GaN and InN nanocolumns as electrochemical sensing elements: Potentiometric response to KCl, pH and urea

GaN and InN nanocolumns have been explored as electrochemical sensing elements. It is shown that these nanostructured sensors respond to anions as their corresponding compact crystals, but with a much lower sensitivity (chloride anion detection). Moreover, even though both kinds of nanocolumns are found to be more vulnerable to HCl etching compared to their flat counterparts, they exhibit quite high pH sensitivity. This fact allows for their use as pH sensors only under mild conditions, such as in biosensing systems, as it is proved with the example of urea biosensors.     

磨削加工对纳米结构陶瓷涂层耐磨性能的影响

对磨削加工后的纳米结构陶瓷涂层进行磨损性能试验.磨损试验首先对纳米结构陶瓷涂层Al2O3/13TiO2的圆柱形工件进行外圆磨削加工,然后将各种不同条件下磨削加工后的圆柱工件装夹到立式铣床的主轴上,进行定速、定载荷的磨损性能试验.磨损性能试验时,圆柱工件在旋转的同时与往复运动的长方形氮化硅陶瓷棒进行滑擦,在其圆柱表面形成磨损沟槽.使用扫描电子显微镜和表面轮廓仪对纳米陶瓷涂层的磨损沟槽进行观察与评定,并与传统陶瓷涂层的磨损沟槽进行对比与分析.为进一步揭示纳米陶瓷涂层的磨损机理,使用有限元法对接触区的应力场进行模拟,并分析纳米陶瓷涂层裂纹的形成与扩展.讨论了磨削工艺参数以及涂层晶粒大小对纳米结构陶瓷涂层耐磨损性能的影响.     

A Generalizable Top‐Down Nanostructuring Method of Bulk Oxides: Sequential Oxygen–Nitrogen Exchange Reaction

A thermal reaction route that induces grain fracture instead of grain growth is devised and developed as a top‐down approach to prepare nanostructured oxides from bulk solids. This novel synthesis approach, referred to as the sequential oxygen–nitrogen exchange (SONE) reaction, exploits the reversible anion exchange between oxygen and nitrogen in oxides that is driven by a simple two‐step thermal treatment in ammonia and air. Internal stress developed by significant structural rearrangement via the formation of (oxy)nitride and the creation of oxygen vacancies and their subsequent combination into nanopores transforms bulk solid oxides into nanostructured oxides. The SONE reaction can be applicable to most transition metal oxides, and when utilized in a lithium‐ion battery, the produced nanostructured materials are superior to their bulk counterparts and even comparable to those produced by conventional bottom‐up approaches. Given its simplicity and scalability, this synthesis method could open a new avenue to the development of high‐performance nanostructured electrode materials that can meet the industrial demand of cost‐effectiveness for mass production.     

Synthesis of nanostructured materials using supercritical CO<Subscript>2</Subscript>: Part I. Physical transformations

Nanostructured materials have been attracting increased attention for a wide variety of applications due to their superior properties compared to their bulk counterparts. Current methods to synthesize nanostructured materials have various drawbacks such as difficulties in control of the nanostructure and morphology, excessive use of solvents, abundant energy consumption, and costly purification steps. Supercritical fluids especially supercritical carbon dioxide (scCO₂) is an attractive medium for the synthesis of nanostructured materials due to its favorable properties such as being abundant, inexpensive, non-flammable, non-toxic, and environmentally benign. Furthermore, the thermophysical properties of scCO₂ can be adjusted by changing the processing temperature and pressure. The synthesis of nanostructured materials in scCO₂ can be classified as physical and chemical transformations. In this article, Part I of our review series, synthesis of nanostructured materials using physical transformations is described where scCO₂ functions as a solvent, an anti-solvent or as a solute. The nanostructured materials, which can be synthesized by these techniques include nanoparticles, nanowires, nanofibers, foams, aerogels, and polymer nanocomposites. scCO₂ based processes can also be utilized in the intensification of the conventional processes by elimination of some of the costly purification or separation steps. The fundamental aspects of the processes, which would be beneficial for further development of the technologies, are also reviewed.     

Influence of feedstock and spraying parameters on the depositing efficiency and microhardness of plasma-sprayed zirconia coatings

In this work, nanostructured and conventional zirconia coatings were deposited by atmospheric air plasma spraying (APS) under different spraying conditions using spray-dried nanostructured powders and conventional powders as feedstocks, respectively. The microstructures of the feedstocks were characterized by TEM and SEM. The depositing efficiencies for both nanostructured and conventional zirconia coatings deposited under different spraying parameters were comparatively measured. The obtained results revealed that the spray-dried nanostructured powders possessed higher deposition efficiency than that of conventional powders. It is significant from economic view of reducing cost. In addition, the influence of spraying parameters on microstructure and microhardness of zirconia coatings were discussed also. It was found that the microhardness of nanostructured zirconia coatings was larger than that of its counterparts.     

块体纳米晶工业纯铁在盐酸溶液中的电化学腐蚀行为

通过静态失重试验,动电位极化曲线,电化学阻抗谱(EIS)实验,研究了块体纳米工业纯铁(BNIPI)和粗晶工业纯铁棒(CGPIR)在室温1mol/l盐酸溶液中的腐蚀行为.结果表明,BNIPI与CGPIR相比,开路腐蚀电位Ecorr正向移动114mV,平均腐蚀速度和腐蚀电流Icorr变小,极化电阻Rp增大为1.58倍.BNIPI抗盐酸的腐蚀能力与CGPIR相比,不但没有下降,相反有所增强.使用扫描电子显微镜(SEM)对静态腐蚀失重试样的形貌进行了观察,显示BNIPI上几乎没有点蚀坑出现.     

Gas phase electrodeposition: a programmable multimaterial deposition method for combinatorial nanostructured device discovery

This article reports and applies a recently discovered programmable multimaterial deposition process to the formation and combinatorial improvement of 3D nanostructured devices. The gas-phase deposition process produces charged <5 nm particles of silver, tungsten, and platinum and uses externally biased electrodes to control the material flux and to turn deposition ON/OFF in selected domains. Domains host nanostructured dielectrics to define arrays of electrodynamic 10 × nanolenses to further control the flux to form <100 nm resolution deposits. The unique feature of the process is that material type, amount, and sequence can be altered from one domain to the next leading to different types of nanostructures including multimaterial bridges, interconnects, or nanowire arrays with 20 nm positional accuracy. These features enable combinatorial nanostructured materials and device discovery. As a first demonstration, we produce and identify in a combinatorial way 3D nanostructured electrode designs that improve light scattering, absorption, and minority carrier extraction of bulk heterojunction photovoltaic cells. Photovoltaic cells from domains with long and dense nanowire arrays improve the relative power conversion efficiency by 47% when compared to flat domains on the same substrate.     

Synthesis and processing of nanostructured WC-Co materials

In this study a novel approach, termed the integrated mechanical and thermal activation (IMTA) process, was used to synthesize nanostructured WC-Co powder. As a result of the integration of mechanical and thermal activation, nanostructured WC-Co powder was synthesized below 1000°C, starting from WO₃, CoO and graphite powder mixtures. Furthermore, consolidation of the nanostructured WC-Co powder via high velocity oxy-fuel (HVOF) thermal spraying and solid state sintering was investigated. The results demonstrated the feasibility of converting the nanostructured WC-Co powder to coatings and bulk components, the properties of which are either comparable to or better than that of the conventional coarse-grained counterparts.     

Electrodeposition of nanostructured coatings and their characterization—A review

Nanostructured materials have gained importance in recent years due to their significantly enhanced properties. In particular, electrochemistry has a special role in producing a variety of nanostructured materials. In the current review, we discuss the superiority of electrochemical deposition techniques in synthesizing various nanomaterials that exhibit improved characteristics compared with materials produced by conventional techniques, as well as their classification, synthesis routes, properties and applications. The superior properties of a nanostructured nickel coating produced by electrochemical deposition are outlined. The properties of various nanostructured coating materials produced by electrochemical techniques are also described. Finally, the importance of nanostructured coatings in industrial applications as well as their potential in future technologies is emphasized.     

Electrodeposition of nanostructured coatings and their characterization—A review

Abstract

Nanostructured materials have gained importance in recent years due to their significantly enhanced properties. In particular, electrochemistry has a special role in producing a variety of nanostructured materials. In the current review, we discuss the superiority of electrochemical deposition techniques in synthesizing various nanomaterials that exhibit improved characteristics compared with materials produced by conventional techniques, as well as their classification, synthesis routes, properties and applications. The superior properties of a nanostructured nickel coating produced by electrochemical deposition are outlined. The properties of various nanostructured coating materials produced by electrochemical techniques are also described. Finally, the importance of nanostructured coatings in industrial applications as well as their potential in future technologies is emphasized.     

Abnormal strain hardening in nanostructured titanium at high strain rates and large strains

Commercial purity nanostructured titanium prepared by equal channel angular pressing plus cold rolling (grain size ∼260 nm) exhibits a nonnegligible strain hardening behavior at large compressive strains (>15%) and quasistatic loading conditions. The degree of the strain hardening increases with increasing strain rates and becomes more pronounced at dynamic loading rates. This behavior is in contrast with what we have seen so far in other nanostructured materials, where flat stress-strain curves are often seen. It was concluded from transmission electron microscopy investigations that in addition to dislocation slips, deformation twinning may have played a significant role in plastic deformation of nanostructured Ti. The structural failure behavior is in-situ recorded by a CCD camera and reasoned according to the microscopic observations.     

Synthesis of hollow CuS nanostructured microspheres with novel surface morphologies

Hollow CuS nanostructured microspheres with novel surface morphologies were synthesized by a facile precipitate-converting reaction. The products were characterized by SEM, XRD, BET measurements and size analysis. The surfaces of the hollow CuS microspheres showed acicular, rod-like, concavo-convex and flat morphologies respectively when using different amounts of thioacetamide as precipitants. The diameters of the hollow CuS microspheres could be tuned to a certain extent by using Cu₂(OH)₂CO₃ microspheres with different sizes as precursors. A solid–solution–solid mechanism for the formation of the hollow CuS nanostructured microspheres was discussed. The method reported here also could be applied for the synthesis of other nanostructured microspheres.     

Effect of molecular adsorption on the electrical conductance of single au nanowires fabricated by electron-beam lithography and focused ion beam etching

Metal nanowires are one of the potential candidates for nanostructured sensing elements used in future portable devices for chemical detection; however, the optimal methods for fabrication have yet to be fully explored. Two routes to nanowire fabrication, electron-beam lithography (EBL) and focused ion beam (FIB) etching, are studied, and their electrical and chemical sensing properties are compared. Although nanowires fabricated by both techniques exhibit ohmic conductance, I-V characterization indicates that nanowires fabricated by FIB etching exhibit abnormally high resistivity. In addition, the resistivity of nanowires fabricated by FIB etching shows very low sensitivity toward molecular adsorption, while those fabricated by EBL exhibit sensitive resistance change upon exposure to solution-phase adsorbates. The mean grain sizes of nanowires prepared by FIB etching are much smaller than those fabricated by EBL, so their resistance is dominated by grain-boundary scattering. As a result, these nanowires are much less sensitive to molecular adsorption, which mediates nanowire conduction through surface scattering. The much reduced mean grain sizes of these nanowires correlate with Ga ion damage caused during the ion milling process. Thus, even though the nanowires prepared by FIB etching can be smaller than their EBL counterparts, their reduced sensitivity to adsorption suggests that nanowires produced by EBL are preferred for chemical and biochemical sensing applications.     

Deposition Behavior of Nanostructured WC–23Co Particles in Cold Spraying Process

The nanostructured WC–23Co particles were deposited on three kinds of substrates in different accelerating gas temperature by using cold spraying process. The morphologies of nanostructured WC–23Co splats attached on the polished surface of different substrates were characterized via scanning electron microscopy. It is revealed that the splats are partially embedded in Q235 and stainless steel with a comparative integrated contour similar to that of the original particles. There exist some revers around the splats and some corrugations or ripples on the Q235 and stainless steel substrates. In contrast, the splats on the surface of WC–12Co substrate present clearly a flat shape with central hump surrounded by a ringy band. By comparison of the morphologies of splats deposited on three kinds of substrates with the accelerating gas temperature of 850 ± 10°C and 750 ± 10°C, it can be found that the deformation of nanostructured WC–23Co particles is enhanced by the increment of substrate hardness and gas temperature.     

Synthesis,electron transport properties of transition metal nitrides and applications

To understand the electron transport properties of transition metal nitrides (MN), electronic structure relationship between metal and corresponding nitrides is important. In binary nitrides, when nitrogen atoms occupy interstitial sites of metal lattice, volume expansion started initially without changing structure of metal lattice. Above certain concentration of nitrogen into interstitial sites of lattice, the system starts stabilizing its energy to minimum that in turn changes to another crystal structure. The chemical bonding in MN is due to the mixing of d-orbitals of M and p-orbitals of N. This is confirmed theoretically and experimentally such as X-ray photoelectron spectroscopy. The Fermi energy is generally lowered by the introduction of vacancies. However, reports on the particle size effect in the electrical resistivity of nitrides are scanty. One reason is that the role of the particle size in resistivity is difficult to determine because there is a need to understand N concentration. It poses a challenge to the synthesis of nanostructured transition metal nitrides. The transition metal binary nitrides show unusual electron transport, optical and magnetic properties as compared to their metal counterparts. Electronic properties of all transition metal nitrides known till date are discussed. Different ways of synthesis of nitrides and their applications are mentioned.     

热喷涂纳米结构涂层的研究现状

介绍了国内外喷涂用纳米结构喂料的制备方法以及在应用热喷涂技术制备纳米结构涂层方面的研究进展.与传统材料的热喷涂涂层相比,纳米结构涂层在力学、摩擦学以及耐磨防腐蚀性能方面有了较大的提高.     

Control of bacterial biofilm growth on surfaces by nanostructural mechanics and geometry

Surface-associated communities of bacteria, called biofilms, pervade natural and anthropogenic environments. Mature biofilms are resistant to a wide range of antimicrobial treatments and therefore pose persistent pathogenic threats. The use of surface chemistry to inhibit biofilm growth has been found to only transiently affect initial attachment. In this work, we investigate the tunable effects of physical surface properties, including high-aspect-ratio (HAR) surface nanostructure arrays recently reported to induce long-range spontaneous spatial patterning of bacteria on the surface. The functional parameters and length scale regimes that control such artificial patterning for the rod-shaped pathogenic species Pseudomonas aeruginosa are elucidated through a combinatorial approach. We further report a crossover regime of biofilm growth on a HAR nanostructured surface versus the nanostructure effective stiffness. When the 'softness' of the hair-like nanoarray is increased beyond a threshold value, biofilm growth is inhibited as compared to a flat control surface. This result is consistent with the mechanoselective adhesion of bacteria to surfaces. Therefore by combining nanoarray-induced bacterial patterning and modulating the effective stiffness of the nanoarray--thus mimicking an extremely compliant flat surface--bacterial mechanoselective adhesion can be exploited to control and inhibit biofilm growth.     

纳米结构陶瓷涂层的外圆磨削力以及磨削表面精度的实验研究

使用功率计监测磨削加工的能量消耗，探讨了纳米结构陶瓷涂层的外圆磨削过程；对纳米陶瓷涂层和传统陶瓷涂层在磨削力和磨削表面精度方面进行了比较．磨削实验使用了外圆磨床和陶瓷结合剂金刚石砂轮．通过测量主轴功率获得切向磨削力，讨论了加工参数，如切深、进给率以及砂轮粒度对切向磨削力的影响．还对磨削后的涂层表面用粗糙度仪和扫描电镜进行了评估，揭示了表面粗糙度与加工参数的关系．     

Shock absorption performance of a motorbike helmet with honeycomb reinforced liner

The enhancement of the energy absorption properties of motorbike helmets could significantly improve the safety of riders. This study reports a novel concept of helmet design, which consists in the use of aluminium honeycomb as reinforcement material of the helmet liner. A modified version of a commercial helmet is presented, in which aluminium honeycombs are used in the energy absorbing liner. The ECE 22.05 standard tests were performed on both the prototype helmets and their commercial counterparts (presenting same dimensions, geometry, material properties and weight), and the dynamic responses were compared. The results showed that the prototype helmets provided better protection to the head from impacts against the kerbstone anvil. More limited improvements were also observed in some of the impacts on flat anvil, although other results indicated to some extent the limitations of the strategy adopted in our research.     

Attenuation of protein adsorption on static and oscillating magnetostrictive nanowires

The research described here investigates the hypothesis that nanoarchitecture contained in a nanowire array is capable of attenuating the adverse host response generated when medical devices are implanted in the body. This adverse host response, or biofouling, generates an avascular fibrous mass transfer barrier between the device and the analyte of interest, disabling the implant if it is a sensor. Numerous studies have indicated that surface chemistry and architecture modulate the host response. These findings led us to hypothesize that nanostructured surfaces will inhibit the formation of an avascular fibrous capsule significantly. We are investigating whether arrays of oscillating magnetostrictive nanowires can prevent protein adsorption. Magnetostrictive nanowires were fabricated by electroplating a ferromagnetic metal alloy into the pores of a nanoporous alumina template. The ferromagnetic nanowires are made to oscillate by oscillating the magnetic field surrounding the wires. Radiolabeled bovine serum albumin, enzyme-linked immunosorbent assay (ELISA), and other protein assays were used to study protein adhesion on the nanowire arrays. These results display a reduced protein adsorption per surface area of static nanowires. Comparing the surfaces, 14-30% of the protein that absorbed on the flat surface adsorbed on the nanowires. Our contact angle measurements indicate that the attenuation of protein on the nanowire surface might be due to the increased hydrophilicity of the nanostructured surface compared to a flat surface of the same material. We oscillated the magnetostrictive wires by placing them in a 38 G 10 Hz oscillating magnetic field. The oscillating nanowires show a further reduction in protein adhesion where only 7-67% of the protein on the static wires was measured on the oscillating nanowires. By varying the viscosity of the fluid the nanowires are oscillated in, we determined that protein detachment is shear-stress modulated. We created a high shearing fluid with dextran, which reduced protein adsorption on the oscillating nanowires by 70% over nanowires oscillating in baseline viscosity fluid. Our preliminary studies strongly suggest that the architecture in the static nanowire arrays and the shear created by oscillating the nanowire arrays would attenuate the biofouling response in vivo.