Effect Of Interface Roughness Research Articles

Shrinkage of New Concrete Restrained by Old Concrete Based on Interface Roughness

Based on the analysis of the early shrinkage mechanism of concrete, shrinkage experiment of new concrete restrained by old concrete were conducted to analyze the impact of the different interface roughness on shrinkage stress of new concrete and bonding surface. It is shown that the inner tensile stress of new concrete decreases with increasing of interface roughness, and increase restrained thickness of the new concrete, but it is not significant effect of interface roughness on the shrinkage at bonding surface; the shrinkage strain of section reduces with reduction of the distance of section to bonding surface and reaches minimum on bonding surface, which reflecte significant nonuniformity and increases gradually with age.

Effect of polarization and interface roughness on the transport properties of AlGaN/GaN heterostructure

The low field mobility of carriers at an AlxGa1−xN/GaN hetero structure is investigated using an ensemble Monte Carlo method. The mobility values are obtained in the temperature range 77–1020K using the energy levels, electron concentrations and wavefunctions obtained from the self-consistent solution of Poisson/Schrödinger equations at the hetero interface. The free electron concentration at the interface results solely from the spontaneous and piezoelectric polarization charges at the interface and the exchange-correlations effects are also considered in the potential energy calculations. Both the role of interface roughness scattering on mobility as a function of temperature and the dependence of carrier concentration at the AlGaN/GaN hetero interface on Al-content are investigated in detail. We found that interface roughness scattering is very effective especially at low temperatures on the drift mobility and it has no observable effect beyond a certain temperature. While increasing alloy composition increases the free electron concentration, it reduces the mobility of electrons because the steepness of the potential at the junction increases. The results of our simulations well-matched with the existing experimentaldata.

Effects of Interface Roughness and Lattice Strain on Perpendicular Magnetic Anisotropy in Co/Pd Multilayer

The effects of strain and interface roughness at the Co/Pd interface are investigated from the viewpoint of perpendicular magnetic anisotropy (PMA) using the DV-Xα cluster model calculation method. It is found that spin projected occupation number ratio of magnetic quantum number |m| = 2 for the Co 3d electrons enhances by expanding the lattice within a close-packed plane of fcc stacking and, hence, enhances the PMA. Rough interface decreases the spin projected occupation number ratio of |m| = 2 and, hence, decreases the PMA. These results explain the PMA properties of Co/Pd multilayers fabricated using molecular beam epitaxy (MBE) technique and RF sputtering techniques.

Effects of interface roughness on the life estimation of a thermal barrier coating layer

Methodology development for life estimation of thermal barrier coating (TBC) applied on a gas turbine engine combustor liner has been undertaken using finite element method. 3-D finite element analyses (FEA) are performed using ABAQUS followed by fatigue analysis through FESAFE for life estimation of a TBC layer. Analysis considers a typical mission cycle of a gas turbine engine while modelling the transition liner of a reverse flow combustion chamber. This paper presents the influence of interface roughness on the life of TBC layer. Three different cases of interface roughness have been studied. Roughness is found to affect TBC life adversely. In addition to effect of interface roughness, the life estimation methodology is also discussed.

Flicker noise in n-channel nanoscale tri-gate fin-shaped field-effect transistors

In n-channel nanoscale tri-gate fin-shaped field-effect transistors with high-k gate dielectric stack, the 1/f noise is investigated, ascribed to the carrier number fluctuations with correlated mobility fluctuations. The overall results show that the gate dielectric trap density is uniform in both top-gate and side-gates and the product Ω=αscμeffCox of the Coulomb scattering coefficient αsc, the effective carrier mobility μeff and the gate oxide capacitance per unit area Cox increase with decreasing the fin thickness due to enhancement of side-gates interface roughness effects.

The study of transport properties in rough ferromagnetic semiconductor rough junctions

The effect of self-affine interface roughness on spin filter tunnelling as a function of interface roughness parameters and the temperature dependent barrier parameters at low biases is studied. The interface roughness is described by the k-correlation model and in terms of self-affine scaling by root-mean-square (rms) deviation Δ, correlation length ξ, and the roughness exponent H(0≤H≤1). In general, the spin-dependent transmission probability is strongly sensitive to roughness and reduced for the case of spin up and down directions in all configurations. Our numerical results show that the roughness affects spin polarization (SP) and tunnelling magnetoresistance (TMR) at different temperatures and decreases the maximum achievable TMR and SP.

Effect of Interfacial Roughness on Slider-Disk Interactions at Near-Contact Regime

One of the major efforts in reducing fly height (FH) in order to achieve higher recording areal density for hard disk drive, is to reduce slider-disk interfacial roughness. However, as roughness improves to the atomically smooth level, various interaction forces such as van der Waals force, electrostatic force, and intermittent contact force affect slider fly stability. In this paper, an electrostatic force manipulation methodology was employed to investigate roughness effect on slider-disk interactions at near-contact regime. In such methodology, an AC excitation with pre-determined frequency was applied across the slider-disk interface. First harmonic vibration response of the excitation was monitored. Such vibration response is sensitive to various interaction forces, as FH is reduced to near-contact regime. The phenomena observed were verified with static and dynamic simulations, using self-developed ABsolution simulation software. It was found that disk with higher roughness has larger adhesive force gradient and hence larger first harmonic vibration at near-contact. First harmonic vibration dip was observed near touchdown point. Simulation result suggests that the phenomenon is due to time-averaging effect of slider intermittently “snap” to the disk surface. It was found that magnitude of the vibration dip is surface roughness dependent. At contact regime, nonlinear contact stiffness-based contact detection is highly sensitive for smooth surface. Abrupt transition of low to high vibration state of smooth surface during contact is attributed to larger adhesion hysteresis effect.

The effects of fiber’s surface roughness on the mechanical properties of fiber-reinforced polymer composites

An improved shear-lag model is developed in this paper to study the effects of interface roughness on the mechanical properties of unidirectional fiber-reinforced polymer composites with a staggered structure, in which the roughness is incorporated by establishing equilibrium equations for the fiber platelets with varying thickness along its axial direction. The stress transfer and effective Young’s modulus of composites are mainly investigated due to the influence of fiber’s surface roughness. Since the polymer matrix can be chosen as thermoplastic or thermosetting materials, a uniformly interfacial shear stress distribution due to the frictional transfer along fiber/matrix interfaces and a non-uniformly one due to the elastic transfer are analyzed, respectively. It is found that when the surface roughness becomes larger, fibers in the former will carry more tensile loads, while the tensile loads keep almost invariant in fibers and the shear stress reduces in matrix in the latter. Moreover, the effective Young’s modulus of composites will be enhanced due to increasing fiber’s surface roughness. However, the enhancing effect will gradually reduce with an increasing aspect ratio of fibers. The results should be very useful for the design of novel fiber-reinforced polymer composites, especially for those that needed interfacial modifications in order to improve the interfacial adhesion, for example, carbon-fiber reinforced polymer composites.

Limit analysis of the undrained bearing capacity of offshore pipelines

The ultimate bearing capacity of a rigid, plane-strain pipe segment embedded in undrained clay is studied using numerical limit analysis. The pipe is considered to be ‘wished in place' at invert penetrations ranging from zero to five pipe diameters, thus providing coverage of both on-bottom (partially embedded) and trenched (fully embedded) offshore pipelines. The soil is modelled as a rigid-plastic Tresca material with either uniform strength or strength proportional to depth. The effects of soil weight, interface roughness and interface tensile capacity are investigated in a systematic manner. All calculations are performed using the finite-element limit analysis code OxLim, which uses adaptive mesh refinement to compute tightly bracketed lower- and upper-bound plasticity solutions. The velocity fields from the upper-bound analyses provide the corresponding failure mechanisms. The paper initially focuses on purely vertical loading (penetration and uplift), and then addresses combined vertical and horizontal loading. A comprehensive set of design curves and failure envelopes is presented, with the results explained in terms of the changing failure mechanisms. These results are immediately applicable in practice. In particular, current industry-standard procedures for design against pipeline upheaval are critically reviewed, and are shown to have potentially unconservative shortcomings.

Modeling the effect of interface roughness on bottom loss from layered interfaces with finite elements

The bottom loss from a layered ocean sediment is determined using a finite element/boundary element (FE/BE) method. First, the pressure and its normal derivative are calculated on the top interface using finite elements. Then the field at a point outside of the domain is determined using the Helmholtz/Kirchhoff integral (BE). Bottom loss is then calculated by comparing the reflected/scattered energy to the incident energy. The finite element method makes no approximations to the Helmholtz equation and is exact within the limits of the discretization. Any number of layers including elastic layers with rough or smooth interfaces can be included. The results of the FE/BE approach will be compared to Geoacoustic Bottom Interaction Model (GABIM) for a number of test cases. [Jackson, et al., IEEE J. Ocean. Eng. 35(3), 603-617 (2010)] GABIM computes the layered reflection coefficient then includes scattering for one rough interface based on “a combination of the Kirchhoff approximation, first-order perturbation theory and an empirical expression for very rough seafloors”. Lastly, the bottom loss of multiple rough interfaces will be compared to that of a single rough interface. [Work supported by ONR, Ocean Acoustics.]

Effects of self-affine roughness characteristics on electron transmission through tunneling structures

By using the transfer matrix method and the nearly free electron approximation, we investigate effects of interfacial roughness on electron transport through double-barrier quantum wells. The barrier roughness is described by the k-correlation model, and the interface is characterized by the roughness exponent, in-plane correlation length, and root mean square height. Our analysis demonstrates that the transmission probability is sensitive to roughness parameters. Two behaviors are observed for this sensitivity depending on whether the incident wavelength is larger or smaller than the correlation length.

Investigation of coherent acoustic phonons in terahertz quantum cascade laser structures using femtosecond pump-probe spectroscopy

The dynamics of acoustic vibrations in terahertz quantum cascade laser structures (THz-QCLs) is studied by means of femtosecond pump-probe spectroscopy. The phonon modes are characterized by the folding of the acoustic dispersion into an effective reduced Brillouin zone. An accurate identification of this dispersion allows the sample structure and periodicity to be determined with high precision on the order of 0.1%. By temperature tuning the energy of the electronic levels of the system and performing wavelength dependent measurements, we are able to study the impulsive resonant generation and detection of coherent acoustic phonon modes. These results are supported by simulations of the electronic system that well explain the experimental observations. The effects of interface (IF) roughness on coherent acoustic phonon spectra are clearly observed for equal nominal THz-QCL structures but with different interface qualities.

Tailoring interfacial exchange coupling with low-energy ion beam bombardment: Tuning the interface roughness

By ascertaining NiO surface roughness in a Ni80Fe20/NiO film system, we were able to correlate the effects of altered interface roughness from low-energy ion-beam bombardment of the NiO layer and the different thermal instabilities in the NiO nanocrystallites. From experiment and by modelling the temperature dependence of the exchange bias field and coercivity, we have found that reducing the interface roughness and changing the interface texture from an irregular to striped conformation enhanced the exchange coupling strength. Our results were in good agreement with recent simulations using the domain state model that incorporated interface mixing.

Interface roughness induced asymmetric magnetic property in sputter-deposited Co/CoO/Co exchange coupled trilayers

The effect of interface roughness on magnetic properties of exchange coupled polycrystalline Co/CoO(tAF)/Co trilayers has been investigated by varying antiferromagnetic layer (CoO) thickness. It has been found that the upper CoO/Co interface becomes rougher with increasing CoO layer thickness, resulting in stronger exchange bias of the upper interface than the lower one. The interfacial exchange coupling is strengthened by the increase of defect-generated uncompensated antiferromagnetic spins; such spins form coupling with spins in the Co layer at the interface. As a result, the CoO layer thickness dependence of exchange bias is much enhanced for the upper Co layer. The transition from anisotropic magnetoresistance to isotropic magnetoresistance for the top Co layer has also been found. This could be attributed to the defects, probably partial thin oxide layers, between Co grains in the top Co layer that leads a switch from spin-orbit scattering related magnetoresistance to spin-dependent electron scattering dominated magnetoresistance.

Effect of interface roughness and polarisation on the optical losses of porous silicon-based waveguides

Optical losses measurements were performed at 1550 nm on both porous silicon ( P Si) and oxidised P Si ( OP Si) planar waveguides as a function of interface roughness. The P Si waveguides were produced at different anodisation temperatures to reduce the interface roughness. The authors noticed a decrease in optical losses with the diminution of roughness. The lowest value of optical losses was equal to 0.5 dB/cm and obtained for OP Si waveguide with a 10 nm interface roughness and anodisation temperature equal to 20 C. The surface scattering losses were modelled. There is a good agreement between the theoretical and experimental values. The optical losses were also carried out in transverse electric (TE) and transverse magnetic (TM) polarisations for both P Si and oxidised OP Si waveguides.

Effect of Interface Roughness on Exchange Bias of an Uncompensated Interface: Monte Carlo Simulation

By means of Monte Carlo simulation, we investigate the effects of interface roughness and temperature on the exchange bias and coercivity in ferromagnetic (FM)/antiferromagnetic (AFM) bilayers. Both exchange bias and coercivity are strongly dependent on interface roughness. For a perfect uncompensated interface a domain wall is formed in the AFM system during FM reversal, which results in a very small exchange bias. However, a finite interface roughness leads to a finite value of the exchange bias due to the existence of pinned spins at the AFM surface adjacent to the mixed interface. It is observed that the exchange bias decreases with increasing temperature, consistent with the experimental results. It is also observed that a bump in coercivity occurs around the blocking temperature.

Effects of interface roughness scattering on radio frequency performance of silicon nanowire transistors

The effects of an atomistic interface roughness in n-type silicon nanowire transistors (SiNWT) on the radio frequency performance are analyzed. Interface roughness scattering (IRS) is statistically investigated through a three dimensional full–band quantum transport simulation based on the sp3d5s* tight–binding model. As the diameter of the SiNWT is scaled down below 3 nm, IRS causes a significant reduction of the cut-off frequency. The fluctuations of the conduction band edge due to the rough surface lead to a reflection of electrons through mode-mismatch. This effect reduces the velocity of electrons and hence the transconductance considerably causing a cut-off frequency reduction.

InGaP/InGaAs MOS-PHEMT with a nanoscale liquid phase-oxidized InGaP dielectric

InGaP/InGaAs metal–oxide–semiconductor (MOS) pseudomorphic high-electron-mobility transistor (PHEMT) with a nanoscale liquid phase-oxidized InGaP as the gate dielectric is demonstrated. Not only does the MOS-PHEMT have the advantages of the MOS structure, but it also has high-carrier density and a high-mobility 2DEG channel. Using selective oxidation of InGaP by liquid phase oxidation, the MOS-PHEMT can be fabricated without additional recess processes. The MOS-PHEMT exhibits larger transconductance, lower gate leakage current, higher breakdown voltage, higher cut-off frequency, lower minimum noise figure, and higher power-added efficiency than does its counterpart (reference PHEMT). The interface roughness effect on the DC and RF performance of devices is also discussed.

The surface cracking behavior in air plasma sprayed thermal barrier coating system incorporating interface roughness effect

The objective of this work is to understand the effect of interface roughness on the strain energy release rate and surface cracking behavior in air plasma sprayed thermal barrier coating system. This is achieved by a parameter investigation of the interfacial shapes, in which the extended finite element method (XFEM) and periodic boundary condition are used. Predictions for the stress field and driving force of multiple surface cracks in the film/substrate system are presented. It is seen that the interface roughness has significant effects on the strain energy release rate, the interfacial stress distribution, and the crack propagation patterns. One can see the completely different distributions of stress and strain energy release rate in the regions of convex and concave asperities of the substrate. Variation of the interface asperity is responsible for the oscillatory characteristics of strain energy release rate, which can cause the local arrest of surface cracks. It is concluded that artificially created rough interface can enhance the durability of film/substrate system with multiple cracks.

Two-dimensional electron transport in MgZnO/ZnO heterostructures: role of interface roughness

Mobility of two-dimensional electron gases in MgZnO/ZnO heterostructures with interface roughness effects was investigated theoretically using path-integral framework. We modelled the roughness-induced fluctuation by including two major effects, i.e. the electron and polarization-induced positive charge concentrations. We showed that both effects cause the scattering potential in the in-plane direction and hence affect the 2D mobility. In this work, we treated both electron and polarization-induced positive charge concentrations as equally important factors and then calculated the electron mobility and compared with the experimental result of Mg0.2Zn0.8O/ZnO heterostructure at high-electron concentrations. We found that the fitting parameters Δ = 0.26 nm, Λ = 2.5 nm gave good description to the mobility data. We also showed that neglecting the polarization-induced positive charge concentration led to overestimating the 2D mobility.