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This paper describes the use of Optical Emission Spectroscopy (OES) to measure electron densities and temperatures in non-equilibrium plasmas. The ways to interpret relative line-intensities of neutral argon atoms are evaluated based upon a collisional-radiative model including atomic collisional processes. A conversion from an excitation temperature determined from relative line intensities assuming a Boltzmann population distribution to the thermal electron temperature in the electron temperature range 1-4 eV and electron density range 10 10 -10 12 cm -3 is given. Procedures to obtain electron temperature T e and density N e of non-equilibrium argon plasma by OES measurement with collisional radiative model.

The electron-hole pair created via photon absorption in organic photoconversion systems must overcome the Coulomb attraction to achieve long-range charge separation. We show that this process is facilitated through the formation of excited, delocalized band states. In our experiments on organic photovoltaic cells, these states were accessed for a short time (< 1 picosecond) via infrared (IR) optical excitation of electron-hole pairs bound at the heterojunction. Atomistic modeling showed that the IR photons promote bound charge pairs to delocalized band states, similar to those formed just after singlet exciton dissociation, which indicates that such states act as the gateway for charge separation. Our results suggest that charge separation in efficient organic photoconversion systems occurs through hot-state charge delocalization rather than energy-gradient-driven intermolecular hopping.

This report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions.

In the present investigation, the synthesis, characterization, and application of triazole‐coated novel magnetic nanoparticles (MNPs) are systematically carried out, focusing on their efficacy as adsorbents for extracting Au(III) ions. The synthesis process involves the sequential coating of magnetite nanoparticles with tetraethylorthosilicate (SiO2), 3‐chloropropyltriethoxysilane (CPTES), and 3,5‐diamino‐1,2,4‐triazole (DAT). The MNPs synthesized at each stage are analyzed using high‐resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray analysis (EDX), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), and thermogravimetric and differential thermal analysis (DT/TGA) to confirm the successful coating of the desired adsorbent. Fe3O4@SiO2@CPTES@DAT MNPs selectively recover Au(III) ions under optimum conditions of pH = 2, 10 mg adsorbent amount, and 20 min contact time, and quantification of Au(III) ions is carried out by inductively coupled plasma‐optical emission spectroscopy (ICP‐OES). The method's suitability to adsorption isotherm and kinetic models is examined and found to be more compatible with the Freundlich isotherm and pseudo‐second‐order kinetic model. Relative standard deviation, limit of detection, and limit of quantification are calculated as 2.51%, 0.019, and 0.065 μg L−1, respectively, as analytical performance parameters. Several water samples are tested for Au(III) concentration using the optimized method. The synthesized magnetic nanoparticles, designated as Fe3O4@SiO2@CPTES@DAT, demonstrate effective recovery of Au(III) ions under optimized conditions at a pH of 2, utilizing 10 mg of the adsorbent, with an interaction time of 20 min. This finely tuned methodology is successfully employed to analyze various water samples regarding the recovery of Au(III).

See how they run Electrons move in solids at very high speed — traversing atomic layers and interfaces within tens to hundreds of attoseconds (an attosecond is a billionth of a billionth of a second). These astonishingly brief travel times will ultimately limit the speed of the electronics of the future. Physicists have now experimentally probed such electron dynamics in real time. The cover illustrates the first attosecond spectroscopic measurement in a solid, revealing a 110-attosecond difference in the travel time of two different types of electrons following photoexcitation in a tungsten crystal. The ability to time electrons moving in solids over merely a few interatomic distances makes it possible to probe the solid-state electronic processes occurring at the ultimate speed limit and thus helps to advance technologies such as computation, data storage and photovoltaics, which all rely on exquisite control of electron transport in ever smaller structures of solid matter. When exposing a tungsten crystal to intense light, the travel times of emitted electrons differ by 110 attoseconds, depending on whether they were originally tightly bound to one atom in the crystal or delocalized over many atoms. This ability to directly probe fundamental aspects of solid-state electron dynamics could aid the further development of modern technologies such as electronics, information processing and photovoltaics. Comprehensive knowledge of the dynamic behaviour of electrons in condensed-matter systems is pertinent to the development of many modern technologies, such as semiconductor and molecular electronics, optoelectronics, information processing and photovoltaics. Yet it remains challenging to probe electronic processes, many of which take place in the attosecond (1 as = 10 -18  s) regime. In contrast, atomic motion occurs on the femtosecond (1 fs = 10 -15  s) timescale and has been mapped in solids in real time 1 , 2 using femtosecond X-ray sources 3 . Here we extend the attosecond techniques 4 , 5 previously used to study isolated atoms in the gas phase to observe electron motion in condensed-matter systems and on surfaces in real time. We demonstrate our ability to obtain direct time-domain access to charge dynamics with attosecond resolution by probing photoelectron emission from single-crystal tungsten. Our data reveal a delay of approximately 100 attoseconds between the emission of photoelectrons that originate from localized core states of the metal, and those that are freed from delocalized conduction-band states. These results illustrate that attosecond metrology constitutes a powerful tool for exploring not only gas-phase systems, but also fundamental electronic processes occurring on the attosecond timescale in condensed-matter systems and on surfaces.

Laser-induced breakdown spectroscopy (LIBS) is an elemental analysis technique that is based on the measurement of atomic emissions generated on a sample surface by a laser-induced microplasma. Although often recognized in the literature as a well-established analytical technique, LIBS remains untested relative to the quantitative analysis of elements in chemically complex matrices, such as soils. The objective of this study was to evaluate the capabilities of LIBS relative to the elemental characterization of surface soils. Approximately 65 surface soil samples from the Pond Creek watershed in east Tennessee were collected and subjected to total dissolution and elemental analysis by inductively coupled argon plasma-optical emission spectroscopy (ICP-OES). The samples were analyzed by LIBS using a Nd:YAG laser at 532 nm, with a beam energy of 25 mJ per pulse, a pulse width of 5 ns, and a repetition rate of 10 Hz. The wavelength range for the LIBS spectra collection was 200 to 600 nm, with a resolution of 0.03 nm. Elemental spectral lines were identified through the analysis of analytical reagent-grade chemicals and the NIST and Kurucz spectral databases. The elements that dominated the LIBS spectra were Al, Ca, Fe, and Mg. In addition, emission lines for Ti, Ba, Na, Cu, and Mn were isolated. The emission lines of Cr, Ni, and Zn, which were >100 mg kg-1 in numerous soil samples, were not detected. Further, spectral emission lines for P and K are >600 nm, eliminating them from LIBS analysis. The integrated peak areas of interference-free elemental emission lines were determined, then normalized to the area of the 288.16 nm Si(I) emission (internal standard) to reduce the variability between replicate analyses. The normalized spectral areas, coupled with linear regression (standard curves for single wavelength response) and multivariate techniques (chemometrics and multiple wavelengths), were used to predict ICP-OES elemental data. In general, the quantitative capabilities of LIBS proved disappointing. Detection and quantitation were generally restricted to those elements with concentrations > 0.5 g kg-1. The correlation between LIBS response and elemental content was poor (r < 0.98). Further, the relative errors of prediction for the LIBS-detected elements were less than acceptable for an analytical technique (<20%), ranging from 20 to 40% using linear regression analysis, and from 18 to 48% using partial least squares analysis. Based on these findings, the analytical capability of the LIBS method for soil metals analysis should be considered questionable.

This work reports the controlled synthesis and characterization of nanoenergetic composites composed of porous silicon (PS) impregnated with sodium perchlorate (NaClO4) for precision energy-release applications. PS films were fabricated by electrochemical anodization of p-type silicon (10–20 Ω·cm), with systematic variation in current density (50–200 mA cm−2) and anodization time (10–25 min) to tailor pore morphology. The energetic behavior of the composites was evaluated through thermal ignition tests, optical emission spectroscopy (300–1000 nm), acoustic analysis (0–500 Hz), and high-speed imaging. Optimal energy release was obtained for PS films anodized at 100 mA cm−2 for 15–20 min, attributed to their hierarchical pore architecture that facilitated complete oxidant infiltration. Overall, this work provides additional insights beyond previous reports by correlating the explosive efficiency with both anodization time—linked to PS film thickness—and current density—associated with porosity. A portable multispectral optical system with fiber-optic access to the explosion chamber was developed for in situ characterization, offering a safe and versatile approach for measurements in explosive environments. To the best of our knowledge, no prior studies have analyzed the correlation between the acoustic signatures and explosion intensity in PS–NaClO4 systems as proposed here.

Optical spectroscopy using ultrafast light pulses has undergone a revolution in the last decade due to the introduction and development of multidimensional coherent techniques. These methods build on established coherent spectroscopic techniques, such as photon echoes, but go beyond them by correlating the coherent dynamics during two time periods. The resulting multidimensional spectra have a number of advantages including disentangling congested spectra, revealing coupling between resonances, and removing the effects of inhomogeneous broadening. Similar ideas are currently being used for imaging. The papers in this 'focus on' collection document some of the current areas of activity in these fields.

The transient nanoscale dynamics of materials on femtosecond to picosecond timescales is of great interest in the study of condensed phase dynamics such as crack formation, phase separation and nucleation, and rapid fluctuations in the liquid state or in biologically relevant environments. The ability to take images in a single shot is the key to studying non-repetitive behaviour mechanisms, a capability that is of great importance in many of these problems. Using coherent diffraction imaging with femtosecond X-ray free-electron-laser pulses we capture time-series snapshots of a solid as it evolves on the ultrafast timescale. Artificial structures imprinted on a Si 3 N 4 window are excited with an optical laser and undergo laser ablation, which is imaged with a spatial resolution of 50 nm and a temporal resolution of 10 ps. By using the shortest available free-electron-laser wavelengths 1 and proven synchronization methods 2 this technique could be extended to spatial resolutions of a few nanometres and temporal resolutions of a few tens of femtoseconds. This experiment opens the door to a new regime of time-resolved experiments in mesoscopic dynamics. High-speed imaging gives us a fascinating insight into ultrafast changes in materials. By combining the speed of optical pulses and the short wavelength of X-ray pulses, imaging with 50-nm spatial and 10-ps temporal resolution is possible, with scope to go much further.