Surface Topographical Features Research Articles

Modeling of pad surface topography and material removal characteristics for computer-controlled optical surfacing process

Computer-controlled optical surfacing (CCOS) technology is an advantageous polishing process for producing optical surfaces with high convergence rates and high form accuracy, especially for fabricating hard and brittle materials. However, the optimum control of polishing parameters depends critically on the understanding of polishing mechanisms and modeling of material removal characteristics to achieve a deterministic process with high polishing efficiency. Removal analysis still requires further enhancement due to the multi-disciplinary, multi-scale complexity of the material removal mechanism involved in CCOS. Thus, this study presents a novel statistical asperity model and a material removal model to provide scientific and quantitative knowledge of the material removal mechanisms in CCOS. The model is developed on the basis of the research on statistical method, contact mechanics, iterative algorithm, abrasive wear mechanism, and cumulative removal process in CCOS. Practical experiments with different polishing parameters are performed to verify the theoretical model. Simulation results reasonably agree with measured data. Simulation experiments also show that the proposed model helps clarify the effect of pad surface topography on the micro-contact behavior and the material removal characteristics in CCOS and thus forms the theoretical basis for optimizing the polishing process.

SANAYİ KAYNAKLI KARBONMONOKSİT SALINIMLARININ AERMOD DAĞILIM MODELİ İLE İNCELENMESİ

This study is the first air quality modeling study for downtown Balikesir where intense air pollution levels are experienced during the winter seasons. The possible effects of atmospheric carbonmonoxide (CO) emissions from an industrial operation in downtown Balikesir were examined by taking into consideration the existing meteorological and surface topography characteristics and the maps showing the distributions of the ground level concentrations for CO releases were created by using the AERMOD.According to the results, the prevailing wind direction was determined as North (N) and North-East (NE) for Balikesir province, and the maximum daily 8-hour means of CO concentration emitted from the source was estimated as 34,01 μg.m-3 for the modeling study. For this reason, it has been determined that the modeled CO concentrations do not exceed the legal limits and there is no adverse effect on the downtown area. In addition, the fact that, there was a full-scaled hospital that was located nearby the source. The location of hospital complex made the air quality modeling study more significant. According to the modeling result, the maximum daily 8-hour means of CO concentration released from the source was estimated to be about 10 μg.m-3 for the hospital area. It has also been determined that the modeled value for hospital does not exceed the legal limits as states in the regulation. Within the scope of the study, the obtained results are also important due to contribution to raising public awareness and also provide suggestions to local authority in decision-making process.

Surface variations effect on electrical resistivity measurement: Aroughness based approach

Electrical Resistivity Imaging technique requires accurately taking surface geometry into account during the inversion process to avoid artefacts. Some terrains (for example volcanology) or materials (at low scale) present important high frequency topography variations that common inversion software cannot take into account. Recent Digital Elevation Model (DEM) tools offer a high resolution that permit to image some characteristics of these rough surfaces. The aim of this paper is to examine the effect on the electrical measurement of different surface topography features at different DEM resolutions. For this purpose, we evaluate the effects on a micro and macro scale. We define mathematical criteria (based on geometrical roughness parameters) to analyse and generate surfaces and we simulate electrical measurements with a Finite Element Analysis code. An initial numerical study shows that roughness parameters play a key role in resistivity measurement. A second study performed on 30 limestone samples shows that a DEM resolution trade-off can be found based on geometrical roughness parameters. This study gives a rule of thumb to determine a resolution threshold for real survey data.

Contributions of lunate cells and wax crystals to the surface anisotropy of Nepenthes slippery zone.

Nepenthes slippery zone presents surface anisotropy depending on its specialized structures. Herein, via macro–micro–nano scaled experiments, we analysed the contributions of lunate cells and wax crystals to this anisotropy. Macroscopic climbing of insects showed large displacements (triple body length within 3 s) and high velocities (6.16–20.47 mm s−1) in the inverted-fixed (towards digestive zone) slippery zone, but failed to climb forward in the normal-fixed (towards peristome) one. Friction force of insect claws sliding across inverted-fixed lunate cells was about 2.4 times of that sliding across the normal-fixed ones, whereas showed unobvious differences (1.06–1.11 times) between the inverted- and normal-fixed wax crystals. Innovative results from atomic force microscope scanning and microstructure examination demonstrated the upper layer of wax crystals causes the cantilever tip to generate rather small differences in friction data (1.92–2.72%), and the beneath layer provides slightly higher differences (4.96–7.91%). The study confirms the anisotropic configuration of lunate cells produces most of the anisotropy, whereas both surface topography and structural features of the wax crystals generate a slight contribution. These results are helpful for understanding the surface anisotropy of Nepenthes slippery zone, and guide the design of bioinspired surface with anisotropic properties.

3D Printing: Rational Design of Ultrasensitive Pressure Sensors by Tailoring Microscopic Features (Adv. Mater. Interfaces 18/2018)

Ultrasensitive resistive pressure sensors are developed by using an additive manufacturing technique (3D printing) to create contacting surfaces with different microstructure features. These new sensors' performance is highly tunable by adjusting the surface topographic features. More details can be found in article number 1800403 by Shuhua Peng, Chun H. Wang, and co-workers.

A Non-Contact Measuring System for In-Situ Surface Characterization Based on Laser Confocal Microscopy.

The characterization of surface topographic features on a component is typically quantified using two-dimensional roughness descriptors which are captured by off-line desktop instruments. Ideally any measurement system should be integrated into the manufacturing process to provide in-situ measurement and real-time feedback. A non-contact in-situ surface topography measuring system is proposed in this paper. The proposed system utilizes a laser confocal sensor in both lateral and vertical scanning modes to measure the height of the target features. The roughness parameters are calculated in the developed data processing software according to ISO 4287. To reduce the inherent disadvantage of confocal microscopy, e.g., scattering noise at steep angles and background noise from specular reflection from the optical elements, the developed system has been calibrated and a linear correction factor has been applied in this study. A particular challenge identified for this work is the in-situ measurement of features generated by a robotized surface finishing system. The proposed system was integrated onto a robotic arm with the measuring distance and angle adjusted during measurement based on a CAD model of the component in question. Experimental data confirms the capability of this system to measure the surface roughness within the Ra range of 0.2–7 μm (bandwidth λc/λs of 300), with a relative accuracy of 5%.

Application of PeakForce tapping mode of atomic force microscope to characterize nanomechanical properties of organic matter of the Bakken Shale

Organic-rich shale, which is a heterogeneous material, has been studied extensively from various perspectives. Among all the components that constitute shale, organic matter is less known in regards to its mechanical properties. Since organic matter is relatively the softer part compared to inorganic minerals, high concentrations of it can have a significant impact on bulk mechanical properties of the rock, which can affect field operations such as hydraulic fracturing. In this study, four shale samples from the Bakken Formation in Williston Basin, North Dakota, were examined by a combination of experimental methods including X-ray diffraction (XRD), Rock-Eval pyrolysis, optical and scanning electron microscopy (SEM) along with atomic force microscope (AFM). PeakForce Quantitative Nano-mechanical Mapping mode in AFM was used particularly, to map the modulus of organic matter in nano-scale. XRD analysis showed that quartz and clays are the main constituent minerals in the shale samples. Geochemical results showed that all samples are extremely organic-rich, and the organic matter is mostly type II, varying from thermally immature to oil generation window. Elastic properties test results demonstrated that surface topographic features including pores, microfractures and grain boundaries would have a negative impact on AFM data, and a data filtering procedure was conducted on AFM data to get rid of wrong values. The elastic modulus of identified organic matter (bitumen and micrinite) was measured in the range of 7–23 GPa with a significant heterogeneity in a single studied organic particle and dependent upon the type of organic particle.

Pattern-Dependent Mammalian Cell (Vero) Morphology on Tantalum/Silicon Oxide 3D Nanocomposites.

The primary goal of this work was to investigate the resulting morphology of a mammalian cell deposited on three-dimensional nanocomposites constructed of tantalum and silicon oxide. Vero cells were used as a model. The nanocomposite materials contained comb structures with equal-width trenches and lines. High-resolution scanning electron microscopy and fluorescence microscopy were used to image the alignment and elongation of cells. Cells were sensitive to the trench widths, and their observed behavior could be separated into three different regimes corresponding to different spreading mechanism. Cells on fine structures (trench widths of 0.21 to 0.5 μm) formed bridges across trench openings. On larger trenches (from 1 to 10 μm), cells formed a conformal layer matching the surface topographical features. When the trenches were larger than 10 μm, the majority of cells spread like those on blanket tantalum films; however, a significant proportion adhered to the trench sidewalls or bottom corner junctions. Pseudopodia extending from the bulk of the cell were readily observed in this work and a minimum effective diameter of ~50 nm was determined for stable adhesion to a tantalum surface. This sized structure is consistent with the ability of pseudopodia to accommodate ~4–6 integrin molecules.

Fractal characteristics of 3D surface topography in laser machining

The measurement of the profile data from carbon steel surface machined by laser machining with the white light interferometer is discussed in this paper, the research of the surface topography characteristics of laser machining is based on fractal geometry analysis, and the Box-counting method is used for 3D fractal dimension calculation of the laser machining surface. The results indicate that a universal fractal dimension beyond scale range is unattainable, and only when the scale r is less than the maximum height of profile Ry, the performance of the fractal characteristics on the laser machining surface is present. When the same laser machining surface is characterized, the Ra of same scale fluctuates greatly along the thickness direction, and the fractal dimension Db can be used to stably characterize the complexity of the whole surface topography. The 3D surface fractal dimension Db is sensitive to the machining surface defects, once the Db becomes smaller, deep cracks and pronounced defects are exhibited in machining surface. In this paper, the characteristic analysis of the laser machining 3D surface is obtained by characterizing the micro-structured surface complexity using the fractal dimension, which is aided by the roughness to evaluate the profile height characteristics of laser machining surface. This study indicates that the Box-counting fractal analysis is an effective method to evaluate laser machining surface comprehensively.

Through hole making by electro-discharge machining on Inconel 625 super alloy using hollow copper tool electrode

A case experimental research on through hole making process on Inconel 625 super alloy by using hollow (tubular) copper tool electrode in electro-discharge machining has been delineated herein. Based on three controllable process variables namely peak discharge current, pulse-on duration, and gap voltage, experiments on through hole making have been carried out following the electro-discharge machining route (die-sinking electro-discharge machining without flushing). In addition to surface morphology, topographical features of the electro-discharge machined work surface have been examined for both internal cylindrical surface of the hole produced and also the external peripheral surface of the removed cylindrical part. The influence of the process parameters have been analyzed on various process performance features like material removal rate, surface roughness, surface crack density, white layer thickness, circularity, radial overcut, and hole taper. An optimal parameter setting has been identified for sound hole making and thereby to improve electro-discharge machining performance. Additionally, energy-dispersive X-ray spectroscopic analysis has been carried out to investigate the extent of carbon enrichment onto the electro-discharge machined work surface of Inconel 625 as affected by the pyrolysis of the dielectric fluid whilst executing electro-discharge machining operation. X-ray diffraction tests have been carried out to compare metallurgy of the electro-discharge machined work surface (various phases/precipitates present in bulk of the matrix material, extent of grain refinement, crystallite size, strain, and dislocation density) with respect to that of “as received” Inconel 625. Results, thus obtained, have also been compared to that of the micro-hardness test data.

Automated Orthorectification of VHR Satellite Images by SIFT-Based RPC Refinement

Raw remotely sensed images contain geometric distortions and cannot be used directly for map-based applications, accurate locational information extraction or geospatial data integration. A geometric correction process must be conducted to minimize the errors related to distortions and achieve the desired location accuracy before further analysis. A considerable number of images might be needed when working over large areas or in temporal domains in which manual geometric correction requires more labor and time. To overcome these problems, new algorithms have been developed to make the geometric correction process autonomous. The Scale Invariant Feature Transform (SIFT) algorithm is an image matching algorithm used in remote sensing applications that has received attention in recent years. In this study, the effects of the incidence angle, surface topography and land cover (LC) characteristics on SIFT-based automated orthorectification were investigated at three different study sites with different topographic conditions and LC characteristics using Pleiades very high resolution (VHR) images acquired at different incidence angles. The results showed that the location accuracy of the orthorectified images increased with lower incidence angle images. More importantly, the topographic characteristics had no observable impacts on the location accuracy of SIFT-based automated orthorectification, and the results showed that Ground Control Points (GCPs) are mainly concentrated in the “Forest” and “Semi Natural Area” LC classes. A multi-thread code was designed to reduce the automated processing time, and the results showed that the process performed 7 to 16 times faster using an automated approach. Analyses performed on various spectral modes of multispectral data showed that the arithmetic data derived from pan-sharpened multispectral images can be used in automated SIFT-based RPC orthorectification.

Characterisation of wear areas on UHMWPE total knee replacement prostheses through study of their areal surface topographical parameters

Total knee replacement is one of the most common elective surgeries in the world, and presents a number of challenges related to the wear of ultra-high molecular weight polyethylene (UHMWPE). This paper presents an analysis of the surface topographical properties of the worn and unworn condylar surfaces on a small cohort of both wear simulated and retrieved prostheses of varying designs. A number of measurement points were taken on each prostheses in a mixture of worn and unworn areas through the use of focus-variation microscopy (FVM), a non-contact method of surface measurement. Surface areal parameters were extracted from this data to analyse and search for patterns within the data. It was found that in general, worn implant surfaces appear to show smoother, less peak dominated surfaces than unworn area. It was also found that wear simulated and retrieved implants display similar characteristics of surface topography. In addition, variation was noted between different designs of TKR device, with posterior stabilised designs found to be peak dominated and cruciate retaining type implants being valley dominated.

Research on Surface Topography Characteristics of Laser Micro-hole Drilling

The surface of laser micro processing has great differences compared with the traditional machining surface. To research surface topography is of great significance for laser processing surface property. Combined with the laser mechanism, the surface characteristics of micro blind-hole drilled with different pulse energy and number were studied in the materials of spring steel 65Mn, stainless steel SUS301 and ceramic Al2O3. The results indicate that large pulse energy makes the hole much irregular and multi-pulse may cause the surface much rough. A large amount of molten material gathers around the hole for 65Mn and SUS301 while not for Al2O3 because of different processing mechanism. Therefore, process parameters and conditions should be explored for better surface topography of laser drilling.

How topographical surface parameters are correlated with CdTe monocrystal surface oxidation

Numerical analysis was applied to three-dimensional (3D) images for a quantitative description of evolution of surface topography of CdTe after oxidation. The results of fractal analysis show the correlation of fractal dimension and statistical characteristics of surface topography. Surface texture analysis provides dependence of topography characteristics on oxidation process. The comprehensive description of the surface micromorphology of the CdTe is an important challenge and it is essential for understanding their properties and their potential technological exploitation. The changes in surface topography were evaluated by atomic force microscopy (AFM). This characterization was carried out for the quantitative analysis of specific microstructural characteristics of samples.

Facile Dry Surface Cleaning of Graphene by UV Treatment

Graphene has been considered an ideal material for application in transparent lightweight wearable electronics due to its extraordinary mechanical, optical, and electrical properties originating from its ordered hexagonal carbon atomic lattice in a layer. Precise surface control is critical in maximizing its performance in electronic applications. Graphene grown by chemical vapor deposition is widely used but it produces polymeric residue following wet/chemical transfer process, which strongly affects its intrinsic electrical properties and limits the doping efficiency by adsorption. Here, we introduce a facile dry-cleaning method based on UV irradiation to eliminate the organic residues even after device fabrication. Through surface topography, Raman analysis, and electrical transport measurement characteristics, we confirm that the optimized UV treatment can recover the clean graphene surface and improve graphene-FET performance more effectively than thermal treatment. We propose our UV irradiation method as a systematically controllable and damage-free post process for application in large-area devices.

Design of a spaceflight biofilm experiment

Biofilm growth has been observed in Soviet/Russian (Salyuts and Mir), American (Skylab), and International (ISS) Space Stations, sometimes jeopardizing key equipment like spacesuits, water recycling units, radiators, and navigation windows. Biofilm formation also increases the risk of human illnesses and therefore needs to be well understood to enable safe, long-duration, human space missions. Here, the design of a NASA-supported biofilm in space project is reported. This new project aims to characterize biofilm inside the International Space Station in a controlled fashion, assessing changes in mass, thickness, and morphology. The space-based experiment also aims at elucidating the biomechanical and transcriptomic mechanisms involved in the formation of a “column-and-canopy” biofilm architecture that has previously been observed in space. To search for potential solutions, different materials and surface topologies will be used as the substrata for microbial growth. The adhesion of bacteria to surfaces and therefore the initial biofilm formation is strongly governed by topographical surface features of about the bacterial scale. Thus, using Direct Laser-Interference Patterning, some material coupons will have surface patterns with periodicities equal, above or below the size of bacteria. Additionally, a novel lubricant-impregnated surface will be assessed for potential Earth and spaceflight anti-biofilm applications. This paper describes the current experiment design including microbial strains and substrata materials and nanotopographies being considered, constraints and limitations that arise from performing experiments in space, and the next steps needed to mature the design to be spaceflight-ready.

Pulsed laser remelting of A384 aluminum, part II: Modeling of surface homogenization and topographical effects

A simulation model is developed for pulsed laser remelting that captures the homogenization of surface chemical composition and height variations that occur due to silicon (Si) precipitates in a hypereutectic aluminum-silicon (Al-Si) casting alloy. The model simulates remelting pulse-by-pulse with two sequential and repeated steps: it first predicts surface homogenization by areal averaging within a laser spot and then generates and adds a surface feature, due to thermocapillary flow, whose size depends on the concentration of Si within the homogenized spot. Compositional data of remelted lines was collected with energy-dispersive x-ray spectroscopy and used to verify the homogenization step of the simulation model. It was found that Si precipitates get redistributed by the laser with the peak in Si concentration occurring in the direction opposite that of beam travel. Height data from remelted lines were measured using white light interferometry to verify the accuracy of the remelting model in simulating surface topographical modifications. It was found that variations of approximately ± 1 μm are induced in the Al-Si alloy during pulsed laser remelting due to the Si proeutectic precipitates. This is attributed to differences in laser absorption of Si and Al. Because the Si precipitates absorb more energy from the laser, they experience higher temperatures and temperature gradients, which cause larger thermocapillary flow. The results provide insights into approaches to model surface compositional homogenization that occurs during laser remelting and provides an understanding of surface microstructural and topographical features often seen in laser polished Al-Si casting alloys.

Flow through microchannels with topographically patterned wall:A spectral theory for arbitrary groove depths

Current technology allows us to build microfluidic channels, which are so thin that incidental and/or surface topographical features engineered for applications such as microfluidic mixing/separations can present significant constrictions and dilatations to the flow passage. Considering such situations, pressure-driven laminar incompressible flow through an infinitely wide channel, one of whose walls has sinusoidal grooves running along the flow direction, is investigated through an accurate semi-analytical and grid-free spectral approach, without placing any restrictions on the pattern amplitude. In the special limits of small pattern amplitude, thick and thin channels, the spectral model recovers asymptotic predictions earlier reported in the literature. The spectral model is also used to provide new closed-form estimates for permeability and effective slip at an order of asymptotic accuracy higher than those currently available from the literature. The effect of unequal degrees of intrinsic hydrodynamic slippage on the corrugated and plane walls is also studied asymptotically. The predictions from the spectral model, which are obtainable with very low computational expense, are also cross-validated against finite-element-method based simulations. In the thick channel limit, the predictions from the spectral model are quantitatively consistent with results from recent molecular dynamic (MD) simulations conducted by Guo et al. (2016). The newly proposed and existing closed-form asymptotic predictions are also assessed numerically against the spectral model. In the long-wave limit, the permeability of the channel increases on increasing the depth of grooves, while in the short wave limit, the permeability decreases. Certain predictions from the spectral model are beyond the resolution of currently available asymptotic theories; e.g. the existence of a finite pattern amplitude for medium-wave patterns, at which the permeability of the channel is minimized.

Nanostructured surface topographies have an effect on bactericidal activity

BackgroundDue to the increased emergence of antimicrobial resistance, alternatives to minimize the usage of antibiotics become attractive solutions. Biophysical manipulation of material surface topography to prevent bacterial adhesion is one promising approach. To this end, it is essential to understand the relationship between surface topographical features and bactericidal properties in order to develop antibacterial surfaces.ResultsIn this work a systematic study of topographical effects on bactericidal activity of nanostructured surfaces is presented. Nanostructured Ormostamp polymer surfaces are fabricated by nano-replication technology using nanoporous templates resulting in 80-nm diameter nanopillars. Six Ormostamp surfaces with nanopillar arrays of various nanopillar densities and heights are obtained by modifying the nanoporous template. The surface roughness ranges from 3.1 to 39.1 nm for the different pillar area parameters. A Gram-positive bacterium, Staphylococcus aureus, is used as the model bacterial strain. An average pillar density at ~ 40 pillars μm−2 with surface roughness of 39.1 nm possesses the highest bactericidal efficiency being close to 100% compared with 20% of the flat control samples. High density structures at ~ 70 pillars μm−2 and low density structures at < 20 pillars μm−2 with surface roughness smaller than 20 nm reduce the bactericidal efficiency to almost the level of the control samples.ConclusionThe results obtained here suggests that the topographical effects including pillar density and pillar height inhomogeneity may have significant impacts on adhering pattern and stretching degree of bacterial cell membrane. A biophysical model is prepared to interpret the morphological changes of bacteria on these nanostructures.

Controlling the Outgrowth and Functions of Neural Stem Cells: The Effect of Surface Topography.

Neural stem cells (NSCs) are self-renewing cells that generate the major cell types of the central nervous system, namely neurons, astrocytes and oligodendrocytes, during embryonic development and in the adult brain. NSCs reside in a complex niche where they are exposed to a plethora of signals, including both soluble and physical signals such as compressive and shear stresses, but also discontinuities and differences in morphology of the extracellular environment, termed as topographical features. Different approaches that incorporate artificial micro- and nano-scale surface topographical features have been developed aiming to recapitulate the in vivo NSC niche discontinuities and features, particularly for in vitro studies. The present review article aims at reviewing the existing body of literature on the use of artificial micro- and nano-topographical features to control NSCs orientation and differentiation into neuronal and/or neuroglial lineage. The different approaches on the study of the underlying mechanism of the topography-guided NSC responses are additionally revised and discussed.