Determination Of Layer Thickness Research Articles

Determination of Layer Thicknesses by Total Electron Yield MeasurementsSubstrate Method

Determination of Layer Thicknesses by Total Electron Yield MeasurementsSubstrate Method

Comparison of Road Mix and Plant Mix Cement-Treated Aggregate Base Course

A study was undertaken to determine the advantages of plant mix over road mix cement-treated aggregate base course (CTABC). Ten projects known to have cement-treated base course were selected. Each had been tested with a falling-weight deflectometer and had been cored to determine layer thicknesses and properties either in the past or as part of the current effort. Three possible benefits were considered: improved uniformity of material properties, reduced deflections, and increased strength or stiffness. Neither the coefficient of variation nor a developed uniformity coefficient showed a significant difference between plant mix and road mix. Plant mix resulted in lower average deflections and lower deflections when sites were compared with equal thicknesses of asphalt above the base course. However, road mix sites had higher compressive strengths than did plant mix sites. Backcalculated moduli for CTABC were higher for plant mix than for road mix, but the elastic moduli were similar for plant and road mix when determined by pulsevelocity testing. It was concluded that no clear benefit could be determined from using plant mix based on the sample of 10 projects, although the benefit of an adequate thickness of asphalt above the CTABC was clearly demonstrated.

An in-line diffuse reflection spectroscopy study of the oxidation of stainless steel under boiling water reactor conditions

A novel cell unit was constructed to measure in-line the oxide layer build-up on a stainless steel sample by Diffuse Reflection Spectroscopy (DRS; ultraviolet, visible, near infrared) under boiling water reactor (BWR) conditions. The stainless steel samples, observed in the cell through a sapphire window, are contacted with oxidising hot water (300 °C, 9.0 MPa). Using a cold finger with the optical fibre probe, the spectroscopic investigations (200–1000 nm wavelength) were performed at a fixed position from the sapphire window. The DRS spectra are the result of the coupling of both absorption (chemical) and interferometric (physical) processes. Analysis of these spectral components allows the independent determination of the oxide layer thickness. The build-up of the oxide layer may be directly observed and quantified, nanometre by nanometre, from 2 to 200 nm. This powerful technique may be used to study the early corrosion rates of stainless steel under BWR conditions and should allow the development of a strategy to reduce corrosion.

Structural and optical characterization of InP/GaxIn1−xAsyP1−y quantum wells and interfacial layers

Several multiquantum wells of InP/GaxIn1−xAsyP1−y grown by chemical-beam epitaxy have been studied by high-resolution x-ray diffraction, low-temperature photoluminescence, and Raman scattering to characterize interfacial layers between the barriers and the wells. These interfacial layers are created during the initial stage of growth of the quaternary material as a result of the longer transient for the saturation of the group-III elements flux. The combination of x-ray diffraction and photoluminescence allows a precise determination of the interfacial layer thickness and composition grading and shows that interface roughness is of the order of 1 monolayer. Raman scattering confirms these results and is used to determine values of the sound velocity and of the index of refraction in the quaternary alloy material.

Refractive index and layer thickness of an adsorbing protein as reporters of monolayer formation

A method is presented for a separate real-time determination of refractive index and layer thickness of an adsorbing thin layer. The changing angular deflections of TE and TM modes in a dedicated planar waveguide structure are measured. A resolution of 0.01 in the refractive index and 0.5 nm in the average thickness is obtained. The method is illustrated with experimental results on the binding of an antibody to the substrate, both in a physisorption and in an immunoreaction. In the latter, results are consistent with an end-on binding of the antibody to the surface.

Effects of acidic conditioners on dentine demineralization and dimension of hybrid layers

Objectives: This study was aimed at investigating the relationships between dentine conditioning for different durations with different acids and (1) the resulting depth of dentinal demineralization and (2) the rebounding capacity of collapsed collagen due to primer and adhesive resin penetration. Methods: Two commercial and four experimental acids were tested directly by light microscopic evaluation of the depth of decalcification of dentine, and indirectly by determination of the hybrid layer thickness and the total depth of demineralization effects on perpendicular sections through Gluma bonded composite resin specimens. Results: Depths of demineralization increased by both acid concentrations and conditioning times following a logarithmic relationship. There was good agreement between the results of the direct and the indirect procedures. Thirty seconds' conditioning with 20% phosphoric-acid gel resulted in 10-μm hybrid layer thickness. This 20% compound was considered a suitable compromise as a uni-etch conditioner since 30-s etch duration also generated an effective enamel retentive pattern and at the same time a frosted enamel appearance for visual control of extent and efficacy of enamel conditioning.

OnLine Raman Analysis of Molecular Beam Epitaxial Growth

Raman scattering is discussed as a tool for on-line monitoring the molecular beam epitaxial (MBE) growth of semiconductor-based multilayer systems. Compared with reflection high-energy electron diffraction (RHEED), the advantages of Raman scattering are the chemical information (stoichiometry) and the possibility of temperature and layer thickness determination. For quantitative analysis, the equations to evaluate the Raman scattering intensities in a multilayer stack of absorbing materials under oblique incidence are given. As an application of in situ on-line Raman scattering, the monitoring of ZnSSe growth by molecular beam epitaxy on GaAs(100) and the formation of a buried InSb reaction layer at the indium/antimony heterointerface are presented.

A direct method of calculating interval velocities and layer thicknesses from wide-angle seismic reflection times

Wide-angle reflections are now routinely recorded in high resolution explosion seismics to study the crustal structure. Use of Dix's hyperbolic approximation to the nonhyperbolic wide-angle reflection travel times causes major errors in the determination of interval velocities and layer thicknesses of a stack of horizontal velocity layers. Here we propose a layer stripping method to directly calculate the interval velocities and layer thicknesses in a vertically heterogeneous earth from the strong and reliable wide-angle reflected events. Synthetic reflection travel times, at wide-angle range, for a given velocity model, contaminated by some random errors, have been used to demonstrate the reliability of the algorithms to determine the interval velocities and thicknesses of various layers. The method has also been tested on two field examples along two deep seismic sounding (DSS) profiles with well identified wide-angle reflection travel times, which illustrates the practical feasibility of the proposed method.

High-resolution x-ray diffraction of self-organized InGaAs/GaAs quantum dot structures

The structural properties of highly strained buried InxGa1−xAs layers on GaAs substrates are investigated by high-resolution x-ray diffraction. Such layers of a few monolayers in thickness serve for the formation of self-organized quantum dots by the Stranski–Krastanow growth mode. Exceeding a critical layer thickness the growth mode changes from two-dimensional Frank–van der Merwe to the three-dimensional Stranski–Krastanow mode resulting in the formation of coherently strained InxGa1−xAs islands. X-ray spectra of such structures below the growth mode transition can be perfectly simulated using dynamical theory allowing for determination of layer thickness with submonolayer sensitivity and composition within 5%. Dot formation manifests itself in a decrease of the effective In content of the wetting layer.

Stability of geosynthetic-reinforced soil above a cavity

Geosynthetic-reinforced soils have been used for bridging cavities. At present there is no generally accepted method for analyzing the stability of soil-geosynthetic-cavity systems. This paper presents methods of analysis as well as parameter interrelationships for the determination of reinforced soil layers thickness and anchor length. Four different methods of layer thickness analysis are presented: they are Giroud's method, the multi-layer method, ultimate strength method and strain-dependent strength method. Of these four methods, the strain-dependent strength method is more rational and is adopted for development of interrelations among parameters having a dominant effect on the stability of a reinforced soil layer overlying a cavity. The parameter interrelations are presented graphically. These graphs are useful not only for the determination of layer thickness and anchor length, but also for evaluating the stability of existing soil-geosynthetic-cavity systems.

MEASUREMENT OF LAYER THICKNESS AND ESTIMATION OF AS-BUILT BULK DENSITY AND VOID POROSITY IN A ROCK ARMOUR REVETMENT AT BEESANDS, SOUTH DEVON.

Results of the measurement of the as-built parameters of armour layer thickness coefficient, bulk density and void porosity of a double-armour layer rock revetment constructed at Beesands, South Devon, during 1992 are presented. Using a number of different surface profile surveying techniques for the determination of armour layer thickness (corresponding to different site practices) layer thickness coefficients, bulk densities and void porosities were calculated and compared for the section studied.

Dielectric reference coatings for the evaluation of thin film characterization techniques

Thin film technology has an increasing demand for industrial reliable characterization techniques. A precise absolute determination of layer thickness, interface width and the quantification of depth profiles in dependence on resolution limits of the measurement are required. Certified reference materials, certified reference coatings (CRCs) and non-destructive evaluation techniques can meet these requirements. Dielectric reference coatings (SiO 2, Si 3N 4) were used for metallographic preparation (e.g. bevelled cross-sections), optical characterization techniques (e.g. spectroscopic ellipsometry (SE)), and films of SiO 2, Si 3N 4 and Al 2O 3 were applied to reference measurements in depth profiling of layer stacks (e.g. radio frequency glow discharge optical emission spectroscopy). Thickness and refractive index of these dielectric single-and multilayer coatings on different substrate materials are accurately determined in advance by means of SE. These values are subsequently used for precise angle determination of bevelled cross-sections, for reference and re-calibration purposes in thin film characterization (system reproducibility) and in surface analysis (determination of sputter and erosion rates, depth profiles). Examples are discussed for different applications and the calculated data are compared with experimental results. It is shown that reproducible commercial coatings are also of importance for use as CRCs.

X-Ray Fluorescence and Reflectivity Analysis of Multiple-Layer Thin Films

The use of X-ray fluorescence and reflectivity techniques for the characterization of the layer structures of multiple-layer thin films is described. The X-ray fluorescence technique is used for the precision determination of composition and layer thicknesses of two triple-layer NiFe, Cu, and Cr thin films. The X-ray reflectivity technique is used to determine the values of layer thickness, density, and roughness of a six-layer Ta/FeMn/NiFe/Cu/NiFe/Ta thin film. Both X-ray fluorescence and reflectivity techniques are used for the analysis of two Au/NiFe multilayers. The results showed that the X-ray fluorescence and reflectivity techniques are complimentary. The use of both techniques for layer-structure determinations improves the reliability of the analysis.

Determination of accurate metal silicide layer thickness by RBS

Rutherford Backscattering Spectrometry (RBS) is a proven useful analytical tool for determining compositional information of a wide variety of materials. One of the most widely utilized applications of RBS is the study of the composition of metal silicides (MSi x ), also referred to as polycides. A key quantity obtained from an analysis of a metal silicide is the ratio of silicon to metal ( Si M ). Although compositional information is very reliable in these applications, determination of metal silicide layer thickness by RBS techniques can differ from true layer thicknesses by more than 40%. The cause of these differences lies in how the densities utilized in the RBS analysis are calculated. The standard RBS analysis software packages calculate layer densities by assuming each element's bulk densities weighted by the fractional atomic presence. This calculation causes large thickness discrepancies in metal silicide thicknesses because most films form into crystal structures with distinct densities. Assuming a constant layer density for a full spectrum of Si M values for metal silicide samples improves layer thickness determination but ignores the underlying physics of the films. We will present results of RBS determination of the thickness various metal silicide films with a range of Si M values using a physically accurate model for the calculation of layer densities. The thicknesses are compared to scanning electron microscopy (SEM) cross-section micrographs. We have also developed supporting software that incorporates these calculations into routine analyses.

A study of thin buried layers in IIl-V compound heterostructures by high-resolution X-ray diffraction

A new method based on X-ray interference for the characterization of extremely thin buried single layers by means of high-resolution X-ray diffraction is presented. The independent determination of layer composition and thickness is obtained by comparing measurements performed in at least two different settings, one of which in the asymmetric grazing emergence geometry. The method is applied to study In segregation in InAs/GaAs monolayers grown by molecular beam epitaxy. In segregation lengths of nearly 6 A are measured.

Nondestructive characterization of semiconductor multilayers

This article reviews the use of spectro-scopic ellipsometry (SE) for determining layer thicknesses, compositions, and surface and interface roughness of complex multilayer structures. An indirect technique, SE relies on an accurate database of dielectric functions and cross-correlation with destructive techniques. Examples shown here use recent data on strained and relaxed Si1−xGex,strained and relaxed Inx Ga1−xAs, and unstrained InxAl1−xAs, obtained from single epilayers, to analyze SE data from both lattice-matched and pseudomorphic multilayer structures. The SE method has great potential for in-line and in-situ use, leading ultimately to realtime process control.

Glancing incidence X‐ray analysis: Forgotten or to be discovered?

AbstractMany analysis methods can be used to characterize surfaces and interfaces of thin layered materials. Glancing incidence x‐ray analysis (GIXA) has the potential of being one of the most powerful and versatile analysis methods that can be used because it combines x‐ray reflectivity (XRR) and x‐ray fluorescence (XRF). This technique enables the non‐destructive determination of layer thickness, interface roughness and elementary depth profile. Sophisticated laboratory instrumentation is described which enables materials to be characterized in detail using newly developed analysis algorithms.

On the mechanism of reflection high-energy electron diffraction oscillations studied by phase-locked epitaxy of ZnSe

Molecular beam epitaxy (MBE) is one of the most promising methods for growth of sophisticated device structures. Starting the growth on a flat surface, reflection high-energy electron diffraction (RHEED) oscillations occur. The question which phase of the oscillations corresponds to lattice plane completion and the most flat surface morphology is not yet fully resolved. There is hardly a direct access to the answer. Phase-locked epitaxy (PLE), however, appears to be a tool for studying this phase problem. PLE permits the growth of layers without losing RHEED oscillations due to damping the thickness of which is great enough to become measurable by common techniques. This enables to compare the directly determined layer thickness with that obtained by counting the number of RHEED oscillation periods. Results are presented that show the phase relation between RHEED oscillations and lattice plane completion.

Analysis of reacted nuclear-waste glass using electron beams

When waste glass reacts with water, secondary phases may form, which will effect the distribution of radionuclides formally contained within the glass. In order to determine the long term behavior of waste glass, the secondary phases formed need to be identified. Analytical electron microscopy (AEM) is being used to characterize the secondary phases. Glasses have been reacted in test vessels at different surface areas to leachate volumes (S/V) and for periods in excess of 700 days. Increasing the S/V permits one to accelerate the reaction. Samples of the reacted waste forms are embedded in epoxy and thin sectioned by ultramicrotomy for observation in the transmission electron microscopy (TEM). Examinations were performed in a JEOL 2000FXII TEM operated at 200 kV. This abstract describes two types of glass tests, a high level waste sludge based glass and a low level waste glassy slag. Many hundreds of glass tests have been performed and examined by TEM to determine layer thickness, morphology of the leach layer, and identification of secondary phases.

ETCH Rate and Thickness Measurements of Layered GaAs, AlAs and AlGaAs Structures Using a Laser Reflectance Technique

ABSTRACTLaser reflectometry has been shown to be a useful tool for etch depth measurements during etching of multiple layer structures. We have extended the use of laser reflectometry to accurately determine the etch rates of GaAs, Al0.4Ga0.6As and AlAs as a function of temperature and to verify layer thickness in-situ. By use of computer simulation we compare a theoretical model to actual data to determine layer thicknesses and accurate etch rates. We compare our data to previously published work for GaAs etching.