Measurement of surface resistivity/conductivity of metallic alloys in aqueous solutions by optical interferometry techniques

Optical interferometry techniques were used for the first time to measure the surface resistivity/conductivity of the pure aluminium (in seawater at room temperature), UNS No.304 stainless steel (in seawater at room temperature), and pure copper (in tap water at room temperature) without any physical contact. This was achieved by applying an electrical potential across the alloys and measuring the current density flow across the alloys, during the cyclic polarization test of the alloys in different solutions. In the mean time, optical interferometry techniques such as holographic interferometry were used in situ to measure the orthogonal surface displacement of the alloys, as a result of the applied electrical potential. In addition, a mathematical model was derived in order to correlate the ratio of the electrical potential to the current density flow (electrical potential/electronic current flow = resistance) and to the surface (orthogonal) displacement of the metallic samples. In other words, a proportionality constant (surface resistivity or conductivity = 1/surface resistivity) between the measured electrical resistance and the surface displacement (by the optical interferometry techniques) was obtained. Consequently the surface resistivity (ρ) and conductivity (σ) of the pure aluminium (in seawater at room temperature), UNS No.304 stainless steel (in seawater at room temperature), and pure copper (in tap water at room temperature) were obtained. Also, electrical resistivity values (ρ) from other source were used for comparison sake with the calculated values of this investigation. This study revealed that the measured value of the resistivity for the pure aluminium (7.7 × 10¹⁰ Ω cm in seawater at room temperature) is in good agreement with the one found in literature for the aluminium oxide, 85% Al₂O₃ (5 × 10¹⁰ Ω cm in air at temperature 30 °C). Unfortunately, there is no measured value for the resistivity of cupric oxide (CuO), cuprous oxide (Cu₂O), or even the oxide of the UNS No.304 stainless steel in literature comparing those values with the measured values in this study.     

Electrochemical impedence spectroscopy versus optical interferometry techniques during anodization of aluminium

In the present investigation, holographic interferometry was utilized for the first time to measure in situ the thickness of the oxide film, alternating current (AC) impedance, and double layer capacitance of aluminium samples during anodization processes in aqueous solution without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out by the electrochemical impedance spectroscopy (EIS), in different concentrations of sulphuric acid (1.0–2.5% H₂SO₄) at room temperature. In the mean time, the real-time holographic interferometric was used to measure the thickness of anodized (oxide) film of the aluminium samples in aqueous solutions. Also, mathematical models were applied to measure the AC impedance, and double layer capacitance of aluminium samples by holographic interferometry, during anodization processes in aqueous solution. Consequently, holographic interferometric is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film, the AC impedance, and the double layer capacitance of the aluminium samples can be determined in situ. In addition, a comparison was made between the electrochemical values obtained from the holographic interferometry measurements and from measurements of EIS. The comparison indicates that there is good agreement between the data from both techniques.     

Review of surface profile measurement techniques based on optical interferometry

With the fast development of modern science and technology, two or three-dimensional surface profile measurement techniques with high resolution and large dynamic range are urgently required. Among them, the techniques based on optical interferometry have been widely used for their good properties of non-contact, high resolution, large dynamic measurement range and well-defined traceability route to the definition of meter. A review focused on surface profile measurement techniques of optical interferometry is introduced in this paper with a detailed classification sorted by operating principles. Examples in each category are discussed and analyzed for better understanding.     

Measurement of surface resistivity/conductivity of different organic thin films by a combination of optical shearography and electrochemical impedance spectroscopy

Shearography techniques were applied again to measure the surface resistivity/conductivity of different organic thin films on a metallic substrate. The coatings were ACE premium-grey enamel (spray coating), a yellow Acrylic lacquer, and a gold nail polish on a carbon steel substrate. The investigation was focused on determining the in-plane displacement of the coatings by shearography between 20 and 60 °C. Then, the alternating current (AC) impedance (resistance) of the same coated samples was determined by electrochemical impedance spectroscopy (EIS) in 3.0% NaCl solution at room temperature. As a result, the proportionality constant (resistivity or conductivity = 1/surface resistivity) between the determined AC impedance and the in-plane displacement was obtained. The obtained resistivity of all investigated coatings, 40:15 × 106–24:6 × 109Ωcm, was found in the insulator range.     

Measurement of the double layer capacitance of aluminium samples by holographic interferometry

In the present investigation, holographic interferometry was utilized for the first time to measure the double layer capacitance of aluminium samples during the initial stage of anodization processes in an aqueous solution without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out chemically in different sulphuric acid concentrations (0.5–3.125% H₂S0₄) at room temperature. In the meantime, a method of holographic interferometry was used to measure the thickness of anodization (oxide film) of the aluminium samples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the double layer capacitance of the aluminium samples in solutions to the thickness of the oxide film of the aluminium samples which forms due to the chemical oxidation. The thickness of the oxide film of the aluminium samples was measured by real-time holographic interferometry. Consequently, holographic interferometry is found to be very useful for surface finish industries, especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film as well as the double layer capacitance of the aluminium samples can be determined in situ. In addition, a comparison was made between the obtained data of the double layer capacitance from the holographic measurements and the double layer capacitance data obtained from measurements of electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data from both techniques.     

Fine structure in the optical conductivity of aluminium

Accurate measurements of the optical conductivity of aluminium reveals fine structure in the range 2–2.5 eV. We show that this can be accounted for by a 4-band model.     

Measurement of the a.c. impedance of aluminium samples by holographic interferometry

In the present investigation, holographic interferometry was utilized for the first time to measure the alternating current (a.c.) impedance of aluminium samples during the initial stage of anodization processes in aqueous solution without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out chemically in different sulphuric acid concentrations (0.5–3.125% H₂SO₄) at room temperature. In the mean time, a method of holographic interferometric was used to measure the thickness of anodization (oxide film) of the aluminium samples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the a.c. impedance of the aluminium samples in solutions to the thickness of the oxide film of the aluminium samples which forms due to the chemical oxidation. The thickness of the oxide film of the aluminium samples was measured by the real-time holographic interferometry. Consequently, holographic interferometry is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film as well as the a.c. impedance of the aluminium samples can be determined in situ. In addition, a comparison was made between the a.c. impedance values obtained from the holographic interferometry measurements and from measurements of electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data from both techniques.     

Measurement of ultrashort optical pulses by two-photon photoconductivity techniques

Two-photon conductivity in GaAs and CdS_0·5Se_0·5 were investigated with modelocked Nd:glass laser pulse excitation, with a view to determine their suitability for picosecond pulsewidth measurement. The contrast ratio using GaAs as twophoton conductor was 1.8 and it increased to 2.4 when CdS_0·5Se_0·5 was used. The improved contrast ratio in the case of CdS_0·5Se_0·5 was partly due to the improved resolution of the crystal (2 ps) and partly due to the extended square-law region.     

Oligonucleotide hybridization observed by surface plasmon optical techniques

Surface plasmon spectroscopy and microscopy are employed to study the hybridization reaction of an oligonucleotide ten-mer from solution to its complement immobilized to a solid support. It is shown that a dilute target monolayer is necessary to allow for an effective dimerization process. Parallel multi-site detection of the DNA binding is demonstrated to be possible with surface plasmon microscopy without the need for any extra labeling of the reaction partners. The simultaneous quantitative evaluation of the degree of dimerization to many different target areas, each as small as a few μm² and each functionalized by different oligonucleotide sequences, can be accomplished by two-dimensional image analysis and should be relevant for DNA sequencing protocols.     

Measurement of the corrosion rate of aluminium in sodium hydroxide using holographic interferometry

The application of holographic interferometry to the measurement of the corrosion rate of aluminium in sodium hydroxide is investigated. Details of the fabrication of the corrosion cell and the experimental procedure are given. Thickness loss of aluminium was found for different dissolution times and compared with the conventional weight-loss method using a microbalance.     

Measurement of complex surface deformation by high-speed dynamic phase-stepped digital speckle pattern interferometry

We describe a high-speed digital speckle pattern interferometer incorporating a line-scan camera and a waveguide phase modulator for the measurement of complex deformation (vibration phase and amplitude) at audio acoustic frequencies. Experimental data show continuous phase-stepped recovery of out-of-plane surface deformation in one dimension, obtained at 100 kHz with 2pi/20-rad (0.02-mum) displacement resolution, for surface velocities of 3.2 mm s>(-1) .     

Surface resistivity/conductivity of different organic-thin films by a combination of optical shearography and electrochemical impedance spectroscopy

Optical shearography and electrochemical impedance spectroscopy (EIS) were used for the first time to measure the surface resistivity/conductivity of different organic-thin films. Different organic coatings i.e., ACE Premium-gray, white, and beige Enamels (spray coatings), on a metallic alloy, i.e., a carbon steel, were investigated at a temperature range between 20–60 °C. The investigation focused on determining the in-plane displacement of the coatings with respect to the applied temperature range by optical shearography. Then, the AC impedance (resistance) of the same coated samples was determined by the technique of EIS in 3.5% NaCl solution at room temperature. In addition, a mathematical model was developed in order to obtain a proportionality constant (surface resistivity = ρ or conductivity = 1/ρ) between the determined AC impedance and the in-plane displacement. The obtained values of ρ of all investigated coatings, 0:25 × 10⁸–0:27 × 10¹⁰ Ωcm was found in the insulator range.     

Measurement of refractive index variation of liquids by surface plasmon resonance and wavelength-modulated heterodyne interferometry

In this study an alternative method based on surface plasmon resonance is proposed for in-situ monitoring of variation in the refractive index of a test sample. A wavelength-modulated light source and an unequal-path-length optical configuration heterodyne interferometer are used to detect the phase difference change, which can then be used to estimate the change in the refractive index of a test sample. The experimental results demonstrate a phase stability of 0.02°. The resolution power of the refractive index is 1.5 × 10^− 6 RIU. This method has several advantages over previously used methods such as simple optical setup, easier operation in real time, and low cost.     

Measurement error in laser interferometry caused by free convective boundary layers on optical windows

When convective heat transfer measurements are made using a laser interferometer, optical windows are often used to separate the test fluid inside the experimental model from the ambient air. In the present study, the measurement error caused by the thermal boundary layers that form on the exterior surfaces of the optical windows has been analyzed. A convenient analytical expression for the error in the fringe gradient has been derived, using the two-dimensional similarity solution for laminar free convective flow. For typical experimental conditions this source of bias error was found to be generally small, except near the leading edge of the thermal boundary layer. Based on the results, it is recommended that the measurement region be at least five centimeters away from the leading edge of these external thermal boundary layers.     

超光滑光学表面粗糙度的测定

讨论了如何确定及消除光学轮廓仪的系统误差,进而测定超光滑光学表面粗糙度的方法及结果。在Ｚｙｇｏ Ｍａｘｉｍ ３Ｄ５７００ 表面轮廓仪上使用２－５ ×和２０ ×Ｍｉｒａｕ 物镜测量ｒｍｓ 在０－３ｎｍ 左右的超光滑硅片,通过对每个取样区域数据１６ 次相位平均,再对多个取样区域高度数据平均,消除了仪器的系统误差,使超光滑光学表面粗糙度得到精确测量。并使用其它光学轮廓仪对样品做了验证测量。作为比较,在同样条件下测量了０－８ｎｍ 左右的光滑硅片。     

The effect of surface roughness on fringe visibility in optical interferometry

A review of theoretical results expressing the fringe visibility as a function of the r.m.s. surface roughness of the test piece for several types of interferometer is presented. Michelson, Fresnel mirror, shearing, holographic, and dual wavelength holographic interferometers are considered. The results for each of these arrangements are compared in terms of a common variable, that is the effective wavelength or contour separation. Results compare well in most cases considered.

The preliminary calibration of the visibility of contour fringes observed in a dual index holographic interferometer with respect to the surface roughness of the object is also described. This experiment demonstrates that, following a more extensive calibration, surface roughness over a very wide range can be measured using the latter technique.

The authors' main interest in these techniques is related to the simultaneous measurement of wear and surface roughness. A demonstration example of this type of measurement is also shown.     

Measurement of trench depth by infrared interferometry

Measurement and control of high-aspect-ratio structures such as dynamic random-access memory trenches is an important step in the manufacture of modern memory devices. We present a novel technique based on infrared interferometry that has been implemented in manufacturing and is capable of measuring sub- 0.25-mum -wide and 10-mum -deep trenches nondestructively and with an accuracy of better than 0.1mum .     

Measurement of surface roughness properties by means of laser speckle techniques

The statistical properties of speckle intensity variations produced by coherent light in the far-field diffraction plane of an iluminated area of an object are studied experimentally as a function of the radius of an illuminating beam over the object and are found to have a relation to its surface roughness and correlation lenght. Measurements of the surface roughness and the correlation lenght become possible by investigating the contrast variation of the speckle intensity as a function of the radius of the illuminating beam.