Scanning White Light Interferometry Research Articles

Growth kinetics and microstructure of carbon deposited on quartz plates and optical fibers by open-air laser-induced chemical vapor deposition

Pyrolytic carbon has been successfully deposited on fused silica optical fibers and fused quartz plates by open-air laser-induced chemical vapor deposition. Raman spectroscopy, scanning electron microscopy, ion-beam sputtering and scanning white-light interferometry were used to investigate the microstructure, composition and uniformity of the carbon film. The pyrolytic carbon was derived from methane, acetylene, propane and butane precursors. Both the axial and the lateral growth rate and threshold deposition (pyrolysis) temperature of the carbon film deposited on a quartz plate were measured. Knowledge gained from deposition on fused quartz plates was used to determine the deposition conditions on optical fibers. The experimental results indicate that among the different precursors used in this study, only acetylene and propane can be used to deposit pyrolytic carbon on moving optical fibers because their threshold deposition temperature is sufficiently low to prevent fiber softening. The effect of laser power, moving fiber speed and precursor gas on the thickness, deposition rate and microstructure of the carbon layer were studied.

Laser induced local and periodic phase transformations in iron oxide thin films obtained by chemical vapour deposition

Iron oxide films have been deposited on Si(100) substrates by chemical vapour deposition (CVD) of iron(III) tert-butoxide ([Fe(O t Bu) 3] 2) in the temperature range 350–450 °C. The precursor flux and substrate temperature were varied to control the phase composition, average grain size and film thickness. The nature of substrate and deposition temperature markedly influence the morphology and iron-oxygen stoichiometry in the CVD deposits. Phase transformations in iron oxide films were achieved through precise local and periodic heating of the films by interfering laser beams. The interaction of iron oxide films with short laser pulses (Nd:YAG, 355 nm) induced partial transformation of hematite (α-Fe 2O 3) to magnetite (Fe 3O 4) or magnetite to wüstite (Fe 1− x O), respectively. The phase characterization and morphology of the hematite and magnetite films were investigated before and after laser irradiation by X-ray diffractometry, high resolution scanning electron microscopy and white light interferometry.

A micro-displacement stage for scanning white-light interferometry

A one-dimension micro-displacement stage used in scanning white-light interferometry (SWLI) profilometer is presented. The stage is a set of two-grade displacement mechanisms that has a hologram diffraction grating fixed on it to form a closed-loop displacement measuring and control system. The stage's vertical scanning range is up to 6 mm, the vertical resolution 1 nm. Finite element analysis has been used to study the behavior of the flexural hinge guided motion nano-positioning stage. The experimental results of surface profiles of standards sample are also presented.

Self-Affine Surface Morphology of Plastically Deformed Metals

We analyze the surface morphology of metals after plastic deformation over a range of scales from 10 nm to 2 mm using atomic force microscopy and scanning white-light interferometry. We demonstrate that an initially smooth surface during deformation develops self-affine roughness over almost 4 orders of magnitude in scale. The Hurst exponent H of one-dimensional surface profiles initially decreases with increasing strain and then stabilizes at H approximately 0.75. We show that the profiles can be mathematically modeled as graphs of a fractional Brownian motion. Our findings can be understood in terms of a fractal distribution of plastic strain within the deformed samples.

Multi-scale rock surface area quantification—a systematic method to evaluate the reactive surface area of rocks

An integration of methods to quantify the surface area of porous solid materials with a broad span of spatial resolution is presented. The application of it is to detect and quantify the rock surface area modifications caused by fluid–rock interactions on different scales from several nanometres to metres. The new approach is to study the fluid-accessible surface area of rock fragments during dissolution processes.In this paper, diverse methods for surface quantification at different levels of surface detail were adapted for the application of rock surface quantification and porosimetry measurements. The geometric external surface area of rock fragments can be determined by paraffin wax coating and, in special cases, by parallelepiped surface estimations. This geometrical surface area of rock polyhedrons is equal to the macroscopic bounding surface area of a rock volume. Representative surface details on the scale of micrometres to millimetres on geometrical surface area can be quantified by mechanical roughness analyses. The resultant roughness factors are compared to optical roughness quantifications by confocal laser scanning microscopy and white light interferometry and can indicate modifications of the pore space up to several hundred nanometres. The comparison of rock pore space data, measured by both mercury intrusion porosimetry and nitrogen adsorption, quantifies the surface area of pores with a diameter of approximately 2nm.These various surface data at different levels of detail were integrated to get an estimation of this surface area, which affects fluid–rock interactions. The proposed concept has the potential to trace the multi-scale rock surface area evolution in response to fluid–rock interaction processes.The importance of this concept is its application beyond the laboratory survey. For example, additionally to their specific surface area, the reactive surface area of rock particles in a mining dump is controlled by geometrical size and surface roughness of particles.

Description of the Discharge Process in Spark Plugs and its Correlation With the Electrode Erosion Patterns

The phases of the discharges in spark plugs were studied with a high-speed camera and an oscilloscope. The discharges were done using samples of nickel alloys and platinum as cathode in air at pressures ranging from 100 to 900 kPa. For low pressures (100 kPa), a glow discharge occurs after the breakdown. For higher pressures, an arc discharge follows the breakdown and changes into a glow discharge when the current decreases. The damage produced on the cathode surface was analyzed with scanning electron microscopy and white light interferometry and was correlated with the corresponding discharge. The craters on the surface are mainly produced by the breakdown and arc discharge. The glow discharge delivers energy to the cathode in a large area and produces a negligible material damage. The movement of the arc hot spot produces further craters that are commonly overlapped. Transitions from glow to arc modes produce new small craters, which in some cases can be arranged along polishing traces. This work is relevant for the development of new electrode materials for spark plugs and electrical contacts.

Tribology of Cermet/NiCrBSi coatings sprayed by HVOF

This work consists on a deep tribological study of the WX system composed by a mechanical blend in different compositions of NiCrBSi and WC-12Co powders: 20% NiCrBSi (W2), 40% NiCrBSi (W4) y 60% NiCrBSi (W6). The coatings have been obtained by high velocity oxy-fuel process (HVOF). The measurements made by Ball-On-Disk test are: the friction coefficient is lower than 0.5 and the exchanged energy between the counterparts is under 10 KJ. To quantify the friction wear rate, the volume loss and the track depth, Scanning White Light Interferometry and SEM have been used. The track depth is proportional to the amount of NiCrBSi. A higher percentage of WC-12Co increases the friction wear resistance and decreases the abrasion wear rate (Rubber Wheel test). In all the coatings studied, no diffusion processes are found between the mixed phases, the adhesion between the coatings and the substrate is excellent, the porosity level is below 2% and an increase of microhardness of the coating due to a strengthening of the matrix produced by impacts of solid particles, takes place.

Valve cone measurement using white light interference microscopy in a spherical measurement geometry

We describe an interference microscope for valve cone angle, roundness, straightness, and waviness using scanning white light interferometry. Our unusual test geometry creates a spherical optical measurement surface centered at an optical datum point that represents the center of curvature of the mating valve needle or ball. A radial scan locates intersections of the measurement surface with respect to the datum point, and software reconstructs the conical sample surface by means of a calibrated mapping function. This flexible approach accommodates a wide range of cone angles and diameters without a change of optics. Experimental results show promising performance, including a 0.02-μm standard deviation for cone roundness, including sample removal and replacement.

Surface morphology analysis of HgI 2 and PbI 2 with interference microscopy – the challenges of measuring fragile materials and deep surface roughness

The surface morphology of lead iodide and mercuric iodide, materials being developed for use in nuclear detectors, has been measured with interference microscopy. This is not easy, since these materials are soft and brittle and present a large surface roughness (<80 μm), localised regions of thin surface films and in certain cases an evolution of the surface structure over time. These different factors can contribute to errors in the measured position of the surface. We have developed our own automated interference microscopy system, based on scanning white light interferometry and Mirau type interference objectives and adapted it for use on these difficult surfaces. Results are shown of typical signals associated with these materials to illustrate the difficulties. Some initial solutions are proposed for improving measurement accuracy, through careful use of the microscope parameters, improved algorithms and the development of a high speed, low noise, and intelligent CCD camera.

Recycled Wool-Based Nonwoven Material as an Oil Sorbent

The aim of this study was to highlight the possibility of using recycled wool-based nonwoven material as a sorbent in an oil spill cleanup. This material sorbed higher amounts of base oil SN 150 than diesel or crude oil from the surface of a demineralized or artificial seawater bath. Superficial modification of material with the biopolymer chitosan and low-temperature air plasma led to a slight decrease of sorption capacity. Loose fibers of the same origin as nonwoven material have significantly higher sorption capacities than investigated nonwoven material. White light scanning interferometry analysis of the fibers suggested that roughness of the wool fiber surface has an important role in oil sorption. The laboratory experiments demonstrated that this material is reusable. Recycled wool-based nonwoven material showed good sorption properties and adequate reusability, indicating that a material based on natural fibers could be a viable alternative to commercially available synthetic materials that have poor biodegradability.

Surface Integrity in Micro-Hole Drilling Using Micro-Electro Discharge Machining

This paper presents an investigation into the drilling of micro-holes of diameter 0.3 mm in tool steel H13 by means of the Micro-EDM process. Scanning Electron Microscopy (SEM) and Scanning White Light Interferometry (SWLI) techniques are used to determine the influence of the drilling process parameters upon the surface roughness. The results reveal a series of randomly overlapped craters upon the machined surface, which represent the position and chronological sequence of individual sparks during the machining process. As the voltage and current increases, the crater appearance changes from a conical to a cylindrical shape, and its depth and diameter both increase. It is shown that surface roughness deteriorates as the pulse voltage increases. Finally a regression equation is established between the diameter of the crater and the pulse voltage, pulse current and pulse-on duration parameters. This equation enables the diameters of the craters, and hence the surface integrity of the machined surface, to be predicted for a given set of process parameters, and is therefore a valuable tool in achieving the goal of precision machining.

Tribological study of NiCrBSi coating obtained by different processes

Thermal spraying offers a wide range of coatings with very different composition and properties. NiCrBSi is a Ni-base superalloy widely used to obtain high wear resistant coatings. This coating is usually heat treated after thermal spraying to improve their tribological properties. In this work a tribological comparison between NiCrBSi coatings obtained by spray&fuse and as-sprayed coatings obtained by Atmospheric Plasma Spraying (APS) and High Velocity Oxy Fuel (HVOF) spraying is carried out. Ball on Disk (BOD) tests are performed with a martensitic plain steel as counterface and wear parameters are calculated by means of Scanning White Light Interferometry (SWLI). Main wear mechanisms are investigated by the characterisation of the coating wear track and debris using Scanning Electron Microscopy (SEM). It is observed that different wear mechanisms take place in the coatings obtained by the diverse processes.

Role of heat treatments in the improvement of the sliding wear properties of Cr 3C 2–NiCr coatings

Thermal sprayed Cr 3C 2–NiCr coatings are widely used due to their excellent properties such as hardness and wear resistance, even at high temperatures or in corrosive environments. During thermal spraying, oxidation as well as Cr 3C 2 dissolution takes place. The present paper analyses the possibility of improving the sliding wear resistance of these coatings using heat treatments carried out at different temperatures in an inert atmosphere and in an oxidising atmosphere. An enhancement of the sliding wear resistance attributed to the precipitation of Cr 3C 2 is demonstrated. Substantial differences are found in samples treated under the different atmospheres due to the role of the oxides formed on the tribological behaviour of the coatings. Sliding wear tests were carried out using Ball-on-Disk equipment and the wear tracks were studied by scanning electron microscopy and scanning white light interferometry. A relationship between wear damage and energy dissipated during the sliding wear tests is found. In addition, the abrasive wear resistance of the coatings assessed by the Rubber Wheel test is reported.

Use of scanning white light interferometry in the characterization of wear mechanisms in thermal-sprayed coatings

Thermal spray coatings are widely used to reduce wear damage in certain engineering applications. There are several methods of measuring coating wear resistance. Among these, one of the easiest is the combination of the ball-on-disk test with interferometric measurements (noncontact profilometer). The main purpose of this article is to analyze the major wear mechanisms that occur in thermal-sprayed coatings tested under sliding conditions. This work shows how scanning white light interferometry can be easily used to study the wear mechanisms of some coatings, and allows abrasive, adhesive, and fatigue wear mechanisms to be distinguished. The main features of each of these mechanisms observed through the images of the interferometric microscope are reported.

Verification of 2-D MEMS model using optical profiling techniques

This paper describes the application of scanning white light interferometry to profile single layer and multilayer, surface micromachined, micromechanical elements. The measured profile data is used to verify a 2-D finite difference model of device deflection under pressure and electrostatic forces. Devices modelled include pressure sensors, switches and process characterisation structures. The model is designed to include effects such as non-rigid structure supports and stress gradients through the structure. The optical profiling is used to quantify the significance and deflection shape resulting from these effects. The optical profiling has been compared with the AFM profiling and some comparisons are made between these methods.

Theoretical limits of scanning white-light interferometry signal evaluation algorithms

Scanning white-light interferometry is widely used for the microstructure analysis of technical and biological specimens. For each pixel in the focal plane of the apparatus a white-light interferogram is acquired and evaluated by means of an algorithm. We discuss some properties of mathematically optimal evaluation methods and the best possible achievable resolution derived therefrom depending on the setup parameters. A comparison of the results to one of the algorithms described in the literature is given.

Estudio mediante técnicas interferométricas de las propiedades tribológicas de recubrimientos de ZrO&lt;sub&gt;2&lt;/sub&gt; obtenidos por proyección térmica

Thermal barrier coatings have a limited mechanical and tribological properties. The sintering thermal treatments can be used to improve these properties. In the present paper the evolution of some mechanical and tribological properties with different time of sintering at 1000 °C is evaluated. It was observed that the sintering thermal treatment produce an increase of the wear resistance, the hardness and the Young modulus. The Ball on disk tests were done using a sliding pair of ZrO 2 and steel and the main wear mechanisms for each case were studied. It was observed that the intersplat delamination and the brittle fracture where the main wear mechanisms during sliding process. The wear tracks were studied with scanning electron microscopy (SEM) and scanning white light interferometry (SWLI) so as to quantify the wear for each case. It was necessary to do a gold sputtering to increase the electric conductivity and reflection of the ZrO 2 samples for their study by SEM and SWLI respectively.

Buried interface characterization in optoelectronic materials by interference microscopy

Abstract In optoelectronic materials development, the analysis of buried interfaces is sometimes necessary in order to achieve the best optical and electrical performance. Interference microscopy has been investigated as a means to characterize interfaces buried under transparent layers. This technique is typically used at the air/material surface but since it is a non-contacting optical far field technique, it can also be used to measure buried interfaces which are innaccessible by near field scanning probes. We have succeeded in measuring the nanometric roughness of interfaces of porous silicon layers on silicon and of up to three successive buried interfaces in rare earth doped fluoride glass planar waveguides having reflectivities as low as 10−4 using phase stepping microscopy. Errors in the measured roughness values were introduced with increased depth of the interface, due to the distortion of the wavefront passing through the overlying transparent layer. Scanning white light interferometry was also used to measure the depth of the different interfaces in cases where the refractive indices were known to be homogeneous. Further work is required to better understand the origin of errors in the measurements due to the presence of the overlying transparent layers in order to improve the accuracy of the technique.

Evaluation of Wear Damage in Zirconia Plasma-Sprayed Coatings Using Scanning White Light Interferometry

The mechanical and tribological properties of thermal barrier coatings (TBCs) can be improved by means of a thermal treatment. The evolution of the mechanical and tribological properties in a NiCr-ZrO2 TBC with different times of thermal treatment has been measured. In this work, scanning white light interferometry (SWLI) is used to observe and quantify the ZrO2 wear damage. ZrO2 shows very poor light reflection, and a sputtering process over the coating has been made to achieve a proper light reflection and make the use of SWLI possible.

Buried interface characterization in optoelectronic materials by interference microscopy

In optoelectronic materials development, the analysis of buried interfaces is sometimes necessary in order to achieve the best optical and electrical performance. Interference microscopy has been investigated as a means to characterize interfaces buried under transparent layers. This technique is typically used at the air/material surface but since it is a non-contacting optical far field technique, it can also be used to measure buried interfaces which are innaccessible by near field scanning probes. We have succeeded in measuring the nanometric roughness of interfaces of porous silicon layers on silicon and of up to three successive buried interfaces in rare earth doped fluoride glass planar waveguides having reflectivities as low as 10−4 using phase stepping microscopy. Errors in the measured roughness values were introduced with increased depth of the interface, due to the distortion of the wavefront passing through the overlying transparent layer. Scanning white light interferometry was also used to measure the depth of the different interfaces in cases where the refractive indices were known to be homogeneous. Further work is required to better understand the origin of errors in the measurements due to the presence of the overlying transparent layers in order to improve the accuracy of the technique.