eV Photon Research Articles

The electronic spectra of trifluoroacetic acid and chlorodifluoroacetic acid in the 4.5 – 10.8 eV photon energy region

Synchrotron radiation has been used to record for the first time absolute vacuum ultraviolet photoabsorption cross-sections of trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CDFA) in the 4.5–10.8 eV energy range. In order to further our knowledge of the major electronic transitions and thus help interpret the photoabsorption data, theoretical calculations using time-dependent density functional theory (TD-DFT) level have been performed. These calculations have provided important information on the nature of the excited electronic states which have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. Due to the lack of any information about CDFA ionic states, we also provide Equation-of-Motion Coupled-Cluster Single and Doubles (EOM-CCSD) vertical ionisation energies. Photolysis lifetimes in the Earth's atmosphere for both chemical compounds have also been estimated from the absolute photoabsorption cross-section data.

VUV absorption spectra of water and nitrous oxide by a double-duty differentially pumped gas filter.

The differentially pumped rare-gas filter at the end of the VUV beamline of the Swiss Light Source has been adapted to house a windowless absorption cell for gases. Absorption spectra can be recorded from 7 eV to up to 21 eV photon energies routinely, as shown by a new water and nitrous oxide absorption spectrum. By and large, the spectra agree with previously published ones both in terms of resonance energies and absorption cross sections, but that of N2O exhibits a small shift in the {\tilde{\bf D}} band and tentative fine structures that have not yet been fully described. This setup will facilitate the measurement of absorption spectra in the VUV above the absorption edge of LiF and MgF2 windows. It will also allow us to carry out condensed-phase measurements on thin liquid sheets and solid films. Further development options are discussed, including the recording of temperature-dependent absorption spectra, a stationary gas cell for calibration measurements, and the improvement of the photon energy resolution.

Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH3, CH2, and CH Fragments.

Under irradiation of a vacuum ultraviolet (VUV) photon, methane dissociates and yields multiple fragments. This photochemical behavior is not only of fundamental importance but also with wide-ranging implications in several branches of science. Despite that and numerous previous investigations, the product channel branching is still under debate, and the underlying dissociation mechanisms remain elusive. In this study, the photofragment imaging technique was exploited for the first time to map out the momentum and anisotropy parameter distributions of the CH3, CH2, and CH fragments at the 118 nm photolysis wavelength (10.48 eV photon energy). In conjunction with previously reported results of the H atom fragment at 121.6 nm (10.2 eV), a complete set of product channel branching in both two-body and three-body fragmentations is accurately determined. We concluded that extensive nonadiabatic transitions partake in the processes with two-body fragmentations accounting for more than 90% of overall photodissociation, for which the channel branching values for CH2 + H2 and CH3 + H are about 0.66 and 0.25, respectively. Careful kinematic analysis enables us to untangle the intertwined triple fragmentations into the CH2(X̃ 3B1 and ã 1A1) + H + H and CH(X2Π) + H + H2 channels and to evidence their underlying sequential (or stepwise) mechanisms. With the aid of electronic correlation and prior theoretical calculations of the potential energy surfaces, the most probable or dominant dissociation pathways are elucidated. Comparisons with fragmentary reports in the literature on various photochemical aspects are also documented, and discrepancies are clarified. This comprehensive study benchmarks the VUV photochemistry of methane and advances our understanding of this important process.

Preservation of Topological Surface States in Millimeter-Scale Transferred Membranes.

Ultrathin topological insulator membranes are building blocks of exotic quantum matter. However, traditional epitaxy of these materials does not facilitate stacking in arbitrary orders, while mechanical exfoliation from bulk crystals is also challenging due to the non-negligible interlayer coupling therein. Here we liberate millimeter-scale films of the topological insulator Bi2Se3, grown by molecular beam epitaxy, down to 3 quintuple layers. We characterize the preservation of the topological surface states and quantum well states in transferred Bi2Se3 films using angle-resolved photoemission spectroscopy. Leveraging the photon-energy-dependent surface sensitivity, the photoemission spectra taken with 6 and 21.2 eV photons reveal a transfer-induced migration of the topological surface states from the top to the inner layers. By establishing clear electronic structures of the transferred films and unveiling the wave function relocation of the topological surface states, our work lays the physics foundation crucial for the future fabrication of artificially stacked topological materials with single-layer precision.

First-principles calculations on electronic, mechanical and optical properties of ScMC2 (M = Ti, V, Cr, and Mn) ternary carbides

First-principles calculations have been employed to investigate the physical properties of scandium-based ternary carbides, denoted as ScMC2 (M = Ti, V, Cr, Mn). All the studied carbides demonstrate both structural and mechanical stability. Mechanical anisotropy and optical properties are reported for the first time to enhance their importance on an industrial scale. The calculated mechanical parameters are correlated with the previously reported results to check the reliability of the current work. Poisson's and Pugh ratios indicate that ScMC2 (M = Ti, V, Cr) compounds are brittle whereas ScMnC2 is ductile. Thermal shock resistance is also investigated which suggests that ScMC2 carbides could be used as TBC's materials. DOS and optical characteristics reflect the metallic behavior of studied carbides. Optical properties indicate the existence of anisotropy in ScMC2 carbides up to 10 eV photon energy. The reflectance spectra suggest that ScMnC2 could be used to reduce solar heating.

Resonant photoemission studies on Fe-Ni alloys

This paper investigates the electronic structure of Fe1−xNix (x = 0.32, 0.36, 0.4, 0.5) alloys employing high resolution photoelectron spectroscopy using synchrotron radiation. The valence bands and the core levels have been recorded at various on-resonance and off-resonance photon energies of Fe and Ni. An anti-resonance dip observed in the valence bands taken at Fe 3p → 3d resonance lies closer to the Fermi level compared to that observed at Ni 3p → 3d resonance, indicating larger density of itinerant Fe 3d electrons. Whereas, Ni 3d states are comparatively less itinerant in these alloys. The hybridization effects increase with increase of Fe content in the alloy system. The intensity of Ni L3M4,5M4,5 Coster-Cronig Auger transition observed with 853 eV (Ni 2p → 3d resonance) photon energy, drops down drastically for the Invar alloy (Fe0.64Ni0.36) as compared to other Fe-Ni alloys due to the existence of Ni in more than one local chemical surroundings as expected for Invar alloy. The electron-electron interaction energy (Udd) of Ni 3d shell is found to decrease with the decrease of Ni concentration. The 3p and 3s core levels of Fe and Ni recorded at 707 eV (Fe 2p → 3d resonance) are overwhelmed by various intense resonant Auger features such as Fe L3M2,3M2,3, Fe L3M2,3M4,5 and Fe L3M1M4,5. The 1S state of Fe L3M2,3M2,3 is greatly enhanced in the Invar alloy as compared to other alloys. The microscopic compositional in-homogeneity present in Invar alloy plays a crucial role in the screening of holes in Ni sites but does not contribute in screening the holes in Fe sites.

Hot carrier photocurrent induced by 0.92 eV photon energy radiation in a Si solar cell

Absorption of the below-bandgap solar radiation and direct pre-thermalizational impact of a hot carrier (HC) on the operation of a single-junction solar cell are ignored by the Shockley-Queisser theory. The detrimental effect of the HC is generally accepted only via the thermalization-caused heating of the lattice. Here, the authors demonstrate experimental evidence of the HC photocurrent induced by the below-bandgap 0.92 eV photon energy radiation in an industrial silicon solar cell. The carriers are heated both through direct free-carrier absorption and by residual photon energy remaining after the electron-hole pair generation. The polarity of the HC photocurrent opposes that of the conventional generation photocurrent, indicating that the total current across the p-n junction is contingent upon the interplay between these two currents. A model of current-voltage characteristics analysis allowing us to obtain a reasonable value of the HC temperature was also proposed. This work is remarkable in two ways: first, it contributes to an understanding of HC phenomena in photovoltaic devices, and second, it prompts discussion of the HC photocurrent as a new intrinsic loss mechanism in solar cells.

Metal-poor star formation at z > 6 with JWST: new insight into hard radiation fields and nitrogen enrichment on 20 pc scales

ABSTRACT Nearly a decade ago, we began to see indications that reionization-era galaxies power hard radiation fields rarely seen at lower redshift. Most striking were detections of nebular C iv emission in what appeared to be typical low-mass galaxies, requiring an ample supply of 48 eV photons to triply ionize carbon. We have obtained deep JWST/NIRSpec R = 1000 spectroscopy of the two z > 6 C iv-emitting galaxies known prior to JWST. Here, we present a rest-UV to optical spectrum of one of these two systems, the multiply-imaged z = 6.1 lensed galaxy RXCJ2248-ID. NIRCam imaging reveals two compact (<22 pc) clumps separated by 220 pc, with one comprising a dense concentration of massive stars (>10 400 M⊙ yr−1 kpc−2) formed in a recent burst. We stack spectra of 3 images of the galaxy (J = 24.8–25.9), yielding a very deep spectrum providing a high-S/N template of strong emission line sources at z > 6. The spectrum reveals narrow high-ionization lines (He ii, C iv, N iv]) with line ratios consistent with powering by massive stars. The rest-optical spectrum is dominated by very strong emission lines ([O iii] EW = 2800 Å), albeit with weak emission from low-ionization transitions ([O iii]/[O ii] = 184). The electron density is found to be very high (6.4–31.0 × 104 cm−3) based on three UV transitions. The ionized gas is metal poor ($12+\log (\rm O/H)=7.43^{+0.17}_{-0.09}$), yet highly enriched in nitrogen ($\log (\rm N/O)=-0.39^{+0.11}_{-0.10}$). The spectrum appears broadly similar to that of GNz11 at z = 10.6, without showing the same AGN signatures. We suggest that the hard radiation field and rapid nitrogen enrichment may be a short-lived phase that many z > 6 galaxies go through as they undergo strong bursts of star formation. We comment on the potential link of such spectra to globular cluster formation.

Photodissociation Dynamics of the Highly Stable ortho-Nitroaniline Cation.

0rtho-Nitroaniline (ONA) is a model for the insensitive high explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) that shares strong hydrogen bonding character between adjacent nitro and amino groups. This work reports femtosecond time-resolved mass spectrometry (FTRMS) measurements and theoretical calculations that explain the high stability of the ONA cation compared with related nitroaromatic molecules. Ab initio calculations found that the lowest-lying electronic excited state of the ONA cation, D1, lies more than 2 eV above the ground state, and the energetic barriers to rearrangement and dissociation reactions exceed this D1 energy. These theoretical results were confirmed by FTRMS pump-probe measurements showing that (1) fragment ions represented less than 30% of the total ion yield when a 1014 W cm-2, 1300 nm, 20 fs pump pulse was used to ionize ONA; and (2) 3.1 eV (400 nm) photons were required to induce dissociation of the ONA cation. Stronger coupling between the ground D0 and excited D4 states of the ONA cation at the geometry of neutral ONA resulted in a transient enhancement of fragment ion yields at <300 fs pump-probe delay times, prior to relaxation of the ONA cation to its optimal geometry.

Mechanism of X-ray excited optical luminescence in NaGdF4-based nanoparticles

X-ray irradiating rare-earth nanoparticles could emit fluorescence (∼50 keV) and luminescence (∼eV) photons simultaneously. Utilizing this phenomenon, it is expected to achieve online multi-modal imaging and integrated radiation and photodynamic therapy for deep tumor. In this scenario, ALnF4: RE3+ (A = alkali metal; Ln = lanthanides acting as matrix; RE3+: rare-earth element used for luminescence center ion) nanoparticles are often selected due to their stable chemical and optical properties. In the application of imaging and therapy, the quantitative calculation of luminescence yield is meaningfully significant for nanoparticle design and to improve the imaging quality and therapeutic effect. However, there is a lack of theoretical calculation on the X-ray excited optical luminescence (XEOL) yield. In this paper, we propose a method to calculate the XEOL yield of ALnF4: RE3+ through theoretical derivation. Taking NaGdF4: Tb3+ as an example, the luminescence mechanism under X-ray irradiation is analyzed and the semi-quantitative formula of luminescence yield is obtained, which is based on the interaction theory of X-ray with materials and the energy transfer principle between different lanthanides. Then, the quantitative XEOL yield formula is gotten by fitting experimental results and the correctness of this formula is verified by the correlation coefficient between fitting results and experimental results. Our results could provide theoretical guidance for the design of NaGdF4-based nanoparticles to manipulate XEOL spectrum and increase XEOL yield. It also laid the foundation for the subsequent development of effective drugs or probes for X-ray driving integrated diagnosis and treatment of deep tumors in vivo.

Low- and High-velocity O vi in Milky Way-like Galaxies: The Role of Stellar Feedback

Milky Way-type galaxies are surrounded by a warm-hot gaseous halo containing a considerable amount of baryons and metals. The kinematics and spatial distribution of highly ionized ion species such as O vi can be significantly affected by supernova (SN) explosions and early (pre-SN) stellar feedback (e.g., stellar winds, radiation pressure). Here we investigate effects of stellar feedback on O vi absorptions in Milky Way−like galaxies by analyzing the suites of high-resolution hydrodynamical simulations under the framework of SMUGGLE, a physically motivated subgrid interstellar medium and stellar feedback model for the moving-mesh code Arepo. We find that the fiducial run with the full suite of stellar feedback and moderate star formation activities can reasonably reproduce Galactic O vi absorptions observed by space telescopes such as the Far-Ultraviolet Spectroscopic Explorer, including the scale height of low-velocity (∣v LSR∣ < 100 km s−1) O vi, the column density–line width relation for high-velocity (100 km s−1 ≤ ∣v LSR∣ < 400 km s−1) O vi, and the cumulative O vi column densities. In contrast, model variations with more intense star formation activities deviate from observations further. Additionally, we find that the run considering only SN feedback is in broad agreement with the observations, whereas in runs without SN feedback this agreement is absent, which indicates a dominant role of SN feedback in heating and accelerating interstellar O vi. This is consistent with the current picture that interstellar O vi is predominantly produced by collisional ionization where mechanical feedback can play a central role. In contrast, photoionization is negligible for O vi production owing to the lack of high-energy (≳114 eV) photons required.

Quantum Efficiency Measurement and Modeling of Silicon Sensors Optimized for Soft X-ray Detection

Hybrid pixel detectors have become indispensable at synchrotron and X-ray free-electron laser facilities thanks to their large dynamic range, high frame rate, low noise, and large area. However, at energies below 3 keV, the detector performance is often limited because of the poor quantum efficiency of the sensor and the difficulty in achieving single-photon resolution due to the low signal-to-noise ratio. In this paper, we address the quantum efficiency of silicon sensors by refining the design of the entrance window, mainly by passivating the silicon surface and optimizing the dopant profile of the n+ region. We present the measurement of the quantum efficiency in the soft X-ray energy range for silicon sensors with several process variations in the fabrication of planar sensors with thin entrance windows. The quantum efficiency for 250 eV photons is increased from almost 0.5% for a standard sensor to up to 62% as a consequence of these developments, comparable to the quantum efficiency of backside-illuminated scientific CMOS sensors. Finally, we discuss the influence of the various process parameters on quantum efficiency and present a strategy for further improvement.

The Near‐Infrared‐II Optical Tuning and Electronic Engineering of MoS2 Bilayers Doped by Halogen Elements

The improvement of optical absorption behavior of the second near‐infrared region (NIR‐II, 1000–1350 nm) based on new function materials is significant for the development of biomedicine and optical imaging. Therefore, the electronic structures and optical absorption of 2H phase MoS2 doped by F, Cl, Br, and I atoms with various doping concentrations are calculated, results show that halogen elements introduced extra transition allowed bands which is about 1.0 eV wide to 2H‐MoS2, and the increasing of impurity concentration can trigger strong spin splits. The transformation of electronic structures leads to 2H‐MoS2 metallic behaviors, improves transition efficiency, and lowers photon energy loss. More importantly, strong light–mass interaction is verified and breaks the energy level degeneracy, makes absorption peaks at 0.6–1.0 eV photon energy region, successfully extends the work region of 2H‐MoS2 to NIR‐II window, greatly improves the optical response and application potential in the photoelectric field. These results not only prove the potential of halogen elements as dopants in bandgap engineering of 2H‐MoS2 but also may indicate a direction for seeking new generation function materials that own excellent performance in the NIR‐II window, which is of great significance to promote the development of optoelectronics and bioimaging applications.

Bright continuously tunable vacuum ultraviolet source for ultrafast spectroscopy

Ultrafast electron dynamics drive phenomena such as photochemical reactions, catalysis, and light harvesting. To capture such dynamics in real-time, femtosecond to attosecond light sources are extensively used. However, an exact match between the excitation photon energy and a characteristic resonance is crucial. High-harmonic generation sources are advantageous in terms of pulse duration but limited in spectral tunability in the vacuum ultraviolet range. Here, we present a monochromatic femtosecond source continuously tunable around 21 eV photon energy utilizing the second harmonic of an optical parametric chirped pulse amplification laser system to drive high-harmonic generation. The unique tunability of the source is verified in an experiment probing the interatomic Coulombic decay in doped He nanodroplets across the He absorption bands. Moreover, we achieved intensities sufficient for driving collective processes in multiply excited helium nanodroplets, which have been previously observed only at free electron lasers.

Dissociative photoionization of acetaldehyde in the 10.2-19.5 eV VUV range.

The valence-shell dissociative photoionization of acetaldehyde has been investigated by means of the photoion photoelectron coincidence technique in conjunction with tuneable synchrotron radiation. The experimental results consist of threshold photoelectron spectra for the parent ion and for each fragment ion in the 10.2-19.5 eV photon energy range, along with (ion, e) kinetic energy coincidence diagrams obtained from measurements at fixed photon energies. The results are complemented by high-level ab initio calculations of potential energy curves as a function of the C-H bond distance. The nudged elastic band (NEB) method has been employed to connect the parent ion Franck-Condon region to the formation of the HCO+, CH3+ and CH4+ ion fragments. Appearance energies have been determined for six fragment ions with an improved accuracy, including two fragmentation channels, which to the best of our knowledge have not been reported previously, i.e. the formation of CH2CO+, lying at 13.10 ± 0.05 eV, and the formation of CH2+ at 15.1 ± 0.1 eV. Based on both experimental and theoretical results, the dissociation dynamics following ionization of acetaldehyde into the different fragmentation channels are discussed.

Exploring the deposition pathway in the notch region of double-graded bandgap ACIGS solar cells

The bandgap widening of Ag-alloyed Cu(In,Ga)Se2 (ACIGS) thin films poses a significant challenge in enhancing their photocurrent. This study demonstrates correlations between element diffusion behavior and notch-point formation in ACIGS films, which ultimately influence the resulting current circuit voltage and fill factor. Our findings delineate a novel approach for fabricating a suitably tailored band gap grading in ACIGS, which serves as a bottom subcell in tandem configuration. This was achieved by modulating a wide range of process temperatures from 340 to 470 °C, which were measured by pyrothermal, to assess the GGI profile during deposition. Experiments were undertaken to variate the second-stage conditions, striving to sustain the photocurrent, mitigate defects, and enhance crystallinity, achieving an impressive performance of 17.7 % without applying post-deposition treatments or anti-reflection coatings. The efficiencies surpassing 8 % were achieved as we measured these cells under a 715 nm long-pass filter, which corresponds to the bandgap of a typical top cell in tandem applications (1.73 eV photon energy). These results emphasize the significance of understanding the deposition temperature and its impact on the properties of ACIGS films, paving the way for further advancements in solar-cell technology.

Broad spectral response to photon energy unlimited by Schottky barrier from NiSi/Si junction

Recent advances in plasmonic absorption devices offer a novel approach for extending the range of silicon light detection. This is achieved by exploiting the Schottky interface energy barrier, which overcomes the limitation of the 1.12 eV photon energy conversion imposed by the silicon intrinsic bandgap. Internal photoemission has been widely accepted as the primary emission mechanism, which is mostly limited by the Schottky barrier height. However, we have discovered that carriers with energy lower than the Schottky barrier can generate electrical responses through the photothermal effect, breaking this restriction. In this study, we closely investigate two forms of photoresponses, namely photoelectric and photothermal, on a NiSi thin film Schottky photodetector, considering various factors such as temperature, applied bias, incident power, and wavelength regime. Without photothermal assistance, the device achieves a responsivity of 0.41 mA/W to a 1550 nm laser. Under bias-driven conditions, highly energized hot carriers generate a 2.18 μA photoelectric response, while a 0.861 μA photothermal response is simultaneously observed under 6 mW 1550 nm laser illumination. Through systematic investigation, we advance the mechanism of both responses by combining the hot carrier model and the Schottky barrier diagram. Finally, we experimentally obtain a 4.85 μA sheer photothermal response to a 0.475 mW 4-μm wavelength signal with 10.21 mA/W responsivity. It is expected that the device will also show responses to longer wavelengths.

First-principle calculations to investigate electronic and optical properties of carbon-doped silicon

Silicon (Si) is a highly promising candidate for the applications of photovoltaics. However, the bandgap constraints, low conductivity, and bounded photon energy absorption make the applications restricted. Herein, we investigated the optimized structural, electronics and optical characteristics of carbon (C) doped Si by first-principle calculations. The analysis of the various doping illustrates that doping of the C atom in Si adds extra stability by reducing the Si–Si bond length from 2.3 Å to 2.002 Å Si–C bond length which leads to the shrinkage of lattice parameters. In addition, the bandgap of Si is reduced from 1.13 eV to 0.2 eV if a 14.28 % C-doping is employed. As the C-doping is reduced to 6.66 %, the bandgap increases to 0.87 eV with a transition from indirect to direct bandgap. Further reduction in C-doping varies the bandgap from 0.87 eV to 1.13 eV. The density of states calculations show that for a low C-doping, the transitions are mainly due to Si-3p and Si-3s orbitals in the valence band which leads to a higher energy level, while for higher C-doping, the C atom 2p orbital contribution causes a reduction in bandgap and addition of stability in the doped structures. The conductivity of the Si can be increased by utilizing higher C-doping which reduces hole effective mass by 46 % and electron effective mass by 24 %. Optical absorption of Si can be enhanced at a higher spectral range while adopting a higher C-doping, which shifts the absorption peak shapes from spikes to flat and extends to 7 eV photon energy.

Study of the Graphene Oxide Nanosheets Synthesized from Pencil Electrode Using Electrochemical Method and Solar Energy as a Source of Power

Graphene Oxide nanosheets were synthesized using electrochemical exfoliation of pencil electrodes in aqueous solution containing 2% of magnesium sulfate salt. A solar panel of 20V was used as a power supply to turn the synthesis into a green method. Several measurements were carried out to investigate the product, namely: Raman scattering, X-ray diffraction, photoluminescence, UV-VIS-NIR spectroscopy, and FTIR spectroscopy. Raman scattering showed the existence of both D-band and G-band, which are an indication of graphene oxide existence. The D-to-G band ratio was 1.5. The results of X-ray showed a diffraction peak at 2θ = 20.7° corresponding to the space distance between graphene oxide nanosheets and a diffraction peak at 2θ = 26.25° corresponding to the short range interplanar spacing. Photoluminescence showed two peaks of emission (at wavelengths 355nm &amp; 701nm) regarding to the π-π* transition. UV-VIS-NIR spectroscopy exhibited a 4.2eV photon energy absorption peak corresponding to the aromatic C=C bonds and 5.4eV photon energy absorption peak corresponding to the carbonyl groups. FTIR showed peaks related to hydroxyl groups, hydrogen-bonded OH groups of COOH, and functional groups such as C-OH (1375 cm-1), and C-O (1039 cm-1). FTIR results approved that graphene oxide nanosheets are functionalized. TEM images show that the synthesized graphene oxide is single-, double-, and multi-layer stacks with an amount of impurities.

High-precision room temperature Fe opacity measurements at 1000-2000eV photon energies

Prior measurements of room temperature (cold) Fe opacity have errors as high as ±10 % and a spread in values that exceeds the uncertainties. These data, along with current cold opacity databases, were used for comparison with experimental solar Fe opacity. The solar Fe opacity is expected to be lower than cold Fe opacity in the ∼1500–2000 eV photon energy range. However, results from this comparison contradicted this assumption and prompted an investigation of the precision and accuracy of cold Fe opacity measurements. Cold Fe opacity is determined here with high precision using transmission measurements of Fe foils at three characteristic line energies in the soft X-ray range (1000–2000 eV). The present opacities are determined with ≲1 % overall uncertainties. This is achieved through precise measurements of transmission and areal density which are related to opacity by the Beer-Lambert Law. Transmission is measured with overall individual uncertainties of ≲1 % and is obtained through simultaneous measurements of attenuated and unattenuated spectra using an X-ray source and a Bragg crystal spectrometer. The required areal density is indepen-dently measured using two different techniques: Rutherford Backscattering Spectroscopy and a recently-developed technique using calibrated cold absorption in the 3–17 keV range. The final areal density used in the opacity determination is an average between both methods. The measured opacity at 1188 eV is in agreement with current opacity databases but is higher by around 5–10 % at the highest photon energy (1924 eV) and lower by around 2–4 % at the lowest photon energy (1012 eV). A caveat is that opacity accuracy is linearly dependent on the areal density. We performed the first direct comparison between the two areal density methods which revealed a 7–11 % discrepancy. If one of the methods is proven correct in future studies, it may impact the opacity accuracy reported here since we use the average of the two methods. This result affects the solar Fe opacity measurements as they also rely on the accuracy of these areal density measurement techniques.