Effects of two types of surface treatments on the structural elasticity of human fingernails.

BACKGROUND: The human nail has a three-layered structure. Although it would be useful to quantitatively evaluate the changes in deformability of the nail due to various surface treatments, few studies have been conducted. METHODS: The effects of two types of surface treatment-a chemically acting nail softener and a physically acting nail strengthener-on the deformability of human fingernails were investigated. The Young's modulus of each plate of the nail samples before and after softening treatment was determined by nanoindentation. The Young's modulus of the strengthener was determined by conducting a three-point bending test on a polyethylene sheet coated with the strengthener. RESULTS: Young's modulus decreased in order from the top plate against the softening treatment time, and the structural elasticity for bending deformation (SEB) of the nail sample, which expresses the deformability against bending deformation independent of its external dimensions, decreased to 60% after 6 h of treatment. The Young's modulus of the nail strengthener was 244.5 MPa, which is less than 10% of the SEB of the nail. When the nail strengthener was applied to the nail surface, the SEB decreased to 73%, whereas the flexural rigidity increased to 117%. CONCLUSION: Changes in nail deformability caused by various surface treatments for softening and hardening were quantitatively evaluated successfully.

Nanostructure-Based Solution Sensor Fabricated with p-CuOx/n-TiO2 Nanojunctions To Identify Species and Concentrations of Alcohol Molecules.

Chemiresistive sensors fabricated based on metal-oxide-semiconductors, the most widely used high-sensitivity sensor materials, are required for detecting target solutions and gases and identifying them with a high degree of accuracy. In this study, we used p-n nanojunctions and nanowire shapes for identifying alcohol solutions. The solution sensors fabricated based on CuOx nanowires with p-CuOx/n-TiO2 nanojunctions detected ethanol, ethylene glycol, and diethylene glycol solutions via DC voltage and electrochemical impedance measurements. The p-n nanojunctions affected the sensors' sensitivity in the diethylene glycol solution, and the nanowire surface areas affected the relaxation time in ethanol and ethylene glycol solutions. To identify alcohol solutions, principal component analysis was performed based on the relationship between the sensor information, such as the presence of p-n nanojunctions and nanowire surface areas, and the sensing performance. This analysis identified alcohol molecular species and predicted alcohol-solution concentrations in the 0.1-20 vol % range with a high degree of accuracy. The concept of using sensors with different surface conditions with respect to p-n nanojunctions and nanowire surface areas offers designs for metal-oxide-semiconductor sensors to identify various molecules in solution.

Nanoindentation study of human fingernail for determining its structural elasticity.

BACKGROUND: Human nails play an important role in transmitting force to the fingertips, and their mechanical properties are important indices. The nail has a three-layered structure consisting of top dorsal, middle intermediate, and under ventral plates, and its internal structure is believed to affect its mechanical properties. However, this has not been investigated in previous studies. METHODS: The Young's moduli of the top, middle, and under plates were measured using nanoindentation, and a theoretical model was developed to estimate the structural elasticity for the bending deformation of human nails, which is an index describing the deformability of the nail without depending on its external dimensions. The structural elasticity of human nails was compared with that of human hair collected from the same person. The effect of the softening treatment on the nails was also evaluated. RESULTS: The Young's moduli of the top, middle, and under plates measured using nanoindentation were 2.9, 3.1, and 2.8 GPa, respectively. The structural elasticity of the nail was estimated to be 2.9 GPa, approximately 75% that of hair. Moreover, softening treatment with a urea cream reduced the structural elasticity of the nail to 70%. CONCLUSION: This paper proposed a method for estimating the structural elasticity of a human nail with a three-layered structure. This index is a mechanical property with "Pa" as a unit, and is useful for comparing deformability with the Young's modulus of other homogeneous materials or for investigating the effect of various treatments quantitatively.

Copper Oxide Solution Sensor Formed on a Thin Film Having Nanowires for Detecting Ethanol in Water.

Solution sensors are required to detect analytes in liquids with high sensitivity and response speed for environmental and health monitoring. In this study, we introduce the concept of a Cu oxide thin film having nanowires as a solution sensor for detecting ethanol in water. The Cu oxide sensor with grains and nanowires of different shapes was fabricated by a simple method of heating a Cu thin film and dropping an Ag conductive paste. Sensing parameters and mechanisms were evaluated by current-voltage and electrochemical impedance spectroscopy measurements. In the Cu oxide sensor formed on thin film having a large number of nanowires fabricated by heating at 400 °C for 5 h, the sensor sensitivity was 0.96 at 0.1 vol % ethanol concentration, and the response time was 313 s at a voltage of 0.1 V. The Cu oxide sensor detects ethanol by the change in electrical resistance caused by the reaction between ethanol molecules and the lattice oxygen on the Cu oxide surface. Therefore, the large nanowire surface area leads to a higher sensor sensitivity and a faster response time. Furthermore, the grain and nanowire regions on the thin film are represented by equivalent circuits. A high correlation was observed between the sensor sensitivity and the time constant calculated from the equivalent circuit. The proposed Cu oxide solution sensor and detection mechanism offer designs to improve the performance of chemical sensors.

Division of force among layers constituting human hair during bending and tension.

Human hair is a three-layered structure comprising the inner medulla, middle cortex, and outer cuticle layer. When a hair is subjected to bending or tensile load, each of these layers absorbs a certain amount of the force applied. However, the magnitude of the force absorbed by each layer is not easy to estimate. This is because, in addition to Young's modulus of each layer, the absorption depends on the area of each layer as seen in the cross-section. This study used a strategic way of combining experiment and theory and found that Young's modulus of the cuticle layer changes in the face of bending and tension. Considering this, the ratio of force sharing inside a human hair was estimated. Bending and tensile tests were conducted on single human hairs to determine the structural elasticity for both deformations which expresses the deformability of the hair independent of its external dimensions. Moreover, Young's modulus of each layer was determined by nanoindentation of hair cross-section. By comparing the structural elasticity determined experimentally with that determined theoretically, Young's modulus of the cuticle layer against tension was found to be 25% of that against bending. Based on this finding, it was found that the cuticle layer bears 35% of the force endured during bending, and the cortex bears the rest; when subjected to tension, the cortex bears more than 90% of the force.

Acoustic resonant imaging technique for visualizing the acoustic properties and thickness of polymer film on substrate.

This paper proposes an acoustic resonant imaging technique for visualizing the acoustic properties and thickness of a polymer film on a substrate. When ultrasound passes through a thin layer, transmission and reflection coefficients of sound pressure attain their extreme values at the resonant frequency. By obtaining the area information of the extreme value and resonant frequency and matching them with a theoretical model, the acoustic properties and thicknesses of a polymer film on a substrate can be visualized. Herein, this technique was applied to a photoresist film coated on a Si wafer, and in addition to visualizing fluctuations in film thickness, the differences in the film hardness that may have occurred during the curing process were successfully detected as the differences in the acoustic impedance of the film. The acoustic resonant imaging technique was successfully used to determine the frequency dependence of both the transmission and reflection coefficients.

Structural elasticity for tensile deformation of a single human hair and the comparison with it for the bending deformation.

Human hair is a multi-layered structure, which consists of the inner medulla, middle cortex, and outer cuticle. Therefore, the mechanical properties of the hair are related not only to the Young's modulus of each layer but also to the internal structures. Although the tensile test of a human hair has been performed elsewhere, the deformability of the hair for the tensile deformation is determined as the Young's modulus of the hair structure, which is similar to that of metals. In this paper, the structural elasticity of a single human hair for the tensile deformation, which expresses the deformability of a hair by tension without being dependent on external dimensions and shape, is defined based on the theoretical model, and is measured by performing the tensile test under the digital microscope observation. The values of the structural elasticity for the tensile deformation of the hair samples collected from healthy persons are compared with the values obtained for bending deformation. The structural elasticity for the tensile deformation of the hair sample is found to be lesser than that of the bending deformation, and this is verified to be always valid provided the Young's modulus of the outer cuticle is greater than that of the middle cortex.

Interfacial Contact Behavior between CNTs and AgNW with Molecular Dynamics Simulation.

The behavior at an interface between carbon nanotubes (CNTs) and silver nanowire (AgNW) could hardly be observed experimentally on an atomic scale, and the interaction is difficult to accurately calculate due to nanometer size effects. In this work, the contact behavior is studied with the molecular dynamics (MD) simulation, which indicates that the CNTs and AgNW can move towards each other to form aligned structures with their interfaces in full contact. In these different composite systems, nanotubes may either keep their form of an inherent cylindrical structure or completely collapse into the nanoribbons that can tightly scroll on the AgNW periphery while wrapping it in a core-shell structure. Thus, the atomic configuration evolution that is affected by the van der Waals (vdW) interaction is closely analyzed to assist the understanding of interfacial contact behavior.

On the correlation between the curvature of the human eyelash and its geometrical features.

Although human eyelashes are generally curved, the cause of the natural curvature of eyelashes has not yet to be clarified elsewhere. Related with this, this paper reports our discovery of a correlation between the curvature of the eyelash and its geometrical features. Eyelashes can be divided into root, middle and tip sections. Because the curvature at the root is larger than that at the tip, we expected that the root section could be more easily deformed by bending compared with the tip section. However, the structural elasticity in bending, which is the flexural rigidity without depending on the external dimensions, at the root was found to be greater than that at the tip, contrary to our initial expectations. Next we examined the internal dimensions of cross sections of the eyelashes, and found that the thicknesses of the cuticle layer at the root were different for the convex and concave sides of the curved eyelash, although these were almost the same at the tip. Theoretical analysis of this variation in thickness of the outer cuticle layer shows that this displaces the neutral axis. Finally, we found that there is a good correlation between the displacement of the neutral axis and the curvature of the eyelash. STATEMENT OF SIGNIFICANCE: Why are human eyelashes naturally curved? To find a hint for this question, the mechanical and geometrical properties of human eyelash were investigated. Although the curvature at the root of the eyelash was larger than that at the tip, this was not related to the deformability of the eyelash by bending. From the cross-sectional observation of eyelash, we noticed that the thickness of the outer cuticle layer was non-uniform depending on the position, and this brought the displacement of the neutral axis of the eyelash for bending. Finally, a good correlation between the curvature and the change in the neutral axis was discovered. With practically using this findings, the curvature of the eyelash might be controlled artificially in the future.

Determination of acoustic properties of thin polymer films utilizing the frequency dependence of the reflection coefficient of ultrasound.

This paper reports on a technique to measure the acoustic properties of a thin polymer film utilizing the frequency dependence of the reflection coefficient of ultrasound reflected back from a system comprising a reflection plate, the film, and a material that covers the film. The frequency components of the echo reflected from the back of the plate, where the film is attached, take their minimum values at the resonant frequency, and from these frequency characteristics, the acoustic impedance, sound velocity, and the density of the film can be determined. We applied this technique to characterize an ion exchange membrane, which has high water absorbability, and successfully determined the acoustic properties of the membrane without getting it wet.

Acoustic study of a linear low-density polyethylene film after modification of the crystalline structure by heating.

We report on a hybrid microscopy technique that enables us to measure the acoustic properties of a thin polymer film together with an optical microscope image of the corresponding area. Linear low-density polyethylene films are heated to various temperatures and examined by the technique. Density of the film is increased by heating and its sound velocity is decreased compared with a film without heating. Also, spherulites can clearly be seen in the optical microscope image, supporting the thermal shrinkage of the film which can be detected by the present technique.

Numerical analysis of the electrical failure of a metallic nanowire mesh due to Joule heating.

To precisely examine the electrical failure behavior of a metallic nanowire mesh induced by Joule heating (i.e., melting), a previously developed numerical method was modified with regard to the maximum temperature in the mesh and the electrical resistivity of the nanowire. A sample case of an Ag nanowire mesh under specific working conditions was analyzed with highly accurate numerical results. By monitoring the temperature in the mesh, the current required to trigger the melting of a mesh segment (i.e., the melting current) could be obtained. The melting process of a mesh equipped with a current source during actual operation was predicted on the basis of the obtained relationship between the melting current and the corresponding melting voltage in the numerical melting process. Local unstable and stable melting could be precisely identified for both the current-controlled and voltage-controlled current sources in the present example.

Simultaneous observation of acoustic resonance phenomena at both surfaces of a plate coated with thin layers.

Acoustic resonance phenomena at the front and back surfaces of a plate coated with thin layers were successfully observed in the amplitude spectrum of the back surface echo. The amplitude ratio of spectra with and without layers takes its maximum and minimum values at the resonant frequencies of the front and back coatings and both frequencies can clearly be distinguished from each other. As an application, the thicknesses of the front and back coatings on a steel plate were measured simultaneously using their resonant frequencies, thus verifying the validity of the principle.

Accurate determination of the structural elasticity of human hair by a small-scale bending test.

This paper reports on a small-scale bending method for human hair. The test sample, which is elliptical in cross-section, is fixed to a hollow steel needle using resin to form a cantilever. A loading probe is used to subject this to a lateral load, where the load is applied parallel to either the long or short axis of the elliptical cross-section. From these tests, load-displacement relationships for the hair were obtained. From the experimental data and analysis, we found that the structural elasticity determined is independent of the direction of bending, and precise measurements of the structural elasticity of human hair with scattering of less than 5% were realized using this test scheme. Finally, changes in the structural elasticity of hair due to hair treatments were detected and the changes are discussed based on a theoretical model of the multi-layered structure.

Sensitivity of acoustic microscopy for detecting three-dimensional nanometer gaps embedded in a silicon structure.

The sensitivity of acoustic microscopy for detecting three-dimensional defects in a Si structure is reported. Circular, nanometer gaps with diameters ranging from 5 to 1000 microm were embedded in Si disks by a direct bonding technique, and these were visualized using acoustic microscopy. The limits of detection for the gap thickness and diameter were observed simultaneously in samples with gaps of 4 and 140 nm. The behavior of the sensitivity in detecting the gaps can be explained by a simple analytical model. It is shown experimentally and theoretically that the gap thickness and diameter are not independent variables as regards detection. The sensitivity of acoustic microscopy is governed by the three-dimensional features of the embedded defects.

Fabrication of Al microspheres by utilizing electromigration.

Aluminum microspheres with diameters of 4-7 microm have been fabricated by utilizing electromigration. In a passivated Al line with a slit at the anode end, atoms accumulated before the slit due to high current density and high substrate temperature are released from the pre-introduced holes in the passivation layer, and form microspheres with aid of surface tension. The spheres are formed at the specific range of the temperature at the anode end of Al line.

Potential of acoustic imaging in the detection of nanometer gaps.

The potential of the water-immersion and dry-contact acoustic imaging techniques for detecting nanometer gaps embedded in silicon is studied. The sensitivity for detecting gaps of over 10 nm in height is governed only by the lateral resolution of the imaging and is independent of the height of the gap.

Design and performance of a thin, solid layer for high-resolution, dry-contact acoustic imaging.

Compared to the usual water immersion case, more effective transmission and reception of high-frequency ultrasound through a thin, solid layer are reported. A theoretical model is presented to perform the signal amplification and the signal modulation toward the higher frequency components for getting the high-quality acoustic images without immersing the object to be imaged. Also, the thin, solid layers are designed from the theoretical model, and the transmission of high-frequency ultrasound is carried out through the layer/silicon interfaces with an applied pressure of about 0.1 MPa. The spectral intensity in the frequency range of 20 to 70 MHz remarkably improves compared with water immersion, and the peak frequencies of the spectra modulate the higher than water immersion. Furthermore, the solder joint inspection of a package is performed. The present dry-contact technique achieves the higher spatial resolution and the higher signal-to-noise ratio (SNR) than the usual water immersion technique, and clearly detects the defective joint without getting the package wet.

Dry-contact technique for high-resolution ultrasonic imaging.

To accomplish a high-resolution ultrasonic imaging without wetting a sample, the efficiency of the dry-contact ultrasonic transmission is discussed. In this study, a dry-contact interface is formed on a sample by inserting a thin film between water and a sample, and the pressure is working on the interface by evacuating the air between the film and the sample. A model of dry-contact ultrasonic transmission is presented to assess the signal loss accompanied with the transmission. From the determination of the signal loss caused by the transmission using various films, it was found that the higher frequency ultrasound is transmitted effectively into the sample by selecting an optimum film, which can keep the displacement continuity between the film and the sample during ultrasonic transmission. At last, ultrasonic imaging with the sufficient signal-to-noise ratio (SNR) and high lateral resolution was performed on the delamination in a package and the jointing interface of the ball-grid-array package without wetting the packages.