Optimisation of a nano-positioning stage for a Transverse Dynamic Force Microscope

This paper describes the optimisation of a nano-positioning stage for a Transverse Dynamic Force Microscope (TDFM). The nano-precision stage is required to move a specimen dish within a horizontal region of 1 μm × 1 μm and with a resolution of 0.3 nm. The design objective was to maximise positional accuracy during high speed actuation. This was achieved by minimising out-of-plane distortions and vibrations during actuation. Optimal performance was achieved through maximising out-of-plane stiffness through shape and material selection as well optimisation of the anchoring system. Several shape parameters were optimised including the shape of flexural beams and the shape of the dish holder. Physical prototype testing was an essential part of the design process to confirm the accuracy of modelling and also to reveal issues with manufacturing tolerances. An overall resonant frequency of 6 kHz was achieved allowing for a closed loop-control frequency of 1.73 kHz for precise horizontal motion control. This resonance represented a 12-fold increase from the original 500 Hz of a commercially available positioning stage. Experimental maximum out-of-plane distortions below the first resonance frequency were reduced from 0.3 μm for the first prototype to less than 0.05 μm for the final practical prototype.     

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。     

Atomic force microscope probe calibration by use of a commercial precision balance

In this paper, we investigate the characteristics of a piezoresistive AFM cantilever in the range of 0–1.6 μN by using nano force calibrator (NFC), which consists of a high precision balance with resolution of 1 nN and 1-D fine positioning stage. Brief modeling of the cantilever is presented and then, the calibration results are shown. Tests revealed a linear relationship between the probing force and sensor output (resistance change), but the force vs. deflection is not as linear as the force vs. sensor output curve. The force constant of the cantilever was measured to 0.26 N/m with a standard deviation of 0.01 N/m. It shows that there is big difference between measured and nominal spring constant of 1 N/m provided by the manufacturer’s specifications.     

Design of elliptically-vibrating ultrasonic actuator for nanocoining

Nanocoining is a method of rapidly creating a cylindrical mold surface covered with features smaller than the wavelength of light. This mold can then be used in a roll-to-roll process to make surfaces whose functionality depends on the wavelength of the illumination. The die replaces the typical diamond tool used to produce overlapping grooves for applications such as reflective signs. The die has a face area approximately 20 μm² that has been patterned in an FIB. It is mounted on a 2D ultrasonic actuator and follows an elliptical path that matches the surface speed of the moving workpiece during the short contact time and creates approximately 6000 features per impact. The spacing of die indents is controlled by the speed of the diamond turning machine axes such that a small overlap exists from previous indents as the die spirals around and along the mold surface. Because the die is small, the indentations must occur rapidly to make nanocoining a feasible process. This work focuses on the design and control of a nominally 40 kHz, 2D resonant actuator that is suitable for this process. A controller to automatically track resonance is described to maintain the elliptical motion during indentation. Methods of tuning the behavior of the actuator and maintaining a constant indent depth are proposed. Finally, 500 nm pitch feature indents were created on a brass workpiece at 40 kHz and scanning electron microscope (SEM) images of the features are provided.     

Design and application of fiber Bragg grating (FBG) geophone for higher sensitivity and wider frequency range

The fiber Bragg grating geophone sensor with higher sensitivity and wider frequency range was reported. The methods to increase the sensitivity of the FBG cantilever sensor were presented. The acceleration sensitivity of the optimized FBG geophone is 220 pm/g, and the resonant frequency can reach to 295 Hz. The experiments show that the FBG geophone system has the minimum detectable acceleration of 1 mm/s². Some factual application examples of using this fiber Bragg grating geophone monitoring system for micro seismic monitoring in coal mine were presented.     

A force-matching method for quantitative hardness measurements by atomic force microscopy with diamond-tipped sapphire cantilevers

We present a new method to improve the accuracy of force application and hardness measurements in hard surfaces by using low-force (<50 μN) nanoindentation technique with a cube-corner diamond tip mounted on an atomic force microscopy (AFM) sapphire cantilever. A force calibration procedure based on the force-matching method, which explicitly includes the tip geometry and the tip-substrate deformation during calibration, is proposed. A computer algorithm to automate this calibration procedure is also made available. The proposed methodology is verified experimentally by conducting AFM nanoindentations on fused quartz, Si(1 0 0) and a 100-nm-thick film of gold deposited on Si(1 0 0). Comparison of experimental results with finite element simulations and literature data yields excellent agreement. In particular, hardness measurements using AFM nanoindentation in fused quartz show a systematic error less than 2% when applying the force-matching method, as opposed to 37% with the standard protocol. Furthermore, the residual impressions left in the different substrates are examined in detail using non-contact AFM imaging with the same diamond probe. The uncertainty of method to measure the projected area of contact at maximum force due to elastic recovery effects is also discussed.     

Wear behaviour of dental enamel at the nanoscale with a sharp and blunt indenter tip

Two different diamond nanoindenter tips, a rounded conical (～1200 nm radius) and a sharp cube corner (20–50 nm radius) were used to abrade bovine enamel. Square abraded areas (2 μm × 2 μm, 5 μm × 5 μm, 10 μm × 10 μm) were generated with loads that varied from 50 μN to 500 μN depending on the indenter tip. In addition normal and lateral forces were simultaneously measured along 10 μm single scratched lines with the sharp cube corner tip. SEM (scanning electron microscopy) and TEM (transmission electron microscopy) were also used to characterise the worn areas and debris. Two different wear mechanisms were observed depending on the geometry of the tip. The rounded tip generates a predominantly elastic contact that mainly compresses and plastically deforms the superficial material and generates severe shear deformation within the sub-surface material which, under certain conditions, fractures and removes material from the sample. The sharp tip cuts into and ploughs the enamel creating a wedge or ridge of material ahead of itself which eventually detaches. This sequence is repeated continuously for every passage of the sharp indenter tip. The different mechanisms are discussed in terms of abrading tip contact angle and enamel microstructure.     

Nanometric cutting in a scanning electron microscope

A nanometric cutting device under high vacuum conditions in a scanning electron microscope (SEM) was developed. The performance, tool-sample positioning, and processing capacity of the nanometric cutting platform were studied. The proposed device can be used to realize a displacement of 7 μm, with a closed-loop resolution of 0.6 nm in both the cutting direction and the depth direction. Using a diamond cutting tool with an edge radius of 43 nm formed by focused ion beam (FIB) processing, nanometric cutting experiments on monocrystalline silicon were performed on the developed cutting device under SEM online observation. Chips and machining results of different depths of cut were studied during the cutting process, and cutting depths of less than 10 nm could be obtained with high repeatability. Moreover, the cutting speed was found to exhibit a strong relationship with the brittle–ductile transition depth on brittle material. The experimental results of taper cutting and sinusoidal cutting indicated that the developed device has the ability to perform multiple degrees of freedom (DOFs) cutting and to study nanoscale material removal behaviour.     

Effect on crystalline structure of AISI M2 steel using tungsten–thorium electrode through MRR,EWR, and surface finish

To investigate on the crystalline structure of AISI M2 steel by using tungsten–thorium electrode in electrical discharge machining (EDM) process was studied. Furthermore, the investigation were carried out for finding the value of material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) of tool steel material depending upon three variable input process parameters. On the basis of weight loss, the value of MRR and EWR were calculated at optimized process parameter. Subsequently, surface topography of the processed material were examined through different characterization techniques like scanning electron microscopy (SEM), Optical surface profiler (OSP) and Atomic force microscopy (AFM), respectively. In XRD study, broadening of the peak was observed which confirmed the change in material properties due to the homogeneous dispersion of the particles inside the matrix. Lowest surface roughness and MRR of 0.001208 mg/min was obtained. Minimum surface roughness was obtained 1.12 μm and 2.18427 nm by OSP and AFM study, respectively. Also, minimum EWR was found as 0.013986 mg/min.     

Uncertainty analysis of slot die coater gap width measurement by using a shear mode micro-probing system

A shear mode micro-probing system was constructed for gap measurement of a precision slot die coater with a nominal gap width of 90 μm and a length of 200 mm. A glass micro-stylus with a nominal tip ball diameter of 52.6 μm was oscillated by a tuning fork quartz crystal resonator with its oscillation direction parallel to the measurement surfaces. An on-line qualification setup was established to compensate for the influences of the uncertainty sources, including the water layers on the measurement surfaces. The measurement uncertainty of the measured gap width was estimated to be less than 100 nm.     

Analysis of load-speed sensitivity of friction composites based on various synthetic graphites

The frictional response of a multi-component phenolic-based friction material is highly complex under a set of variable loads and speeds. The present paper discusses the sensitivity of friction coefficient (μ) of friction composites containing synthetic graphite with different particle sizes (with similar crystallinity range) to braking pressure and sliding speed. The friction studies were carried out on a sub scale brake-test-rig, following 4 loads × 3 speeds experimental design. The best combination of performance properties was observed for the composite containing synthetic graphite with an average particle size of 410 μm. Other particle sizes which resulted in good performance were 38 and 169 μm. Very fine particle sizes were not beneficial for desired combination of performance properties. Regression analysis of μ following an orthogonal L₉(3 × 3) experimental design method revealed that the first order influences of sliding speed and braking pressure were significant. When all the combinatorial influences of braking pressure and sliding speed are taken into account together their simultaneous effects would be most effective in the range of graphite particle size ～80–250 μm.     

A piezoelectric motor for precision positioning applications

This study presents a novel precise piezoelectric motor capable of operating in either an AC drive mode or DC drive mode. In the AC drive mode, the motor acts as an ultrasonic motor which is driven by two orthogonal mechanical vibration modes to generate elliptical motion at the stator to push the slider into motion. In the DC drive mode, stick-slip friction between the stator and slider is used to drive the motor step-by-step. The experimental results show that the AC drive mode can drive the motor at a high moving speed, while the DC drive mode can simply drive the motor with a nanoscale resolution. In our experiments, a prototype motor is fabricated and its actions are measured. The results demonstrate that in the AC drive mode, the piezoelectric motor can achieve a 106 mm/s speed without a mechanical load and a 34 mm/s speed with 340 g of mechanical load when applying two sine waves with a drive of 11.3 V at 38.5 kHz. Meanwhile, in a DC driving mode, the motor is capable of performing precision positioning with a displacement resolution of 6 nm when driving at 100 Hz.     

Electrogenerated chemical polishing of copper

Stress free polishing method is preferred for a damage free surface of copper with ultra-flatness and ultra-smoothness. Such a surface offers a perfect substrate for integrated circuits and micro-electromechanical systems fabrication. A new polishing method, called electrogenerated chemical polishing (EGCP), is proposed based on the principle of the scanning electrochemical microscope (SECM) and the diffusion controlled chemical reaction. Roughness of a Cu surface is reduced from 100.5 nm to 3.6 nm by the proposed method. To demonstrate the planarization capability of this new method, a patterned Cu surface with an array of micro-columns is planarized with a peak-valley (PV) value from 4.7 μm to 0.059 μm.     

Effect of silicon nitride coating thickness on fatigue of silicon microbeams

In this paper, two silicon nitride layers with thickness, 0.2 and 0.4 μm, are coated onto single crystal silicon (SCS) in order to achieve Si₃N₄/Si cantilever microbeams. The effect of LPCVD silicon nitride surface coatings on fatigue properties of SCS cantilever microbeams is investigated. Fatigue testing is conducted at both 40 Hz and 100 Hz. Typical S–N (strain amplitude–fatigue cycle) curves of the beams are achieved and correlated fatigue failure modes are investigated. It is found that thinner Si₃N₄ coating of 0.2 μm results in better fatigue lives of Si₃N₄/Si beams than thicker Si₃N₄ coating of 0.4 μm. Both thinner and thicker coated beams have major fatigue crack planes along {1 1 1} planes; however, thicker coated beams possess specific failure mode of delamination, which is not found in thinner coated beams. Delamination reduces the reinforcing effect of thicker Si₃N₄ coating and leads to its shorter fatigue life. For thicker coated beams, fatigue life at 100 Hz is longer than that at 40 Hz. The mechanism for delamination and the effect of cyclic frequency is investigated, and factors for better fatigue life are proposed.     

Study of the sensitivity of the first four flexural modes of an AFM cantilever with a sidewall probe

The resonant frequency and sensitivity of flexural vibration for an atomic force microscope (AFM) cantilever with a sidewall probe have been analyzed. A closed-form expression for the sensitivity of vibration modes has been obtained using the relationship between the resonant frequency and contact stiffness of cantilever and sample. The results show that a sidewall scanning AFM is more sensitive when the contact stiffness is lower and that the first mode is the most sensitive. However, the high-order modes become more sensitive than the low-order modes as the contact stiffness increases. The resonance frequency of an AFM cantilever is low when contact stiffness is small. However, the frequency rapidly increases as contact stiffness increases. In addition, it can be found that the effects of the vertical extension on the sensitivity and the resonant frequency of an AFM cantilever are significant. Decreasing the length of vertical extension can increase the resonance frequency and sensitivity of mode 1 when the contact stiffness is small. However, the situation is reverse when the contact stiffness becomes large.     

Tribological interaction between multi-walled carbon nanotubes and silica surface using lateral force microscopy

This work presents the tribological interaction between multi-walled carbon nanotubes (MWCNTs) and silica surface using lateral manipulation in the atomic force microscope (AFM). The MWCNT is mechanically manipulated by a pyramidal silicon probe of an AFM using the same scan mechanism as in the imaging mode. With a controlled normal force of the AFM probe, it was found that lateral force applied to the MWCNT could overcome the tribological adhesion between MWCNT and silica surface, causing individual MWCNT to rotate on the silica. According to the results, the shear stresses due to tribological interacting with the MWCNTs and the silica are 59.6 MPa and 64.8 MPa for the MWCNT 1 (100 nm diameter) and the MWCNT 2 (60 nm diameter), respectively. Experimental results show that the shear stress increases with the increasing rotation angle for each manipulation, from which we determine the linear fitting function. In addition, we determine the relationship between push point and pivot point to realize the rotation behavior. The implications of tribological interaction between the MWCNTs and silica surface are discussed in detail.     

Digital filtering methodology used to reduce scale of measurement effects in roughness parameters for magnetic storage supersmooth hard disks

Roughness of disk media influences the tribological interaction of head-disk interfaces, especially when the intended flying-height is below 5 nm that is required to achieve extremely high-density recording (EHDR). Roughness parameters such as the root-mean-square (RMS) amplitude, however, are influenced by the scale of measurement, such as the scan size. Effects related to scale of measurement such as varying the scan size were investigated and means to reduce such effects were proposed by establishing an “ad hoc” digital filtering procedure. Two types of magnetic disks intended for EHDR were measured by an atomic force microscope (AFM) at various scan dimensions ranging from 0.5 μm × 0.5 μm to 112 μm × 112 μm. The proposed filtering method used the RMS values as a filter design parameter for choosing the appropriate high-pass cutoff wavelength for each scan size. The study revealed the existence of a unique cutoff wavelength that would identify different wavelength regimes and the associated critical scan size in each disk. To substantiate the effectiveness of the proposed filtering method in reducing the scale of measurement effects related to the scan size, other roughness parameters were also calculated subsequent to the filtering procedure. It was found that the proposed filtering scheme effectively reduced the scale of measurement effects in the amplitude parameters (e.g., RMS and the ten-point height variation) and the functional parameters (e.g., material and core void volumes). These parameters exhibited steady-state trends with respect to increasing scan size, indicating reduced scale of measurement effects.     

A long-stroke 3D contact scanning probe for micro/nano coordinate measuring machine

This paper presents a long-stroke contact scanning probe with high precision and low stiffness for micro/nano coordinate measuring machines (micro/nano CMMs). The displacements of the probe tip in 3D are detected by two plane mirrors supported by an elastic mechanism, which is comprised of a tungsten stylus, a floating plate and two orthogonal Z-shaped leaf springs fixed to the outer case. A Michelson interferometer is used to detect the vertical displacement of the mirror mounted on the center of the floating plate. An autocollimator based two dimensional angle sensor is used to detect the tilt of the other plane mirror located at the end of the arm of the floating plate. The stiffness and the dynamic properties are investigated by simulation. The optimal structural parameters of the probe are obtained based on the force-motion model and the constrained conditions of stiffness, measurement range and horizontal size. The results of the performance tests show that the probe has a contact force gradient within 0.5 mN/μm, a measuring range of (±20 μm), (±20 μm), and 20 μm, respectively, in X, Y and Z directions, and a measurement standard deviation of 30 nm. The feasibility of the probe has preliminarily been verified by testing the curved surface of a convex lens.     

A 3-axis precision positioning device using PZT actuators with low interference motions

For expected applications of fast tool servo (FTS) and vibration machining, a 3-axis positioning device with low interference motions is proposed in this paper. The positioning device was composed of a XY stage and a Z-axis stage, which were actuated by piezoelectric (PZT) actuators combined with specially-designed symmetric flexure hinges. Through fundamental experiments, when the applied voltage was 50 V, the displacements along the X-, Y-, and Z-axes were measured as 6.35 μm, 6.61 μm, and 10.12 μm, respectively, with the corresponding small percentages of interference displacement of 3.80%, 4.02%, and 3.30%. In addition, the resonant frequencies were obtained as 1.06 kHz, 0.65 kHz, and 0.54 kHz. To examine control performances, a real-time control system considering hysteresis effect of PZT actuators was implemented by the field-programmable gate array (FPGA) modules to conduct tracing controls for sinusoidal waveform, 3D Lissajous motion, and 3D spiral motion. The tracing errors along 3-axis actuations were under 30 nm. The performances of a 3-axis positioning device were well demonstrated. Future work is to perform machining examinations on a machine tool.     

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 2: Investigation of profile and surface grinding

After finishing the precision conditioning of mono-layer nickel electroplated coarse-grained diamond wheels with 151 μm (D151), 91 μm (D91) and 46 μm (D46) grain size, resp., profile and surface grinding experiments were carried out on a five-axis ultra-precision grinding machine with BK7, SF6 optical glasses and Zerodur glass ceramic. A piezoelectric dynamometer was used to measure the grinding forces, while an atomic force microscopy (AFM), white-light interferometer (WLI)) and scanning electron microscope (SEM) were used to characterize the ground surface quality in terms of micro-topography and subsurface damage. Moreover, the wear mechanics of the coarse-grained diamond wheels were analyzed and the grinding ratio was determined as well, in aiming to evaluate the grinding performance with the conditioned coarse-grained diamond wheels. Finally, the grinding results were compared with that of the fine-grained diamond wheels with regard to the ground specimen surface quality, process forces and wheel wear as a function of stock removal. The experimental results show that the precision conditioned coarse-grained diamond wheels can be applied in ductile mode grinding of optical glasses with high material removal rates, low wheel wear rates and no dressing requirement yielding excellent surface finishes with surface roughness in the nanometer range and subsurface damage in the micrometer range, demonstrating the feasibility and applicability of the newly developed diamond grinding technique for optical glasses.