Fabrication and characterization of ZnO thin film for hydrogen gas sensing prepared by RF-magnetron sputtering

A ZnO thin film-based gas sensor was fabricated using a SiO₂/Si substrate with an integrated platinum comb-like electrode and heating element. The structural characteristics, morphology, and surface roughness of the as-grown ZnO nanostructure were investigated. The optical properties were examined by UV–vis spectrophotometry. The film revealed the presence of a c-axis oriented (0 0 2) phase of 20.8 nm grain size. The sensor response was tested for hydrogen concentrations of 50, 70, 100, 200, 400, and 500 ppm at operating temperatures ranging from 250 °C to 400 °C. The sensitivity toward 50 and 200 ppm of hydrogen at the optimum operating temperature of 350 °C were about 78% and 98%, respectively. The response was linear within the range of 50–200 ppm of hydrogen concentration. Our results demonstrated the potential application of ZnO nanostructure for fabricating cost-effective and high-performance gas sensors.     

Traceable pico-meter level step height metrology

The atomic force microscope (AFM) increasingly being used as a metrology tool in the semiconductor industry where the features measured are at the nanometer level and continue to decrease. Usually the height sensors of the AFM are calibrated using step height specimens ranging from 8 nm to a few μm, however there are no calibration standards at the sub-nanometer level. Recently we have explored the use of stepped silicon single atom specimens as sub-nanometer height calibration artifacts. We have also developed a calibrated atomic force microscope (C-AFM), an AFM with direct traceability to the definition of length to calibrate standards for other AFMs. Earlier, we evaluated the step height of silicon single atomic steps along the (1 1 1) direction (with native oxide) using the C-AFM and obtained a value 304 ± 8 pm (k = 2). To validate the utility of these specimens and the applicability of our analysis technique, we conducted an industry comparison to determine the reproducibility of results obtained when using our procedure. The comparison included AFM vendors and semiconductor device manufacturers. The average standard deviation was 6 pm, and indicates that these specimens and our procedure could be used for sub-nanometer height calibrations.In this paper we will present our evaluation procedure, results of the comparison, and derivation of a value for Si(1 1 1) step height. We will also explore the trends in each participant's data, its effect on the calculation of the mean value, and implications on the reproducibility of our technique. Finally, we will outline the procedure for use of these specimens.     

Development of high-precision micro-coordinate measuring machine: Multi-probe measurement system for measuring yaw and straightness motion error of XY linear stage

Today, with the development of microsystem technologies, demands for three-dimensional (3D) metrologies for microsystem components have increased. High-accuracy micro-coordinate measuring machines (micro-CMMs) have been developed to satisfy these demands. A high-precision micro-CMM (M-CMM) is currently under development at the National Metrology Institute of Japan in the National Institute of Advanced Industrial Science and Technology (AIST), in collaboration with the University of Tokyo. The moving volume of the M-CMM is 160 mm × 160 mm × 100 mm (XYZ), and our aim is to achieve 50-nm measurement uncertainty with a measuring volume of 30 mm × 30 mm × 10 mm (XYZ). The M-CMM configuration comprises three main parts: a cross XY-axis, a separate Z-axis, and a changeable probe unit. We have designed a multi-probe measurement system to evaluate the motion accuracy of each stage of the M-CMM. In the measurement system, one autocollimator measures the yaw error of the moving stage, while two laser interferometers simultaneously probe the surface of a reference bar mirror that is fixed on top of an XY linear stage. The straightness motion error and the reference bar mirror profile are reconstructed by the application of simultaneous linear equations and least-squares methods. In this paper, we have discussed the simulation results of the uncertainty value of the multi-probe measurement method using different intervals and standard deviations of the laser interferometers. We also conducted pre-experiments of the multi-probe measurement method for evaluating the motion errors of the XY linear stage based on a stepper motor system. The results from the pre-experiment verify that the multi-probe measurement method performs the yaw and straightness motion error measurement extremely well. Comparisons with the simulation results demonstrate that the multi-probe measurement method can also measure the reference bar mirror profile with a small standard deviation of 10 nm.     

Studies of high temperature sliding wear of metallic dissimilar interfaces IV: Nimonic 80A versus Incoloy 800HT

Wear variations of Nimonic 80A slid against Incoloy 800HT between room temperature (RT) and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ were investigated using a ‘reciprocating-block-on-cylinder’, low debris retention configuration. These were considered alongside previous observations at 0.654 m s⁻¹.Different wear types occurring were mapped, including high transfer ‘severe wear’ (RT and 270 °C, also 0.905 m s⁻¹ at ≤570°C), low transfer ‘severe wear’ (0.314 m s⁻¹ at 390 °C to 510 °C oxide abrasion assisted at 510 °C), and ‘mild wear’ (0.314 m s⁻¹ at ≥570 °C; 0.905 m s⁻¹ at ≥630 °C). Wear surfaces at 750 °C were cross-sectioned and profiled.     

Using a monocular optical microscope to assemble a wetting contact angle analyser

The ability of a solid surface to be wetted by a liquid can be classified by its wetting contact angle, θ_C: hydrophilic (θ_C < 90°), hydrophobic (90° ? θ_C ? 150°), or super-hydrophobic (θ_C > 150°). To study the wetting behaviour of material surfaces, commercial contact angle analysers are generally employed. In this paper, we report on the construction and testing of a wetting contact angle analyser. To test the performance of the measurement system, we have measured the contact angles of films from commercial paraffin wax and polytetrafluoroethylene (PTFE). The contact angles are found to be in good agreement with the values described in the literature; thus, our analyser can be useful not only for research but also for educational purposes.     

Micro- and nano-tribological behavior of soybean oil-based polymers of different crosslinking densities

Biobased polymers produced from renewable and inexpensive natural resources, such as natural oils, have drawn considerable attention over the past decades, due to their low cost, ready availability, environmental compatibility, and their inherent biodegradability. In this study, the micro/nanotribological wear behavior of biopolymers with different crosslinking densities prepared from low saturated soybean oil (LSS) by cationic copolymerization with divinyl benzene and polystyrene are evaluated and compared. Microtribological measurements were performed using a ball-on-flat reciprocating microtribometer using two different probes −1.2 mm radius Si₃N₄ spherical probe and a 100 μm radius conical diamond probe with 90° cone angle. Nanoscale wear tests were performed using a DLC coated antimony (n) doped silicon probe of radius ∼200 nm in an atomic force microscope (AFM). Wear volumes were estimated from AFM topography maps of groove geometry and wear coefficients were evaluated for the materials. Elastic modulus and hardness information were evaluated using nanoindentation tests. Correlations between crosslinking density and observed wear behavior across scales are discussed. These results provide some insight into the wear behavior of soybean oil-based polymers.     

A large deflection and high payload flexure-based parallel manipulator for UV nanoimprint lithography: Part I. Modeling and analyses

This paper presents a flexure-based parallel manipulator (FPM) that delivers nanometric co-planar alignment and direct-force imprinting capabilities to automate an ultra-violet nanoimprint lithography (UV-NIL) process. The FPM is articulated from a novel 3-legged prismatic-prismatic-spherical (3PPS) parallel-kinematic configuration to deliver a θ_x–θ_y–Z motion. The developed FPM achieves a positioning and orientation resolution of ±10 nm and 0 . 05″ respectively, and a continuous output force of 150 N/Amp throughout a large workspace of 5°×5°×5 mm. Part I mainly focuses on a new theoretical model that is used to analyze the stiffness characteristics of the compliant joint modules that formed the FPM, and experimental evaluations of each compliant joint module. Part II presents the stiffness modeling of the FPM, the performance evaluations of the developed prototype, and the preliminary results of the UV-NIL process.     

Measuring temperature dependence of photoelectric conversion efficiency with dye-sensitized solar cells

It’s well known that the drift velocity of electrons in conductors depends on temperature in accordance with thermodynamics, which influences also photoelectric conversion efficiency of solar cells. The article presents experimental data for studying temperature influence of photoelectric conversion efficiency with dye-sensitized solar cells (DSSCs). The measured DSSCs were built in three layers, the photoelectrode, the electrolyte, and the counter electrode, which were made in the CCT laboratory, National Taipei University of Technology, Taiwan. The photoelectrode is coated by using ? = 21 nm nano TiO₂ and dye as well as the counter electrode using ? = 5 nm nano carbon black on their individual ITO glass. The fluidic electrolyte is used in this work due to its good ionic drift property. In process, the DSSC was waterproof and immersed in the constant temperature water tank for temperature adjusting. The measured temperature range was from ca. 5 °C to 80 °C at an interval of ca. 10 °C. The results show the higher temperature, the lower photoelectric conversion efficiency of DSSCs.     

Calibration of linear encoders with sub-nanometer uncertainty using an optical-zooming laser interferometer

The nonlinear errors of high-precision linear encoders were calibrated by using a nanometer-length calibrator that was based on the optical-zooming laser interferometer with an optical frequency comb. A transmission-type linear encoder and a reflection-type linear encoder were calibrated, and the cyclic nonlinear errors were evident. The magnitudes of the observed cyclic errors were 0.1 nm and 0.2 nm, respectively, and the best calibration uncertainties were 0.55 nm (k = 2). A traceable calibration service for linear encoders with the best calibration uncertainty in the sub-nanometer range has started based on this work.     

Studies of high temperature sliding wear of metallic dissimilar interfaces III: Incoloy MA956 versus Incoloy 800HT

Wear variations of Incoloy MA956 slid against Incoloy 800HT between room temperature and 750 °C, and sliding speeds of 0.314, 0.654 and 0.905 m s⁻¹ were investigated using a ‘reciprocating block-on-cylinder’ (low debris retention) configuration.Three forms of wear depending largely on sliding temperature were observed: ‘severe wear’ with high transfer between room temperature and 270 °C, ‘severe wear’ with low transfer between 390 and 570 °C and ‘glaze formation’ (retarded by increased sliding speed) at 630 °C and above. The differences in wear behaviour are discussed, with wear behaviour mapped and wear surfaces at 750 °C (0.314 and 0.905 m s⁻¹) cross-sectioned and profiled.     

Nanometer profile measurement of large aspheric optical surface by scanning deflectometry with rotatable devices: Uncertainty propagation analysis and experiments

High-accuracy mirrors and lenses with large dimensions are widely used in huge telescopes and other industrial fields. Interferometers are widely used to measure near flat surfaces and spherical optical surfaces because of their high accuracy and high efficiency. Scanning deflectometry is also used for measuring optical near flat surfaces with sub-nanometer uncertainty. However, for measuring an aspheric surface with a large departure from a perfect spherical surface, both of these methods are difficult to use. The key problem for scanning deflectometry is that high-accuracy autocollimators usually have a limited measuring range less than 1000″, so it cannot be used for measuring surfaces having a large slope. We have proposed a new method for measuring large aspheric surfaces with large slopes based on a scanning deflectometry method in which rotatable devices are used to enlarge the measuring range of the autocollimator. We also proposed a method to connect the angle data which is cut by the rotation of the rotatable devices. An analysis of uncertainty propagation in our proposed method was done. The result showed that when measuring a large aspheric surface with a diameter over 300 mm and a slope of 10 arc-deg, the uncertainty was less than 10 nm. For the verification of our proposed method, experimental devices were set up. A spherical optical mirror with a diameter of 35 mm and curvature radius of 5000 mm was measured. The measuring range of the autocollimator was successfully enlarged by our proposed method. Experimental results showed that the average standard deviation of 10 times measurement was about 20 nm.     

A large deflection and high payload flexure-based parallel manipulator for UV nanoimprint lithography: Part II. Stiffness modeling and performance evaluation

This paper presents a flexure-based parallel manipulator (FPM) that delivers nanometric co-planar alignment and direct-force imprinting capabilities to automate an ultra-violet nanoimprint lithography (UV-NIL) process. The FPM is articulated from a 3-legged Prismatic-Prismatic-Spherical (3PPS) parallel-kinematic configuration to deliver a θ_x–θ_y–Z motion. The developed FPM achieves a positioning and orientation resolution of ±10 nm and 0.05″, respectively, and a continuous output force of 150 N/A throughout a large workspace of 5°×5°×5 mm. Part I mainly focuses on a new theoretical model that is used to analyze the stiffness characteristics of the compliant joint modules that formed the FPM, and experimental evaluations of each compliant joint module. Part II presents the stiffness modeling of the FPM, the performance evaluations of the developed prototype, and the preliminary results of the UV-NIL process.     

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.     

Reliability of parameters of associated base straight line in step height samples: Uncertainty evaluation in step height measurements using nanometrological AFM

Step height is widely used as one of the important nanometrological standards for the calibration of nanometrological instruments. In the calculation of step height, a method of determining a base straight line as a reference line is very important. In nanometrology, which is a field of dimensional metrology, an associated feature (Gaussian associated feature), such as a base straight line, is normally calculated from a measured dataset of a metrological instrument on a real feature using the least squares method. The reliability of a base straight line varies depending on the position and number of measured points for the line and the uncertainty in step height calibration also varies depending on the reliability of the base straight line. In this study, we carried the out step height measurement of micropatterned thin films (10, 7, 5, and 3 nm) using an atomic force microscope (AFM) equipped with a three-axis laser interferometer (nanometrological AFM) and evaluated the uncertainty in these measurements. From the uncertainty evaluation results, the uncertainty derived from the reliability of the parameters of the base straight line was one of the major sources of uncertainty when the measured points for the base straight line were varied. An expanded uncertainty (k = 2) of less than 0.4 nm was obtained. Furthermore, the reliable range of an associated base straight line in a single step height, such as that in an atomic step sample, was calculated and in importance of the calculation of the reliable range was shown in the uncertainty evaluation and in determining the measurement strategy.     

Erosive wear on ceramic materials obtained from solid residuals and volcanic ashes

In this study, the performance of ceramic materials that were subjected to solid particle erosion was analyzed. This research was performed to characterize the materials in relation to the wear process. The materials could be used in the construction of devices and machine components that are commonly exposed to environments where volatile, abrasive particles typically cause a high rate of wear. The types of composites used in this study could have useful applications in mechanical components, automotive coatings, etc. These materials are usually obtained from solid residuals and volcanic ashes, in which clay and epoxy resin were used as binders.The erosion testing was performed in accordance with the ASTM G76-95 standard. The samples had a rectangular shape, and their dimensions were 50×25 mm² and 10 mm in thickness. The abrasive particles used were angular silicon carbide (SiC) with a particle size of 420-450 μm. The tests were performed using three different incident angles (30°, 45° and 90°) with a particle velocity of 24±2 m/s. The abrasive flow rate was 70 g/min. The particle velocity and the abrasive flow rate were low in all the tests to reduce the interaction between the incident particles and the rebounding particles in the system. Additionally, the total time of each test was 10 min, and the specimens were removed every 2 min to determine the amount of mass lost. The test specimens were located a distance of 7 mm from the shot blast. The surface of the specimens was examined with a scanning electron microscope (SEM), which characterized the erosive wear damage.The results indicated that all of the ceramic materials reached their maximum erosion rate at an incident angle of 90°. The erosion rate was significantly decreased when the angle of incidence was 30°. Additionally, the ceramics that consisted of volcanic ashes and sand mixed with epoxy resin gave a better erosion resistance compared with the materials that were combined with clay. It was assumed that the combination that was mixed with epoxy resin produced a more compact structure in the specimens, which resulted in a less severe attack of the particles that were acting on the surface of the material. The sand and the volcanic ashes that were mixed with clay, which had the poorest performance in the tests, exhibited similar behavior.It was also observed that the damaged area was extended in all of the cases that used an incident angle of 45°, whereas the depth of the wear scars was higher when an incident angle of 90° (normal incidence) was used. The wear scars were characterized by an elliptical shape at 30° and 45°, which is a characteristic feature when the specimens are impacted at low-impact angles (α≤45°), whereas a circular shape was observed at 90°.     

Design and performance of an advanced metrology building for MIKES

Fundamental metrology is closely linked to the development of science and needs good facilities to achieve low measurement uncertainty in demanding experiments. The laboratories must have good temperature stability, low vibration level, good electromagnetic shielding, clean room air, and humidity control. This paper outlines specification and design principles of a compact laboratory building that brings most of the activities of MIKES under one roof, thus attaining the performance of the most demanding laboratories. The most demanding specifications of temperature and vibration were set for the length and mass laboratories. The tightest room temperature specification was (20 ± 0.05) °C. The vibration level was specified at the tightest level to 1 μm/s at frequencies of 0.1-5 Hz. Electromagnetic shielding was specified at best to 100 dB for plane waves up to 20 GHz. Relative humidity was specified (48 ± 2)% at 20 °C. The specifications were clearly achieved and state of the art metrology laboratories implemented.     

Calibration of step heights and roughness measurements with atomic force microscopes

In this paper we present a method for the vertical calibration of a metrological atomic force microscope (AFM), which can be applied to most AFM systems with distance sensors. A thorough analysis describes the physical z-coordinate of an imaged surface as a function of the observed and uncorrected z-coordinate and the horizontal position. The three most important correction terms in a Taylor expansion of this function are identified and estimated based on series of measurements on a calibrated step height and a flat reference surface. Based on this calibration a number of step heights are calibrated by the AFM with measured values consistent with reference values, where available. Relative standard uncertainty of about 0.5% is achieved for step heights above 200 nm. For step heights below 50 nm, the standard uncertainty is about 0.5 nm. While a calibration of step heights done by AFM and interference microscopy can be compared directly as demonstrated here, this is not straightforward for roughness measurement. To asses this, the exact same area on an important applied surface (a hip joint prosthesis) was measured by both AFM and interference microscopy. Similarities in the images were seen; however, the calculated roughness was significantly different (R_q=3 and 1.5 nm). Applying a low-pass filter with a cut-off wavelength of λ_c=1.5 μm, the appearance of the images and the calculated roughness become almost identical. This strongly suggests that the two methods are consistent, and that the observed differences in shape and roughness in the nanometer range can be explained by the limited lateral resolution of the interference microscope.     

Characterization of MEMS piezoresistive pressure sensors using AFM

Atomic force microscope (AFM) is adapted to characterize an ultrasensitive piezoresistive pressure sensor based on microelectromechanical system (MEMS) technology. AFM is utilized in contact mode to exert force on several different micromachined diaphragm structures using a modified silicon cantilever with a particle attached to its end. The applied force is adjusted by changing the trigger voltage during each engage step of the probe-tip on the diaphragm surface. The contact force is determined from the force plots obtained for each trigger voltage in advanced force mode. Low force values in the range of 0.3–5 μN have been obtained with this method. This force induces strain on the bridge-arm of the diaphragm where the polysilicon resistor is located. The resultant change in the resistance produced due to varying force/pressure is measured using a delta mode current–voltage (I–V) measurement set-up. The contact mode AFM in conjunction with a nanovoltmeter enables the calibration of very sensitive force sensors down to 0.3 μN.     

Accurate determination of spring constant of atomic force microscope cantilevers and comparison with other methods

We present calibration results of commercial AFM cantilevers using the KRISS nanoforce calibrator (NFC) that can determine traceably spring constants with an uncertainty better than 1%, along with the results obtained from other four calibration methods: the dimensional method, the cantilever-on-cantilever method, the Sader method, and the thermal noise method. Two types (contact and tapping mode) of beam-shaped AFM cantilevers with nominal spring constants of 0.9 N m⁻¹ and 42 N m⁻¹, respectively, were investigated in this study. Because of its small uncertainty, the NFC method was used to assess the uncertainties of other four methods through comparisons between values obtained from other methods and those from the NFC method for the same cantilever. Results from other methods were generally in good agreement with those from the NFC method within the uncertainties of other methods claimed in other literatures, but values obtained from the Sader method were differed by up to 40% from the NFC values, which is 2 times worse than the known uncertainty.