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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Ultrafast UV AlGaN Metal–Semiconductor–Metal Photodetector With a Response Time Below 25 ps

Here, aluminum-gallium-nitride photodetectors were successfully fabricated with micrometer-scale metal–semiconductor–metal structures and tested with ultrafast, UV laser pulses. The measurements were performed with single-shot oscilloscopes. Pulse-broadening effects caused by the measurement system were systematically evaluated and reduced to resolve the intrinsic response time of the detector. The best-performing devices showed a response time of below 25 ps and dark currents below 20 pA. The devices showed linear response with the bias voltage and the laser energy

42 ENGINEERING↗
DOE OSTI2023

Laser Scribing for Electrode Patterning of Perovskite Spectrometer-Grade CsPbBr 3 Gamma-ray Detectors

Making semiconductor radiation detectors that work at room temperature relies heavily on the deposition and pixelation of electrodes. Electrode patterning of perovskite solar cells widely implements laser scribing techniques, which is a convenient, scalable, and inexpensive technique. However, this method has not found its application in radiation detector patterning yet, and the question whether laser scribing can achieve high-quality patterns with minimum damage to a detector crystal and low interpixel cross-talk remains largely unanswered. To prove that laser scribing is a practical method for electrode patterning on perovskite CsPbBr 3 detectors, we use the material to create a variety of patterns. A very low lateral leakage current (60 nA at 10 V) and high mobility-lifetime product (9.7(3) x 10 -4 cm 2 /V) were observed between the pixel and the guard ring in tests of single-pixel devices with a separation of 200 or 100 μm between the central electrode and the guard ring. The 122 and 136 keV photopeaks in 57 Co gamma-ray spectra were very well resolved with an energy resolution of up to 6.1% at 122 keV. Finally, a further reduction in gap size to 50 mu m is conceivable, but more process optimization is needed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Prominent radiative contributions from multiply-excited states in laser-produced tin plasma for nanolithography

Extreme ultraviolet (EUV) lithography is currently entering high-volume manufacturing to enable the continued miniaturization of semiconductor devices. The required EUV light, at 13.5 nm wavelength, is produced in a hot and dense laser-driven tin plasma. The atomic origins of this light are demonstrably poorly understood. Here we calculate detailed tin opacity spectra using the Los Alamos atomic physics suite ATOMIC and validate these calculations with experimental comparisons. Our key finding is that EUV light largely originates from transitions between multiply-excited states, and not from the singly-excited states decaying to the ground state as is the current paradigm. Moreover, we find that transitions between these multiply-excited states also contribute in the same narrow window around 13.5 nm as those originating from singly-excited states, and this striking property holds over a wide range of charge states. We thus reveal the doubly magic behavior of tin and the origins of the EUV light.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

FEMTOSECOND LASER DRILLING OF SILICON NITRIDE

Ceramics are employed in various engineering applications including electronics, semiconductors, automotive and aerospace industry, among others. Ceramics are desirable materials due to their high hardness, thermal resistance, chemical, thermal, and mechanical properties. A drawback of engineering ceramics is the manufacturing process. Ceramics are hard and brittle and conventional drilling or cutting methods can damage the material. These challenges in manufacturing have limited the application of ceramics in certain engineering applications. The non-contact machining of ceramics through ultrashort pulsed laser drilling offers a possible solution to the manufacturing issues. The advantage of laser drilling is the ability to machine hard and brittle materials. A laser, pulsed in the time regime of femtoseconds (fs), drills/machines sharp and well-defined holes and cuts. Additionally, the short pulse width results in limited melting, cracking, or heat transfer to the surrounding material, as well as no residual stresses. This non-contact process can greatly aid in the machining of hard materials. This study focuses on drilling into silicon nitride to produce zero-taper through holes. With this, other thicknesses can be explored, to achieve zero-taper holes.

Femtosecond laser ablation, Ceramics, Silicon Nitr↗
DOE OSTI2022

A study on sub-bandgap photoexcitation in nitrogen- and boron-doped diamond with interdigitated device structure

Diamond is an ultrawide-bandgap semiconductor suitable for high power devices that require high current carrying capacity, high blocking voltages, and smaller form factors. We investigated various diamond structures for extrinsic photoconductive semiconductor switches, including an insulating high-pressure high-temperature type Ib (highly nitrogen-doped) substrate, a chemical vapor deposited (CVD) type IIa (unintentionally doped) substrate, a CVD grown semiconducting boron-doped epilayer on a type IIa substrate, and boron-implanted type Ib and IIa substrates. Using these samples, we fabricated and characterized planar interdigitated photoconductive switches with 30 μm, electrode gaps. 532 and 1064 nm Nd:YAG laser pulses with energies up to 3.5 mJ/pulse were used to trigger the switches. Photoresponses were measured at bias voltages ranging from 10 to 100 V, corresponding to electric fields of 3.3–33 kV/cm. In this field range, the type Ib device exhibited the highest average on/off-state current ratio, on the order of 10 11 , when triggered with 0.8 mJ/pulse, 532 nm laser pulses. However, only the CVD grown boron-doped epilayer and boron implanted IIa devices showed decent sensitivity to 1064 nm.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Quantum Shell in a Shell: Engineering Colloidal Nanocrystals for a High-Intensity Excitation Regime

Many optoelectronic processes in colloidal semiconductor nanocrystals (NCs) suffer an efficiency decline under high-intensity excitation. This issue is caused by Auger recombination of multiple excitons, which converts the NC energy into excess heat, reducing the efficiency and life span of NC-based devices, including photodetectors, X-ray scintillators, lasers, and high-brightness light-emitting diodes (LEDs). Recently, semiconductor quantum shells (QSs) have emerged as a promising NC geometry for the suppression of Auger decay; however, their optoelectronic performance has been hindered by surface-related carrier losses. Here, we address this issue by introducing quantum shells with a CdS–CdSe–CdS–ZnS core–shell–shell–shell multilayer structure. Further, the ZnS barrier inhibits the surface carrier decay, which increases the photoluminescence (PL) quantum yield (QY) to 90% while retaining a high biexciton emission QY of 79%. The improved QS morphology allows demonstrating one of the longest Auger lifetimes reported for colloidal NCs to date. The reduction of nonradiative losses in QSs also leads to suppressed blinking in single nanoparticles and low-threshold amplified spontaneous emission. We expect that ZnS-encapsulated quantum shells will benefit many applications exploiting high-power optical or electrical excitation regimes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Structural measurement of electron-phonon coupling and electronic thermal transport across a metal-semiconductor interface

Scattering of energetic charge carriers and their coupling to lattice vibrations (phonons) in dielectric materials and semiconductors are crucial processes that determine the functional limits of optoelectronics, photovoltaics, and photocatalysts. The strength of these energy exchanges is often described by the electron-phonon coupling coefficient, which is difficult to measure due to the microscopic time- and length-scales involved. In the present study, we propose an alternate means to quantify the coupling parameter along with thermal boundary resistance and electron conductivity by performing a high angular-resolution time-resolved X-ray diffraction measurement of propagating lattice deformation following laser excitation of a nanoscale, polycrystalline metal film on a semiconductor substrate. Our data present direct experimental evidence for identifying the ballistic and diffusive transport components occurring at the interface, where only the latter participates in thermal diffusion. This approach provides a robust measurement that can be applied to investigate microscopic energy transport in various solid-state materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Giant self-driven exciton-Floquet signatures in time-resolved photoemission spectroscopy of MoS 2 from time-dependent GW approach

Time-resolved, angle-resolved photoemission spectroscopy (TR-ARPES) is a one-particle spectroscopic technique that can probe excitons (two-particle excitations) in momentum space. We present an ab initio, time-domain GW approach to TR-ARPES and apply it to monolayer MoS 2 . We show that photoexcited excitons may be measured and quantified as satellite bands and lead to the renormalization of the quasiparticle bands. These features are explained in terms of an exciton-Floquet phenomenon induced by an exciton time–dependent bosonic field, which are orders of magnitude stronger than those of laser field–induced Floquet bands in low-dimensional semiconductors. Our findings imply a way to engineer Floquet matter through the coherent oscillation of excitons and open the new door for mechanisms for band structure engineering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Laser ultrasonic imaging of subsurface defects with the linear sampling method

Laser ultrasonics is a remote nondestructive evaluation technique suitable for real-time monitoring of fabrication processes in semiconductor metrology, advanced manufacturing, and other applications where non-contact, high fidelity measurements are required. Here we investigate laser ultrasonic data processing approaches to reconstruct images of subsurface side drilled holes in aluminum alloy specimens. We demonstrate through simulation that the model-based linear sampling method (LSM) can perform accurate shape reconstruction of single and multiple holes and produce images with well-defined boundaries. We experimentally confirm that LSM produces images that represent the internal geometric features of an object, some of which may be missed by conventional imaging.

42 ENGINEERING↗
DOE OSTI2024

Applications of LIF to Document Natural Variability of Chlorophyll Content and Cu Uptake in Moss

Chlorophyll has long been used as a natural indicator of plant health and photosynthetic efficiency. Laser-induced fluorescence (LIF) is an emerging technique for understanding broad spectrum organic processes and has more recently been used to monitor chlorophyll response in plants. Previous work has focused on developing a LIF technique for imaging moss mats to identify metal contamination with the current focus shifting toward application to moss fronds and aiding sample collection for chemical analysis. Two laser systems (CoCoBi a Nd:YGa pulsed laser system and Chl-SL with two blue continuous semiconductor diodes) were used to collect images of moss fronds exposed to increasing levels of Cu (1, 10, and 100 nmol/cm 2 ) using a CMOS camera. The best methods for the preprocessing of images were conducted before the analysis of fluorescence signatures were compared to a control. The Chl-SL system performed better than the CoCoBi, with dynamic time warping (DTW) proving the most effective for image analysis. Manual thresholding to remove lower decimal code values improved the data distributions and proved whether using one or two fronds in an image was more advantageous. A higher DTW difference from the control correlated to lower chlorophyll a/b ratios and a higher metal content, indicating that LIF, with the aid of image processing, can be an effective technique for identifying Cu contamination shortly after an event.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

III/V silicon hybrid laser based on a resonant Bragg structure

We demonstrate a laser tunable in intensity with gigahertz tuning speed based on a III/V reflective semiconductor optical amplifier (RSOA) coupled to a silicon photonic chip. The silicon chip contains a Bragg-based Fabry–Perot resonator to form a passive bandpass filter within its stopband to enable single-mode operation of the laser. We observe a side mode suppression ratio of 43 dB, linewidth of 790 kHz, and an optical output power of 1.65 mW around 1530 nm. We also investigate using a micro-ball lens as an alternative coupling method between the RSOA and the silicon chip.

Davis, Jordan A. (ORCID:0000000343483295)↗
DOE OSTI2024

Revealing the role of redox reaction selectivity and mass transfer in current–voltage predictions for ensembles of photocatalysts

Photocatalysts are conceptually simple reaction units where nanoscale semiconductors integrated with catalysts drive a pair of redox reactions on illumination. However, the proximity of reaction sites performing cathodic and anodic reactions poses dire challenges to realize large light-to-fuel conversion efficiencies. In this study, a powerful, yet straightforward, equivalent-circuit detail-balance modeling framework is developed and applied to evaluate the performance of photocatalytic systems featuring multiple light absorbers. Specifically, low bandgap iridium-doped strontium titanate is modeled as a Z-scheme photocatalyst to achieve desirable hydrogen evolution and iron-based redox shuttle oxidation reactions. Our model has unique capabilities to simulate competing redox reactions and address mass-transfer limitations. In a significant departure from state-of-the-art circuit models, our study develops tools to perform load-line analyses by incorporating a net electrochemical load curve that includes both desired and competing redox reactions. Consequently, reaction selectivity is predicted from equivalent circuit models for photocatalytic and photoelectrochemical systems. Our investigation into ensembles comprised of multiple, semi-transparent light absorbers reveals their potential to outperform a single, optically thick light absorber, particularly when operated under mass-transfer-limited conditions. However, this outcome hinges on minimizing mass-transfer rates of select redox species to prevent undesired reactions of hydrogen oxidation and/or redox shuttle reduction. Our findings demonstrate that reaction selectivity can be achieved by tuning asymmetry in redox species mass-transfer even with perfectly symmetric electrocatalytic charge-transfer coefficients. The influences of various kinetic, mass-transfer, and thermodynamic parameters are explored to offer crucial insights for synthesis of the next-generation of photocatalysts and selective coatings, and reactor designs.

25 ENERGY STORAGE↗
DOE OSTI2023

Nanosecond Laser Drying in Wafer Foundries for Significant Energy Efficiency Improvement

Surface drying is a critical process in microelectronics wafer fabrication. In order to reduce and eliminate watermarks, many surface drying processes have been studied and used. Most of the wafer foundries currently use drying processes based on Isopropyl Alcohol (IPA), which causes serious safety (fire), health, environmental, and energy efficiency issues. The long-term goal of this project is to develop a fast, effective, chemical-free, and extremely energy efficient wafer drying technology that employs nanosecond laser-induced sub-surface evaporation and explosion. The objectives of this project are to 1) experimentally develop and verify the laser surface drying method, explore and identify how and to what extent various physical parameters influence the drying efficiency and effectiveness; and 2) understand and optimize the underlying thermodynamics in the proposed laser surface drying, including micro/nanoscale sub-surface superheating, evaporation, explosion, and photo/thermochemical bond breaking via atomistic modeling and experimental characterization. Toward these objectives, five tasks have been accomplished successfully, including 1) develop in-lab laser surface drying setup and study the effect of varied laser parameters, 2) use multiscale hybrid-modeling to study and understand the physics of water behavior during drying toward process optimization, 3) investigate the effect of drying conditions on the drying effectiveness, 4) develop a large-scale laser drying scanning system with automatic scanning, and 5) conduct large-scale simulation to study the effect of dopant level and develop strategies for system development toward industry deployment.

42 ENGINEERING↗
DOE OSTI2021

Cadmium Magnesium Telluride for Next Generation X-Ray Free Electron Laser, Synchrotron and Many Other Applications

We developed a picosecond photodetector based on our Bridgman grown and specially engineered Cadmium Magnesium Telluride (Cd 1-x Mg x Te) single crystal that is sensitive to both optical and x-ray pulses for coarse timing in Free Electron Laser applications. Cd 1-x Mg x Te is a wide bandgap semiconductor material with potential applications, not only in optoelectronics, but also in particle physics as an intense pulse radiation detector for bremsstrahlung, X-ray/gamma ray radiation, thermal neutrons, and medical imaging. However, for femtosecond optical and x-ray cross correlation, the material has to have very short lifetime, a condition that is opposite to that required for nuclear spectroscopy applications. At the same time, the material also needs to have very low bulk leakage current, in the 0.10 pA range. Hence the ability to tailor or engineer the material is very crucial. In this paper, picosecond response and the crystal growth of this specially engineered cadmium magnesium telluride material will be presented. Other material characterization and transient measurements will also be discussed along with room temperature semiconductor detector performance for other nuclear radiation detection applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Structured light approaches in laser-based plasma diagnostics

There is a growing demand for plasma diagnostics suitable for industrial plasma reactors employed in semiconductor nanofabrication, especially relevant to microelectronics and quantum information systems. Such reactors typically have limited optical access and pose considerable diagnostic challenges, including intense background emission, significant thermal loads, and contamination of optical viewports. In this study, we outline research into structured light techniques (laser beams with tailored spatial, temporal, or phase characteristics) that effectively overcome these issues using laser-induced fluorescence (LIF) as an example. The focus of presented diagnostics is on ion kinetics analysis within an industrial plasma source, although this approach is broadly applicable to other plasma systems and diagnostic contexts. We present a confocal LIF implementation using an axicon-generated Bessel annular beam, achieving spatial resolutions of approximately 5 mm at a focal distance of 300 mm, with potential improvements to about 1 mm. This approach matches conventional orthogonal LIF performance but requires only one optical port. Wavelength-modulation LIF employs nonlinear laser wavelength tuning to measure spectral line derivatives, suppressing background emission and enhancing details of spectral line shape. Additionally, we present new results on applying vortex beams (laser beams carrying orbital angular momentum, OAM) for LIF measurements in an industrial plasma device. These measurements enable simultaneous axial and tangential velocity determination using a single laser beam and have been tested with xenon ion transition. Initial quantification of results was performed. Together, these structured-light approaches provide robust, background-resilient, multi-dimensional diagnostics for complex plasma environments.

Romadanov, Ivan [Princeton Plasma Physics Laborato↗
DOE OSTI2023

Enhanced Photoluminescence and Prolonged Carrier Lifetime through Laser Radiation Hardening and Self-Healing in Aged MAPbBr3 Perovskites Encapsulated in NiO Nanotubes

Organic-inorganic perovskites hold great promise as optoelectronic semiconductors for pure color light emitting and photovoltaic devices. However, challenges persist regarding their photostability and chemical stability, which limit their extensive applications. This paper investigates the laser radiation hardening and self-healing-induced properties of aged MAPbBr3 perovskites encapsulated in NiO nanotubes (MAPbBr3@NiO) using photoluminescence (PL) and fluorescence lifetime imaging (FLIM). After deliberately subjecting the MAPbBr3@ NiO to atmospheric conditions for two years, the sample remains remarkably stable. It exhibits no changes in PL wavelength during UV laser irradiation and self-healing. Furthermore, exposure to UV light at 375 nm enhances the PL of the self-healed MAPbBr3@NiO. FLIM analysis sheds light on the mechanism behind photodegradation, self-healing, and PL enhancement. The results indicate the involvement of many carrier-trapping states with low lifetime events and an increase in peak lifetime after self-healing. The formation of trapping states at the perovskite/nanotube interface is discussed and tested. This study provides new insights into the dynamics of photo-carriers during photodegradation and self-healing in organic-inorganic perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Polarization Flipping of Even-Order Harmonics in Monolayer Transition-Metal Dichalcogenides

We present a systematic study of the crystal-orientation dependence of high-harmonic generation in monolayer transition-metal dichalcogenides, WS 2 and MoSe 2 , subjected to intense linearly polarized midinfrared laser fields. The measured spectra consist of both odd- and even-order harmonics, with a high-energy cutoff extending beyond the 15th order for a laser-field strength around ~1 V/nm. In WS 2 , we find that the polarization direction of the odd-order harmonics smoothly follows that of the laser field irrespective of the crystal orientation, whereas the direction of the even-order harmonics is fixed by the crystal mirror planes. Furthermore, the polarization of the even-order harmonics shows a flip in the course of crystal rotation when the laser field lies between two of the crystal mirror planes. By numerically solving the semiconductor Bloch equations for a gapped-graphene model, we qualitatively reproduce these experimental features and find the polarization flipping to be associated with a significant contribution from interband polarization. In contrast, high-harmonic signals from MoSe 2 exhibit deviations from the laser-field following of odd-order harmonics and crystal-mirror-plane following of even-order harmonics. We attribute these differences to the competing roles of the intraband and interband contributions, including the deflection of the electron-hole trajectories by nonparabolic crystal bands.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ultranarrow electroluminescence from magnetic excitons in the van der Waals antiferromagnetic semiconductor NiPS 3

Electrically driven light emission from two-dimensional (2D) semiconducting materials has enabled numerous optoelectronic technologies, including light-emitting diodes, solid-state lasers, and single-photon sources for quantum communication. Here we report ultranarrow electroluminescence from the magnetic excitonic state of the van der Waals antiferromagnetic semiconductor NiPS 3 . This electroluminescence is enabled by the fabrication of gate-tunable NiPS 3 devices that remain electrically conductive below the antiferromagnetic ordering temperature of 155 K, ultimately allowing field-effect mobilities of 1.3 cm 2 V –1 s –1 and 4.5 cm 2 V –1 s –1 to be directly measured at room temperature and 7 K, respectively. By applying a high-frequency square wave voltage to the gate electrode of the resulting field-effect transistors, electroluminescence is capacitively induced from the magnetic excitons of NiPS 3 . Due to the coupling of these excitons with the underlying NiPS 3 antiferromagnetic order, the electroluminescence has an ultranarrow linewidth of 1 meV and a high degree of linear polarization (ρ = 0.78). In addition to facilitating fundamental studies of the coupling between spin states and excitons in van der Waals magnetic semiconductors, this work will accelerate the development of emerging 2D opto-spintronic applications.

two-dimensional materials↗