Nanoscale potential measurements in liquid by frequency modulation atomic force microscopy

We have developed a method for local potential measurements in liquid using frequency modulation atomic force microscopy. In this method, local potential is calculated from the first and second harmonic vibrations of a cantilever induced by applying an ac bias voltage between a tip and a sample. The use of an ac bias voltage with a relatively high frequency prevents uncontrolled electrochemical reactions and redistribution of ions and water. The nanoscale resolution of the method is demonstrated by imaging potential distribution of a dodecylamine thin film deposited on a graphite surface in 1 mM NaCl solution.     

Experimental study on the sensitivity and accuracy of electric potential local flow measurements

A measuring system based on potential difference probes is presented which makes possible the determination of very small values of the velocity in liquid metal flows. The resolution limit, the size of the sensor, and the induction of the static measuring field have always been a compromise. These opposite demands were countered with state of the art analog instrumentation, and by meticulously avoiding potential sources of error such as induced noise and thermoelectricity. The present paper instances the flow driven by a rotating magnetic field, in which the scaling of velocity versus strength of the driving electromagnetic force was examined. Measurements of the transition from a Stokes regime to a laminar boundary layer regime demonstrate the improvement in velocity resolution by about two orders of magnitude.     

High-pressure apparatus for dielectric measurements in high frequency

The present article describes an experimental apparatus for the measurement of low-loss dielectric material under conditions of high pressures (maximum pressure 1500 bars) and high frequencies (1-15 MHz.) The measurements of these losses are based on the classical method of the Q-meter with a general Radio type 1690-A sample holder, located in a high-pressure bomb. All the manual operations made on the holder during the measurements are controlled by dc motors. The first results have shown that the dielectric losses of polyethylene (PE) vary with the pressure. This apparatus will later be used in the measurement of the dielectric losses of the insulating materials used for submarine telecommunication cables.     

Collective Thomson scattering measurements with high frequency resolution at TEXTOR

We discuss the development and first results of a receiver system for the collective Thomson scattering (CTS) diagnostic at TEXTOR with frequency resolution in the megahertz range or better. The improved frequency resolution expands the diagnostic range and utility of CTS measurements in general and is a prerequisite for measurements of ion Bernstein wave signatures in CTS spectra. The first results from the new acquisition system are shown to be consistent with theory and with simultaneous measurements by the standard receiver system.     

A high frequency sensor for optical beam deflection atomic force microscopy

We demonstrate a novel electronic readout for quadrant photodiode based optical beam deflection setups. In our readout, the signals used to calculate the deflections remain as currents, instead of undergoing an immediate conversion to voltages. Bipolar current mirrors are used to perform all mathematical operations at the transistor level, including the signal normalizing division. This method has numerous advantages, leading to significantly simpler designs that avoid large voltage swings and parasitic capacitances. The bandwidth of our readout is solely limited by the capacitance of the quadrant photodiode junctions, making the effective bandwidth a function of the intensity of photocurrents and thus the applied power of the beam deflection laser. Using commercially available components and laser intensities of 1-4 mW we achieved a 3 dB bandwidth of 20 MHz with deflection sensitivities of up to 0.5-1 V/nm and deflection noise levels below 4.5 fm/Hz. Atomic resolution imaging of muscovite mica using FM-AFM in water demonstrates the sensitivity of this novel readout.     

Multi-objective optimal design of high frequency probe for scanning ion conductance microscopy

Scanning ion conductance microscopy(SICM) is an emerging non-destructive surface topography characterization apparatus with nanoscale resolution. However, the low regulating frequency of probe in most existing modulated current based SICM systems increases the system noise, and has difficulty in imaging sample surface with steep height changes. In order to enable SICM to have the capability of imaging surfaces with steep height changes, a novel probe that can be used in the modulated current based hopping mode is designed. The design relies on two piezoelectric ceramics with different travels to separate position adjustment and probe frequency regulation in the Z direction. To further improve the resonant frequency of the probe, the material and the key dimensions for each component of the probe are optimized based on the multi-objective optimization method and the finite element analysis. The optimal design has a resonant frequency of above 10 kHz. To validate the rationality of the designed probe, microstructured grating samples are imaged using the homebuilt modulated current based SICM system. The experimental results indicate that the designed high frequency probe can effectively reduce the spike noise by 26% in the average number of spike noise. The proposed design provides a feasible solution for improving the imaging quality of the existing SICM systems which normally use ordinary probes with relatively low regulating frequency.     

Conditioning of FRF measurements for use with frequency based substructuring

Frequency based substructuring approaches have been used for the generation of system models from component data. While numerical models show successful results, there have been many difficulties with actual measurements in many instances. Previous work has identified some of these typical problems using simulated data to incorporate specific measurement difficulties commonly observed along with approaches to overcome some of these difficulties.This paper presents the results using actual measured data for a laboratory structure subjected to both analytical and experimental studies. Various commonly used approaches are shown to illustrate some of the difficulties with measured data. A new approach to better condition the measured functions and purge commonly found data measurement contaminants is utilized to provide dramatically improved results.Several cases are explored to show the difficulties commonly observed as well as the improved conditioning of the measured data to obtain acceptable results.     

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.     

Critical AC frequency for stable operation of electrowetting-driven optofluidic devices with polymeric electrolyte solutions

Journal of Mechanical Science and Technology - EWOD (electrowetting on dielectric) is a viable scheme to drive optofluidic devices that utilize the liquid interface as a refractive surface....     

A digital modification for beam current measurements in electron microscopy

A digital microammeter with 0.1 μA sensitivity has been employed in the TEM beam current circuit to increase the accuracy to which the electron beam can be recorded and adjusted.     

Optimum condition of convergent beam illumination for observation of local structure by high resolution transmission electron microscopy

We propose the convergent beam illumination as a technique for the local structural analysis by high resolution transmission electron microscopy. The image contrast is lower in the convergent beam illumination than in the parallel beam illumination because of the lower coherency. However the intensity oscillation around an atom image, which appears due to interference effect, is much reduced with the convergent beam illumination, and pseudo-images do not appear at termination of crystal periodicity. The convergent beam illumination, rather than parallel beam illumination, precisely reveals non-periodic local structures, such as interfaces, surfaces and fine particles, which are even embedded in a crystal. From theoretical analysis the optimum condition is derived as divergence of q(s )* = 0.44 and focus of delta(z)* = 1.35 in generalized coordinates. Using the convergent beam illumination the point resolution is improved by 20% compared to conventional parallel beam illumination.     

An optimum reinforcement solution for a torsionless grillage with given minimum strength

The paper presents the minimum reinforcement solution for a simply-supported square torsionless grillage, with beams parallel to the sides of the square, for specified uniformly distributed transverse load at collapse, for the case where a minimum proportion of reinforcement (and therefore a minimum bending strength) must be provided at every point. The optimal design collapses in a mode satisfying certain conditions on curvature, and the corresponding moment field is developed using lines of load transfer (with finite jumps in moment) for concentrated forces, and the equation of bimoments for finite grillage segments. A solution is obtained only for a limited range of load magnitudes (up to about twice what may be carried with the specified minimum bending strength alone). However, the minimum volume of reinforcement is not much less than that for a simple practical design, with crossed uniform bands of extra reinforcement near midspan, which can cope with any magnitude of load.     

Image processing for resonance frequency mapping in atomic force modulation microscopy

It has been demonstrated that the resonance frequency of the cantilever in atomic force modulation microscopy can be used to study local mechanical properties. We developed a numerical method to achieve mapping of the resonance frequency without significant modification of the device. By making the assumption that the resonance spectrum can be approximated by a Lorentzian curve, we established analytical expressions of the resonance frequency and the width of the curve (damping) depending on the real and imaginary parts of the vibration at a single frequency. Then, resonance frequency and damping images were produced from the recording of both the real and imaginary part images of the complex amplitude. The results on a standard high-impact polystyrene sample are shown.     

Integration of impedance measurements with acoustic measurements for accurate two phase flow metering in case of high water-cut

Previous studies have yielded promising results as to the use of impedance measurements in two phase flow metering in estimating the flow rate of individual flows in oil fields (i.e. water and oil flows). However, most of these approaches are not accurate in the case of high water-cut or within the water-cut range 40% to 60%, where the mixed liquid is neither a good conductor, nor a good insulator. With the increased out-aging of the oil fields, these two ranges are usually dominant which require the usage of new methods. This paper presents a new non-radioactive probe which combines acoustic measurements with the impedance measurements to accurately provide in real-time the flow rate of each individual flow within the whole water-cut range. A dedicated pattern recognition algorithm using a neural network and relying on the physical properties of the fluid dynamic has been implemented. Experimental measurements performed on a laboratory scale two phase flow loop show that the proposed flow meter can in fact become a competitive two phase flow meter, since less than 5% relative error could be achieved for the whole water-cut range.     

Two-dimensional, electrostatic finite element study of tip-substrate interactions in electric force microscopy of high density interconnect structures

Two-dimensional electrostatic finite element modeling is used to estimate the variation of tip force as a function of potential, dielectric film thickness, and tip-substrate spacing when imaging using electric force microscopy. Blanket dielectric films and approximately 1000 nm thick interconnect structures were studied. We conclude that sidewall damage regions can be detected but will require special processing to make an unambiguous measurement.     

Wideband phase-locked loop circuit with real-time phase correction for frequency modulation atomic force microscopy

We have developed a wideband phase-locked loop (PLL) circuit with real-time phase correction for high-speed and accurate force measurements by frequency modulation atomic force microscopy (FM-AFM) in liquid. A high-speed operation of FM-AFM requires the use of a high frequency cantilever which, however, increases frequency-dependent phase delay caused by the signal delay within the cantilever excitation loop. Such phase delay leads to an error in the force measurements by FM-AFM especially with a low Q factor. Here, we present a method to compensate this phase delay in real time. Combined with a wideband PLL using a subtraction-based phase comparator, the method allows to perform an accurate and high-speed force measurement by FM-AFM. We demonstrate the improved performance by applying the developed PLL to three-dimensional force measurements at a mica/water interface.     

Machine learning-based personal thermal comfort model for electric vehicles with local infrared radiant warmers

Journal of Mechanical Science and Technology - Thermal comfort of occupants in conventional vehicles driven by an internal combustion engine is controlled by heating, ventilation, and air...     

Polarization microscopy probe for applications in a high magnetic field

A microscopy probe designed for use in high field magnets is presented. It was developed to observe and continuously measure the position and shape of a magnetically driven grain boundary in a magnetically anisotropic material. The approach utilizes the anisotropy of reflectivity of visible light for orientation contrast to determine the boundary location. The major components of the system are the polarizing microscope with video camera and the sample chamber with a resistive heater for annealing at elevated temperatures up to 500 degrees C in an inert gas atmosphere. The results of test measurements are presented.     

Multifrequency channel microwave reflectometer with frequency hopping operation for density fluctuation measurements in Large Helical Device

In order to measure the internal structure of density fluctuations using a microwave reflectometer, the broadband frequency tunable system, which has the ability of fast and stable hopping operation, has been improved in the Large Helical Device. Simultaneous multipoint measurement is the key issue of this development. For accurate phase measurement, the system utilizes a single sideband modulation technique. Currently, a dual channel heterodyne frequency hopping reflectometer system has been constructed and applied to the Alfve?n eigenmode measurements.