A new method for high-resolution quantitative measurement of the dielectric function by using scattering scanning near-field optical microscopy (s-SNOM) is presented. The method is based on a ...calibration procedure that uses the s-SNOM oscillating dipole model of the probe-sample interaction and quantitative s-SNOM measurements. The nanoscale capabilities of the method have the potential to enable novel applications in various fields such as nano-electronics, nano-photonics, biology or medicine.
The dependence of the near-field signal on the dielectric function of a specific material proposes scattering-type near-field optical microscopy (s-SNOM) as a viable tool for material ...characterization studies. Our experiment shows that specific material identification by s-SNOM is not a straightforward task as parameters involved in the detection scheme can also influence material contrast measurements. More precisely, we demonstrate that s-SNOM contrast in a pseudo-heterodyne detection configuration depends on the oscillation amplitude of the reference mirror and that for reliable measurements of the contrast between different materials this aspect needs to be taken into consideration.
A new composite matrix was developed for a cutting tool based on tungsten carbide ligated with cobalt (WC-Co) using sintering technique. The admixtures of niobium carbide, tantalum carbide, and ...titanium carbide with the WC-Co matrix aim to inhibit the grain growth of WC and to promote covalent bonding at the interface. The modified WC-Co tools were coated with titanium nitride and titanium carbonitride layers by CAE-PVD technique. To substantiate the performances of the new coating-substrate systems, we have performed X-ray diffraction, atomic force microscopy, and scratch test measurements to estimate: phase content, average crystallite size, average texture coefficient, residual stress level, coating thickness, average roughness, square mean root, fractal dimension, cohesive adhesion, and adhesive adhesion. The results enable the in-depth understanding of the coating growth mechanisms and provide an objective evaluation of the coatings adhesion to the new cutting tools matrix. The results provide evidence to support the potential of TiN and TiCN coatings to enhance the working performances of the composite WC-Co cutting tools and to differentiate their properties. TiCN coating is shown to be superior to TiN coating in terms of adhesion and thus represents a better alternative for coating the modified WC-Co composite matrix.
In this work, 2,3,7,8,12,13,17,18-Octaethyl-21H,23H-porphine (OEP) in its free base form and metalated with iron (III) chloride (FeOEP), magnesium(II) (MgOEP) and cobalt(II) (CoOEP) have been used to ...fabricate Langmuir–Blodgett (LB) thin films. Using the surface pressure–surface area (
Π–
A) isotherm graphs optimum conditions for thin film deposition have been determined and by changing the deposition parameters various thin films have been deposited. Quartz Crystal Microbalance (QCM) system was used to investigate their gas sensing performances during exposure to Volatile Organic Compounds (VOCs) including chloroform, benzene and toluene. The surface properties have been investigated using Atomic Force Microscopy (AFM) and analyzed together with the QCM results to understand the effect of the surface properties on gas sensing mechanism. It is observed that larger surface area leads to higher response in gas sensing applications in terms of resonance frequency change.
This paper presents a calorimetric approach to the measurement of mechanical dissipation in specimens subjected to cyclic tensile tests. Mechanical dissipation, that is, the heat power produced by ...the material due to mechanical irreversibility, can potentially be deduced from the temperature changes captured on the specimen surface by infrared thermography. However, a difficulty arises for long‐term cyclic tests: Results are easily skewed by any change in the specimen's environment. The problem is amplified by the fact that mechanical dissipation is in general small compared to the heat sources associated with thermomechanical couplings, making its estimation difficult. The paper proposes a simple procedure to extract a well‐resolved estimation of mechanical dissipation by solving two key points specific to long‐term cyclic tests: (a) the reduction of the parasitic effects associated with changes in the specimen's environment by using a specific device based on two references samples and (b) the choice of relevant thermal data acquisition parameters. A test is performed on a copper‐based shape‐memory alloy whose calorific response comprises three origins of heat sources: thermoelastic coupling, phase transformation, and mechanical irreversibility. The results obtained demonstrate the relevancy of the approach in extracting mechanical dissipation from the thermal response of the specimen subjected to long‐term tensile tests in fatigue.
The effects of a turnstile operation on the current-induced vibron dynamics in nanoelectromechanical systems (NEMS) are analyzed in the framework of the generalized master equation. In our ...simulations each turnstile cycle allows the pumping of up to two interacting electrons across a biased mesoscopic subsystem which is electrostatically coupled to the vibrational mode of a nanoresonator. The time-dependent mean vibron number is very sensitive to the turnstile driving, rapidly increasing/decreasing along the charging/discharging sequences. This sequence of heating and cooling cycles experienced by the nanoresonator is due to specific vibron-assisted sequential tunneling processes along a turnstile period. At the end of each charging/discharging cycle the nanoresonator is described by a linear combination of vibron-dressed states sν associated to an electronic configuration ν. If the turnstile operation leads to complete electronic depletion the nanoresonator returns to its equilibrium position, i.e., its displacement vanishes. It turns out that a suitable bias applied on the NEMS leads to a slow but complete cooling at the end of the turnstile cycle. Our calculations show that the quantum turnstile regime switches the dynamics of the NEMS between vibron-dressed subspaces with different electronic occupation numbers. We predict that the turnstile control of the electron-vibron interaction induces measurable changes on the input and output transient currents.
The high reversibility of the martensitic transformation occurring in shape-memory alloys (SMAs) is at the origin of the mechanical performance of these materials. Infrared thermography is employed ...in this study to measure the mechanical dissipation produced by Cu–Zn–Al SMA specimens during stress-induced phase transformation. In practice, temperature change is first measured on the surface of a specimen subjected to cyclic mechanical loading at constant ambient temperature. The heat produced by the material can then be deduced from the temperature change by using the heat diffusion equation. The heat associated to mechanical irreversibility is expected to be very low compared to the other heat quantities produced by the material (such as the latent heat due to phase change and the heat due to thermoelastic coupling), so measuring this quantity requires special attention, as emphasized in this paper. The procedure which enables us to extract the mechanical dissipation from the measured heat source is first presented. The technique is then applied to two types of specimens: martensitic and austenitic. Different values of mechanical dissipation were measured, thus revealing different levels of mechanical irreversibility.
Silicon carbide has been identified as a potential inert matrix candidate for advanced fuel. In this work, the growth of SiC thin films by pulsed laser deposition is reported. The stoicheometry and ...thickness of deposited films was investigated by non-Rutherford backscattering spectrometry. The influence of the deposition parameters, i.e. substrate temperature and laser fluence on the structure, morphology and optical properties of the deposited thin layers was studied. It was found that polycrystalline SiC thin films with uniform surface morphology were obtained at 873
K.
Polymer coatings of metallic surfaces offer them not only aesthetic value but at the same time provide anticorrosive protection or even improvement of some mechanical properties of the composite ...structure. The mechanical properties of paints are often negligible although the two aspects considered: aesthetics and durability are related to the mechanical properties of both the base material and the paint. The durability of the paint depends on how it adheres to the substrate, but at the same time a jump in the bending stress value occurs in the separation area of the two materials, which leads to the appearance of shear stress. The shear stress value depends on the ratio of the modulus of elasticity of the base material and the paint. In this paper it will follow, starting from the mechanical properties of the substrate, the metallic sheet in general, to determine the new properties of the assembly of substrate and the two painting layers, also the determination of mechanical properties of the layers. From the analysis of laser signals obtained by the impulse excitation of the samples, one can determine the elastic modulus. These results come to validate the results based on Finite Element Analysis (FEA) of the same samples. From the analysis of Bernoulli's equation for the two situations: the uncovered beam and the painted beam, the ratio of natural frequencies is determined as a function depending on the modulus of elasticity, density and geometric dimensions of the substrate, respectively the same elements of the coating paint. From this ratio, Young's modulus of the paint can be determined.
The effect of deformation on the damping capacity of a copper-base shape memory alloy produced by standard methods is studied. The metallographic analysis is performed with the help of scanning ...electron microscopy. The internal friction is measured at different temperatures. The damping capacity of the alloy is analyzed and its relation to the mechanical and physical properties is determined.
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