Mechanical characterization of nickel nanowires by using a customized atomic force microscope

A new experimental method to characterize the mechanical properties of metallic nanowires is introduced. An accurate and fast mechanical characterization of nanowires requires simultaneous imaging and testing of the nanowires. However, existing mechanical characterization techniques fail to accomplish this goal due either to the lack of imaging capability of the mechanical test setup or the difficulty of individual alignment and manipulation of single nanowires for each test. In this study, nanowire specimens prepared by an electroplating technique are located on a silicon substrate with trenches. A customized atomic force microscope is located inside a scanning electron microscope (SEM) in order to establish the visibility of the nanowires, and the tip of the atomic force microscope cantilever is utilized to bend and break the nanowires. The ability to visualize the nanowires in an SEM improves the speed and accuracy of the tests. Experimentally obtained force versus bending displacement curves are fitted into existing analytical formulations to extract the mechanical properties. Experimental results reveal that nickel nanowires have significantly higher strengths than their bulk counterparts, although their elastic modulus values are comparable to bulk nickel modulus values.     

Formation of chiral branched nanowires by the Eshelby Twist

Manipulating the morphology of inorganic nanostructures, such as their chirality and branching structure, has been actively pursued as a means of controlling their electrical, optical and mechanical properties. Notable examples of chiral inorganic nanostructures include carbon nanotubes, gold multishell nanowires, mesoporous nanowires and helical nanowires. Branched nanostructures have also been studied and been shown to have interesting properties for energy harvesting and nanoelectronics. Combining both chiral and branching motifs into nanostructures might provide new materials properties. Here we show a chiral branched PbSe nanowire structure, which is formed by a vapour-liquid-solid branching from a central nanowire with an axial screw dislocation. The chirality is caused by the elastic strain of the axial screw dislocation, which produces a corresponding Eshelby Twist in the nanowires. In addition to opening up new opportunities for tailoring the properties of nanomaterials, these chiral branched nanowires also provide a direct visualization of the Eshelby Twist.     

Mechanical properties of ultrahigh-strength gold nanowires

Nanowires have attracted considerable interest as nanoscale interconnects and as the active components of both electronic and electromechanical devices. Nanomechanical measurements are a challenge, but remain key to the development and processing of novel nanowire-based devices. Here, we report a general method to measure the spectrum of nanowire mechanical properties based on nanowire bending under the lateral load from an atomic force microscope tip. We find that for Au nanowires, Young's modulus is essentially independent of diameter, whereas the yield strength is largest for the smallest diameter wires, with strengths up to 100 times that of bulk materials, and substantially larger than that reported for bulk nanocrystalline metals (BNMs). In contrast to BNMs, nanowire plasticity is characterized by strain-hardening, demonstrating that dislocation motion and pile-up is still operative down to diameters of 40 nm. Possible origins for the different mechanical properties of nanowires and BNMs are discussed.     

Force-deflection spectroscopy: a new method to determine the Young's modulus of nanofilaments

We demonstrate the determination of Young's modulus of nanowires or nanotubes via a new approach, that is, force-deflection spectroscopy (FDS). An atomic force microscope is used to measure force versus deflection (F-D) curves of nanofilaments that bridge a trench patterned in a Si substrate. The FD data are then fit to the Euler-Bernoulli equation to determine Young's modulus. Our approach provides a generic platform from which to study the mechanical and piezoelectric properties of a variety of materials at the nanoscale level. Young's modulus measurements on ZnS (wurtzite) nanowires are presented to demonstrate this technique. We find that the Young's modulus for rectangular cross section ZnS nanobelts is 52 +/- 7.0 GPa, about 30% smaller than that reported for the bulk.     

一维单体纳米材料弹塑性变形机理的原位研究进展EI北大核心CSCD

近年来,随着研究技术手段的发展,纳米线表现出了大量具有潜在应用价值的新现象。清晰描绘纳米线结构与力学性能的构效关系对纳米器件的设计、服役以及性能优化具有重要的指导意义。本文首先归纳了纳米线力学性能几种常用的原位测试方法,其次介绍了各类纳米线在拉伸实验中的弹性和强度等力学性能,阐述了纳米线与尺寸相关的塑性变形,此外简述了纳米线在原位测试中所表现出的奇特力学行为。今后,系统地研究原位电镜表征过程中电子束辐照对纳米线变形行为的影响,探究纳米线在复杂外场环境下所展现的力学性能,从而建立一套完备的理论指导体系,是纳米材料性能原位表征领域的重要发展方向。     

仿生有序结构羟基磷灰石研究进展

羟基磷灰石(hydroxyapatite,HAP)与人体硬组织主要无机组分具有相同的化学组成,因而被认为具备良好的生物相容性、可降解性和生物活性,并已在生物医学领域得到广泛应用。迄今为止,形态丰富的HAP纳米材料及其合成方法已经被报道出来,但是具有仿生有序结构的HAP材料及其制备方法仍然是相关领域最具挑战性的方向。在包括牙釉质、皮质骨和松质骨在内的硬组织中,纳米尺度的HAP通常会按照人体受力分布情况呈可控有序结构排列。因此,通过仿生天然硬组织微结构实现HAP的可控有序组装,有望进一步提升传统HAP基生物材料的力学和生物学性能。近年来,包括氧化铝模板法、有机溶剂/小分子调控法、磷酸氢钙相转化法、高分子/蛋白分子诱导矿化法、冷冻铸造等在内的HAP有序结构制备方法已经被发展出来,并实现了在纳米、微米等尺度上有序结构的制备。最近,作者课题组报道了HAP纳米线的扩大化溶剂热制备方法,并进一步提出了适用于控制HAP纳米线有序排列的表面小分子介导的液相自组装策略,获得了尺寸和方向均可控的宏观尺度HAP纳米线仿生有序结构。相比于传统无序结构HAP基生物材料,具有仿生有序结构的HAP表现出了良好的力学和生物学性能,对新型无机生物材料的设计、制备及其生物医学应用研究具有重要的指导意义。综述了仿生有序结构HAP的研究进展,包括其结构组成、合成方法及调控机制,最后总结了仿生有序结构HAP研究领域当前面临的挑战以及未来的发展前景。     

25th Anniversary Article: Semiconductor Nanowires – Synthesis,Characterization, and Applications

Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of “bottom‐up” growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one‐dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.     

AFM-based force spectroscopy measurements of mature amyloid fibrils of the peptide glucagon

We report on the mechanical characterization of individual mature amyloid fibrils by atomic force microscopy (AFM) and AFM-based single-molecule force spectroscopy (SMFS). These self-assembling materials, formed from the 29-residue amphiphatic peptide hormone glucagon, were found to display a reversible elastic behaviour. Based on AFM morphology and SMFS studies, we suggest that the observed elasticity is due to a force-induced conformational transition which is reversible due to the β-helical conformation of protofibrils, allowing a high degree of extension. The elastic properties of such mature fibrils contribute to their high stability, suggesting that the internal hydrophobic interactions of amyloid fibrils are likely to be of fundamental importance in the assembly of amyloid fibrils and therefore for the understanding of the progression of their associated pathogenic disorders. In addition, such biological amyloid fibril structures with highly stable mechanical properties can potentially be used to produce nanofibres (nanowires) that may be suitable for nanotechnological applications.     

Capillary-driven assembly of ZnO nanowire arrays into micropatterns

The vertically aligned ZnO nanowire arrays prepared by vapor transport process can be assembled into complex micropatterns under capillary force. The deflection of the flexible ceramic nanowire is closely related to the liquid tension coefficient, mechanical and structural properties of the ZnO nanowires. The bended nanowires are adhesive together because the solid adhesion energy is sufficient to withstand the restoring elastic force of the deformed nanowires. The size of the bundling pattern can be controlled by varying the aspect ratio of the nanowire. The deflection of the ZnO nanostructure composed of a nanowire and a base is multifarious.     

Correlation between Anisotropy and Lattice Distortions in Single Crystal Calcite Nanowires Grown in Confinement

Growing nanostructures in confinement allows for the control of their shape, size and structure, as required in many technological applications. We investigated the crystal structure and morphology of calcite nanowires, precipitated in the pores of track‐etch membranes, by employing transmission electron microscopy and selected area electron diffraction (SAED). The data showed that the nanowires show no preferred growth orientation and that the crystallographic orientation rotated along the length of the nanowire, with lattice rotation angles of several degrees per micrometer. Finite element calculations indicated that the rotation is caused by the anisotropic crystallographic nature of the calcite mineral, the nanoscale diameter of the wires and the confined space provided by the membrane pore. This phenomenon should also be observed in other single crystal nanowires made from anisotropic materials, which could offer the potential of generating nanostructures with tailored optical, electronic and mechanical properties.