Scanning Interference Microscopy Research Articles

Heterodyne phase shifting method in scanning probe microscopy.

The present paper describes a novel implementation of the continuous phase shifting method (PSM), named heterodyne holography, in a scanning probe microscope configuration, able to retrieve the complex scattered field in on-axis configuration. This can be achieved by acquiring a continuous sequence of holograms at different wavelengths in just a single scan through the combination of scanning interference microscopy and a low-coherent signal acquired in the frequency domain. This method exploits the main advantages of the phase shifting technique and avoids some limits relative to off-axis holography in providing quantitative phase imaging.

Robust 3D surface recovery by applying a focus criterion in white light scanning interference microscopy.

White light scanning interference (WLSI) microscopes provide an accurate surface topography of engineered surfaces. However, the measurement accuracy is substantially reduced in surfaces with low-reflectivity regions or high roughness, like a surface affected by corrosion. An alternative technique called shape from focus (SFF) takes advantage of the surface texture to recover the 3D surface by using a focus metric through a vertical scan. In this work, we propose a technique called SFF-WLSI, which consists of recovering the 3D surface of an object by applying the Tenegrad Variance (TENV) focus metric to WLSI images. Extensive simulation results show that the proposed technique yields accurate measurements under different surface roughness and surface reflectivity, outperforming the conventional WLSI and the SFF techniques. We validated the simulation results on two real objects with a Mirau-type microscope. The first was a flat lapping specimen with Ra=0.05 μm for which we measured an average value of Ra=0.055 μm and standard deviation σ=0.008 μm. The second was a metallic sphere with corrosion, which we reconstructed with WLSI versus the proposed SFF-WLSI technique, producing a better 3D reconstruction with less undefined depth values.

Abrasion of 6 dentifrices measured by vertical scanning interference microscopy

ObjectivesThe abrasion of dentifrices is well recognized to eliminate the dental plaque. The aims of this study were to characterize the abrasive powders of 6 dentifrices (3 toothpastes and 3 toothpowders) and to measure the abrasion on a test surface by Vertical Scanning Interference microscopy (VSI). Material and MethodsBright field and polarization microscopy were used to identify the abrasive particles on the crude dentifrices and after prolonged washes. Scanning electron microscopy and microanalysis characterized the shape and nature of the particles. Standardized and polished blocks of poly(methylmethacrylate) were brushed with a commercial electric toothbrush with the dentifrices. VSI quantified the mean roughness (Ra) and illustrated in 3D the abraded areas.ResultsToothpastes induced a limited abrasion. Toothpowders induced a significantly higher roughness linked to the size of the abrasive particles. One powder (Gencix® produced a high abrasion when used with a standard testing weight. However, the powder is based on pumice particles covered by a plant homogenate that readily dissolves in water. When used in the same volume, or after dispersion in water, Ra was markedly reduced. ConclusionLight and electron microscopy characterize the abrasive particles and VSI is a new tool allowing the analysis of large surface of abraded materials.

Towards real time 3D quantitative characterisation of in situ layer growth using white light interference microscopy

Quantitative 3D characterisation of layer growth or modification in situ in liquid systems is a challenge because of the changing morphology of the layer and the presence of the growth liquid. Because of the limited bandwidth of many surface profiling techniques, measurement of microscopic surface roughness is generally limited to that of static surfaces. The aim of the present work is to develop a new technique using high speed scanning interference microscopy combined with an adapted immersion head for use in liquid growth systems. For several years we have been developing a real time 3D surface analysis system based on a high speed camera and cabled logic processing, combined with continuous scanning white light interferometry. An optical measurement head is also being developed for use in liquid immersion conditions, with the view of measuring layer growth or modification in biomaterials. In this paper we report on the present status of the development of our second prototype 4D system and also of the optical immersion head for in situ measurements, describing the achievements made and the difficulties still to be overcome.

Spurious Mild Wear Measurement Using White Light Interference Microscopy in the Presence of Antiwear Films

Commercial scanning white light interference microscopes are able to map surface topography to very high resolution and can thus measure very small amounts of wear on rubbed surfaces. These instruments are therefore being increasingly used to study aspects of mild wear. It is shown in this Technical Note that, when used on surfaces that have been rubbed in lubricants containing the antiwear additive zinc dialkyldithiophosphate (ZDDP), some white light interference microscopes can produce an apparent but spurious wear measurement. The transparent and relatively thick antiwear film generated by ZDDP on rubbed surfaces produces an optical path difference that is incorrectly interpreted as wear. It is thus suggested that surfaces that have been rubbed in lubricants containing ZDDP or other thick film-forming additives should be treated to remove tribofilms prior to wear measurement using scanning interference microscopy.

Membrane Deformation at Integrin Adhesions

In order to measure the nucleation of nouveau adhesions on the ventral surface of a cell, we have combined phase shifting laser feedback interferometry with a high numerical aperture inverted fluorescence microscope. We use fluorescence to image molecules at the adhesion site and stage scanning interference microscopy in order to measure the distance between the ventral surface of a cell and the substratum with several nanometer precision. Our analytic and Monte Carlo simulations of integrin mediated adhesions predict several features of these nouveau adhesions. An analysis of the energetics of membrane bending and the effects of a composite system of freely diffusing repellers and receptors and a fixed network of ligands on the extracellular matrix predicts that a small bundle of actin filaments should be able to push the membrane down to the extracellular matrix and nucleate a nouveau adhesion with critical radius below the diffraction limit. We have obtained a map of the reflectivity of the ventral surface of fixed metastatic mammary adenocarcinoma cells and we have shown that the data are correlated with markers for a focal adhesion adaptor protein. We are modeling the interference of the incident electric field with the field reflected from the ventral surface so as to obtain the surface topography at focal adhesions from the optical phase data.

Real time surface morphology analysis of semiconductor materials and devices using 4D interference microscopy

Recently, 4D microscopy (3D + t) has been demonstrated in confocal, near field, digital holographic and scanning interference microscopy. The last technique is of particular interest to semiconductor materials and device analysis because of its nanometric axial resolution over a large depth of field. In our first prototype system based on scanning white light interferometry we recently demonstrated real time 3D measurement of non-periodic movement at a rate of 5 i/s over 2 μm using a high speed CCD camera (250 i/s) and FPGA based image processing. In the present work we report on a second prototype based on a higher performance CMOS camera having a frame rate of 500 i/s at full frame and up to 16,000 i/s at reduced frame size. Results are shown of a 3D measurement rate of 18 i/s over a depth of 8 μm using post-processing. Different algorithms are being modeled in VHDL for performing the processing on a more complex FPGA based board in real time. It is reasonable to expect 3D image rates of tens and hundreds of images per second depending on the frame size and scanning depth. This will open the way for performing new types of high speed surface morphology characterization in semiconductor materials and device development.

The metrology of a miniature FT spectrometer MOEMS device using white light scanning interference microscopy

Micro-optical electro-mechanical systems (MOEMS) technology, making use of existing silicon based fabrication techniques shows great potential for making complete miniaturized hybrid devices. Such technology has been used to make a Fourier transform spectrometer based on a time-scanning Michelson interferometer. An electrostatic comb drive actuator moves the scanning mirror over a distance of 40 μm. The measured resolution of the spectrometer is 6 nm at a wavelength of 633 nm. The dimensions of the device are 5×5×0.5 mm, and the depth of feature is 75 μm. During quality control of such devices it is necessary to check the dimensions of micron wide structures that are tens of microns deep, over areas of tens of square millimeters. In this work we have investigated the use of white light scanning interference (WLSI) microscopy for making rapid, non-destructive precision three-dimensional measurements. While a high axial precision can be achieved, an artifact has been observed with classical configurations that tend to extend the location of deep step discontinuities by up to 3 μm and so broaden narrow structures. With certain modifications in the optical configuration, this error can be considerably reduced. The results of this work demonstrate that WLSI shows great potential for the rapid and precise quality control of MOEMS devices.

Buried interface characterization by interference microscopy

White light scanning interference microscopy is most commonly used for measuring single air/material surfaces. In this work, the technique has been modified for the non-destructive measurement of interface structures buried under a thick transparent layer. Test samples consisting of step structures (<2 μm) etched in silicon and then covered by a thick layer of photo resist have been studied. The heights of the steps were measured before and after the deposition of the resist layer. Initial measurements of the profile of the buried silicon step through the transparent layer were made with a precision of 9%, the main errors in measurement being due to the degradation of the wavefront as it passes through the layer.

Scanning interference and confocal microscopy

The form of the interference term image in scanning confocal and scanning conventional interference microscopes is identical in all respects including optical sectioning. This observation is used to obtain confocal images and surface profiles from conventional scanning interference microscope images.

Fibre-optical confocal scanning interference microscopy

Fibre-optical confocal scanning interference microscopy is investigated. The interference axial response in a confocal system consisting of either optical fibres or finite-sized pinhole detectors is studied. It is shown that the fringe visibility of confocal interferometry using optical fibres is unity even for finite values of the fibre spot size, while that using pinhole masks is degraded on increasing the pinhole size. The confocal interference axial responses were also measured, revealing good agreements with theoretical predictions.

Quantitative measurement of a phase object by fringe scanning interference microscopy

A simple interference microscope based on a fringe scanning technique is described. This interference microscope can provide quantitative phase information of a phase object. The theory and experimental results are presented.

Changes in dry weight and projected area of human epidermal cells undergoing keratinization as determined by scanning interference microscopy

Cells, obtained from human leg by successive treatments with trypsin, were air dried on microscope slides before mounting in glycerol. Dry weights and projected areas of individual cells were measured using a Vickers M 86 scanning microinterferometer. The dry weights of cells varied from 100 pg for basal cells to 700 pg for large squames. Corresponding projected areas varied from 100 to 1500 mum2.

Preparation of cells from suspensions for correlative scanning electron and interference microscopy.

Neutrophils from bovine milk and blood platelets from dog plasma were washed in PBS, fixed in GA, dehydrated, suspended in a drop on a formvar-coated slide and immediately critical-point-dried in CO2. After coating with Pt-Pd the specimens were examined in an SEM. The same cells were then examined by interferometry (Int) in a light microscope, and the dry mass was determined. It is shown that this preparation method for both types of microscopes (SEM and Int) appears to give adequate results as far as fine surface structure (SEM-appearance) and dry mass determinations (Int) are concerned. The method has the advantage of a more precise characterization of individual particles, than would have been possible, if both methods of microscopy (SEM and Int) had been employed on the same sample, but on different specimens.

Effects of radiation, antibiotics and alkylating agents on cell division and growth in the ciliate Spathidium spathula.

SYNOPSIS. Spathidium spathula is very sensitive to division inhibition after X‐irradiation. Five kr delivered to animals 1 hr into the cell cycle prolong the period until the next division to about 2 times the normal length. The next 2 cell cycles, however, are shorter than normal, and by the 4th division irradiated cells have recovered the normal division rate. During this division delay, scanning interference microscopy shows that growth in dry mass continues; at the 1st post‐irradiation division the cells average 3 times the normal dry mass. After the 2nd post‐irradiation division, dry mass is 1.5 times the normal amount. Dry mass measurements were not made beyond the 2nd division.Giant cells produced by X‐rays have enlarged macronuclei, indicating that DNA synthesis is not inhibited by a dose of X‐rays that blocks division. Mitomycin C and triethylene melamine, agents which attack or damage DNA, also produce division blockage and giantism in Spathidium. This suggests that damage to DNA in either the macronucleus, the micronucleus or other organelles may be much more effective in delaying cell division than cell growth.