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1.
The polymer has been proved to be nano machined by a vibrating tip in tapping mode of Atomic Force Microscope (AFM). The force between the tip and the surface is an important factor which determines success of the machining process. Controlling this force with high accuracy is the foundation of nanomachining in AFM tapping mode. To achieve a deeper understanding on this process, the tip is modeled as a driving oscillator with damping. Factors affecting the nano machining process are studied. The Hertz elastic contact theory is used to calculate the maximum contact pressure applied by the tip which is employed as a criterion to judge the deformation state of the sample. The simulation results show that: The driven amplitude can be used as a main parameter of controlling the machined depth. Sharper tips and harder cantilevers should be used for successful nanomachining with the vibrating tip. Under the same conditions, a larger tip radius will not only result in the machining error, but also lead to failure of the nanomachining process. The higher driving frequency will lead to a larger tapping force. However it cannot be used as a parameter to control the machined depth because of its narrow variation range. But it is a main error source for the nanomachining process in AFM tapping mode. Moreover, a larger Young's modulus polymer sample will induce a smaller machined depth, a larger maximum contact pressure and a bigger tapping force.  相似文献   

2.
How to measure energy dissipation in dynamic mode atomic force microscopy   总被引:2,自引:0,他引:2  
When studying a mechanical system like an atomic force microscope (AFM) in dynamic mode it is intuitive and instructive to analyse the forces involved in tip–sample interaction. A different but complementary approach is based on analysing the energy that is dissipated when the tip periodically interacts with the sample surface. This method does not require solving the differential equation of motion for the oscillating cantilever, but is based entirely on the analysis of the energy flow in and out of the dynamic system. Therefore the problem of finding a realistic model to describe the tip–sample interaction in terms of non-linear force–distance dependencies and damping effects is omitted. Instead, it is possible to determine the energy dissipated by the tip–sample interaction directly by measuring such quantities as oscillation amplitude, frequency, phase shift and drive amplitude. The method proved to be important when interpreting phase data obtained in tapping mode, but is also applicable to a variety of scanning probe microscopes operating in different dynamic modes. Additional electronics were designed to allow a direct mapping of local energy dissipation while scanning a sample surface. By applying this technique to the cross-section of a polymer blend a material specific contrast was observed.  相似文献   

3.
A comprehensive model on the dynamics of a tilted tapping mode atomic force microscopy (AFM) is presented, which includes the multimodal analysis, mode coupling mechanisms, adhesion, contact and friction forces induced by the tilting angle. A displacement criterion of contact/impact is proposed to eliminate the assumptions of the previous models such as infinite stiffness of sample or zero impact velocity, which makes the model presented here suitable for more general AFM application scenario, especially for the soft sample case. The AFM tip mass, tip–sample damping, contact forces and intermittent contact can all induce the higher modes participation into the system motion. One degree of freedom or one mode study on the AFM contact dynamics of tapping mode is shown to be inaccurate. The Hertz and Derjaguin–Muller–Toporov models are used for the comparison study of the non-adhesive and adhesive contacts. The intermittent contact and the contact forces are the two major sources of the system nonlinearity. The rich dynamic responses of the system and its sensitivity to the initial conditions are demonstrated by presenting various subharmonic and nonperiodic motions.  相似文献   

4.
根据扫描探针声显微镜(SPAM)轻敲工作模式中探针作周期振动的特点,以及在探针与试样相接触过程中激振力和悬臂探针自由振动的阻尼力很小的假设下,解析求解了探针与试样的碰撞运动方程,得到了最大压痕深度和碰撞时间与探针半径、等效杨氏模量以及界面吸附能等之间的关系式,较直观地说明了SPAM中轻敲模式的相位像反差机理:信号的相位与试样微区的性质、探针振幅、设置点以及试样形貌等有关。并定量预计了纳米金刚石像中的相位差值72.59°,与实验测量平均值73.2°±8.2°一致。同时,合理地解释了实验得到的光学薄膜试样相位像的反差。这些表明SPAM轻敲模式的相位成像是一种纳米分辨率测量材料表面物理性质的成像技术。  相似文献   

5.
In dynamic force microscopy the cantilever of an atomic force microscope is vibrated at ultrasonic frequencies in the range of several 10 kHz up to several MHz while scanning a sample surface. The amplitude and phase of the cantilever vibration as well as the shift of the cantilever resonance frequencies provide information about local sample surface properties. In several operation modes of dynamic force microscopy, for example force modulation microscopy, tapping mode or atomic force acoustic microscopy, the sensor tip is in contact with the sample at least during a fraction of its vibration cycle. The periodic indentation of the tip with the sample surface generates ultrasonic waves. In this paper, the ultrasonic radiation of a vibrating cantilever into a sample and its contribution to the damping of the cantilever vibration are calculated. The theoretical results are compared to experiments.  相似文献   

6.
Near-field Scanning Optical Microscopy (NSOM) in liquid environment is expected to allow time resolved morphological mappings on cellular surfaces on the nanoscale level. Near-field Optical Analysis (NOA) via NSOM exploits the energy transfer from the tip of an optical element (tip diameter > or = 20nm), oscillating within the range of the characteristic length of the energy transfer ( approximately 10nm) in the near-field of the surface to be analysed. In NOA, a molecular assembly is monitored by visible light with a resolution far below the wavelength of visible light. Actually, NOA is successfully applied in mapping local optical contrasts, for instance in photonic crystals with dielectric periodicities on the nanoscale. NSOM could in principle be performed in two different modes: tapping mode, with tip-oscillations perpendicular, or shear force mode, with tip-oscillations parallel to the substrate. Both basic modes have specific advantages and disadvantages. In biological systems (e.g. in cell cultures), where scanning in liquids is prevalent, elongated optical elements non-invasively operated in the shear force modus could have some specific advantages when compared to contact modus systems. While tapping mode NSOM provides satisfactory nanoscale images even on solid surfaces covered with millimetres of liquids, the performance of shear force mode NSOM is presently largely confined to operations on dry samples. This is due to the inability of conventional shear force mode NSOM systems to provide sharp topographic images of sample surfaces substantially covered with liquids. By equipping a conventional NSOM system with hydrophobic optical elements, shear force mode based topographic images could be obtained on biological samples in dry as well as in aqueous environment, and with resolutions on the nanoscale level.  相似文献   

7.
More and more AFMs and AFM profilers will be used to quantify micro- and nanostructures. For a correct characterization and evaluation of the measured structural details, in the nanoscale range, knowledge of the current shape of the AFM tip is needed. Often, the interaction between the AFM tip and the sample leads to a change in the tip shape. Our concept for the determination of tip shapes is based on the measurement of a well-known sharp-edged silicon structure. Each calibration sample contains a selected structure serving as a calibrated width standard, and has a certified pitch. Consequently, the shape of AFM tips can be determined with an accuracy of 10 nm. Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-3641/206-199, E-mail: huebner@ipht-jena.de  相似文献   

8.
Considering that capillary force is one of the most important forces between nanoparticles and atomic force microscope (AFM) tips in ambient atmosphere, we develop an analytic approach on the capillary force between an AFM tip and a nanoparticle. The results show that the capillary forces are considerably affected by the geometry of the AFM tip, the humidity of the environment, the vertical distance between the AFM tip and the nanoparticle, as well as the contact angles of the meniscus with an AFM tip and a nanoparticle. It is found that the sharper the AFM tip, the smaller the capillary force. The analyses and results are expected to be helpful for the quantitative imaging and manipulating of nanoparticles by AFMs.  相似文献   

9.
李渊  钱建强  李英姿 《中国物理 B》2010,19(5):50701-050701
The periodic impact force induced by tip-sample contact in a tapping mode atomic force microscope(AFM) gives rise to the non-harmonic response of a micro-cantilever.These non-harmonic signals contain the full characteristics of tip-sample interaction.A complete theoretical model describing the dynamical behaviour of tip-sample system was developed in this paper.An analytic formula was introduced to describe the relationship between time-varying tip-sample impact force and tip motion.The theoretical analysis and numerical results both show that the timevarying tip-sample impact force can be reconstructed by recording tip motion.This allows for the reconstruction of the characteristics of the tip-sample force,like contact time and maximum contact force.It can also explain the ability of AFM higher harmonics imaging in mapping stiffness and surface energy variations.  相似文献   

10.
An analytical solution of the vibration responses of biological specimens using atomic force microscopy (AFM), which often requires operation in a liquid, is developed. In this study, the modal superposition method is employed to analyze the vibration responses of AFM cantilevers in tapping mode (TM) operated in a liquid and in air. The hydrodynamic force exerted by the fluid on AFM cantilevers is approximated by additional mass and hydrodynamic damping. The tip–sample interaction forces were transformed into axial, distributed transversal, and bending loading, and then applied to the end region of the AFM through the tip holder. The effects of transverse stress and bending stress were adopted to solve the dynamic model. With this model, a number of simulations were carried out to investigate the relationship between the transient responses of the cantilever in a liquid and the parameters considered in nanoscale processing. The simulations show that the vibration of AFM cantilevers in a liquid has dramatically different dynamic characteristics from these of that in air. The liquid reduces the magnitude of the transversal response and reduces the cantilever resonances. Moreover, the magnitudes of response become larger with increasing intermolecular distances and smaller with decreasing tip length. The cantilever vibration amplitudes significantly depend on the damping constant and the mass proportionality constant.  相似文献   

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