Scanning White Light Research Articles

Characterization of the hydroxyapatite layer formed by fine hydroxyapatite particle peening and its effect on the fatigue properties of commercially pure titanium under four-point bending

Abstract Fine particle peening (FPP) using hydroxyapatite (HAp) shot particles was introduced to form the HAp surface layer and improve the fatigue properties of commercially pure (CP) titanium. The surface microstructure of the FPP-treated specimens was characterized using a micro-Vickers hardness tester, optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), and non-contact scanning white light interferometry. FPP could create a HAp layer on the surface of CP titanium within a relatively short time (1 s) by shot particle transfer. In addition, FPP increased the surface hardness and generated compressive residual stress at the treated surface. Four-point bending fatigue tests were performed at a stress ratio of 0.1 in air at room temperature to examine the effect of FPP using HAp shot particles on the fatigue properties of CP titanium. It was found that the fatigue limit for the FPP-treated specimen was higher than that for the unpeened specimen. The fatigue fracture mechanism for the CP titanium treated with FPP was discussed from the viewpoint of fractography. The HAp layer remained on the surface without delamination after the fatigue tests.

Investigation of diffractive optical element femtosecond laser machining

This paper presents an explorative study on the machining of diffractive optical elements (DOEs) in transparent materials using a femtosecond laser source. A simple form of DOE, a binary phase grating with a period of 20.85μm (σ=0.5μm), a groove depth and width of 0.7μm (σ=0.2μm) and 8.8μm (σ=0.5μm) respectively, was successfully machined in BK7. The topographic characteristics were measured by white light interferometry and scanning electron microscopy (SEM). The processing was carried out on high precision stages with an ultrafast fibre laser (350fs) emitting a 343nm pulse focused onto the sample with a stationary microscope objective. A diffracted efficiency of 27%, obtained with a spectro goniometer, was corroborated by the theoretical results obtained by the Fourier modal method (FMM), taking into account the measured topographic values. These encouraging results demonstrate that high-speed femtosecond laser manufacturing of DOE in bulk glasses can be achieved, opening the way to rapid prototyping of multi-layered-DOEs.

Scratch resistance of the ventral skin surface in four snake species (Squamata, Serpentes)

Snakes are limbless tetrapods highly specialized for sliding locomotion on various substrates. Their skin is constantly exposed to high friction forces, which promotes abrasion. Snake skin has material and surface specializations, presumably optimized for friction and abrasion resistance. We found that different snake species living in different habitats have different abrasion patterns and hypothesized that this correlates with specific epidermal architecture and surface topography. To test this hypothesis artificial scratches, under controlled load conditions, were created on the ventral skin material (epidermis) of four snake species adapted to different habitats: Lampropeltis getula californiae (stony and sandy soil substrates), Epicrates cenchria cenchria (trees, soil and water), Morelia viridis (trees), and Gongylophis colubrinus (burrowing in sand). Abrasion appearance on the skin surface was examined using scanning electron microscopy and white light interferometry. The material failure was different between the species, which we attribute to differences in the epidermis' response to the same abrasive challenge. We also discuss abrasion resistance mechanisms and the correlation with the different ultrastructure and surface microstructure.

Interpreting the Rock Paintings of Abri Faravel: laser and white-light scanning at 2,133m in the southern French Alps

The Abri Faravel, discovered in 2010 at 2,133m asl in the Parc National des Ecrins, Freissinieres, Southern French Alps, is probably the most enigmatic high altitude site in the Alps. This rock shelter saw phases of human activity from the Mesolithic through to the medieval period; the artefactual assemblages comprise Mesolithic and Neolithic flint tools, Iron Age hand-thrown pottery, a Roman fibula and some medieval metalwork. However, the most interesting and unique feature on the site are the prehistoric rock paintings; the highest representations of animals (quadrupeds) in Europe. These paintings are presented in this article. The paintings themselves were the object of a white-light scan, whilst the rock-shelter and surrounding landscape was scanned using a Faro laser scanner. Both of these models are presented here, and their interpretation elucidated by an assessment of the different phases of activity at the shelter, combined with a synthesis of other evidence from the area and pertinent environmental evidence.

調和組織を有する工業用純チタンの低温窒化挙動

Commercially pure titanium with harmonic structure, which consists of a coarse-grained structure surrounded by a network structure of fine-grains, was produced by sintering mechanically milled powders to achieve high strength and high ductility. The effect of subsequent nitriding on the commercially pure titanium with harmonic structure was investigated. Nitriding was performed at relatively low temperatures of 773, 873 and 973 K (500, 600 and 700 °C). The surface microstructures of the nitrided specimens with harmonic structure were characterized using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and a non-contact scanning white light interferometry. The nitrided titanium specimen with harmonic structure had higher hardness than a nitrided-only titanium specimen because the fine-grained structure in the harmonic structure accelerated the formation of titanium nitrides during nitriding. Furthermore, fine grains created by mechanical milling were not coarsened during the nitriding process. These results indicate that low temperature nitriding is effective to increase the surface hardness of commercially pure titanium with harmonic structure while grain-coarsening is also suppressed.

Improved phase-shifting diffraction interferometer for microsphere topography measurements

In this study, an improved phase-shifting diffraction interferometer for measuring the surface topography of a microsphere is developed. A common diode-pumped solid state laser is used as the light source to facilitate apparatus realization, and a new polarized optical arrangement is designed to filter the bias light for phase-shifting control. A pinhole diffraction self-calibration method is proposed to eliminate systematic errors introduced by optical elements. The system has an adjustable signal contrast and is suitable for testing the surface with low reflectivity. Finally, a spherical ruby probe of a coordinate measuring machine is used as an example tested by the new phase-shifting diffraction interferometer system and the WYKO scanning white light interferometer for experimental comparison. The measured region presents consistent overall topography features, and the resulting peak-to-valley value of 84.43 nm and RMS value of 18.41 nm are achieved. The average roughness coincides with the manufacturer’s specification value.

Strain Measurement of Micrometre-Sized Structures under Tensile Loading by Using Scanning White-Light Interferometry

Strain Measurement of Micrometre-Sized Structures under Tensile Loading by Using Scanning White-Light Interferometry

백색광과 청색광 스캐너를 이용한 지대치 인상체 스캐닝의 반복재현성 비교

백색광과 청색광 스캐너를 이용한 지대치 인상체 스캐닝의 반복재현성 비교

Effect of shot peening using ultra-fine particles on fatigue properties of 5056 aluminum alloy under rotating bending

Shot peening using particles 10μm in diameter (ultra-fine particle peening: Ultra-FPP) was introduced to improve the fatigue properties of 5056 aluminum alloy. The surface microstructures of the Ultra-FPP treated specimens were characterized using a micro-Vickers hardness tester, scanning electron microscopy (SEM), X-ray diffraction (XRD), non-contact scanning white light interferometry, and electron backscatter diffraction (EBSD). The Ultra-FPP treated specimen had higher hardness than the conventional FPP treated specimen with a short nozzle distance due to the high velocity of the ultra-fine particles. Furthermore, the surface hardness of the Ultra-FPP treated specimen tended to increase as the peening time decreased. Fatigue tests were performed in air at room temperature using a cantilever-type rotating bending fatigue testing machine. It was found that the fatigue life of the Ultra-FPP treated specimen tended to increase with decreasing peening time. Mainly, the Ultra-FPP improved the fatigue properties of 5056 aluminum alloy in the very high cycle regime of more than 107 cycles compared with the un-peened specimens. This is because the release of the compressive residual stress is small during fatigue tests at low stress amplitudes.

A novel surface recovery algorithm in white light interferometry

White-light interferometry (WLI) is an established method for surface measurement. In WLI, surface recovery algorithm from series of vertical scanning white light interferogram is pivotal technique and has been researched widely. However, the effectiveness of existing surface recovery algorithms is easy to be affected by some conditions like mechanical vibrations, low-reflection of the test surface and phase change caused by the reflection. In this paper, a new recovery algorithm is presented, in which correlation analysis of WLI envelop curves and a multi reference position based phase solution method are employed for robust and high precision surface recovery. Mathematical derivation of the algorithm is carried out, and simulation and experimental testing and comparison experiments are conducted, which show that the new algorithm is effective.

Impact of GEM foil hole geometry on GEM detector gain

Detailed 3D imaging of Gas Electron Multiplier (GEM) foil hole geometry was realized. Scanning White Light Interferometry was used to examine six topological parameters of GEM foil holes from both sides of the foil. To study the effect of the hole geometry on detector gain, the ANSYS and Garfield ++ software were employed to simulate the GEM detector gain on the basis of SWLI data. In particular, the effective gain in a GEM foil with equally shaped holes was studied. The real GEM foil holes exhibited a 4% lower effective gain and 6% more electrons produced near the exit electrode of the GEM foil than the design anticipated. Our results indicate that the GEM foil hole geometry affects the gain performance of GEM detectors.

Tribological performance of sub-100-nm femtosecond laser-induced periodic surface structures on titanium

Sub-100-nm laser-induced periodic surface structures (LIPSS) were processed on bulk titanium (Ti) surfaces by femtosecond laser pulse irradiation in air (30fs pulse duration, 790nm wavelength). The laser peak fluence, the spatial spot overlap, and the number of overscans were optimized in a sample-scanning geometry in order to obtain large surface areas (5mm×5mm) covered homogeneously by the LIPSS. The laser-processed regions were characterized by optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM). The friction coefficient of the nanostructured surfaces was tested during 1000 cycles under reciprocal sliding conditions (1Hz, 1.0N normal load) against a 10-mm diameter ball of hardened 100Cr6 steel, both in paraffin oil and in engine oil used as lubricants. Subsequently, the corresponding wear tracks were qualified by OM, SEM, and energy dispersive X-ray analyses (EDX). The results of the tribological tests are discussed and compared to that obtained for near wavelength-sized fs-LIPSS, processed under somewhat different irradiation conditions. Some constraints for a beneficial effect of LIPSS on the tribological performance are provided.

Estimation of measurement uncertainty caused by surface gradient for a white light interferometer

Although the scanning white light interferometer can provide measurement results with subnanometer resolution, the measurement accuracy is far from perfect. The surface roughness and surface gradient have significant influence on the measurement uncertainty since the corresponding height differences within a single CCD pixel cannot be resolved. This paper presents an uncertainty estimation method for estimating the measurement uncertainty due to the surface gradient of the workpiece. The method is developed based on the mathematical expression of an uncertainty estimation model which is derived and verified through a series of experiments. The results show that there is a notable similarity between the predicted uncertainty from the uncertainty estimation model and the experimental measurement uncertainty, which demonstrates the effectiveness of the method. With the establishment of the proposed uncertainty estimation method, the uncertainty associated with the measurement result can be determined conveniently.

A Comparison between 3D Scanning and CMM Dimensional Inspection of Small Size Gas Turbine

The paper presents a comparison between Coordinate Measuring Machine and 3D white light scanning technologies as applied to the dimensional inspection of turbo-machinery parts such as turbine blade. The results were compared with the CAD model and each other. The results indicate that, even both methods are enough accurate with a slightly better accuracy for CMM, the operational speed and the variety of scanable surfaces give significant advantages to the 3D scanning method when prototypes require dimensional inspection by an alternative rapid route especially when dealing with objects with thin walls or sharp edges.

Metrology of Al2O3 Barrier Film for Flexible CIGS Solar Cells

Flexible Cu (In, Ga) Se2 (CIGS) solar cells are very attractive renewable energy sources because of their high conversion efficiencies, their low cost potential and their many application possibilities. However, they are at present highly susceptible to long term environmental degradation as a result of water vapor ingress through the protective encapsulation layer to the absorber (CIGS) layer. The basic methodology to prevent the water vapor permeation is to combine an oxide layer (e.g. AlOx) coating with suitable polymer substrates. Nevertheless, micro and nano-scale defects can appear at any stage of the coating process thus affecting the module efficiency and lifespan. The main aim of this research paper is to use surface metrology techniques including: White Light Scanning Interferometry (WLSI), Atomic Force Microscopy (AFM) and Environmental Scanning Electron Microscopy (ESEM) to characterise the aluminum oxide (Al2O3) barrier film defects, which appear to be directly responsible for the water vapor permeability. This paper reports on the development of a characterisation method for defect detection based on “Wolf Pruning” method and then correlates this with measured water vapor transmission rates (WVTRs) using standard MOCON® test. The results presented in this paper provided a detailed knowledge of the nature of micro and nano-scale defects on the Al2O3 barrier films which are responsible for water vapor and oxygen ingress. This result can then be used to provide the basis for developing roll-to-roll in process metrology devices for quality control of flexible PV module manufacture.

Development of aspheric surface profilometry using curvature method

A curvature method is one promising possibility for the measurement of optical aspheric or freeform surface, which is the major part of an optical system, such as google glasses, and wearable devices. Increasing demand for highly accurate optical components requires accurate and efficient measurement techniques. In this paper, we have presented a method of aspheric surface reconstruction from curvature data by using white-light-interferometer as a curvature sensor. This sensor was found to be robust to mechanical position error and environmental noise via error diagnosis. The primary mirror of cassegrain type astronomical telescope was tested. The measurement results showed that white-light scanning interferomete was found to be suitable for measuring the aspheric surface profile as a curvature sensor.

Microstructures and thermal damage mechanisms of sintered polycrystalline diamond compact annealing under ambient air and vacuum conditions

The microstructures and thermal damage mechanisms of sintered polycrystalline diamond compact (PDC) were studied in ambient air and vacuum at the temperature up to 1000°C. The microstructures and compositions of the annealed PDC were characterized by white light interferometer, X-ray diffractometry (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The results showed that no visible change in the morphologies of surface of PCD layers (PDC surfaces) was observed at 200°C both in ambient air and vacuum. After annealing at 500°C, numbers of spalling pits appeared on the PDC surface, and the stress-induced spall mechanism was the dominant thermal damage mechanism in ambient air and vacuum. With the temperature up to 800°C, the annealed PDC surface in ambient air was seriously damaged with a mixed thermal damage mechanism such as graphitization, oxidation and stress-induced micro-cracks. Whereas, the thermal damage mechanism in vacuum was nearly the same as that at 500°C. At 900°C, only a dendritic phase of Co3O4 was contained on the annealed PDC surface due to extensive graphitization and oxidation in ambient air. When it comes to vacuum environment, many cracks were observed on the PDC surface and some fine diamond grains near the cracks spalled, which demonstrated that the thermal damage mechanisms consisted of stress-induced crack and spall mechanisms caused by the different thermal expansion coefficients between the diamond and Co phase. Compared with that at 900°C, the degree of thermal damage reduced at 1000°C in vacuum because of the diffusion of unevenly distributed Co.

Smoothing of GaN Substrate by Ultraviolet Assisted Polishing in KOH Solution

In this study, we investigated the possibility of smoothing a GaN substrate utilizing ultraviolet (UV) assisted polishing method in potassium hydroxide (KOH) solution. In this polishing method, GaN substrate was excited by an UV radiation, and then an oxide layer on the GaN substrate was formed by photochemical reaction. Simultaneously, generated oxide layer was removed by synthetic quartz tool and chemically etched by KOH solution. Finally, smoothed GaN surface could be realized. The surface quality and removal depth were measured and evaluated using a scanning white light interferometer and Normalski type differential interference microscopy. Obtained results show that the surface morphology and the removal rate are strongly dependent on the existence of the UV irradiation. Moreover, the processed surface has revealed that many scratches on the preprocessed GaN surface could be completely removed. The microroughness of the processed GaN surface profile was improved to be 0.18 nm (Rms), 1.06 nm (Rz).

Three-dimensional evaluation of the repeatability of scanned conventional impressions of prepared teeth generated with white- and blue-light scanners

Statement of problemDigital scanning is increasingly used in prosthodontics. Three-dimensional (3D) evaluations that compare the repeatability of the blue-light scanner with that of the white-light scanner are required. PurposeThe purpose of this in vitro study was to evaluate the repeatability of conventional impressions of abutment teeth digitized with white- and blue-light scanners and compare the findings for different types of abutment teeth. Material and methodsImpressions of the canine, premolar, and molar abutment teeth were made and repeatedly scanned with each scanner type to obtain 5 sets of 3D data for each tooth. Point clouds were compared, and error sizes per tooth and scanner type were measured (n=10). One-way ANOVA with Tukey honest significant differences multiple comparison and independent t tests were performed to evaluate repeatability (α=.05). ResultsRepeatability (mean ±SD) of the white- and blue-light scanners for canine, premolar, and molar teeth was statistically significant (means: P=.001, P<.001, P<.001; ±SD: P<.001, P<.001, P=.003). Means of discrepancies with the white-light scanner (P<.001) were 5.8 μm for the canine, 5.9 μm for the premolar, and 8.6 μm for the molar teeth and 4.4 μm, 2.9 μm, and 3.2 μm, respectively, with the blue-light scanner (P<.001). Corresponding SDs of discrepancies with the white-light scanner (P<.001) were 15.9 μm for the canine, 23.2 μm for the premolar, and 14.6 μm for the molar teeth and 9.8 μm, 10.6 μm, and 11.2 μm, respectively, with the blue-light scanner (P=.73). ConclusionsOn evaluation of the digitized abutment tooth impressions, the blue-light scanner exhibited greater repeatability than the white-light scanner.

High-resolution LA-ICP-MS trace element mapping of igneous minerals: In search of magma histories

We report experiments on optimisation of LA-ICP-MS mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals. The experimental design was refined with maps on clinopyroxene and amphibole macrocrysts (mainly antecrysts) from a porphyritic lamprophyre in NE Spain, as well as on a high precision metal wire grid. In terms of spatial resolution, we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0.4 and 0.7μm of material, depending on ablation parameters. Maps were produced with square laser beam spots of 12 and 24μm. It was found that complexities can be resolved in the sample even though they are smaller than the beam diameter (e.g., 7–10μm discontinuities using 12μm laser beam). Resolution in x and y was found to be identical, probably reflecting the fast washout of the two-volume ablation cell and the short total dwell time of the analyte menu selected. Due to the excellent stage reproducibility and the limited ablation depth, it is feasible to re-ablate the identical map area many times employing different instrument parameters or analyte menus.On the magmatic crystals, LA-ICP-MS maps define very sharp compositional zoning in trace elements, highlighting complex crystallisation histories where ‘normal’ magmatic fractionation is not the only process. Events of mafic recharge are easily recognised as zones enriched in compatible metals such as Cr, Ni or Sc. Further, trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data. These include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones. Therefore, LA-ICP-MS mapping opens a new window of opportunity for analysis of magmatic histories. The wide combination of instrumental parameters, such as laser beam size, scan speed and repetition rate, make it possible to carry out experiments at different levels of detail. We recommend a two-step approach to mapping. The initial step involves rapid maps to gain an overview of potential complexities in the sample; this enhances representativeness of the analysed materials, as a large number of crystals and trace elements can be tested in little time. Subsequently, detailed maps can be carried out on areas of interest. An additional functionality is to create 1D-profiles from 2D-maps. The potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond.