Mechanical property measurements of nanoscale structures using an atomic force microscope

This paper describes nanometer-scale bending tests of fixed single-crystal silicon (Si) and silicon dioxide (SiO2) nanobeams using an atomic force microscope (AFM). The technique is used to evaluate elastic modulus of the beam materials and bending strength of the beams. Nanometer-scale Si beams with widths ranging from 200 to 800 nm were fabricated on a Si diaphragm using field-enhanced anodization using an AFM followed by anisotropic wet etching. Subsequent thermal oxidation of Si beams was carried out to create SiO2 beams. Results from the bending tests indicate that elastic modulus values are comparable to bulk values. However, the bending strength appears to be higher for these nanoscale structures than for large-scale specimens. Observations of the fracture surface and calculations of the crack length from Griffith's theory appear to indicate that the maximum peak-to-valley distance on the beam top surfaces influence the values of the observed bending strengths.     

硅的微观硬度测试研究

对微机械而言 ,不仅微观环境对其工作性能有所影响 ,而且微构件本身的力学性能也直接影响到微机械的服役寿命和工作性能。在微小尺度下 ,材料的微观力学性能与宏观力学性能之间有很大的差别 ,如何测试其力学性能参数 ,如弹性模量和表面硬度等 ,就成为微机械设计的关键和保证其可靠运行的基础。本文介绍了纳米硬度计的工作原理和微小尺度下材料的弹性模量和硬度的计算方法 ,并对微构件制备中最常用的材料硅的微观力学特性进行了初步测试。试验结果表明 :硅在微小载荷下表现出了很好的力学性能 ,其表面硬度随压入深度的增大而减小 ,并逐渐趋近硅的宏观硬度值     

纳米硬度计研究多晶硅微悬臂梁的弹性模量

利用纳米硬度计通过微悬臂梁的弯曲试验来测量其力学特性是一种简便而有效的方法,具有很高的载荷分辨率,可精确测量微悬臂梁纳米级弯曲形变。运用该方法在研究微悬臂梁的弯曲形变过程中,必须考虑压头在微悬臂梁上的压入以及微悬臂沿宽度方向的挠曲。微悬臂梁采用普通的集成电路工艺(IC)制造。试验研究表明,多晶硅微悬臂梁的纯挠曲与载荷成很好的线性关系,呈现弹性变形,通过该线性关系可计算得到梁的弹性模量。测得的多晶硅微悬臂梁的弹性模量为156±(2.9%-6.3%)GPa。     

MECHANICAL DEFLECTION OF POLYSILICON MICROCANTILEVER BEAMS USING NANOINDENTATION

0INTRODUCTIONThe miniaturization of microelectronic device is now reaching the mechanical field, allowing the integration of micromechanisms together with their operation electronics in a single device. This leads to interesting perspectives in the design of monolithic microrobtic systems by the micromachining techniques directly derived from standard silicon technology. Scientists have already moved MEMS into various stages of conception and development for making laboratories on chips,…     

单晶硅纳米力学性能的测试

对材料纳米力学性能测试手段进行了研究,着重分析了纳米压痕技术的原理和方法.结合纳米压痕技术,采用尖端四面体Vickers型单晶金刚石压头对单晶硅(100)晶面进行了纳米压痕实验测试.实验发现,在载荷为1 000 mN时,晶体硅出现了明显的裂纹和脆性断裂;而在载荷低于80 mN的情况下,晶体硅则表现出延性特性.此外,在不同载荷条件下对晶体硅的硬度进行了实验测试,测试结果发现,不同载荷条件下晶体硅的硬度测量值存在较大的差异,认为导致这种差异的原因在于压痕区域晶体硅所受压力不同,使得晶体硅内部结构发生了改变,较为准确的单晶硅的硬度测量值为15.7 GPa.     

Modelling of frictional and adhesive contacts at silicon/polymer interface for nanotechnological applications

Abstract

The minimisation of friction and adhesion during sliding contacts is crucial for the industrial fabrication of many micro/nanodevices (e.g. MEMS/NEMS), as well as in nanotechnological processes, e.g. in nanoimprint lithography where a silicon mould is used to fabricate polymeric nanostructures by imprinting. We have conducted intensive research on the contact between the mould and PMMA polymeric resist film via advanced modelling and computer simulations. The properties of the contacting surfaces have been identified with the atomic force microscope and nanoindentation, as well as wettability tester applied for the identification of the surface free energy. A model of contact has been elaborated and adequate original software was used to calculate the frictional and adhesive forces in particular at the silicon mould/polymeric resist interface.     

Substrate Effects on the Micro/Nanomechanical Properties of TiN Coatings

Nanoindentation and nanoscratch tests were performed for titanium nitride (TiN) coatings on different tool steel substrates to investigate the indentation/scratch induced deformation behavior of the coatings and the adhesion of the coating–substrate interfaces and their tribological property. In this work, TiN coatings with a thickness of about 500 nm were grown on GT35, 9Cr18 and 40CrNiMo steels using vacuum magnetic-filtering arc plasma deposition. In the nanoindentation tests, the hardness and modulus curves for TiN/GT35 reduced the slowest around the film thickness 500 nm with the increase of indentation depth, followed by TiN/9Cr18 and TiN/40CrNiMo. Improving adhesion properties of coating and substrate can decrease the differences of internal stress field. The scratch tests showed that the scratch response was controlled by plastic deformation in the substrate. The substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. TiN/GT35 exhibited the best load-carrying capacity and scratch/wear resistance. As a consequence, GT35 is the best substrate for TiN coatings of the substrate materials tested.     

Finite element analysis of nanostructures with roughness and scratches

Finite element analysis facilitates optimal design of MEMS/NEMS devices for reliability. A finite element method (FEM) was developed to analyze the effect of types of surface roughness and scratches on stresses of nanostructures. Beams with surface roughness in the form of semicircular and grooved asperities in varying numbers in the longitudinal direction were considered. In the transverse direction semicircular asperities and scratches in varying numbers and with different pitch were modeled. Furthermore semicircular asperities were truncated both in longitudinal and transverse direction and analyzed. It was observed that the asperities and scratches increase the bending tensile stresses which could lead to failure of MEMS/NEMS devices. The beam material was assumed to be purely elastic, elastic-plastic and elastic-perfectly plastic to observe the variations in the bending stresses and displacements for both smooth nanobeam and nanobeam with defined roughness. The results of the analysis can be useful to designers to develop the most suitable geometry for nanostructures.     

Nanowear Mapping: A Novel Atomic Force Microscopy Based Approach for Studying Nanoscale Wear at High Sliding Velocities

Most micro/nanoelectromechanical system (MEMS/NEMS) devices and components such as microgears and micromotors operate at very high sliding velocities (of the order of tens of mm/s to few m/s). Nanoscale tribology and mechanics of these devices is crucial for evaluating reliability and failure issues, including those stemming from high wear. We have developed a novel AFM based approach for studying nanoscale wear at sliding velocities up to 10 mm/s. The technique is demonstrated by mapping wear of silicon resulting from two- and three-body abrasions, and that of diamondlike carbon (DLC) resulting from phase transformation of DLC to a graphite-like phase. The novel AFM based approach for nanowear mapping provides a reliable as well as a fast means for investigating wear on the nanoscale as a function of normal load and sliding velocity.     

Nano/Microtribological Properties of Ultrathin Functionalized Imidazolium Wear-Resistant Ionic Liquid Films on Single Crystal Silicon

Ionic liquids (ILs) are considered as a new kind of lubricant for micro/nanoelectromechanical system (M/NEMS) due to their excellent thermal and electrical conductivity. However, so far, only few reports have investigated the tribological behavior of molecular thin films of various ILs. Evaluating the nanoscale tribological performance of ILs when applied as a few nanometers-thick film on a substrate is a critical step for their application in MEMS/NEMS devices. To this end, four kinds of ionic liquid carrying methyl, hydroxyl, nitrile, and carboxyl group were synthesized and these molecular thin films were prepared on single crystal silicon wafer by dip-coating method. Film thickness was determined by ellipsometric method. The chemical composition and morphology were characterized by the means of multi-technique X-ray photoelectron spectrometric analysis, and atomic force microscopic (AFM) analysis, respectively. The nano- and microtribological properties of the ionic liquid films were investigated. The morphologies of wear tracks of IL films were examined using a 3D non-contact interferometric microscope. The influence of temperature on friction and adhesion behavior at nanoscale, and the effect of sliding frequency and load on friction coefficient, load bearing capacity, and anti-wear durability at microscale were studied. Corresponding tribological mechanisms of IL films were investigated by AFM and ball-on-plane microtribotester. Friction reduction, adhesion resistance, and durability of IL films were dependent on their cation chemical structures, wettability, and ambient environment.     

Friction-Induced Nanofabrication:A Review

As the bridge between basic principles and applications of nanotechnology,nanofabrication methods play significant role in supporting the development of nanoscale science and engineering,which is changing and improving the production and lifestyle of the human.Photo lithography and other alternative technologies,such as nanoimprinting,electron beam lithography,focused ion beam cutting,and scanning probe lithography,have brought great progress of semiconductor industry,IC manufacturing and micro/nanoelectromechanical system(MEMS/NEMS)devices.However,there remains a lot of challenges,relating to the resolution,cost,speed,and so on,in realizing high-quality products with further development of nanotechnology.None of the existing techniques can satisfy all the needs in nanoscience and nanotechnology at the same time,and it is essential to explore new nanofabrication methods.As a newly developed scanning probe microscope(SPM)-based lithography,friction-induced nanofabrication provides opportunities for maskless,flexible,low-damage,low-cost and environment-friendly processing on a wide variety of materials,including silicon,quartz,glass surfaces,and so on.It has been proved that this fabrication route provides with a broad application prospect in the fabrication of nanoimprint templates,microfluidic devices,and micro/nano optical structures.This paper hereby involved the principals and operations of friction-induced nanofabrication,including friction-induced selective etching,and the applications were reviewed as well for looking ahead at oppor-tunities and challenges with nanotechnology development.The present review will not only enrich the knowledge in nanotribology,but also plays a positive role in promoting SPM-based nanofabrication.     

Micro/Nanotribological and Mechanical Studies of TiN Thin-Film for MEMS Applications

Micro/nanotribological and mechanical characterization of TiN film and single-crystal silicon was investigated. Hardness, friction, and wear properties of both materials were measured by a nanoindenter system. The results demonstrate the similarities and differences between both materials and show that TiN film has more preferable properties in hardness and wear resistance than those of single-crystal silicon. It is more likely that a methodology based on this study can be used for evaluating the quality of micro/nanofilms, and TiN film possesses desirable micro/nanotribological and mechanical characterization for MEMS applications.     

弹性阶段扭转尺度效应的研究

在非均匀有限弹性变形理论的基础上,推导出考虑一个微旋转的扭转新弹性理论公式,并对在弹性变形阶段的扭转尺度效应进行了预测,探讨了微杆扭转动、静态的尺度效应的问题,研究表明在弹性变形阶段微杆扭转存在着很大的尺度效应.     

纳米压入法MEMS材料力学能测量与评定标准化的初步设想

根据纳米压入法测量与评定MEMS材料力学性能的原理,对诸如测量仪器、压头、评定模型、测试条件等影响力学性能测量精确度、测量结果的可比性的主要原因因素进行了分析。在此基础上,提出对MEMS材料力学性能测量与评定进行标准化的初步设想。     

Nanostructure-Textured Surfaces with Low Friction and High Deformation Resistance

Nanotextured surfaces can effectively reduce friction and adhesion, especially in applications with micro- and nanoscale contact interactions. However, for these surfaces, a common weakness is a lack of structural integrity of the individual nanotextures when subjected to contact loading, resulting in permanent deformation at even the moderate contact forces encountered in microscale systems. Nanostructure-textured surfaces (NSTSs), composed of arrays of novel Al/a-Si core–shell nanostructures (CSNs), have been developed with a desirable combination of low friction and high deformation resistance. When subjected to nanoscratch testing, these surfaces are shown to have extremely low coefficients of friction (as low as ～0.015), as well as no detectable nanostructure deformation at contact forces up to 8,000 μN (estimated contact pressure greater than 1 GPa). In addition, the NSTSs have low adhesion (pull-off) forces on the order of less than 1 μN. The unique properties of these NSTSs provide avenues for designing low-friction, deformation-resistant surfaces that could benefit a variety of fields, including micro/nanoelectromechanical systems (MEMS/NEMS), microelectronics, magnetic recording, or any other application where the mechanical integrity of nanostructures is important.     

Large Deformation Analysis and Synthesis of Elastic Closed-loop Mechanism Made of a Certain Spring Wire Described by Free Curves

Recently novel mechanisms with compact size and without many mechanical elements such as bearing are strongly required for medical devices such as surgical operation devices. This paper describes analy...     

Nanotribological characterization of molecularly thick lubricant films for applications to MEMS/NEMS by AFM

Molecularly thick perfluoropolyether (PFPE) films are considered to be good protective films for micro/nanoelectromechanical systems (MEMS/NEMS) to reduce stiction, friction, and improve their durability. Understanding the nanotribological performance and mechanisms of these films are quite important for efficient lubrication for MEMS/NEMS devices. These devices are used in various operating environments and their effect on friction, adhesion and durability needs to be clarified. For this purpose, mobile and chemically bonded PFPE films were deposited by dip coating technique. The friction and adhesion properties of these films were characterized by atomic force microscopy (AFM). The effect of rest time, velocity, relative humidity, and temperature on nanotribological properties of these films was studied. Durability of these films was also measured by repeated cycling tests. The adhesion, friction mechanisms of PFPE at molecular scale, and the mechanisms of the effect of operating environment and durability are subject of this paper. This study found that adsorption of water, formation of meniscus and its change during sliding, viscosity, and surface chemistry properties play a big role on the friction, adhesion, and durability of the lubricant films.     

薄膜的力学测试技术

对薄膜力学性能的测试方法、技术以及所取得的主要成果进行简要的综合介绍。     

SiCp/2024Al复合材料高应变率热变形行为的新本构模型#br#

通过分离式霍普金森压杆(SHPB)动态压缩试验研究了体积分数为45%的铝基碳化硅颗粒增强复合材料（SiCp/2024Al）在大应变率和变形温度范围内的热变形行为,分析了热变形参数（变形温度和应变率）对流动应力的影响。研究发现：变形温度和应变率对复合材料的流变应力、抗压强度、弹性模量、应变率敏感性有显著影响;抗压强度、弹性模量随变形温度的增大而减小,而抗压强度、弹性模量、应变率敏感性随应变率的增大出现了拐点。根据试验结果,结合热力学和统计损伤力学理论,建立了描述SiCp/2024Al复合材料动态热变形行为的连续损伤本构模型,预测的流动应力与试验结果吻合较好,表明所建立的模型能够准确地描述SiCp/2024Al复合材料动态热变形行为。     

计及二阶效应的大位移柔性梁杆系统动力学分析

结合小变形条件下梁杆单元精确有限元方法和大位移随动坐标法,建立了计及二阶效应的大位移运动柔性梁单元的动力学方程.首先从小变形结构入手,建立考虑二阶效应的柔性梁压弯力学模型,推导出二阶理论条件下平面压弯梁的精确有限元方程,进而获取二阶理论条件下梁单元精确刚度阵.运用大位移随动坐标法建立大位移几何非线性弹性梁杆单元平衡方程,使用柔性多体动力学的相对描述方法推导大位移梁单元在局部坐标系下的动力学方程.通过结点位移、速度和加速度在随动坐标系与整体坐标系间的相互关系得到梁单元在整体坐标系下的包含二阶效应的动力学方程.对某型港口起重机臂架系统的变幅工况进行了计及二阶效应的弹性动力分析.