White Light Interference Microscopy Research Articles

Picosecond Laser Processing of Hierarchical Micro–Nanostructures on Titanium Alloy upon Pre‐ and Postanodization: Morphological, Structural, and Chemical Effects

Recent publications indicate that the order of electrochemical anodization (before or after the laser processing step) plays an important role for the response of bone‐forming osteoblasts—an effect that can be utilized for improving permanent dental or removable bone implants. For exploring these different surface functionalities, multimethod morphological, structural, and chemical characterizations are performed in combination with electrochemical pre‐ and postanodization for two different characteristic microspikes covered by nanometric laser‐induced periodic surface structures on Ti–6Al–4V upon irradiation with near‐infrared ps‐laser pulses (1030 nm wavelength, ≈1 ps pulse duration, 67 and 80 kHz pulse repetition frequency) at two distinct sets of laser fluence and beam scanning parameters. This work involves morphological and topographical investigations by scanning electron microscopy and white light interference microscopy, structural material examinations via X‐ray diffraction, and micro‐Raman spectroscopy, as well as near‐surface chemical analyses by X‐ray photoelectron spectroscopy and hard X‐ray photoelectron spectroscopy. The results allow to qualify the mean laser ablation depth, assess the spike geometry and surface roughness parameters, and provide new detailed insights into the near‐surface oxidation that may affect the different cell growth behavior for pre‐ or postanodized medical implants.

Tribological Performance Study of Low-Friction PEEK Composites under Different Lubrication Conditions

This study introduces a low-friction composite based on PEEK to improve its friction and wear properties. The composite incorporates PTFE as a solid lubricant and utilizes PPTA as a reinforcing material within the PEEK matrix. These components were prepared utilizing a compression molding method, followed by a series of exploratory experiments to identify the optimal preparation conditions for PEEK. This research assesses how the PTFE/PPTA/PEEK composites perform in terms of friction and wear under dry and oil-lubricated conditions. By examining wear tracks using scanning electron microscopy and white light interference microscopy, this study aims to uncover the wear mechanisms of PEEK and its composites under different lubrication scenarios. Results show that the main wear mechanisms for the PTFE/PPTA/PEEK composites and bearing steel are ploughing and adhesive wear. The presence of PPTA helps reduce wear by leveraging its strong fibers and thermal stability, while the coefficient of friction decreases as PTFE creates a smooth, solid lubricating film on the surface. Notably, PEEK composites containing 25 wt% PTFE and 6 wt% PPTA demonstrate the lowest wear rates and reduced coefficient of friction in both dry and oil-lubricated conditions.

Corrosion Study of Picosecond‐Laser Structured and Anodized Ti6Al4V for Bone Screws

A corrosion study is performed on six variations of titanium grade 5 (Ti6Al4V) samples. Samples are prepared in different conditions by variation of preanodization, postanodization, and picosecond‐laser (ps‐laser) surface treatment, while polished and anodized samples serve as reference. Microcones and nanosized periodic surface features are successfully produced on Ti6Al4V samples. The morphology and topography of the structures are visualized by scanning electron microscopy and white light interference microscopy. Furthermore, the relative electrochemically active surface area (ECSA) is determined for the ps‐laser‐treated samples. It is determined that the preanodized and laser‐treated sample has 3.5 times larger ECSA than a polished sample, and that the laser‐treated sample has 4.1 times larger area. Moreover, Tafel analysis is performed to determine the corrosion properties of the samples. It is shown that the corrosion resistance improves for both laser‐structured samples after the anodization. To further study the surface of the samples, electrochemical impedance spectroscopy measurements are conducted. The study indicates that the ps‐laser‐treated and anodized Ti6Al4V is suitable to be used for the fabrication of bone screws and plates due to its improved corrosion resistance as compared to nonanodized samples.

Investigation of laser-induced contamination on dielectric thin films in MHz sub-ps regime

High-repetition rate diode-pumped sub-ps lasers are widely used in the industrial sector for high-quality material processing applications. However, for their reliable operation, it is crucial to study the power handling capabilities of the optical components used in these systems. The optical components, such as mirrors, gratings, dichroic filters, and gain media, are designed based on dielectric thin films. When subjected to high-intensity laser radiation, the phenomenon of laser-induced contamination (LIC) can lead to the growth of a nanometric, highly absorbent layer on an irradiated optical surface, which can result in transmission or reflection loss and eventual permanent damage. In this study, we investigate LIC growth on dielectric oxide thin films in an air environment irradiated by MHz sub-ps laser at 515 nm. We examine the effect of thin film deposition method, material, and thickness on LIC growth dynamics. The irradiated spots on the surface are inspected using multiple observation methods, including white light interference microscopy and fluorescence imaging. Our results show that the LIC growth dynamics depend on the laser intensity and irradiation time and can be affected by the thin film deposition method, material, and thickness. These findings could be used to inform the development of more resistant optical components, ensuring long-term reliable laser operation required for industrial applications. The study highlights the need for validating optical components using tests that closely mimic real-world applications and provides insight into the complex processes that lead to LIC.

Wear mechanism and leakage failure analysis of the mechanical seal end face of an oil transfer pump

The John Crane 48 V mechanical seal is a long-distance oil transfer pump station shaft end seal; its sealing effect directly affects pipeline production safety. However, it has been found that there is oil leakage at the shaft end of the pump station. In order to explore the oil transfer pump mechanical seal abnormal leakage failure causes, to ensure the safety and stability of production, the end face of the 48 V mechanical seal was analyzed by white light interference and scanning electron microscope technology. The failure mechanism of the 48 V mechanical seal was explored from the perspective of the wear mechanism of moving and stationary rings. Results showed that the wear mechanism of the 48 V mechanical seal stationary ring was mainly abrasive wear, and substantial furrows, bulges, and depressions existed on the wear surface. The material removal mechanism was brittle spalling, and the roughness of the wear surface increased with the increase in wear depth and decreased with the increase in wear average width. Uneven wear occurred on the end face of the stationary ring of the mechanical seal, resulting in the leakage of the sealing medium from the end cover of the mechanical seal. The working condition could be improved by adding a spring compensation device to the stationary ring or increasing the gap between the stationary ring and the shaft sleeve.

Ion‐Conducting Non‐Flammable Liquid Crystal–Polymer Composites for High‐Frequency Soft Actuators

AbstractHigh‐frequency actuators are reported based on non‐flammable lithium‐ion conducting phosphate liquid crystal–polymer composite electrolytes, which exhibit a bending response at frequencies up to 80 Hz under an AC voltage of 2 V, owing to its high ionic conductivity reaching 10−4 S cm−1 at room temperature. An equimolar complex of a phosphate‐containing mesogenic molecule and lithium bis(trifluoromethylsulfonyl)imide through the ion‐dipole interactions induced a room‐temperature smectic A liquid‐crystalline (LC) phase forming 2D ion‐transport pathways comprising the 2D array of the phosphate moieties. A blend of 80 wt% LC electrolyte and 20 wt% polymers (poly(vinyl chloride) and poly(vinylidene fluoride‐co‐hexafluoropropylene)) formed a flexible, mechanically robust LC–polymer composite film. Scanning electron microscopy and white light interference microscopy revealed a microphase‐segregated structure consisting of a continuous LC phase and a porous polymer matrix. In addition, the continuity of porous structure across the film is confirmed by permeation experiments of solvents thorough the membrane with a homemade filter in a dead‐end filtration mode. The LC–polymer composite film sandwiched between two poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) electrodes is found to simultaneously exhibit high bending strain (0.63%) and high output force (0.35 mN), owing to the high ion migration into the composite electrolyte and electrode.

Study on wear resistance of local aluminum alloy reinforced by carbon fiber transfer membrane region

In order to study the effect of fiber reinforced resin matrix composites on the friction properties of aluminum alloy, 7075 aluminum alloy, Carbon fiber reinforced plastic (CFRP) and 7075-Al/CFRP hybrid samples were selected for pin-disk friction test. White light interference and scanning electron microscopy were used to analyze the surface morphology of the friction samples. Secondly, the formation process of the transfer membrane was analyzed by Raman test and energy spectrum. Finally, the strength of the transfer film was verified by scratch test. The results showed that the friction coefficients of 7075-W and 7075-T6 aluminum alloy are 0.419 and 0.398, and the wear rates are 0.288% and 0.273%, respectively. For CFRP and 7075-Al/CFRP hybrid samples, the microscopic study of friction interface showed that CFRP and aluminum alloy abrasive particles exchanged elements under the dual action of pressure and shear force, thus forming Transfer Membrane Region (TMR). TMR with strong self-lubrication preferentially supported the friction load during the friction process, thus reducing the friction and wear of aluminum alloy. The friction coefficient and the wear rate of the 7075-Al/CFRP hybrid sample were reduced by 62.5% and 78.2%, respectively in comparison to pure 7075 aluminum alloy sample.

Application of imaging ellipsometry and white light interference microscopy for detection of defects in epitaxially grown 4H–SiC layers

Critical defects, also known as device killers, in wide bandgap semiconductors significantly affect the performance of power electronic devices. We used the methods imaging ellipsometry (IE) and white light interference microscopy (WLIM) in a hybrid optical metrology study for fast and non-destructive detection, classification, and characterisation of defects in 4H–SiC homoepitaxial layers on 4H–SiC substrates. Ellipsometry measurement results are confirmed by WLIM. They can be successfully applied for wafer characterisation already during production of SiC epilayers and for subsequent industrial quality control.

Laser-induced contamination deposit growth mechanisms on space optics

Lasers in space often suffer from light absorbing deposits forming inside the resonator. This effect is commonly called laser-induced contamination (LIC), and its mechanism can be compared with laser chemical vapor deposition. LIC experiments were carried out in a dedicated vacuum chamber using a q-switched 355-nm laser, hafnia- or silica-coated fused silica samples and contamination by epoxy adhesive outgassing, or toluene vapor in vacuum. The typical deposit formation was observed at different experimental conditions and analyzed by in situ laser-induced fluorescence imaging and ex situ white light interference microscopy. We determined the average growth rate during the first growth stage (bump-shaped growth) and analyzed it as a function of the laser fluence, sample nature, and used contamination. The data show that the band gap of the sample is important for the LIC process in the first growth stage. The light absorbed in the sample leads to a temperature rise that drives the deposit growth. This knowledge opens a new pathway to minimize LIC that is complementary to studies that aim to reduce the adsorption of contaminant molecules by making chemical surface treatments.

Effect of electromagnetic stirring frequency on tribological performance and corrosion resistance of Al-Sn bearing alloy

The Al-Sn bearing alloy was prepared by electromagnetic stirring (EMS) technique, and the effect of stirring frequency on tribological performance and corrosion resistance of Al-Sn bearing alloy was studied. The samples were subjected to tribological experiments and electrochemical tests. The microstructure of the sample was observed by an optical microscope, the wear surface and corrosion morphology were observed by a scanning electron microscope(SEM), the 3D morphology and wear volume of the wear mark were measured by a white light interference microscope, and the composition of corrosion product film was analyzed by X-ray photoelectron spectroscopy(XPS). The microstructure shows that when the stirring current is 60 A and the stirring frequency is 30 Hz, the electromagnetic force has a strong refining effect, and the crystal grains are fine and uniformly distributed throughout the sample. With the increase of the stirring frequency, the wear surface becomes smoother, and more wear debris adhesion phenomenon appears, showing better friction performance. The application of EMS changes the alloy microstructure, which in turn improves the distribution of Sn and enhances the tribological properties. At the same time, the sample with EMS generates a dense corrosion product film in the later stage of immersion, which has good corrosion resistance.

Topography measurement of helical grooves on a hemisphere based on stitching interference microscopy

Hemispherical bearings fabricated with helical grooves on the working surface show improved aerodynamic performance which depends to a large extent on the machining accuracy of the grooves. Topography measurement of the entire groove from macro to micro scale is thus important to evaluate the bearing performance. White light interference microscopy is widely used in topography measurement. However, subaperture stitching is necessary to extend the field of view (FOV) for large area measurement but limited to planar surfaces. This paper presents a method of interference microscopy combined with subaperture stitching. The long groove is divided into a series of subapertures with overlapping regions. Each subaperture meets the requirement of FOV and measurable slope limit of the microscope. We show that the helical curve is approximately located on a geodesic circle of the hemisphere. Accordingly a special fixture is designed with a rotary table to rotate the groove around the axis perpendicular to the geodesic circle. A four-axis scanning platform is integrated with the interference microscope. Based on the principle of minimal deviations in overlapping regions, six-degree-of-freedom motion error introduced in subaperture scanning is simultaneously corrected through an iterative stitching algorithm. It is experimentally verified by measuring a real part with helical grooves etched on a hemisphere bearing rotor. Complete high-resolution topography of the entire groove is reconstructed and the stitching map shows no overlap sliding effect, which is instructive for assessment of the machining error and further evaluation of the bearing performance.

Hybrid optical measurement technique for detection of defects in epitaxially grown 4H-SiC layers

Recent developments in power electronics require the use of new wide bandgap compound semiconductor. We demonstrate the use of the ellipsometry and white light interference microscopy to detect defects in epitaxially grown SiC layers on SiC substrates. Such hybrid optical metrology methods can be used to better understand the mechanism of the development of the defects as well as their effects on the material´s optoelectronic properties.

Particle erosion under multiphase bubble flow in horizontal-vertical-upward elbows

The erosion of particles is one of the main reasons of damage to the multiphase flow pipelines in black water treatment systems. In this study, the particle erosion of liquid–solid–gas multiphase bubble flow in a horizontal-vertical-upward elbow was analysed. The optical microscope, scanning electron microscope (SEM) and white light interference microscope were used for detection of failed pipe samples. An erosion simulation method based on the volume of fluid (VOF) model and discrete phase model (DPM) was adopted to study the influencing factors on the erosion. The results showed that the particles and bubbles lead to lots of pits and furrows on the pipe surfaces, and the erosion at the outer elbow is relatively severe due to the effect of multiphase bubble flow. The most severe damage occurred at θ = 25° of the elbow, and erosion rate is positively correlated with the particle diameter, volume fraction and inlet velocity.

Q-factor modification of LN based WGM resonator

We demonstrated a monolithic optical whispering-gallery-mode (WGM) resonator made of lithium niobate (LN) single crystal. The effect of WGM resonator side roughness on the quality factor (Q-factor) of resonator was simulated by finite-difference time-domain (FDTD) method. WGM resonators were annealed at high temperature(1050 °C) to improve the Q-factor, and measured the side roughness of the WGM resonator before and after annealing with a white light interference microscope. It found that Q-factor of WGM resonator can be increased by more than 2 orders of magnitude by thermal treatment at 1050 °C.

Effects of Contact Load and Torsion Angle on Crack Propagation Behaviors of Inclined Crossed Steel Wires during Tension–Torsion Fretting Fatigue in Acid Solution

The hoisting rope in the kilometer-deep coal mine exhibits the tension–torsion fretting fatigue behaviors of inclined crossed steel wires in acid solution. Distinct contact load and torsion angles of steel wires in the rope cause different crack propagation behaviors, which greatly affect the fatigue lives of steel wires. Therefore, the effects of contact load and torsion angle on the crack propagation behaviors of inclined crossed steel wires during tension–torsion fretting fatigue in acid solution were investigated in the present study. The three-dimensional X-ray tomographic micro-imaging system was used to reveal evolutions of crack profiles and crack propagation depths during the test. The evolution of friction coefficient between steel wires during the test is presented. The three-dimensional white light interference microscope, electrochemical analyzer, and scanning electron microscope were employed to investigate the wear depth profiles, Tafel polarization curves and impedance spectra, and wear scar morphologies, respectively, of steel wires. Effects of contact load and torsion angle on crack propagation behaviors of inclined crossed steel wires during the tests were explored through analyses of friction and wear mechanisms and electrochemical corrosion damage. The results show that as the contact load and torsion angle increase, the crack propagation depth and rate of steel wire both increase and the fatigue life of steel wire decreases. Those are mainly attributed to the increases in the average tangential force between steel wires, wear depth, electrochemical corrosion tendency, and surface damage of steel wire as well as the decrease in corrosion resistance.

Spatially Resolved Optical Characterization of Functional Materials Using Coherence Scanning Interferometry

Herein, some of the work in adapting white light interference microscopy to perform local spectroscopy for measuring the optical properties of microscopic structures is reviewed. Theoretical and experimental results are shown in which Fourier transform processing of the polychromatic fringe signal combined with careful calibration of the optical system is used to make measurements of local reflectance spectra. This approach captures the spectral information within the entire field of view in a single scan, allowing rapid spectral mapping of spatially extended surfaces. Results are shown of local reflectance spectra measured on different materials and buried under transparent layers with a lateral spot size of between 0.5 μm and several micrometer over a field of view up to 650 × 650 μm. The technique is extended to the measurement of local refractive index and thickness of transparent layers as well as to the size determination of small spherical beads buried in transparent and scattering layers with a priori information. The significance of the work is the potential for local materials characterization in complex, hybrid, and functional materials and even disease detection through the study of living cells.

Wide-field parallel mapping of local spectral and topographic information with white light interference microscopy.

Fourier analysis of interferograms captured in white light interference microscopy is proposed for performing simultaneous local spectral and topographic measurements at high spatial resolution over a large field of view. The technique provides a wealth of key information on local sample properties. We describe the processing and calibration steps involved to produce reflectivity maps of spatially extended samples. This enables precise and fast identification between different materials at a local scale of 1 µm. We also show that the recovered spectral information can be further used for improving topography measurements, particularly in the case of samples combining dielectric and conducting materials in which the complex refractive index can result in nanometric height errors.

Effect of Using High-Pressure Gas Atmosphere with UV Photocatalysis on the CMP Characteristics of a 4H-SiC Substrate

The objective of this study was to realize high-efficiency and high-quality chemical mechanical polishing (CMP) of a silicon carbide (SiC) substrate. Consequently, the effect of a gas atmosphere on the CMP characteristics of a SiC substrate was investigated. The experimental results show that increasing the partial pressure of oxygen (O2) in the atmosphere to 300 kPa led to an over 2-fold increase in the material removal rates (MRRs) of the Si and carbon (C) faces compared to an open-air atmosphere. White light interference microscopy, energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were used to analyze the face morphology and surface elements after processing. Si face atoms were more difficult to oxidize than C face atoms, resulting in a low MRR of the Si face after CMP. The MRR of the Si face was improved by using an ultraviolet (UV) photocatalysis reaction in the high-pressure O2 atmosphere. Excitation of O2 molecules in the slurry into HO 2 • with a stronger oxidation capability promoted the chemical reaction at the solid-liquid interface. The processing mechanism was elucidated.

Research on Defect Detection Method of Whole Surface of Small Ball Based on Field Scan

This paper introduces a detection method that uses a white-light interference microscope to scan along the circle of latitude line to detect defects on the entire surface of microsphere with a diameter of 2mm. The surface of the microsphere is exposed under the white light interference microscope from the top to the equator in turn according to the annular belts of different latitudes to make the acquired image cover the entire surface of the ball. The topography data is processed, the defects are identified, and the number of defects of different horizontal and vertical sizes is counted, so as to achieve the quantitative evaluation of the surface defects of the small ball.

Surface studies of optical glasses by white-light interferometry

Topographic surface studies of optical glasses after they come in contact with a moist atmosphere are carried out by white-light interference microscopy. It is shown that the roughness changes are minimal in silicate glasses and maximal in borosilicate glasses, while borate glasses occupy an intermediate position. The increase of the roughness in silicate glasses is caused by the growth of peaks on the surface and in borosilicate and borate glasses by the growth of both peaks and valleys.