Extreme Ultraviolet Research Articles

Investigating coronal loop morphology and dynamics from two vantage points

Coronal loops are the fundamental building blocks of the solar corona. Therefore, comprehending their properties is essential in unraveling the dynamics of the upper solar atmosphere. In this study, we conduct a comparative analysis of the morphology and dynamics of a coronal loop observed from two different spacecraft: the High Resolution Imager (HRIEUV) of the Extreme Ultraviolet Imager on board the Solar Orbiter, and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. These spacecraft were separated by 43° during this observation. The main findings of this study are that (1) the observed loop exhibits similar widths in both the HRIEUV and AIA data, suggesting that the cross-sectional shape of the loop is circular; (2) the loop maintains a uniform width along its entire length, supporting the notion that coronal loops do not exhibit expansion; and (3) notably, the loop undergoes unconventional dynamics, including thread separation and abrupt downward movement. Intriguingly, these dynamic features also appear similar in data from both spacecraft. Although based on observation of a single loop, these results raise questions about the validity of the coronal-veil hypothesis and underscore the intricate and diverse nature of the complexity within coronal loops.

Extreme Ultraviolet Lithographic Performance and Reaction Mechanism of Polymeric Resist─Utilizing Radical- and Acid-Amplified Cross-Linking

Extreme Ultraviolet Lithographic Performance and Reaction Mechanism of Polymeric Resist─Utilizing Radical- and Acid-Amplified Cross-Linking

Study in the Extreme UV Range of the Spectral Transmission of Nickel Plasma Created under the Effect of an X-Ray Pulse of the Z-Pinch

Study in the Extreme UV Range of the Spectral Transmission of Nickel Plasma Created under the Effect of an X-Ray Pulse of the Z-Pinch

Angular distribution separation of the extreme ultraviolet emission and suprathermal ions with energy reduction

We have demonstrated angular distribution separation of the extreme ultraviolet (EUV) emission and suprathermal ions with a significant energy reduction for ions produced using dual pulse irradiation of a planar gadolinium (Gd) target. The pulse separation time between the pre-pulse and the main laser heating pulse was set at 30 ns, and the pre-plasma was irradiated at a distance of 50 μm above the target. Angular distributions of the EUV emission and the suprathermal ions were almost isotropic and followed a cos4θ distribution, respectively. The suprathermal ions were emitted normal to the target along the pre-pulse laser axis. The most probable energy of the suprathermal ions was less than 2 keV, while their maximum charge state was Gd6+ with the pre-plasma, compared to an energy of about 10 keV with a maximum charge state Gd15+ without the pre-plasma. The results suggest that the collector mirror position may be chosen to achieve a long lifetime, by avoiding damage from fast ion collisions.

Development of a dynamic gas lock inhibited model for EUV-induced carbon deposition.

The optical surface of extreme ultraviolet (EUV) lithography machines is highly vulnerable to contamination by hydrocarbons, resulting in the formation of carbon deposits that significantly degrade the quality and efficiency of lithography. The dynamic gas lock (DGL) has been proven as an effective approach to alleviate carbon deposition. However, the majority of existing studies on carbon deposition neglect the influence of the DGL. This paper is dedicated to investigating the phenomena of hydrocarbon adsorption, desorption, and cleavage with considering the effects of the DGL. A comprehensive mathematical model of the carbon deposition process is established, and the impact of radiation intensity, temperature, and hydrocarbon types on the depositing rate is considered. The results suggest that the primary cause of carbon deposition is the direct cracking of hydrocarbons induced by photons with a wavelength range between 12.5 and 14.5nm. Additionally, it has been observed that the carbon deposition rate decreases exponentially as clean gas flow increases when EUV radiation intensity exceeds 50 mW/mm2. Conversely, at low EUV radiation intensity, clean gas flow has little effect on the carbon deposition rate. An effective approach to mitigate carbon deposition is to elevate the temperature of the optical surface and employ light hydrocarbon materials in the EUV process.

Unraveling femtosecond spin and charge dynamics with extreme ultraviolet transverse MOKE spectroscopy

The magneto-optical Kerr effect (MOKE) in the extreme ultraviolet (EUV) regime has helped to elucidate some of the key processes that lead to the manipulation of magnetism on ultrafast timescales. However, as we show in this paper, the recently introduced spectrally resolved analysis of such data can lead to surprising experimental observations, which might cause misinterpretations. Therefore, an extended analysis of the EUV magneto-optics is necessary. Via experimental determination of the dielectric tensor, we find here that the nonequilibrium excitation in an ultrafast magnetization experiment can cause a rotation of the off-diagonal element of the dielectric tensor in the complex plane. In direct consequence, the commonly analyzed magneto-optic asymmetry may show time-dependent behavior that is not directly connected to the magnetic properties of the sample. We showcase such critical observations for the case of ultrafast magnetization dynamics in Ni, and give guidelines for the future analysis of spectrally resolved magneto-optical data and its comparison with theory. Published by the American Physical Society 2024

A Review of Emerging Technologies in Ultra-Smooth Surface Processing for Optical Components.

Advancements in astronomical telescopes and cutting-edge technologies, including deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography, have escalated demands and imposed stringent surface quality requirements on optical system components. Achieving near-ideal optical components requires ultra-smooth surfaces with sub-nanometer roughness, no sub-surface damage, minimal surface defects, low residual stresses, and intact lattice integrity. This necessity has driven the rapid development and diversification of ultra-smooth surface fabrication technologies. This paper summarizes recent advances in ultra-smooth surface processing technologies, categorized by their material removal mechanisms. A subsequent comparative analysis evaluates the roughness and polishing characteristics of ultra-smooth surfaces processed on various materials, including fused silica, monocrystalline silicon, silicon carbide, and sapphire. To maximize each process's advantages and achieve higher-quality surfaces, the paper discusses tailored processing methods and iterations for different materials. Finally, the paper anticipates future development trends in response to current challenges in ultra-smooth surface processing technology, providing a systematic reference for the study of the production of large-sized freeform surfaces.

EUV-induced hydrogen desorption as a step towards large-scale silicon quantum device patterning

Atomically precise hydrogen desorption lithography using scanning tunnelling microscopy (STM) has enabled the development of single-atom, quantum-electronic devices on a laboratory scale. Scaling up this technology to mass-produce these devices requires bridging the gap between the precision of STM and the processes used in next-generation semiconductor manufacturing. Here, we demonstrate the ability to remove hydrogen from a monohydride Si(001):H surface using extreme ultraviolet (EUV) light. We quantify the desorption characteristics using various techniques, including STM, X-ray photoelectron spectroscopy (XPS), and photoemission electron microscopy (XPEEM). Our results show that desorption is induced by secondary electrons from valence band excitations, consistent with an exactly solvable non-linear differential equation and compatible with the current 13.5 nm (~92 eV) EUV standard for photolithography; the data imply useful exposure times of order minutes for the 300 W sources characteristic of EUV infrastructure. This is an important step towards the EUV patterning of silicon surfaces without traditional resists, by offering the possibility for parallel processing in the fabrication of classical and quantum devices through deterministic doping.

SuNeRF: 3D Reconstruction of the Solar EUV Corona Using Neural Radiance Fields

To understand its evolution and the effects of its eruptive events, the Sun is permanently monitored by multiple satellite missions. The optically thin emission of the solar plasma and the limited number of viewpoints make it challenging to reconstruct the geometry and structure of the solar atmosphere; however, this information is the missing link to understand the Sun as it is: a 3D evolving star. We present a method that enables a complete 3D representation of the uppermost solar layer (corona) observed in extreme ultraviolet (EUV) light. We use a deep-learning approach for 3D scene representation that accounts for radiative transfer to map the entire solar atmosphere from three simultaneous observations. We demonstrate that our approach provides unprecedented reconstructions of the solar poles and directly enables height estimates of coronal structures, solar filaments, coronal hole profiles, and coronal mass ejections. We validate the approach using model-generated synthetic EUV images, finding that our method accurately captures the 3D geometry of the Sun even from a limited number of 32 ecliptic viewpoints (∣latitude∣ ≤ 7°). We quantify the uncertainties of our model using an ensemble approach that allows us to estimate the model performance in the absence of a ground truth. Our method enables a novel view of our closest star and is a breakthrough technology for the efficient use of multi-instrument data sets, which paves the way for future cluster missions.

A study of extreme C iii]1908 & [O iii]88/[C ii]157 emission in Pox 186: Implications for JWST+ALMA (FUV+FIR) studies of distant galaxies

Abstract Carbon spectral features are ubiquitous in the ultraviolet (UV) and far-infrared (FIR) spectra of the reionization-era galaxies. We probe the ionized carbon content of a dwarf galaxy Pox 186 using the UV, optical, mid-infrared and FIR data taken with Hubble, Gemini, Spitzer and Herschel, respectively. This local (z∼0.0040705) galaxy is likely an analogue of reionization-era galaxies, as revealed by its extreme FIR emission line ratio, [O iii] 88μm/[C ii] 157μm (>10). The UV spectra reveal extreme C iii] λλ 1907, 1909 emission with the strongest equivalent width (EW) = 35.85 ± 0.73 Å detected so far in the local (z∼0) Universe, a relatively strong C iv λλ 1548, 1550 emission with EW = 7.95 ±0.45 Å, but no He ii λ 1640 detection. Several scenarios are explored to explain the high EW of carbon lines, including high effective temperature, high carbon-to-oxygen ratio, slope and upper mass of top-heavy initial mass function, hard ionizing radiation and in-homogeneous dust distribution. Both C iii] and C iv line profiles are broadened with respect to the O iii] λ 1660 emission line. Each emission line of C iv λλ 1548, 1550 shows the most distinct double-peak structure ever detected, which we model via two scenarios, firstly a double-peaked profile that might emerge from resonant scattering and secondly, a single nebular emission line along with a weaker interstellar absorption. The study demonstrates that galaxies with extreme FIR properties may also show extreme UV properties, hence paving a promising avenue of using FIR+UV in the local (via Hubble+Herschel/SOFIA) and distant (via JWST+ALMA) Universe for unveiling the mysteries of the reionization-era.

First principal calculations for understanding physical properties and possible applications of vacancy ordered double perovskite Cs2ZrI6 (CZI)

First principal calculations are performed to understand structural, elastic, electronic, thermoelectric, thermodynamic and optical properties of inorganic vacancy ordered double perovskite, the Cs2ZrI6 (CZI). Calculated lattice constant of the rock-salt structured CZI shows closeness to that reported in the Materials Project Database. It exhibits mechanical stability, elastic anisotropy, brittleness, dominating ionic bonding, predominant stretching in chemical bonds, fair thermal stability and high melting temperature. It is an indirect band-gap (Γ-X) semiconductor with a band-gap of 2.267eV, which would be suitable for fabricating low-cost tandem solar cells. Calculated thermoelectric properties predicted holes as the majority charge carriers and also shows its thermoelectric efficiency in the higher temperature region. Though, calculated specific heat at constant volume in the very low temperature region obeys the Debye's T3 law, it reaches the Dulong-Petit limit in the very high temperature region. The temperature and pressure dependence of some other thermodynamic parameters are also calculated in the present study. In terms of real and imaginary part of the dielectric function as well as some other auxiliary parameters, we have investigated the optical properties of the CZI and found its high optical absorbance capability in the far UV to extreme UV region of solar spectra.

Free light-shape focusing in extreme-ultraviolet radiation with self-evolutionary photon sieves

Extreme-ultraviolet (EUV) radiation is a promising tool, not only for probing microscopic activities but also for processing nanoscale structures and performing high-resolution imaging. In this study, we demonstrate an innovative method to generate free light-shape focusing with self-evolutionary photon sieves under a single-shot coherent EUV laser; this includes vortex focus shaping, array focusing, and structured-light shaping. The results demonstrate that self-evolutionary photon sieves, consisting of a large number of specific pinholes fabricated on a piece of Si3N4 membrane, are capable of freely regulating an EUV light field, for which high-performance focusing elements are extremely lacking, let alone free light-shape focusing. Our proposed versatile photon sieves are a key breakthrough in focusing technology in the EUV region and pave the way for high-resolution soft X-ray microscopy, spectroscopy in materials science, shorter lithography, and attosecond metrology in next-generation synchrotron radiation and free-electron lasers.

Structured illumination ptychography and at-wavelength characterization with an EUV diffuser at 13.5 nm wavelength.

Structured illumination is essential for high-performance ptychography. Especially in the extreme ultraviolet (EUV) range, where reflective optics are prevalent, the generation of structured beams is challenging and, so far, mostly amplitude-only masks have been used. In this study, we generate a highly structured beam using a phase-shifting diffuser optimized for 13.5 nm wavelength and apply this beam to EUV ptychography. This tailored illumination significantly enhances the quality and resolution of the ptychography reconstructions. In particular, when utilizing the full dynamics range of the detector, the resolution has been improved from 125 nm, when using an unstructured beam, to 34 nm. Further, ptychography enables the quantitative measurement of both the amplitude and phase of the EUV diffuser at 13.5 nm wavelength. This capability allows us to evaluate the influence of imperfections and contaminations on its "at wavelength" performance, paving the way for advanced EUV metrology applications and highlighting its importance for future developments in nanolithography and related fields.

A Partial Eruption of a Sigmoid Filament in the Small Dipole Active Region 12734

We present a detailed analysis of a partial eruption of a sigmoid filament lying along the polarity inversion line (PIL) of the small active region (AR) NOAA 12734 (with an area of 1.44 ×103 square megameters). The active filament was rooted in a dipole sunspot of the AR. The eruption was associated with a C1.3 flare and subsequent large-scale coronal disturbances. During its solar disk passage before the flare, the AR had the following characteristics: (1) Most of the time, the magnetic field lines in the AR showed a sigmoidal structure (‘L1’) in the low corona and arc-shaped loops (i.e., ‘L2’) in the upper atmosphere. (2) An ‘X’-shaped structure was formed between the original ‘S’-shaped magnetic loop (‘L1’) and the newly rising one (‘L3’) between the main positive and negative magnetic polarities of the sunspots, and the intersection point of flux ropes ‘L1’ and ‘L3’ corresponds well with the area where the initial extreme-ultraviolet (EUV) 1600 Å brightening of the flare occurred. (3) The AR disobeyed the hemispherical helicity rule and had magnetic twist and writhe of the same signs, i.e., its magnetic helicity/current helicity were positive in the northern hemisphere. (4) Sustained magnetic emergence and cancellation occurred before the flare. Therefore, the magnetic reconnection of highly twisted helical flux ropes under the confinement of the overlying magnetic fields is probably responsible for the partial eruption of the filament.

Influence of a laser intensity on EUV brightness and ion speed from a laser-assisted discharge-produced plasma

Laser-assisted discharge-produced plasma (LDP) is one of the ways to generate extreme ultraviolet (EUV) light used in the semiconductor manufacturing processes. This light source uses a pulsed laser and a high-current pulsed electrical discharge to make a high-temperature and high-density tin plasma. One of two rotating disk electrodes, of which surfaces are coated by liquid tin (Sn), is irradiated by the laser to produce tin plasma. The plasma propagates from one electrode (cathode) to the other (anode) and ignites an electrical breakdown between the electrodes. The low-inductance circuit connected to the electrodes provides a current of approximately 15 kA and 150 ns to the tin plasma. The plasma implodes due to its own magnetic pressure, and EUV radiation is emitted from the resultant hot and dense plasma. High-speed ions are also emitted from the plasma and limit the lifetime of the mirror used to collect the EUV light. We need to maximize the light emission and minimize the ion emission. The role of the laser is essential in the LDP EUV source not only to ignite the discharge but also to condition the initial plasma. It influences EUV energy, EUV brightness, and emitted ion speed distribution of the plasma. The experiment suggested that laser intensity higher than 25 GW/cm2 produced high EUV brightness and low emitted ion speed.

Research on High-Precision Position Detection Based on a Driven Laser Spot in an Extreme Ultraviolet Light Source

Laser-spot-location detection technology based on photodetectors is widely used in the aerospace, medical, military and communication fields. However, most of the current research focuses on continuous laser detection in the visible and near-infrared bands, and the real-time high-precision position detection of a long-wave infrared pulsed laser is lacking. In this paper, a spot-position detection system based on a four-quadrant detector is designed for a 10.6 μm CO2-driven laser in extreme ultraviolet light source, and a second-order extended error compensation algorithm based on a Gaussian-spot model is proposed. Finally, the algorithm is verified and analyzed experimentally by a spot-position detection system under both focusing and defocusing conditions. The experimental results show that the root-mean-square error, maximum absolute error and average absolute error of the second-order error compensation algorithm are significantly reduced compared with the traditional algorithm, and the detection accuracy of the spot-position is better than 9 μm. The above results show that this spot-position detection system has obvious advantages and high accuracy, which can realize the high-precision real-time detection of a laser’s spot position to obtain accurate spot position information, provide feedback adjustments for subsequent beam pointing control, and provide a theoretical basis for the beam pointing stability of the extreme ultraviolet light source system.

Coronal line emitters are tidal disruption events in gas-rich environments

ABSTRACT Some galaxies show little to no sign of active galactic nucleus (AGN) activity, yet exhibit strong coronal line (CL) emission relative to common narrow emission lines. Many of these CLs have ionization potentials of ≥100 eV, thus requiring strong extreme ultraviolet and/or soft X-ray flux. It has long been thought that such events are powered by tidal disruption events (TDEs), but owing to a lack of detailed multiwavelength follow-up, such a connection has not been firmly made. Here, we compare coronal line emitters (CLEs) and TDEs in terms of their host-galaxy and transient properties. We find that the mid-infrared (MIR) colours of CLE hosts in quiescence are similar to those of TDE hosts. Additionally, many CLEs show evidence of a large dust reprocessing echo in their MIR colours, a sign of significant dust in the nucleus. The stellar masses and star formation rates of the CLE hosts are largely consistent with TDE hosts, with many CLEs residing within the green valley. The blackbody properties of CLEs and TDEs are similar, with some CLEs showing hot (T ≥ 40 000 K) blackbody temperatures. Finally, the location of CLEs on the peak-luminosity/decline-rate parameter space is much closer to TDEs than many other major classes of nuclear transients. Combined, these provide strong evidence to confirm the previous claims that CLEs are indeed TDEs in gas-rich environments. We additionally propose a stricter threshold of CL flux ≥1/3 × [O iii] flux to better exclude AGNs from the sample of CLEs.

Textrm{O}^+ density distribution in the nightside ionosphere reconstructed from ISS-IMAP/EUVI data

The textrm{O}^+ density distribution in the nightside ionosphere has been reconstructed from extreme ultraviolet (EUV) images taken by the EUVI-B imager of the International Space Station Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere mapping (ISS-IMAP) cameras. The EUVI-B imager covers the wavelength range from about 70 nm to 110 nm and mainly observes the 91.1 nm emission from the recombination of textrm{O}^+ ions and electrons. Assuming that the electron density is equal to the textrm{O}^+ density in the F-region where the imager observes, the EUV intensity observed by EUVI-B is approximately proportional to the line-of-sight integral of the square of the textrm{O}^+ density. This enables us to estimate the textrm{O}^+ density distribution in the F-region from a sequence of EUVI-B data in each International Space Station (ISS) orbit with a Bayesian method. We demonstrate the reconstruction of the textrm{O}^+ distribution. In particular, the textrm{O}^+ density structure of the equatorial ionization anomaly (EIA) in the vicinity of an ISS orbit is obtained.Graphical

Recurrently Propagating Intensity Disturbances along Polar Plumes Observed in White Light and Extreme Ultraviolet

We study properties of intensity disturbances along polar coronal rays that are associated with plumes below. For this, we draw azimuth–time images of extreme ultraviolet (EUV) emission of 171 Å band observed by the SDO/AIA and white light (WL) observed by the SOHO/LASCO C2 in 2020 July. From the azimuth–time image, we define two tracks in which the EUV intensities were recurrently enhanced during two weeks. The two EUV tracks are rooted at 78.°8 and 81.°4 latitudes, but their projected azimuth angles are changed with time as the Sun rotates. Coherent WL tracks at different altitudes are determined by scaling the azimuth angles of the EUV tracks, accounting for the effect of inclination of coronal rays. From this, we construct time–distance images of WL intensities along WL tracks, whose projected azimuth angle changes along time and altitude, but the intensities are correlated with the EUV intensities measured below. The time–distance images of WL show repeated and inclined intensity features. The propagation speeds in the altitude range 2.3–6 solar radii are calculated to be 159 ± 8 km s−1 and 300 ± 24 km s−1. The EUV and WL intensities are found to be coherent at 1–2 day periods. It is also found that dynamic burst events along the EUV track are responsible for the enhanced emission. We conclude that the variation of the WL intensity along the polar coronal rays is related with the evolution of the EUV intensity below.

Extreme ultraviolet lithography reaches 5 nm resolution.

Extreme ultraviolet (EUV) lithography is the leading lithography technique in CMOS mass production, moving towards the sub-10 nm half-pitch (HP) regime with the ongoing development of the next generation high numerical aperture (high NA) EUV scanners. Hitherto, EUV interference lithography (EUV-IL) utilizing transmission gratings has been a powerful patterning tool for the early development of EUV resists and related processes, playing a key role in exploring and pushing the boundaries of photon-based lithography. However, achieving patterning with HPs well below 10 nm using this method presents significant challenges. In response, this study introduces a novel EUV-IL setup that employs mirror-based technology and circumvents the limitations of diffraction efficiency towards the diffraction limit that is inherent in conventional grating-based approaches. The results are line/space patterning of the HSQ resist down to HP 5 nm using the standard EUV wavelength 13.5 nm, and the compatibility of the tool with shorter wavelengths beyond EUV. Mirror-based interference lithography paves the way towards the ultimate photon-based resolution at EUV wavelengths and beyond. This advancement is vital for scientific and industrial research, addressing the increasingly challenging needs of nanoscience and technology and future technology nodes of CMOS manufacturing in the few-nanometer HP regime.