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。     

原子力显微镜测量杨木细胞特征参数

在微/纳米尺度下原子力显微镜已成为研究木质材料的重要工具。本文基于原子力显微镜对速生杨木细胞的特征参数进行测量。结果表明:利用原子力显微镜,完全可以在微/纳米尺度下对速生杨木的细胞形态特征进行测量;杨木细胞横截面的导管壁厚平均尺寸为2.230 μ m;木纤维壁厚平均为2.044 μ m,壁长平均为9.498μm;细胞外径平均为19.723 μ m。     

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.     

Quantification of the lateral detachment force for bacterial cells using atomic force microscope and centrifugation

To determine the lateral detachment force for individual bacterial cells, a quantitative method using the contact mode of an atomic force microscope (AFM) was developed in this study. Three key factors for the proposed method, i.e. scan size, scan rate and cantilever choice, were evaluated and optimized. The scan size of 40×40 μm² was optimal for capturing sufficient number of adhered cells in a microscopic field and provide adequate information for cell identification and detachment force measurement. The scan rate affected the measurement results significantly, and was optimized at 40 μm/s considering both force measurement accuracy and experimental efficiency. The hardness of applied cantilevers also influenced force determination. The proposed protocol for cantilever selection is to use those with the lowest spring constant first and then step up to a harder cantilever until all cells are detached. The lateral detachment force of Escherichia coli cells on polished stainless steel and a glass-slide coated with poly-l-lysine were measured as 0.763±0.167 and 0.639±0.136 nN, respectively. The results showed that the established method had good repeatability and sensitivity to various bacteria/substrata combinations. The detachment force quantified by AFM (0.639±0.136 nN) was comparable to that measured by the centrifugation method (1.12 nN).     

Nanotribological characterization of digital micromirror devices using an atomic force microscope

Texas Instruments’ digital micromirror device (DMD) comprises an array of fast digital micromirrors, monolithically integrated onto and controlled by an underlying silicon memory chip. The DMD is one of the few success stories in the emerging field of MEMS. In this study, an atomic force microscope (AFM) has been used to characterize the nanotribological properties of the elements of the DMD. An AFM methodology was developed to identify and remove micromirrors of interest. The surface roughness, adhesion, friction, and stiffness properties of the DMD elements were studied. The influence of relative humidity and temperature on the behavior of the DMD element surfaces was also investigated. Potential mechanisms for wear and stiction are discussed in light of the findings.     

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.     

Investigation of penetration force of living cell using an atomic force microscope

Recently, the manipulation of a single cell has been receiving much attention in transgenesis, in-vitro fertilization, individual cell based diagnosis, and pharmaceutical applications. As these techniques require precise injection and manipulation of cells, issues related to penetration force arise. In this work the penetration force of living cell was studied using an atomic force microscope (AFM). L929, HeLa, 4T1, and TA3 HA II cells were used for the experiments. The results showed that the penetration force was in the range of 2∼22 nN. It was also found that location of cell penetration and stiffness of the AFM cantilever affected the penetration force significantly. Furthermore, double penetration events could be detected, due to the multi-membrane layers of the cell. The findings of this work are expected to aid in the development of precision micro-medical instruments for cell manipulation and treatment. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.recommended for publication in revised form by Associate Editor Keum-Sik Hong Eun-Young Kwon received her B.S. and M.S degrees in Mechanical Engineering from Yonsei University, Korea, in 2005 and 2007, respectively. Ms. Kwon is currently an Engineer at Digital Printing Division of Samsung Electronics. Her research interests include biotribology, tribology, and electrophotography. Young-Tae Kim received his B.S. in Automotive Engineering from Seoul National University of Technology, Korea, in 2003. He then received his M.S. degree from Yonsei University in Seoul, Korea in 2005. Mr. Kim is currently a Ph. D. candidate at the Graduate School of Mechanical Engineering at Yonsei University in Seoul, Korea. His research interests include biotribology, tribology, and biomechanics. Dae-Eun Kim received his B.S. in Mechanical Engineering from Tufts University, USA, in 1984. He then received his M.S. and Ph.D. degrees from M.I.T. in 1986 and 1991, respectively. Dr. Kim is currently a Professor at the School of Mechanical Engi-neering at Yonsei University in Seoul, Korea. His research interests include tribology, functional surfaces, and micromachining.     

原子力显微镜在生物医学中的应用

原子力显微镜 (AFM)是近十几年来表面成像技术中最重要的进展之一。它具有非常高的分辨率。本文将阐述原子力显微镜的工作原理 ,分析原子力显微镜在生物医学中的应用现状 ,包括生物医学样品的表面形貌观测 ,在液体中的观测 ,生物分子之间力谱曲线的观测 ,以及生物医学样品制备技术等。     

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.     

Surface profile measurement of a sinusoidal grid using an atomic force microscope on a diamond turning machine

This paper describes the surface profile measurement of a XY-grid workpiece with sinusoidal microstructures using an atomic force microscope (AFM) on a diamond turning machine. The sinusoidal micro-structures, which are fabricated on an aluminum plate by fast tool servo-assisted diamond turning, are a superposition of periodic sine-waves along the X- and Y-directions (wavelength (XY): 150 μm, amplitude (Z): 0.25 μm). A linear encoder with a resolution of 0.5 nm is integrated into the AFM-head for accurate measurement of the Z-directional profile height in the presence of noise associated with the diamond turning machine. The spindle and the X-slide of the machine are employed to spirally scan the AFM-head over the sinusoidal grid workpiece. Experiments fabricating and measuring the sinusoidal grid workpiece are carried out after accurate alignment of the AFM cantilever tip with the spindle centerline.     

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.     

Optimizing AC-mode atomic force microscope imaging

We have operated an atomic force microscope in ambient air with several oscillating cantilever modes to establish the optimal scanning parameters to maximize image resolution and to minimize probe and sample damage. This was done by scanning a surface in air and correlating scan parameters such as oscillation amplitude and damping with image resolution. We also examined the geometry of the probe with a scanning electron microscope, before and after scanning, in order to determine whether the scanning technique had an effect on the geometry of the probe tip. If the probe is oscillated such that it contacts the surface on each oscillation, substantial damage or “wear” to the probe occurs and significant degradation of image quality was observed. In ambient air, the optimal conditions are achieved when the probe penetrates the contamination layer and reverses direction before touching the surface. Under these “near-contact” conditions no probe damage is observed and high-image resolution can be maintained indefinitely.     

A new model for investigating the flexural vibration of an atomic force microscope cantilever

A new model for the flexural vibration of an atomic force microscope cantilever is proposed, and a closed-form expression is derived. The effects of angle, damping and tip moment of inertia on the resonant frequency were analysed. Because the tip is not exactly located at one end of the cantilever, the cantilever is modelled as two beams. The results show that the frequency first increases with increase in angle and then decreases to a constant value for high values of the angle. Moreover, the damping is increased at lower contact positions. The tip moment of inertia is also sensitive to the resonant frequency at small values for the odd modes and large values for the even modes.     

Processing outcomes of atomic force microscope tip-based nanomilling with different trajectories on single-crystal silicon

Atomic force microscope (AFM) tip-based nanomilling is an emerging technology for machining nanostructures with a high rate of material removal and slight tip wear. However, subsurface damage induced by nanomilling is poorly understood. In this study, we investigated nanomilling-induced subsurface damage of single-crystal silicon experimentally and with molecular dynamics simulations. We studied the effect of clockwise and anticlockwise trajectories on the nanochannel morphology. The clockwise trajectory resulted in a ‘U’-shaped nanochannel at a relatively low normal load. Transmission electron microscopy and Raman spectroscopy analysis of the nanochannel subsurface revealed atomic-scale defects, including dislocations, stacking faults, and amorphous silicon. Molecular dynamics simulations described the evolution of the phase transformation and subsurface damage. This work reveals the mechanism of subsurface damage of single-crystal silicon in nanomilling, which will facilitate the machining of nanostructures with minimal subsurface damage.     

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.     

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.     

Nanodissection and noncontact imaging of plasmid DNA with an atomic force microscope

In this paper we report that a combination of noncontact and contact atomic force microscopy is a convenient and reliable method for imaging and dissecting single plasmid deoxyribonucleic acid (DNA) strands on mica at ambient conditions without leaving feedback and without damage to the scanning tips. The width and thickness measured at different points of the DNA strands agree with literature data and are the same before and after dissection.     

Intermittency in amplitude modulated dynamic atomic force microscopy

From a mathematical point of view, the atomic force microscope (AFM) belongs to a special class of continuous time dynamical systems with intermittent impact collisions. Discontinuities of the velocity result from the collisions of the tip with the surface. Transition to chaos in non-linear systems can occur via the following four routes: bifurcation cascade, crisis, quasi-periodicity, and intermittency. For the AFM period doubling and period-adding cascades are well established. Other routes into chaos, however, also may play an important role. Time series data of a dynamic AFM experiment indicates a chaotic mode that is related to the intermittency route into chaos. The observed intermittency is characterized as a type III intermittency. Understanding the dynamics of the system will help improve the overall system performance by keeping the operation parameters of dynamic AFM in a range, where chaos can be avoided or at least controlled.     

Investigation of the morphological and fractal behavior at nanoscale of patterning lines by scratching in an atomic force microscope

In this work, the topographical effect of the scratching trajectory and the feed direction on the formation of lithographed lines on the (001) InP surface was investigated using an atomic force microscope (AFM) tip-based nanomachining approach. Nanoscratching tests were carried out using the sharp face of a diamond AFM tip in contact mode. From the topographic maps obtained by AFM, several morphological and fractal parameters were obtained and analyzed. Surface morphology presented a surface smoothing for surfaces with scratches produced in [011] and [001] directions. The height parameters confirmed this behavior because scratches in [001] direction exhibited lower roughness. Moreover, this scratch direction promoted the height distribution most symmetrical and platykurtic. The other morphological parameters revealed that this direction provided a more irregular surface (smaller S_mc and S_xp), peak distribution, denser and pointed, smaller portion of material in the core, less deep furrows, higher spatial frequency components, and high isotropy. Fractal parameters revealed that FRE90 has the highest spatial complexity, it is dominated by higher spatial frequencies, and has the lowest surface percolation. Furthermore, all samples exhibited high topographic uniformity.     

Manipulation, dissection, and lithography using modified tapping mode atomic force microscope

A modified tapping mode of the atomic force microscope (AFM) was introduced for manipulation, dissection, and lithography. By sufficiently decreasing the amplitude of AFM tip in the normal tapping mode and adjusting the setpoint, the tip-sample interaction can be efficiently controlled. This modified tapping mode has some characteristics of the AFM contact mode and can be used to manipulate nanoparticles, dissect biomolecules, and make lithographs on various surfaces. This method did not need any additional equipment and it can be applied to any AFM system.