Rough Metal Surfaces Research Articles

Interaction of fast charges with a rough metal surface

Abstract We use the Green function formulation of a dielectric response formalism to study the dynamic polarization of a rough metal surface by a single charged particle and by a pair of charged particles that move parallel to the surface. While the surface roughness is treated nonperturbatively, the plasmon excitation of the metal electron gas is described locally. We find that the magnitudes of both the image potential and the stopping power of a single particle are increased by the increasing roughness and decreasing correlation length of the surface. On the other hand, both the long-range wake potential of a single charged particle and the interaction potential between two particles are weakly affected by the surface roughness. However, the strongest effects of the surface roughness are seen in the correlated stopping power of two charged particles, giving rise to oscillations in the dependence of the stopping ratio on their distance, both when the interparticle axis is perpendicular to their direction of motion and when the wake-related oscillations are damped by adiabatic suppression of plasmon excitations at low particle speeds.

Degradation of metallic surfaces under space conditions, with particular emphasis on Hydrogen recombination processes

The widespread use of metallic structures in space technology brings risk of degradation which occurs under space conditions. New types of materials dedicated for space applications, that have been developed in the last decade, are in majority not well tested for different space mission scenarios. Very little is known how material degradation may affect the stability and functionality of space vehicles and devices during long term space missions.Our aim is to predict how the solar wind and electromagnetic radiation degrade metallic structures. Therefore both experimental and theoretical studies of material degradation under space conditions have been performed. The studies are accomplished at German Aerospace Center (DLR) in Bremen (Germany) and University of Zielona Góra (Poland).The paper presents the results of the theoretical part of those studies. It is proposed that metal bubbles filled with Hydrogen molecular gas, resulting from recombination of the metal free electrons and the solar protons, are formed on the irradiated surfaces. A thermodynamic model of bubble formation has been developed. We study the creation process of H2-bubbles as function of, inter alia, the metal temperature, proton dose and energy. Our model has been verified by irradiation experiments completed at the DLR facility in Bremen.Consequences of the bubble formation are changes of the physical and thermo-optical properties of such degraded metals. We show that a high surface density of bubbles (up to 108cm-2) with a typical bubble diameter of ∼0.4μm will cause a significant increase of the metallic surface roughness. This may have serious consequences to any space mission.Changes in the thermo-optical properties of metallic foils are especially important for the solar sail propulsion technology because its efficiency depends on the effective momentum transfer from the solar photons onto the sail structure. This transfer is proportional to the reflectivity of a sail. Therefore, the propulsion abilities of sail material will be affected by the growing population of the molecular Hydrogen bubbles on metallic foil surfaces.

The Influence of Metal Surface Roughness on Bonding Strength of Metal and Composite Material

The fiber metal laminates have a wide range of applications today, owing to its high-performance and light weight. However, the interface properties between the fiber face sheet and metal substrate are weak and there are differences in their mechanical properties, causing structural damage or failure. Therefore, this article has come up with a new way to enhance the bonding strength. Through the mechanical methods to get different surfaces, choosing Ra as the evaluating parameter. By conducting the mechanics tests of each specimen, the results showed that with the rising of the Ra, the maximum load of the specimen was rising, too. But the trend wasn’t always the same. After the best Ra, the load declined and kept steady. So, in a small range of roughness, the leading role of bonding strength is the surface of the metal, otherwise, the leading role is the surface of fiber face sheet.

Tsallis threshold analysis of digital speckle patterns generated by rough surfaces

In this work we report on a study of entropic threshold of digital speckle patterns images produced by rough surfaces using Tsallis entropy. The speckle pattern images were obtained in the diffraction plane at the normal direction and they are the outcome of the incidence of a laser beam in the rough metallic surfaces. The speckle pattern images were segmented in order to verify the sensitivity of the optimal Tsallis entropic threshold value as a function of the surface roughness. We show that the surface roughness can be sensed and tuned by this method.

Experimental study on tool condition monitoring in boring of AISI 316 stainless steel

In this article, effect of cutting parameters, namely, cutting speed, feed rate and tool nose radius, on the tool life was examined experimentally. The experiments were performed on boring of AISI 316 steel with cemented carbide tool inserts. Design of experiments was prepared, and eight experiments were performed with two levels of the cutting parameters. The effects of cutting parameters were analyzed by evaluating the amplitude of workpiece vibration, surface roughness and volume of metal removed. The experimental data were taken for evaluation of tool life for a flank wear of 0.6 mm in all the eight trials. A laser Doppler vibrometer was used for online data acquisition of workpiece vibration, and a high-speed fast Fourier transform analyzer was used to process the acousto-optic emission signals for the workpiece vibration. Taguchi, analysis of variance and regression analysis methods were used to identify significant cutting parameters affecting the workpiece vibrations, surface roughness and volume of metal removed. All selected analysis methods used in this study predicted similar cutting parameter.

A pressure effect on the nonlinear reflection of elastic waves from the boundary of two solid media

Experimental studies of how static pressure affects the features of reflection of a monochromatic longitudinal elastic wave from the boundary of two rough metal surfaces with different interface layers were performed. The following layers were investigated: (a) two flat metal surfaces; (b) two metal surfaces with a layer of 10-μm-thick foil between them; (c) a one-dimensional layer of steel spheres between two metal surfaces; and (d) a one-dimensional layer of steel spheres with 10-μm-thick foil between the spheres and one of the surfaces. Apart from a wave at the fundamental frequency, a second-harmonic wave was observed in the reflected-wave spectrum. The reflected-wave amplitudes depended on the value of the static pressure applied to the layer. It is pointed out that the structural elastic nonlinearity at the solid-layer interface significantly exceeds the elastic nonlinearity related to the anharmonicity of molecular forces in the investigated materials.

Light depolarization in off-specular reflection on submicro rough metal surfaces with imperfectly random roughness.

Depolarization at a rough surface relates to its roughness and irregularity (e.g., sags and crests) besides the material property. However, there is still lack of general theory to clearly describe the relationship between depolarization ratios and surface conditions, and one important reason is that the mechanism of depolarization relates to geometric parameters such as microcosmic height/particle distributions of sub-micro to nm levels. To study the mechanism in more detail, a compact laser instrument is developed, and depolarization information of a linearly polarized incident light is used for analyzing the roughness, during which a He-Ne laser source (λ = 632.8 nm) is used. Three nickel specimens with RMS roughness (Rq) less than λ/4 are fabricated and tested. Six different areas in each specimen are characterized in detail using an AFM. Rq are in the range of 34.1-155.0 nm, and the heights are non-Gaussian distribution in the first specimen and near-Gaussian distribution in the others. Off-specular inspection is carried out exactly on these 18 characterized areas, and results show that the cross-polarization ratios match quite well with Rq values of the first sample that has Rq ≤ λ/10 (or Rt ≤ λ), while they match well with maximum height, Rt, values of the other two that have Rt > λ (the maximum derivation is 11%). In addition, since this instrument is simple, portable, stable, and low-cost, it has great potential for practical online roughness testing after a linear calibration.

Plasmonics-based SERS nanobiosensor for homogeneous nucleic acid detection

Developing a simple and efficient nucleic acid detection technology is essential for clinical diagnostics. Here, we describe a new conceptually simple and selective “turn on” plasmonics-based nanobiosensor, which integrates non-enzymatic DNA strand-displacement hybridization for specific nucleic acid target identification with surface-enhanced Raman scattering (SERS) detection. This SERS nanobiosensor is a target label-free, and rapid nanoparticle-based biosensing system using a homogeneous assay format that offers a simple and efficient tool for nucleic acid diagnostics. Our results showed that the nanobiosensor provided a limit of detection of ~0.1nM (200amol) in the current bioassay system, and exhibited high specificity for single nucleotide mismatch discrimination. From the Clinical EditorSurface-enhanced Raman scattering (SERS) is a sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces. The enhancement means that the technique may even detect single molecules. In this article, the authors describe a simple and efficient nucleic acid detection technology using SERS, with "OFF-to-ON" signal switch upon nucleic acid target identification and capture, which provides high sensitivity and specificity for single nucleotide mismatch discrimination. This new technology will be most welcomed in clinical diagnostics.

Secondary electron emission from rough metal surfaces: a multi-generation model

We develop a multi-generation model to examine secondary electron emission (SEE) from a rough metal surface. In this model, the traces of both primary electrons (PEs) and secondary electrons (SEs) are tracked by combining the electron scattering in the material and the multi-interaction with the rough surface. The effective secondary electron emission yield (SEY) is then obtained from the final states of the multi-generation SEs. Using this model, the SEE properties of the surfaces with rectangular and triangular grooves have been examined. We find that a rectangular groove can be used for effective SEE suppression. For a triangular groove, the criterion of SEY enhancement/suppression has been achieved, indicating that a small groove angle is required for effective SEE suppression, especially for a high PE energy. Furthermore, the SEE properties for some random rough surfaces are examined and some preliminary results are presented. Accordingly, our model and results could provide a powerful tool to give a comprehensive insight into the SEE of rough metal surfaces.

On process analysis and optimisation of wire electric discharge machining of Ti 6-2-4-2 using regression modelling and genetic algorithms

Titanium alloys are considered as 'metals of future' because of their exceptional properties such as high strength to weight ratio, high specific strength, corrosion resistance etc and there is a crucial need to develop cost effective methods for their machining. The present paper highlights the analysis of variation of objective functions namely, metal removal rate, surface roughness and dimensional deviation depending upon the process parameters of wire electric discharge machining in machining of Ti 6-2-4-2 alloy. Box-Behnken designs are used to plan and analyse the experiments. Mathematical models are developed for metal removal rate, surface roughness and dimensional deviation using regression technique and consequently opted for optimisation of objective functions. As the parametric effect on metal removal rate, surface roughness and dimensional deviation is opposite, the problem is considered a multi objective optimisation problem. Pareto optimal solutions satisfying the conflicting objective functions are obtained using non-dominated sorting algorithm -II. The solutions obtained so can be utilised as machining recommendations to set levels of process parameters to satisfy the set of aforesaid process yield criteria.

Development of hybrid assembled composites with sensory function

The assembly of piezoelements with sheet metals enables direct functional integration into formed sheet parts. Joining a thermoplastic polymer highly enriched with piezoceramic powder with thin metal sheets opens up new application areas. The re-meltable matrix of the composite is multi formable with a high degree of freedom. The properties, mainly the bonding strength, were investigated in processing separate samples. The analysis of the signal quality showed a good correlation between flat and formed hybrid assembled composites (HAC). However, the properties of the HAC and the signal amplitudes depend on compound formulation and surface roughness of the sheet metal.

Multi-objective Optimization of Electro-chemical Machining by Non-dominated Sorting Genetic Algorithm

Quality of machined surface strongly depend on the selection of optimal parameter settings and type of machining process. Electro-chemical machining (ECM) offers several unique feature, like higher machining rate, better surface finish, and it is suitable for machining a wide range of materials. In this regard, an attempt has been made to develop a mathematical model for responses i.e. metal removal rate (MRR) and surface roughness (SR) through regression analysis for electro-chemical machining on EN 19. And analysis of variance (ANOVA) test is perform to check the aptness of the developed mathematical models. The performance for ECM process is optimized through Non-dominated Sorting Genetic Algorithm-II (NSGA-II) for maximizing the metal removal rate and minimizing the surface roughness. Through this non-dominated optimum parameter settings has been obtained and reported.

Optimization of the EDM Parameters on Machining Ti-6Al-4V Alloy with Multiple Quality Characteristics

Conventional machining methods are unable to meet the challenges postured by the demand for economic machining of ultra-hard and high strength materials. Electro discharge machining (EDM) is a promising technique with great potential for application to machining hard materials over conventional techniques. In recent years, researchers have explored a number of ways to improve the EDM process performance by studying the different factors that affect the quality characteristics. The theoretical and experimental studies showed that process performance can be improved significantly by proper selection of EDM parameters, material parameters and operating parameters. In this study, an attempt has been made for simultaneous optimization of the process performances like, metal removal rate, surface roughness and overcut based on Grey Taguchi methodology for machining of Ti-6A-4V Titanium alloy by EDM.

Optimization of Machining Parameters for Drilling Al-SiC MMC Using ANOVA and Grey Relational Analysis

Machining of composite materials is an important and current topic in modern researches on manufacturingprocesses. This paper presents the detailed experimental investigation on drilling Aluminium Silicon Carbideparticulate Metal Matrix Composite (Al-SiC –MMC). Experiments were carried out on Radial Drilling Machine.A plan of experiments, based on the techniques of Taguchi, was performed. The objective of this research is tostudy the effect of cutting speed, feed, diameter of cut, machining time on metal removal rate, specific energy,surface roughness, volume fraction and flank wear. The optimum machining parameters were obtained by Greyrelational analysis. Finally, confirmation test was performed to make a comparison between the experimentalresults and developed modelKeywords: Composite materials; drilling processes; Rey relational analysis Optimization

Optical temperature sensor using speckle field

This paper presents a newly developed, laserbased, noncontact and remote temperature sensor suitable for high as well as low temperature measurements, which can be adapted to a commercial tensile testing machine equipped with an electrical furnace to monitor temperature. It can also be a miniaturized sensor for remote measurement of body temperature for biomedical diagnostics (e.g. as a sensor integrated into an endoscope to measure internal temperature during surgical procedure). The basic principle of the sensor is based on determining the changes occurring to a secondary speckle pattern generated by the scattered laser beam from a rough surface. In the present case a rough metal surface is used. As the surface of the metal plate changes due to cantilever action when exposed to heat, the resulting speckle pattern also changes. This change in the speckle pattern is computed by comparing it to a reference speckle pattern recorded at known temperature and can so be related to the temperature change. From the value of correlation coefficient we were able to measure the temperature. Furthermore, the paper presents the description of the signal processing algorithm and the optical arrangement. Based on the experimental data, it can be shown that this sensor can be successfully used for the remote extraction of temperature.

Optimization of Electric Discharge Machining Parameters of Al-7%Si-4%Mg with 20% of Red Mud Metal Matrix Composites

An investigation was carried out to find out the influence of process parameters on surface roughness (SR) and material removal rate (MRR) in electric discharge machine of Al-7%Si-4%Mg with 20% of red mud Metal Matrix Composites since electric discharge machining is a thermo-electric machining process, an electronic die sinking electric discharge machine was used to drill holes in the composite work piece, copper is used as tool material. Experiment was carried out to find surface roughness, material removal rate and tool wear rate by varying the peak current, flushing pressure of dielectric fluid and pulse on time. It was found that the surface roughness of composite metal increases with the increase peak current ,pulse on time and flushing pressure due larger and deeper craters on the drilled surface. It was also found that there was increase in metal removal rate with the increase in peak current and flushing pressure and slightly decreases with the increase in pulse on time due carbon deposits on the electrodes. Experimental analysis is carried using Taguchi’s Design of Experiment method with various parameters like peak current, flushing pressure of dielectric fluid and pulse on time to identify the key factors that influence the surface roughness, material removal rate and tool wear rate. It was found that the peak current was the most significant parameter that influences surface roughness, material removal rate and tool wear rate. The Taguchi experiments results confirm the actual results obtained from the numerical calculation.

SERS Study of Molecular Adsorbates on Catalytic Metal Surfaces with Various Atomic Arrangements

Surface enhanced Raman scattering (SERS) spectroscopy is normally conducted at a roughened surface of coinage metals. Although the nanometric surface roughness is needed for the signal enhancement, the use of the roughness often prevents deeper understanding of metal-molecule interactions at a specific surface site. Moreover, very limited surface enhancement is available on platinum group metals (PGMs) because of their localized d-electrons. In the field of electrocatalysis, it is essentially important to study molecular adsorbates on an atomically defined catalytic metal surface under electrochemical conditions. Therefore, these disadvantages limit application of SERS technique despite the potential of this technique for in-situ observation. Recently, there are several reports on SERS observations on single crystalline metal surfaces including non-SERS-active PGMs, in which the signal enhancement is induced by using sphere-plane type nanogap structures.1-6 In the present work, we observe SERS spectra of arylisocyanides adsorbed on catalytic metal substrates of various surface features at nanometric and atomic scale. Single crystal beads of gold, platinum, and palladium were obtained using the Clavilier method. The (111) facets of these beads were utilized for SERS observation. Pd-modified Au(111) was electrochemically prepared using the underpotential deposition (UPD). Pt-modified Au(111) was obtained by galvanic replacement of Cu-UPD monolayers on Au(111) with Pt2+ions. As a model Raman scatterer, 4-chlorophenylisocyanide (CPI) was utilized to form self-assembled monolayers (SAMs) on these metal surfaces. SERS measurements were conducted using a home-built Raman microscope with a 632.8-nm He-Ne laser light source after Au nanoparticles (Au-NPs) were physisorbed on top of the SAMs. Electrochemically roughened metal surfaces were also utilized for conventional SERS measurements. Figure 1 shows AFM images of electrochemically roughened polycrystalline Pt, mirror finished polycrystalline Pt, and single crystalline Pt(111) facet. One can see that the height of the surface features is around several 10 nm for the roughened Pt, a few nm for the smooth Pt, and monoatomic height for Pt(111). Among these surfaces, SERS effect is available only on the roughened Pt in the conventional method. Figure 2 shows conventional SERS spectrum measured on the roughened Pt and gap-mode SERS spectrum on smooth Pt. These spectra were very similar except for the signal intensity, indicating that the nanometric surface features do not affect molecular adsorption geometry. In addition, the chemical contribution of the adsorbed Au-NPs to the molecules is also negligible in the present case. On the other hand, the atomic surface feature significantly affected the molecular adsorption. As shown in Fig. 3, gap-mode SERS spectrum on Pt(111) was very different from that on the smooth polycrystalline Pt, suggesting three-hold hollow configuration. Moreover, when the Pt lattice was expanded by the monolayer formation on Au(111), the preferential configuration was changed to atop. We will also present SERS observations on other crystal orientations, the controbution of step-terrace structures, and electrochemical behavior of the adsorbates on these surfaces.

Formation of reliable electrical and thermal contacts between graphene and metal electrodes by laser annealing

A new approach for electrical and thermal improvement of contacts between carbon nanostructures (multi-wall carbon nanotubes – MWCNTs and multi-layer graphene – MLG) and metal electrodes by localized laser heating is presented. The nanostructures were deposited over electrodes using the dielectrophoresis (DEP) technique. A focused laser beam was used for direct heating the samples in ambient atmosphere. The Raman spectroscopy was used to determine the process temperature by observations of the graphitic G-line downshift. In the laser annealing experiments, the G-line position was found first to downshift linearly with laser power indicating gradual heating of the sample proportional to the absorbed power. However, with increasing power the shift was found to saturate at levels that depend on the metal and the contact area. This saturation was attributed to gradual increase of the contact area and improvement of the thermal contacts between the nanostructures and metal electrode that can occur during sample heating. The maximum sample temperature in the beginning of the annealing process was always higher for MLG samples, due to smaller area of contact established between rigid multi-layer graphene and initially rough metal surface. The final result is the increased heat losses to the electrodes and, subsequently, the reduction of the samples temperature.The main advantage of this method, when compared with traditional and rapid thermal annealing, is that the thermal treatment is localized in a small pre-determined region, allowing individually controlled annealing process.

Optimum deposition conditions of ultrasmooth silver nanolayers

Reduction of surface plasmon-polariton losses due to their scattering on metal surface roughness still remains a challenge in the fabrication of plasmonic devices for nanooptics. To achieve smooth silver films, we study the dependence of surface roughness on the evaporation temperature in a physical vapor deposition process. At the deposition temperature range 90 to 500 K, the mismatch of thermal expansion coefficients of Ag, Ge wetting layer, and sapphire substrate does not deteriorate the metal surface. To avoid ice crystal formation on substrates, the working temperature of the whole physical vapor deposition process should exceed that of the sublimation at the evaporation pressure range. At optimum room temperature, the root-mean-square (RMS) surface roughness was successfully reduced to 0.2 nm for a 10-nm Ag layer on sapphire substrate with a 1-nm germanium wetting interlayer. Silver layers of 10- and 30-nm thickness were examined using an atomic force microscope (AFM), X-ray reflectometry (XRR), and two-dimensional X-ray diffraction (XRD2).PACS63.22.Np Layered systems; 68. Surfaces and interfaces; thin films and nanosystems (structure and nonelectronic properties); 81.07.-b Nanoscale materials and structures: fabrication and characterization

A qualitative correlation between friction coefficient and steel surface wear in linear dry sliding contact to polymers with SGF

Abstract In this paper we tried to present a qualitative correlation, based on extensive experimental determinations between the value and the evolution of the friction coefficient, wear, and contact temperature, in the case of linear dry contact, for thermoplastic material reinforced with short glass fibers (SGF) and various steel surfaces. The aim was to highlight the evolution of the wear process depending on the evolution of the friction coefficient. As a result, it was possible to graphically illustrate the evolution of the friction coefficient and the change of the wear process, emphasizing the abrasive, adhesive and corrosive wear. The evolution of the plastic material transfer function of the contact temperature, namely of the power lost by friction (product between the contact pressure and sliding speed, p and v) was aimed and it was highlighted. It has been demonstrated that in the case of a 30% SGF content it can reach and even exceed contact temperatures very close to the flow limit of the plastic material. We tried, believing successfully, the graphic illustration of the evolution of the steel surface wear and of the contact temperature, depending on the friction coefficient. The influence of the normal load and sliding speed was evaluated in detail, but also the influence of the metallic surface roughness on the friction coefficient was discussed.