Measurement Of Thickness Changes Research Articles

Measuring material thickness changes through tri-aperture digital speckle pattern interferometry

A configuration for the measurement of thickness changes in materials through one-shot digital speckle pattern interferometry (DSPI) was developed. The phase maps calculation was made by adding carrier fringes by the multiple aperture principle and Fourier Transform Method (FTM). With this setup, interferometry configurations verified that the simultaneous and instantaneous visualization of two opposite faces of a surface is possible. In addition, the combination of the simultaneous results obtained from both sides of the material makes it possible to determine displacements with greater sensitivity or to identify changes in their thickness. The validation and demonstrative tests were carried out with a 1-mm-thick aluminum plate with a 5-mm diameter through hole coated. Thickness changes to 2 μm were measured.

Designing a reference electrode – An approach to fabricate laser perforated reference electrodes for lithium-ion batteries

Reference electrodes (REs) are powerful tools to analyze electrochemical phenomena within lithium ion batteries. However, their design and material choice are under debate. Recently, lithium titanate oxide (LTO, Li4Ti5O12) and lithium iron oxide (LFP, LiFePO4) have been dip-coated onto wide-meshed metal nets to reduce the blocking effect. Still, this process is elaborate and not common in electrode manufacturing.In this study, we show a post-processing method to fabricate user-defined REs based on LFP via an ultrashort pulse laser. The REs are designed in such a way that the blocking of the Li+ ion pathways should be as small as possible. Testing these special REs in NMC811/graphite full pouch cells revealed slim to no influence on the cell capacity while delivering reproducible voltages at low to moderate C-rates. Moreover, cell thickness change measurements at the RE site showed no influence on the cell expansion during cycling. Finally, we compare the measured graphite profiles with the ones measured by a conventional Li RE and confirm the comparability of both systems.

Designing a Reference Electrode – an Approach to Fabricate Laser Perforated Reference Electrodes for Lithium-Ion Batteries

The implementation of reference electrodes (RE) in lithium-ion battery cells represents a promising way to optimize fast-charging, evaluate the C-rate capability of new electrode materials, and monitor cell aging more precisely. However, their design and material choice are under debate. Recently, lithium titanate oxide (LTO, Li4Ti5O12) and lithium iron oxide (LFP, LiFePO4) have been dip-coated onto wide-meshed metal nets to reduce the blocking effect. Still, this process is elaborate and not common in electrode manufacturing.In this study, we show a new post-processing method to fabricate user-defined REs based on LFP via an ultrashort pulse laser. The REs were designed in such a way that the blocking of the Li+ ion pathways should be as small as possible. Testing these special REs in NMC811/graphite full pouch cells revealed slim to no influence on the cell capacity while delivering reproducible voltages, even at high C-rates. Moreover, cell thickness change measurements at the RE site during cycling and post-mortem analysis showed no sign of blocking.

Fast and functionally specific cortical thickness changes induced by visual stimulation.

Structural characteristics of the human brain serve as important markers of brain development, aging, disease progression, and neural plasticity. They are considered stable properties, changing slowly over time. Multiple recent studies reported that structural brain changes measured with magnetic resonance imaging (MRI) may occur much faster than previously thought, within hours or even minutes. The mechanisms behind such fast changes remain unclear, with hemodynamics as one possible explanation. Here we investigated the functional specificity of cortical thickness changes induced by a flickering checkerboard and compared them to blood oxygenation level-dependent (BOLD) functional MRI activity. We found that checkerboard stimulation led to a significant thickness increase, which was driven by an expansion at the gray-white matter boundary, functionally specific to V1, confined to the retinotopic representation of the checkerboard stimulus, and amounted to 1.3% or 0.022mm. Although functional specificity and the effect size of these changes were comparable to those of the BOLD signal in V1, thickness effects were substantially weaker in V3. Furthermore, a comparison of predicted and measured thickness changes for different stimulus timings suggested a slow increase of thickness over time, speaking against a hemodynamic explanation. Altogether, our findings suggest that visual stimulation can induce structural gray matter enlargement measurable with MRI.

Electrochemical–mechanical multi-scale model and validation with thickness change measurements in prismatic lithium-ion batteries

A multi-scale model able to evaluate volume changes from atomic level of active material up to battery level of prismatic lithium iron phosphate–graphite batteries is presented in this work. The model goes through the scales according to the following steps: changes of lattice parameters as a function of lithium intercalation and consequent lattice volume deformation; active material particles deformation; electrode volume changes and porosity reduction; evaluation of the effects of the hard case on the overall battery thickness change through finite element modelling. From the experimental side, the thickness change of prismatic LFP–graphite batteries is measured during operation at different current rates with high-precision optical sensors and the statistical analysis of the results is carried out. Scanning electron microscope analyses are carried out on electrode samples for measuring model parameters and to give a visual proof of the existence of different scales in lithium ion batteries. Finally, the results of the multi-scale model are validated with the experiments.

In-situ measurement of temporal changes in thickness of polymer adsorbed films from lubricant oil by vertical-objective-based ellipsometric microscopy

Understanding the formation mechanism and conformation of the adsorbed film formed by additives is critical to clarify the boundary lubrication characteristics. In this study, using the vertical-objective-based ellipsometric microscope (VEM), which can measure nm-gaps between solid surfaces, we proposed a new method for in-situ measuring the thickness of additive adsorbed film in the lubricant oil. In this method, the adsorbed film thickness was measured by measuring the gap between the solids, which was filled by the additive film. The formation process of polyalkylmethacrylate (PAMA) polymer additive adsorbed film was successfully observed. Moreover, we revealed that the PAMA adsorbed films adopted two different conformations depending on the molecular weight and concentration of the polymer: the flattened single-layer conformation and double-layer conformation.

Mitigation and In Situ Probing of Volume Expansion in Silicon/Graphene Hybrid Anodes for High‐Capacity, High‐Rate‐Capable Lithium‐Ion Batteries

Internal macropores in silicon/graphene/graphene nanoribbon (Si/Gr/GNR) hybrid anodes by facile thermal removal of sacrificial polymer, polyvinyl alcohol (PVA), are incorporated, to mitigate the volume expansion of silicon and to increase the silicon utilization and rate capability of the anode. The resulting Si/Gr/GNR hybrid anodes give a high capacity of 1874 mAh g−1 at 0.1 C, based on total weight of the electrode including binder and carbon, as well as great capacity retention of above 800 mAh g−1 after 350 cycles at 0.3 C. The mitigation of volume expansion by carrying out in situ thickness change measurements of small pouch cells via a dilatometer is further demonstrated, exhibiting the saturation of volume expansion below 40% after 100 cycles due to the incorporation of the macropores. Moreover, Si/Gr/GNR anodes with pores exhibit superior rate capability, yielding 1,250 mAh g−1 at 2 C rate due to the effective network of graphene sheets and GNRs.

Synthesis and corrosion behavior of cold sprayed dual nanoparticle reinforced Al coatings

This study investigates the synergistic and individual effects of nano boron carbide (nB4C) and boron nitride nanoplatelets (BNNP) on the corrosion behavior of cold spray aluminum matrix composite (MMC) coatings. Cryomilling and cold spraying were used to synthesize four novel Al MMC coatings with reinforcements consisting of either 2 vol.% nB4C, 2 vol.% BNNP, or dual nanoparticle reinforcement consisting of 1 vol.% nB4C plus 1 vol.% BNNP. Cold sprayed coatings were evaluated using microhardness testing which revealed an 11.7% increase in hardness in the dual nanoparticle reinforced composite coating. Coatings were subjected to 500 h and 2000 h corrosion tests in a salt fog chamber consisting of 3.5% NaCl to simulate an aggressive marine environment. Coatings were evaluated post-salt fog chamber by mass and thickness change measurements, optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Following 500 h corrosion testing, each composite coating experienced mild to severe pitting throughout a significant portion of the coating. Following 2000 h exposure, in addition to severe pitting, all coatings experienced galvanic corrosion at the coating/substrate interface.

Influence of debris cover on glacier response to climate change: insights from Koxkar glacier using dynamic simulation

The response of debris-covered glaciers to climate change is more heterogeneous and complex than that of debris-free glaciers. The debris has a significant effect on glacier dynamic characteristics, which causes uneven mass balance changes, and then affects the change of glacier geometry evolves in response to climate. In our study, both energy balance and a two-dimensional mass and momentum conservation equation were used to simulate the ice temperature and velocity respectively at the main stream line of Koxkar glacier. The influence of the debris on ice temperature was described in the model. The ice velocity simulation was coupled with a description of ice viscosity under the influence of ice temperature. Our simulation results showed that the debris could increase the ice velocity and ablation in the middle of the glacier. Especially in the surface from 3200 to 3400 m.a.s.l, where the debris had great influence for ice velocity and temperature. From simulation results, we inferred that the ice thickness in this region would change obviously. Comparing with the measured thickness changes by ground-penetrating radar (GPR) between 1981 and 2008, the simulation result is consistent with measured results. Therefore, supraglacial lakes are easily developed in this region because of the high ice temperature and uneven ice surface. And the Landsat 8 remote-sensing image had verified this conclusion.

High-resolution Interferometric Measurement of Thickness Change on a Lithium-Ion Pouch Battery

Volume change of graphite leads to change in thickness of battery storage layers during discharging and charging. Pouch cell lithium ion batteries are used in the field of electric vehicles and solar home storage. This paper shows a measurement setup for the three-dimensional measurement of thickness change on a flat 6.7mm thick pouch cell using a white light interferometer. With a measuring field of 7.05mm diameter the resulting 3D thickness change record contains 226000 3D readings. The measuring points have a lateral distance of 13.1μm. The repeatability of the measurement is 312.8nm for the individual values and 64.1nm for the average value. In addition, this paper shows how the storage capacity of this pouch cell drops over 30 charge cycles.

Simulation of Lithium-Ion Battery with Effect of Volume Expansion of Active Materials

In order to increase cell performance of lithium-ion batteries, not only material development but also optimum design of electrode structure is important. However, it is difficult to examine the effect of volume expansion of anode active material on internal phenomena, so there are few studies to understand the its effect for optimum electrode layer. In this study, we investigate the effects of the expansion ratio of active materials on net charge capacity and net charge rate performance in the case of graphite and silicon for anode active material. Charging properties were calculated using equations based on the porous-electrode theory and expressing the parameter changes caused by expansion. In addition, the validity of this simulation model was confirmed by comparing with the experimental measurement of thickness change and charging curve. As results, in the case of high rate condition, cell capacity of graphite cell is higher than that of Si cell. The dynamic structural property, which is the parameter of effective ionic conductivity depends on the porous structure, decreased near separator, and the resistance of ionic conduction increase. As reaction concentrate remarkably near separator in the case of Si, so the utilization of Si active material was lower than that of graphite.

Reduced Anisotropy in Tetramethylammonium Hydroxide Based Silicon Etchants

At sub-10 nm technology nodes, silicon etching is critical to FEOL processes such as FinFET thinning, gap filler removal, pre-III-V deposition etch, and nanowire release etching. The key to developing solutions for these applications is being able to control the anisotropy of the Si etch, or the etch selectivity between Si (111), Si (100), and Si (110). For this study, we focused on the impact of modifications to tetramethylammonium hydroxide (TMAH) on Si etch selectivity, with the ultimate goal of developing an isotropic Si etchant based on TMAH. Initial studies focused on etch selectivity testing of TMAH based chemistries on Si (SOI) wafers of varying orientations. Etch rates were based on measuring thickness changes by cross-sectional SEM. Differences in surface roughness were also characterized by atomic force microscopy. Finally, solutions were evaluated for anisotropy by performing an etch of patterned pSi wafers. As expected, aqueous TMAH solutions showed a high level of anisotropy (111/100/110 = 1:5:5) and significant level of surface roughening. In contrast, some of the modified TMAH solutions tested had decreased surface roughening and an decreased level of anisotropy (111/100/110 = 1:2:2). Pattern etching on implanted pSi wafers is used to highlight the differences in anisotropy between TMAH and the different modifications.

Characterizing Low-Z erosion and deposition in the DIII-D divertor using aluminum

We present measurements and modeling of aluminum erosion and redeposition experiments in separate helium and deuterium low power, low density L-mode plasmas at the outer divertor strike point of DIII-D to provide a low-Z material benchmark dataset for tokamak erosion-deposition modeling codes. Coatings of Al ∼100nm thick were applied to ideal (smooth) and realistic (rough) surfaces and exposed to repeat plasma discharges using the DiMES probe. Redeposition in all cases was primarily in the downstream toroidal field direction, evident from both in-situ spectroscopic and post-mortem non-spectroscopic measurements. The gross Al erosion yield was estimated from film thickness change measurements of small area samples, and was found to be ∼40–70% of the expected erosion yield based on theoretical physical sputtering yields after including sputtering by a 1–3% carbon impurity. The multi-step redeposition and re-erosion process, and hence the measured net erosion yield and material migration patterns, were found to be influenced by the surface roughness and/or porosity. A time-dependent model of material migration accounting for deposit accumulation in hidden areas was developed to reproduce the measurements in these experiments and determine a redeposition probability distribution function for sputtered atoms.

An inverse method for estimating thickness and volume with time of a thin CO2‐filled layer at the Sleipner Field, North Sea

AbstractMigration of CO2 through storage reservoirs can be monitored using time lapse seismic reflection surveys. At the Sleipner Field, injected CO2 is distributed throughout nine layers within the reservoir. These layers are too thin to be seismically resolvable by direct measurement of the separation between reflections from the top and bottom of each layer. Here we develop and apply an inverse method for measuring thickness changes of the shallowest layer. Our approach combines differences in traveltime down to a specific reflection together with amplitude measurements to determine layer thicknesses from time lapse surveys. A series of synthetic forward models were used to test the robustness of our inverse approach and to quantify uncertainties. In the absence of ambient noise, this approach can unambiguously resolve layer thickness. If a realistic ambient noise distribution is included, layer thicknesses of 1–6 m are accurately retrieved with an uncertainty of ±0.5 m. We used this approach to generate a thickness map of the shallowest layer. The fidelity of this result was tested using measurements of layer thickness determined from the 2010 broadband seismic survey. The calculated volume of CO2 within the shallowest layer increases at a rate that is quadratic in time, despite an approximately constant injection rate into the base of the reservoir. This result is consistent with a diminished growth rate of the areal extent of underlying layers. Finally, the relationship between caprock topography and layer thickness is explored and potential migration pathways that charge this layer are identified.

Applications of Optical Interferometer Techniques for Precision Measurements of Changes in Temperature, Growth and Refractive Index of Materials

Optical metrology techniques used to measure changes in thickness; temperature and refractive index are surveyed. Optical heterodyne detection principle and its applications for precision measurements of changes in thickness and temperature are discussed. Theoretical formulations are developed to estimate crystal growth rate, surface roughness and laser cooling/heating of solids. Applications of Michelson and Mach-Zehnder interferometers to measure temperature changes in laser heating of solids are described. A Mach-Zehnder interferometer is used to measure refractive index and concentration variations of solutions in crystal growth experiments. Additionally, fluorescence lifetime sensing and fluorescence ratio method are described for temperature measurement. For all the above techniques, uncertainty calculations are included.

Measuring thickness changes of edgewise compression loaded corrugated board panels using digital image correlation

This study examines thickness changes in web-core sandwich panels under edgewise compressive loading. Both undamaged and damaged panels were examined. Three-dimensional full-field digital image correlation systems were used to determine deflections on both sides of loaded panels. The change in thickness at any given point in the panel was obtained as the difference between the two displacement fields. It was observed that the thickness was reduced in the post-buckling regime. Damage introduced into the corrugated core by lateral compression proved to significantly reduce the load-carrying capability panels and elevate the thickness reduction of the panels.

Temperature-adaptive Insulation Based on Multicomponent Fibers of Various Cross-sections

ABSTRACTWe have developed a thermal insulation based on bi-component fibers that adapts to its thermal environment, providing greater insulation at low temperatures than at warmer temperatures. The analysis of bi-metallic strips done by Timoshenko [1] for strips of rectangular cross-section concluded that “…curvature is proportional to the difference in elongation of the two metals and inversely proportional to the thickness of the strip.” We have extended Timoshenko’s formulation and applied it to bi-component fibers of circular and triangular cross-sections. In each case, the curvature resulting from the balance of the axial forces and bending moments has been brought into a standard form inversely proportional to (A+Bn+C/n) where n is the ratio of the moduli and A, B, and C are functions of the geometry of the two components. An important consequence of this result is that for any “n” there is a maximum curvature where (A+Bn+C/n) is a minimum. We have used the process of melt-spinning to produce fibers with circular and triangular cross-sections, varying the proportion of the two components. The polymers used have widely different coefficients of thermal expansion. These fibers spontaneously form mats at room temperatures. The experimentally measured thickness changes are in good agreement with the analytical results for fiber bending. The most effective samples to date change thickness by more than 1.5% per degree C (30% over a temperature range from approximately 20°C to 0°C).

Modification of the phased-tracking method for reduction of artifacts in estimated artery wall deformation

Noninvasive measurement of mechanical properties, such as elasticity, of the arterial wall, is useful for diagnosis of atherosclerosis. For assessment of mechanical properties, it is necessary to measure the deformation of the arterial wall. In this study, a modification of the previously proposed phased-tracking method was conducted to improve measurement of the small change in thickness (deformation) of the arterial wall due to the heartbeat. In our previous method, a set of two points along an ultrasonic beam was initially assigned, and the change in thickness of the layer between these two points during an entire cardiac cycle was estimated. In motion estimation with ultrasound, the motion of an interface or a scatterer, which generates an echo, can be obtained by estimating the change in time delay of the echo. For example, in the case of a carotid artery of a healthy subject, there are only two dominant echoes from the lumen-intima and media-adventitia interfaces. Thus, only the displacements of the lumen-intima and media-adventitia interfaces can be estimated, which means that ultrasound can estimate only the change in distance (thickness) between these two interfaces. However, even in this case, our previous method gives different estimates of the change in thickness, depending on the depths (positions in the arterial radial direction) of the two initially assigned points. In this study, modifications of the previous method in terms of the strategy for assignment of layers and the required thickness of an assigned layer were made to reduce such an artificial spatial variation in the estimated changes in thickness. Using the proposed method, errors in estimated changes in thickness were reduced from 21.2 +/- 24.1% to 0.19 +/- 0.04% (mean +/- standard deviation) in simulation experiments. As in the case of the simulation experiments, the spatial variation in estimated changes in thickness also was reduced in in vivo experiments in a carotid artery of a healthy subject and in vitro experiments using two excised, diseased arteries.

In situ measurements of thickness changes and mechanical stress upon gasochromic switching of thin MoOx films

Thin films of MoOx coated with platinum as a catalyst were prepared by dc magnetron sputtering from a molybdenum target in an oxygen and argon atmosphere. The films were colored and bleached by exposure to diluted hydrogen gas and air, respectively. In situ measurements of x-ray reflectance and substrate curvature were performed during switching cycles. Upon hydrogen exposure a remarkable thickness decrease of 11% and a density increase of 6.5% are observed by x-ray reflectance measurements. Corresponding changes in optical transmittance and mechanical stress up to several hundreds of MPa are also observed. These changes are not fully reversible as revealed by measurements of multiple switching cycles. Both the change of thickness and density, as well as the change of optical transmittance and mechanical stress can be explained by the existence of a mixed phase of edge and corner sharing MoO3 octahedra whereupon the first coloration the ratio between edge and corner sharing octahedra is changed.

Nondestructive Measurement of Porosity in Thermal Barrier Coatings

Porosity is an integral part of thermal barrier coatings (TBC) and is required to provide thermal insulation and to accommodate operational thermal stresses. The effective use of TBC in hot-section components of aircraft engines requires nondestructive testing (NDT) methods to detect porosity variations and measure thickness changes to reduce the risk of damage to the coating due to such variations. The eddy current method has been used to measure the thickness of a plasma-sprayed TBC coating and either ultrasonic or capacitance techniques have been applied to assess porosity content based on thickness values obtained using the eddy current tests. The porosity values estimated by the NDT methods have been confirmed by destructive testing, which included metallography and vacuum volumetric measurement using nitrogen absorption.