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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Tuning the Magnetic Properties of CrI 3 Using Ni Thin Film Deposition for Applications in Spintronic Devices

Chromium triiodide (CrI 3 ), a van der Waals magnet, has recently been shown to host Ising ferromagnetism down to the monolayer limit. It is a potentially important material in 2D magnet-based applications, such as magnetic sensors and spintronic devices. Prior studies have revealed the coexistence of two different types of interlayer magnetic coupling, the antiferromagnetic (AFM) coupling near the surface and ferromagnetic (FM) coupling in the deep bulk layers, in pristine CrI 3 crystals below the Curie temperature. In this study, we used Ni thin film deposition to tune the surface magnetic states in bulk CrI 3 . A nanometer thickness (4 nm thick) of Ni was deposited on the surface of CrI 3 using electron-beam evaporation to form a Ni/CrI 3 heterostructure. The deposited Ni thin layer forms nanoclusters that completely cover the CrI 3 surface. Magnetic states of CrI 3 before and after Ni deposition are probed by ultralow-frequency magneto-Raman spectroscopy. Instead of seeing three spin wave branches in Raman scattering below 2 T, as in pristine bulk CrI 3 , in Ni/CrI 3 , we observe only a single spin wave branch, which is softened compared to that in pristine CrI 3 and displays a Zeeman shift under an out-of-plane magnetic field up to 7 T. This observation reveals that the AFM layers on pristine CrI 3 crystal surfaces transit into FM layers, so the entire CrI 3 crystal is in the FM state after Ni deposition. First-principles calculations show that Ni atoms tend to diffuse into the CrI 3 lattice, and the FM interlayer coupling has a much lower energy than AFM coupling in the presence of Ni atoms. As a result, our studies show that the magnetic state of CrI 3 can be modified through deposition of a thin metal layer on the surface, offering a route for controlling the spin degree of freedom in van der Waals magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Molecular beam epitaxy of superconducting zirconium nitride on GaN substrates

Epitaxial integration of metals and semiconductors can enable enhanced performance and novel functionality. Achieving such pristine interfaces with superconducting materials is of increasing interest for quantum devices and detectors, but the experimental demonstration remains challenging, given the very limited studies on single crystalline systems. To expand the potential materials for these systems, this work explores the deposition of zirconium nitride superconducting thin films on GaN substrates at various temperatures using molecular beam epitaxy. A general trend of decreasing superconducting critical temperature is observed as the deposition temperature is reduced. The optical properties reveal a transition from metallic to dielectric behavior with colder deposition. The plasma frequency of the metallic films is also observed to be a function of growth temperature. These results pave the way for the integration of a highly tunable metal nitride with a well-established semiconductor system.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Efficient laser-driven proton acceleration from a petawatt contrast-enhanced second harmonic mixed-glass laser system

Efficient laser-driven plasma acceleration of ion beams requires precision control of the target–plasma profile, which is crucial to optimize the laser energy transfer. Along the laser propagation direction, this can be achieved by tailoring the temporal structure of the laser pulse. We show for the first time that frequency-doubling of a short pulse (hundreds-femtosecond range) petawatt-class mixed-glass laser system, which results in temporal intensity contrast enhancement, enables surface and volumetric laser–energy coupling, and the acceleration of proton beams from few-nanometer-thick foil targets. Experimentally, maximum ion energies and laser-to-proton energy conversion efficiencies were found to be both maximized at optimum laser and target conditions manifested when the normalized target density nearly equalizes the normalized laser vector potential, which is in agreement with theory and simulations. These signatures are recognized as a unique indication of the interaction between ultra-intense laser pulses with high temporal intensity contrast and ultra-thin nanometer-scale targets. Transverse modulations of accelerated proton beams in the form of bubble- and ring-like structures measured in the thinnest targets provide additional evidence of volumetric laser-driven particle acceleration regimes and transitional features in ultra-thin foil targets specific to laser–plasma interactions characterized by a high temporal intensity contrast. These results open avenues in the generation of high contrast laser pulses from short-pulse-femtosecond petawatt mixed-glass laser systems and demonstrate the feasibility of this technique for applications requiring high laser intensity contrast with high efficiency.

Physics↗
DOE OSTI2024

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers

The advancement in thin-film exfoliation for synthesizing oxide membranes has led to possibilities for creating artificially assembled heterostructures with structurally and chemically incompatible materials. The sacrificial layer method is a promising approach to exfoliate as-grown films from a compatible material system, allowing for their integration with dissimilar materials. Nonetheless, the conventional sacrificial layers often possess an intricate stoichiometry, thereby constraining their practicality and adaptability, particularly when considering techniques such as molecular beam epitaxy (MBE). This is where easy-to-grow binary alkaline-earth-metal oxides with a rock salt crystal structure are useful. These oxides, which include (Mg, Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range of lattice parameters compared to conventional sacrificial layers and are easily dissolvable in deionized water. In this study, we show the epitaxial growth of the single-crystalline perovskite SrTiO 3 (STO) on sacrificial layers consisting of crystalline SrO, BaO, and Ba 1–x Ca x O films, employing a hybrid MBE method. Our results highlight the rapid (≤5 min) dissolution of the sacrificial layer when immersed in deionized water, facilitating the fabrication of millimeter-sized STO membranes. Using high-resolution X-ray diffraction, atomic-force microscopy, scanning transmission electron microscopy, impedance spectroscopy, and scattering-type near-field optical microscopy (SNOM), we demonstrate single-crystalline STO membranes with bulk-like intrinsic dielectric properties. The employment of alkaline earth metal oxides as sacrificial layers is likely to simplify membrane synthesis, particularly with MBE, thus expanding the research and application possibilities.

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

In situ Study on the Evolution of Atomic and Electronic Structure of LaTiO 3 /SrTiO 3 System

As with other transition-metal oxide interfaces, LaTiO 3 /SrTiO 3 interfaces exhibit interesting electronic properties, such as a two-dimensional electron gas. While the available Mott states and multiple pathways to metallicity in LaTiO 3 can lead to a variety of applications in oxide electronics, the origin of the different properties remains uncertain. Herein, utilizing real-time, in situ x-ray diffraction at the synchrotron, robust but thin LaTiO 3 /SrTiO 3 heterostructures were fabricated using oxide molecular beam epitaxy. A thickness of six unit cells was determined to be critical, at which point the LaTiO 3 /SrTiO 3 heterostructures begin to sustain sharp, well-defined interfaces. The layers of LaTiO 3 and SrTiO 3 were sufficiently thin to benefit from the finite escape length of electrons at resonant soft x-ray photoemission, and the heterostructures were transferred in vacuo after growth to another chamber for synchrotron-based x-ray photoemission spectroscopy studies. With the x-ray energy tuned to the Ti-2p resonance, the LaTiO 3 /SrTiO 3 interfaces could be probed with enough penetration depth and selectivity. It is shown that all of the heterointerfaces exhibit the two-dimensional electron gas.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Experimental and theoretical investigation of the crystalline surface, film, and interface properties of antiperovskite Mn 3 GaN grown by molecular beam epitaxy on MgO(001)

Here, we present a study of the epitaxial growth, characterization, and theoretical modeling of thin film antiperovskite Mn 3 GaN, an antiferromagnetic material with kagome structure which is grown on MgO (001) substrates using N-plasma-assisted molecular beam epitaxy. Reflection high energy electron diffraction is used to assess the in-plane evolution of the film structure during growth, and the surface is investigated in-situ using scanning tunneling microscopy and Auger electron spectroscopy. These results are combined with precision measurements done ex-situ determining the film lattice constants using a combination of x-ray diffraction with reciprocal space mapping and scanning transmission electron microscopy. Overall, a uniform, homogeneous film with an atomically smooth vacuum surface and atomically sharp substrate interface is found having very small in-plane tensile strain and mild out-of-plane compressive strain. First-principles theoretical calculations are applied in order to ascertain the lowest energy models for both the Mn 3 GaN surface and the Mn 3 GaN/MgO film/substrate interface. Models including MnGa versus MnN surface layers and MnGa versus MnN interfacial layers are considered as functions of both the Mn and Ga chemical potentials. The predictions are discussed in comparison to the experimental results. The overall findings suggest that Mn 3 GaN on MgO(001) is a viable epitaxial film which can be further explored in connection with antiferromagnetic spintronics.

Density functional theory↗
DOE OSTI2022

Title Coherent X-ray Studies of Surface Growth and Patterning Processes

X-ray Photon Correlation Spectroscopy (XPCS) is being developed as a tool to study nanoscale dynamics of fluctuations during thin film growth and surface patterning. XPCS examines the evolution of the X-ray scattering speckle pattern in reciprocal space to reveal dynamics information not accessible through any other means. Unlike low-coherence conventional X-ray scattering, which incoherently averages over different regions of a sample, coherent X-ray scattering is sensitive to the detailed structure of a given sample at that moment in time. In thin film growth processes, heterodyning, which occurs due to coherent mixing of two scattered signals, can be used to investigate the relationship between surface growth velocity and defect propagation. And, for polycrystalline thin film growth, the spatial coherence of the X-ray beam can substitute for the missing spatial coherence of the growth process to track layered growth in detail, even in a growth regime in which there are no conventional growth oscillations of the X-ray intensity. This has opened the door for detailed dynamics studies of individual atomic layers during real-world growth and patterning, not just in perfect single-crystal growth cases, which greatly expands the applicability of in-situ X-ray scattering methods. Step-flow dynamics in mounded polycrystalline growth has been studied separately for two thin film organic semiconductors deposited by thermal deposition in a vacuum environment, C60 and diindenoperylene (DIP). Highly oriented polycrystalline thin films are readily obtained in both systems, where mounds are composed of crystalline monolayer-height steps and terraces in a so-called wedding cake morphology. The formation of mounds is understood to be due to significant Ehrlich-Schwoebel step edge barriers that inhibit molecules from hopping down from one layer to the one below. The mounds exhibit local step flow, which can be monitored using coherent X-ray scattering. This is made possible due to heterodyning between scattering from the average mounds and the moving steps, which becomes visible in XPCS analysis. The effect of desorption, i.e. re-evaporation of deposited molecules is found to be important for understanding these processes. The impact of this work is to enable testing of models of step dynamics, the shape of mounds, and merging of mounds to form continuous thin films. Highly ordered polycrystalline thin films deposited on inexpensive substrates have applications in thin film solar cells and other organic electronic devices. In a separate set of experiments, speckle analysis during self-organized ion beam nanopatterning reveals memory stretching back to the beginning of patterning in the early stages and enables measurement of the velocity of self-organized patterns across surfaces providing the possibility of stringent new tests of the theory of pattern formation and motion.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Development of a pulsed, variable-energy positron beam for atomic scale defect studies

Positron annihilation spectroscopy provides a sensitive means of non-destructive characterization of materials, capable of probing single atom vacancies in solids with 10 –7 sensitivity. Here, in this work, we detail the development of a magnetically guided, variable energy, pulsed positron beam designed to conduct depth-dependent defect studies in metals, semiconductors, and dielectrics, which will be the first of its kind in the United States. The design of the target stage provides capabilities for measurements during in situ annealing up to 800 °C and incorporates a new approach to minimize the background due to energetic backscattered positrons. The developed beam at Bowling Green State University provides a powerful tool for characterization of thin films, devices, and ion irradiated materials.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Multiport High-pressure Fluid Cell (MHPFC) for Photon and Electron Beams

A multiport high-pressure fluid cell was developed based on an engineered thin film membrane solution with a reinforced frame of boron-doped silicon, optimized to withstand better pressure with an increase of 17.6% in average burst pressure over similar membranes without frame. The novel cells (patent pending) have 8 microfluidic ports, two intra-cavity electrodes and two pressure sensors on a 8 mm x 8 mm Si chip. The prototypes resisted up to 60 bar with 50-nm-thick silicon nitride membranes of size 70 nm x 70 nm. The cells can be used for testing reactions in fluids in medium-high pressure (up to 300 bar) using X-rays (primary application), electron beams, IR or visible light. Improvements in the pressure sensing setup and customization for applications are supposed to follow.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Sensitivity of an early dark matter search using the electromagnetic calorimeter as a target for the Light Dark Matter eXperiment

The Light Dark Matter eXperiment (LDMX) is proposed to employ a thin tungsten target and a multi-GeV electron beam to carry out a missing momentum search for the production of dark matter candidate particles. We study the sensitivity for a complementary missing-energy-based search using the LDMX Electromagnetic Calorimeter as an active target with a focus on early running. In this context, we construct an event selection from a limited set of variables that projects sensitivity into previously-unexplored regions of light dark matter phase space — down to an effective dark photon interaction strength y of approximately 2 × 10 −13 (5 × 10 −12 ) for a 1 MeV (10 MeV) dark matter candidate mass.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Extreme Ultraviolet and Beyond Extreme Ultraviolet Lithography Using Amorphous Zeolitic Imidazolate Resists Deposited by Atomic/Molecular Layer Deposition

Amorphous zinc-imidazolate (aZnMIm) resists show potential to meet the demands for next-generation high-numerical aperture (high-NA) metal-containing extreme ultraviolet (EUV) resist materials, given their ease of deposition by atomic/molecular layer deposition (ALD/MLD) at thicknesses of 20 nm and below. Here, this study demonstrates that aZnMIm thin films, previously identified as high-resolution electron beam resists, can also function as negative-tone EUV photoresists. Water development achieves high sensitivity (5 mJ/cm 2 ) but leaves significant residue, while acetic acid development results in poor contrast. A hybrid approach─water followed by acetic acid─enables residue-free development with a sensitivity of 181 mJ/cm 2 . Dry development using 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH) is also possible but shows lower sensitivity (375 mJ/cm 2 ) compared to wet development methods. EUV photoelectron spectroscopy (PES), reflectometry/EUV absorption, total electron yield (TEY), residual gas analysis (RGA), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used to investigate the effects of EUV irradiation on aZnMIm resists. Reflectometry experiments reveal an aZnMIm EUV absorption coefficient of 6.2 μm –1 , while PES and TEY analyses show that, compared to poly(4-hydroxystyrene) (PHS), a polymer-based reference resist, aZnMIm emits more primary and secondary electrons but generates fewer slow electrons relative to its primary electron emission; its total electron yield is similar to that of poly(methyl methacrylate) (PMMA) resists. When exposed to EUV, aZnMIm predominantly outgasses H 2 , as determined by RGA. TOF-SIMS measurements demonstrate that high-dose EUV exposure only partially fragments the 2-methylimidazole (2MIm) organic linkers, unlike high-dose electron beam exposure, which is known to completely degrade them. Additionally, aZnMIm resists show promise for potential beyond EUV lithography (BEUVL) due to the presence of Zn, which provides higher sensitivity at a wavelength of 6.7 nm compared to other metal ions, such as Sn, that are currently used in the best-performing EUV metal–organic resists. TEY measurements demonstrate that aZnMIm emits nearly twice as many electrons as PHS at 6.7 nm. The BEUV TEY of aZnMIm also surpasses that of PMMA, poly(pentafluorostyrene), and poly(4-iodostyrene), with the latter two being known for their high EUV TEYs. This work provides insight into zeolitic imidazolate framework (ZIF)-based EUV and BEUV resists and highlights their potential for both wet and dry development.

lithography↗
DOE OSTI2022

Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators

In intrinsic magnetic topological insulators, Dirac surface-state gaps are prerequisites for quantum anomalous Hall and axion insulating states. Unambiguous experimental identification of these gaps has proved to be a challenge, however. Here, we use molecular beam epitaxy to grow intrinsic MnBi 2 Te 4 thin films. Using scanning tunneling microscopy/spectroscopy, we directly visualize the Dirac mass gap and its disappearance below and above the magnetic order temperature. We further reveal the interplay of Dirac mass gaps and local magnetic defects. We find that, in high defect regions, the Dirac mass gap collapses. Ab initio and coupled Dirac cone model calculations provide insight into the microscopic origin of the correlation between defect density and spatial gap variations. Finally, this work provides unambiguous identification of the Dirac mass gap in MnBi 2 Te 4 and, by revealing the microscopic origin of its gap variation, establishes a material design principle for realizing exotic states in intrinsic magnetic topological insulators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Defect Complexes in CrSBr Revealed Through Electron Microscopy and Deep Learning

Atomic defects underpin the properties of van der Waals materials, and their understanding is essential for advancing quantum and energy technologies. Scanning transmission electron microscopy is a powerful tool for defect identification in atomically thin materials, and extending it to multilayer and beam-sensitive materials would accelerate their exploration. Here, we establish a comprehensive defect library in a bilayer of the magnetic quasi-1D semiconductor CrSBr by combining atomic-resolution imaging, deep learning, and calculations. We apply a custom-developed machine learning work flow to detect, classify, and average point vacancy defects. This classification enables us to uncover several distinct Cr interstitial defect complexes, combined Cr and Br vacancy defect complexes, and lines of vacancy defects that extend over many unit cells. We show that their occurrence is in agreement with our computed structures and binding energy densities, reflecting the intriguing layer interlocked crystal structure of CrSBr. Our ab initio calculations show that the interstitial defect complexes give rise to highly localized electronic states. These states are of particular interest due to the reduced electronic dimensionality and magnetic properties of CrSBr and are, furthermore, predicted to be optically active. Our results broaden the scope of defect studies in challenging materials and reveal new defect types in bilayer CrSBr that can be extrapolated to the bulk and to over 20 materials belonging to the same FeOCl structural family.

deep learning↗
DOE OSTI2021

Electromechanical response of piezoelectric thin films subjected to large strain

The use of piezoelectric thin sensors, when subjected to large static strain levels in ultrasonic applications is reported in this paper. A novel flipped beam bending method is proposed to induce static strain level nearing twice the incipient yield strain in the beam material (~0.39%). First, the effect of static large strain on ultrasonic guided wave propagation in the beam was studied using the velocity measurements obtained from a laser Doppler vibrometer. Next, the ultrasonic response of thin sensors is studied under compressive and tensile static strain (±0.72%) with the sensors symmetrically bonded on the lower and upper surfaces, and at the same axial location. The ultrasonic guided wave response to varying levels of static strain is recorded at different center frequencies (50–400 kHz) of the narrow banded ultrasonic excitation. As a case study, the variation of the ultrasonic guided wave response of polyvinylidene difluoride (PVDF) thin sensors with center frequencies at different static strain levels was analyzed and compared with that of lead zirconate titanate (PZT) thin sensors. PZT sensors show a higher variation of sensing performance with strain when compared to PVDF sensors. Apart from static strain, the possible effects on the change in performance of sensors, such as the change in the capacitance is discussed. The characterization method provides a reusable beam arrangement to study the ultrasonic sensor performance at large static strain levels. Characterization at large strain level allows the development of fail-safe sensors even under large strain and permanent plastic deformation of structure on which they are bonded, allowing accurate ultrasonic structural health monitoring even in the presence of damage progression. Piezopolymer sensor like PVDF are least susceptible to static strain due to large yield strain and low modulus and can serve as fail-safe sensors under large strain.

Rathod, Vivek↗
DOE OSTI2023

Simulations Supporting the Development of Northstar's Indirect Beam Parameters Monitoring System

NorthStar Medical Radioisotopes, LLC is planning to produce the important medical radioisotope molybdenum-99 (Mo-99), the parent of technetium-99m (Tc-99m), through photonuclear reactions in molybdenum-100 (Mo-100). In this approach, a target comprising multiple thin disks of enriched molybdenum metal is bombarded with a 40-MeV electron beam. Electrons impinged on the molybdenum target produce bremsstrahlung X-rays that cause the nuclear reaction. Because enriched Mo-100 is expensive, there is a desire to utilize as much beam power as possible to achieve maximum production yield and minimize the size of the target. This requirement leads to very high beam power density (and heat deposition in the target), which creates challenging requirements for the cooling of the target. The critical part of the target is the target window. It separates the high-pressure helium cooled target from the vacuum beamline and the subject of structural and thermal stress. The temperature of the target window is proportional to the energy density deposited by the beam, so it is critical to maintain the desired beam profile on the target window. The feasibility of indirectly monitoring the maximum energy density of the beam on the beam window through beam losses at the main collimator (Collimator) before the production target was verified. A model of the NorthStar beam transport line was constructed for this purpose using MAD-X and Tao/Bmad codes. Beam optics were computed for the standard operational scenario, followed by an investigation involving approximately 400 cases with parameter variations in the last tuning quadrupoles. This was done to assess the correlation between losses in the collimator and the peak energy density on the target. We developed a model to explore the potential application of Optical transition radiation (OTR) for controlling beam parameters in the NorthStar beam delivery system. This model was based on a generic formula derived from the fundamental solution of the inhomogeneous wave equation of the vector potential, and allowed us to consider various surfaces, even those with irregular or random features, using numerical integration. We applied the model to OTR generated by relativistic electrons impacting an Inconel® 718 beam window. We examined cases with different levels of the window’s surface roughness, ranging from 0.5 to 3.0 microns of root square mean (RMS) deviation. The results of the OTR simulations provided distributions of OTR photons that can be used to study the limitations of optical systems for controlling beam parameters.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Visualizing the unusual spectral weight transfer in DyBa2Cu3O7–δ thin film

Abstract We report a Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM) study of a DyBa 2 Cu 3 O 7-δ (DBCO) thin film ( T c ~ 79 K) synthesized by the molecular beam epitaxy (MBE). We observed an unusual transfer of spectral weight in the local density of states (LDOS) spectra occurring only within the superconducting gap. By a systematic control of the tip-sample distance and the junction resistance, we demonstrate that the spectral weight transfer can be switched at a nano-meter length scale. These results suggest that an interaction between the STM tip and the sample alters the electronic configurations in the film. This probably originates from a combination of an intrinsic band bending at the interface between the surface and the bulk, and a tip-induced band bending. These results may open a new avenue for band engineering and applications of thin films of high- T c cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Hierarchical, Self-Assembled Metasurfaces via Exposure-Controlled Reflow of Block Copolymer-Derived Nanopatterns

Here, nanopatterning for the fabrication of optical metasurfaces entails a need for high-resolution approaches like electron beam lithography that cannot be readily scaled beyond prototyping demonstrations. Block copolymer thin film self-assembly offers an attractive alternative for producing periodic nanopatterns across large areas, yet the pattern feature sizes are fixed by the polymer molecular weight and composition. Here, a general strategy is reported that overcomes the limitation of fixed feature size by treating the copolymer thin film as a hierarchical resist, in which the nanoscale pattern motif is defined by self-assembly. Feature sizes can then be tuned by thermal reflow controlled locally by irradiative crosslinking or chemical alteration using lithographic ultraviolet light or electron beam exposure. Using blends of polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) with PS and PMMA homopolymer, we demonstrate both self-assembled PS grating and hexagonal hole patterns; exposure-controlled reflow is then used to reduce hole diameter by as much as 50% or increase PS grating linewidth by more than 180%. Transferring these nanopatterns, or their inverse obtained by a lift-off approach, into silicon yields structural colors that may be prescriptively controlled based on nanoscale feature size. Furthermore, patterned exposure enables area-selective feature size control, yielding uniform structural color patterns across centimeter square areas. Electron beam lithography is also used to show that the lithographic resolution of this selective-area control can be extended to the nanoscale dimensions of the self-assembled features. The exposure-controlled reflow approach demonstrated here takes a pivotal step towards fabricating complex, hierarchical optical metasurfaces using scalable self-assembly methods.

77 NANOSCIENCE AND NANOTECHNOLOGY↗