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.     

基于CAN总线和STM32的智能步进电机驱动模块设计

本文针对传统仪用步进电机驱动控制系统中存在的不足,设计了基于CAN总线和STM32的智能步进电机驱动控制模块。文中重点对两种系统框架的优缺点进行比较,阐述了系统的软硬件设计方案,实现了对多个步进电机的分布式控制。测试结果表明,系统性能稳定,实现了细分驱动模式下的精确定位。     

Design and performance of a combined secondary ion mass spectrometry-scanning probe microscopy instrument for high sensitivity and high-resolution elemental three-dimensional analysis

State-of-the-art secondary ion mass spectrometry (SIMS) instruments allow producing 3D chemical mappings with excellent sensitivity and spatial resolution. Several important artifacts however arise from the fact that SIMS 3D mapping does not take into account the surface topography of the sample. In order to correct these artifacts, we have integrated a specially developed scanning probe microscopy (SPM) system into a commercial Cameca NanoSIMS 50 instrument. This new SPM module, which was designed as a DN200CF flange-mounted bolt-on accessory, includes a new high-precision sample stage, a scanner with a range of 100 μm in x and y direction, and a dedicated SPM head which can be operated in the atomic force microscopy (AFM) and Kelvin probe force microscopy modes. Topographical information gained from AFM measurements taken before, during, and after SIMS analysis as well as the SIMS data are automatically compiled into an accurate 3D reconstruction using the software program "SARINA," which was developed for this first combined SIMS-SPM instrument. The achievable lateral resolutions are 6 nm in the SPM mode and 45 nm in the SIMS mode. Elemental 3D images obtained with our integrated SIMS-SPM instrument on Al/Cu and polystyrene/poly(methyl methacrylate) samples demonstrate the advantages of the combined SIMS-SPM approach.     

Simulation-aided design and fabrication of nanoprobes for scanning probe microscopy

We proposed and demonstrated a flexible and effective method to design and fabricate scanning probes for atomic force microscopy applications. Computer simulations were adopted to evaluate design specifications and desired performance of atomic force microscope (AFM) probes; the fabrication processes were guided by feedback from simulation results. Through design-simulation-fabrication iterations, tipless cantilevers and tapping mode probes were successfully made with errors as low as 2% in designed resonant frequencies. For tapping mode probes, the probe tip apex achieved a 10 nm radius of curvature without additional sharpening steps; tilt-compensated probes were also fabricated for better scanning performance. This method provides AFM users improved probe quality and practical guidelines for customized probes, which can support the development of novel scanning probe microscopy (SPM) applications.     

Vertical inertial sliding drive for coarse and fine approaches in scanning probe microscopy

Mechanisms for controlled approach of a probe tip toward the sample surface are essential in high resolution imaging by scanning probe microscopy (SPM). This work describes the development and performance of an inertial sliding drive capable of translating a relatively large mass (25 g) at up to 1 mms over 1 cm with step sizes of 10-250 nm in ambient conditions using various wave forms as measured by fiber optic interferometry. The drive functions independent of orientation with a threshold voltage of less than 15 V using a single drive signal. Use of piezotube actuators in a radially symmetric arrangement provides guided motion and minimizes differential thermal expansion between critical components. Controlled translation of the entire scanning component in both ambient and electrochemical scanning tunneling microscopy has been routinely achieved with no evidence of tip crash. This device has been specifically designed for use in in situ SPM applications where stability of the sample and that of the liquid environment are paramount.     

Iterative image-based modeling and control for higher scanning probe microscope performance

In this article, we develop an image-based approach to model and control the dynamics of scanning probe microscopes (SPMs) during high-speed operations. SPMs are key enabling tools in the experimental investigation and manipulation of nano- and subnanoscale phenomena; however, the speed at which the SPM probe can be positioned over the sample surface is limited due to adverse dynamic effects. It is noted that SPM speed can be increased using model-based control techniques. Modeling the SPM dynamics is, however, challenging because currently available sensing methods do not measure the SPM tip directly. Additionally, the resolution of currently available sensing methods is limited by noise at higher bandwidth. Our main contribution is an iterative image-based modeling method which overcomes these modeling difficulties (caused by sensing limitations). The method is applied to model an experimental scanning tunneling microscope (STM) system and to achieve high-speed imaging. Specifically, we model the STM up to a frequency of 2000 Hz (corresponds to approximately 23 of the resonance frequency of our system) and achieve approximately 1.2% error in 1 nm square images at that same frequency.     

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。     

Charge drives for scanning probe microscope positioning stages

Due to hysteresis exhibited by piezoelectric actuators, positioning stages in scanning probe microscopes require sensor-based closed-loop control. Although closed-loop control is effective at eliminating non-linearity at low scan speeds, the bandwidth compared to open loop is severely reduced. In addition, sensor noise significantly degrades achievable resolution in closed loop. In this work, charge drives are evaluated as a simple positioning alternative when feedback control cannot be applied or provides inadequate performance. These situations arise in high-speed imaging, where position sensor noise can be large or where no feedback sensors are present. Charge drives can reduce the error caused by hysteresis to less than 1% of the scan range. We review the design of charge drives and compare them to voltage amplifiers for driving lateral SPM scanners. The first experimental images using charge drive are presented.     

Compact ultra-fast vertical nanopositioner for improving scanning probe microscope scan speed

The mechanical design of a high-bandwidth, short-range vertical positioning stage is described for integration with a commercial scanning probe microscope (SPM) for dual-stage actuation to significantly improve scanning performance. The vertical motion of the sample platform is driven by a stiff and compact piezo-stack actuator and guided by a novel circular flexure to minimize undesirable mechanical resonances that can limit the performance of the vertical feedback control loop. Finite element analysis is performed to study the key issues that affect performance. To relax the need for properly securing the stage to a working surface, such as a laboratory workbench, an inertial cancellation scheme is utilized. The measured dominant unloaded mechanical resonance of a prototype stage is above 150 kHz and the travel range is approximately 1.56 μm. The high-bandwidth stage is experimentally evaluated with a basic commercial SPM, and results show over 25-times improvement in the scanning performance.     

开放式SPM控制系统的设计与实现

本文设计并实现了一种新的扫描探针显微镜的开放式控制系统。该控制系统设计了灵活开放的总线接口，并对电路模块进行了优化，采取了一系列抗干扰措施，从而使之具备了接口开放、稳定性高等优点，特别适合于个性化的科学研究。本文所采用的开放式设计思想及总线接口的具体实现，对SPM的结构改进及商品化有一定的参考价值。     

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。     

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.     

A nanopositioner for scanning probe microscopy: the KoalaDrive

We present a new type of piezoelectric nanopositioner called KoalaDrive which can have a diameter less than 2.5 mm and a length smaller than 10 mm. The new operating principle provides a smooth travel sequence and avoids shaking which is intrinsic to nanopositioners based on inertial motion with sawtooth driving signals. In scanning probe microscopy, the KoalaDrive can be used for the coarse approach of the tip or sensor towards the sample. Inserting the KoalaDrive in a piezo tube for xyz-scanning integrates a complete scanning tunneling microscope (STM) inside a 4 mm outer diameter piezo tube of <10 mm length. The use of the KoalaDrive makes the scanning probe microscopy design ultracompact and accordingly leads to a high mechanical stability. The drive is UHV, low temperature, and magnetic field compatible. The compactness of the KoalaDrive allows building a multi-tip STM as small as a single tip STM.     

High-resolution scanning near-field EBIC microscopy: application to the characterisation of a shallow ion implanted p+-n silicon junction

High-resolution electron beam induced current (EBIC) analyses were carried out on a shallow ion implanted p⁺–n silicon junction in a scanning electron microscope (SEM) and a scanning probe microscope (SPM) hybrid system. With this scanning near-field EBIC microscope, a sample can be conventionally imaged by SEM, its local topography investigated by SPM and high-resolution EBIC image simultaneously obtained. It is shown that the EBIC imaging capabilities of this combined instrument allows the study of p–n junctions with a resolution of about 20 nm.     

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。     

Components for high speed atomic force microscopy

Many applications in materials science, life science and process control would benefit from atomic force microscopes (AFM) with higher scan speeds. To achieve this, the performance of many of the AFM components has to be increased. In this work, we focus on the cantilever sensor, the scanning unit and the data acquisition. We manufactured 10 microm wide cantilevers which combine high resonance frequencies with low spring constants (160-360 kHz with spring constants of 1-5 pN/nm). For the scanning unit, we developed a new scanner principle, based on stack piezos, which allows the construction of a scanner with 15 microm scan range while retaining high resonance frequencies (>10 kHz). To drive the AFM at high scan speeds and record the height and error signal, we implemented a fast Data Acquisition (DAQ) system based on a commercial DAQ card and a LabView user interface capable of recording 30 frames per second at 150 x 150 pixels.     

基于CAM的STM和AFM的一种过载保护装置研究

根据SIM和AFM的扫描原理,通过CAM设计了一种过载保护装置,使STM和AFM在测试过程中,对超过测试高度的样品停止退针,以免损坏仪器,弥补了仪器设计的不足.     

一个由LabVIEW编写的扫描探针显微镜控制程序

本文的主要目的是通过具体示例的详细讲解,来降低自制扫描探针显微镜的门槛.本文用简约易懂的 LabVIEW编程实现了复杂的扫描探针显微镜的控制与图像处理的功能.本控制程序由三大模块用顺序结构完成.它们分别是设备初始化模块、扫描控制与显像模块和设备安全关机模块.控制程序中最复杂、最关键的扫描控制与显像模块采用完全并行处理的方式实现.这种模块化设计,使主控程序简单明了;既方便修改又方便维护.并行处理模块主要有扫描区域调整与像素调整模块、Y方向扫描控制模块、X方向扫描控制与图像传输模块、扫描过程中参数再调整模块、扫描中断与紧急停机模块等组成.FPGA模块的主要功能是完成控制信号的输出与Z方向的实时反馈控制,在主控程序发出紧急停机命令时,FPGA 模块将消除系统可能的振荡,把扫描探针恢复到初始位置以及关闭高压控制信号等等.文章最后,介绍了如何使用该控制器.杂乱无章、横七竖八的连线是 LabVIEW编程中的最大的诟病.当程序复杂时,这一问题更加严重.本文向读者展示了用 LabVIEW实现完全结构化与并行编程的方法;读者可以按照本文描述的编程技巧,用简单、易懂、易维护的模块化程序实现复杂的虚拟仪器应用.     

Automatization of nanotomography

An approach for automated nanotomography, a layer-by-layer imaging technique based on scanning probe microscopy (SPM), is presented. Stepwise etching and imaging is done in situ in a liquid cell of an SPM. The flow of etching and rinsing solutions after each etching step is controlled with solenoid valves which allow for an automated measuring protocol. The thermal drift and the drift of the piezo scanner is corrected by applying offsets calculated from the cross correlation coefficients between successive images. As an example, we have imaged human bone with approximately 10 nm resolution using tapping mode SPM and successive etching with hydrochloric acid.     

扫描探针显微镜的进展

扫描探针显微镜（SPMs）经过近30年的发展，已经应用到科学研究的各个方面。为适应不同研究的需要，扫描探针显微镜本身的发展也非常迅速。如其中原子力显微镜（AFM）从发明初期的单一的接触工作模式发展到包括可以测量粘弹性的相位模式在内的多种工作模式，同时通用型方面也高度发展，已经形成了一个庞大的高度自动化的扫描探针显微镜的家族。在这个家族中，严格环境控制的扫描探针显微镜的出现，很好的解决了各种务件下对样品的原位观察，环控化扫描探针显微镜的发展已经引起了人们的足够重视，必将成为扫描探针显微镜发展的一个重要方向。新近出现的各种显微镜集成的扫描探针显微镜系列是这个家族中的新成员，这个成员可以同时完成大范围、高分辨和精确定位等各种研究，必将在半导体制造厂的异物检查、金属和绝缘体等表面测定以及生物大分子研究等领域发挥重要作用。扫描探针显微镜的发明和发展促进了一门新兴的高科技——一纳米科学技术的诞生，宣告一个科枝新纪元，纳米科技时代已经来临。