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.     

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.     

Ferrule-top atomic force microscope

Ferrule-top cantilevers are a new generation of all-optical miniaturized devices for utilization in liquids, harsh environments, and small volumes [G. Gruca et al., Meas. Sci. Technol. 21, 094033 (2010)]. They are obtained by carving the end of a ferruled fiber in the form of a mechanical beam. Light coupled from the opposite side of the fiber allows detection of cantilever deflections. In this paper, we demonstrate that ferrule-top cantilevers can be used to develop ultra compact AFMs for contact mode imaging in air and in liquids with sensitivity comparable to that of commercial AFMs. The probes do not require any alignment procedure and are easy to handle, favoring applications also outside research laboratories.     

High-resolution microscope for tip-enhanced optical processes in ultrahigh vacuum

An optical microscope based on tip-enhanced optical processes that can be used for studies on adsorbates as well as thin layers and nanostructures is presented. The microscope provides chemical and topographic informations with a resolution of a few nanometers and can be employed in ultrahigh vacuum as well as gas phase. The construction involves a number of improvements compared to conventional instruments. The central idea is to mount, within an UHV system, an optical platform with all necessary optical elements to a rigid frame that also carries the scanning tunneling microscope unit and to integrate a high numerical aperture parabolic mirror between the scanning probe microscope head and the sample. The parabolic mirror serves to focus the incident light and to collect a large fraction of the scattered light. The first experimental results of Raman measurements on silicon samples as well as brilliant cresyl blue layers on single crystalline gold and platinum surfaces in ultrahigh vacuum are presented. For dye adsorbates a Raman enhancement of approximately 10(6) and a net signal gain of up to 4000 was observed. The focus diameter ( approximately lambda2) was measured by Raman imaging the focal region on a Si surface. The requirements of the parabolic mirror in terms of alignment accuracy were experimentally determined as well.     

An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging

We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8 x 8 microm(2). The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area.     

Print your atomic force microscope

Progress in scanning probe microscopy profited from a flourishing multitude of new instrument designs, which lead to novel imaging modes and as a consequence to innovative microscopes. Often these designs were hampered by the restrictions, which conventional milling techniques impose. Modern rapid prototyping techniques, where layer by layer is added to the growing piece either by light driven polymerization or by three-dimensional printing techniques, overcome this constraint, allowing highly concave or even embedded and entangled structures. We have employed such a technique to manufacture an atomic force microscopy (AFM) head, and we compared its performance with a copy milled from aluminum. We tested both AFM heads for single molecule force spectroscopy applications and found little to no difference in the signal-to-noise ratio as well as in the thermal drift. The lower E modulus seems to be compensated by higher damping making this material well suited for low noise and low drift applications. Printing an AFM thus offers unparalleled freedom in the design and the rapid production of application-tailored custom instruments.     

Lateral force microscope calibration using a modified atomic force microscope cantilever

A proof-of-concept study is presented for a prototype atomic force microscope (AFM) cantilever and associated calibration procedure that provide a path for quantitative friction measurement using a lateral force microscope (LFM). The calibration procedure is based on the method proposed by Feiler et al. [Rev. Sci. Instrum. 71, 2746 (2000)] but allows for calibration and friction measurements to be carried out in situ and with greater precision. The modified AFM cantilever is equipped with lateral lever arms that facilitate the application of normal and lateral forces, comparable to those acting in a typical LFM friction experiment. The technique allows the user to select acceptable precision via a potentially unlimited number of calibration measurements across the full working range of the LFM photodetector. A microfabricated version of the cantilever would be compatible with typical commercial AFM instrumentation and allow for common AFM techniques such as topography imaging and other surface force measurements to be performed.     

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.     

多模态动态原子力显微镜系统

动态原子力显微镜(atomic force microscope,AFM)是通过检测悬臂谐振状态的变化来对物体表面形貌进行测量的。通过对谐振状态的三种因素即振幅、相位、频率的检测,动态AFM可以分为三种工作模式,即振幅反馈、相位反馈与频率反馈模式,这三种反馈模式有着不同的扫描特点。基于硅悬臂具有高阶谐振的特性,动态原子力显微镜可以在悬臂工作于高阶谐振状态时对物体进行扫描。综合上述工作模式研制了一套多模态动态AFM,可以在三种反馈模式、不同阶谐振状态下对物体进行扫描测量。利用该系统在不同反馈模式、不同阶谐振状态下进行了扫描测试,结果显示,系统在各模式下具有亚纳米分辨力,其中在相位反馈模式,悬臂二阶谐振时可达到最优灵敏度与分辨力,分别为17.5V/μm和0.29nm,在最优灵敏度与分辨力状态下对光栅试样进行了三维扫描,得到光栅的三维形貌图。     

Stick–slip motion in the atomic force microscope

Measurements of atomic friction in the atomic force microscope frequently show periodic variations at the lattice spacing of the surface being scanned, which have the saw‐tooth wave form characteristic of “stick–slip” motion. Simple models of this behaviour have been proposed, in which the “dynamic element” of the system is provided by the elastic stiffness and inertia of the cantilever which supports the tip of the microscope, in its lateral, i.e., torsional mode of vibration. These models have been successful in predicting the observed motion, but only by assuming that the cantilever is heavily damped. However, the source of this damping in a highly elastic cantilever is not explained. To resolve the paradox, it is shown in this note that it is necessary to introduce the elastic stiffness of the contact into the model. The relationship between the contact stiffness, the cantilever stiffness and the amplitude of the periodic friction force is derived in order for stick–slip motion at lattice spacing to be achieved. This revised version was published online in July 2006 with corrections to the Cover Date.     

计量型原子力显微镜的位移测量系统(英文)

针对纳米结构表征和纳米制造的质量控制需要,中国计量科学研究院设计并搭建了一台计量型原子力显微镜用于纳米几何结构的测量.为了将位移精确溯源到国际单位米,研制了单频8倍程干涉仪测量位移,样品表面形貌则由接触式原子力显微镜测量.一个立方体反射镜与原子力显微镜的测头固定,作为干涉仪的参考镜.两个互相垂直的干涉仪用于测量样品与探针在x-y方向的相对位置.样品台置于具有三面反射镜的零膨胀玻璃块上,由压电陶瓷位移台驱动.另外两台干涉仪测量样品与探针在z方向的位移,探针针尖位于干涉仪光束的交点以减小Abbe误差.由于光学器件的缺陷产生的相位混合会引起非线性误差,采用谐波分离法拟合干涉信号来修正误差,修正后干涉仪测量误差减小为0.7 nm.     

原子力显微镜在液相环境中的应用研究

简要介绍了原子力显微镜的工作原理 ,着重分析了液相探头的设计 ,并利用该探头进行了液相环境的样品表面形貌测量 ,给出了测量的图像。实验表明 ,该液相探头具有良好的液态环境扫描性能 ,图像稳定 ,分辨力高。     

Environmental chamber for an atomic force microscope

A commercial atomic force microscope (AFM), originally designed for operation in ambient conditions, was placed inside a compact aluminum chamber, which can be pumped down to high vacuum levels or filled with a desired gaseous atmosphere, including humidity, up to normal pressure. The design of this environmental AFM is such that minimal intrusion is made to the original setup, which can be restored easily. The performance inside the environmental chamber is similar to the original version.     

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。     

Dynamic behavior of amplitude detection Kelvin force microscopy in ultrahigh vacuum

The acquisition rate of all scanning probe imaging techniques with feedback control is limited by the dynamic response of the control loops. Performance criteria are the control loop bandwidth and the output signal noise power spectral density. Depending on the acceptable noise level, it may be necessary to reduce the sampling frequency below the bandwidth of the control loop. In this work, the frequency response of a vacuum Kelvin force microscope with amplitude detection (AM-KFM) using a digital signal processing (DSP) controller is characterized and optimized. Then, the main noise source and its impact on the output signal is identified. A discussion follows on how the system design can be optimized with respect to output noise. Furthermore, the interaction between Kelvin and distance control loop is studied, confirming the beneficial effect of KFM on topography artefact reduction in the frequency domain. The experimental procedure described here can be generalized to other systems and allows to locate the performance limitations.     

Visualization of cytoskeletal elements by the atomic force microscope

We describe a novel application of atomic force microscopy (AFM) to directly visualize cytoskeletal fibers in human foreskin epithelial cells. The nonionic detergent Triton X-100 in a low concentration was used to remove the membrane, soluble proteins, and organelles from the cell. The remaining cytoskeleton can then be directly visualized in either liquid or air-dried ambient conditions. These two types of scanning provide complimentary information. Scanning in liquid visualizes the surface filaments of the cytoskeleton, whereas scanning in air shows both the surface filaments and the total "volume" of the cytoskeletal fibers. The smallest fibers observed were ca. 50 nm in diameter. The lateral resolution of this technique was ca.20 nm, which can be increased to a single nanometer level by choosing sharper AFM tips. Because the AFM is a true 3D technique, we are able to quantify the observed cytoskeleton by its density and volume. The types of fibers can be identified by their size, similar to electron microscopy.     

原子力显微镜在DNA领域中研究应用

原子力显微镜(AFM)是研究DNA有力工具,在对DNA研究中有其独特优势。本文概述原子力显微镜DNA研究中应用以及取得进展。虽然原子力显微镜在研究DNA研究中仍有局限性,但随着原子力显微技术及相关技术发展,原子力显微镜在DNA中研究必将不断深入。     

Wear characteristics of diamond-coated atomic force microscope probe

In atomic force microscope (AFM) applications, the wear of the probe is undoubtedly a serious concern since it affects the integrity of the measurements. In this work, wear tests were performed using an AFM with lateral force monitoring capability with the aim to better understand the wear characteristics of diamond-coated probes. For the assessment of the probe wear, a transmission electron microscope (TEM) as well as a scanning electron microscope were utilized. The degree of the probe wear was quantified using the Archard's wear equation. The structure of the diamond-coated probe was analyzed by using the TEM and Raman spectroscopy. From the experimental results, two different wear characteristics, the gradual wear and the abrupt fracture of the diamond coating, were observed. In the case of gradual wear, the wear coefficient of the diamond-coated probe slid against a silicon nitride specimen was about 10(-5)-10(-6). It was also found that the wear rate significantly decreased with increase in the sliding distance. Raman spectroscopy analysis showed that the difference in the chemical structure of the diamond coating may induce the different wear phenomena. These results may be effectively utilized for fundamental understanding of nano-wear characteristics of AFM probes.     

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。