Random Surface Structures Research Articles

Influence of Inner Surface Roughness on the Spectral Induced Polarization Response—A Numerical Study

AbstractSpectral induced polarization (SIP) laboratory measurements on water‐saturated rocks show a strong correlation between the electrical polarization strength and the inner surface area of rocks. We investigate the influence of inner surface roughness on the SIP response by simulating the frequency‐dependent complex conductivity of micro‐scale rock models. Starting with smooth grain models, we introduce surface roughness using two different approaches: increasing the surface roughness in a fractal‐like manner, and creating random surface structures, resulting in more natural‐looking surfaces. We find that surface roughness has two distinct effects on the SIP response: (a) a shift in the position and magnitude of the primary relaxation frequency to lower frequencies and lower magnitudes, respectively, and (b) the formation of secondary polarizations above the polarization frequency of the primary polarization. We also compare the relaxation time and normalized chargeability obtained by Debye decomposition and the imaginary conductivity at 1 Hz of our models with mechanistic models and empirical relations. We point out the congruences and offer explanations for the discrepancies between our models and the empirical observations. We conclude that the results of our study are applicable to real rocks and that the SIP method has the potential to detect inner surface roughness. However, the SIP method it not able to discriminate between signals from rough particles and a distribution of smooth particles.

Laser-induced formation of holograms for generation of plasmons

Methods of fabrication of precisely adjusted surface structures are indispensable to development of new technologies. Different surface structuring techniques resulting in solitary nanobumps, random surface structures and laser induced periodic surface structures were in focus in the past. Here we consider a physical model and numerical simulation allowing understanding a high field plasmonics formation process of a smooth periodic perturbation of surface on a metal film with a period equal to the surface plasmon-polariton wavelength at a frequency of laser wave. Such surface structure is a hologram produced by thermomechanical response to interference between an incident laser wave, a reflected laser wave, and an electromagnetic field in the running plasmon-polariton wave. The following laser irradiation of the manufactured hologram generates a new plasmon-polariton wave identical to that used for formation of the hologram.

Speckle phase near random surfaces

Based on Kirchhoff approximation theory, the speckle phase near random surfaces with different roughness is numerically simulated. As expected, the properties of the speckle phase near the random surfaces are different from that in far field. In addition, as scattering distances and roughness increase, the average fluctuations of the speckle phase become larger. Unusually, the speckle phase is somewhat similar to the corresponding surface topography. We have performed experiments to verify the theoretical simulation results. Studies in this paper contribute to understanding the evolution of speckle phase near a random surface and provide a possible way to identify a random surface structure based on its speckle phase.

Self-assembled monolayers of sulfonate-terminated alkanethiols investigated by frequency modulation atomic force microscopy in liquid

A molecular-scale understanding of self-assembled monolayers (SAMs) of sulfonate-terminated alkanethiols is crucial for interfacial studies of functionalized SAMs and their various applications. However, such an understanding has been difficult to achieve because of the lack of direct information on these molecular-scale structures in real space. In this study, we investigated the structures of sulfonate SAMs of sodium 11-mercapto-1-undecanesulfonate (MUS) by frequency modulation atomic force microscopy (FM-AFM) in liquid. The subnanometer-resolution FM-AFM images showed that the single-component MUS SAM prepared in pure water had random surface structures. In contrast, the MUS SAM prepared in a water–ethanol mixed solvent showed periodic striped structures with a flat-lying conformation. The results suggest a significant solvent effect on molecular-scale structures of long-chain sulfonate SAMs. In addition, we investigated the molecular-scale structures of mixed SAMs of MUS and 11-mercapto-1-undecanol (MUO) with alkane chains of the same length. The FM-AFM images of the mixed SAMs showed clear phase separation between MUS SAM and MUO SAM domains. In the MUO SAM domains, the incorporated MUS molecules appeared as protrusions. The results obtained in this study provide direct structural information on long-chain sulfonate and mixed SAMs.

PENYISIHAN ION LOGAM MERKURI (Hg2+) MENGGUNAKAN ADSORBEN BERBAHAN BAKU LIMBAH PERTANIAN DAN GULMA TANAMAN

This research was conducted to prepare adsorbents from agricultural and weeds waste biomass to remove Hg2+ metal ions from water phase. Water hyacinth biomass (agricultural waste) and rice husk (weed) was cleaned, dried in an oven dryer, and carbonized in a furnace at 500oC for 2 hours. Then, dried carbon was milled to get 100 mesh of size and was followed by activation using 0.5 N NaOH. The adsorption process was conducted by mix 1 gram of activated adsorbent on a 100 ml water containing 3 ppm Hg2+ metal ions at 100 rpm, pH 5, and 30oC. Hg2+ concentration in water phase were analyzed using AAS, Shimadzu AA-6300 for a specified time within a period of 20-100 minutes. This study shows that at the beginning process of adsorption, adsorbent from rice husk has ability to decrease 69.91% concentration of Hg2+ for 20 minutes, while adsorbent from water hyacinth reaches to 94.26%. The characterization results of FTIR spectra and SEM shows that adsorbent from water hyacinth was able to absorb more Hg2+ metal ions in a short time because it has a functional group that was able to bind heavy metals, and also has a random surface structure, compared with the adsorbent from rice husks that has less functional groups with uniform morphology structure

Multi-height structures in injection molded polymer

We present the fabrication process for injection molded multi-height surface structures for studies of wetting behavior. We adapt the design of super hydrophobic structures to the fabrication constrictions imposed by industrial injection molding. This is important since many super hydrophobic surfaces are challenging to realize by injection molding due to overhanging structures and very high aspect ratios. In the fabrication process, we introduce several unconventional steps for producing the desired shapes, using a completely random mask pattern, exploiting the diffusion limited growth rates of different geometries, and electroforming a nickel mold from a polymer foil. The injection-molded samples are characterized by contact angle hysteresis obtained by the tilting method. We find that the receding contact angle depends on the surface coverage of the random surface structure, while the advancing contact angle is practically independent of the structure. Moreover, we argue that the increase in contact angle hysteresis correlates with the concentration of pinning sites among the random surface structures.

Femtosecond laser surface structuring technique for making human enamel and dentin surfaces superwetting

It is known that good wettability of enamel and dentin surfaces is a key factor in enhancing adhesion of restorative materials in dentistry. Here, we report on a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this new approach produces engineered surface structures. The surface structure engineered and tested here is an array of femtosecond laser-produced parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

Color effects from scattering on random surface structures in dielectrics

We show that cheap large area color filters, based on surface scattering, can be fabricated in dielectric materials by replication of random structures in silicon. The specular transmittance of three different types of structures, corresponding to three different colors, have been characterized. The angle resolved scattering has been measured and compared to predictions based on the measured surface topography and by the use of non-paraxial scalar diffraction theory. From this it is shown that the color of the transmitted light can be predicted from the topography of the randomly textured surfaces.

Making human enamel and dentin surfaces superwetting for enhanced adhesion

Good wettability of enamel and dentin surfaces is an important factor in enhancing adhesion of restorative materials in dentistry. In this study, we developed a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this approach produces engineered surface structures. The surface structure engineered and tested here is an array of parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

Optical properties of nanostructured materials: a review

Depending on the size of the smallest feature, the interaction of light with structured materials can be very different. This fundamental problem is treated by different theories. If first order theories are sufficient to describe the scattering from low roughness surfaces, second order or even higher order theories must be used for high roughness surfaces. Random surface structures can then be designed to distribute the light in different propagation directions. For complex structures such as black silicon, which reflects very little light, the theory needs further development. When the material is periodically structured, we speak about photonic crystals or metamaterials. Different theoretical approaches have been developed and experimental techniques are rapidly progressing. However, some work still remains to understand the full potential of this field. When the material is structured in dimension much smaller than the wavelength, the notion of complex refractive index must be revisited. Plasmon resonance can be excited by a progressing wave on metallic nanoparticles inducing a shaping of the absorption band and of the dispersion of the extinction coefficient. This addresses the problem of the permittivity of such metallic nanoparticles. The coupling between several metallic nanoparticles induces a field enhancement in the surrounding media, which can increase phenomena like scattering, absorption, luminescence, or Raman scattering. For semiconductor nanoparticles, electron confinement also induces a modulated absorption spectra. The refractive index is then modified. The bandgap of the material is changed because of the discretization of the electron energy, which can be controlled by the nanometers size particles. Such quantum dots behave like atoms and become luminescent.

Improved Corona-Charging-Assisted Surface-Relief Amplification on Polymer Film for Low-Noise Holograms

The corona-charging-assisted technique for amplifying surface-relief holograms on a polymer film has been reported in recent years. However, it was found that light-scattering noise was undesirably superimposed on the reconstructed image of the amplified hologram. With a view to improving the technique for amplifying the surface relief, we explored the possible origins of the noise produced during the process. It was found that the noise originates from random submicron-scale surface structures produced during corona charging. In investigating the possibility of reducing this noise, we found that prebaking the polymer film at 150 °C for 10 min before inscribing the gratings was effective in inhibiting the generation of random surface structures. By inhibiting the generation of light-scattering noise, this prebaking process improved the optical quality of the amplified hologram. This tendency was also confirmed using a surface-relief-templated hologram recording to a glass substrate; that is, a nearly noiseless hologram was successfully transferred to the glass substrate.

AN EXACT SOLUBLE PATH INTEGRAL MODEL FOR STOCHASTIC BELTRAMI FLUXES AND ITS STRING PROPERTIES

We propose an exactly soluble path integral model for stochastic Beltrami fluxes in three-dimensional space-time with a fixed eddie scale. We show further the appearance of a three-dimensional self-avoiding random surface structure for the spatial vortex loop in our exactly soluble turbulence reduced model.

Viscoelastic buckling and plastic flow?deterministic mechanisms for ripple initiation on ion-bombarded amorphous solids

The great majority of current theoretical studies of the initiation or ripple morphology on ion-bombarded amorphous solids advocate the need for stochastic sputtering processes to initiate random surface structures from which ripples evolve. The present approach considers the initiation to be deterministic and resulting from viscoelastic buckling of a surface layer that is compressively stressed. The orientation of the ripple wave vector parallel to the incident ion projection on the surface is believed to result from beam-induced plastic flow preferentially in this direction.

Surface melting of clusters and implications for bulk matter.

Surface melting on clusters is investigated by a combination of analytic modeling and computer simulation. Homogeneous argonlike clusters bound by Lennard-Jones forces and Cu-like clusters bound by ``embedded-atom'' potentials are the systems considered. Molecular-dynamics calculations have been carried out for clusters with 40--147 atoms. Well below the bulk melting temperature, the surfaces become very soft, exhibiting well-defined diffusion constants even while the cores remain nearly rigid and solidlike. The simulations, particularly animations, of atomic motion reveal that the surface melting is associated not with amorphous, random surface structures in constant, irregular motion, but rather with large-amplitude, organized, collective motion of most of the surface atoms accompanied by a few detached atoms (``floaters'') and holes. At any time, a few of the surface atoms are out of the surface layer, leaving vacancies; these promoted particles wander diffusively, the holes also but less so; the floaters occasionally exchange with atoms in the surface layer. This result is the basis for an analytic, statistical model. The caloric curves, particularly the latent heats, together with the results from an analytical model, show that surface melting of clusters is a ``phase change'' different from the homogeneous melting of clusters.

Random bilayer phases of dilute surfactant solutions

Surfactant molecules in dilute solution may aggregate reversibly into extended structures. For suitably chosen molecules, the preferred packing involves a locally flat bilayer which tends to wander entropically at large distances. At low temperatures (and/or high concentrations) the system forms a stack of flat sheets with one-dimensional quasi-long range order (a smectic liquid crystal), but at high temperatures or low concentrations, the stack can melt into a random surface structure that resembles a multiply connected labyrinth or 'sponge' of bilayer in a sea of solvent. Recent theoretical and experimental progress in understanding the properties of the sponge is reviewed. The authors argue that the sponge phase may provide a good system for the study of various liquid-state critical phenomena.

Surface Melting and Surface Diffusion on Clusters

ABSTRACTSurface melting on clusters is investigated by a combination of analytic modeling and computer simulation. Homogeneous, argon-like clusters bound by Lennard-Jones forces and Cu-like clusters bound by ‘embedded atom’ potentials are the systems considered. Molecular dynamics (MD) calculations have been carried out for clusters with 40–147 atoms. Well below the bulk melting temperature, the surfaces become very soft, exhibiting well-defined diffusion constants even while the cores remain nearly rigid and solid-like. The simulations, particularly animations, of atomic motion reveal that the surface melting is associated not with amorphous, random surface structures in constant, irregular motion, but rather in large-amplitude, organized, collective motion of most of the surface atoms accompanied by a few “floaters” and holes. At any time, a few of the surface atoms move out of the surface layer, leaving vacancies; these promoted particles wander diffusively, the holes also but less so, and occasionally exchange with atoms in the surface layer. This result is the basis for an analytic, statistical model. The caloric curves, particularly the latent heats, show that surface melting of clusters is a “phase change” different from the bulk melting of clusters.