Modeling scanning probe microscope lateral dynamics using the probe-surface interaction signal

In this paper, a novel scanning probe microscope (SPM) modeling technique is presented. The novelty of this technique is that it exploits the SPM's probe-surface interaction measurement capabilities [e.g., the topography signal in atomic force microscopy (AFM)] to determine the SPM's lateral positioning dynamics. SPM operation speed is limited due to mechanical vibrations induced by movement of the SPM nanopositioner. In order to facilitate high-speed SPM operation, the dynamics of the SPM can be modeled and used to design feedforward and feedback controllers that reduce nanopositioner vibrations. The proposed technique seeks to develop a transfer function model of the SPM dynamics using only the SPM probe-surface interaction signal obtained while scanning a calibration sample. The technique is presented in the context of an AFM example, errors associated with the method are analyzed, and the method is experimentally verified using a commercial AFM. Experimental modeling results show that the method is capable of modeling the dynamics of SPM systems.     

The FAST module: an add-on unit for driving commercial scanning probe microscopes at video rate and beyond

We present the design and the performance of the FAST (Fast Acquisition of SPM Timeseries) module, an add-on instrument that can drive commercial scanning probe microscopes (SPM) at and beyond video rate image frequencies. In the design of this module, we adopted and integrated several technical solutions previously proposed by different groups in order to overcome the problems encountered when driving SPMs at high scanning frequencies. The fast probe motion control and signal acquisition are implemented in a way that is totally transparent to the existing control electronics, allowing the user to switch immediately and seamlessly to the fast scanning mode when imaging in the conventional slow mode. The unit provides a completely non-invasive, fast scanning upgrade to common SPM instruments that are not specifically designed for high speed scanning. To test its performance, we used this module to drive a commercial scanning tunneling microscope (STM) system in a quasi-constant height mode to frame rates of 100 Hz and above, demonstrating extremely stable and high resolution imaging capabilities. The module is extremely versatile and its application is not limited to STM setups but can, in principle, be generalized to any scanning probe instrument.     

MEMS-based fast scanning probe microscopes

Scanning probe microscopy is a frequently used nanometer-scale surface investigation technique. Unfortunately, its applicability is limited by the relatively low image acquisition speed, typically seconds to minutes per image. Higher imaging speeds are desirable for rapid inspection of samples and for the study of a range of dynamic surface processes, such as catalysis and crystal growth. We have designed a new high-speed scanning probe microscope (SPM) based on micro-electro mechanical systems (MEMS). MEMS are small, typically micrometer size devices that can be designed to perform the scanning motion required in an SPM system. These devices can be optimized to have high resonance frequencies (up to the MHz range) and have very low mass (10⁻¹¹ kg). Therefore, MEMS can perform fast scanning motion without exciting resonances in the mechanical loop of the SPM, and hence scan the surface without causing the image distortion from which conventional piezo scanners suffer. We have designed a MEMS z-scanner which we have integrated in commercial AFM (atomic force microscope) and STM (scanning tunneling microscope) setups. We show the first successful AFM experiments.     

High-speed force load in force measurement in liquid using scanning probe microscope

This article presents an inversion-based iterative feedforward-feedback (II-FF/FB) approach to achieve high-speed force load in force measurement of soft materials in liquid using scanning probe microscope (SPM). SPM force measurement under liquid environment is needed to interrogate a wide range of soft materials, particularly live biological samples. Moreover, when dynamic evolution of the sample occurs during the measurement, and/or measuring the rate-dependent viscoelasticity of the sample, the force measurement also needs to be acquired at high-speed. Precision force load in liquid, however, is challenged by adverse effects including the thermal drift effect, the reduction of the signal to noise ratio, the distributive hydrodynamic force effect, and the hysteresis and vibrational dynamics effects of the piezoelectric actuators (for positioning the probe relative to the sample), particularly during high-speed measurement. Thus, the main contribution of the article is the development of the II-FF/FB approach to tackle these challenges. The proposed method is illustrated through an experimental implementation to the force-curve measurement of a poly (dimethylsiloxane) sample in liquid at high-speed.     

Efficient Imaging and Real-Time Display of Scanning Ion Conductance Microscopy Based on Block Compressive Sensing

Scanning Ion Conductance Microscopy (SICM) is one kind of Scanning Probe Microscopies (SPMs), and it is widely used in imaging soft samples for many distinctive advantages. However, the scanning speed of SICM is much slower than other SPMs. Compressive sensing (CS) could improve scanning speed tremendously by breaking through the Shannon sampling theorem, but it still requires too much time in image reconstruction. Block compressive sensing can be applied to SICM imaging to further reduce the reconstruction time of sparse signals, and it has another unique application that it can achieve the function of image real-time display in SICM imaging. In this article, a new method of dividing blocks and a new matrix arithmetic operation were proposed to build the block compressive sensing model, and several experiments were carried out to verify the superiority of block compressive sensing in reducing imaging time and real-time display in SICM imaging.     

Whispering-gallery acoustic sensing: characterization of mesoscopic films and scanning probe microscopy applications

Full understanding of the physics underlying the striking changes in viscoelasticity, relaxation time, and phase transitions that mesoscopic fluid-like films undergo at solid-liquid interfaces, or under confinement between two sliding solid boundaries, constitutes one of the major challenges in condensed matter physics. Their role in the imaging process of solid substrates by scanning probe microscopy (SPM) is also currently controversial. Aiming at improving the reliability and versatility of instrumentation dedicated to characterize mesoscopic films, a noninvasive whispering-gallery acoustic sensing (WGAS) technique is introduced; its application as feedback control in SPM is also demonstrated. To illustrate its working principle and potential merits, WGAS has been integrated into a SPM that uses a sharp tip attached to an electrically driven 32-kHz piezoelectric tuning fork (TF), the latter also tighten to the operating microscope's frame. Such TF-based SPMs typically monitor the TF's state of motion by electrical means, hence subjected to the effects caused by the inherent capacitance of the device (i.e., electrical resonance differing from the probe's mechanical resonance). Instead, the novelty of WGAS resides in exploiting the already existent microscope's frame as an acoustic cavity (its few centimeter-sized perimeter closely matching the operating acoustic wavelength) where standing-waves (generated by the nanometer-sized oscillations of the TF's tines) are sensitively detected by an acoustic transducer (the latter judiciously placed around the microscope's frame perimeter for attaining maximum detection). This way, WGAS is able to remote monitoring, via acoustic means, the nanometer-sized amplitude motion of the TF's tines. (This remote-detection method resembles the ability to hear faint, but still clear, levels of sound at the galleries of a cathedral, despite the extraordinary distance location of the sound source.) In applications aiming at characterizing the dynamics of fluid-like mesoscopic films trapped under shear between the TF probe and the solid substrate, WGAS capitalizes on the well-known fact that the TF's motion is sensitively affected by the shear-forces (the substrate and its adsorbed mesocopic film playing a role) exert on its tip, which occurs when the latter is placed in close proximity to a solid substrate. Thus, WGAS uses a TF as an efficient transducer sandwiched between (i) the probe (that interact with the substrate and mesoscopic film), and (ii) the acoustic cavity (where an assessment of the probe mechanical motion is obtained). In short, WGAS has capability for monitoring probe-sample shear-force interactions via remote acoustic sensing means. In another application, WGAS can also be used as feedback control of the probe's vertical position in SPM. In effect, it is observed that when the microscope's probe stylus approaches a sample, a monotonic change of the WGAS acoustic signal occurs in the last ~20 nm before the probe touches the solid sample's surface, which allows implementing an automated-control of the probe-sample distance for safely scanning the tip across the sample surface. This principle is demonstrated by imaging the topographic features of a standard sample. Finally, it is worth to highlight that this alignment-free acoustic-based method offers a very direct assessment of the probe's mechanical motion state (the mechanical and the WGAS acoustic frequency responses coincide), which makes the WGAS a convenient metrology tool for studying surface interactions, including interfacial friction at the nanometer scale.     

模块化扫描探针显微镜的研究

介绍一种多功能、模块化扫描探针显微镜,它综合了ＳＴＭ、ＡＦＭ、ＭＦＭ、ＦＦＭ等的功能,不仅能检测物质表面微观形貌,还能检测微小静电力、磁力、原子力和摩擦力,具有较好的灵活性和较宽的应用范围。     

Applications of Scanning Probe Microscopies in Technology and Manufacturing

Within the last 10 years the scanning probe microscopies (SPMs) have been applied to a variety of problems with the main emphasis on scientific applications. The SPM techniques have to date also found their technical applications. The simple concept can easily be adapted to a variety of different applications in high technologic manufacturing processes. The scanning tunneling microscope is now considered as a standard measuring equipment, in the meantime there exists a whole family of SPMs with promising applications in not only a pure scientific environment but also in a manufacturing environment. As examples for industrial applications, we report on magnetic force microscopic investigations, on magnetic storage device components, and on a relatively new technique for nanohardness investigations of thin-films by an atomic force microscope.     

Atomic-force-microscope-compatible near-field scanning microwave microscope with separated excitation and sensing probes

We present the design and experimental results of a near-field scanning microwave microscope working at a frequency of 1 GHz. Our microscope is unique in that the sensing probe is separated from the excitation electrode to significantly suppress the common-mode signal. Coplanar waveguides were patterned onto a silicon nitride cantilever interchangeable with atomic force microscope tips, which are robust for high speed scanning. In the contact mode that we are currently using, the numerical analysis shows that contrast comes from both the variation in local dielectric properties and the sample topography. Our microscope demonstrates the ability to achieve high resolution microwave images on buried structures, as well as nanoparticles, nanowires, and biological samples.     

Design of a scanning probe microscope with advanced sample treatment capabilities: An atomic force microscope combined with a miniaturized inductively coupled plasma source

We describe the design and performance of an atomic force microscope (AFM) combined with a miniaturized inductively coupled plasma source working at a radio frequency of 27.12 MHz. State-of-the-art scanning probe microscopes (SPMs) have limited in situ sample treatment capabilities. Aggressive treatments such as plasma etching or harsh treatments such as etching in aggressive liquids typically require the removal of the sample from the microscope. Consequently, time consuming procedures are required if the same sample spot has to be imaged after successive processing steps. We have developed a first prototype of a SPM which features a quasi in situ sample treatment using a modified commercial atomic force microscope. A sample holder is positioned in a special reactor chamber; the AFM tip can be retracted by several millimeters so that the chamber can be closed for a treatment procedure. Most importantly, after the treatment, the tip is moved back to the sample with a lateral drift per process step in the 20 nm regime. The performance of the prototype is characterized by consecutive plasma etching of a nanostructured polymer film.     

基于电化学研磨的SPM钨探针制备方法研究

钨探针是扫描隧道显微镜(STM)常用探针之一。为了将钨探针应用于扫描探针显微镜(SPM)，根据钨探针的受力，通过理论分析确定了钨探针的理想轮廓：钨探针的直径变化应具有指数曲线。为了获得指数曲线轮廓、尖锐测头等良好特性的钨探针，分别提出并研究了改进的钨探针液面直流电化学研磨法和薄膜直流电化学研磨法。通过这两种电化学研磨法获得的探针以及通过传统的交流电化学研磨法获得的钨探针，分别在探针的形状、探针尖端曲率半径、表面质量、研磨速度、可复现性等多个方面进行了观察和比较。通过实验发现，除了研磨速度外，改进的液面直流电化学研磨法和薄膜直流电化学研磨法在其他各方面都优于交流电化学研磨法。     

开放式多功能扫描探针显微镜系统

开放式多功能扫描探针显微镜、集成扫描隧道显微镜、原子力显微镜、横向力显微镜和静电力显微镜．具有接触、半接触和非接触工作模式，可进行作用力、电流、电位、光能量等参数的高度局域综合测量,具有极高的开放性和可扩展性，支持用户进行二次开发。     

扫描探针显微镜的研究

介绍了扫描探针显微镜的起源及其发展过程，同时对扫描探针显微镜中最常用的两种：STM、AFM作了原理和结构介绍，最后介绍了SPM探针的形状及其性能数据。     

A fast and versatile scan unit for scanning probe microscopy

In scanning probe microscopy (SPM), the image acquisition time is usually very long because of the limited speed with which the scanning device can trace the topography of the specimen under feed-back control. This limitation is often brought about by the natural frequency of the scanner in the direction perpendicular to the sample plane that confines the usable bandwidth of the feed-back loop. In this paper, we present a piezo-ceramic scanner that provides a large scan range and at the same time allows for adjustment of the probe-to-sample distance faster by about one order of a magnitude than a conventional setup. This is achieved through the combination of a large single tube scanner that provides a high-scan range and a small piezo element for swift motion in the direction perpendicular to the sample plane. The natural frequency in this direction lies at about 275 kHz. We outline the design considerations to avoid disturbing excitation of the scanner through the fast piezo element.     

Scanning probe microscopy studies of cereal seed storage protein structures

Scanning probe microscopes (SPMs) share a number of common features which give the techniques advantages over conventional light and electron microscopy. First, high resolution, up to the atomic level, is possible in certain cases, and second, they are nondestructive, requiring no staining or coating and the images can be obtained in the hydrated state or under water. Scanning probe microscopes, particularly scanning tunnelling microscopes (STM) and atomic force microscopes (AFM), have been used to study food-related systems, ranging from relatively large structures such as starch granules to the organisation of secondary structures in proteins and the interaction of proteins. The seed storage proteins (gluten) of wheat are responsible for the viscous and elastic properties of wheat doughs that allow them to be used for a wide range of different food products. Using AFM and STM, images of individual and groups of proteins have been obtained in both the dry and hydrated states. The ability to work in liquid environments allows the conformation of proteins to be determined under conditions approaching “native.” The AFM and STM have been used to image both gliadins and glutenins and to study their aggregative behaviour in relation to gluten and dough systems.     

Miniature active damping stage for scanning probe applications in ultra high vacuum

Scanning probe microscope (SPM) experiments demand a low vibration level to minimize the external influence on the measured signal. We present a miniature six-degree of freedom active damping stage based on a Gough-Stewart platform (hexapod) which is positioned in ultra high vacuum as close to the SPM as possible. In this way, vibrations originating from the experimental setup can be effectively reduced providing a quiet environment for the SPM. In addition, the hexapod provides a rigid reference point, which facilitates wiring as well as sample transfer. We outline the main working principle and show that for scanning tunneling microscopy (STM) measurements of a Si(111) 7 × 7 surface, the hexapod significantly improves the stability and quality of the topographic images.     

Imaging biological macromolecules by STM: quantitative interpretation of topographs

Methods are discussed which permit the calibration of x-, y-, z-sensitivities, non-linearities and frequency responses of the scanning device of a scanning tunneling microscope (STM) either by interferometry or directly from STM topographs. A technique is presented to measure the frequency response of the complete STM feedback unit and to derive a maximum speed in z direction which allows one to estimate the maximum scanning speed still permitting one to track surface corrugations. The signal transfer characteristics of a STM are evaluated in a direct comparison with high resolution transmission electron microscopy on an identical specimen area. The various effects of contaminants between tip and specimen and the finite tip radius receive special attention.     

Note: long range and accurate measurement of deep trench microstructures by a specialized scanning tunneling microscope

A compact but practical scanning tunneling microscope (STM) with high aspect ratio and high depth capability has been specially developed. Long range scanning mechanism with tilt-adjustment stage is adopted for the purpose of adjusting the probe-sample relative angle to compensate the non-parallel effects. A periodical trench microstructure with a pitch of 10 μm has been successfully imaged with a long scanning range up to 2.0 mm. More innovatively, a deep trench with depth and step height of 23.0 μm has also been successfully measured, and slope angle of the sidewall can approximately achieve 67°. The probe can continuously climb the high step and exploring the trench bottom without tip crashing. The new STM could perform long range measurement for the deep trench and high step surfaces without image distortion. It enables accurate measurement and quality control of periodical trench microstructures.     

An integrated approach to piezoactuator positioning in high-speed atomic force microscope imaging

In this paper, an integrated approach to achieve high-speed atomic force microscope (AFM) imaging of large-size samples is proposed, which combines the enhanced inversion-based iterative control technique to drive the piezotube actuator control for lateral x-y axis positioning with the use of a dual-stage piezoactuator for vertical z-axis positioning. High-speed, large-size AFM imaging is challenging because in high-speed lateral scanning of the AFM imaging at large size, large positioning error of the AFM probe relative to the sample can be generated due to the adverse effects--the nonlinear hysteresis and the vibrational dynamics of the piezotube actuator. In addition, vertical precision positioning of the AFM probe is even more challenging (than the lateral scanning) because the desired trajectory (i.e., the sample topography profile) is unknown in general, and the probe positioning is also effected by and sensitive to the probe-sample interaction. The main contribution of this article is the development of an integrated approach that combines advanced control algorithm with an advanced hardware platform. The proposed approach is demonstrated in experiments by imaging a large-size (50 microm) calibration sample at high-speed (50 Hz scan rate).     

Developments of scanning probe microscopy with stress/strain fields

An innovative stress/strain fields scanning probe microscopy in ultra high vacuum (UHV) environments is developed for the first time. This system includes scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM). Two piezo-resistive AFM cantilever probes and STM probes used in this system can move freely in XYZ directions. The nonoptical frequency shift detection of the AFM probe makes the system compact enough to be set in the UHV chambers. The samples can be bent by an anvil driven by a step motor to induce stress and strain on their surface. With a direct current (dc) power source, the sample can be observed at room and high temperatures. A long focus microscope and a monitor are used to observe the samples and the operation of STM and AFM. Silicon(111) surface in room temperature and silicon(001) surface in high temperature with stress were investigated to check the performance of the scanning probe microscope.