Scanning White Light Interferometry Research Articles

Light-assisted drying for anhydrous preservation of biological samples: optical characterization of the trehalose preservation matrix.

Protein-based drugs have been developed to treat a variety of conditions and assays use immobilized capture proteins for disease detection. Freeze-drying is currently the standard for the preservation of proteins, but this method is expensive and requires lengthy processing times. Anhydrous preservation in a trehalose amorphous solid matrix offers a promising alternative to freeze-drying. Light assisted drying (LAD) is a processing method to create an amorphous trehalose matrix. Proteins suspended in a trehalose solution are dehydrated using near-infrared laser light. The laser radiation accelerates drying and as water is removed the trehalose forms a protective matrix. In this work, LAD samples are characterized to determine the crystallization kinetics of the trehalose after LAD processing and the distribution of amorphous trehalose in the samples. These characteristics influence the long-term stability of the samples. Polarized light imaging revealed that LAD processed samples are stable against crystallization during low-humidity storage at room temperature. Scanning white light interferometry and Raman spectroscopy indicated that trehalose was present across samples in an amorphous form. In addition, differential scanning microcalorimetry was used to measure the thermodynamic characteristics of the protein lysozyme after LAD processing. These results demonstrate that LAD does not change the properties of this protein.

Fiber optic white light interferometer for areal surface measurement

White light interferometers (WLI) are extremely powerful tools in the context of areal surface topography instrumentation. With lateral scanning mechanisms, larger objects with trans-scale structures are also measurable. However, the existing commercial WLIs are usually only applicable for off-line measurements in the laboratory. This paper presents a flexible WLI, in which the light source and the vertical scanning mechanism are separated from the interference probe using fiber-optic components. As a result, the interference probe is more compact, and portable for on-machine measurement. Meanwhile, a comprehensive algorithm that combines the improved gravity center method and phase-shifting technique is proposed for signal processing, which can balance computation time and noise robustness. The simulation results show the effectiveness by comparing with the traditional white light scanning interferometry methods. A 1000 nm step height standard was used as a test specimen to evaluate the proposed system and algorithm. The experimental data show that the measurement results are basically in good agreement with the calibrated value.

A Study of Scratch Speed Effects on Ductile–Brittle Transition in Silicon

A unique rotational double-taper scratching setup is used to study ductile brittle transitions in single crystal (100) p-type silicon using a conical diamond tool at room temperature and scratching speeds ranging between 0.1 m/s and 0.3 m/s. In such a setup, transition from brittle to ductile occurs twice in a single-tapered scratch, during tool entry and tool exit. A well-defined way to determine critical depth of cut via linear crack density per unit crack length is proposed. The scratches were studied using scanning electron microscopy (morphology) and white light interferometry (depth measurements). A comprehensive study of critical depth of cut, compiled from the literature together with data from this study, with scratching speeds from very low to high shows that critical depth of cut decreases from very low scratch speeds to medium scratch speeds and then increases again at very high scratch speeds. An inference from this study is that diamond turning should be conducted at higher cutting speeds than being undertaken today to make use of larger critical depths of cut.

Structuring of Bioceramics by Micro-Grinding for Dental Implant Applications.

Metallic implants were the only option for both medical and dental applications for decades. However, it has been reported that patients with metal implants can show allergic reactions. Consequently, technical ceramics have become an accessible material alternative due to their combination of biocompatibility and mechanical properties. Despite the recent developments in ductile mode machining, the micro-grinding of bioceramics can cause insufficient surface and subsurface integrity due to the inherent hardness and brittleness of these materials. This work aims to determine the influence on the surface and subsurface damage (SSD) of zirconia-based ceramics ground with diamond wheels of 10 mm diameter with a diamond grain size (dg) of 75 μm within eight grinding operations using a variation of the machining parameters, i.e., peripheral speed (vc), feed speed (vf), and depth of cut (ae). In this regard, dental thread structures were machined on fully sintered zirconia (ZrO2), alumina toughened zirconia (ATZ), and zirconia toughened alumina (ZTA) bioceramics. The ground workpieces were analysed through a scanning electron microscope (SEM), X-ray diffraction (XRD), and white light interferometry (WLI) to evaluate the microstructure, residual stresses, and surface roughness, respectively. Moreover, the grinding processes were monitored through forces measurement. Based on the machining parameters tested, the results showed that low peripheral speed (vc) and low depth of cut (ae) were the main conditions investigated to achieve the optimum surface integrity and the desired low grinding forces. Finally, the methodology proposed to investigate the surface integrity of the ground workpieces was helpful to understand the zirconia-based ceramics response under micro-grinding processes, as well as to set further machining parameters for dental implant threads.

Electrode Scratching Technique As a Robust Way to Decouple Erosion-Corrosion Components

The substantial number of parameters and their interdependence makes the modelling and prediction of erosion-corrosion rates a rather challenging task, yet owing to increasing computational capacity one that is potentially solvable. To accurately estimate the rate of material loss, universally accepted explanations of the mechanisms of combined erosion and corrosion must be developed. The absence of reliable data can undermine safety and predictability of industrial processes, such as oil and gas transportation. The aim of this work is to demonstrate the application of an electrode scratching technique coupled with microstructural characterisation for improved understanding of synergy in erosion-corrosion. In this work, a rotating disc electrode scratching setup, with well-defined and controlled flow conditions, was developed to study individual contributions to erosion-corrosion. Linear potentiodynamic and potentiostatic polarization techniques were used to reproducibly monitor the kinetics of dissolution and repassivation of API X65 steel electrodes upon scratching. Samples characterized using high-resolution scanning electron microscopy (SEM) and white-light interferometry (WLI), confirm the synergy; the losses due to erosion-corrosion are larger than that of the summation of the separate contributions of erosion and corrosion. Focused Ion Beam (FIB) milling was implemented for in-situ lift-out of lamellae from scratched samples for Transmission Electron Microscopy (TEM) characterisation. We confirm distinct microstructural changes take place in the vicinity of scratches: with nanoscale grain refinement and orientation changes observed (See Figure 1). These results, coupled with electrochemical data and micro-hardness measurements, suggest time-dependent surface-hardening processes affect material loss rates during mechanical-electrochemical coupled corrosion. Figure 1

Multiple method micromachining laser platform for fabricating anti-counterfeit elements with multiple-scaled features

Textured metallic parts with multiple-scaled micro-structures have significant advantages for anti-counterfeit applications. For this purpose, the development of an automatized micromachining laser-platform is introduced, which is capable of handling different laser based fabrication methods including direct laser writing (DLW) and direct laser interference patterning (DLIP), using only one laser source (Nd:YAG laser, 1064 nm wavelength, 500 ps pulse duration). Using DLW, line, cross-like and rectangular structures with length scales from 50 to 150 µm were produced, while DLIP was used to produce line-like patterns structures, with 3.7 and 25 µm spatial periods. In addition, laser induced periodic surface structures (LIPSS) were also combined and thus obtaining hierarchical patterns with three different length scales in one process. Finally, additional samples were automatically structured to produce examples of definable security features at the touch of a button. The surface topography of the treated samples is analyzed using scanning electron microscopy, optical microscopy and white light interferometry methods.

Film Thickness and Friction of ZDDP Tribofilms

Tribofilm formation by several zinc dialkyl- and diaryldithiophosphate (ZDDP) solutions in thin film rolling-sliding conditions has been investigated. A primary, a secondary alkyl and a mixed alkyl ZDDP show similar rates of film formation and generate films typically 150 nm thick. Another secondary ZDDP forms a tribofilm much faster and the film is partially lost after extended rubbing. An aryl ZDDP forms a tribofilm much more slowly. The films all have a pad-like structure, characterised by flat pad regions separated by deep valleys. Three different techniques have been used to analyse the thickness and morphology of the tribofilms: spacer layer imaging (SLIM), scanning white light interferometry (SWLI) of the gold-coated film and contact mode atomic force microscopy (AFM). The SLIM method measures considerably thicker films than the other two techniques, probably because of lack of full conformity of a glass disc loaded against the rough tribofilm. No evidence of a highly viscous layer on top of the solid tribofilm is seen. SWLI and contact mode AFM measure similar film thicknesses. The importance of coating the tribofilm with a reflective layer prior to using SWLI is confirmed. As noted in previous work, the formation of a ZDDP tribofilm is accompanied by a marked shift in the Stribeck friction curve towards higher entrainment speed. For a given ZDDP this shift is found to correlate with the measured tribofilm roughness, proving that it results from the influence of this roughness on fluid entrainment in the inlet.

基于扫描白光干涉法的LCOS芯片像素级相位分析

基于扫描白光干涉法的LCOS芯片像素级相位分析

3D Information Retrieving of Concealing Surface beneath Opaque Resin Layer by Fast-Fourier Low Coherence Interferometer

A normalized contrast method on a Superluminescent diode (SLD) low coherence interferometer could retrieve 2D image concealing under a light-scattering medium. In addition, a continuous wavelet transform on both white light and SLD vertical scanning interferometry could construct 3D profile of the interfaces in a dual-layer structure. In this research, 3D information on surface, concealing beneath opaque resin layer, will be produced by using SLD phase difference interferometry with a Fast Fourier Transform. The effect of opaqueness of coating resin layer to quality of 3D image from our method will be revealed.

Local inspection of refractive index and thickness of thick transparent layers using spectral reflectance measurements in low coherence scanning interferometry

For a long time, obtaining the optical and morphological properties of a transparent sample with high accuracy without degrading the layer has been challenging. To achieve these expectations, contactless techniques are used and have not only been proven well-suitable but have also brought optical methods to the forefront. Over recent years white light scanning interferometry has been increasingly used for studying and characterizing transparent materials with thicknesses ranging from a few hundred nanometers to several micrometers. Then, multiple techniques have been developed to retrieve the transparent layer properties from interferometric data. The more recent techniques, based on the use of an error function which defines the best fit between the experimental and theoretical data, allow the determination of the thickness of very thin films (<1 μm). We show here that a method based on this principle can be applied to thicker layers (>1 μm) for simultaneously measuring their optical and morphological properties, provided that a crucial step is carefully considered during the data acquisition process. This enables the simultaneous measurements of both the thickness and the refractive index (dispersion) without any prior assumptions about one of the two parameters. We demonstrate the proposed method by accurate measurements on a few micrometers thick PMMA layer as well as on a SnO2 layer, which is a much more dispersive sample.

Sidewall profile reconstruction of microstructures with high aspect ratio based on near-infrared light scanning interferometry

Sidewall profile reconstruction of microstructures with the high aspect ratio is a problem urgently to be solved in MEMS field. In this paper, a measuring method based on near-infrared light scanning interferometry (NILSI) is presented according to the transmission principle of semiconductor materials in the infrared light region. The NILSI is extended from the white light to near-infrared light and from surface profile reconstruction to sidewall profile reconstruction. The NILSI system is constituted by a near-infrared light source, an interference microscope, infrared CCD, piezoelectric ceramics (PZT) with high accuracy and the data acquisition system. The test sample is taken from GaAs microstructures with high aspect ratio and made by two different height steps for measuring with different typical testing equipment. Near-infrared light vertical scanning interference (NILVSI) is improved to compensate optical path difference (OPD) and the large surface roughness. The sidewall profile of the sample is obtained and compared with that of scanning electron microscopy (SEM) and white light scanning interferometry (WLSI). Test results demonstrate that the steps have 2.115 μm and 0.762 μm relative heights and 1.34 % and 2.14% relative errors respectively. There is a good agreement with the results of SEM and WLSI. The system can reconstruct the sidewall profile of microstructures with high aspect ratio.

The Topology of the Leg Joints of the Beetle Pachnoda marginata (Scarabaeidae, Cetoniinae) and Its Implication for the Tribological Properties.

Locomotion of walking insects is exceptionally efficient. The function of their leg joints in different movement scenarios depends on their kinematics and contacting conditions between moving parts. The kinematics was previously studied in some insects, but contact mechanics within the joints remains largely unknown. In order to understand the complex topology of the contacting surfaces of the leg joints in the Congo rose beetle Pachnoda marginata peregrina (Scarabaeidae, Cetoniinae), we have investigated the shape, the waviness, and the roughness of the joint base and its counter body by applying confocal laser scanning microscopy and white light interferometry. Additionally, we performed nanoindentation tests on the contacting joint surfaces, in order to analyze material properties (elasticity modulus and hardness) of the joint cuticle. We found two topological design principles of the contact surfaces that might be considered as adaptations for reducing frictional drag during leg movements. First, the contact pairs of all leg joints studied consist of convex and concave counterparts. Second, there is a smooth and a rough surface in contact in which microprotuberances are present on the rough surface. These principles might be potentially interesting for technical implications, to design bioinspired joints with both reduced friction and wear rate.

Solubility Modulation of Polyfluorene Emitters by Thermally Induced (Retro)-Diels–Alder Cross-Linking of Cyclopentadienyl Substituents

For cost-efficient organic electronic devices, the consecutive deposition of active layers by solution-based processes is a key benefit. We report a synthetic approach enabling solubility reduction of bis(cyclopentadienyl)-substituted polyfluorenes as emissive layers in organic light-emitting diodes (OLEDs). Thermally induced retro-Diels–Alder reaction liberates free cyclopentadiene as “protecting group” and pending cyclopentadienyl units, which cross-link the polymer strands upon cooling via [4+2] cycloadditions. The activation temperature is tuned in the range of 180–250 °C through alkyl, alkoxy, or ester linkages. Ultimately, macrocyclic self-protected bis(cyclopentadienylene) moieties avoid extrusion of volatile cyclopentadiene during activation. The solvent resistance of the emissive layers after cross-linking is examined by absorption spectroscopy and white light scanning interferometry. The influence of the desolubilization procedure on the performance of solution-processed OLEDs is investigated.

Spatial Modulation-Assisted Scanning White-Light Interferometry for Noise Suppression

A route of spatial modulation-assisted scanning white-light interferometry with the inhibition of background noises and light source fluctuations for the topography measurement of micro-/nano-structure surface was explored in this letter. The spatial modulation frequency was introduced by tilting the sample at a small angle to separate the noise signals and interference signals in the spatial frequency domain. A bandpass filter and a normalization processing were also applied with the purpose of signal-to-noise-ratio improvement and contrast enhancement. The frequency domain analysis was then enrolled in the elimination of 2π ambiguity for the surface recovery with high-presicion. Both the theoretical analysis and the experiment results reveal the validity of spatial modulation-assisted scanning white-light interferometry and its potentials in high-fidelity measurement of smooth surfaces regardless of external disturbances.

Subsurface metrology using scanning white light interferometry: absolute z coordinates deep inside displays.

Mobile devices with interactive displays are ubiquitous commodities. Efficient quality control (QC) drives competitiveness. Scanning white light interferometry imaging offers a fast and nondestructive tool for QC purposes. Relying on optical compensation and image stitching, one can rapidly and cost-effectively produce sharp 3D images of a display's inner structures with a few nanometers' accuracy along the z direction. As a practical example, 3D images of a mobile device display revealed 0.92±0.02 μm height variation in the top glass assembly. The proposed method improves quality assurance methods of display manufacturing.

Surface recovery algorithm in white light interferometry based on combined white light phase shifting and fast Fourier transform algorithms.

Quality control of micro-nano structured and freeform surfaces is becoming increasingly important, which leads to challenging requirements in the measurement and characterization of rough and highly reflective surfaces. As an important measurement technique, white light scanning interferometry (WLSI) is a fast noncontact method to measure three-dimensional (3D) surface profiles. Nevertheless, the existing WLSI 3D surface reconstruction algorithms are prone to environmental vibrations and phase changes caused by reflections on the tested surface. A novel peak detecting algorithm that combines the white light phase-shifting interferometry (WLPSI) method and fast Fourier transform (FFT) coherence-peak-sensing technique is proposed in this paper, which can accurately determine the local fringe peak and improve the vertical resolution of the measurement. A microcomponent (10μm standard step height) and a spherical surface were used as test specimens to evaluate the proposed method. Both simulated and experimental results show that the proposed algorithm improves the precision and anti-interference ability of the WLPSI and FFT methods, which can effectively reduce the batwing effects at the edges and solve the problem of positioning error in the maximum modulation.

White Light Scanning Interferometry Based on Generalized Cross-Correlation Time Delay Estimation

Based on generalized cross-correlation time delay estimation (GCTDE), a new white light scanning interferometry (WLSI) method is proposed, in which the profile information usually achieved with the zero optical path difference (ZOPD) position is replaced with the relative displacement of interference signal between different pixels. Because all spectral information of interference signal (envelope and phase) and filter is utilized, the proposed GCTDE-based WLSI method reveals the advantages of higher accuracy and better noise suppression capability. Especially, in the case where the shape of interference signal envelope is irregular, the proposed method can achieve profile measurement with high accuracy while the conventional ZOPD position locating method cannot work. Moreover, by introducing laser interferometry system to calibrate the vertical displacement of a piezoelectric ceramic transducer scanning system, the measuring accuracy of the proposed GCTDE-based WLSI is further improved. Both the simulation and the experimental results demonstrate the significant accuracy advantage of the proposed GCTDE-based WLSI.

Effect of steel hardness on soot wear

Due to incomplete combustion, high levels of soot can accumulate in engine lubricants between drain intervals. This soot can promote wear of engine parts such as timing chains and cam followers. One standard approach to reducing wear is to increase the hardness of the rubbing components used. According to the Archard wear equation, wear rate should be broadly inversely proportional to hardness.To explore this approach for controlling soot wear, wear tests have been conducted in a High Frequency Reciprocating Rig (HFRR) with HFRR steel discs of various hardness against a hard steel ball. Carbon black (soot surrogate) dispersions in model lubricants based on solutions of ZDDP and dispersant in GTL base oils have been studied. Wear volumes have been measured and wear scars and tribofilms analysed using scanning white light interferometry and SEM-EDS.It is found that, while most oils show wear that reduces with increasing hardness, for blends that contain both ZDDP and carbon black, wear rate markedly increases with disc hardness as the latter approaches the hardness of the ball. The results support the prevalence of a corrosive-abrasive wear mechanism when carbon black and ZDDP are both present in a lubricant and suggests that selection of very hard surfaces may not be a useful way to control soot.

Nucleation and growth of CuCl thin films on commercially available SnO2/glass substrates by the sublimation method

Studies on cuprous chloride (CuCl) sublimation, thin film deposition, and growth on commercially available tin oxide coated glass substrates were performed by adjusting substrate and vapor source thermal parameters. A systematic method for measuring CuCl film thicknesses was implemented using scanning white light interferometry. Furthermore, structural characteristics of the films were evaluated via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Thickness measurements at established locations determined the growth rates of CuCl thin films with respect to deposition conditions. SEM and EDS results revealed that localized clusters (islanding) occurred at the initial stages of growth. As growth continued, the islands began to coalesce and develop nonuniform CuCl grain networks across the substrate. The results support the Volmer–Weber growth mode as the primary mechanism responsible for such growth behavior.

Comparative evaluation of topographical data of dental implant surfaces applying optical interferometry and scanning electron microscopy

ObjectiveComparability of topographical data of implant surfaces in literature is low and their clinical relevance often equivocal. The aim of this study was to investigate the ability of scanning electron microscopy and optical interferometry to assess statistically similar 3-dimensional roughness parameter results and to evaluate these data based on predefined criteria regarded relevant for a favorable biological response. MethodsFour different commercial dental screw-type implants (NanoTite Certain Prevail, TiUnite Brånemark Mk III, XiVE S Plus and SLA Standard Plus) were analyzed by stereo scanning electron microscopy and white light interferometry. Surface height, spatial and hybrid roughness parameters (Sa, Sz, Ssk, Sku, Sal, Str, Sdr) were assessed from raw and filtered data (Gaussian 50μm and 5μm cut-off-filters), respectively. Data were statistically compared by one-way ANOVA and Tukey–Kramer post-hoc test. For a clinically relevant interpretation, a categorizing evaluation approach was used based on predefined threshold criteria for each roughness parameter. ResultsThe two methods exhibited predominantly statistical differences. Dependent on roughness parameters and filter settings, both methods showed variations in rankings of the implant surfaces and differed in their ability to discriminate the different topographies. Overall, the analyses revealed scale-dependent roughness data. Compared to the pure statistical approach, the categorizing evaluation resulted in much more similarities between the two methods. SignificanceThis study suggests to reconsider current approaches for the topographical evaluation of implant surfaces and to further seek after proper experimental settings. Furthermore, the specific role of different roughness parameters for the bioresponse has to be studied in detail in order to better define clinically relevant, scale-dependent and parameter-specific thresholds and ranges.