Curvature Of Peaks Research Articles

Optimizing the Radius of Curvature of Black Silicon Peaks for Solar Cell Using Matlab Simulations

As part of our research on efficiency improvement of PERC (Passivated Emitter Rear Solar Cell), achieving very low reflectivity values of solar cell surface is a must. One of the most advance technologies to do so is the use of advanced texturing for the front surface of the cells. This texture, also known as Black Silicon, consists of peaks and valleys of nano metric dimensions and capable of dramatically reducing the reflectance of the front surface. A reflectance around 5% was reached ,using simulation, when using a Black-Silicon texturing with height of 50nm with peak rounding of 5nm. Even though this texturing may affect other parameters such as series resistance or surface recombination, as a starting point, simulation was used to find the optimum peak rounding, where the radius of curvature of the peak is maximum, while keeping reflectance as low as possible.

Evolution of the road bitumen/aggregate interface under traffic-induced polishing

Road skid resistance decreases under traffic and climate actions. For a surface made of bituminous concrete, the skid resistance evolution involves a removal of the bitumen layer and a polishing of the aggregates. Previous researches have been focused on polishing mechanisms and less is known about bitumen removal phase. This paper presents a laboratory study to better understand the behavior of the stone mastic asphalt under simulated actions of traffic. Due to its formulation, this bituminous concrete contains more bitumen than other materials used for road surfacing. Polishing tests are performed on circular cores using tWehner/Schulze machine, which simulates the traffic-induced polishing by means of rolling rubber cones and measures the tire friction by means of sliding rubber pads. Tests are stopped at predefined numbers of passes for friction measurements, 3D cartographies of surface texture and scanning electron microscopic observations of the cores' surface. Statistical tests are performed to identify relevant texture parameters to explain friction evolution. During bitumen removal phase (i.e. before 20,000 passes of polishing), Ssc (average curvature of peaks) and Sdq (average quadratic slope of asperities) are correlated with friction values. After 50,000 passes, volume parameter Vvc is more adapted due to the abrasion of asphalt mix surface. Then, scanning electron microscopic observations show that a layer composed by bitumen and particles (small aggregates and sand) is a third-body surrounding aggregates, which evolves in thickness and size of aggregates during polishing. The system composed of the aggregates, the bitumen–particles layer and the polishing cones can be assimilated to a tribosystem with a tribological circuit at the interface. The bitumen–particles layer acts as an internal flow, before leaving the contact area. The movement of the layer under the shear stress induced by the polishing cones explains the ejection of big aggregates and the heterogeneity of the layer around aggregates.

Assessment of Surface Roughness Using Curvature Parameters of Peaks and Valleys of the Profile

A methodology has been developed to assess the roughness of a surface from the parameters of the curvature of peaks and valleys of the profile based on computer spectral analysis. The dependence of these parameters on the type and modes of processing, as well as on the material, is established.

Novel Directional Blanket Covering Method for Surface Curvature Analysis at Different Scales and Directions

The curvature of surface topography is quantified in this study using a newly developed directional blanket covering curvature (DBCC) method. The novel method addresses a long-standing problem of a measurement of a local surface curvature at individual scales and directions. The curvature data are obtained using the first and second derivations of the quadratic polynomial fitted to the local surface profile extracted from the surface height image data at individual scale and direction. The range of scales is set between an instrument spatial resolution and 1/10 of the image shortest size. Using the surface curvature data, three parameters, i.e. curvature, peak and valley dimensions, are calculated as the slopes of lines fitted to data point subsets of log–log plots of surface areas (differences between dilated and eroded surface curvature matrices) against scales of calculation. The dimensions quantify directional changes in the overall curvature and the curvature of peaks and valleys at individual scales. The scale corresponds to the centre of the subset. A flat surface criterion based on the surface areas was also proposed. Using the criterion, a flat surface was identified in computer images of dome, corrugated plate and fractal surface. The DBCC method was applied to computer-generated fractal surfaces with increasing curvature complexity, sine waves with decreasing curvature at single scale and microscope images of isotropic (sandblasted) and anisotropic (ground) surfaces of titanium plates. Results showed that the method is accurate in the measurement of surface curvature and the detection of minute changes occurring in the curvature of real surfaces over a wide range of scales.

Improvement of Tribological Properties of Metal Matrix Composites by Means of Slide Burnishing

Burnishing of metal surfaces can affect positively tribological and mechanical properties such as fatigue strength, wear resistance, contact stiffness and bearing capacity. Burnishing affects the entire surface topography, including surface roughness, radii of curvature of peaks and valleys, slope angles and more. We have studied A1Mg1SiCu (6xxx series) aluminum matrix composites with a reinforcing phase of Al2O3 which exhibits good workability but poor machinability. The second series studied was based on an AlSi alloy (A-390) reinforced with SiC – this one characterized by poor workability but good machinability. Materials have been prepared by mixing metal powders with the reinforcement, cold pressing, sintering, hot extrusion and heat treatment. We have determined surface roughness with a Hommel tester; the arithmetical mean for A1Mg1SiCu (A6061 + Al2O3) was ~1 µm before burnishing and ~0.15 mm after burnishing. We have also determined the bearing capacity at 50 % with the same tester: before burnishing 2.30 µm and 0.47 µm afterwards for A6061 + Al2O3; before 2.30 µm, afterwards 0.37 µm for A390 + SiC. Vickers microhardness at the surface with respect to the core increases 30 % for the Al2O3 containing composite and 50 % for the SiC containing composite.DOI: http://dx.doi.org/10.5755/j01.ms.19.4.2404

Tribological properties of asperity arrays coated with self-assembled monolayers

The effects of a self-assembled monolayer (SAM) coating on the friction and pull-off forces were determined by using two-dimensional asperity arrays on silicon wafers. The arrays were coated with SAM composed of one of five different alkylchlorsilanes. First, two-dimensional asperity arrays were created by using a focussed ion beam (FIB) system to mill patterns on silicon plates. Each silicon plate had different patterns of equally spaced asperities. Each pattern (5 × 5 μm2) had a different radius of curvature of the asperity peaks, ranging from about 200 to 2500 nm. Then, each silicon plate was immersed in a solution of a different alkylchlorsilane in hexane (either hexyltrichlorosilane, octyltrichlorosilane, dodecyltrichlorosilane, tetradecyltrichlorosilane, or octadecyltrichlorosilane), thus coating the asperity arrays with SAM. The friction and pull-off forces on the SAM-coated arrays were measured by using an atomic force microscope (AFM) that had a square flat probe. The pull-off force for SAM-coated silicon was roughly proportional to the radius of curvature of the asperity peaks. The magnitude of the pull-off force corresponded approximately to the capillary force calculated by using the contact angle of water on the surface of SAM. The friction coefficient correlated with the inverse of the alkyl-chain length of the SAM.

Constraining the shape of the CMB: A peak-by-peak analysis

The recent measurements of the power spectrum of cosmic microwave background anisotropies are consistent with the simplest inflationary scenario and big bang nucleosynthesis constraints. However, these results rely on the assumption of a class of models based on primordial adiabatic perturbations, cold dark matter and a cosmological constant. In this paper we investigate the need for deviations from the $\ensuremath{\Lambda}$-CDM scenario by first characterizing the spectrum using a phenomenological function in a $15$ dimensional parameter space. Using a Monte Carlo Markov chain approach to Bayesian inference and a low curvature model template we then check for the presence of new physics and/or systematics in the CMB data. We find an almost perfect consistency between the phenomenological fits and the standard $\ensuremath{\Lambda}$-CDM models. The curvature of the secondary peaks is weakly constrained by the present data, but they are well located. The improved spectral resolution expected from future satellite experiments is warranted for a definitive test of the scenario.

Surface-topography assessment: precursor to the prediction of pressed-contact behaviour

The deformation mechanisms ensuing when a contact between two nominally-flat surfaces is subjected to mechanical and thermal stresses have been examined and the surface properties essential for the prediction of the contact's behaviour identified. These parameters include: the surface micro-hardness (in order to estimate the total true area of contact); the root-mean-square roughness as well as the mean absolute asperity-slope (so as to be able to predict the number and mean size of micro-contacts); the mean radius of curvature of the asperity peaks (which will help to indicate whether the surface deformations will be predominantly plastic or elastic); and surface wavelength parameters, such as autocorrelation and power spectral density functions (which are needed to estimate how micro-contact populations cluster at contacts formed between wavy surfaces). Various methods for surface-topography assessment and appropriate data manipulation in order to deduce values for meaningful parameters are described.

Investigation of the wear mechanism of carbon-fiberreinforced acetal

The friction and wear characteristics of acetal reinforced with 25 wt.% of randomly dispersed carbon fibers were investigated and compared with those of the base resin. The addition of carbon fibers to the polymer decreased the coefficient of friction and wear rate for the composite material sliding against a hardened and ground steel disk for extended periods of time. A number of surface topography parameters pertinent to the wear process, i.e. arithmetic average roughness, autocorrelation function, asperity density, tip radius of curvature, distribution of the radii of curvature and heights of asperity peaks, and ordinale heights, were calculated and evaluated for the sliding surface of the disk. The worn surfaces of filled and unfilled polymer pins were examined by scanning electron microscopy to investigate the probable wear mechanism for these materials. It was found that the wear of reinforced polymers proceeds by the pulling-out of the broken and worn fibers.

Rigidity of polymer sealing rings for locks of ball cocks

The contact of the sealing ring with the metallic ball cock should be elastic and the material of the ring should function within the viscoelastic zone ensuring, by virtue of its elastic properties, dependable sealing of the gaps when the cock is turned. Uses standard elements of ball cock seal in the investigation of the relationship of the polymer ring displacement with the acting axial load. In the case of elastic contact, the rigidity depends not only on the physicomechanical properties of the materials, shape, and size of the sealing rings, but also on the contact rigidity which depends on the roughness of the working surfaces, waviness, radii of curvature of the projection peaks, and the number of contact points. The relationship between the rigidity of the sealing rings and the specific pressure, which was derived by analyzing the experimental data, makes it possible to calculate the load on polymer sealing rings of the locks of ball cocks and to ascertain their elastic properties.

Effect of surface roughness on contact between solid surfaces

The analysis of the mechanism of contact between two solids was carried out considering the distribution of the radii of curvature of asperity peaks. The analytical results show that the mean radius of curvature of asperity peaks has a considerable effect on the nature of the deformation of contact asperities, i.e. whether the contact is plastic or elastic, and more effect on the real area of contact than the variation of the distribution of the radii of curvature. The radii of curvature at the asperity peaks and the real area of contact between two smooth surfaces were measured for comparison with the theoretical results. The results for isotropic surfaces produced by buffing and sandpaper agree with the theory; the real area of contact increases with decreasing surface roughness.