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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Delamination imaging in composites using cross-correlation method by non-contact air-coupled Lamb waves

Abstract This paper presents a cross-correlation damage detection technique using damage scattered waves of all directions cross-correlate with the incident waves for delamination imaging in carbon fiber reinforced polymer (CFRP) composite plate. The presented imaging can not only detect the delamination but also precisely quantify the damage with locations and sizes. First, a CFRP composite sample with interlaminar delamination by inserting the Teflon layer is designed and manufactured in house using the hot-press machine. And a three-dimensional model of composite sample is simulated using the finite element method. Next, the cross-correlation imaging algorithm is introduced in detail, and the cross-correlation imaging proof-of-concept study is conducted with the simulated Lamb waves in the composite sample. Finally, a fully non-contact air-coupled transducer and scanning laser Doppler vibrometer system with a single-mode Lamb wave method is established to actuate and sense the interrogating Lamb waves in the structure. The imaging method is experimentally implemented for the one delamination and two delaminations imaging and quantification.

Instruments & Instrumentation↗
DOE OSTI2021

New Approach Methodology for Assessing Inhalation Risks of a Contact Respiratory Cytotoxicant: Computational Fluid Dynamics-Based Aerosol Dosimetry Modeling for Cross-Species and In Vitro Comparisons

Regulatory agencies are considering alternative approaches to assessing inhalation toxicity that utilizes in vitro studies with human cells and in silico modeling in lieu of additional animal studies. In support of this goal, computational fluid-particle dynamics models were developed to estimate site-specific deposition of inhaled aerosols containing the fungicide, chlorothalonil, in the rat and human for comparisons to prior rat inhalation studies and new human in vitro studies. Under bioassay conditions, the deposition was predicted to be greatest at the front of the rat nose followed by the anterior transitional epithelium and larynx corresponding to regions most sensitive to local contact irritation and cytotoxicity. For humans, simulations of aerosol deposition covering potential occupational or residential exposures (1–50 µm diameter) were conducted using nasal and oral breathing. Aerosols in the 1–5 µm range readily penetrated the deep region of the human lung following both oral and nasal breathing. Under actual use conditions (aerosol formulations >10 µm), the majority of deposited doses were in the upper conducting airways. Beyond the nose or mouth, the greatest deposition in the pharynx, larynx, trachea, and bronchi was predicted for aerosols in the 10–20 µm size range. Only small amounts of aerosols >20 µm penetrated past the pharyngeal region. Using the ICRP clearance model, local retained tissue dose metrics including maximal concentrations and areas under the curve were calculated for each airway region following repeated occupational exposures. These results are directly comparable with benchmark doses from in vitro toxicity studies in human cells leading to estimated human equivalent concentrations that reduce the reliance on animals for risk assessments.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2021

Preliminary Experiences with the Rexon UL-320-FDR: An Automated Thermoluminescent Dosimeter Reader with Removable Contact Heating Planchets and an Infrared Temperature Feedback System

The Rexon UL-320 FDR is a novel resistive-heating thermoluminescent dosimeter reader with a unique temperature measurement system and an automated dosimeter processing mechanism. The removable contact heating planchets have black-body adhesives on the back for capturing temperature information with infrared sensors. A heating cycle feedback loop ensures accurate, precise, and reproducible heating sequences. Heating rates between 0.8 and 40°C s -1 for up to 1,000 s are possible. Photomultiplier tube sensitivity and drift, dark current counts, and planchet glow were measured experimentally. Additionally, 25 LiF:Mg,Ti dosimeters were calibrated to demonstrate reader performance. Sensitivity was optimized at 1,200 V, which produced the highest reference light count to dark current count ratio while extending photomultiplier tube life. Dark current counts measured with typical time-temperature profiles for LiF:Mg,Ti were below 10 counts per channel but increased by up to 2.5% for more extreme heating cycles. Reader sensitivity drifts of up to 10% were observed during extended automated operations with typical time-temperature profiles. Total counts resulting from planchet glow decreased with faster heating rates. Calibrations performed with LiF:Mg,Ti dosimeters yielded results comparable to more established reader designs. Spikes were observed in ~3% of the glow curves from planchet dust and oil burning off at elevated temperatures. The use of N 2 gas and sensitivity drift corrections are recommended to improve dosimetry performance for the UL-320 FDR reader.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2021

Autocrine and paracrine interferon signalling as ‘ring vaccination’ and ‘contact tracing’ strategies to suppress virus infection in a host

The innate immune response, particularly the interferon response, represents a first line of defence against viral infections. The interferon molecules produced from infected cells act through autocrine and paracrine signalling to turn host cells into an antiviral state. Although the molecular mechanisms of IFN signalling have been well characterized, how the interferon response collectively contribute to the regulation of host cells to stop or suppress viral infection during early infection remain unclear. Here, we use mathematical models to delineate the roles of the autocrine and the paracrine signalling, and show that their impacts on viral spread are dependent on how infection proceeds. In particular, we found that when infection is well-mixed, the paracrine signalling is not as effective; by contrast, when infection spreads in a spatial manner, a likely scenario during initial infection in tissue, the paracrine signalling can impede the spread of infection by decreasing the number of susceptible cells close to the site of infection. Furthermore, we argue that the interferon response can be seen as a parallel to population-level epidemic prevention strategies such as ‘contact tracing’ or ‘ring vaccination’. Thus, our results here may have implications for the outbreak control at the population scale more broadly.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Nonmagnetic fractional conductance in high mobility InAs quantum point contacts

In this paper, we report the magnetoelectronic properties of high mobility InAs quantum point contacts grown on InP substrates. The InAs quantum well is embedded between In 0.72 ⁢Ga 0.28 ⁢As cladding layers and In 0.81 ⁢Al 0.19 ⁢As barrier layers, and is populated via self-accumulation. The one-dimensional (1D) conductance reaches a maximum value of 17 plateaus, quantized in units of 2⁢𝑒 2 /ℎ, where 𝑒 is the fundamental unit of charge and ℎ is Planck's constant. The in-plane effective 𝑔 factor was estimated to be −10.9 ± 1.5 for subband 𝑁 = 1 and −10.8 ± 1.6 for subband 𝑁 = 2. Furthermore, a study of the nonmagnetic fractional conductance states at 0.2 (𝑒 2 /ℎ) and 0.1 (𝑒 2 /ℎ) is provided. While their origin remains under discussion, evidence suggests that they arise from strong electron-electron interactions and momentum-conserving backscattering between electrons in two distinct channels within the 1D region. This phenomenon may also be interpreted as an entanglement between the two channel directions facilitated by momentum-conserving backscattering.

Ballistic transport↗
DOE OSTI2024

Andreev reflection of quantum Hall states through a quantum point contact

Here, we investigate the interplay between the quantum Hall (QH) effect and superconductivity in InAs surface quantum well (SQW)/NbTiN heterostructures using a quantum point contact (QPC). We use QPC to control the proximity of the edge states to the superconductor. By measuring the upstream and downstream resistances of the device, we investigate the efficiency of Andreev conversion at the InAs/NbTiN interface. Our experimental data is analyzed using the Landauer Büttiker formalism, generalized to allow for Andreev reflection processes. We show that by varying the voltage of the QPC, V QPC , the average Andreev reflection, A, at the QH-SC interface can be tuned from 50% to ~ 10%. The evolution of A with V QPC extracted from the measurements exhibits plateaus separated by regions for which A varies continuously with V QPC . The presence of plateaus suggests that for some ranges of V QPC the QPC might be pinching off almost completely from the QH-SC interface some of the edge modes. Our work shows a new experimental setup to control and advance the understanding of the complex interplay between superconductivity and QH effect in two-dimensional gas systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Contact solitons as spin pistons in one-dimensional ferromagnetic channels

Ferromagnetic channels subject to spin injection have been theoretically shown to sustain dissipative exchange flows (DEFs). In the strong injection regime, a soliton is stabilized at the injection site, which has been termed a contact soliton DEF or CS-DEF. Here, in this work, we investigate the modulation of CS-DEFs as a mechanism to inject magnons into a DEF. By varying the injection current, the parameters connecting the soliton with the DEF via a boundary layer are varied. These lead to a modification in the DEF which is interpreted as a spin piston. The injected magnons follow the expected dispersion relation of DEFs, akin to the Bogoliubov–de Gennes dispersion relation. As a result, this work demonstrates that changes in the injected current can pump magnons along a ferromagnetic channel via dissipative exchange flows.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Large- N c analysis of two-nucleon neutrinoless double-β decay and charge-independence-breaking contact terms

The interpretation of experiments that search for neutrinoless double- β decay relies on input from nuclear theory. Cirigliano et al. [Phys. Rev. Lett. 120, 202001 (2018)] recently showed that, for the light Majorana exchange formalism, effective field theory calculations require a nn → ppe - e - contact term at leading order. They estimated the size of this contribution by relating it to measured charge-independence-breaking (CIB) nucleon-nucleon interactions and making an assumption about the relative sizes of CIB operators. We show that the assumptions underlying this approximation are justified in the limit of the number of colors, N c , being large. Finally, we also obtain a large-N c hierarchy among CIB nucleon-nucleon interactions that is in agreement with phenomenological results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Half-Integer Conductance Plateau at the ν = 2 / 3 Fractional Quantum Hall State in a Quantum Point Contact

The v = 2/3 fractional quantum Hall state is the hole-conjugate state to the primary Laughlin v = 1/3 state. Here, we investigate transmission of edge states through quantum point contacts fabricated on a GaAs/AlGaAs heterostructure designed to have a sharp confining potential. When a small but finite bias is applied, we observe an intermediate conductance plateau with G = 0.5⁢(e 2 /ℎ). This plateau is observed in multiple QPCs, and persists over a significant range of magnetic field, gate voltage, and source-drain bias, making it a robust feature. Using a simple model that considers scattering and equilibration between counterflowing charged edge modes, we find this half-integer quantized plateau to be consistent with full reflection of an inner counterpropagating -1/3 edge mode while the outer integer mode is fully transmitted. In a QPC fabricated on a different heterostructure which has a softer confining potential, we instead observe an intermediate conductance plateau at G = (1/3)⁢(e 2 /ℎ). These results provide support for a model at v = 2/3 in which the edge transitions from a structure having an inner upstream -1/3 charge mode and outer downstream integer mode to a structure with two downstream 1/3 charge modes when the confining potential is tuned from sharp to soft and disorder prevails.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Unusual Quasiparticles and Tunneling Conductance in Quantum Point Contacts in 𝜈 = 2/3 Fractional Quantum Hall Systems

Understanding topological matter in the fractional quantum Hall (FQH) effect requires identifying the nature of edge state quasiparticles. FQH edge state at the filling factor 𝜈 = 2/3 in the spin-polarized and unpolarized phases is represented by the two modes of composite fermions (CF) with the parallel or opposite spins described by the chiral Luttinger liquids. Tunneling through a quantum point contact (QPC) between different or similar spin phases is solved exactly. With the increase of the applied voltage, the QPC conductance grows from zero and saturates at 𝑒 2 /2⁢ℎ while a weak electron tunneling between the edge modes with the same spin transforms into a backscattering carried by the charge 𝑞 = 𝑒/2 quasiparticles. These unusual quasiparticles and conductance plateau emerge when one or two CF spin-polarized modes in the QPC tunnel into a single mode. Here, we propose experiments on the applied voltage and temperature dependence of the QPC conductance and noise that can shed light on the nature of edge states and FQH transport.

Anyons↗
DOE OSTI2022

Surface Wave Based Non-conductor-contact Reflectometry Method for Insulation and Jacket Damage Detection in Multi-Conductor Cables

This paper presents a non-conductor-contact surface wave reflectometry technique to locate insulation and jacket damage on multi-conductor cables at a distant location from the sensor. Simulation studies were conducted using Ansys high frequency structure simulator (HFSS). A GHz range surface wave launcher was employed such that maximum surface wave energies were confined in the insulation layer while minimizing attenuation. The wave launcher can potentially be mounted on the outer surface of live cables or cable conduits and requires no physical connection to the conductors. Multiple simulations involving a 4 GHz wave launcher and a three-conductor cable with an 8 mm outer diameter were carried out demonstrating the efficacy of the proposed method. Water leak and different types of insulation/jacket damage were simulated and detected.

reflectometry, multi-conductor cable, frequency do↗
DOE OSTI2021

Multiscale Characterization of Photovoltaic Modules—Case Studies of Contact and Interconnect Degradation

The current popularity of photovoltaic (PV) systems is due in large part to their exceptional reliability and significantly lower cost than other energy sources. Studying cell and module degradation is key to promote further development in the state of the art. Fielded or accelerated aged modules exhibit different failure modes, of which metallization degradation (contacts and interconnections) is prevalent. In this work, we discuss how multiscale characterization methods can be applied to a variety of module technologies that have been field exposed and have undergone accelerated age testing. These methods include performing characterization on the module level, cell level, and finally the materials level. The observed performance losses from the module- and cell-level characterization can be correlated with materials properties to find out the root cause of degradation. We recommend an initial nondestructive characterization suite, including module- and cell-level current-voltage ( I--V ), Suns-V OC , photoluminescence and electroluminescence imaging, quantum efficiency, ultraviolet fluorescence imaging, and thermal infrared imaging. Samples are then extracted from particularly degraded regions of the module and prepared for materials characterization techniques, such as top-down and cross-sectional scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, Raman spectroscopy, and transmission electron microscopy, allowing a deeper look into the mechanism behind the metallization degradation. This article serves as an instructional review to introduce the different multiscale characterization methods and how they can be effectively applied to perform PV degradation studies. Furthermore, we also share some of our examples and discuss the strengths, limitations, and best practices for each of the characterization techniques.

14 SOLAR ENERGY↗
DOE OSTI2025

Characterization of Field-Exposed Photovoltaic Modules Featuring Signs of Contact Degradation

Here, this work investigates several photovoltaic (PV) modules that have shown signs of metal contact corrosion due to field exposure in a hot and humid climate. This includes two multicrystalline silicon aluminum back surface field systems with 10 and 14 years of exposure and one monocrystalline silicon passivated emitter and rear cell system with four years of exposure. A comprehensive, multiscale characterization process is used to evaluate these PV modules in great detail. Current–voltage (I−V), Suns-V OC measurements, electroluminescence imaging, infrared imaging, and ultraviolet fluorescence imaging were performed, and locations of interest were cored and analyzed using cross-sectional scanning electron microscopy (SEM). A rigorous, quantitative analysis procedure for the cross-sectional SEM images is proposed and implemented. Careful characterization does reveal that some of these PV modules do indeed exhibit the same classic signs of acetic-acid-based corrosion of the glass frit that is present at the silver/silicon interface, which have been observed previously in PV modules exposed to damp heat in an environmental chamber.

14 SOLAR ENERGY↗
DOE OSTI2020

Design of Thermophotovoltaic Cells for Optimal System Efficiency, Accounting for Photon Reuse from Front and Back Contacts

We develop a model showing how reflection from both the front and back contacts of thermophotovoltaic (TPV) cells affects the system efficiency. From this foundation we determine the design rules for front grids for TPV cells, and assess the consequences of those rules on cell design and system performance. We show that these design rules are different and more complex than the corresponding design rules for solar photovoltaic (PV) cells, and can lead to substantially different grid design and system performance than if the simpler solar PV design rules were used.

14 SOLAR ENERGY↗
DOE OSTI2020

Nonuniform Charge Collection in SiOx-Based Passivated-Contact Silicon Solar Cells

In this contribution, we report on the charge-collection characteristics of silicon photovoltaic devices using passivated contacts based on the c-Si/SiO x /poly-Si structure. Using electron-beam induced current (EBIC) imaging in plan-view and cross-section orientations, we find that charge collection in a device with a 1.5-nm-thick SiO x layer is fairly uniform in the p-n junction region and does not appear to be influenced by pyramidal surface texture. In contrast, a device with a 2.2-nm-thick oxide layer shows significant spatial variation in the charge-collection signal. The apexes of the pyramids exhibit reduced EBIC signal whereas the valleys between adjacent pyramids show the strongest collection. Our results indicate that charge collection in c-Si/SiO x /poly-Si structures can be influenced by both the properties of the SiO x layer and surface texture.

14 SOLAR ENERGY↗
DOE OSTI2021

Transparent MgO for Back-Contact Passivation of CdTe-Based Solar Cells

The passivating effects of MgO have been studied by integrating into an existing superstrate CdTe thin film solar cell device architecture. When implemented as an emitter to replace the typical MZO, the device performance was below par, but improved PL and TRPL was detected with significant carrier lifetimes in comparison to the MZO devices. However, when integrated at the back, the PL signal was detected upon the illumination of excitation laser from the back. This has opened the possibility of probing the back of the CdTe thin film solar cells with transparent back contact with improved back passivation and a bifacial device structure. Further, the TRPL measurements suggests that the MgO shows passivating effects to a CdTe surface irrespective of method of deposition implemented.

bifacial↗
DOE OSTI2021

Improving GaAsP/Si Tandem Solar Cells Using Silicon Passivated Contacts

The degradation of photocarrier bulk lifetime in Si wafer substrates during the heteroepitaxial growth of III-V materials has been widely reported and is known to limit the efficiency of III-V/Si tandem solar cells. There have been prior strategies to protect Si lifetime in III-V growth chambers, but most require the use of a protective layer that must be removed in subsequent device processing. It would be advantageous for protective layers to remain an active part of the device. In this work, we demonstrate that a polycrystalline silicon (poly-Si) passivated contact can protect the minority carrier lifetime of the Si base wafer during the organometallic vapor phase epitaxy of III-V materials on silicon substrates.

Exascale Computing Project↗
DOE OSTI2021

Pinhole Formation in Poly-Si/SiOx Passivating Contacts on Si(111)-Oriented Textures

Poly-Si/SiOx passivating contacts were grown on inverted pyramid and random pyramid textured wafers to investigate the hypothesis that pinhole formation is most susceptible at the valleys and edges of a textured surface. Tetramethylammonium hydroxide (TMAH) etching and electron beam induced current (EBIC) were used to assess pinhole formation and charge-carrier transport. Scanning electron microscopy revealed that TMAH etching can expose pinhole locations on textured surfaces. We show that pinholes may preferentially form at the vertices of inverted pyramids. Our TMAH and EBIC analyses on random pyramids show no preferential oxide breakup at the pyramid valleys.

41 EE - Solar Energy Technologies Office (EE-4S)↗