Optical Interference Measurements Research Articles

Optical constants of crystalline Bi2Sr2CaCu2O by Brillouin light scattering spectroscopy

Room-temperature optical constants of crystalline Bi2Sr2CaCu2O were determined using data extracted from Brillouin light scattering spectra. Optical extinction coefficient-to-refractive index ratios at a wavelength of 532 nm were obtained from bulk phonon peak linewidth and frequency shift measurements and range from for directions close to the crystallographic c-axis. These ratios, and optical extinction coefficients, absorption coefficients, and imaginary parts of the dielectric function determined from these ratios and known refractive index, are in general agreement with values found in optical reflectance studies, but are 5–7 times larger than those extracted from optical interference measurements.

The effect of moisture on the nonlinearly viscoelastic behavior of an epoxy

The shear and bulk relaxation moduli required to characterize a homogeneous, isotropic, and linearly viscoelastic material were determined using a confined compression experiment and by introducing a new iterative scheme that accounts for the fact that the hoop and radial strains are not step functions. In addition, the coefficients of thermal and hygral expansion of the epoxy being considered were determined along with its diffusive behavior. Fickian diffusion of moisture was confirmed by coupling radial diffusion in an epoxy disk with optical interference measurements of the out-of-plane displacements. These properties are essential components of the modified free-volume model of nonlinear viscoelasticity established by Popelar and Liechti (J. Eng. Mater. Technol. 119:205–210, 1997, Mech. Time-Depend. Mater. 7(2):89–141, 2003). For the nonlinear component of the model, its distortional parameters were evaluated from Arcan pure shear test results at one strain rate and temperature/humidity state. The nonlinear viscoelasticity model was then used to predict the shear stress-strain response under other conditions. The dilatational parameters were extracted from uniaxial tensile test results at one strain rate and temperature humidity state and predictions under other conditions compared favorably with the results from experiments. This exercise adds to a growing list of glassy polymers whose nonlinear stress-strain behavior can be modeled by this modified free-volume model.

Effect of Low-Cycle Fatigue on Fracture Mechanics Parameters According to Speckle Interferometry

Evolution of parameters of fracture mechanics at various stages of low-cycle damage is studied. The developed approach is based on elaboration of optical interference measurements of the deformation response to a small crack length increment. Three sequential symmetrical notches simulate the fatigue crack growth process across the cumulative fatigue damage zone caused by low-cycle fatigue. The values of tangential components of displacement that are measured at several points on cut edges by electronic speckle interferometry are initial experimental information. The coefficients of stress intensity (SIC) and T strains are determined on the basis of the Williams solution. Values of opening and coefficients of stress intensity (SIC) and T strains for cracks of different length with fixed values of preloading cycles Nc equal 0, 100, 1000, 1800, 2500, and 3300 are obtained. The dependences of the parameters of fracture mechanics for cracks of the fixed length on Nc are constructed.

28pm1-F-5 光干渉法を用いた薄膜計測に関する研究 : 表面の反射率分布に起因する油膜厚さの測定誤差

This study presented a measurement error for determining the thickness of thin film lubrication based on optical interference methods. The measurement error is caused by the reflective index distribution on the sliding surface, which is characterized by the profile of the surface. In order to demonstrate the measurement error, two types of model specimens with different surface roughness were prepared. Using these specimens, the optical interference measurements of film thickness were performed. As a result, it was found that the reflective index distribution sometimes acts to underestimate the measurement values of the film thickness. The finding of this study provided a new insight for improving the measurement accuracy of thin film measurement using optical interference methods.

Thermo-Optic Coefficients of 4H-SiC, GaN, and AlN for Ultraviolet to Infrared Regions up to 500 °C

The temperature dependence of the refractive indices of 4H-SiC, GaN, and AlN were determined in a wavelength range from the near band edge (392 nm for 4H-SiC, 367 nm for GaN, and 217 nm for AlN) to infrared (1700 nm) and a temperature range from room temperature to 500 °C. Optical interference measurements with vertical incidence along a c-axis configuration were employed to precisely evaluate ordinary refractive indices. Near the band-edge region, the temperature dependence of the refractive index mainly originates from the temperature change of the bandgap. At 450 nm, the thermo-optic coefficients of 4H-SiC, GaN, and AlN were measured to be 7.8 ×10-5, 1.6 ×10-4, and 3.6 ×10-5 K-1, respectively.

Thermo-Optic Coefficients of 4H-SiC, GaN, and AlN for Ultraviolet to Infrared Regions up to 500 °C

The temperature dependence of the refractive indices of 4H-SiC, GaN, and AlN were determined in a wavelength range from the near band edge (392 nm for 4H-SiC, 367 nm for GaN, and 217 nm for AlN) to infrared (1700 nm) and a temperature range from room temperature to 500 °C. Optical interference measurements with vertical incidence along a c-axis configuration were employed to precisely evaluate ordinary refractive indices. Near the band-edge region, the temperature dependence of the refractive index mainly originates from the temperature change of the bandgap. At 450 nm, the thermo-optic coefficients of 4H-SiC, GaN, and AlN were measured to be 7.8 ×10-5, 1.6 ×10-4, and 3.6 ×10-5 K-1, respectively.

Electric-Field-Controlled Flow in Nanoscale-Thin Wetting Films

A novel nanofluidic system based on electroosmotic flow in nanoscale-thin aqueous wetting films is reported. The water films formed spontaneously on mica substrates in a saturation humidity environment. The film thickness was determined to be a few tens of nanometers by optical interference and fluorescence intensity measurements and was consistent with a theoretical evaluation of the thickness of a film based on the competing forces of electrostatic repulsion and capillary pressure. Lateral flow was induced by applying a dc electric field tangential to the film and characterized by tracking the position of a fluorescent probe. The mobilities of the thin fluid layer and the flow marker were lower than the predictions of the electrokinetic theory, which may be a result of adsorption of the fluorescent molecules to the mica. Confinement of the film to two-dimensional "channels" was achieved by microcontact printing of patterned hydrophobic monolayers onto the substrate. This system has the advantage of simple and inexpensive fabrication in comparison to nanofluidic devices made by traditional lithography techniques.

Determination of the thermo‐optic coefficients of GaN and AlN up to 515 °C

AbstractThe refractive index dispersions of hexagonal GaN and AlN have been investigated to determine the thermo‐optic coefficients. Measurements were conducted at temperatures ranging from room temperature up to 515 °C in the wavelength range from the near band‐edge to 1000 nm. Optical interference measurements with vertical incident configuration were employed to precisely evaluate the ordinary refractive indices. Optical simulation of AlGaN/GaN distributed Bragg reflectors was also carried out by using the obtained thermo‐optic coefficients. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The temperature dependence of the refractive indices of GaN and AlN from room temperature up to 515 °C

The temperature dependence of the refractive indices of GaN and AlN was investigated in the wavelength range from the near band edge (367 nm for GaN and 217 nm for AlN) to 1000 nm and the temperature range from room temperature to 515 °C. Optical interference measurements with vertical incident configuration were employed to precisely evaluate the ordinary refractive indices.

Self-Assembled Monolayers on Mercury Probed in a Modified Surface Force Apparatus

Self-assembled monolayers (SAMs) of three thiol compounds formed on mercury are investigated by a combination of cyclic voltammetry, electrocapillary curves, and a novel method of measuring electrical double-layer properties. The last method involves a modified surface force apparatus in which a flat mica surface is pressed down toward a fixed mercury drop held beneath it, while both are immersed in aqueous electrolyte solution. Optical interference measurements are made of the mica-mercury separation as a function of electrical potential applied to the mercury, which yields information on the double-layer interaction between the two surfaces. Mercury is decorated by SAMs of 11-mercapto-1-undecanoic acid, which is shown to bring negative charge to the mercury/aqueous interface due to dissociation of the carboxylic acid groups; 11-mercapto-1-undecanol, which although it is uncharged changes the dipole potential of the interface; and 1-undecanethiol, which likewise changes the dipole potential, but by a different amount. The difference between the changes in dipole potential (90 mV) can be related to the different terminal groups of these two SAMs, -CH3 compared to -OH, that are in contact with the aqueous phase.

Ultrasonic measurement of film thickness in mechanical seals

Measurement of the interface film thickness of mechanical seals has been of interest to researchers and industry for many years. This feature describes work to measure the liquid film using a novel ultrasonic approach with a view to developing a condition monitoring tool. Initial tests were based on a laboratory simulation, to compare the method with optical interference and capacitance measurements. Tests were then carried out on a seal test rig. Film thickness was successfully recorded as speed and load was varied.

Secondary ion mass spectrometry backside analysis of barrier layers for copper diffusion

Secondary ion mass spectrometry (SIMS) backside analyses have been performed on a Cu/TaN/Ta/SiO2/Si structure to determine barrier effectiveness for Cu diffusion. Sample backside access to the barrier layers was obtained by removal of the Si substrate using a polishing method that maintains parallelism between the sample surface and the polished back side by monitoring changes in facets at the four corners of the specimen. Determination of the Si thickness remaining during the polishing process was improved through the use of optical interference measurements using a narrow band pass optical filter. Samples having slopes with respect to the original surface less than 6 nm over 60 μm have been obtained. A difference in polishing rate between SiO2 and Si was exploited to obtain this parallelism. For SIMS analyses, the presence of a SiO2 layer required electron gun charge neutralization for the O2+ 0.5 keV impact energy analysis. SIMS analyses show the ability to distinguish all layers and to monitor copper through the barrier material. With the high depth resolution conditions used, SIMS analyses were able to provide detailed elemental distribution information such as the presence of nitrogen at specific interfaces.

Electric-field-induced rupture of polymer-stabilized oil films

Water-in-oil emulsions stabilized by polymeric surfactants are robust, but the reasons for their stability are poorly understood. We studied oil films stabilized by a comb–graft copolymer having a poly(siloxane) backbone and poly(ethylene oxide)/poly (propylene oxide) and C16 grafts (Abil EM-90) with a total number-average molecular weight of 62,000. Electric fields imposed in the aqueous phases on either side of the oil films were used to induce rapid rupture, and the response of the film was monitored using optical interference and electrical conductance measurements. Film thickness values ranged between 30 and 50 nm and rupture at field strength values between 2 × 107 and 5 × 107 V/m. Unexpectedly, in some cases, stable pores were formed and the films became electrically conductive. Often the pores persisted for more than 20 min after the voltage had been removed. Since the current was independent of film area, very few pores are involved in conduction. This behavior is similar to that found in lipid films; however, the persistence time is greater for polymer-stabilized films. Because the films are thick, it is possible that pores are formed by multimolecular self-assembly as with pore-forming proteins. Polymer purification also influenced film stability.

Measurement of saturation magnetostriction using novel strained substrate techniques and the control of the magnetic anisotropy

A simple new technique is described for the measurement of saturation magnetostriction in thin films deposited onto rigid substrates. The method is based on mechanically introducing a small curvature in the substrate either during the deposition (strained growth) or post-deposition. The strain-induced anisotropy is measured using the magneto-optical Kerr effect. Quantification of the film strain is obtained using optical interference and stylus measurements; coupled with mechanical finite-element modelling, this allows the saturation magnetostriction to be determined. No information about the mechanical properties of the substrate is required, and providing that the Young's modulus of the film is known accurately, the values of magnetostriction obtained are accurate and absolute. It is envisaged that the technique could be applied to a wide variety of films deposited onto commercially important substrates. Here, it is applied to amorphous films based on the METGLAS ® 2605SC composition deposited onto glass and silicon substrates. A high degree of control is also demonstrated in tailoring the anisotropy field, by the technique of substrate straining.

Texture and stress profile in thick polysilicon films suitable for fabrication of microstructures

In this paper we report on results concerning the texture and mechanical stress of thick polycrystalline silicon films, grown in an epitaxial reactor. These phosphorus doped films were subjected to different annealing treatments at temperatures at or above 1100 °C in nitrogen and oxygen ambients, respectively. The morphology and texture of the films, respectively, were obtained using TEM and X-ray diffraction analysis. The samples texture does not present any significant changes related to the used annealing treatment. The stress gradient of released micromachined test structures was determined with optical interference measurements and compared with -Raman spectroscopy stress profiles and X-ray diffraction stress data using the sin 2÷-method obtained at different depths. We show that annealing in oxygen changes the stress state in the top regions of the polycrystalline films to a more compressive value, thus causing released beams to bend downwards. On the contrary, annealing in nitrogen atmosphere shifts the stress towards tensile values and released beams bend upwards.

H2O Condensation Coefficient and Refractive Index for Vapor-Deposited Ice from Molecular Beam and Optical Interference Measurements

The condensation of H2O on ice multilayers on Ru(001) was studied using both molecular beam and optical interference techniques as a function of surface temperature. From the beam reflection technique, the H2O sticking coefficient, S, was determined to be S = 0.99 ± 0.03 at temperatures between 85 and 150 K and was independent of incident angle (0−70°) and beam energy (1−40 kcal/mol). The condensation coefficient, α, was dependent on both the incident H2O flux and the desorption H2O flux at the various surface temperatures. The magnitude of α varied continuously from unity at T < 130 K to zero at higher temperatures. The optical interference experiments yielded condensation coefficients and sticking coefficients of α = S = 0.97 ± 0.10 at temperatures from 97 to 145 K where the H2O desorption flux was negligible with respect to the incident flux. The optical interference measurements monitored the ice film thickness versus H2O exposure time and were dependent on the refractive index, n, and the density, ρ,...

Real refractive indices of infrared‐characterized nitric‐acid/ice films: Implications for optical measurements of polar stratospheric clouds

The infrared spectra of nitric‐acid/ice films representative of polar stratospheric clouds (PSCs) were collected with simultaneous optical interference measurements to determine the real refractive indices at λ = 632 nm. Ice and amorphous nitric‐acid/ice films were prepared by condensation of water and nitric acid vapors onto a wedged Al2O3 substrate. The real refractive indices of these films were determined from the optical interference of a reflected helium‐neon laser during film growth. The indices of the amorphous films varied smoothly from n = 1.30 for ice to n = 1.49 for nitric acid, similar to observations in previous work. We were unable to obtain the refractive index of crystalline films during adsorption because of optical scattering caused by surface roughness. Therefore crystalline nitric acid hydrate films were prepared by annealing amorphous nitric‐acid/ice films. Further heating caused desorption of the crystalline hydrate films. During desorption, the refractive indices for ice, NAM (nitric acid monohydrate), α‐ and β‐NAT (nitric acid trihydrate) films were measured using the optical interference technique. In agreement with earlier data, the real refractive indices for ice and NAM determined in desorption were n = 1.30±0.01 and n = 1.53±0.03, respectively. The real refractive indices for α‐ and β‐NAT were found to be n = 1.51±0.01 and n ≥ 1.46, respectively. Our measurements also suggest that the shape of crystalline nitric acid particles may depend on whether they nucleate from the liquid or by vapor deposition. If confirmed by future studies, this observation may provide a means of distinguishing the nucleation mechanism of crystalline PSCs.

Asymmetric Shielding in Interfacial Fracture Under In-Plane Shear

The toughness of a glass/epoxy interface was measured over a wide range of mode mixes. A toughening effect was associated with increasing positive and negative inplane shear components. Optical interference measurements of normal crack opening displacements near the crack front and complementary finite element analyses were used to examine near-front behavior during crack initiation. Estimates of the toughening based on plastic dissipation, bulk viscoelastic dissipation, and interface asperity shielding did not fully account for the measured values. The results suggest that the inelastic behavior of the epoxy, frictional, and, perhaps, three-dimensional effects should be considered.

Crack‐Tip Transformation Zones in Toughened Zirconia

Transformation zones surrounding cracks in several toughened magnesia‐partially‐stabilized zirconia ceramics are characterized by optical interference measurements of surface uplift and by Raman microprobe spectroscopy. The measurements demonstrate that the volume fraction of transformation is nonuniform within the zone and that the extent of the frontal zone is approximately the same as that of the wake. Results are used to evaluate the crack‐tip shielding stress intensity factor and to compare with the measured fracture toughness.

High Resolution Optical Interference Measurements of Changes in Bond-Line Thickness—A Review

Abstract A novel moire optical interference method, originally developed1 to measure the swelling displacement normal to the plane of a simple butt joint during water uptake at the joint edge, was subsequently used to investigate the unexpected occurrence of shrinkage and, at the same time, swelling during exposure to organic solvents. In later experiments, synergistic displacement fields generated during simultaneous exposure to water and organic solvents were studied. The same method has also been used to investigate the origin of adhesion failures at copper plated-through holes in thermally cycled multi-layer circuit boards. The method employs a thin glass cover slip as one adherend. Changes in bondline thickness flex the cover slip thereby changing the gap between the latter and a nearby optical flat. By using monochromatic light to illuminate the specimen, interference between incident and reflected light is achieved. The small displacements of individual fringes associated with changes in gap size are used to generate moire patterns which bear a 1:1 relationship to the local changes in bondline thickness. Application of thin plate elasticity theory to the flexing of the cover slip yields the stress acting normal to the joint. The magnitude of this normal stress is strongly inhomogeneous, oscillating in sign and reaching compressive values as high as 50MNm−2 for water uptake by a simple butt joint, and exceeding the yield strength of oxygen-free high conductivity copper (1MNm−2) for the thermal expansion that accompanies simulated soldering of a multi-layer circuit board. Attention is drawn to the high resolution achievable with the method. Changes in bond-line thickness of the order of Δ/10, where Δ is the wavelength of the light giving rise to the interference pattern, are readily resolved. It is pointed out that the method may well be sufficiently sensitive to detect the effects of different physical properties (thermal conductivity, specific heat capacity) of adherend surface on the nature of the cured adhesive and hence on the mechanical behaviour of the bond-line.