扫描隧道显微镜和原子力显微镜

介绍了扫描隧道显微镜(STM)和原子力显微镜(AFM)的原理和目前情况。     

新型电化学原子力显微镜的研制

电化学原子力显微镜将电化学分析技术与原子力显微镜结合起来,能对生物传感器,新型电池和电腐蚀进行原位电化学扫描探针显微测量分析。为了实现电化学与扫描探针功能的系统集成,在控制电路设计中采用现场可编程门阵列,提高了系统的可靠性。电化学控制箱与原子力显微镜的头部紧密集成,保证微弱信号不受干扰,并具有多种电化学工作模式。系统具有稳定性好,重复性高,抗干扰能力强等优点。     

原子力显微镜发展近况及其应用

扫描隧道显微镜(简称STM)和原子力显微镜(简称AFM),它们也可统称为扫描探针显微镜(简称SPM)。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。与扫描电子显微镜相比,它具有较高的分辨率。本文将讨论原子力显微镜的工作原理、原子力显微镜的发展概况和应用。     

原子力显微镜矩形测力臂弹性系数计算方法研究

原子力显微镜测力臂弹性系数的准确性直接影响其测量精度,是仪器标定的一个重要指标。分别运用理论计算方法、动态计算方法和静态计算方法计算原子力显微镜测力臂弹性系数。以矩形测力臂为例,对其进行灵敏度分析,找出影响测力臂弹性系数的参数。分别选取矩形测力臂原始参数值及参数上下极限值,构成3组实验数据。利用上述3种计算方法,分别计算出3组不同参数值的矩形测力臂的弹性系数,然后对这3种计算方法计算所得的弹性系数进行分析并和生产商给出的名义值进行比较,所得结果为原子力显微镜矩形测力臂弹性系数的精确计算提供参考。     

卧式原子力显微镜的研制

提出原子力显微镜 (AFM)的新设计 ,讨论卧式 AFM的工作原理及其性能特点 ,简要介绍 AFM的控制电路系统及其图像扫描和图像处理软件系统 ,给出 AFM扫描获得的部分样品的图像结果。     

原子力显微镜力传感器的设计

着重介绍原子力显微镜力传感器的要求和力传感器设计的有关问题，并提供一种用图表设计结构尺寸的方法。     

原子力显微镜成像技巧的探讨

原子力显微镜(Atomic Force Microscopy,AFM)的一个重要应用是对样品表面的微纳米尺寸特征进行成像,在扫描的过程中,实际成像图是原子力探针和样品共同卷积的结果,所以探针的选择、样品的制备直接决定成像质量。本文总结了探针的弹性系数、曲率半径、悬臂镀层对成像的影响,以及制样、装样时可能存在的问题,因此为获得更准确的成像,需要克服样品可能存在的这些问题,并选择适合的探针对其成像。     

一种新颖的点衍射干涉轻敲模式原子力显微镜

论述了一种新颖的原子力显微镜,它利用硅微探针的特殊结构和相关光学系统所引起的点衍射干涉现象[1]来扫描成像,因为硅微探针被用作反射型点衍射板,故光路完全共路,再结合锁相检测技术,使得该仪器抗干扰力极强且结构精巧紧凑,可适用于测试软硬不同材料样品,对软质高分子膜材料检测得到了实际的链状结构。     

原子力显微镜原理与应用技术

本文简述原子力显微镜的工作原理,对比说明敲击模式的优越性,指出针尖-样品卷积效应和假象产生的原因,并例证其应用领域及其测试效果。     

Velocity dependent friction laws in contact mode atomic force microscopy

Friction forces in the tip–sample contact govern the dynamics of contact mode atomic force microscopy. In ambient conditions typical contact radii between tip and sample are in the order of a few nanometers. In order to account for the large interaction area the dynamics of contact mode atomic force microscope (AFM) is investigated under the assumption of a multi-asperity contact interface between tip and sample. Thus, the kinetic friction force between tip and sample is the product of the real contact area between both solids and the interfacial shear strength. The velocity strengthening of the lateral force is modeled assuming a logarithmic relationship between shear-strength and velocity. Numerical simulations of the system dynamics with this empirical model show the existence of two different regimes in contact mode AFM: steady sliding and stick–slip where the tip undergoes periodically stiction and kinetic friction. The state of the system depends on the scan velocity as well as on the velocity dependence of the interfacial friction force between tip and sample. Already small viscous damping contributions in the tip–sample contact are sufficient to suppress stick–slip oscillations.     

Fast contact-mode atomic force microscopy on biological specimen by model-based control

The dynamic behavior of the piezoelectric tube scanner limits the imaging rate in atomic force microscopy (AFM). In order to compensate for the lateral dynamics of the scanning piezo a model based open-loop controller is implemented into a commercial AFM system. Additionally, our new control strategy employing a model-based two-degrees-of-freedom controller improves the performance in the vertical direction, which is important for high-speed topographical imaging. The combination of both controllers in lateral and vertical direction compensates the three-dimensional dynamics of the AFM system and reduces artifacts that are induced by the systems dynamic behavior at high scan rates. We demonstrate this improvement by comparing the performance of the model-based controlled AFM to the uncompensated and standard PI-controlled system when imaging pUC 18 plasmid DNA in air as well as in a liquid environment.     

A symmetrical stretching stage for electrical atomic force microscopy

We present a remotely-controlled device for sample stretching, designed for use with atomic force microscopy (AFM) and providing electrical connection to the sample. Such a device enables nanoscale investigation of electrical properties of thin gold films deposited on polydimethylsiloxane (PDMS) substrate as a function of the elongation of the structure. Stretching and releasing is remotely controlled with use of a dc actuator. Moreover, the sample is stretched symmetrically, which gives an opportunity to perform AFM scans in the same site without a time-consuming finding procedure. Electrical connections to the sample are also provided, enabling Kelvin probe force microscopy (KPFM) investigations. Additionally, we present results of AFM imaging using the stretching stage.     

Comparative study of lithium fluoride and graphite by atomic force microscopy (AFM)

The atomic force microscope (AFM) offers the possibility to image the topography of insulating as well as conductive surfaces. Highly oriented pyrolytic graphite (HOPG) was chosen as an example for a layered material and compared to single crystalline lithium fluoride (LiF). Both materials are easily prepared and inert at ambient pressure. Furthermore they are well characterized by Helium atom scattering experiments and other techniques. On HOPG atomic resolution has been achieved. Distortions can be observed which we interpret as a frictional effect. In addition we performed large area scans where we seldomly observed dislocations. For the first time we present measurements on LiF, showing steps of one unit cell height. On larger areas the surface of LiF showed terraces, separated by steps of variable heights, ranging from a few ångströms to 100 Å. We used a static method to get information about the distance dependence of the force between lever and sample. By slowly expanding and retracting the sample piezo and simultaneous measurement of the lever deflection, plots were recorded, showing the force as a function of sample position. The results were compared with theoretical calculations. We could determine the tip radius and found differences between LiF and HOPG being characteristic for the samples.     

Spectroscopy and atomic force microscopy of biomass

Scanning probe microscopy has emerged as a powerful approach to a broader understanding of the molecular architecture of cell walls, which may shed light on the challenge of efficient cellulosic ethanol production. We have obtained preliminary images of both Populus and switchgrass samples using atomic force microscopy (AFM). The results show distinctive features that are shared by switchgrass and Populus. These features may be attributable to the lignocellulosic cell wall composition, as the collected images exhibit the characteristic macromolecular globule structures attributable to the lignocellulosic systems. Using both AFM and a single case of mode synthesizing atomic force microscopy (MSAFM) to characterize Populus, we obtained images that clearly show the cell wall structure. The results are of importance in providing a better understanding of the characteristic features of both mature cells as well as developing plant cells. In addition, we present spectroscopic investigation of the same samples.     

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。     

Use of atomic force microscopy (AFM) for microfabric study of cohesive soils

Microfabric reflects the imprints of the geologic and stress history of the soil deposit, the depositional environment and weathering history. Many investigators have been concerned with the fundamental problem of how the engineering properties of clay depend on the microfabric, which can be defined as geometric arrangement of particles within the soil mass. It is believed that scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are the only techniques that can reveal particle arrangements of clayey soils directly; however, current research introduces a novel and more advanced technique, atomic force microscopy, to evaluate the microfabric of cohesive materials. The atomic force microscopy has several advantages over SEM/TEM for characterizing cohesive particles at the sub‐micrometre range by providing 3D images and 2D images with Z‐information used in quantitative measurements of soil microfabric using SPIP software, and having the capability of obtaining images in all environments (ambient air, liquids and vacuums). This paper focuses on the use of atomic force microscopy technique to quantify the microfabric of clayey soils by developing the criteria for average and maximum values of angle of particle orientation within the soil mass using proposed empirical equations for intermediate and extreme microfabrics (dispersed, flocculated).     

Phase imaging with intermodulation atomic force microscopy

Intermodulation atomic force microscopy (IMAFM) is a dynamic mode of atomic force microscopy (AFM) with two-tone excitation. The oscillating AFM cantilever in close proximity to a surface experiences the nonlinear tip-sample force which mixes the drive tones and generates new frequency components in the cantilever response known as intermodulation products (IMPs). We present a procedure for extracting the phase at each IMP and demonstrate phase images made by recording this phase while scanning. Amplitude and phase images at intermodulation frequencies exhibit enhanced topographic and material contrast.     

Development and testing of hyperbaric atomic force microscopy (AFM) and fluorescence microscopy for biological applications

A commercially available atomic force microscopy and fluorescence microscope were installed and tested inside a custom-designed hyperbaric chamber to provide the capability to study the effects of hyperbaric gases on biological preparations, including cellular mechanism of oxidative stress. In this report, we list details of installing and testing atomic force microscopy and fluorescence microscopy inside a hyperbaric chamber. The pressure vessel was designed to accommodate a variety of imaging equipment and ensures full functionality at ambient and hyperbaric conditions (≤85 psi). Electrical, gas and fluid lines were installed to enable remote operation of instrumentation under hyperbaric conditions, and to maintain viable biological samples with gas-equilibrated superfusate and/or drugs. Systems were installed for vibration isolation and temperature regulation to maintain atomic force microscopy performance during compression and decompression. Results of atomic force microscopy testing demonstrate sub-nanometre resolution at hyperbaric pressure in dry scans and fluid scans, in both contact mode and tapping mode. Noise levels were less when measurements were taken under hyperbaric pressure with air, helium (He) and nitrogen (N(2) ). Atomic force microscopy and fluorescence microscopy measurements were made on a variety of living cell cultures exposed to hyperbaric gases (He, N(2) , O(2) , air). In summary, atomic force microscopy and fluorescence microscopy were installed and tested for use at hyperbaric pressures and enables the study of cellular and molecular effects of hyperbaric gases and pressure per se in biological preparations.