Electron Beam Surface Treatment. Part I: Surface Hardening of AISI D3 Tool Steel

The effects of electron beam surface hardening treatment on the microstructure and hardness of AISI D3 tool steel have been investigated in this paper. The results showed that the microstructure of the hardened layer consisted of martensite, a dispersion

Instability Analysis of Nonlinear Surface Waves in a Circular Cylindrical Container Subjected to a Vertical Excitation

Singular perturbation theory of two-time scale expansions was developed both in inviscid and weak viscous fluids to investigate the motion of single surface standing wave in a liquid-filled circular cylindrical vessel, which is subject to a vertical periodical oscillation. Firstly, it is assumed that the fluid in the circular cylindrical vessel is inviscid, incompressible and the motion is irrotational, a nonlinear evolution equation of slowly varying complex amplitude, which incorporates cubic nonlinear term, external excitation and the influence of surface tension, was derived from solvability condition of high-order approximation. It shows that when forced frequency is low, the effect of surface tension on mode selection of surface wave is not important. However, when forced frequency is high, the influence of surface tension is significant, and can not be neglected. This proved that the surface tension has the function, which causes free surface returning to equilibrium location. Theoretical results much close to experimental results when the surface tension is considered. In fact, the damping will appear in actual physical system due to dissipation of viscosity of fluid. Based upon weakly viscous fluids assumption, the fluid field was divided into an outer potential flow region and an inner boundary layer region. A linear amplitude equation of slowly varying complex amplitude, which incorporates damping term and external excitation, was derived from linearized Navier-Stokes equation. The analytical expression of damping coefficient was determined and the relation between damping and other related parameters (such as viscosity, forced amplitude and depth of fluid) was presented. The nonlinear amplitude equation and a dispersion, which had been derived from the inviscid fluid approximation, were modified by adding linear damping. It was found that the modified results much reasonably close to experimental results. Moreover, the influence both of the surface tension and the weak viscosity on the mode formation was described by comparing theoretical and experimental results. The results show that when the forcing frequency is low, the viscosity of the fluid is prominent for the mode selection. However, when the forcing frequency is high, the surface tension of the fluid is prominent. Finally, instability of the surface wave is analyzed and properties of the solutions of the modified amplitude equation are determined together with phase-plane trajectories. A necessary condition of forming stable surface wave is obtained and unstable regions are illustrated. (c) 2005 Elsevier SAS. All rights reserved.

Polysiloxane surfactants for the dispersion of carbon nanotubes in nonpolar organic solvents.

We develop two new amphiphilic molecules that are shown to act as efficient surfactants for carbon nanotubes in nonpolar organic solvents. The active conjugated groups, which are highly attracted to the graphene nanotube surface, are based on pyrene and porphyrin. We show that relatively short (C18) carbon tails are insufficient to provide stabilization. As our ultimate aim is to disperse and stabilize nanotubes in siloxane matrix (polymer and cross-linked elastomer), both surfactant molecules were made with long siloxane tails to facilitate solubility and steric stabilization. We show that the pyrene-siloxane surfactant is very effective in dispersing multiwall nanotubes, while the porphyrin-siloxane makes single-wall nanotubes soluble, both in petroleum ether and in siloxane matrix.

Damping of Vertically Excited Surface Wave in Weakly Viscous Fluid

In a vertically oscillating circular cylindrical container, singular perturbation theory of two-time scale expansions is developed in weakly viscous fluids to investigate the motion of single free surface standing wave by linearizing the Navier-Stokes equation. The fluid field is divided into an outer potential flow region and an inner boundary layer region. The solutions of both two regions are obtained and a linear amplitude equation incorporating damping term and external excitation is derived. The condition to appear stable surface wave is obtained and the critical curve is determined. In addition, an analytical expression of damping coefficient is determined. Finally, the dispersion relation, which has been derived from the inviscid fluid approximation, is modified by adding linear damping. It is found that the modified results are reasonably closer to experimental results than former theory. Result shows that when forcing frequency is low, the viscosity of the fluid is prominent for the mode selection. However, when forcing frequency is high, the surface tension of the fluid is prominent.

Surface plasmons and effects of losses in propagating modes in a chain of silver nanoparticles

In this work a chain of 4000 silver nanoparticles embedded in a glass medium is considered, and its leftmost particle is excited by an electric field pulse of Gaussian shape. Considering Drude’s model, losses of the system are taken into account by γ factor, which stands for the Ohmic losses, and different quantities, such as frequencies of excited modes and group velocities are calculated. Besides, these results are compared to those obtained from the dispersion relation of an infinite chain. The increase of losses affects the lifetime and propagation length of the plasmon; besides, although the response dispersion relation for an infinite chain seems to remain invariable, this is not the case for a finite chain. The mismatches are bigger for higher losses. Furthermore, plasmon propagation velocities are analysed, and an explanation for the mismatch of longitudinal modes close to the intersection point with the dispersion of light is suggested. Finally, some concepts to treat this problem from the energy transport point of view are introduced.

Guided propagation of surface acoustic waves and piezoelectric field enhancement in ZnO/GaAs systems

The characteristics and dispersion of the distinct surface acoustic waves (SAWs) propagating in ZnO/GaAs heterostructures have been studied experimentally and theoretically. Besides the Rayleigh mode, strong Sezawa modes, which propagate confined in the overlayer, arise due to the smaller sound velocity in ZnO than in the substrate. The design parameters of the structure providing the strongest piezoelectric field at a given depth within the layered system for the different modes have been determined. The piezoelectric field of the Rayleigh mode is shown to be more than 10 times stronger at the interface region of the tailored ZnO/GaAs structure than at the surface region of the bulk GaAs, whereas the same comparison for the first Sezawa mode yields a factor of 2. This enhancement, together with the capacity of selecting waves with different piezoelectric and strain field depth profiles, will facilitate the development of SAW-modulated optoelectronic applications in GaAs-based systems. © 2011 American Institute of Physics.

Alternative methods for surface texturing

Surface texturing has a great potential to improve tribological performance. First, possible texturing methods were identified and classified according to their physical principles. In sequence, some alternative texturing methods are presented. Some of them are already currently used either in industry or in laboratory, and innovations or simplifications are described for them. Others are innovative techniques. Some were explored only tentatively, where basic ideas and simple experimental investigations were developed to check their validity. Others were explored in more detail, so that their practical applicability could be identified. The first texturing method was photochemical texturing using a simple and cheap apparatus. Masking with inkjet printing before chemical etching was also successful to texture metallic samples. A new method involving electrochemical texturing, without the need to previously mask the samples to be textured have been studied in terms of voltage, current, mechanical configuration of the apparatus and electrolyte flushing. Another method aims to generate randomly distributed circular pockets on steel surfaces and involves dispersion of small acid droplets in oil. The final method involves the selective formation of hard areas on a steel surface by locallised diffusion, which should then develop into a texture during wear.

Low attenuation of GHz Rayleigh-like surface acoustic waves in ZnO/GaAs systems immersed in liquid helium

Low attenuation of Sezawa modes operating at GHz frequencies in ZnO/GaAs systems immersed in liquid helium has been observed. This unexpected behaviour for Rayleigh-like surface acoustic waves (SAWs) is explained in terms of the calculated depth profiles of their acoustic Poynting vectors. This analysis allows reproduction of the experimental dispersion of the attenuation coefficient. In addition, the high attenuation of the Rayleigh mode is compensated by the strengthening provided by the ZnO layer. The introduction of the ZnO film will enable the operation of SAW-driven single-photon sources in GaAs-based systems with the best thermal stability provided by the liquid helium bath. © 2013 American Institute of Physics.

Electron tunneling through double magnetic barriers on the surface of a topological insulator

We study electron tunneling through a planar magnetic and electric barrier on the surface of a three-dimensional topological insulator. For the double barrier structures, we find (i) a directional-dependent tunneling which is sensitive to the magnetic field configuration and the electric gate voltage, (ii) a spin rotation controlled by the magnetic field and the gate voltage, (iii) many Fabry-Perot resonances in the transmission determined by the distance between the two barriers, and (iv) the electrostatic potential can enhance the difference in the transmission between the two magnetization configurations, and consequently lead to a giant magnetoresistance. Points (i), (iii), and (iv) are alike with that in graphene stemming from the same linear-dispersion relations.

Flat Surface Plasmon Polariton Bands in Bragg Grating Waveguide for Slow Light

The formations of the surface plasmonpolariton (SPP) bands in metal/air/metal (MAM) sub-wavelength plasmonic grating waveguide (PGW) are proposed. The band gaps originating from the highly localized resonances inside the grooves can be simply estimated from the round trip phase condition. Due to the overlap of the localized SPPs between the neighboring grooves, a Bloch mode forms in the bandgap and can be engineered to build a very flat dispersion for slow light. A chirped PGW with groove depth varying is also demonstrated to trap light, which is validated by finite-difference time-domain (FDTD) simulations with both continuous and pulse excitations.

Preparation, Surface Properties and Biological Activity of the Composite of Poly (lactide-co-glycolide) and Bioglass Nanoparticles Surface Grafted with Poly(L-lactide)

SiO2-CaO-P2O5 gel bioglass (BG) nanoparticles with the diameter of 40 nm were synthesized by sol-gel approach. The surface of BG nanoparticles was grafted through the ring-open polymerization of the L-lactide to yield poly (L-lactide) (PLLA) grafted gel particle (PLLA-g-BG). The PLLA-g-BG was further blended with poly(lactide-co-glycolide) (PLGA) to prepare the nanocomposites of PLLA-g-BG/PLGA with the various blend ratios of two phases. PLLA-g-BG accounted 10%, 20% and 40% in the composite, respectively. TGA, ESEM and EDX were used to analyze the graft ratio of PLLA-g-BG, the dispersion of nano-particles and the surface elements of the composites respectively. The rabbit osteoblasts were seeded and cultured on the thin films of composites in vitro. The cell adhesion, spreading and growth of osteoblasts were analyzed with FITC staining, NIH Image J software and MTT assay. The change of cell cycle was monitored by flow cytometry (FCM). The results demonstrated that the Surface modification of BG with PLLA could significantly improve the dispersing of the particles in the matrix of PLGA. The nanocomposite with 20% PLLA-g-BG exhibited superior surface properties, including roughness and plenty of silicon, calcium and phosper, to enhance the adhesion, spreading and proliferation of osteoblasts.

Influences of catalysis and dispersion of organically modified montmorillonite on flame retardancy of polypropylene nanocomposites

The degradation and flame retardancy of polypropylene/organically modified montmorillonite (PP/OMMT) nanocomposite were studied by means of gas chromatography-mass spectrometry and cone calorimeter. The catalysis of hydrogen proton containing montmorillonite (H-MMT) derived from thermal decomposition of (alkyl) ammonium in the OMMT on degradation of PP strongly influence carbonization behavior of PP and then flame retardancy. Bronsted acid sites on the H-MMT could catalyze degradation reaction of PP via cationic mechanism, which leads to the formation of char during combustion of PP via hydride transfer reaction. A continuous carbonaceous MMT-rich char on the surface of the burned residues, which work as a protective barrier to heat and mass transfer, results from the homogeneous dispersion of OMMT in the PP matrix and appropriate char produced.

A novel strategy to construct a flat-lying DNA monolayer on a mica surface

Flat-lying, densely packed DNA monolayers in which DNA chains are well organized have been successfully constructed on a mica surface by dropping a droplet of a DNA solution on a freshly cleaved mica surface and subsequently transferring the mica to ultrapure water for developing. The formation kinetics of such monolayers was studied by tapping mode atomic force microscopy (TMAFM) technique. A series of TMAFM images of DNA films obtained at various developing times show that before the sample was immersed into water for developing the DNA chains always seriously aggregated by contacting, crossing, or overlapping and formed large-scale networks on the mica surface. During developing, the fibers of DNA networks gradually dispersed into many smaller fibers up to single DNA chains. At the same time, the fibers or DNA chains also experienced rearrangement to decrease electrostatic repulsion and interfacial Gibbs free energy. Finally, a flat-lying, densely packed DNA monolayer was formed. A formation mechanism of the DNA monolayers was proposed that consists of aggregation, dispersion, and rearrangement. The effects of both DNA and Mg2+ concentration in the formation solution on DNA monolayer formation were also investigated in detail.

Preparation of polyimide-BaTiO3 hybrid films by a dispersion process and their microstructure

Barium titanate (BaTiO3) powders with particle sizes of 30 similar to 50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO3 nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO3 content was less than 1 wt%. Highly loaded hybrid film containing 30 wit % BaTiO3 was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide.