Inducing dendrite formation using an atomic force microscope tip

Atomic force microscope (AFM) tip-induced nucleation, and dendrite growth of vapor deposited PETN films on Si (100) have been investigated at room temperature. The AFM tip induces a change from smooth and flat morphology to islands and dendrites, which is owing to the lowering and vanishing of 2-D nucleation barrier at the tip contact area; this action gives rise to the formation of large islands in the scanned area and dendrite growth along the scanning boundary.     

Guiding self-assembly with the tip of an atomic force microscope

We report the guided self-assembly of nanoparticles to geometrically well-defined charge patterns written on a dielectric surface with the conductive tip of an atomic force microscope (AFM). Charges are deposited in 30-90-nm thick fluorocarbon layers by applying voltage pulses to the conductive AFM tip. The samples are being developed by dipping them into an organic suspension of silica nanoparticles. Coulomb forces draw the nanoparticles to the charge patterns. With this simple process, we achieve a resolution of about 800 nm.     

Influence of the atomic force microscope tip on the multifractal analysis of rough surfaces

In this paper, the influence of atomic force microscope tip on the multifractal analysis of rough surfaces is discussed. This analysis is based on two methods, i.e. on the correlation function method and the wavelet transform modulus maxima method. The principles of both methods are briefly described. Both methods are applied to simulated rough surfaces (simulation is performed by the spectral synthesis method). It is shown that the finite dimensions of the microscope tip misrepresent the values of the quantities expressing the multifractal analysis of rough surfaces within both the methods. Thus, it was concretely shown that the influence of the finite dimensions of the microscope tip changed mono-fractal properties of simulated rough surface to multifractal ones. Further, it is shown that a surface reconstruction method developed for removing the negative influence of the microscope tip does not improve the results obtained in a substantial way. The theoretical procedures concerning both the methods, i.e. the correlation function method and the wavelet transform modulus maxima method, are illustrated for the multifractal analysis of randomly rough gallium arsenide surfaces prepared by means of the thermal oxidation of smooth gallium arsenide surfaces and subsequent dissolution of the oxide films.     

Low temperature ultrahigh vacuum noncontact atomic force microscope in the pendulum geometry

A noncontact atomic force microscope (nc-AFM) operating in magnetic fields up to ±7 T and liquid helium temperatures is presented in this article. In many common AFM experiments the cantilever is mounted parallel to the sample surface, while in our system the cantilever is assembled perpendicular to it; the so called pendulum mode of AFM operation. In this mode measurements employing very soft and, therefore, ultrasensitive cantilevers can be performed. The ultrahigh vacuum conditions allow to prepare and transfer cantilevers and samples in a requested manner avoiding surface contamination. We demonstrate the possibility of nc-AFM and Kelvin force probe microscopy imaging in the pendulum mode. Ultrasensitive experiments on small spin ensembles are presented as well.     

Wear characterisation of articular cartilage surfaces at a nano-scale using atomic force microscopy

Osteoarthritis originates and progresses with changes in surface topographies and mechanical properties of cartilage. This study was aimed to characterise cartilage surface topography and its changes with wear progression at a nano-scale. Cartilage samples were generated in wear tests. Three dimensional (3D) cartilage surface data was obtained using atomic force microscopy (AFM) and then quantitatively characterised using both conventional and feature parameters. The results have given a new insight to the wear process which could not be achieved previously.     

3D mechanical measurements with an atomic force microscope on 1D structures

We have developed a simple method to characterize the mechanical properties of three dimensional nanostructures, such as nanorods standing up from a substrate. With an atomic force microscope the cantilever probe is used to deflect a horizontally aligned nanorod at different positions along the nanorod, using the apex of the cantilever itself rather than the tip normally used for probing surfaces. This enables accurate determination of nanostructures' spring constant. From these measurements, Young's modulus is found on many individual nanorods with different geometrical and material structures in a short time. Based on this method Young's modulus of carbon nanofibers and epitaxial grown III-V nanowires has been determined.     

Design of mechanical components for vibration reduction in an atomic force microscope

Vibration is a key factor to be considered when designing the mechanical components of a high precision and high speed atomic force microscope (AFM). It is required to design the mechanical components so that they have resonant frequencies higher than the external and internal vibration frequencies. In this work, the mechanical vibration in a conventional AFM system is analyzed by considering its mechanical components, and a vibration reduction is then achieved by reconfiguring the mechanical components. To analyze the mechanical vibration, a schematic of the lumped model of the AFM system is derived and the vibrational influences of the AFM components are experimentally examined. Based on this vibration analysis, a reconfigured AFM system is proposed and its effects are compared to a conventional system through a series of simulations and experiments.     

A tensile test device for in situ atomic force microscope mechanical testing

The microstructure and mechanical behavior of polymeric-based materials can be controlled at the micro- and nanometer length scales through blending, copolymerization, and the incorporation of micro- and nanometer particles. To facilitate the study of morphology, deformation mechanisms, and mechanical properties of micro- and nanocomposite materials, a tensile testing machine with an integral commercial atomic force microscope (AFM) was designed and built. This testing machine determines the macroscopic stress–strain behavior of materials under different controlled loading conditions, and simultaneously allows the microscopic structure changes to be observed using the AFM.     

原子力显微镜在聚合物研究中的应用

原子力显微镜以其分辨率高、样品无需特殊制备、实验可在大气环境中进行等优点而广泛应用于聚合物研究之中,弥补扫描隧道显微镜不能观测非导电样品的缺憾。近年来,其应用已由对聚合物表面几何形貌的观测发展到纳米级结构和表面性能的研究领域。在介绍原子力显微镜工作原理的基础上,简要回顾其在聚合物研究方面的若干新应用,并对其应用前景作展望。     

Nanometer-scale layer modification of polycarbonate surface by scratching with tip oscillation using an atomic force microscope

This paper presents a simple and reliable technique for nanometer-scale layer modification of a polycarbonate (PC) surface using an atomic force microscope (AFM). The AFM tip, coated with amorphous carbon was made to oscillate vertically at its resonance frequency. With tip oscillating in tapping mode, it scan-scratched the PC surface to make the desired modification. This action carved the PC surface without distorting it. The bottom of the depression made by scan-scratching with the oscillating tip was obviously flat in comparison with the area scan-scratched without tip oscillation in contact mode. The depth of the scan-scratched depression was controlled by adjusting the amplitude of oscillation and the scanning speed of scratching. This technique is very interesting for microtribology and surface modification.     

Fabrication of ionic liquid thin film by nano-inkjet printing method using atomic force microscope cantilever tip

We demonstrate the fabrication of thin films of ionic liquid (IL), 1-butyl-3-methyl-imidazolium tetrafluoborate, by nano-inkjet printing method using an atomic force microscope (AFM) cantilever. The IL filled in a pyramidal hollow of the AFM cantilever tip was extracted from an aperture at the bottom of the hollow and deposited onto a Pt substrate when the bias voltage was applied between the cantilever and the substrate. We succeeded in fabricating IL thin films with a thickness of 4 nm. The areas and thicknesses of IL thin films were controlled by the fabrication conditions in this method, which is also useful for the investigations of nanometer-scale properties of ionic liquid.     

Effect of tip shape on line edge roughness measurement based on atomic force microscopy

Atomic force microscopy (AFM) is an important tool in line edge roughness (LER) measurements, where accuracy for line edge identification is influenced by the shape of the tip. In this article, the effect of tip shape on LER measurement based on AFM is studied theoretically. The formulas for calculating the distance between the measured and actual line edge of the sample are presented. The effects of the three kinds of tips with different shapes are experimentally compared for validation. Suggestions on how to reduce measuring error caused by tip shape are also given.     

原子力显微镜测量高分子纳米材料力学性能探针选择的研究

以高分子单晶为测试样本,主要研究了利用原子力显微镜(AFM)对高分子纳米材料进行力学性能测试时样本的厚度和探针的弹性系数(k)对其测试结果的影响。结果表明测试的样本厚度比较低时测试结果受基底影响较大;在样本确定足够厚度的前提下,探针采用k值过小的探针得到的测试值偏低,采用合适k值的探针才能得到较接近真实值得测试结果。     

无线控制式原子力显微镜系统

提出了一种基于嵌入式系统和WiFi无线控制的接触模式原子力显微镜(AFM)系统。该AFM系统直接由迷你型移动电源给扫描与反馈电路及嵌入式系统等供电;嵌入式系统由微型电脑树莓派和微小型ADDA模块构成,通过WiFi与笔记本电脑实现无线数据通信。利用这一方法,成功研发了无线控制式AFM系统,并开展了微纳米样品的扫描成像实验。实验结果表明,该AFM系统的横向分辨率达到纳米量级,纵向分辨率达到0.1nm,最大扫描范围为3.6μm×3.6μm。该系统的显著特点是无需交流市电供电,无需直流高压电源,也无需与计算机之间的线缆连接,可在约100m远处通过无线控制的方式实现AFM的扫描成像。这一新型AFM系统,不仅能够在微纳米技术的常规领域得到应用,而且在野外考察、隔离环境、真空条件、气体氛围环境及星际探测等特殊领域具有广阔的应用前景。     

原子力显微镜的力曲线分析与转化

原子力显微镜测定的力曲线需转化为力位移曲线来应用.力位移曲线是以任意点为零点的,当研究粘附或者分子模型对比时,需要知道针尖样品间的作用力或确切的零点位置,这时需将其转化为力-距离曲线.本文首先从力曲线的测定原理得出了典型的力曲线,之后从理论上分析了力曲线、力位移曲线和力-距离曲线间的转化,从中得出了转化过程中需要的两个重要参量:灵敏度和零距离,并提出了确定方法.最后,利用MATLAB实现了曲线的自动转化.     

The comparison between force volume and peakforce quantitative nanomechanical mode of atomic force microscope in detecting cell's mechanical properties

Atomic force microscope (AFM) has been widely used in the biological field owing to its high sensitivity (subnanonewton), high spatial resolution (nanometer), and adaptability to physiological environments. Nowadays, force volume (FV) and peakforce quantitative nanomechanical (QNM) are two distinct modes of AFM used in biomechanical research. However, numerous studies have revealed an extremely confusing phenomenon that FV mode has a significant difference with QNM in determining the mechanical properties of the same samples. In this article, for the case of human benign prostatic hyperplasia cells (BPH) and two cancerous prostate cells with different grades of malignancy (PC3 and DU145), the differences were compared between FV and QNM modes in detecting mechanical properties. The results show measured Young's modulus of the same cells in FV mode was much lower than that obtained by QNM mode. Combining experimental results with working principles of two modes, it is indicated that surface adhesion is highly suspected to be a critical factor resulting in the measurement difference between two modes. To further confirm this conjecture, various weight ratios of polydimethylsiloxane (PDMS) were assessed by two modes, respectively. The results show that the difference of Young's modulus measured by two modes increases with the surface adhesion of PDMS, confirming that adhesion is one of the significant elements that lead to the measurement difference between FV and QNM modes.     

Refined tip preparation by electrochemical etching and ultrahigh vacuum treatment to obtain atomically sharp tips for scanning tunneling microscope and atomic force microscope

A modification of the common electrochemical etching setup is presented. The described method reproducibly yields sharp tungsten tips for usage in the scanning tunneling microscope and tuning fork atomic force microscope. In situ treatment under ultrahigh vacuum (p ≤10(-10) mbar) conditions for cleaning and fine sharpening with minimal blunting is described. The structure of the microscopic apex of these tips is atomically resolved with field ion microscopy and cross checked with field emission.     

Traceable atomic force microscope based on monochromatic light interference

Atomic force microscope (AFM) is widely applied to the measurement of the micro-nano structures due to its three-dimensional spatial resolution of sub-nanometer. However, the height measurement traceability in the z-axis is complex to be implemented in conventional AFMs. In this paper, a traceable AFM is developed based on the monochromatic light interference (MLI) principle without probe calibration. The height change of the AFM's probe is directly detected by extracting the phase change of the MLI fringes on the probe tip with the Hilbert transform based phase extraction algorithm, and the three-dimensional surface topography is reconstructed with a surface recovery algorithm. The configuration of tracing to the wavelength of the monochromatic light in real-time further improves the measurement accuracy of the MLI-AFM. A prototype MLI-AFM is established to demonstrate its measurement accuracy enhancement.     

Surface charges and adhesion measured by atomic force microscope influence on friction force

A good correlation has been found between friction force measured using a ball-on-disc tribometer (normal load 200 mN) and adhesion hysteresis measured by atomic force microscopy. Both adhesion and friction forces were investigated in liquid media (water, ethanol, formamide, ethylene glycol) and involved interactions between silicon nitride and several materials (Si(1 0 0), Si(1 1 1), silica glass, DLC and TiN coatings). Despite the difference between the two scales of measurement, comparison between the measured friction force and the dissipated energy during the adhesion process has shown that the two quantities follow the same trend. Additional experiments were conducted in NaCl 10⁻³ M at various pH values in order to investigate surface charge effect on adhesion and friction.