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Atomic scale evidence of the switching mechanism in a photomagnetic CoFe dinuclear Prussian Blue Analogue
摘要： Molecular complexes based on Prussian Blue Analogues have recently attracted considerable interest for their unique bistable properties combined to ultimately reduced dimensions. Here, we investigate the first dinuclear FeCo complex exhibiting both thermal and photomagnetic bistability in solid state. Through an experimental and theoretical approach combining local techniques - X-ray Absorption Spectroscopy (XAS), X-ray Magnetic Circular Dichroism (XMCD) and Ligand Field Multiplet calculations, we were able to evidence the changes occuring at the atomic scale in the electronic and magnetic properties. The spectroscopic studies were able to fully support at the atomic level the following conclusions: (i) the 300 K phase and the light-induced excited state at 4 K are both built from FeIII LS—CoII HS paramagnetic pairs with no apparent reorganization of the local structure, (ii) the 100 K phase is composed of FeII LS—CoIII LS diamagnetic pairs, and (iii) the light-induced excited state is fully relaxed at an average temperature of ≈ 50 K. In the paramagnetic phase at 2 K, XAS and XMCD reveal that, both Fe and Co ions exhibit a rather large orbital magnetic moment (0.65 μB and 0.46 μB, respectively under an external magnetic induction of 6.5 T) but it was not possible to detect a magnetic interaction between spin centers above 2 K.
关键词： Ligand Field Multiplet calculations,X-ray Absorption Spectroscopy,X-ray Magnetic Circular Dichroism,photomagnetic bistability,Prussian Blue Analogues
更新于2025-09-10 09:29:36
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A broadband cavity enhanced absorption spectrometer for aircraft measurements of glyoxal, methylglyoxal, nitrous acid, nitrogen dioxide, and water vapor
摘要： We describe a two-channel broadband cavity enhanced absorption spectrometer (BBCEAS) for aircraft measurements of glyoxal (CHOCHO), methylglyoxal (CH3COCHO), nitrous acid (HONO), nitrogen dioxide (NO2), and water (H2O). The instrument spans 361–389 and 438–468 nm, using two light-emitting diodes (LEDs) and a single grating spectrometer with a charge-coupled device (CCD) detector. Robust performance is achieved using a custom optical mounting system, high-power LEDs with electronic on/off modulation, high-reflectivity cavity mirrors, and materials that minimize analyte surface losses. We have successfully deployed this instrument during two aircraft and two ground-based field campaigns to date. The demonstrated precision (2σ) for retrievals of CHOCHO, HONO and NO2 are 34, 350, and 80 parts per trillion (pptv) in 5 s. The accuracy is 5.8, 9.0, and 5.0 %, limited mainly by the available absorption cross sections.
关键词： broadband cavity enhanced absorption spectroscopy,water vapor,nitrous acid,methylglyoxal,aircraft measurements,glyoxal,nitrogen dioxide
更新于2025-09-09 09:28:46
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Membership Function-Weighted Non-Linear Fitting Method for Optical-Sensing Modeling and Reconstruction
摘要： Imprecise measurements present universally due to variability in the measurement error. We devised a very simple membership function to evaluate fuzzily the quality of optical sensing with a small dataset, where a normal distribution cannot be assumed. The proposed membership function was further used as a weighting function for non-linear curve fitting under expected mathematical model constraints, namely the membership function-weighted Levenberg–Marquardt (MFW-LM) algorithm. The robustness and effectiveness of the MFW-LM algorithm were demonstrated by an optical-sensing simulation and two practical applications. (1) In laser-absorption spectroscopy, molecular spectral line modeling was greatly improved by the method. The measurement uncertainty of temperature and pressure were reduced dramatically, by 53.3% and 43.5%, respectively, compared with the original method. (2) In imaging, a laser beam-profile reconstruction from heavy distorted observations was improved by the method. As the dynamic range of the infrared camera increased from 256 to 415, the detailed resolution of the laser-beam profiles increased by an amazing 360%, achieving high dynamic-range imaging to capture optical signal details. Therefore, the MFW-LM algorithm provides a robust and effective tool for fitting a proper physical model and precision parameters from low-quality data.
关键词： non-linear curve fitting,sensing modeling and reconstruction,image reconstruction-restoration,optical-sensing signal processing,laser-absorption spectroscopy
更新于2025-09-09 09:28:46
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Surface Chemistry and Long-Term Stability of Amorphous Zn-Sn-O Thin Films
摘要： Amorphous (a-) oxides form an important category of transparent conducting/semiconducting thin films used as electrodes and channel layers in thin film transistors. The compositional flexibility of amorphous states, through doping, makes it possible to fine tune the electrical properties of films from conducting to semiconducting. However, surface chemistry and stability of these films are rarely addressed. Surface studies of amorphous materials, in general, are scarce due to disorder. Here, long-term surface stability of a-Zn-Sn-O films is investigated using grazing incidence X-ray absorption spectroscopy techniques. We present a detailed description of film surface structures and their evolution over time. It is found that the surface structure is, locally, a close analogue of the crystalline counterpart and that surface chemistry is governed by vacancies, strain, composition, and film density. It will be shown that the long-term stability of a film is questionable when the film has a high Zn content and a low density.
关键词： Zn-Sn-O thin films,Long-term stability,Grazing incidence X-ray absorption spectroscopy,Surface chemistry,Amorphous oxides
更新于2025-09-09 09:28:46
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Sensitive X-ray Absorption Near Edge Structure Analysis on the Bonding Properties of Au <sub/>30</sub> (SR) <sub/>18</sub> Nanoclusters
摘要： Au nanoclusters (NCs) with organothiolate protecting ligands are a field of great interest and X-ray absorption spectroscopy is a useful tool for the structure and property studies of these Au NCs. However, the Au NCs normally show broad and low-intensity features in the gold X-ray absorption near-edge structure (XANES) region, lowering the sensitivity of the technique and making it difficult to use for the analysis of Au NCs. In this work we report a sensitive gold L3-edge XANES study on the bonding properties of the newly discovered Au30(SR)18 NCs utilizing a combined approach of the first derivative XANES spectra and quantum simulations. First derivative XANES spectra are compared with the well-studied Au25(SR)18 with the aim of determining the unique features of Au30(SR)18. It is found that the early XANES region of the Au NCs is significantly influenced by the gold?gold bonding environment in the surface sites, as the varying surface Au?Au bond lengths in Au25(SR)18 and Au30(SR)18 result in pronounced difference in the first derivative XANES. These findings can be consistently explained using site-selective quantum simulations of the XANES spectra based on the Au NC structural models. The XANES method presented in this work offers a useful tool for the sensitive analysis on structure and bonding properties of Au NCs.
关键词： Au nanoclusters,bonding properties,quantum simulations,XANES,X-ray absorption spectroscopy
更新于2025-09-09 09:28:46
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AIP Conference Proceedings [Author(s) PHYSICS, TECHNOLOGIES AND INNOVATION (PTI-2018): Proceedings of the V International Young Researchers’ Conference - Ekaterinburg, Russia (14–18 May 2018)] - Reduction of uranium(VI) species in alkali chloride melts: An electronic absorption spectroscopy study of formation of uranium(V) ions
摘要： Reaction of uranyl chloride with gaseous hydrogen was studied in a range of alkali chloride based melts between 350 and 850 oC. The reaction leads to the formation of soluble uranium(V) dioxochloro-species and solid uranium dioxide. In situ electronic absorption spectroscopy was employed to follow the reaction. Electronic absorption spectra of uranium(V) dioxo-species were recorded between 300 and 1600 nm. The effect of temperature and second coordination sphere cations on the absorption spectra is discussed.
关键词： alkali chloride melts,hydrogen reduction,uranium(V),electronic absorption spectroscopy,uranyl chloride
更新于2025-09-09 09:28:46
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In situ Study of EDC/NHS Immobilization on Gold Surface Based on Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS)
摘要： In this study, the time-dependent reaction between 11-mercaptoundecanoic acid (11-MUA) and 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC/NHS) is precisely characterized using surface enhanced infrared absorption spectroscopy (SEIRAS). According to the high correlation between the spectral results of SEIRAS and the electrochemical behavior, it strongly demonstrates that the EDC/NHS reaction would be obviously interfered by phosphate ions in the neutral pH condition (pH = 7.0).
关键词： EDC/NHS,Attenuated Total Reflection (ATR),Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS)
更新于2025-09-09 09:28:46
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Spectral analysis of the <scp>EBT</scp> 3 radiochromic films for clinical photon and electron beams
摘要： Purpose: To investigate the spectral response of the EBT3 radiochromic films to different beam qualities for radiation therapy dosimetry. Dose, dose rate, and inter-batch dependencies on the spectral response of the films are investigated as well. Methods: Pieces of EBT3 films placed between layers of solid water phantoms were irradiated with 6 and 15 MV photon beams, 6 and 10 MV-FFF photon beams, and 6 and 20 MeV electron beams at dose levels between 0.4-50 Gy. Net absorbance was measured as a function of wavelength from the spectra acquired in the wavelength range of 400-800 nm using a fiber-coupled spectrometer and broadband light source. Results: No significant change was observed in the absorption spectra of the EBT3 films irradiated with the same amount of dose using different beam qualities. Also, no spectral change with dose rate was observed. The measured net absorbance per Gy was independent of beam quality in the 1-50 Gy dose range. Slight differences in the spectral shape and absorption band positions were observed in film samples from different batches. The net absorbance spectra showed two absorption bands centered around 634-636 nm (primary) and 583-585 nm (secondary). However, depending on the film batch, for doses above a certain level the primary absorption band appears to “split” into two bands centered around ~624-628 and ~641-645 nm. Conclusions: The spectral shape of the EBT3 radiochromic films irradiated with photons (including FFF) and electron beams is beam quality and dose rate independent; however it varies with dose level, batch, and spectroscopy system used.
关键词： EBT3,film dosimetry,Radiochromic film,absorption spectroscopy
更新于2025-09-04 15:30:14
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Ultrafast Excited State Dynamics of a Stilbene–Viologen Charge Transfer Complex and Its Interaction with Alkanediammonium Salts
摘要： The spectral and thermodynamic properties of charge transfer complexes D?A and D?A?D between (E)-bis(18-crown-6)stilbene (D) and 1,1'-bis(2-ammonioethyl)-4,4'-bipyridinium tetraperchlorate (A) in MeCN were studied. The complex D?A is highly stable, while the complex D?A?D is weakly stable. D?A does not fluoresce due to fast intramolecular processes of direct and reverse electron transfer. The efficiency of D?A fluorescence ignition upon adding alkanediammonium salts depends on the length of a carbon chain. The spectral and kinetic characteristics of D?A and D?A?D CT states were obtained by femtosecond transient absorption spectroscopy. It was established that the characteristic time of back electron transfer in the CT state of D?A?D (770 fs) is significantly higher than that in the CT state of D?A (400 fs). In a number of charge transfer complexes, formed by derivatives of 4,4'-bipyridinium and di-(4-pyridinium)-ethylene with ammonioethyl and ammoniopropyl N-substituents, the rate of back electron transfer depends weakly on the acceptor nature, but is determined by the length of the carbon chain of terminal groups.
关键词： fluorescence,charge transfer complex,ultrafast electron transfer,transient absorption spectroscopy,bis-crown ether
更新于2025-09-04 15:30:14
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Cavity-enhanced absorption sensor for carbon monoxide in a rapid compression machine
摘要： A sensor based on cavity-enhanced absorption spectroscopy (CEAS) was implemented for the first time in a rapid compression machine (RCM) for carbon monoxide concentration measurements. The sensor consisted of a pulsed quantum cascade laser (QCL) coupled to a low-finesse cavity in the RCM using an off-axis alignment. The QCL was tuned near 4.89 μm to probe the P(23) ro-vibrational line of CO. The pulsed mode operation resulted in rapid frequency down-chirp (6.52 cm ?1 / μs) within the pulse as well as a high time resolution (10 μs). The combination of rapid frequency down-chirp and off-axis cavity alignment enabled a near complete suppression of the cavity coupling noise. A CEAS gain factor of 133 was demonstrated in experiments, resulting in a much lower noise-equivalent detection limit than a single-pass arrangement. The sensor thus presents many opportunities for measuring CO formation at low temperatures and for studying kinetics using dilute reactive environments; one such application is demonstrated in this work using dilute n-heptane/air mixtures in the RCM. The formation of CO during first-stage ignition of n-heptane was measured over 802–899 K at a nominal pressure of 10 bar. These conditions correspond to the NTC region of n-heptane and such results provide useful metrics to test and compare the predictions of low-temperature heat release by different kinetic models.
关键词： n-heptane,Low-temperature heat release,Cavity-enhanced absorption spectroscopy,Rapid compression machine,Carbon monoxide
更新于2025-09-04 15:30:14