基于相位反馈控制的压电微音叉扫描探针显微镜

压电微音叉具有谐振频率稳定、品质因数高和易于实现音叉臂的振动检测等优点。利用微音叉的这些特性,将其与钨探针结合,构成了压电微音叉扫描探针显微镜(SPM)测头,可实现对微观表面的测量。该测头扫描时,压电微音叉的谐振频率被试样表面原子和钨探针尖端原子间的作用力调制。探针的谐振状态通过锁相环路(PLL)实现,微音叉测头与试样间的恒定测力及测头的Z向定位通过相位反馈控制实现。此外,测量系统可同时获得试样表面的微观轮廓图和相位图。     

压电微音叉扫描探针显微镜测头研究

压电微音叉具有良好的谐振特性，并易于实现其振动的检测。利用这些特性，与钨探针结合，构成了一种新型的表面轮廓扫描测头。该新型测头与X-Y压电工作台结合，采用与TM-AFM相同的工作原理，构成了扫描探针显微镜。介绍了压电微音叉扫描测头的构成、工作原理及主要特性，给出了所构成的扫描探针显微镜测量系统。通过实验及其结果，证明了新型测头具有高垂直分辨率、低破坏力等优点。除此之外，由于采用了有效长度大的钨探针，使大台阶微观表面的测量成为可能。     

基于聚偏氟乙烯的扫描探针显微镜系统

采用聚偏氟乙烯(PVDF)压电薄膜和压电陶瓷(PZT),并结合由电化学研磨得到的钨探针,研制了一种具有对称结构的新型轻敲模式扫描测头。在该测头中,PVDF压电薄膜作为振动梁,其下方中间位置固定有钨探针,在PZT的驱动下,PVDF和探针处于谐振振动状态,同时,PVDF作为微力传感器检测探针顶端原子与试样表面原子间的作用力。所构建测头结合三维纳米定位台、控制程序等构成了新型扫描探针显微镜系统。介绍了测头的构成、工作原理、特性以及SPM系统的整体结构、测量原理、三维工作台的定位控制、信号处理过程和整系统特性测试,并以一维标准光栅为试样进行三维图像扫描,证明了该新型扫描探针显微镜系统的可行性和有效性。     

石英音叉三维谐振触发定位系统

为实现对微器件等三维测量时在三维方向上任意单点的高精度触发定位,提出一种新型三维谐振触发定位系统.以石英音叉作为微力传感器,与一体式光纤微测杆测球相结合,利用其谐振参数(谐振振幅、谐振频率/谐振相位)对微力的高敏感性构建三维谐振触发测头.将该测头与三维纳米定位台、反馈控制模块、信号处理电路结合,分别构成完整的振幅反馈和相位反馈三维谐振触发定位系统.工作时驱动石英音叉测头处于谐振状态,检测顶端测球与试样表面接触微力引起的振幅变化或频率变化.测头顶端测球与试样表面在Z向以轻敲模式接触,在X、Y向以摩擦模式接触.实验结果显示:系统在X、Y、Z3个方向的触发分辨力分别达到0.17 nm、0.20 nm、0.18 nm;三维重复性误差分别达到37.0 nm、70.6 nm、41.0 nm.实验结果验证了提出的三维谐振触发定位系统纳米量级精确定位的可行性和有效性.     

表面轮廓测定用扫描探针测头研究

利用压电聚偏氟乙烯(PVDF, Polyvinilidene fluoride)薄膜和压电微音叉(Micro-fork),分别与钨探针结合,构成了三种新型的表面轮廓扫描测头。该新型测头与x-y压电工作台结合,采用与TM-AFM（Tapping mode atomic force microscope）相同的工作原理,构成了扫描探针显微镜。分别介绍了这些测头的构成及特点,给出了所构成测量系统所获得的试验结果,证明了这几种新型扫描测头的有效性。     

基于PVDF扫描测头的电路系统构建及性能测试

一种采用PVDF薄膜和压电传感器结合钨探针构成的新型扫描测头可以对柔软易损坏及具有大台阶特征的表面实现高精度非破坏性测量.基于该新型测头构建了硬件电路系统,并通过相关试验测试了系统特性.试验结果证明:该扫描测头在垂直方向上可实现亚纳米级的分辨率.     

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。     

MEMS器件圆度误差纳米级测量方法研究

为了测量毫米以下尺寸MEMS零件的圆度参数,建立了将扫描探针显微镜(SPM)系统的原子力测头作为测量传感器,配合精密回转气浮轴系实现对待测试件进行转位的测试系统;讨论了精密气浮轴系、驱动电机、装夹调心装置等关键部件的设计问题及测量系统的工作原理.应用测试系统测量了直径约为0.2mm的微细电极外表面形貌,对获得的表面数据进行了滤波处理,最后使用最小二乘圆度评定准则计算其圆度误差为3.210μm.这种方法可以为圆形MEMS器件的制造工艺提供可行的测量方法与手段.     

硅微机械音叉式谐振器

应用体硅微机械加工技术,制作了一种双端固定音叉式谐振器。它在音叉的两个臂上连接了梳齿电容结构,用来驱动音叉臂在硅片平面内侧向、反相振动,同时检测音叉的振动频率。当驱动力的频率等于音叉的固有频率时,音叉产生谐振。此时,检测梳齿电容输出的电流最大。用有限元方法对谐振器进行了模态分析和结构优化。音叉臂长800μm,宽5μm,梳齿电容齿长25μm,结构层厚度为80μm,在30V交流电压激励下,测得其谐振频率为25kHz。当音叉受到轴向力的作用时,音叉的固有频率会发生变化,根据这一原理,设计了谐振式加速度计。用有限元分析软件对加速度计工作情况仿真,估算其灵敏度约为2Hz/g。这种音叉式谐振器结构和工艺简单,性能可靠,成本较低,对于进一步研究微机电系统谐振器件具有重要意义。     

用于超精表面损伤检测的微探针系统设计与测试

电子产品高集成度与高性能化的发展,对超精表面微观形貌轮廓纳米尺度微裂纹损伤检测要求越来越高.设计灵敏度高、重现性好、响应快速的微探针系统是实现纳米尺度分辨率、大视场损伤检测的关键部件之一.文中对设计的微探针系统受力阻尼谐振过程进行了分析,给出共振频率的测试方法.在此基础上进行了共振频率测试对比试验,并对微探针振动进行了测试.试验结果表明,设计的微探针系统满足检测性能要求.     

A versatile multipurpose scanning probe microscope

A combined scanning probe microscope has been developed that allows simultaneous operation as a non‐contact/tapping mode atomic force microscope, a scattering near‐field optical microscope, and a scanning tunnelling microscope on conductive samples. The instrument is based on a commercial optical microscope. It operates with etched tungsten tips and exploits a tuning fork detection system for tip/sample distance control. The system has been tested on a p‐doped silicon substrate with aluminium depositions, being able to discriminate the two materials by the electrical and optical images with a lateral resolution of 130 nm.     

A method for manufacturing a probe for a combined scanning tunneling and atomic-force microscope on the basis of a quartz tuning fork with a supersharp metal tip

A method for manufacturing a probe for a combined scanning tunneling and atomic-force microscope on the basis of a quartz tuning fork with a metal tip, which is equipped with an independent conductor, is described. When the probe is manufactured, the billet for a tip has the form of a rather small (in order not to change the frequency and quality factor of the quartz tuning fork) metal cone, which is glued to the end of the beam of the quartz resonator-tuning fork together with a carbon fiber as a conductor. A spark is used to form a melted ball at the vertex of the cone. The thickness of the cone near the ball is reduced to a diameter of <0.5 μm by the electrochemical technique, and the ball is then mechanically detached. The main advantage of this method is that it allows manufacturing a high-quality-factor force detector with a single super sharp and clean tip, which is made of platinum (or platinum alloys) and tungsten, with a yield of ≥80%.     

Angled long tip to tuning fork probes for atomic force microscopy in various environments

We expand the range of applications of a tuning fork probe (TFP) in frequency-modulation atomic force microscopy (FM-AFM) by attaching a long metal tip at a certain angle. By the combined flexure of the metal tip and the tuning fork prong, this TFP can change the direction of the detectable force by switching the resonance frequency, which has not been realized with conventional TFPs with short tips. The oscillatory behavior of the tip apex of the TFP is predicted by computer simulations and is experimentally confirmed with scanning electron microscope. FM-AFM operations using this TFP are performed in various environments, i.e., in ultrahigh vacuum, air, and water. FM-AFM images obtained at an atomic step of highly oriented pyrolytic graphite in air show a clear difference depending on the excitation frequency. It is also revealed that the higher order flexural modes of this TFP are advantageous for FM-AFM in water due to the reduction in the degree of hydrodynamic damping.     

The tuning fork as sensor for dynamic force distance control in scanning near-field optical microscopy

The dynamic force distance control for scanning near-field optical microscopy on the basis of a tuning fork as piezoelectric force sensor is remarkably sensitive. In order to gain a better understanding of this sensitivity the vibrational properties of the tuning fork are modelled within the framework of two coupled harmonic oscillators. As a result, the effective force constant of the tuning fork at resonance frequency is determined. Furthermore, the influence of the additional mass by the attachment of the near-field probe is investigated.     

The tuning fork as sensor for dynamic force distance control in scanning near-field optical microscopy

The dynamic force distance control for scanning near-field optical microscopy on the basis of a tuning fork as piezoelectric force sensor is remarkably sensitive. In order to gain a better understanding of this sensitivity the vibrational properties of the tuning fork are modelled within the framework of two coupled harmonic oscillators. As a result, the effective force constant of the tuning fork at resonance frequency is determined. Furthermore, the influence of the additional mass by the attachment of the near-field probe is investigated.     

Calibrating a tuning fork for use as a scanning probe microscope force sensor

Quartz tuning forks mounted with sharp tips provide an alternate method to silicon microcantilevers for probing the tip-substrate interaction in scanning probe microscopy. The high quality factor and stable resonant frequency of the tuning fork allow accurate measurements of small shifts in the resonant frequency as the tip approaches the substrate. To permit an accurate measure of surface interaction forces, the electrical and piezoelectromechanical properties of a tuning fork have been characterized using a fiber optical interferometer.     

Tunneling/shear force microscopy using piezoelectric tuning forks for characterization of topography and local electric surface properties

Characterization of novel nanoelectronic structures and materials requires advanced and high-resolution diagnostic methods. In this article new approach for high sensitivity measurements of electric surface properties using scanning probe microscopy is presented. In this procedure topography and tunneling current flowing between the metallic tip and the surface are observed simultaneously. In our design piezoelectric tuning fork equipped with metallic tip in shear force microscope is used.     

Implementation of a short-tip tapping-mode tuning fork near-field scanning optical microscope

We present the implementation of a short‐tip tapping‐mode tuning fork near‐field scanning optical microscope. Tapping frequency dependences of the piezoelectric signal amplitudes for a bare tuning fork fixed on the ceramic plate, a short‐tip tapping‐mode tuning fork scheme and an ordinary tapping‐mode tuning fork configuration with an 80‐cm optical fibre attached are demonstrated and compared. Our experimental results show that this new short‐tip tapping‐mode tuning fork scheme provides a stable and high Q factor at the tapping frequency of the tuning fork and will be very helpful when long optical fibre probes have to be used in an experiment. Both collection and excitation modes of short‐tip tapping‐mode tuning fork near‐field scanning optical microscope are applied to study the near‐field optical properties of a single‐mode telecommunication optical fibre and a green InGaN/GaN multiquantum well light‐emitting diode.     

A tuning fork based wide range mechanical characterization tool with nanorobotic manipulators inside a scanning electron microscope

This study proposes a tuning fork probe based nanomanipulation robotic system for mechanical characterization of ultraflexible nanostructures under scanning electron microscope. The force gradient is measured via the frequency modulation of a quartz tuning fork and two nanomanipulators are used for manipulation of the nanostructures. Two techniques are proposed for attaching the nanostructure to the tip of the tuning fork probe. The first technique involves gluing the nanostructure for full range characterization whereas the second technique uses van der Waals and electrostatic forces in order to avoid destroying the nanostructure. Helical nanobelts (HNB) are proposed for the demonstration of the setup. The nonlinear stiffness behavior of HNBs during their full range tensile studies is clearly revealed for the first time. Using the first technique, this was between 0.009 N/m for rest position and 0.297 N/m before breaking of the HNB with a resolution of 0.0031 N/m. For the second experiment, this was between 0.014 N/m for rest position and 0.378 N/m before detaching of the HNB with a resolution of 0.0006 N/m. This shows the wide range sensing of the system for potential applications in mechanical property characterization of ultraflexible nanostructures.