较浅压入下针尖曲率半径对纳米压入硬度影响的比较研究

基于3种不同曲率半径压头针尖对熔融石英进行纳米压入,用原子力显微镜（AFM）直接法测得压头针尖的面积函数及针尖曲率半径。研究表明,在极浅压入条件下,压头曲率半径的变化会导致硬度值的测量误差,曲率半径越小的压头针尖随接触深度的变化会更快得到真实值;相同的压入深度,曲率半径小的压头针尖测得的压入硬度值比曲率半径大的测得的压入硬度值更接近其真实值。     

较浅压入下针尖曲率半径对纳米压入硬度影响研究

基于3种不同曲率半径压头针尖对熔融石英进行纳米压入,用原子力显微镜(AFM)直接法测得压头针尖的面积函数及针尖曲率半径。研究表明,在极浅压入条件下,压头曲率半径的变化会导致硬度值的测量误差,曲率半径越小的压头针尖随接触深度的变化会更快得到真实值;相同的压入深度,曲率半径小的压头针尖测得的压入硬度值比曲率半径大的测得的压入硬度值更接近其真实值。     

纳米压痕仪的压头面积函数校准方法的比较研究

基于原子力显微镜的直接测量法和通过熔融石英标准样块校准的间接测量法对纳米压痕仪的压头面积函数及机架柔度进行校准,并将这2种方法的校准结果分别应用到熔融石英和聚碳酸酯2种标准样块的压痕测试。压痕实验结果表明,在较浅压入深度,直接测量法测得的硬度值和折合模量值比间接方法测得的结果准确,在较大压入深度,2种方法的测量结果相差不大。     

确定纳米压入面积函数的改进方法

针对薄膜等微小结构材料力学性能测试面积函数测量问题,提出了一种改善微小压入深度下压头面积函数准确性的方法.该方法将压头与被测样品之间的投影接触面积与压头针尖曲率半径和角度相关联,解决常用的面积函数确定方法在50 nm以下浅压痕测量中不可靠的问题.经实验验证,该面积函数确定方法可以提高微小接触深度下压入硬度和折合模量的测...     

应用纳米压痕法测定柱状纳米材料的力学特性（英文）

纳米压痕法在确定纳米结构材料,特别是具有较大高宽比的一维纳米结构/对象的力学特性时,若纳米结构沿压入方向的等效刚度远小于针尖-样品的接触刚度,应用常规数据分析(Oliver-Pharr)模型会导致较大的测量偏差.对常规Oliver-Pharr解析模型进行了推广,以补偿一维纳米材料等效刚度对测量结果的影响,进而提出了适用于此类测量对象的通用纳米压痕分析模型,并应用于分析柱状微纳米结构的准静态压痕测量数据.实验中应用原子力显微镜(AFM)定量测量了湿法刻蚀获得的一维单晶硅柱状结构的几何参数(包括硅纳米柱的直径和长度).实验结果表明,应用常规模型分析对较大高宽比的硅纳米柱(直径386 nm,长500 nm)的压痕数据会导致大于50%的偏差.应用修正模型分析实验数据时,测量结果不受被测对象几何参数的影响,因而可以有效提高应用纳米压痕法对微纳米结构材料,特别是一维材料的测量精度.     

SiN_x薄膜在纳米压痕下的变形和断裂行为

利用磁控溅射方法在Si(111)衬底上制备了厚度为1μm的非晶SiN_x薄膜,采用纳米压痕方法研究了薄膜的变形和断裂行为。傅立叶变换红外光谱显示实验获得了较为纯净的SiN_x薄膜。SiN_x薄膜在纳米压痕下呈现出放射状的脆性断裂特征,随着压入深度的增大,放射状裂纹的长度逐渐增加。最大压入深度达到1 500nm时,薄膜和衬底间出现了扇形的界面断裂,并且这一界面断裂是在卸载过程中发生的。到最大压入深度达到2 500nm时,原位原子力显微镜照片可以清晰的观察到界面断裂及放射状裂纹。界面断裂韧性计算结果表明,SiN_x薄膜和Si(111)衬底间易形成脆性较大的共价结构界面,这是其界面断裂韧性较小的原因。     

基于AFM纳米硬度测量系统的实验

为了解决用AFM自身压痕软件进行纳米硬度测量时无法直接获得载荷-压深曲线和由于受到扫描陶管扫描范围的限制而进行多点压痕实验范围有限的问题,建立了三维微动工作台和原子力显微镜相结合的纳米压痕硬度测量系统.基于该系统,对单晶薄膜材料进行了单点压痕实验,得出该系统适合进行纳米硬度测量的结论;并对薄膜材料的纳米硬度和弹性模量进行了分析,讨论了尺寸效应对两者的影响.另外,进行了40×40的点阵压痕实验,得到了材料整个压痕面的三维形貌图和三维硬度图.     

单晶铝纳米级硬度试验研究

使用纳米硬度计对单晶铝进行了纳米压痕试验,利用原子力显微镜对压痕形貌进行扫描并计算硬度值,重点观察和分析了纳米级条件下单晶铝的硬度性质,结果表明,当压痕深度小于2000nm时,单晶铝纳米硬度存在尺寸效应现象;从材料性质的角度分析了纳米硬度尺寸效应现象;探讨了纳米硬度和传统硬度本质上的区别,指出其根本原因在于不同尺度下人们对材料性质的关注点不同。     

纳米压痕硬度计测方法的研究进展

针对纳米尺度下的材料硬度测量,利用纳米硬度计得到压痕的载荷-压深曲线,并用原子力显微镜得到压痕的三维形貌图.通过载荷-压深曲线和压痕形貌图,以及相应的计算方法,可以得到纳米压痕硬度.纳米压痕硬度计测方法不同,得到的材料硬度值也不同.分析现有的几种纳米压痕硬度计测方法,找出它们的优缺点,并对未来发展方向做了展望.     

纳米压痕法测试微纳米涂层的力学性能

采用G200型微/纳米压痕仪,测试了不同微纳米级涂层材料的力学性能。结果表明:使用纳米压痕法能检测和表征微纳米涂层材料的硬度和弹性模量及其随涂层厚度的变化趋势,从而了解涂层的力学性能以及与基体的结合质量情况;纳米压痕法测试涂层力学性能时存在明显的表面效应,一般建议压入深度不小于20μm,以保证表面粗糙度引起的压入深度的不确定度小于5%。     

Adhesion mechanism of friction in nanotribocontacts

An adhesion mechanism is proposed for the frictional force between the tip of an atomic force (friction) microscope and a surface, whereby the frictional force is determined by the energy of breaking and formation of adhesive bonds for a discrete microslide step of length close to the atomic radii of the contacting bodies. Calculations were made of the frictional force as a function of the radius of curvature and the distance between the tip and the surface for silicon-silicon and tungsten-iron contacts. Pis’ma Zh. Tekh. Fiz. 24, 44–50 (October 12, 1998)     

Subsurface damage of single crystalline silicon carbide in nanoindentation tests

The response of single crystalline silicon carbide (SiC) to a Berkovich nanoindenter was investigated by examining the indents using a transmission electron microscope and the selected area electron diffraction technique. It was found that the depth of indentation-induced subsurface damage was far larger than the indentation depth, and the damaging mechanism of SiC was distinctly different from that of single crystalline silicon. For silicon, a broad amorphous region is formed underneath the indenter after unloading; for SiC, however, no amorphous phase was detected. Instead, a polycrystalline structure with a grain size of ten nanometer level was identified directly under the indenter tip. Micro cracks, basal plane dislocations and possible cross slips were also found around the indent. These finding provide useful information for ultraprecision manufacturing of SiC wafers.     

A method to quantitatively measure the elastic modulus of materials in nanometer scale using atomic force microscopy

A method is proposed for quantitatively measuring the elastic modulus of materials using atomic force microscopy (AFM) nanoindentation. In this method, the cantilever deformation and the tip-sample interaction during the early loading portion are treated as two springs in series, and based on Sneddon's elastic contact solution, a new cantilever-tip property α is proposed which, together with the cantilever sensitivity A, can be measured from AFM tests on two reference materials with known elastic moduli. The measured α and A values specific to the tip and machine used can then be employed to accurately measure the elastic modulus of a third sample, assuming that the tip does not get significantly plastically deformed during the calibration procedure. AFM nanoindentation tests were performed on polypropylene (PP), fused quartz and acrylic samples to verify the validity of the proposed method. The cantilever-tip property and the cantilever sensitivity measured on PP and fused quartz were 0.514?GPa and 51.99?nm?nA(-1), respectively. Using these measured quantities, the elastic modulus of acrylic was measured to be 3.24?GPa, which agrees well with the value measured using conventional depth-sensing indentation in a commercial nanoindenter.     

Estimation of AFM tip shape and status in linewidth and profile measurement

An atomic force microscopy image is a dilation of the specimen surface with the probe tip. Tips wear or are damaged as they are used. And AFM tip shape and position status make AFM images distorted. So it is necessary to characterize AFM tip shape and position parameters so as to reconstruct AFM images. A geometric model-based approach is presented to estimate AFM tip shape and position status by AFM images of test specimens and scanning electron microscope (SEM) images of AFM tip. In this model, the AFM tip is characterized by using a dynamic cone model. The geometric relationship between AFM tip and the sample structure is revealed in linewidth and profile measurement. The method can easily calculate the tip parameters including half-cone angle, installation angle, scanning tilting angle and curvature radius, and easily estimate the position status of AFM tip when AFM tip moves on the specimen. The results of linewidth and profile measurement are amended accurately through this approach.     

Application of the work of indentation approach for the characterization of aluminium 2024-T351 and Al cladding by nanoindentation

Nanoindentation has been used to characterize the mechanical properties of aerospace-grade Al2024-T351 with and without a clad layer of pure aluminium. The clad layer is introduced by means of a roll-bonding process which can cause significant work-hardening of the material in the clad layer. The hardness and Young’s modulus of the pure aluminium and the Al2024 have been determined by a number of methods, including the traditional Oliver and Pharr method, and a number of other methods, including direct measurement of the indentation by atomic force microscopy, and evaluation of the work of indentation. The Oliver and Pharr method was found to underestimate the area of contact as it did not include the area of piled-up material around the indentation periphery. This gave a corresponding overestimation of both hardness and modulus. The area of the indentation measured by atomic force microscopy was similarly found to underestimate the contact area owing to relaxation of material around the indent between indentation and imaging. The work of indentation approach was found to give good agreement between the hardness calculated by nanoindentation and those found in the literature.     

Characterization of microfabricated probes for combined atomic force and high-resolution scanning electrochemical microscopy

A combined atomic force and scanning electrochemical microscope probe is presented. The probe is electrically insulated except at the very apex of the tip, which has a radius of curvature in the range of 10-15 nm. Steady-state cyclic voltammetry measurements for the reduction of Ru(NH3)6Cl3 and feedback experiments showed a distinct and reproducible response of the electrode. These experimental results agreed with finite element simulations for the corresponding diffusion process. Sequentially topographical and electrochemical studies of Pt lines deposited onto Si3N4 and spaced 100 nm apart (edge to edge) showed a lateral electrochemical resolution of 10 nm.     

A resolution study for electrostatic force microscopy on bimetallic samples using the boundary element method

Electrostatic force microscopy (EFM) is a special design of non-contact atomic force microscopy used for detecting electrostatic interactions between the probe tip and the sample. Its resolution is limited by the finite probe size and the long-range characteristics of electrostatic forces. Therefore, quantitative analysis is crucial to understanding the relationship between the actual local surface potential distribution and the quantities obtained from EFM measurements. To study EFM measurements on bimetallic samples with surface potential inhomogeneities as a special case, we have simulated such measurements using the boundary element method and calculated the force component and force gradient component that would be measured by amplitude modulation (AM) EFM and frequency modulation (FM) EFM, respectively. Such analyses have been performed for inhomogeneities of various shapes and sizes, for different tip-sample separations and tip geometries, for different applied voltages, and for different media (e.g., vacuum or water) in which the experiment is performed. For a sample with a surface potential discontinuity, the FM-EFM resolution expression agrees with the literature; however, the simulation for AM-EFM suggests the existence of an optimal tip radius of curvature in terms of resolution. On the other hand, for samples with strip-?and disk-shaped surface potential inhomogeneities, we have obtained quantitative expressions for the detectability size requirements as a function of experimental conditions for both AM-?and FM-EFMs, which suggest that a larger tip radius of curvature is moderately favored for detecting the presence of such inhomogeneities.     

Direct Probing of Polarization Charge at Nanoscale Level

Ferroelectric materials possess spontaneous polarization that can be used for multiple applications. Owing to a long‐term development of reducing the sizes of devices, the preparation of ferroelectric materials and devices is entering the nanometer‐scale regime. Accordingly, to evaluate the ferroelectricity, there is a need to investigate the polarization charge at the nanoscale. Nonetheless, it is generally accepted that the detection of polarization charges using a conventional conductive atomic force microscopy (CAFM) without a top electrode is not feasible because the nanometer‐scale radius of an atomic force microscopy (AFM) tip yields a very low signal‐to‐noise ratio. However, the detection is unrelated to the radius of an AFM tip and, in fact, a matter of the switched area. In this work, the direct probing of the polarization charge at the nanoscale is demonstrated using the positive‐up‐negative‐down method based on the conventional CAFM approach without additional corrections or circuits to reduce the parasitic capacitance. The polarization charge densities of 73.7 and 119.0 µC cm^?2 are successfully probed in ferroelectric nanocapacitors and thin films, respectively. The obtained results show the feasibility of the evaluation of polarization charge at the nanoscale and provide a new guideline for evaluating the ferroelectricity at the nanoscale.