Scanning White Light Interferometry Research Articles

Nanometer depth resolution in 3D topographic analysis of drug-loaded nanofibrous mats without sample preparation

We showed that scanning white light interferometry (SWLI) can provide nanometer depth resolution in 3D topographic analysis of electrospun drug-loaded nanofibrous mats without sample preparation. The method permits rapidly investigating geometric properties (e.g. fiber diameter, orientation and morphology) and surface topography of drug-loaded nanofibers and nanomats. Electrospun nanofibers of a model drug, piroxicam (PRX), and hydroxypropyl methylcellulose (HPMC) were imaged. Scanning electron microscopy (SEM) served as a reference method. SWLI 3D images featuring 29 nm by 29 nm active pixel size were obtained of a 55 μm × 40 μm area. The thickness of the drug-loaded non-woven nanomats was uniform, ranging from 2.0 μm to 3.0 μm (SWLI), and independent of the ratio between HPMC and PRX. The average diameters (n=100, SEM) for drug-loaded nanofibers were 387 ± 125 nm (HPMC and PRX 1:1), 407 ± 144 nm (HPMC and PRX 1:2), and 290 ± 100 nm (HPMC and PRX 1:4). We found advantages and limitations in both techniques. SWLI permits rapid non-contacting and non-destructive characterization of layer orientation, layer thickness, porosity, and surface morphology of electrospun drug-loaded nanofibers and nanomats. Such analysis is important because the surface topography affects the performance of nanomats in pharmaceutical and biomedical applications.

STUDY OF THE MAJOR CONDITIONS INFLUENCING STEP HEIGHT MEASUREMENT USING INTERFERENCE MICROSCOPE

Step height measurements in micro and nano scale are essential to the micro-technology. The interferometric measurement is carried out using two main techniques: white light scanning interferometry (WLI) and phase stepping interferometry (PSI). A step height standard sample of nominal step height value h of 90.1 nm has been studied using the PSI mode with an optical filter light of λ = 633.4 nm against three parameters: vertical distance (z) between objective and sample, intensity of the incident light and the inclination angles of the sample to the incident light. The effect of numerical aperture of objectives has been referenced to some literature. The total budget of studied parameters for the sample 90.1 nm leads to expanded uncertainty of 0.46 nm.

IMPROVING THE ACCURACY OF INTERFERENCE MICROSCOPE MEASUREMENTS BY APPLYING GENETIC ALGORITHM

The interference microscope measurements with white light scanning interferometry (WLSI) and phase stepping interferometry (PSI) have been improved by optimizing the experimental conditions such as vertical distance between the objective and the surface under test (z), the tilt angles of the incident light beam with the surface and incident light intensity (I). Finally an accurate surface parameters measurement is obtainable. A genetic algorithm code has been developed to determine the best values of experimental conditions instead of manual adjustment by the operator. The combined uncertainty has been successfully reduced from 3.01 nm to 0.84 nm for the WLSI roughness measurement. While it has been reduced from 0.18 nm to 0.08 nm for the PSI step height measurement.

Ceramic Femoral Component Fracture in Total Knee Arthroplasty: An Analysis Using Fractography, Fourier-Transform Infrared Microscopy, Contact Radiography and Histology

Ceramic components in total knee arthroplasty (TKA) are evolving. We analyze the first case of BIOLOX delta ceramic femoral component fracture. A longitudinal midline fracture in the patellar groove was present, with an intact cement mantle and no bony defects. Fractographic analysis with laser scanning microscopy and white light interferometry showed no evidence of arrest lines, hackles, wake hackles, material flaws, fatigue or crack propagation. Analysis of periprosthetic tissues with Fourier-transform infrared (FT-IR) microscopy, contact radiography, histology, and subsequent digestion and high-speed centrifugation did not show ceramic debris. A macrophage-dominated response was present around polyethylene debris. We conclude that ceramic femoral component failure in this case was related to a traumatic event. Further research is needed to determine the suitability of ceramic components in TKA.

Identifying Diagonal Cutter Marks on Thin Wires Using 3D Imaging

We present work on matching 2-mm-thick wires using optical 3D imaging methods. Marks on such small surfaces are difficult to match using a comparison microscope as this 2D imaging method does not provide height data about the sample surface. Moreover, these 2D microscopy images may be affected by illumination. Hence, the reference and investigated sample should be present at the same time. We employed scanning white light interferometry and confocal microscopy to provide quantitative 3D profiles for reliable comparison of samples that are unavailable for simultaneous analysis. We show that 3D profiling offers a solution by allowing illumination-independent sample comparison. We correctly identified 74 of 80 profiles using consecutive matching striae (CMS) criteria, and we were able to match samples based on profiles measured using different 3D imaging devices. The results suggest that the used methods allow matching cutter marks on thin wires, which has been difficult previously.

Comparative analysis of oxidation methods of reaction-sintered silicon carbide for optimization of oxidation-assisted polishing

Combination of the oxidation of reaction-sintered silicon carbide (RS-SiC) and the polishing of the oxide is an effective way of machining RS-SiC. In this study, anodic oxidation, thermal oxidation, and plasma oxidation were respectively conducted to obtain oxides on RS-SiC surfaces. By performing scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX) analysis and scanning white light interferometry (SWLI) measurement, the oxidation behavior of these oxidation methods was compared. Through ceria slurry polishing, the polishing properties of the oxides were evaluated. Analysis of the oxygen element on polished surfaces by SEM-EDX was conducted to evaluate the remaining oxide. By analyzing the three oxidation methods with corresponding polishing process on the basis of schematic diagrams, suitable application conditions for these methods were clarified. Anodic oxidation with simultaneous polishing is suitable for the rapid figuring of RS-SiC with a high material removal rate; polishing of a thermally oxidized surface is suitable for machining RS-SiC mirrors with complex shapes; combination of plasma oxidation and polishing is suitable for the fine finishing of RS-SiC with excellent surface roughness. These oxidation methods are expected to improve the machining of RS-SiC substrates and promote the application of RS-SiC products in the fields of optics, molds, and ceramics.

Thin film thickness measurements using Scanning White Light Interferometry

Scanning White Light Interferometry is a well-established technique for providing accurate surface roughness measurements and three dimensional topographical images. Here we report on the use of a variant of Scanning White Light Interferometry called coherence correlation interferometry which is now capable of providing accurate thickness measurements from transparent and semi-transparent thin films with thickness below 1μm. This capability will have many important applications which include measurements on optical coatings, displays, semiconductor devices, transparent conducting oxides and thin film photovoltaics. In this paper we report measurements of thin film thickness made using coherence correlation interferometry on a variety of materials including metal-oxides (Nb2O5 and ZrO2), a metal-nitride (SiNx:H), a carbon-nitride (SiCxNy:H) and indium tin oxide, a transparent conducting oxide. The measurements are compared with those obtained using spectroscopic ellipsometry and in all cases excellent correlation is obtained between the techniques. A key advantage of this capability is the combination of thin film thickness and surface roughness and other three-dimensional metrology measurements from the same sample area.

Single-exposure surface profilometry using partitioned aperture wavefront imaging

We demonstrate a technique for instantaneous measurements of surface topography based on the combination of a partitioned aperture wavefront imager with a lamp-based reflection microscope using standard objectives. The technique can operate at video rate over large fields of view, and provides nanometer axial resolution and submicrometer lateral resolution. We discuss performance characteristics of this technique, which we experimentally compare with scanning white light interferometry.

Tribocorrosive behaviour of commonly used temporomandibular implants in a synovial fluid-like environment: Ti–6Al–4V and CoCrMo

The temporomandibular joint implant metal alloys, Ti6Al4V and CoCrMo, (n = 3/group) were tested under free-potential and potentiostatic conditions using a custom-made tribocorrosion apparatus. Sliding duration (1800 cycles), frequency (1.0 Hz) and load (16 N) mimicked the daily mastication process. Synovial-like fluid (bovine calf serum, pH = 7.6 at 37 °C) was used to simulate the in vivo environment. Changes in friction coefficient were monitored throughout the sliding process. Changes in surface topography, total weight loss and roughness values were calculated using scanning electron microscopy and white-light interferometry. Finally, statistical analyses were performed using paired t-tests to determine significance between regions within each metal type and also independent sample t-tests to determine statistical significance between metal alloy types. Ti6Al4V demonstrated a greater decrease of potential than CoCrMo, a higher weight loss from wear (Kw = 257.8 versus 2.62 µg; p < 0.0001), a higher weight loss from corrosion (Kc = 17.44 versus 0.14 µg; p < 0.0001) and a higher weight loss from the combined effects of wear and corrosion (Kwc = 275.28 versus 2.76 µg; p < 0.0001). White-light interferometry measurements demonstrated a greater difference in surface roughness inside the wear region in Ti6Al4V than CoCrMo after the sliding (Ra = 323.80 versus 70.74 nm; p < 0.0001). In conclusion, CoCrMo alloy shows superior anti-corrosive and biomechanical properties.

3D Measurement of TSVs Using Low Numerical Aperture White-Light Scanning Interferometry

We have proposed and demonstrated a low numerical aperture technique to measure the depth of through silicon vias (TSVs) using white-light scanning interferometry. The high aspect ratio hole like TSV's was considered to be impossible to measure using conventional optical methods due to low visibility at the bottom of the hole. We assumed that the limitation of the measurement was caused by reflection attenuation in TSVs. A novel interference theory which takes the structural reflection attenuation into consideration was proposed and simulated. As a result, we figured out that the low visibility in the interference signal was caused by the unbalanced light intensity between the object and the reference mirror. Unbalanced light can be balanced using an aperture at the illumination optics. As a result of simulation and experiment, we figured out that the interference signal can be enhanced using the proposed technique. With the proposed optics, the depth of TSVs having an aspect ratio of 11.2 was measured in 5 seconds. The proposed method is expected to be an alternative method for 3-D inspection of TSVs.

Wear behaviour of tetrahedral amorphous diamond-like carbon (ta-C DLC) in additive containing lubricants

Diamond-like carbon (DLC) coatings offer excellent mechanical and tribological properties. They provide ultra-low friction and superior wear resistance. In recent years, the research of DLC coating focuses on the application of these coating in mechanical components which work under boundary lubricated conditions. Since conventional lubricants and lubricant additives were formulated for metal surfaces, the effects of these lubricants on DLC contact and interaction between lubricant additives and DLC surfaces are still unclear. In this work, we present the influence of lubricant additives and counterbody materials on the wear behavior of ta-C DLC coating under boundary lubrication conditions. Tribological tests were performed in a home-build pin-on-disc tribometer. Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), Nano-indenter, X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and scanning white light interferometry were used for characterization of ta-C DLC and worn surface analysis. The results show that ta-C DLC were totally wear out in DLC/steel contact tested in base oil. Addition of lubricant additives into the base oil significantly reduced the wear in the DLC/steel contact. ta-C DLC exhibited totally different wear behavior in DLC/steel and DLC/DLC contact depending on lubricant formulation. It is concluded that combination of lubricant formulation and counterbody material is a crucial factor for the use of DLC in lubricated conditions.

Adaptive Phenotypic Plasticity of Siberian Elm in Response to Drought Stress: Increased Stomatal Pore Depth

Leaf stomatal characteristics of Siberian elm (Ulmus pumila) were investigated by electron microscopy and white light scanning interferometry. On the basis of average annual precipitations, two types of tree specimens were collected from Korea, China, and Mongolia: (1) trees under normal environmental conditions and (2) trees under arid conditions. Field emission scanning electron microscopy revealed oval-shaped stomata on the lower surface, and they were ca. 20 μm in width. In-lens secondary electron imaging showed differences in electron density and stomatal pore depth between the two types. According to the line profile analysis by white light scanning interferometry, stomata under arid conditions appeared to have higher levels of the stomatal pore depth than ones under normal conditions. Focused ion beam-field emission electron microscopy supported the increased stomatal pore depth with the increasing drought stress gradient. These results suggest that complementary microscopy can be employed to unravel the adaptive phenotypic plasticity of Siberian elm in response to drought stress.

SIMS sputtering rates in biogenic aragonite: implications for culture calibration studies for palaeoenvironmental reconstruction

We used scanning white light interferometry to view the craters produced during secondary ion mass spectrometry (SIMS) analysis of the CaCO3 skeleton of an aragonitic coral. The dimensions and volumes of craters sputtered during trace element, δ18O, δ13C and δ11B analyses were determined. Sputtering rates were ~6 µm3 nA−1 min−1 for a 16O− primary beam and ranged from ~12 µm3 nA−1 min−1 (for δ18O analyses) to ~19 µm3 nA−1 (for δ13C analyses) using a Cs+ primary beam. Sputter yields (atoms sputtered/impinging primary ions) ranged from 1.3 to 1.4 for a 16O− primary beam and from 2.5 to 4.5 using a Cs+ primary beam. Useful ion yields (ions detected/atoms sputtered), using instrument conditions typically used in geoscience applications, were of the order of 10−4 for B, Mg, Ca, Sr, Ba and C and 10−2 for O. The maximum lengths of the SIMS craters, at the sample surface, range from ~17 µm (δ13C analyses) to ~36 µm (δ11B analyses) and crater depths range from ≤3 µm (δ18O analyses) to &gt;20 µm (δ11B analyses). These dimensions are significant in relation to accretion rates in a range of biogenic carbonates and SIMS analyses typically sample carbonate deposited over time periods of days to months depending on the organism and structure analysed. In culture calibration studies, accurate determination of the temporal resolution of the analysed volume is crucial to ensure that the entire volume reflects the culture conditions and does not include carbonate deposited prior to introduction of the organism to the culture system. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Assessment of the surface reactivity of AA1050 aluminium alloy

During processing from cast slab to thin gauge material, the AA1050 aluminium alloy proceeds through various stages of thermomechanical processing, with the conditions at each processing stage influencing the microstructure of the final coil. The reactivity of the material in defined chemical and electrochemical processes has been demonstrated as a useful method to describe variance in the microstructure and surface chemical properties of the aluminium. Various techniques have been employed to assess the reactivity of the surface, e.g. sodium hydroxide etching and open circuit potential measurements. Etching in hydrochloric acid was also carried out on samples that had been previously alkaline etched. The weight losses in both alkaline and acid solutions were measured, and the surface responses were examined and analysed using scanning electron microscopy and white light interferometry. Visible and measurable differences in the sample surfaces were observed. Finally, the novel state‐of‐the‐art technique of in‐SEM 3D electron tomography was used to characterize the near‐surface microstructure in a way that has not previously been possible for such a representative volume. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Mechanical stresses and amorphization of ion-implanted diamond

Scanning white light interferometry and Raman spectroscopy were used to investigate the mechanical stresses and structural changes in ion-implanted natural diamonds with different impurity content. The uniform distribution of radiation defects in implanted area was obtained by the regime of multiple-energy implantation of keV He+ ions. A modification of Bosia’s et al. (Nucl. Instrum. Meth. B 268 (2010) 2991) method for determining the internal stresses and the density variation in an ion-implanted diamond layer was proposed that suggests measuring, in addition to the surface swelling of a diamond plate, the radius of curvature of the plate. It is shown that, under multiple-energy implantation of He+, mechanical stresses in the implanted layer may be as high as 12GPa. It is shown that radiation damage reaches saturation for the implantation fluence characteristic of amorphization of diamond but is appreciably lower than the graphitization threshold.

Room-Temperature Si Etching in NO/F2 Gases and the Investigation of Surface Reaction Mechanisms

We have been investigating a plasmaless Si chemical dry etching in NO/F2 gas mixtures using the F produced by the exothermic reaction of F2 + NO → FNO + F at room temperature. The effect of the change in the flow rate ratio of NO and F2, fNO/fF2, on the etch rate, the chemical bonding structures, and the surface morphology was measured by laser microscopy, Fourier transform infrared spectrometer, scanning electron microscopy, and scanning white light interferometry and results were compared with the calculated F flux. Total energy variations and their changes in chemical bonding structures before and after the reactions of molecules in the gas phase and the Si surface were considered using the molecular orbital (MO) method. On the basis of the MO calculation using a Si(100)-2×1 cluster model, F was necessary to form a dangling bond at the surface of Si that would trigger subsequent chemical reactions of Si with F2, NO, F, or FNO. The etch rate and surface roughness increased with the addition of NO up to the fNO/fF2 = 1.0 to 1.5 and then decreased due to the reduction of F flux in the gas phase together with the presence of the Si-NO and the Si-FNO bonds that would block the interaction of Si with F2 and F.

Stroboscopic scanning white light interferometry at 27 MHz with 16 µm coherence length using a non-phosphor LED source

Stroboscopic scanning white light interferometry (SSWLI) allows precise three dimensional (3D) measurements of oscillating samples. Commercial SSWLI devices feature limited pulsing frequency. To address this issue we built a 400-620 nm wideband 150 mW light source whose 1.6 µm wide interferogram is without side peaks. The source combines a non-phosphor white LED with a cyan LED. We measured a calibration artifact with 10 nm precision and obtained 40 nm precision when measuring the 3D profile of a capacitive micromachined ultrasonic transducer membrane operating at 2.72 MHz. This source is compatible with solid state technology.

Multilayered Alkyd Resin/Nanocellulose Coatings for Use in Renewable Packaging Solutions with a High Level of Moisture Resistance

A surprisingly simple and rapid methodology for large-area, lightweight, and thin laminate coatings with remarkable moisture barrier properties is introduced. Commercially available paperboards are coated with thin layers of nanocellulose. The nanocellulose coating induces a surface smoothening effect on the coated sheets as characterized by environmental scanning electron microscopy and white light interferometry. A moisture-protective layer of renewable alkyd resins is deposited on the nanocellulose precoated sheets using a water-borne dispersion coating process or lithographic printing. Through an auto-oxidation process, the applied alkyd resins are transformed into moisture sealant layers. The moisture barrier properties are characterized in detail by water vapor permeability measurements at different levels of relative humidity. The water vapor barrier properties of the nanocellulose precoated substrates were significantly improved by thin layers of renewable alkyd resins. The effect of the alkyd res...

Mechanical and Frictional Properties of the Elytra of Five Species of Beetles

The mechanical and frictional properties of different parts of the elytra of five species of beetle were measured using a nano-indenter and a micro-tribometer. The surface microstructures of the elytra were observed by optical microscopy and scanning white light interferometry. The surface microstructures of the elytra of all five species are characterized as non-smooth concavo-convex although specific morphological differences demonstrate the diversity of beetle elytra. Young's modulus and the hardness of the elytral materials vary with the species of beetle and the sampling locations, ranging from 1.80 GPa to 12.44 GPa, and from 0.24 GPa to 0.75 GPa, respectively. In general, both the Young's modulus and the hardness are lower in samples taken from the center of the elytra than those taken from other regions, which reflects the functional heterogeneity of biological material in the process of biological evolution. The elytra have very low friction coefficient, ranging from 0.037 to 0.079, which is related to their composition and morphology. Our measurements indicate that the surface texture and its microstructural size of beetle elytra contribute to anti-friction effects.

Low coherent Linnik interferometer optimized for use in nano-measuring machines**This article was presented at the 56th International Scientific Colloquium on ‘Precision Engineering and Precision Measurement Technology’ held at Ilmenau University of Technology, Germany, and submitted for publication in the July 2012 special issue of this journal devoted to papers from that meeting.

The precise acquisition of three-dimensional geometrical data in micro- and nanotechnologies plays a crucial role in advanced fabrication processes. Scanning white-light interferometry achieves nanometer resolution in the axial direction, but the lateral resolution is far more critical. The requirements for an area-based optical sensor in a nano-measuring machine are very high. The resolution in every dimension and the working distance have to be as high as possible. In contrast to a Mirau interferometer, a Linnik interferometer does not need any optical components in front of the objective lens. This benefit permits both a long working distance and a high lateral resolution. In the EC-funded project ‘NanoCMM’ we developed a Linnik interferometer providing a working distance of more than 5 mm and a lateral resolution of 0.44 µm. This is achieved by near-UV illumination. The interferometer measures the full modulation depth and the rectangular shape of a pitch standard with 0.6 µm pitch length.