Inhomogeneity Surface Research Articles

Exploring the interfacial behavior of SiNWs/Sulphur and Nitrogen-doped carbon dot based heterostructure for near-infrared photodetection application

A near-infrared (NIR)-based photodetector has been designed for carbon dot and silicon nanowire heterostructures by tuning the surface modification via sulphur (S-CQD) and nitrogen (N-CQD) doping in carbon dots. The ideality factor (η), barrier height (ϕB), and series resistance (Rs) are evaluated at various temperatures (303 K–250 K) to shed light on inhomogeneity and potential surface barriers at the interfaces between two nanostructures. Such control of the dopants and inhomogeneity between the interfaces has been postulated with the Cheung model, which provides a negligible difference between sulphur and nitrogen-based CQDs. The electron-withdrawing effect of sulphur on the CQD surface induces more p-type character, and p-n junction formation enhances the responsivity (622.22 mA/W) and detectivity (2.15 × 1012Jones).

Research on Metal Corrosion Resistant Bioinspired Special Wetting Surface Based on Laser Texturing Technology: A Review.

Metal substrates are widely used in engineering production. However, material life reduction and economic loss due to chemical and electrochemical corrosion are a major problem facing people. Electrochemical corrosion is the main corrosion mode of metals, such as seawater corrosion. It is found that the superhydrophobic surface treated by laser texturing plays an important role in the corrosion resistance of the substrate, with the laser texturing process and post-treatment affecting the corrosion resistance. The corrosion resistance is positively correlated with the superhydrophobic property of the surface. For the mechanism of corrosion resistance, this paper summarizes the effect of micro-nano structure, surface-modified coating, oxidation layer or new product layer, surface inhomogeneity, crystal structure, and slippery surface on corrosion resistance. Superhydrophobic surface and slippery surface are two common types of bioinspired, special wetting surfaces. In order to prepare better superhydrophobic and corrosion-resistant surfaces, this paper summarizes the selection and optimization of laser parameters, surface structure, processing media, and post-treatment from the point of view of mechanism and law. In addition, after summarizing the corrosion resistance mechanism, this paper introduces a series of characterization experiments that can measure the corrosion resistance, providing a reference for preparation and evaluation of the surface.

Opto-electronic characterization of starch capped zinc chalcogenides (core-shell) nanocomposites and their application as Schottky device

Optoelectronic properties of starch capped zinc chalcogenides (ZnO-ZnS and ZnS-ZnO) core-shell nanocomposites are found to be suitable for use in photoconductive devices. An increase in shell thickness can enhance the charge separation that thereby the efficiency. Schottky diodes based on ZnO-ZnS and ZnS-ZnO core–shells nanocomposites exhibit suitable rectifying behaviour in dark. The fundamental device parameters such as barrier height saturation current (Is) and ideality factor (β) are calculated at 300 K (room temperature) from the I–V curve and the effects of the shell thickness on the device performance has thus been investigated. Variation of ideality factor may be attributed to increasing inhomogeneity and interfacial surface defects across the junction. Schottky diodes are also observed as photodetector in response to blue and green LED lights. Responsivity and quantum efficiency of core/shell based Schottky photodiodes are found to be higher than that of core-based Schottky photodiodes.

Effect of spherical pores coalescence on the overall conductivity of a material.

The problem about steady-state temperature distribution in a homogeneous isotropic medium containing a pore or an insulating inhomogeneity formed by two coalesced spheres of the same radius, under arbitrarily oriented uniform heat flux, is solved analytically. The limiting case of two touching spheres is analyzed separately. The solution is obtained in the form of converged integrals that can be calculated using Gauss-Laguerre quadrature rule. The temperature on the inhomogeneity's surface is used to determine components of the resistivity contribution tensor for the insulating inhomogeneity of the mentioned shape. An interesting observation is that the extreme values of these components are achieved when the spheres are already slightly coalesced.

A statistical interphase damage model of random particulate composites

A new approach to modeling of progressive damage of interphases in random particulate composites is proposed. In the model the interphases are represented by layers of springs whose stiffness parameters change as a result of damage associated with gradually increasing loading. Consequently, due to local degradation of the interphase, variation of these parameters over the inhomogeneity surface becomes progressively non-uniform. This, in turn, causes the effective properties of the composite to become increasingly anisotropic. To describe the effects of interphase damage on the overall properties of the composite three ideas proposed in the past with the authors’ participation are utilized. One is the Method of Conditional Moments (MCM), a statistical homogenization technique developed in the past to analyze the effective properties of random composites without interphases. The second idea is the recently introduced notion of Energy Equivalent Inhomogeneity (EEI), which replaces the original inhomogeneities and their interphases with uniform inhomogeneities; the notion of EEI allows methods devised to examine composites without interphases (such as MCM) to analyze composites with interphases. The most important, and novel in application to problems considered in this work, is the third idea concerning the statistical interphase damage model. In the proposed approach local micro-damage of interphases is modelled by an increasing fraction of randomly distributed destructed springs in the spring layers surrounding the inhomogeneities of the composite. The model assumes that the local interphase micro-strength at the points located on the surface of different inhomogeneities and specified by the same spherical coordinates is described by one-point Weibull distribution function. In view of the strong nonlinearity of the problem, an incremental/iterative scheme is used in practical evaluation of effective properties. The approach is illustrated considering unidirectional and triaxial stretching of a composite.

Grain size and nanoscale effects on the nonlinear pull-in instability and vibrations of electrostatic actuators made of nanocrystalline material

Presented herein is the study of grain size, grain surface energy and small scale effects on the nonlinear pull-in instability and free vibration of electrostatic nanoscale actuators made of nanocrystalline silicon (Nc-Si). A Mori–Tanaka micromechanical model is utilized to calculate the effective material properties of Nc-Si considering material structure inhomogeneity, grain size and grain surface energy. The small-scale effect is also taken into account using Mindlin’s strain gradient theory. Governing equations are derived in the discretized weak form using the variational differential quadrature method based on the third-order shear defamation beam theory in conjunction with the von Kármán hypothesis. The electrostatic actuation is modeled considering the fringing field effects based upon the parallel plate approximation. Moreover, the Casimir force effect is considered. The pseudo arc-length continuation technique is used to obtain the applied voltage-deflection curve of Nc-Si actuators. Then, a time-dependent small disturbance around the deflected configuration is assumed to solve the free vibration problem. By performing a numerical study, the influences of various factors such as length scale parameter, volume fraction of the inclusion phase, density ratio, average inclusion radius and Casimir force on the pull-in instability and free vibration of Nc-Si actuators are investigated.

Parametric study on stressed volume and its application to the quantification of rolling contact fatigue performance of heterogeneous material

This research explores the influence of distributed inhomogeneities and surface asperities on the stressed volume of heterogeneous material in contact with a sphere. The recently developed modeling method for solving rough-surface contact problems involving distributed inhomogeneities, incorporated with FFT algorithms and a mesh differential refinement scheme, is utilized. The effective stressed volume, quantitatively described by effective depth, length and width, is investigated to characterize the rolling-contact-fatigue influence zone in heterogeneous material. Furthermore, a parametric study is conducted for the influences of inhomogeneity distribution and surface roughness on volumetric stress integral in order to understand the rolling contact fatigue performance of particle-laden inhomogeneous materials.

Effects of the ink concentration on multi-layer gravure-printed PEDOT:PSS

To date, highly conductive PEDOT:PSS is the most promising transparent electrode for printing-based flexible organic electronics. Spin-coating and slot-die coating have been commonly used for printing this material. Among the roll-to-roll printing processes, gravure is the most promising for manufacturing large area electronics offering the advantages of high speed and high printing definition. However, gravure printing highly conductive PEDOT encounters some technological limitations such as low thickness, layer inhomogeneity and high surface roughness resulting in a layer not suitable as electrode in electronic devices. In order to realize an electrode of highly conductive PEDOT by gravure printing, a multilayer approach with variable ink concentration was tried using IPA as process solvent. Variable solvent amount of overlapped printed layers was found to play an important role in the spreading of the PEDOT ink onto the pre-printed layers and in the smoothing of its existent peaks. In particular, adopting increasing ink dilution with increasing of the overlapped layers, multi-layer gravure-printed highly conductive PEDOT was successfully realized with characteristics suitable as transparent electrode for organic electronic devices (sheet resistance lower than 130 Ω/sq, conductivity higher than 450 S/cm and optical transmittance over 80%). This is the first time that such results were reached by gravure printing technique thanks to the easy proposed approach.

Optical Properties of Cu<sub>2</sub>ZnSnSe<sub>4</sub> Nanocrystalline Thin Films for Photovoltaic Devices

Presents a study of optical properties from transmittance measurements as a function of wavelength to CZTSe thin films (Cu2ZnSnSe4) using Bhattacharyya model and basic elements from the Swanepoel theory. The optical constants such as the absorption coefficient (α), the refractive index (n), the extinction coefficient (k) and physical properties such as gap (Eg), the real and imaginary part of the dielectric function (ε1 and ε2) and the film thickness (d), were determined. Gap values between 1.2 and 1.7 eV were obtained for compound when the mass (MX) of ZnSe was varied during the deposition stage. Inhomogeneity and high surface roughness were observed by SEM measurements for all samples. Size grain varying between 458.16 and 630.28 nm were obtained while the ZnSe binary mass varied from 0.171 to 0.153 g. Refractive index and extinction coefficient of Cu2ZnSnSe4 films were obtained for λ = 800 nm. A decrease of ε1 and ε2 was observed as the wavelength increases; it is associated with the presence of binary phases in the XRD patterns.

The interaction of a screw dislocation with a circular inhomogeneity near the free surface

The interaction of a screw dislocation with a circular inhomogeneity near the free surface is discussed in this paper. By using the complex potential and conformal mapping technique, an explicit series solution is obtained. Then, the solution is cast into a new expression to separate the interaction effects between the dislocation, inhomogeneity, and free surface. The new expression is not only convenient to reveal the coupling interaction effects, but also helpful to improve the convergence of the solution. As an application of the new expression, a simple approximate formula is presented with high accuracy. Finally, the full-field interaction energy and image force are evaluated and studied graphically. It is found that when the screw dislocation, inhomogeneity, and free surface are close to each other, their interaction effects strongly and intricately couple in the near field. In the case of a soft inhomogeneity or a hole, there is an unstable equilibrium point of the screw dislocation between the inhomogeneity and free surface, whereas in the case of a hard or rigid inhomogeneity, there is an unstable equilibrium point on the opposite side of the inhomogeneity.

Serial evaluation of hepatic function profile after Fontan operation

Moderate persistent elevation of the γ-glutamyltransferase (γGT) level is a frequent finding during long-term follow-up of patients with total cavopulmonary connection (TCPC) for palliation of functionally univentricular hearts. Serial intraindividual data revealed a significant increase in the γGT level within a minimum 4-year interval in more than 80 % of cases. The level of γGT elevation showed a significant correlation to hemodynamic parameters such as systemic ventricular end diastolic pressure and mean pulmonary artery pressure, but did not strongly correlate with duration of follow-up or other liver function parameters, which were less frequent and less impressively deranged. None of the patients had signs of synthetic dysfunction. With increasing postoperative follow-up, abnormalities of sonographic hepatic texture including increased echogenicity, inhomogeneity, or liver surface nodularity were found. All 17 patients with liver surface nodularity had a follow-up period of over 10years. Structural abnormalities did not correlate with biochemical or hemodynamic parameters. Doppler evaluation revealed inspiratory dependence of hepatic vein flow in more than 90 % as a relevant finding after TCPC; a decrease in portal vein flow velocity was observed in many patients. Since long-term survivors after Fontan procedure are at an increased risk of cardiac hepatopathy and cirrhosis, detailed routine investigation and monitoring of hepatic morphology are needed.

Nanoscale surface potential imaging of the photocatalytic TiO2 films on aluminum

The change in the surface potential of TiO2 coatings upon UV-illumination was investigated on the nanoscale using Scanning Kelvin Probe Force microscopy and on the micro-scale using photo-electrochemical measurements. A good correlation between the two techniques was obtained. The changes in the surface potential of TiO2 coatings upon UV-illumination are closely correlated to the band gap and thickness of the coatings. The inhomogeneity surface potential distribution of a 100 nm TiO2 film indicates a heterogeneous coating. Transition to a homogeneous surface potential distribution was observed with increasing thickness of the TiO2 coating.

Dual-luminophor pressure-sensitive paint: I. Ratio of reference to sensor giving a small temperature dependency

Pressure-sensitive paint (PSP) is playing an important role in aerodynamic testing. Its use provides a number of advantages over discrete pressure taps traditionally used on conventional wind tunnel models: (i) obtaining continuous quantitative pressure distributions over a surface; (ii) visualizing dynamic flow processes that measure areas not possible with conventional pressure taps (e.g. thin trailing edges); and (iii) real time modeling. The result is better integration of experimental and computational fluid dynamics leading to significant reductions in time for prototyping of new designs. The use of PSP relies on accurate measurement of changes in the paint’s luminescent intensity as a function of pressure change, which in turn requires careful monitoring and placement of light sources and pre-calibration of the PSP covered surface in “wind-off” conditions. Paint in-homogeneity and inconsistent surface illumination require exact registration of the calibration ‘wind-off’ image with subsequent ‘wind-on’ images for intensity change calculations to be meaningful. Model motion between ‘wind-on’ and ‘wind-off’ images leads to systematic errors that are hard to quantify. A dual-luminophor paint containing both a sensor and a reference luminophor molecule should alleviate these technical problems. This paper introduces such a dual-luminophor PSP made from our newly developed oxygen-sensitive molecule platinum tetra(pentafluorophenyl)porpholactone (PtTFPL), which provides I sen, and magnesium tetra(pentafluorophenyl)porphine (MgTFPP), which provides I ref as the pressure-independent reference. The ratio I ref/ I sen in the FIB polymer produced ideal PSP measurements with a temperature dependency of −0.1%/°C.

The energy of a growing elastic surface

The potential energy of the elastic surface of an elastic body which is growing by the coherent addition of material is derived. Several equivalent expressions are presented for the energy required to add a single atom, also known as the chemical potential. The simplest involves the Eshelby stress tensors for the bulk medium and for the surface. Dual Lagrangian/Eulerian expressions are obtained which are formally similar to each other. The analysis employs two distinct types of variations to derive the governing bulk and surface equations for an accreting elastic solid. The total energy of the system is assumed to comprise bulk and surface energies, while the presence of an external medium can be taken into account through an applied surface forcing. A detailed account is given of the various formulations possible in material and current coordinates, using four types of bulk and surface stresses: the Piola-Kirchhoff stress, the Cauchy stress, the Eshelby stress and a fourth, called the nominal energy-momentum stress. It is shown that inhomogeneity surface forces arise naturally if the surface energy density is allowed to be position dependent.

Variational properties of stationary inviscid incompressible flows with possible abrupt inhomogeneity or free surface

The inviscid flows, possibly rotational and nonsmooth, which satisfy the equation of stationary incompressible hydrodynamics, are characterized as giving zero variation rate to some real functional when the corresponding scalar and vector fields are transported by what is called a carrier, i.e. a mobile differential manifold. This transport does not have to preserve volumes; the Bernoulli function figures as the natural unknown scalar field rather than the pressure. Inhomogeneity may be sharp, implying in particular the presence of free surfaces. The key mathematical concept is that of a divergence-free vector measure convected by a carrier. For easier handling of this concept, some versions of the main variational statement are derived, involving vector potentials and stream functions in two or three dimensions; axially symmetric flows are also considered.

Fracture of parallel elements

A new approach to modeling of progressive damage of interphases in random particulate composites is proposed. In the model the interphases are represented by layers of springs whose stiffness parameters change as a result of damage associated with gradually increasing loading. Consequently, due to local degradation of the interphase, variation of these parameters over the inhomogeneity surface becomes progressively non-uniform. This, in turn, causes the effective properties of the composite to become increasingly anisotropic. To describe the effects of interphase damage on the overall properties of the composite three ideas proposed in the past with the authors’ participation are utilized. One is the Method of Conditional Moments (MCM), a statistical homogenization technique developed in the past to analyze the effective properties of random composites without interphases. The second idea is the recently introduced notion of Energy Equivalent Inhomogeneity (EEI), which replaces the original inhomogeneities and their interphases with uniform inhomogeneities; the notion of EEI allows methods devised to examine composites without interphases (such as MCM) to analyze composites with interphases. The most important, and novel in application to problems considered in this work, is the third idea concerning the statistical interphase damage model. In the proposed approach local micro-damage of interphases is modelled by an increasing fraction of randomly distributed destructed springs in the spring layers surrounding the inhomogeneities of the composite. The model assumes that the local interphase micro-strength at the points located on the surface of different inhomogeneities and specified by the same spherical coordinates is described by one-point Weibull distribution function. In view of the strong nonlinearity of the problem, an incremental/iterative scheme is used in practical evaluation of effective properties. The approach is illustrated considering unidirectional and triaxial stretching of a composite.