A switchable cantilver for a chemically sensitive scanning force microscope

We describe a cantilever device for a novel ’Time-Of-Flight Scanning Force Microscope (TOF-SFM)’ concept that has the capability of chemical analysis. The cantilever device consists of a switchable cantilever (SC), a microfabricated extraction electrode, and a LEGO-type microstage, which combines two different systems. It allows quasi-simultaneous topographical and chemical imaging of a sample surface to be performed in the same way as with conventional scanning probe techniques. This is achieved by the micromachined SC with a bimorph actuator that provides a reasonable switching speed in comparison with mechanically operated switches. Secondly, a short tip-electrode distance to minimize the ions extraction voltage can be realized by LEGO-type microfabrication. The measured SC tip deflection is -100 μm at 35 mW, corresponding to an estimated heater temperature of -250°C. The maximum switching speed between the two modes is -10 msec, and the sensitivity ΔR/R of an integrated piezoresistive deflection sensor is -6.7× 10^-7/nm. The tip-electrode distance is only 10 μm. The TOF-SFM is currently integrated in an ultra-high-vacuum system to perform several measurements.     

Pulsed interferometric calorimetry

The possibility of using semiconductor single crystals (Si, GaP, etc.) as calorimeters for pulsed heat flux measurements is discussed. The method of laser interferometric thermometry in the reflected light at a wavelength of 1.15 μm makes it possible to detect changes δθ≈2×10⁻⁵ K in the temperature of a 1-mm-thick Si single crystal. The sensitivity of a calorimeter with laser readout is sufficient for detection of the absorbed energy δE≈15 μJ/cm² and is independent of the Si plate thickness. The method for selecting the working point in the resonance curve for achieving maximum sensitivity in detection of pulse fluxes is discussed.     

Vacuum suction aid for microlens array formation using LIGA-like process

Microlens array fabrication using a vacuum suction process combed with the LIGA-like process is presented in this paper. The circular patterned array was designed on a photomask and transferred onto a substrate using photoresist patterning. Electroforming technology was used to convert the photoresist patterns into a metallic molds with an array of nozzles. Liquid JSR resist was spun onto the substrate joining the metallic mold to remove microlens array under vacuum conditions. The exposure energy and vacuum pressure were essential parameters in the microlens array manufacturing process. Microlens arrays with 50 μm in diameter at -50 cm-Hg vacuum pressure and 100 μm in diameter at -60 cm-Hg vacuum pressure were successfully formed. The produced microlens arrays presented smooth measured surface profiles coincident with the optical lens geometry.     

Coupled lateral bending-torsional vibration sensitivity of atomic force microscope cantilever

We study the influence of the contact stiffness and the ration between cantilever and tip lengths on the resonance frequencies and sensitivities of lateral cantilever modes. We derive expressions to determine both the effective resonance frequency and the mode sensitivity of an atomic force microscope (AFM) rectangular cantilever. Once the contact stiffness is given, the resonance frequency and the sensitivity of the vibration modes can be obtained from the expression. The results show that each mode has a different resonant frequency to variations in contact stiffness and each frequency increased until it eventually reached a constant value at very high contact stiffness. The low-order vibration modes are more sensitive to vibration than the high-order mode when the contact stiffness is low. However, the situation is reversed when the lateral contact stiffness became higher. Furthermore, increasing the ratio of tip length to cantilever length increases the vibration frequency and the sensitivity of AFM cantilever.     

A promising thermal pressing used in fabricating microlens array

This paper describes a simple and inexpensive technique for designing and fabricating polygon microlens arrays using a thermal pressing process. Polygon microlens array molds were fabricated using lithography and an electroforming process. The microlens patterns were designed on a photomask and transferred to a substrate through photoresist patterning. Electroforming technology was used to convert the photoresist microlens patterns into metallic molds. A hot pressing machine was then used to produce the microlens array in a polycarbonate (PC) substrate. The experimental variables were compression pressure, temperature, and the pressing time. The surface roughness of the produced microlens array was measured using atomic force microscopy (AFM). The average microlens radii of curvature ranged from 315 to 420 μm and the average sag heights were from 2.98 to 4.03 μm, respectively. The experimental result showed that this fabrication process is useful for microlens array production.     

A nanosecond optical parametric oscillator in the mid-IR region with double-pass pump

An optical parametric oscillator (OPO) with double-pass pump based on MgO:PPLN and PPLN periodic structures is described. A compact nanosecond Nd:YLF laser has been used as a pump source at 1.053 μm (the pumping pulse duration is 5–7 ns at a maximum pulse energy of 300 μJ at frequencies of 1–7 kHz). The oscillation threshold of the OPO based on MgO:PPLN was varied in a range of 11–28 μJ at wavelength of 2.1–4.3 μm. The conversion efficiency from the pump wave to an idler wave decreased from 8.6 to 2.5% in the range of 2.0–4.3 μm. For PPLN-OPO the measured threshold was 36 μJ at 4.2 μm and 49 μJ at 4.7 μm. The conversion efficiency of the pump energy into the energy of an idler wave was 3.3μ-0.4% at wavelengths of 4.2–4.7 μm.     

Wide frequency range capacitive detection of loss in a metallic cantilever using resonance and relaxation modes

The impedance of a capacitor which embraces a charged cantilever is used to measure the mechanical properties of the cantilever material. The technique has been tested with an amorphous metallic specimen, but is applicable for many other solids. The material damping can be measured at the resonance frequency of the cantilever via the width of the resonance curve or by recording the ring-down behavior. Additionally, several decades in frequency are accessible below the resonance frequency, where values as low as nu=0.03 Hz are achieved easily. The data are analyzed with a single equation that captures the damping at all frequencies in terms of the material specific Young's modulus E and its loss angle tan delta=E"/E'.     

Evaluating local elasticity of the metal nano-films quantitatively based on referencing approach of atomic force acoustic microscopy

Traditional technique such nanoindenter(NI) can’t measure the local elastic modulus at nano-scale(lateral). Atomic force acoustic microscopy (AFAM) is a dynamic method, which can quantitatively determine indentation modulus by measuring the contact resonance spectra for high order modes of the cantilever. But there are few reports on the effect of experimental factors, such length of cantilever, contact stiffness on measured value. For three different samples, including copper(Cu) film with 110 nm thickness, zinc(Zn) film of 90 nm thickness and glass slides, are prepared and tested, using referencing approach in which measurements are performed on the test and reference samples (it’s elastic modulus is known), and their contact resonance spectra are measured used the AFAM system experimentally. According to the vibration theory, from the lowest two contact resonance frequencies, the tip-sample contact stiffness is calculated, and then the values for the elastic properties of test sample, such as the indentation modulus, are determined. Using AFAM system, the measured indentation modulus of copper nano-film, zinc nano-film and glass slides are 113.53 GPa, 87.92 GPa and 57.04 GPa, which are agreement with literature values MCu=105-130 GPa, MZn=88.44 GPa and MGlass=50-90 GPa. Furthermore, the sensitivity of contact resonance frequency to contact stiffness is analyzed theoretically. The results show that for the cantilevers with the length 160μm, 225μm and 520μm respectively, when contact stiffness increases from 400 N/m to 600 N/m, the increments of first contact resonance frequency are 126 kHz, 93 kHz and 0.6 kHz, which show that the sensitivity of the contact resonance frequency to the contact stiffness reduces with the length of cantilever increasing. The novel method presented can characterize elastic modulus of near surface for nano-film and bulk material, and local elasticity of near surface can be evaluated by optimizing the experimental parameters using the AFAM system.     

Measurements of nonstationary temperatures by the spectral pyrometry method

Recording of a sequence of thermal-radiation spectra allows determination of a nonstationary temperature T(t) without using the data on the emissivity of an object. For a КЭФ-4.5 silicon single crystal heated with radiation from a continuous-wave Nd:YAG laser (λ = 1.064 μm), sequences of hundreds of emission spectra in wavelength ranges of λ = 350–760 nm and λ = 650–1000 nm were recorded at a signal storage time of a CCD array of τ = 15–35 ms and a frequency of recording spectra of f ≈ 30–66 Hz. The spectra were automatically processed, and the dependences of the crystal temperature on the time after the irradiation onset were obtained in the range T ≈ 1100–1450 K.     

Characteristics of a dynamic atomic force microscopy based on a higher-order resonant silicon cantilever and experiments

In order to improve the sensitivity and scanning speed of the dynamic AFM, a surface scanning method using higher-order resonant cantilever is adopted and investigated based on the higher-order resonance characteristics of the silicon cantilever, and the theoretical analysis and experimental verification on the higher-order resonance characteristics of the corresponding dynamic AFM cantilever are given. In this method, the cantilever is excited to oscillate near to its higher-order resonant frequency which is several times higher than that of the fundamental mode. Then the characteristic changes a lot compared with the first-order resonant cantilever. Because of the changes of the quality factor, amplitude and the mode shape of the cantilever, the higher-order resonant AFM gets higher sensitivity and scanning speed. Based on the home-built tapping-mode AFM experiment system, the resolution and the response time of the first and second order resonance measured by experiment are respectively: 0.83 nm, 0.42 nm; 1265 μs, 573 μs. The higher-order resonance cantilever has higher sensitivity and the dynamic measurement performance of the cantilever is significantly improved from the experimental results. This can be a useful method to develop AFM with high speed and high sensitivity. Besides above, the surface profile of a grating sample and its three-dimensional topography are obtained by the higher-order resonant mode AFM.     

Frictional Properties of a Mesoscopic Contact with Engineered Surface Roughness

Friction between titanium spheres and an artificially structured silicon surface was measured with a friction force microscope. Two spheres with radii of 2.3 μm and 7.9 μm were firmly glued to the tip of the microscope cantilever. A periodic stripe pattern with a groove depth of 26 nm and systematically increasing groove width from 500 nm to 3500 nm was fabricated from a silicon wafer with a focused ion beam. The sphere substrate friction coefficient shows a strong enhancement at a certain groove periodicity, which is related to geometrical interlocking of the two surfaces. This shows that careful modification of the surface roughness can help to control the tribological behavior of mesoscale contacts.     

Expanded beam deflection method for simultaneous measurement of displacement and vibrations of multiple microcantilevers

Here we present an extension of optical beam deflection (OBD) method for measuring displacement and vibrations of an array of microcantilevers. Instead of focusing on the cantilever, the optical beam is either focused above or below the cantilever array, or focused only in the axis parallel to the cantilevers length, allowing a wide optical line to span multiple cantilevers in the array. Each cantilever reflects a part of the incident beam, which is then directed onto a photodiode array detector in a manner allowing distinguishing between individual beams. Each part of reflected beam behaves like a single beam of roughly the same divergence angle in the bending sensing axis as the incident beam. Since sensitivity of the OBD method depends on the divergence angle of deflected beam, high sensitivity is preserved in proposed expanded beam deflection (EBD) method. At the detector, each spot's position is measured at the same time, without time multiplexing of light sources. This provides real simultaneous readout of entire array, unavailable in most of competitive methods, and thus increases time resolution of the measurement. Expanded beam can also span another line of cantilevers allowing monitoring of specially designed two-dimensional arrays. In this paper, we present first results of application of EBD method to cantilever sensors. We show how thermal noise resolution can be easily achieved and combined with thermal noise based resonance frequency measurement.     

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。     

PZN-PT based smart probe for high temperature fluid viscosity measurements

A smart sensing system is proposed for high-temperature (up to 90 °C) viscosity measurement of viscous fluids. The proposed sensing system is based on a smart cantilever probe on which a new generation of piezoelectric materials, relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3−x)PbTiO(3) (PZN-PT), is bonded. The proposed system utilizes a PZN-PT single crystal for actuation and a laser displacement sensor for vibration detection. By analyzing the vibrational properties of the cantilever probe, the viscosity of measured fluids at different temperatures (up to 90 °C) were extracted. Lab tests were carried out to verify and evaluate the effect of this system on high-temperature measurements. Results show a consistent agreement with theoretical analysis. In comparison to the existing high-performance piezoelectric material, lead magnesium niobate-lead titanate solid solution (1−x)[Pb(Mg1/3Nb2/3)O3]−x[PbTiO3] (PMN-PT), PZN-PT has a steady performance at high temperatures and shows more reliability. The proposed sensing system can be applied to real-time monitoring of viscous fluids in high-temperature environments, such as vehicle cooling systems, power plant cooling tower fluid monitoring, and other heat transfer systems.     

Torque detected broad band electron spin resonance

We present a novel technique to measure high frequency electron spin resonance spectra in a broad frequency range (30-1440 GHz) with high sensitivity. We use a quasioptical setup with tunable frequency sources to induce magnetic resonance transitions. These transitions are detected by measuring the change in the magnetic torque signal by means of cantilever torque magnetometry. The setup allows tuning of the frequency, magnetic field, polarization, and the angle between the sample and the external magnetic field. We demonstrate the capabilities of this technique by showing preliminary results obtained on a single crystal of an Fe(4) molecular nanomagnet.     

Investigation of single phase frictional pressure loss in circular micro tubes

Single phase pressure drops in micro tubes were investigated through an experimental measurement and a numerical simulation. Experimental Po was obtained in circular micro tubes with 87 and 118 μm diameter with distilled water. Experiments were carried out in laminar flow region with varying the Re 15–450 for the 87 μm diameter tubes and 60–1300 for the 118 μm diameter tube. No early transition from laminar to turbulent flow was detected for the experimental range. The computational estimation of pressure drop in the 87 μm diameter tube was performed with the aid of CFD software. Boundary conditions from experiments were used for the numerical simulation. The results of experimental and numerical studies showed a good agreement with the conventional macro theory.     

Dual resonance excitation system for the contact mode of atomic force microscopy

We propose an improved system that enables simultaneous excitation and measurements of at least two resonance frequency spectra of a vibrating atomic force microscopy (AFM) cantilever. With the dual resonance excitation system it is not only possible to excite the cantilever vibrations in different frequency ranges but also to control the excitation amplitude for the individual modes. This system can be used to excite the resonance frequencies of a cantilever that is either free of the tip-sample interactions or engaged in contact with the sample surface. The atomic force acoustic microscopy and principally similar methods utilize resonance frequencies of the AFM cantilever vibrating while in contact with the sample surface to determine its local elastic modulus. As such calculation demands values of at least two resonance frequencies, two or three subsequent measurements of the contact resonance spectra are necessary. Our approach shortens the measurement time by a factor of two and limits the influence of the AFM tip wear on the values of the tip-sample contact stiffness. In addition, it allows for in situ observation of processes transpiring within the AFM tip or the sample during non-elastic interaction, such as tip fracture.     

Effects of fluid-structure interaction on trailing-edge noise

This study numerically investigates the effects of fluid-structure interaction (FSI) on the trailing-edge noise, particularly for the cases of wake instability and Karman vortex shedding. The trailing edge is modeled as a flat plate with an elastic cantilever end and its flow-induced vibration is solved by an eigenmode analysis with the Galerkin method. The flow and sound coupled in the FSI analysis are computed on the moving grid by a direct numerical simulation (DNS) procedure. The computed result of wake instability shows that when the first-eigenmode natural frequency ω _n of the cantilever is close to be resonant with the wake characteristic frequency ω _c , the sound pressure level (SPL) is significantly reduced by 20 dB at ω _n /ω _c =0.95, or increased by 15 dB at ω _n /ω _c =1.05, for all angles. For the Karman vortex shedding, a similar frequency modulation occurs via FSI, if ω _n is close to ω _c . The flow and acoustic details are somewhat different for this case but a considerable noise reduction was also possible for angles from −120° to +120°.     

Automated surface finishing of plastic injection mold steel with spherical grinding and ball burnishing processes

This study investigates the possibilities of automated spherical grinding and ball burnishing surface finishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding tool holder has been accomplished in this study. The optimal surface grinding parameters were determined using Taguchi’s orthogonal array method for plastic injection molding steel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the combination of an abrasive material of PA Al₂O₃, a grinding speed of 18000 rpm, a grinding depth of 20 μm, and a feed of 50 mm/min. The surface roughness R_a of the specimen can be improved from about 1.60 μm to 0.35 μm by using the optimal parameters for surface grinding. Surface roughness R_a can be further improved from about 0.343 μm to 0.06 μm by using the ball burnishing process with the optimal burnishing parameters. Applying the optimal surface grinding and burnishing parameters sequentially to a fine-milled freeform surface mold insert, the surface roughness R_a of freeform surface region on the tested part can be improved from about 2.15 μm to 0.07 μm.     

Numerical investigation on frictional pressure loss in a perfect square micro channel with roughness and particles

A numerical study is performed to investigate the effect of inner surface roughness and microparticles on adiabatic single phase frictional pressure drop in a perfect square micro channel. With the variation of particles sizes (0.1 to 1 μm) and occupied volume ratio (0.01 to 10%) by particles, the Eulerian multi-phase model is applied to a 100 μm hydraulic diameter perfect square micro channel in laminar flow region. Frictional pressure loss is affected significantly by particle size than occupied volume ratio by particles. The particle properties like density and coefficient of restitution are investigated with various particle materials and the density of particle is found as an influential factor. Roughness effect on pressure drop in the micro channel is investigated with the consideration of roughness height, pitch, and distribution. Additionally, the combination effect by particles and surface roughness are simulated. The pressure loss in microchannel with 2.5% relative roughness surface can be increased more than 20% by the addition of 0.5 μm diameter particles.