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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Defect-Limited Carrier Lifetime in Epitaxially Strained Germanium-On-Silicon Heterostructures

Epitaxially strained germanium-on-silicon (Ge-on-Si) heterostructures are central to next-generation photonic and electronic devices, yet their performance remains strongly constrained by defect-limited carrier lifetimes. In this work, we investigate the impact of defects on the carrier lifetime in relaxed Ge-on-Si and strained Ge-on-Si heterostructures. High-resolution X-ray diffraction quantifies the strain-state in Ge and reveals signatures of strain relaxation due to lattice mismatch. Cross-sectional and plan-view transmission electron microscopy analyses enable direct visualization of interfacial defects and quantification of threading dislocation densities (TDDs) within the Ge layer. However, the presence of a dense misfit dislocation network obscures the threading dislocation signatures, preventing reliable TDD determination by plan-view transmission electron microscopy in strained-Ge (..epsilon..-Ge). To assess the defect density in this case, etch-pit density measurements were performed, providing an alternative means of quantifying the TDDs in the ..epsilon..-Ge layer. Carrier lifetime measurements by microwave-reflection photoconductive decay reveal a clear relationship with TDDs ranging from 5 x 103 cm-2 to 2 x 1010 cm-2, confirming Shockley-Read-Hall recombination as the limiting mechanism at lower defect densities, with TDD-dominated recombination at higher defect densities. The Ge-on-Si relaxed heterostructure exhibited lifetimes much lower (~12 ns) than the lattice-matched Ge on gallium arsenide (GaAs) (~158 ns) heterostructure. Introducing controlled tensile strain reduces defect formation, suppresses strain-relaxation pathways, and leads to measurable improvements in minority carrier lifetime from 12 ns to 171 ns. These results establish a direct relation between defect suppression and carrier recombination dynamics in both relaxed Ge-on-Si grown directly on Si and strained Ge-on-Si heterostructures incorporating compound-semiconductor buffer layers, offering a materials-driven pathway for engineering Ge with improved carrier lifetime for photonic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Alpha-relaxation by scattering and medium-range atomic correlation in simple liquids

The relaxation dynamics of liquid and glass can be studied by inelastic x-ray or neutron scattering through the intermediate scattering function F(Q, t), where Q is the momentum transfer of scattering. Because of the time-consuming nature of these measurements, F(Q, t) is usually measured only at the first peak of the structure function S(Q), and its principal decay time is referred to as the α-relaxation time τ α . τ α is generally considered to describe the relaxation time of the bulk, which is related to viscosity and is controlled by the atomic cage around an atom. Here, through simulations on metallic liquids, we show that the α-relaxation time determined by scattering experiments does not purely reflect viscosity but is influenced by changes in spatial cooperativity. We also demonstrate that atomic caging is not exerted by the nearest neighbors but involves more cooperative atomic dynamics of the atomic medium-range order.

Glass transitions↗
DOE OSTI2025

Static and dynamic properties of the frustrated spin-$\frac{1}{2}$ depleted-kagome antiferromagnet Cu 7 (TeO 3 ) 2 (SO 4 ) 2 (OH) 6

The structural and magnetic properties of the two-dimensional spin-$\frac{1}{2}$ depleted-kagome compound Cu 7 (TeO 3 ) 2 (SO 4 ) 2 (OH) 6 are investigated using x-ray diffraction, magnetization, heat capacity, and 1 H Nuclear Magnetic Resonance (NMR) measurements. From the analysis of magnetic susceptibility, we found a large Curie-Weiss temperature [𝜃 CW = −50⁢(2)⁢K] and the coexistence of antiferromagnetic and ferromagnetic interactions. The value of 𝜃 CW gives an estimate of the average nearest-neighbor antiferromagnetic interaction of 𝐽/𝑘 B ≃ 66K. The NMR relaxation rates (1/𝑇 1 and 1/𝑇 2 ) exhibit a peak, providing evidence for a magnetic long-range order at 𝑇* ≃ 4K which appears to be canted antiferromagnetic type. Heat capacity also features a broad maximum at 𝑇* that moves towards higher temperatures with increasing magnetic field, reflecting defect induced Schottky anomaly. The frustration parameter 𝑓 𝑟 = |𝜃 CW |/𝑇* ≃ 12.5 renders the compound a highly frustrated low-dimensional magnet.

Akshay, K. U. [Indian Institute of Science Educati↗
DOE OSTI2025

Etching-Chemistry-Driven Ruthenium Doping on Ti 3 C 2 T x MXene for Optimizing Electrochemical Performance

We demonstrate that the etching chemistry used during MXene synthesis from Ti 3 AlC 2 MAX phase significantly influences surface functionalization and structural vacancies, which in turn affect ruthenium (Ru) ion interactions. Using hydrofluoric acid (HF) and ammonium bifluoride (NH 4 HF 2 ) as etchants, we obtained MXene surfaces with distinct functional groups and Ti vacancies that impact Ru ion interactions and electrochemical performance. Both MXene variants (labeled MX(H) and MX(N), respectively) exhibited negative zeta potentials in their pristine state, but upon the addition of Ru the zeta potential for MX(H) reached 12.9 mV while that for MX(N) remained negative at −6.4 mV. This adsorption resulted in a 14.4-fold increase in the specific capacitance of MX(H)/Ru compared to pristine MX(H), whereas MX(N)/Ru exhibited only a 4.4-fold increase over its pristine counterpart. X-ray diffraction analysis identified the formation of ammonium titanium oxide fluoride, (NH 4 ) 3 TiOF 5 , on MX(N), which likely contributed to its reduced Ru adsorption. X-ray photoelectron spectroscopy suggested the presence of Ti vacancies in both MXene variants; however, their behavior toward Ru accommodation differed markedly, with MX(H) showing the most obvious shift in the Ti 2p peak in the XPS survey spectrum, while MX(N) showed the most obvious shift in the C 1s peak. Electron paramagnetic resonance spectroscopy further demonstrated a distinct alteration in the spectral signatures of MX(H) upon Ru addition, in contrast to the negligible changes in MX(N), indicating effective passivation of the Ti defect sites in MX(H) via vacancy-assisted Ru doping. Cyclic voltammetry showed that Ru-incorporated MX(H) nanocomposites exhibit more efficient redox-active sites, as reflected in their higher capacitance values. These findings highlight the pivotal role of MXene surface chemistry in controlling cation adsorption, providing valuable insights for the rational design of high-performance electrodes.

2D surface engineering↗
DOE OSTI2026

Structure of Complex Liquid–Liquid Extraction Organic Phases for Rare Earth Separations

Complex, multicomponent liquids with hierarchical structure and phase transitions are encountered in many natural and industrial processes, including in chemical separations. One notable example is aggregation and organic phase splitting in liquid–liquid extraction (LLE) of metal ions. While these two phenomena that have long been closely associated, a mechanistic link between mesoscale structure and the capacity-limiting organic phase splitting remains elusive due to complexity of these systems. Here, in this study, we combine small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS), and molecular dynamics simulation to reveal a comprehensive picture of structure at the nano- and mesoscale in these complex solutions. For the representative case of rare earth extraction from an acidic aqueous phase by a malonamide extractant in dodecane, we investigate a wide range of process-relevant extractant and acid concentrations to provide a complete picture of how aggregation depends on composition. We decompose organic phase structure from SAXS into two contributions, which together can capture the scattering at all compositions: composition fluctuations described by the Ornstein–Zernike equation at low wavenumber Q, and nanostructure modeled by a “pre-peak” at intermediate Q. The former contains information about the thermodynamics of demixing, while the latter reflects nanoscopic self-assembly of the extractant and extracted solutes. While fluctuations have typically not been considered in the literature, we find they in fact dominate the total structure for nearly all practical conditions. As only the fluctuations have a strong temperature response, we confirm this attribution with temperature-dependent SAXS measurements, including for extracted europium nitrate complexes. SAXS and XPCS measurements near the critical point find static and dynamic scaling consistent with theory. Overall, this new paradigm for understanding LLE organic phases connects composition, nanoscale, and mesoscale structuring to phase behavior, providing both a comprehensive picture of solution structure and a quantitative link between aggregation and third phase formation.

Peroutka, Allison A. [Argonne National Laboratory ↗
DOE OSTI2025

In situ Visible Light and Thermal Imaging Data from a Laser Powder Bed Fusion Additive Manufacturing Process Co-Registered to X-ray Computed Tomography and Fatigue Data

This dataset is comprised of in situ sensing data collected during a laser-based powder bed fusion additive manufacturing process, as well as rasterized scan path information, post-build X-ray computed tomography (XCT), and fatigue test results. A total of 64 cylinders, approximately 15 mm in diameter and 102 mm tall, were printed out of stainless steel 316H on a Colibrium Additive Concept Laser M2 Series 5 machine. Parameters known to produce dense material were used to construct 56 of these cylinders, while the remaining 8 cylinders were printed with relatively high energy density parameters prone to producing keyhole pores. In addition, two spatter generation blocks were constructed upstream of the 64 cylinders such that ejecta produced during the melting of the spatter generators were stochastically seeded onto the 64 cylinders. Based on previous experiments, these spatter particles were theorized to produce stochastic lack-of-fusion pores. During the construction of the build, high-resolution images of reflected light in the visible spectrum were captured both before and after recoating for each print layer. Additionally, temporally integrated thermal imaging in the near infrared spectrum produced integrated sum and max images on a layerwise basis. The multimodal in situ data has been co-registered to the build plate coordinate system, allowing for identification of process anomalies (e.g., spatter particles) apparent in the two sensors. Following construction of the build, the cylinders were subjected to XCT to identify internal flaws, and the resulting data have also been registered to the build plate coordinate system. Finally, 60 of the 64 cylinders were machined into fatigue coupons conforming to ASTM E466 and subsequently subjected to either high- or -low-cycle fatigue testing. The results of the fatigue tests have also been included in the dataset, and the XCT data corresponded to the approximate location of the gauge sections of the machine fatigue specimen geometry.

42 ENGINEERING↗
DOE OSTI2026

Pressure-Stabilized MnSb2 with Complex Incommensurate Magnetic Order

Marcasite-type compounds have been proposed as promising hosts of exotic magnetic quantum states, yet experimental realizations in stoichiometric, disorder-free systems remain limited. Here, we report the high-pressure stabilization and magnetic characterization of MnSb2, a marcasite-type compound that is thermodynamically metastable under ambient pressure. Single crystals were synthesized using a cubic multianvil press at 3.3 GPa and 490 °C for 24 h, and powder and single-crystal X-ray diffraction confirm the orthorhombic Pnnm structure. These crystals are stable at ambient pressure for a long time up to between 450 and 500 K. Heat-capacity measurements reveal phase transitions at approximately T0 ∼ 118 K and T1 ∼ 220 K. Neutron diffraction uncovers an unconventional magnetic state below T1 ∼ 220 K. Magnetic powder neutron diffraction refinements reveal possible multiple magnetic configurations that provide comparably acceptable fits to the experimental data. While most solutions are consistent with a spin-density-wave (SDW) description, helical models systematically yield inferior agreement factors. Across a broad range of models, the Mn ordered moment reaches a maximum value of approximately 2 μB and remains predominantly collinear, with minimal canting along the c-axis. At 200 K, the magnetic propagation vector is q = (0, 0.3975, 0.3783); upon cooling, the b component increases toward 0.5, reflecting a temperature-dependent evolution of the modulation. The need for modification of the magnetic model between high and low temperatures further highlights the complex and strongly temperature-dependent nature of the magnetic order in this system. These results establish MnSb2 as a pressure-stabilized marcasite magnet with a tunable, complex magnetic state and a compelling stoichiometric platform for exploring unconventional magnetic behavior, including potential altermagnetism.

Xu, Mingyu [Michigan State University , , , ,; Iow↗
DOE OSTI2025

Massive compression for high data rate macromolecular crystallography (HDRMX): impact on diffraction data and subsequent structural analysis

New higher-count-rate, integrating, large-area X-ray detectors with framing rates as high as 17400 images per second are beginning to be available. These will soon be used for specialized macromolecular crystallography experiments but will require optimal lossy compression algorithms to enable systems to keep up with data throughput. Some information may be lost. Can we minimize this loss with acceptable impact on structural information? To explore this question, we have considered several approaches: summing short sequences of images, binning to create the effect of larger pixels, use of JPEG-2000 lossy wavelet-based compression, and use of Hcompress, which is a Haar-wavelet-based lossy compression borrowed from astronomy. We also explore the effect of the combination of summing, binning, and Hcompress or JPEG-2000. In each of these last two methods one can specify approximately how much one wants the result to be compressed from the starting file size. These provide particularly effective lossy compressions that retain essential information for structure solution from Bragg reflections.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Structural Investigation of Six Quinary Sulfides Synthesized via the Flux-Assisted Boron-Chalcogen Mixture (BCM) Method: Eu 2+ Containing Members of the RE 3 MTQ 7 (M and T = Transition or Main Group Metals, Q = Chalcogens) Family

For this work, a series of six quinary rare-earth sulfides Ce 4+ 1.85 Eu 2+ 1.15 Na 0.30 SiS 7 , Ce 4+ 1.91 Eu 2+ 1.09 K 0.18 SiS 7 , Ce 4+ 1.96 Eu 2+ 1.04 Rb 0.08 SiS 7 , Ce 4+ 1.98 Eu 2+ 1.02 Cs 0.05 SiS 7 , Ce 4+ 1.97 Eu 2+ 1.03 Ag 0.06 SiS 7 , and Ce 4+ 1.50 Eu 2+ 1.50 CuSiS 7 were obtained in an alkali iodide flux using the boron-chalcogen mixture (BCM) method. Single crystal X-ray diffraction was used to determine the structures of the high quality single crystals that were grown; their elemental compositions were confirmed by energy-dispersive spectroscopy (EDS). The compounds crystallize in the hexagonal crystal system in the noncentrosymmetric space group P63. The crystal structure consists of a three-dimensional network composed of mixed cerium and europium bicapped trigonal prisms, isolated SiS4 tetrahedra, and monovalent metals (Na, K, Rb, Cs, Ag, and Cu) located in cavities created by linked Ce/EuS 8 polyhedra. The structures are charge-balanced when Ce and Eu are in their +4 and +2 oxidation states, respectively. The effective magnetic moment of Ce 1.50 4+ Eu 1.50 2+ CuSiS 7 determined from the temperature dependence of the magnetic susceptibility data is consistent with the presence of Ce 4+ and Eu 2+ . Clear correlations between the alkali ion site occupancy, the ionic radius of the alkali cations, and the average bond length of Ce 4+ /Eu 2+ –S, were established. UV–vis diffuse reflectance data were collected for Ce 1.50 4+ Eu 1.50 2+ CuSiS 7 and a band gap of 1.9(1) eV was established.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Pervasive symmetry-lowering nanoscale structural fluctuations in the cuprate La 2−𝑥 ⁢Sr 𝑥 ⁢Cu⁢O 4

The cuprate superconductors are among the most widely studied quantum materials, yet there remain fundamental open questions regarding their electronic properties and the role of structural degrees of freedom. Recent neutron and x-ray scattering measurements uncovered exponential scaling with temperature of the strength of orthorhombic fluctuations in the tetragonal phase of La 2−𝑥⁢ Sr 𝑥 ⁢Cu⁢O 4 and Tl 2 ⁢Ba 2 ⁢Cu⁢O 6+𝛿 , unusual behavior that closely resembles prior results for the emergence of superconducting fluctuations, and that points to a common origin rooted in inherent correlated structural inhomogeneity. Here, in this study, we use neutron and x-ray diffuse scattering to provide further insight into structural fluctuations in La 2−𝑥 ⁢Sr 𝑥 ⁢Cu⁢O 4 . We perform measurements up to temperatures that approach the melting point of the undoped parent compound, and we investigate the effects of in situ in-plane uniaxial elastic stress and plastic deformation. Our neutron scattering results for the parent compound La 2 ⁢Cu⁢O 4 reveal that short-range orthorhombic fluctuations persist to the maximum experimental temperature of nearly 1000 K, i.e., to a significant fraction of the crystallization temperature. At this temperature, the spatial characteristic length extracted from the momentum-space data is still about three lattice constants. The neutron scattering experiment enables quasistatic discrimination and reveals that the response is increasingly dynamic at higher temperatures. We also find that neither compressive elastic stress along the tetragonal [110] direction nor irreversible plastic deformation activating the ⟨100⟩⁢[001] slip system significantly alter the robust orthorhombic fluctuations. Overall, these results support the notion that these fluctuations couple to subtle, underlying inhomogeneity that underpins the cuprate phase diagram. Finally, in La 1.8⁢ Sr 0.2⁢ Cu⁢O 4 , we uncover low-energy structural fluctuations at a nominally forbidden reflection that are distinct from the orthorhombic distortions. While the origin of these fluctuations is not clear, they might be related to the presence of extended defects such as dislocations or stacking faults.

Spieker, R. J. [Univ. of Minnesota, Minneapolis, M↗
DOE OSTI2026

Energy density driven ultrafast electronic excitations in a cuprate superconductor

Controlling nonequilibrium dynamics in quantum materials requires ultrafast probes with spectral selectivity. We report femtosecond reflectivity measurements on the cuprate superconductor Bi 2⁢ Sr 2⁢ CaCu 2 ⁢O 8+𝛿 using free-electron laser extreme-ultraviolet (23.5–177 eV) and near-infrared (1.5 eV) pump pulses. EUV pulses access deep electronic states, while NIR light excites valence-band transitions. Despite these distinct channels, both schemes produce nearly identical dynamics: above 𝑇 𝑐 , excitations relax through fast (100–300 fs) and slower (1–5 ps) channels; below 𝑇 𝑐 , a delayed component signals quasiparticle recombination and condensate recovery. We find that when electronic excitations are involved, the ultrafast response is governed mainly by absorbed energy rather than by the microscopic nature of the excitation. In contrast, bosonic driving in the THz or midinfrared produces qualitatively different dynamics. By demonstrating that EUV excitation of a correlated superconductor yields macroscopic dynamics converging with those from optical pumping, this work defines a new experimental paradigm: FEL pulses at core-level energies provide a powerful means to probe and control nonequilibrium electronic states in quantum materials on their intrinsic femtosecond timescales. This establishes FEL-based EUV pumping as a new capability for ultrafast materials science, opening routes toward soft x-ray and attosecond studies of correlated dynamics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Epitaxial registry and transport properties in V4O7 thin films

We report the growth of V4O7 thin films deposited simultaneously on amorphous SiO2 and crystalline c-cut Al2O3 substrates. x-ray diffraction shows that films grown on SiO2 are polycrystalline with no preferred orientation, while films grown on Al2O3 exhibit a well-defined out-of-plane orientation and an in-plane registry consistent with epitaxial growth. Transmission electron microscopy confirms the crystallographic relationship between the V4O7 film and the Al2O3 substrate. Atomic force microscopy indicates substantially lower surface roughness for films grown on Al2O3 (~6 nm) compared to those grown on SiO2 (~22 nm), and Raman spectroscopy confirms stabilization of the same V4O7 phase on both substrates. Electrical transport measurements reveal a metal–insulator transition near 244 K for both substrates, with thermal hysteresis not exceeding ~1 K. Although the transition temperature remains essentially unchanged, films grown on Al2O3 exhibit higher conductivity over the entire temperature range, exceeding that of films grown on SiO2 by approximately two orders of magnitude at 100 K and by a factor of five at 300 K. These results indicate that the conductivity differences are consistent with variations in microstructural connectivity associated with crystallographic order.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Frustration-driven magnetic correlations in the spin-$\frac{5}{2}$ triangular lattice antiferromagnet RbFe⁢(HPO 3 ) 2

Here, a detailed study of the structural and magnetic properties of a spin-5/2 triangular lattice antiferromagnet RbFe⁢(HPO 3 ) 2 is presented using x-ray diffraction, magnetization, heat capacity, and 31 P nuclear magnetic resonance (NMR) experiments on a polycrystalline sample. The crystal structure features an equilateral triangular lattice of Fe 3+ ions. The thermodynamic measurements reveal the onset of a magnetic long-range order at 𝑇 N⁢1 ≃7.8K in zero field, followed by another low-temperature field-induced ordering at 𝑇 N⁢2 in higher fields. The transition at 𝑇 N⁢1 is further confirmed from the NMR spin lattice relaxation measurements. The value of the frustration ratio (𝑓≃7) implies moderate spin frustration in the compound. The 31 P NMR spectra exhibit two distinct spectral lines corresponding to two inequivalent phosphorus sites (P1 and P2), consistent with the crystal structure. The P1 site is strongly coupled with an isotropic hyperfine coupling of 𝐴$^{iso}_{hf}$ = 0.55⁢(2)⁢ T/𝜇 B while the P2 site is weakly coupled with 𝐴$^{iso}_{hf}$ = 0.25⁢(3)⁢ T/𝜇 B with the Fe 3+ ions. The magnetic susceptibility and NMR shift data are described well assuming a spin-5/2 isotropic triangular lattice antiferromagnetic model with an average exchange coupling of 𝐽/𝑘 B = 2.8⁢(2)⁢K. Below 𝑇 N⁢1 , the spectra evolve into a nearly rectangular powder pattern, indicating a commensurate antiferromagnetic type order. The 31 P spin-lattice relaxation rate well below 𝑇N⁢1 follows a 𝑇 3 temperature dependence, implying a two-magnon Raman scattering mechanism in the ordered state. Three well-defined phase regimes are clearly ascertained in the 𝐻−𝑇 phase diagram, reflecting a weak magnetic anisotropy in the compound.

Nagpal, V. [Indian Institute of Science Education ↗
DOE OSTI2025

Structural and Mechanistic Advances in the Chemistry of Methyl-Coenzyme M Reductase (MCR)

Methane represents 34% of U.S. energy consumption and is a major greenhouse gas related to the global carbon cycle and energy production. However, current industrial practices significantly increase atmospheric methane levels, necessitating a deeper understanding of its biosynthesis and oxidation. Methyl-coenzyme M reductase (MCR) is central to biological methane metabolism, catalyzing the final step of methanogenesis and the first step in anaerobic methane oxidation. It is also a key target for strategies to capture and transform methane into value-added chemicals.The active site of MCR is a buried Ni-based cofactor only accessible by the substrates via a 50 Å long tunnel. Although the Ni(I) state is required to initiate catalysis, capturing this state remains a challenge for the current structural techniques. Recent advances in structural biology using X-ray Free-Electron Laser serial crystallography have provided insights into MCR's inactive Ni(II) state at room temperature and show promise for capturing its active Ni(I) form.Our team has established several critical aspects of the MCR mechanism using a combination of experimental and computational studies. MCR uses CH 3 -SCoM and CoBSH as substrates, producing methane and a disulfide product CoMSSCoB. Kinetic analysis showed that productive substrate binding requires CH 3 -SCoM to bind first, inducing conformational changes that optimize the active site for subsequent CoBSH binding. Following substrate binding, four proposed methane production/oxidation mechanisms were examined, establishing whether the reaction proceeds through an organometallic methyl-nickel(III), methyl anion ion, or methyl radical intermediate. Experimental measurements using CoBSH analogs successfully slowed the reaction, allowing for mechanistic insight that demonstrated the methyl radical pathway, where the initial interactions involve homolytic cleavage of the methyl-sulfur bond, generating a methyl radical that quickly abstracts the thiol hydrogen atom of CoBSH to form methane. Computational studies further confirmed that, compared to other mechanisms, the methyl radical mechanism is thermodynamically more favorable and accessible under physiological conditions.Spectroscopic and computational studies challenged the conventional understanding of substrate binding in MCR by proposing an alternative positioning of CH 3 -SCoM and CoMSSCoB in the active site pocket. The research suggested that CH 3 -SCoM (substrate) and CoMSSCoB (product) bind via their sulfonate groups to the Ni(I) center of cofactor F 430 . This binding allows for the reaction without substrate reorganization in the pocket but would require a long-range electron transfer. Altogether, the work summarized in this review reflects our current understanding of the enzyme's catalytic mechanism and structural dynamics. This is essential for developing efficient methane conversion technologies that could mitigate its environmental impact while harnessing energy-storage properties.

03 NATURAL GAS↗
DOE OSTI2025

Revealing mechanisms of processing defect mitigation in laser powder bed fusion via shaped beams using high-speed X-ray imaging

The laser powder bed fusion (LPBF) process utilizing a focused Gaussian-shaped beam faces challenges, including pore formation, melt pool fluctuation and liquid spattering. While beam shaping technology has been explored as a potential approach for defect mitigation, the beam-matter interaction dynamics during melting with shaped beams remain unclear. Here, we report the direct observation of ring-shaped beam-matter interaction dynamics, including pore formation, melt pool fluctuation and liquid spattering, and unveil defect mitigation mechanisms in ring-shaped beam laser powder bed fusion process. Here, we find that, by spatially manipulating incident laser rays, the ring-shaped beam controls keyhole morphology, thereby managing the distribution of the reflected rays. This manipulation can effectively eliminate the formation of an unstable cavity at the keyhole tip, stabilizing the keyhole and mitigating keyhole pores. This enhanced keyhole stability effectively reduces the melt pool fluctuation, the formation of liquid breakup induced spatters and liquid droplet colliding induced large spatters in the laser powder bed fusion process. Additionally, the high-energy forefront of the ring-shaped beam effectively melts the powder bed, reducing agglomeration liquid spatter in the laser powder bed fusion process. The discovered defect mitigation mechanisms may guide the design of beam shaping strategies for simultaneously increasing the quality and productivity of metal additive manufacturing.

Beam shaping↗
DOE OSTI2025

Development of fiber orientation in injection molding: Comparison of glass fiber, carbon fiber and their hybrid composites

Fiber orientation distribution (FOD) in injection-molded panels with respect to distance from the gate was analyzed using X-ray computed tomography (X-CT) for glass fiber (GF), carbon fiber (CF), and hybrid CF/GF (CGF) reinforced nylon 66. To understand the reason behind the FOD with different fiber types, computational fluid dynamics (CFD) and rheology were performed. Samples were extracted at three locations: near the gate, center, and opposite end. Thickness of the layers of typical skin-shell-core type FOD varied with fiber type and location. GF achieved flow direction alignment (in shell) earlier than viscous CF and CGF near the gate, whereas CF showed the highest flow-direction alignment at the center due to shear induced orientation. At the opposite end, GF experienced more backflow than others indicating faster mold filling owing to its lower viscosity. Hybrid CGF exhibited GF-dominated center and CF-dominated end region. The numerical model used to obtain FOD and rheological predictions for the CF and GF composites served to corroborate the trends observed in the experimental trials. The FOD responses across fiber types and location were reflected in their longitudinal and transverse properties. Only GF showed higher longitudinal modulus over transverse modulus near the gate attributed to rapid alignment, whereas CF and CGF exhibited opposite trend. However, fountain flow enhanced the longitudinal modulus over transverse modulus with the distance for all, particularly for CF. This study offers insights into mold filling behavior of different fibers which are critical in optimizing injection molding conditions for tailored final properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Optical and Plasmonic Properties of High-Electron-Density Epitaxial and Oxidative Controlled Titanium Nitride Thin Films

The present paper reports on the fabrication, detailed structural characterizations, and theoretical modeling of titanium nitride (TiN) and its isostructural oxide derivative, titanium oxynitride (TiNO) thin films that have excellent plasmonic properties and that also have the potential to overcome the limitation of noble metal and refractory metals. The TiNO films deposited at 700 °C in high vacuum conditions have the highest reflectance (R = ~ 95%), largest negative dielectric constant (ε 1 = –161), and maximal plasmonic figure of merit (FoM = –ε 1 /ε 2 ) of 1.2, followed by the 600 °C samples deposited in a vacuum (R = ~ 85%, ε 1 = –145, FoM = 0.8) and 700 °C–5 mTorr sample (R = ~ 82%, ε 1 = –8, FoM = 0.3). To corroborate our experimental observations, we calculated the phonon dispersions and Raman active modes of TiNO by using the virtual crystal approximation. From the experimental and theoretical studies, a multilayer optical model has been proposed for the TiN/TiNO epitaxial thin films for obtaining individual complex dielectric functions from which many other optical parameters can be calculated. The advantages of oxide derivatives of TiN are the continuation of similar free electron density as in TiN and the acquisition of additional features such as oxygen-dependent semiconductivity with a tunable bandgap.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Variable Bragg x-ray beam splitters

Beam splitters are utilized in a variety of advanced x-ray instruments and are essential for extending quantum optics techniques to x rays. A new fabrication method has produced thinned Bragg diffracting silicon devices with variable reflectivity and transmission coefficients and negligible absorption losses. Diffraction measurements confirm that silicon continues to exhibit perfect crystal diffraction even for thicknesses below two microns. Devices are machined from standard wafers, with the thinned regions contained within the robust frame of an unperturbed crystal for ease of handling.

Powers, L. T. (ORCID:000900047481248X)↗