteristics on the coating properties was discussed to suggest the desirable morphology of feedstock for thermal spraying. For the nanostructured Cr₂O₃ based solid-lubricant coatings, the advanced feedstock has been developed in order to solve the inhomogeneity problem of the conventional coatings. Various properties of the nanostructured coatings were evaluated and compared with those of the conventional counterparts. These results clearly demonstrate that the significant improvement in coating performance can be achieved by utilizing proper nanostructured coatings.     

Elastic properties of nanostructured materials with layered grain boundary structure

Atomistic calculations of the elastic constants for a bulk nanostructured material that consists of a layered structure where alternating layers meet along high angle grain boundaries and where atoms interact via a Lennard-Jones potential are presented. The calculations of the elastic constants were performed in the frame of homogeneous deformations for a wide range of layer widths ranging from 2.24 up to 74.62 nm. The results showed that the relaxation of the atomic structure affects the elastic constants for the cases where more than 5% of atoms are located in the GB region. Also it was found that the way that external stresses are applied on the system affects the values of the obtained elastic properties, with the elastic constants related to the characteristic directions of the grain boundary being the most affected ones. The findings of this work are of interest for the fabrication methods of nanostructured materials, the measurement methods of their elastic properties as well as multiscale modeling schemes of nanostructured materials.     

Monte Carlo simulation of magnetic nanostructured thin films

Using Monte Carlo simulation, we have compared the magnetic properties between nanostructured thin films and two-dimensional crystalline solids. The dependence of nanostructured properties on the interaction between particles that constitute the nanostructured thin films is also studied. The result shows that the parameters in the interaction potential have an important effect on the properties of nanostructured thin films at the transition temperatures.     

纳米结构非晶合金材料研究进展

迄今为止,人类社会新技术的发展主要是基于各种晶体材料(如金属、半导体等)的应用.晶体材料的性能可以通过改变它们的微观缺陷结构和/或微观化学结构来调控,但这对于当前的非晶材料而言却是难以实现的.新型的纳米结构非晶材料可以通过引入大量的非晶/非晶界面来改变非晶材料的微观缺陷结构和/或微观化学结构,从而实现对其性能的调控.本文主要讨论了目前纳米结构非晶合金材料的研究进展,包括其制备方法、结构特征和新性能.通过利用这些新特性,有可能会开启一个基于非晶材料的新技术时代.     

Optical spectra of nanoceramics of yttrium-iron garnet Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> obtained by the method of intense plastic deformation

The features of the optical properties of nanostructured samples of iron-yttrium garnet Y₃Fe₅O₁₂ (YIG) in the range of 0.5 to 4.7 eV, which includes both the fundamental-absorption region and low-energy electron excitations, have been investigated by spectroscopic ellipsometry. The results are discussed in comparison with the measurement data of a YIG single crystal. The dispersion of the optical functions in nanostructured samples is significantly different from that for the single crystal: the spectral density is redistributed from the energy region above the fundamental absorption edge to the region below the edge. It has been shown that the energy positions of the main electronic transitions in nanostructured samples are on the whole the same as in the single crystal; at the same time, the intensity of low-energy transitions increases. The possible causes of this increase and the resolution of the fine absorption structure in the bandgap of nanostructured Y₃Fe₅O₁₂ are discussed.     

Grain Boundaries in Magnetic Nanostructured Systems

The nanostructured systems are characterized by a density of grain boundaries which is higher than that of microcrystalline systems, giving rise to unusual properties. Both the structural nature and the thickness of grain boundaries which are dependent on the synthesis conditions, strongly influence the total magnetic properties. We report several examples based on metallic and insulating nanostructured systems to illustrate how the presence of grain boundaries can be experimentally evidenced, as well as their structure and magnetic behavior, and finally the significant role of grain boundaries on the magnetic properties.     

铝纳米晶的低温导电特性研究

采用真空热压技术将电磁感应加热-自悬浮定向流法制备的铝纳米粉末压制成块体样品.通过X射线衍射、透射电子显微镜、扫描电子显微镜及X射线能谱分析了铝纳米晶的微观结构,并用四探针法测量了不同温度下(8—300 K)样品的电阻率,研究了铝纳米晶的电阻率(ρ)随温度的变化规律.结果表明:由于晶界(非晶氧化铝)对电子的散射以及晶界声子对电子的散射效应,低温(40 K)下,铝纳米晶的本征电阻率随温度变化关系明显不同于粗晶铝,不仅呈现出T~4变化,还表现出显著的T3变化规律.因晶界等缺陷和非晶氧化铝杂质对电子的散射,铝纳米晶残余电阻率比粗晶铝电阻率大5—6个数量级.     

Control of the shell structure of ZnO–ZnS core-shell structure

Nanostructured ZnO–ZnS core-shell powders were synthesized through a solution method using a thioacetamide (TAA) solution in deionized water. ZnO powder and TAA solution were employed to supply zinc and sulfur ions to form the ZnO–ZnS core-shell structures. The structure of the ZnS shell was strongly affected by the mole concentration of the TAA, and the structural properties were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The optical properties of the nanostructured powders were also compared with those of pure ZnO powder. The ultraviolet (UV) emission was greatly enhanced compared to when pure ZnO powder was used in the nanostructured powder synthesized using the 0.5 M TAA solution, while the UV emission of that with the 0.05 M TAA solution was reduced. The green emission of the nanostructured powders was reduced compared to when the pure ZnO powder was used. The mechanism of the structural changes in the core-shell structures is proposed here and its effect on the luminescent properties is discussed.     

Morphology and Fracture Toughness of Nanostructured Epoxy Resin Containing Amino-Terminated Poly(propylene oxide)

Amino-terminated poly(propylene oxide) (ATPPO) was incorporated into epoxy resin to toughen thermosets. It was found that nanostructured thermosets were obtained; the nanostructures were characterized by means of atomic force microscopy and small-angle X-ray scattering. The formation of the nanostructures is interpreted on the basis of the occurrence of the reaction of terminal groups of ATPPO with diglycidyl ether of bisphenol A; this reaction is suggested to result in the formation of star-shaped block copolymers composed of poly(propylene oxide) (PPO) and epoxy blocks. Due to the presence of the star-shaped block copolymer produced in situ, the phase separation of PPO induced by the reaction was confined to the nanometer scale. The glass-transition behavior and fracture toughness of the nanostructured thermosets were investigated by means of differential scanning calorimetry, dynamic mechanical thermal analysis, and the measurement of critical stress intensity factors. The epoxy thermosets were significantly toughened by the inclusion of a small amount of ATPPO. The thermal and mechanical properties of the nanostructured thermosets are compared to the binary blends of epoxy resin containing hydroxyl-terminated poly(propylene oxide) (HTPPO) with identical molecular weight. With the identical composition, the nanostructured thermosets displayed higher fracture toughness than that of their binary blends. The difference in morphology and properties is interpreted in terms of the formation of the nanostructures.     

Luminescence properties of ytterbium and erbium doped silica-zirconia nanostructured optical fiber under near infrared excitation

We present here the luminescence properties of erbium and ytterbium doped silica-zirconia nanostructured optical fibers prepared by the chemical sol-gel method. After describing the preparation process, their waveguiding properties as well as luminescence properties under continuous pumping in the near infrared domain (NIR) are reported; the effects of the zirconia nanocrystals that are dispersed in the core of the fibers on their optical properties are finally discussed.     

Fractal description of significant nano-effects in polymer composites with nanosized fillers. Aggregation,phase interaction,and reinforcement

The paper analyzes experimental data obtained on physical and mechanical properties of nanostructured particle-reinforced composites with elastomer matrices and nano- and microsized carbon-containing particles by scanning probe microscopy and nanoindentation with specialized 3D computer processing. The nano-effects observed in the elastomer matrices are described using the fractal approach. A fractal model of nanoparticle aggregation in a polymer matrix is proposed. Phase interactions in the nanostructured polymer materials are described and fractal relations that predict the reinforcing effect of this type of media are presented. It is shown that interphase regions in the nanostructured composites are the same reinforcing elements as a nanofiller for the medium. It is found that reinforcement of elastomer composites by nanosized particles is a true nano-effect.     

Enhancing low-field magnetoresistance of La0.67Ca0.33MnO3 films deposited on anodized aluminium-oxide membranes

In this paper we report a new method to fabricate nanostructured films, La0.67Ca0.33MnO3 （LCMO） nanostructured films have been fabricated by using pulsed electron beam deposition （PED） on anodized aluminium oxide （AAO） membranes, The magnetic and electronic transport properties are investigated by using the Quantum Design physics properties measurement system （PPMS） and magnetic properties measurement system （MPMS）. The resistance peak temperature （Tp） is about 85 K and the Curie temperature （To） is about 250 K for the LCMO film on an AAO membrane with a pore diameter of 20nm. Large magnetoresistance ratio （MR） is observed near Tp. The MR is as high as 85% under 1 T magnetic field. The great enhancement of MR at low magnetic fields could be attributed to the lattice distortion and the grain boundary that are induced by the nanopores on the AAO membrane.     

The study on porosity and thermophysical properties of nanostructured La2Zr2O7 coatings

Lanthanum-zirconium nano-powders were synthesized by molten salts method. Nanostructured lanthanum-zirconium coatings were deposited by air plasma spraying. Scanning electron microscopy and X-ray diffraction were carried out to analyze the as-sprayed coatings and powders. The pore size distribution and buck density of coatings were identified by mercury intrusion porosimetry. The thermophysical properties of the nanostructured coatings were also examined through laser flash technique and differential scanning calorimetry. The results demonstrate that the as-sprayed nanostructured coatings consist of the pyrochlore-type phase. The as-sprayed nanostructured lanthanum-zirconium coatings have a very low porosity. The thermal conductivity of the as-sprayed nanostructured lanthanum-zirconium coating is lower than that of the conventional coating between 200 °C and 950 °C, but when the temperature between 950 °C and 1300 °C, the result is reverse.     

Facile synthesis of group-I elements (K,Li and Na)-doped nanostructured CdO films

In this study, we report an application of facile and low-cost successive ionic layer adsorption and reaction method to investigate nanostructured CdO films. We have tried to enhance some physical properties of nanostructured CdO films by group-I (K, Li and Na) elements doping. The crystal structures, morphology, absorption, transmittance, reflectance behaviour and optical band gap values of CdO films were characterized by using X-ray diffraction (XRD), scanning electron microscopy and ultraviolet–visible spectroscopy techniques. XRD analysis reveals formation of CdO cubic crystalline structure. From these characterizations, it was seen that there are important distinctions in the structural, morphological and optical properties of undoped and K-, Li- and Na-doped nanostructured CdO films.     

Effect of the primary particle morphology on the micromechanical properties of nanostructured alumina agglomerates

Depending on the application of nanoparticles, certain characteristics of the product quality such as size, morphology, abrasion resistance, specific surface, dispersibility and tendency to agglomeration are important. These characteristics are a function of the physicochemical properties, i.e. the micromechanical properties of the nanostructured material. The micromechanical properties of these nanostructured agglomerates such as the maximum indentation force, the plastic and elastic deformation energy and the strength give information on the product properties, e.g. the efficiency of a dispersion process of the agglomerates, and can be measured by nanoindentation. In this study a Berkovich indenter tip was used for the characterisation of model aggregates out of sol–gel produced silica and precipitated alumina agglomerates with different primary particle morphologies (dimension of 15–40 nm). In general, the effect of the primary particle morphology and the presence or absence of solid bonds can be characterised by the measurement of the micromechanical properties via nanoindentation. The micromechanical behaviour of aggregates containing solid bonds is strongly affected by the elastic–plastic deformation behaviour of the solid bonds and the breakage of solid bonds. Moreover, varying the primary particle morphology for similar particle material and approximately isotropic agglomerate behaviour the particle–particle interactions within the agglomerates can be described by the elementar breaking stress according to the formula of Rumpf.     

Problems of the mesomechanics of strength and plasticity of nanostructured materials

The results of the investigations performed in collaboration with our co-workers are reviewed and used to formulate a conceptual framework of the physical mesomechanics of nanostructured materials. Low plasticity of materials of this kind is associated with suppression of the microscale deformation due to the motion of dislocations and with development of meso- and macroscale localized-deformation bands. For an optimum combination of strains at the micro- and mesoscale levels, formation of a nanocrystalline structure provides high strength and plastic properties of the materials. Strain localization at the macroscale level impairs the strength and plasticity of nanostructured materials.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 4–17, August, 2004.     

Nanoscale high energetic materials: a polymeric nitrogen chain N(8) confined inside a carbon nanotube

We present a theoretical study of a new hybrid material, nanostructured polymeric nitrogen, where a polymeric nitrogen chain is encapsulated in a carbon nanotube. The electronic and structural properties of the new system are studied by means of ab initio electronic structure and molecular dynamics calculations. Finite temperature simulations demonstrate the stability of this nitrogen phase at ambient pressure and room temperature using carbon nanotube confinement. This nanostructured confinement may open a new path towards stabilizing polynitrogen or polymeric nitrogen at ambient conditions.     

Detection of internal cracks and ultrasound characterization of nanostructured Bi₂Te₃-based thermoelectrics via acoustic microscopy

The search for thermoelectric (TE) materials for highly efficient devices aims at improving the TE efficiency and broadening their areas of applications. We created nanostructured thermoelectric Bi-Sb-Te-family materials by high energy (ball milling) pre-treatment of the parent materials followed by high-pressure/high-temperature treatment. Bi_0.5Sb_1.5Te₃ compositions with the superfluous maintenance of tellurium was used for the synthesis of the samples with p-type electrical conductivity. Acoustic microscopy was used to study elastic properties and bulk irregularities and to detection of internal cracks both in the parent materials and in the created nanostructured samples. The data has been used for optimization of parameters of synthesis of nanostructured thermoelectrics.     

Photocatalytic activity of nanostructured TiO2 films produced by supersonic cluster beam deposition

The photocatalytic activity of thin, nanostructured films of titanium dioxide, synthesized by supersonic cluster beam deposition (SCBD) from the gas phase, has been investigated employing the photodegradation of salicylic acid as test reaction. Because of the low deposition energy, the so-deposited highly porous TiO₂ films are composed of nanoparticles maintaining their original properties in the film, which can be fully controlled by tuning the deposition and post-deposition treatment conditions. A systematic investigation on the evolution of light absorption properties and photoactivity of the films in relation to their morphology, determined by AFM analysis, and phase composition, determined by Raman spectroscopy, has been performed. The absorption and photocatalytic activity of the nanostructured films in the visible region could be enhanced either through post-deposition annealing treatment in ammonia containing atmosphere or employing mild oxidation conditions, followed by annealing in N₂ at 600 °C.