Atomic resolution ultrafast scanning tunneling microscope with scan rate breaking the resonant frequency of a quartz tuning fork resonator

We present an ultra-fast scanning tunneling microscope with atomic resolution at 26 kHz scan rate which surpasses the resonant frequency of the quartz tuning fork resonator used as the fast scan actuator. The main improvements employed in achieving this new record are (1) fully low voltage design (2) independent scan control and data acquisition, where the tuning fork (carrying a tip) is blindly driven to scan by a function generator with the scan voltage and tunneling current (I(T)) being measured as image data (this is unlike the traditional point-by-point move and measure method where data acquisition and scan control are switched many times).     

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.     

Force-gradient-induced mechanical dissipation of quartz tuning fork force sensors used in atomic force microscopy

We have studied the dynamics of quartz tuning fork resonators used in atomic force microscopy taking into account the mechanical energy dissipation through the attachment of the tuning fork base. We find that the tuning fork resonator quality factor changes even in the case of a purely elastic sensor-sample interaction. This is due to the effective mechanical imbalance of the tuning fork prongs induced by the sensor-sample force gradient, which in turn has an impact on dissipation through the attachment of the resonator base. This effect may yield a measured dissipation signal that can be different from the one exclusively related to the dissipation between the sensor and the sample. We also find that there is a second-order term in addition to the linear relationship between the sensor-sample force gradient and the resonance frequency shift of the tuning fork that is significant even for force gradients usually present in atomic force microscopy, which are in the range of tens of N/m.     

石英音叉扫描探针显微镜

石英音叉是一种谐振频率稳定、品质因数高的时基器件,其音叉臂的谐振参数(谐振振幅和谐振频率)对微力极其敏感。利用石英音叉对外力的敏感性,与钨探针结合,构成一种新型的表面形貌扫描测头。该测头与xyz压电工作台结合,利用测头音叉臂谐振频率对扫描微力的敏感性,研制基于相位反馈控制的扫描探针显微镜。首先介绍石英音叉测头的构成、工作原理和特性测试,以及由该测头构建的扫描探针显微镜的结构和测试、分析。通过对测头和系统的测试结果分析,系统达到1.2 nm的垂直分辨率,并通过对一维栅的测量,给出扫描获得的试样表面微观形貌图以及相位图,证明系统的有效性。另外,由于采用大长径比的钨探针,该系统具有测量大深宽比微器件表面轮廓的能力。     

Topography and near-field image measurement of soft biological samples in liquid by using a tuning fork based bent optical-fiber sensor

The fabrication of a tuning fork based bent optical-fiber sensor and its application for topography and near-field image measurement of soft biological samples in physiological solution are reported. By adopting the bent optical fiber and tuning fork feedback scheme, the possibility of signal interference with stray light is minimized, which is especially important for near-field applications. From the measured tuning fork amplitude and its calibration with the preamplifier output voltage, it was determined that the interaction force between the fiber tip and a soft sample in liquid needs to be controlled within approximately 10 nN level and that the image quality depends sensitively to the interaction force. The results of topography measurements of fixed COS-7 and MCF-7 cells in phosphate buffered saline and of the near-field imaging of red blood cell also in phosphate buffered saline with a resolution of about 100 nm are presented.     

A new device built to measure the mechanical characters of the double ended tuning Fork

Journal of Mechanical Science and Technology - A new device is built to measure the mechanical characters of the double ended tuning fork which is used as the sensitive element of resonant sensor....     

谐振式超磁致伸缩音频驱动器设计

超磁致伸缩驱动器具有输出振幅过小导致转换效率不高的问题,针对此问题提出了谐振式超磁致伸缩音频驱动器的理念,利用音叉的机械结构实现了超磁致伸缩驱动器振幅的放大,同时利用音叉的频响曲线去修正超磁致伸缩驱动器的频响曲线,以提升扬声器响度。研究了音叉的选择,及其中超磁致伸缩驱动器的具体设计过程,并在专业消音室对谐振式超磁致伸缩音频驱动器进行了性能测试,测试结果表明驱动器改进后超磁致伸缩扬声器在音响上有显著提升。     

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.     

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%.     

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.     

An improved dynamic model of tuning fork probe for scanning probe microscopy

This paper presents a two coupled oscillators model to describe the dynamics of a tuning fork with a probe attached. The two coupled oscillators are unbalanced only in their effective masses and the damping ratios. By applying a frequency domain system identification approach in experimental investigation of various probe attachment cases, a good accuracy of the model is demonstrated. The effectiveness of the model is further demonstrated in quantitative analysis of the noise performance and the sensitivity of force sensing with a tuning fork probe. Compared with existing models, the proposed model can more accurately characterize the dynamics of a tuning fork probe.     

双质量块调谐输出式硅MEMS陀螺仪

硅MEMS陀螺仪成本低、体积小、功耗低,是微小型无人系统及制导武器的核心惯性器件,本文提出一种双质量块调谐输出式硅MEMS陀螺仪,采用两块反相、同频、等幅振动质量块作为敏感单元,通过测量谐振器谐振频率变化来计算转速的大小,通过动力学分析,推导了哥氏力与输入转速的传递函数,用瑞利－里茨法求得在轴向力作用下梁的固有频率方程,利用马蒂厄方程分析了双端音叉谐振器的运动数学表达式及陀螺仪标度因数方程。最后利用ANSYS有限元软件对谐振器进行了稳定性及有预载荷的模态分析,验证了理论推导的正确性。该陀螺仪通过端部支撑结构将两质量块的振动能量相互抵消,减少了振动噪声及能量损耗,利用杠杆反相差分效应,消除了外界加速度引起的误差。     

双端调谐音叉石英谐振器的结构设计方法研究

叙述了双端调谐音叉石英振梁式重力传感器的结构和工作原理。根据石英谐振器的谐振频率公式和石英晶体的压电效应原理，确定了石英谐振器的主要结构尺寸和电极设置。应用有限元法计算了该谐振器的谐振频率，显示了一阶模态振型，这为设计不同用途的石英振梁式加速度传感器提供了理论依据。     

氢原子钟的设计改进与性能

氢原子钟是至今为止除极短时间测量间隔之外最稳定的频率标准,由于环境温度的变化及谐振腔老化而引起谐振腔频率的变化,导致氢原子钟长期性能降低.为了减小这些影响需借助一种自动调谐器来确保谐振腔的频率始终工作在所需的频率上,改善氢原子钟的长期性能,日稳定度可达到1.0×10-14.这篇文章描述了上海天文台研制的氢原子钟的技术改造与性能.     

双端固定音叉式硅微机械谐振器的研究与应用

提出了一种使用双端固定音叉的新型结构的谐振式硅微机械加速度计。它用硅梁侧壁形成的静电电容进行激振，并通过在音叉臂上制作的压敏电阻检测振动。该加速度计输出的是频率信号，具有精度高、抗干扰能力强的优点。探讨了传感器的工作原理，并用有限元方法进行了仿真模拟，结果显示传感器的灵敏度约为2Hz/g。     

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.     

Analytical modeling and FEM Simulations of single-stage microleverage mechanism

Microleverage mechanisms have potentially wide applications in micro-electro-mechanical systems (MEMS) for transferring an input force/displacement to an output to achieve mechanical or geometrical advantages. Constrained by micro-fabrication technology, a microleverage mechanism is made of planar flexures, achieving mechanical transformation through elastic deformation. This kind of mechanism is referred to as a compliant mechanism. In this paper, the analysis and optimization of a single-stage microleverage mechanism is presented with a double-ended tuning fork as the output system in a resonant accelerometer to address the design issues. A very good agreement is obtained between the results of analytical modeling and those of FEM simulation with a SUGAR software package. Although the SUGAR data are more accurate, the analytical equations give clearer insights as to how to design a microleverage mechanism. While high axial spring constants and low rotational spring constants are desirable, the axial and rotational spring constants at pivot need to match those at the output system to achieve the maximum force amplification factor. This compliance-match concept is very important for the design of both single-stage and multiple-stage leverage mechanisms.     

A low temperature scanning tunneling microscope for electronic and force spectroscopy

In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision.     

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.     

Angle dependence of the interaction distance in the shear force technique

We study the interaction distance in the lateral force detection, using a standard quartz tuning fork as a force transducer. That is the distance at which the interaction sample-probe starts to be detected. We study in particular the dependence on the approaching angle. For angles smaller than 0.366 radians, we found an exponential behavior of the interaction distance as a function of the approaching angle. We show an equation that adjusts well with the experimental data, and discuss the possible phenomena.