Non-destructive Characterization Method Research Articles

Developing Quantitative Nondestructive Characterization of Nanomaterials: A Case Study on Sequential Infiltration Synthesis of Block Copolymers.

The sequential infiltration synthesis (SIS) of inorganic materials in nanostructured block copolymer templates has rapidly progressed in the last few years to develop functional nanomaterials with controllable properties. To assist this rapid evolution, expanding the capabilities of nondestructive methods for quantitative characterization of the materials properties is required. In this paper, we characterize the SIS process on three model polymers with different infiltration profiles through ex situ quantification by reference-free grazing incidence X-ray fluorescence. More qualitative depth distribution results were validated by means of X-ray photoelectron spectroscopy and scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy.

High-throughput computation of Raman spectra from first principles

Raman spectroscopy is a widely-used non-destructive material characterization method, which provides information about the vibrational modes of the material and therefore of its atomic structure and chemical composition. Interpretation of the spectra requires comparison to known references and to this end, experimental databases of spectra have been collected. Reference Raman spectra could also be simulated using atomistic first-principles methods but these are computationally demanding and thus the existing databases of computational Raman spectra are fairly small. In this work, we developed an optimized workflow to calculate the Raman spectra efficiently and taking full advantage of the phonon properties found in existing material databases. The workflow was benchmarked and validated by comparison to experiments and previous computational methods for select technologically relevant material systems. Using the workflow, we performed high-throughput calculations for a large set of materials (5099) belonging to many different material classes, and collected the results to a database. Finally, the contents of database are analyzed and the calculated spectra are shown to agree well with the experimental ones.

Visualizing changes of metabolites during iron deficiency chlorosis in field-grown pear leaves using micro-Raman spectral imaging.

Owing to iron chlorosis, pear trees are some of the most severely impacted by iron deficiency, and they suffer significant losses every year. While it is possible to determine the iron content of leaves using laboratory-standard analytical techniques, the sampling and analysis process is time-consuming and labor-intensive, and it does not quickly and accurately identify the physiological state of iron-deficient leaves. Therefore, it is crucial to find a precise and quick visualization approach for metabolites linked to leaf iron to comprehend the mechanism of iron deficiency and create management strategies for pear-tree planting. In this paper, we propose a micro-Raman spectral imaging method for non-destructive, rapid, and precise visual characterization of iron-deficiency-related metabolites in pear leaves. According to our findings, iron deficiency significantly decreased the Raman peak intensities of chlorophylls and lipids in leaves. The spatial distributions of chlorophylls and lipids in the leaves changed significantly as the symptoms of iron insufficiency worsened. The technique offers a new, prospective tool for rapid recognition of iron deficiency in pear trees because it is capable of visual detection of plant physiological metabolites induced by iron deficiency.

Assessment of 3D micro-computed tomography for PV interconnection technology development

X-ray (micro-)computed tomography is a non-destructive characterization method using photons to obtain multiple radiographic projections, which generates a 3D volume rendering of a scanned object after reconstruction. It is recently used in the research and development of photovoltaic modules to investigate smaller volumes in a PV module, for example, detection of cavities in solder joints and visualization of module volumes up to connection ribbon sizes. This work shows that current advanced devices are able to scan larger volumes, using a single-cell 20 × 20 × 0.5 cm 3 module with back-contact multi-ribbon interconnection technology as an example. The generated 3D volume renderings show the interconnection structures and give information on ribbon-metallization interconnections. Next to this, also the solder reflow volume is visible, indicating that the technology has great potential to be used in further interconnection technology development. Finally, a destructive cross section analysis using scanning electron microscopy is performed; it has a higher resolution and can differentiate elements with similar photon absorption coefficients, thus enabling microstructure and intermetallic compound analysis. The findings show the potential for micro-computed tomography as a non-destructive and relatively fast visualization method and how it can give complementary information to other characterization techniques for photovoltaic interconnection research. • X-ray computed tomography is a non-destructive visual inspection technique. • Scanning electron microscopy and x-ray tomography are complementary. • X-ray tomography can aid PV interconnection technology developments.

Preparation and refractive index characterization of chalcogenide glasses with gradient refractive index

AbstractInfrared gradient refractive index (GRIN) lenses have great application value and potential in multispectral imaging systems. This study reports various chalcogenide axial GRIN glasses prepared using the hot‐pressing diffusion method. It is worth noting that the S4–S60 GRIN sample has a difference in refractive index (RI) Δn of greater than 0.3 and a diffusion depth of about 5 mm, which is the deepest diffusion depth reported in chalcogenide glass to date. In addition, the linear portion in the profile of the GRIN sample has a RI difference of 0.15 and a thickness of 1.2 mm. The effects of the temperature, concentration difference, and diffusion time on the sample diffusion process are discussed. The dispersion properties of the GRIN samples were further calculated, providing a new option for correcting chromatic aberrations in optical systems. In addition, a method for the indirect nondestructive characterization of sample RI using the Raman intensity ratio is proposed, and the reliability of the method is verified by practical experiments, which is convenient for the subsequent measurement of the GRIN profile.

Neutron phase contrast imaging of PbWO4 crystals for G experiment test masses using a Talbot-Lau neutron interferometer

The use of transparent test/source masses can benefit future measurements of Newton’s gravitational constant G. Such transparent test mass materials can enable nondestructive, quantitative internal density gradient measurements using optical interferometry and allow in-situ optical metrology methods to be realized for the critical distance measurements often needed in a G apparatus. To confirm the sensitivity of such optical interferometry measurements to internal density gradients it is desirable to conduct a check with a totally independent technique. We present an upper bound on possible internal density gradients in lead tungstate (PbWO4) crystals using a Talbot-Lau neutron interferometer on the Cold Neutron Imaging Facility at NIST. We placed an upper bound on a fractional atomic density gradient in two PbWO4 test crystals of cm−1. This value is about two orders of magnitude smaller than required for G measurements. We discuss the implications of this result and of other nondestructive methods for characterization of internal density inhomogeneties which can be applied to test masses in G experiments.

A top-down spectroscopic approach for correlating coating thickness distributions with the dissolution profiles of enterically coated pellets

Pharmaceutical dosage forms such as tablets and capsules are often coated with a functional polymer to modify the drug release. To obtain the drug release profiles, ensure quality control and predict in-vivo performance, dissolution studies are performed. However, dissolution tests are time-consuming, sample destructive and do not readily allow for at-line or in-line characterization. Rapid assessment of functional coatings is essential for products where a single capsule is comprised of hundreds of functionally-coated pellets and the collective drug release kinetics of the entire capsule depends on contributions from each pellet. Here, single Raman measurements were used to evaluate the coating thickness distributions of a dosage form comprised of small, functionally-coated pellets in capsules. First, the composition and physicochemical properties of pellets were characterized by multivariate analysis assisted Raman mapping of pellet cross-sections. Second, a method of collecting single Raman spectrum with spectral contributions from the coating and API layers was developed and optimized to estimate the thickness of coatings. The coating thicknesses obtained from single Raman measurements of pellets in each capsule revealed thickness distributions that correlated with the dissolution profiles (capsules with one distribution had single stage release and capsules with two distributions had a two-stage release). Finally, an unsupervised multivariate analysis method was demonstrated as a rapid and efficient way to correlate dissolution profiles of enterically coated pellets. In summary, this study presents a non-destructive and rapid characterization method for assessing coating thickness and has the potential to be applied in process analytical technologies to ensure coating uniformity and predict product dissolution rate performance.

Fast spatially resolved optical characterization of multi-layer CVD graphene

A new quantitative and spatially resolved optical method was developed to quickly analyze the spatial distribution of multilayer graphene grown on large flat substrates, i.e., on one or more 4″ Si wafers. An image processing analysis shows that the background-corrected reflection image of graphene on the flat substrate can be normalized so that the highest image intensity is related to the thinnest or absent layer of graphene. Which of these two most typical cases is in effect for a given sample can be easily determined by a calibration wafer using laser Raman spectroscopy 2D/G peak intensity ratio. We show that the spatial distribution of multilayer graphene can be determined by relating reflected light intensity from an intensity-calibrated reflection image to the layer numbers of a local graphene film. By dividing the greyscale reflection intensity into bins, the spatial multilayer graphene distribution can be visualized with a false-colored contour plot where each graphene layer quantity is represented by a unique color for easy visualization of their spatial distribution regions. The spatial distribution over extended spatial regions of multilayer graphene grown on a flat substrate, for example, a Ni or Cu films on a 4ʺ Si or Ge wafer, can quickly be analyzed and visualized through this non-destructive characterization method by locally sampling and analyzing multiple regions of interest across a full spatially extended large substrate. Selected applications of this method are, for example, process uniformity and quality optimization for one or more large Si wafers grown in a single batch or different batches, as well as for fast and non-destructive automated multilayer graphene growth quality control methods.

Polarization contrast neutron imaging of magnetic crystallographic phases

Non-destructive characterization methods to observe phase transformations and thus, gain insights to transformation mechanisms in representative volumes are key for the development of advanced materials and manufacturing. Conventional methods are constrained to the surface and small sizes, thus, access to the bulk often implies tedious destructive approaches and hinders in-situ observations of phase evolution. In this work, we introduce a non-destructive technique that overcomes key limitations prevailing today for mapping the spatial distribution of magnetic phases in bulk materials. The use of polarized neutrons, being sensitive to sub-percent fractions of ferromagnetic phases and able to penetrate centimeter sized samples, enables micrometer-scale spatial and second-scale time resolutions. We demonstrate ex-situ and in-situ quantitative mapping of magnetic phases, in particular the evolution of martensite induced by uniaxial- and biaxial deformation in metastable 304 steel. The quantitative results obtained during in-situ deformation testing prove polarization contrast neutron imaging to be particularly effective in detecting small fractions of martensite. Especially during early stages of deformation where neutron diffraction, which in contrast does not provide full field spatial resolution, fails. The short exposure times and high sensitivity renders the method well suited for rapid 3D tomographic mapping and/or operando investigations of phase distributions.

Upgraded imaging capabilities at the BAMline (BESSY II).

The BAMline at the BESSY II synchrotron X-ray source has enabled research for more than 20 years in widely spread research fields such as materials science, biology, cultural heritage and medicine. As a nondestructive characterization method, synchrotron X-ray imaging, especially tomography, plays a particularly important role in structural characterization. A recent upgrade of key equipment of the BAMline widens its imaging capabilities: shorter scan acquisition times are now possible, in situ and operando studies can now be routinely performed, and different energy spectra can easily be set up. In fact, the upgraded double-multilayer monochromator brings full flexibility by yielding different energy spectra to optimize flux and energy resolution as desired. The upgraded detector (based on an sCMOS camera) also allows exploiting the higher flux with reduced readout times. Furthermore, an installed slip ring allows the sample stage to continuously rotate. The latter feature enables tomographic observation of processes occurring in the time scale of afew seconds.

A novel aging characterization method for silicone rubber based on terahertz absorption spectroscopy

To address the challenge of the lack of aging characterization methods for outdoor silicone rubber-based insulation materials in power engineering applications, this paper proposes a novel high precision non-destructive characterization method for aging of organic materials based on the vibration characteristics of silicone rubber materials in the terahertz frequency band. In order to analyze and verify the method proposed in this paper, the sources of vibration peaks in the THz band absorption spectrum of aged silicone rubber are discussed by accelerating test, microscopic characterization, and molecular simulation. Finally, the characteristic peak frequency and quantitative calculation method of aged silicone rubber are obtained. Compared to other aging assays, this method overcomes the limitations of the existing THz assay which requires testing in a nitrogen atmosphere, and has the advantage of not damaging the sample.

Investigation of micro-arc oxidation coatings using sub-THz ellipsometry

The paper is devoted to the investigation of the structure and properties of coatings obtained by micro-arc oxidation (MAO). For the first time, the possibility of using sub-terahertz ellipsometry with an operating frequency f = 0.14 THz for non-destructive non-contact determination of the integral values of the thickness, structure, and composition of such coatings is studied. The frequency was chosen since the corresponding wavelength ( λ = 2.14 mm) significantly exceeds the characteristic size of the roughness of the coatings, which makes it possible to use the geometrical optics approximation in the analysis of experimental results. When constructing models of the structure of coatings and determining their parameters, additional independent methods were used, such as optical microscopy, XRD, SEM, terahertz reflectometry, and the theoretical modeling of the electric field distribution during the microplasma oxidation process. The A1 alloy 1100 was used as the material for research. It is shown that ellipsometry is very sensitive to processes on the surface during MAO even at the earliest stages of oxide layer formation. Based on the data of the ellipsometry experiment, several planar models of the surface structure were constructed, and their parameters were determined at different stages of oxidation. The constructed models and their parameters (thickness, phase composition, and optical constants) are in good agreement with the results of independent measurements and do not contradict the physical concepts of the processes occurring during MAO. For the first time, it was proposed to use piecewise models for interpreting ellipsometric measurements of film structures non-uniform over the surface. The proposed model adequately describes the structure of MAO coatings at all stages of the technological process. It makes it possible to use ellipsometry for non-destructive non-contact express control of the state of these coatings during production without resorting to additional more complex analytical methods (XRD, SEM, etc). When analyzing ellipsometric data, estimates for the optical constants of mullite (Al 5 SiO 10− x ) in the terahertz range were obtained for the first time. It is also shown that the main results of the work can be used in the analysis of MAO coatings on other metals. • THz ellipsometry is found to be an efficient non-destructive method for MAO coatings characterization. • Information about the coating parameters was obtained, consistent with the data of structural and other independent studies. • Estimates for the optical constants of mullite in the sub-THz region are obtained. • A new model is proposed for the analysis of ellipsometric measurements of coatings non-uniform over the surface.

Crystallographic Methods for Non-destructive Characterization of Mineral Inclusions in Diamonds

Crystallographic Methods for Non-destructive Characterization of Mineral Inclusions in Diamonds

Applicability of a Flat-Bed Birefringence Setup for the Determination of Threading Dislocations of Silicon Carbide Wafers

Screw-type dislocations like micropipes (MP) and threading screw dislocations (TSD) are prohibiting the function or at least diminishing the efficiency of electronic devices based on silicon carbide (SiC). Therefore, it is essential to characterize wafers in an efficient and fast manner. Molten potassium hydroxide (KOH) etching or white-beam X-ray topography (SWXRT) are either destructive or not economically viable for an in-depth characterization of every wafer of one SiC crystal. Birefringence microscopy is being utilized as a fast and non-destructive characterization method. Instead of microscopic setups, commercially available flat-bed scanners equipped with crossed polarizer foils can be used for fast large-area scans. This work investigates the feasibility of such a setup regarding the detection rate of MPs and TSDs. The results of a full-wafer mapping are compared with birefringence microscopy and KOH etching. In the investigated sample clusters of MPs caused by a polytype switch in the beginning of the growth could be identified by both birefringence microscopy and the flat-bed scanner setup, as well as small angle grain boundaries and TED arrays. However, the resolution of the scanner was not sufficient to identify TSDs. Nevertheless the setup proves to be an easy-to-setup and cheap characterization method, able to quickly identify defect clusters in 4H-SiC wafers.

PCA-based sub-surface structure and defect analysis for germanium-on-nothing using nanoscale surface topography

Empty space in germanium (ESG) or germanium-on-nothing (GON) are unique self-assembled germanium structures with multiscale cavities of various morphologies. Due to their simple fabrication process and high-quality crystallinity after self-assembly, they can be applied in various fields including micro-/nanoelectronics, optoelectronics, and precision sensors, to name a few. In contrast to their simple fabrication, inspection is intrinsically difficult due to buried structures. Today, ultrasonic atomic force microscopy and interferometry are some prevalent non-destructive 3-D imaging methods that are used to inspect the underlying ESG structures. However, these non-destructive characterization methods suffer from low throughput due to slow measurement speed and limited measurable thickness. To overcome these limitations, this work proposes a new methodology to construct a principal-component-analysis based database that correlates surface images with empirically determined sub-surface structures. Then, from this database, the morphology of buried sub-surface structure is determined only using surface topography. Since the acquisition rate of a single nanoscale surface micrograph is up to a few orders faster than a thorough 3-D sub-surface analysis, the proposed methodology benefits from improved throughput compared to current inspection methods. Also, an empirical destructive test essentially resolves the measurable thickness limitation. We also demonstrate the practicality of the proposed methodology by applying it to GON devices to selectively detect and quantitatively analyze surface defects. Compared to state-of-the-art deep learning-based defect detection schemes, our method is much effortlessly finetunable for specific applications. In terms of sub-surface analysis, this work proposes a fast, robust, and high-resolution methodology which could potentially replace the conventional exhaustive sub-surface inspection schemes.

Additive manufacturing of biomimetic Titanium-Tantalum lattices for biomedical implant applications

Although additively manufactured titanium-tantalum alloys can offer unique mechanical and biological advantages for implant applications, their use in conjunction with engineered lattice architectures is yet to be explored. In the present study, the promising gyroid, diamond and Schwarz primitive minimal surfaces are used for the design of 3D lattices for biomedical implants. The lattices are fabricated using laser powder-bed fusion and a blend of elemental titanium-tantalum powder. The processability, compressive mechanical properties and in vitro biological properties of the dense and lattice samples are assessed via non-destructive and destructive characterization methods. The topologies from the designed structures are retained through processing and the compressive tests results show that the strength-to-modulus ratios are comparable to the conventional Ti-6Al-4 V alloy. However, the higher ductility and absence of toxic elements make the Ti-25Ta lattices a more favourable option for a new generation of implants. Compared to conventional lattices, the designs presented here also show advantageous mechanical properties for use in bone implants with higher elastic admissible strains. The in vitro cell cultures confirm the high biocompatibility of the material and improved biological response of the interconnected lattices over dense material.

Stress imaging by guided wave tomography based on analytical acoustoelastic model.

A nondestructive method ( M) for stress characterization in plate-like structures is proposed. In this method, the acoustoelastic effects (AEEs) on Lamb and shear horizontal guided waves are used to reconstruct a nonuniform multiaxial stress field. The development of M starts by deriving an analytical acoustoelastic model (An-AEM) to predict AEEs induced by a triaxial stress tensor as a function of the stress components, its orientation, the wave propagation direction, and three acoustoelastic coefficients (AECs). The AECs are independent of stress but specific to each mode. The An-AEM allows one to retrieve the three components of the stress tensor and its orientation from AEEs, assuming the stress to be uniform in the plane of the plate and through its thickness. To deal with stress that is nonuniform in the plane, the An-AEM is combined with time-of-flight straight ray tomography to enable stress field reconstruction. Numerical simulation is used to illustrate how such reconstruction can be performed. It is shown that in some cases, stress components can be reconstructed with arbitrary accuracy, and in other cases, the tensorial nature of stress renders the accuracy of its reconstruction dependent on spatial variations of the stress orientation.

Advanced Estimation of Compressive Strength and Fracture Behavior in Ceramic Honeycombs by Polarimetry Measurements of Similar Epoxy Resin Honeycombs.

Finding a non-destructive characterization method for cellular ceramics’ compressive strength and fracture behavior has been a challenge for material scientists for years. However, for transparent materials, internal stresses can be determined by the non-destructive photoelastic measurements. We propose a novel approach to correlate the photoelastic stresses of polymer (epoxy resin) prototypes with the mechanical properties of ceramics (alumina). Regular and inverse epoxy honeycombs were 3D-printed via stereolithography with varying structure angles from −35° to 35°, with negative angles forming an auxetic and positive hexagonal lattice. Photoelastic measurements under mechanical loading revealed regions of excess stress, which directly corresponded to the initial fracture points of the ceramic honeycombs. These honeycombs were made by a combination of 3D printing and transfer molding from alumina. The photoelastic stress distribution was much more homogeneous for angles of a smaller magnitude, which led to highly increased compressive strengths of up to 446 ± 156 MPa at 0°. By adapting the geometric structural model from Gibson and Ashby, we showed that we could use a non-destructive technique to determine the compressive strength of alumina honeycombs from the median photoelastic stress measured on similar epoxy honeycomb structures.

Ultrafast strain waves reconstruction from coherent acoustic phonons reflection

Picosecond ultrasonics, which studies laser-induced high-frequency strain waves, is a reliable and versatile method for nondestructive materials' characterization. Strain waves are generated through a light interaction with charges and their subsequent relaxation, and these waves conceal a wealth of information on the material. However, strain waves are detected through their convolution with a sensitivity function, which blurs much of this information. Here, we show that the reflection of strain waves at a free surface leads to the appearance of a Fano resonance in the reflectivity spectrum, accompanied by a drastic increase in the detection bandwidth. We take advantage of this feature to provide a method for the reconstruction of strain waves. We apply it to unambiguously highlight the exact origin of the generation of coherent acoustic phonons in Stranski–Krastanov grown quantum dots, revealing that both the wetting layer and quantum dots are responsible for the generation. Our results will offer the possibility to understand better the interaction of light with charges and their interactions with the lattice.

Application of HRGS for forensic characterization of uranium oxides, pure uranium metals and uranium alloys

A nondestructive iterative method for uranium-bearing material characterization with HRGS developed earlier in Burdeinyi et al. (2020) is applied to determine matrix densities, uranium mass fraction and uranium isotope masses of uranium ore, UO2 and U3O8 powders, fuel elements in the form of UO2 microspheres, uranium metal and uranium alloys. It is shown that U3O8 powders with uranium mass fraction of about 84% can be distinguished from the powders of UO2 with uranium mass fraction of about 87%; uranium products in the form of liquid or loose powder with matrix density of 0.5–2.0g/cm3 can be distinguished from uranium products in the form of compacted fuel elements with matrix density of 6.0–10.0g/cm3 and from pure metal uranium and uranium alloys with matrix density of 14.0–19.0g/cm3. In fuel microspheres based on UO2 the uranium mass fraction 88.02% measured by HRGS is consistent, within the measurement uncertainties, with the results of isotope dilution mass spectrometry 87.76±0.64% and also is confirmed by X-ray diffraction technique. The uranium mass fraction of the uranium ore estimated as 0.08% by HRGS is consistent, within the measurement uncertainties, with the value 0.09±0.01% determined with WDXRF. Densities of two different uranium metal samples, estimated as 18.42g/cm3 and 19.33g/cm3 by HRGS are consistent with values 18.24±0.55g/cm3 and 18.86±0.59g/cm3, respectively, obtained by the gas pycnometry technique.