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The Analysis of Starlight (Two Centuries of Astronomical Spectroscopy) || Introduction to spectroscopy, spectroscopes and spectrographs
摘要： A favourite quotation by astronomers is a passage by the French philosopher, Auguste Comte (1798–1857). The nineteenth lesson of his Cours de Philosophie Positive appeared in 1835 and was one of several lessons dealing with the theory of knowledge in astronomy. With reference to the stars, he wrote: We understand the possibility of determining their shapes, their distances, their sizes and their movements; whereas we would never know how to study by any means their chemical composition, or their mineralogical structure, and, even more so, the nature of any organized beings that might live on their surface. In a word, our positive knowledge with respect to the stars is necessarily limited solely to geometric and mechanical phenomena, without being able to encompass at all those other lines of physical, chemical, physiological and even sociological research which comprise the study of the accessible [i.e. terrestrial] beings by all our diverse methods of observation. [1] A little later he continued: ‘I persist in the opinion that every notion of the true mean temperatures of the stars will necessarily always be concealed from us’ [1]. These passages may be amusing in the light of present knowledge, and it seems probable that Comte was ignorant of Fraunhofer’s investigations from about 1814 to 1823 in which he described the absorption lines in solar and stellar spectra (see Sections 2.4 and 2.5). In any case, the implications of Fraunhofer’s spectroscopic work were far from apparent at that time, even in scienti?c circles. However, Comte has been much maligned, mainly by astronomers ignorant of his overall positivist philosophy. Immediately preceding the much quoted passage on chemical composition of the stars is the statement: ‘Every research that is not ?nally reducible to simple visual observations is therefore necessarily disallowed in our study of the stars’ [1]. Comte therefore preached that true science was impossible if not based on direct observation or experiment (in the case of astronomy, on observation), a philosophy that scientists today should be happy to espouse. In spite of my defence of Comte’s views on the composition of the stars, which were admittedly erroneous yet pardonable, this book is largely a study of the subsequent investigations by many astronomers who reached the opposing view to Comte’s by the analysis of starlight using the spectroscope or spectrograph. This is the story of how ?rst the different chemical elements were identi?ed in stars from their spectra, of how the temperatures and other physical properties of the outer layers of stars were measured, and ?nally of how the chemical composition of the stars themselves has been quantitatively determined. The story described here spans more than three centuries if the prismatic dispersion and analysis of sunlight by Isaac Newton in 1666 is taken as the starting point. Alternatively, it encompasses nearly two centuries from the early investigations of Joseph Fraunhofer mentioned earlier, or nearly one and a half centuries from the rebirth of stellar spectroscopy with work by Huggins, Secchi and others in 1863. The studies of Newton and Fraunhofer were relatively isolated events in the history of astronomical spectroscopy, and the continuous development of the subject took place from about 1860 onwards. The scope of this book covers the main events in this development until about the end of the twentieth century, though the last decade or so of the century is not covered in the same detail as the earlier epochs. The remainder of this introductory chapter concerns some of the basic concepts in spectroscopy, which may be skipped by those already familiar with them. In addition, some historical comments on the development of astronomical spectroscopes and spectrographs are included.
关键词： Huggins,stars,spectroscopes,spectroscopy,Fraunhofer,Newton,Secchi,astronomy,spectrographs,chemical composition
更新于2025-09-10 09:29:36
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Physical, photochemical, and extended piezoelectric studies of orthorhombic ZnSnN2 nanocolumn arrays
摘要： This study reports the piezo-related properties of ZnSnN2 (ZTN) fabricated through natural Sn3N4 and Zn thickness gradients deposited oppositely on a fluorine-doped tin oxide substrate to form Zn–Sn3N4 composition spreads to enhance the relative variation of the cation ratios and to promote the formation of orthorhombic ZTN. No moving shutter was incorporated into combinatorial magnetron sputtering to minimize fabrication complexity. The Sn3N4-rich deposition (Location 1) of the Zn–Sn3N4 composition spread exhibited Sn3N4 and the single crystallinity of orthorhombic (Pna21) ZTN nanocolumn arrays, which grew along the [0 0 1] direction, confirmed by locked-coupled X-ray diffraction and transmission electron microscopy. The constituent element diffusion and variation of the atomic binding state of constituent elements along the substrate normal were tracked by depth profiling using secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. The band gap of ZTN (approximately 2.0 eV) was estimated from a UV–vis spectrum. The piezotronic and piezophototronic effects of ZTN were determined through a facile current–voltage measurement, which were explained by the Schottky barrier height variations. Piezophotocatalysis exhibited the highest rate constant (k, approximately 9 × 10?3/min) of the measurements, which was attributed to the reduced recombination of the photogenerated e?–h+ pairs because of the piezopotential distribution. Additionally, O2? radicals were predominantly indicated in the degradation process.
关键词： Piezotronic effect,Orthorhombic ZnSnN2 nanocolumn array,Piezophotocatalysis,Piezophototronic effect,Combinatorial Zn–Sn3N4 composition spread
更新于2025-09-10 09:29:36
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A challenge for x-ray photoelectron spectroscopy characterization of Cu(In,Ga)Se2 absorbers: The accurate quantification of Ga/(Ga?+?In) ratio
摘要： CIGS (Cu(In,Ga)Se2) layers are among the more efficient photovoltaic absorbers for thin film solar cells and remain competitive in the worldwide landscape of solar cells devices and modules with also new emerging markets (flexible or metallic substrates, tandem, low or high band gap CIGS…). Their properties are governed by different key composition parameters, and among them the GGI ratio ([Ga]/[Ga]+[In])) which controls the gap value. Indeed, the GGI determination is an important metrological challenge at the surface of the CIGS layer, particularly before the buffer deposition. Using X-Ray Photoelectron Spectroscopy (XPS), we propose here a specific methodology to determine this ratio at the surface. In order to, a surface preparation of the CIGS by chemical treatments, combining an initial flattening by HBr:Br2:H2O etching with a finishing step performed in KCN:H2O, is implemented. This chemical engineering leads to a quasi “perfect” surface, flattened and cleared from surface oxide and selenide phase on which our XPS methodology for GGI determination is tested. The photopeaks choice to obtain the most coherent GGI ratio quantification is discussed. In particular we focus on the Ga3d-In4d region, situated in narrow binding energy domain, and discuss why this photopeak combination can be considered as the most adapted for a representative GGI determination. Quantitative fitting procedure of the Ga3d-In4d region is qualified on a reference epitaxial InxGa1-xAs layer and its implementation in the CIGS case is shown.
关键词： X-ray photoelectron spectroscopy,Surface chemical engineering,Gallium,Indium,copper indium gallium selenide,Surface composition
更新于2025-09-10 09:29:36
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Implementing a method based on near infrared spectroscopy for the “in-situ” determination of ammonia/water composition in an absorber test bench
摘要： This study presents the first results of composition measurement in an ammonia/water mixture determined at real time using near-infrared (NIR) spectroscopy in an absorber test bench. Two cells were designed and constructed; a static cell for calibrating and a dynamic cell for measuring in the absorber test bench. The ammonia absorption band was not significantly affected by the solution flow rate and neither by small variations in the temperature and pressure. A linear regression model between the absorbance value at 1033 nm and the ammonia concentration was established. This model was used to estimate the concentration in an ammonia/water absorber test bench. The methodology was validated by density measurements of the samples. The value of the mean deviation was 0.0024.
关键词： ammonia/water composition,near-infrared spectroscopy,absorber test bench,real-time measurement
更新于2025-09-10 09:29:36
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Structure and Stability of C:H:O Plasma Polymer Films Co-Polymerized Using Dimethyl Carbonate
摘要： C:H:O plasma polymer ?lms (PPFs) were deposited by means of plasma-enhanced chemical vapour deposition using the non-toxic, biodegradable organic compound dimethyl carbonate (DMC) at various plasma powers and pressures in order to control the degradation properties related to the carbonate ester group. Coating properties using pure DMC monomer vapours were compared to co-polymerized ?lms from gaseous mixtures of DMC with either ethylene (C2H4) or carbon dioxide (CO2) affecting deposition rate and chemical composition. C:H:O ?lm properties were found to depend primarily on the amount of oxygen in the plasma. To investigate the PPF stability during aging, changes in the composition and properties were studied during their storage both in air and in distilled water over extended periods up to 5 months. It was shown that aging of the ?lms is mostly due to oxidation of the plasma polymer matrix yielding slow degradation and decomposition. The aging processes and their rate are dependent on the intrinsic amount of oxygen in the as-prepared C:H:O ?lms which in turn depends on the experimental conditions and the working gas mixture. Adjustable ?lm properties were mainly attained using a pure DMC plasma considering both gas phase and surface processes. It is thus possible to prepare C:H:O PPFs with controllable degradability both in air and in water.
关键词： plasma polymerization,aging,degradability,thin ?lms,chemical composition
更新于2025-09-09 09:28:46
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Unlocking higher harmonics in atomic force microscopy with gentle interactions
摘要： In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity.
关键词： composition,phase,heterogeneity,chemistry,higher harmonics,atomic force microscopy
更新于2025-09-09 09:28:46
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Unveiling the Chemical Composition of Halide Perovskite Films Using Multivariate Statistical Analyses
摘要： The local chemical composition of halide perovskites is a crucial factor in determining their macroscopic properties and their stability. While the combination of scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX) is a powerful and widely used tool for accessing such information, electron-beam-induced damage and complex formulation of the films make this investigation challenging. Here we demonstrate how multivariate analysis – including statistical routines derived from “big data” research, such as Principal Component Analysis, PCA – can be used to dramatically improve the signal recovery from fragile materials. We also show how a similar decomposition algorithm (Non-negative Matrix Factorisation, NMF) can unravel elemental composition at the nanoscale in perovskite films, highlighting the presence of segregated species and identifying the local stoichiometry at the nanoscale.
关键词： hybrid perovskite,big data,multivariate analysis,chemical composition,STEM-EDX,nanoscale
更新于2025-09-09 09:28:46
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Potential use of nir and visible spectroscopy to analyze chemical properties of thermally treated wood
摘要： The modification of wood by thermal treatments produces characteristic changes in its chemical composition and surface color and can improve the structural and esthetic quality. The objective of this paper is to evaluate the potential of near infrared and visible spectroscopy to predict the modifications in chemical composition of Eucalyptys grandis and Pinus taeda after thermal treatment. Near infrared and visible spectra were collected directly on the longitudinal surface of wood samples. The thermally modified wood of both species showed higher content of lignin and extractives than the untreated wood. There was darkening of thermally modified wood, as a result of chemical modification caused by heat. The Near infrared/visible technique identified the groups that were modified by treatment. NIR and visible spectroscopy can be used to predict chemical composition of natural or thermally treated Eucalyptus grandis and Pinus taeda.
关键词： Eucalyptus grandis,Pinus taeda,wood composition,Chemical analysis,wood color,thermal modification
更新于2025-09-09 09:28:46
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Effect of BaO on the phase composition and properties of aluminates for Ba-W cathodes
摘要： In this study, we prepared (4.8+x)BaO·CaO·2Al2O3(0≤x≤1.6) aluminates by calcining the precursors under static air at 1500 °C for 120 min. The precursor powders were prepared using a liquid phase co-precipitation method. The effects of the molar content of BaO on the phase composition (before and after melting), melting properties, environmental stability, evaporation, and emission properties of the aluminates was investigated systematically The results showed that the phase of the aluminates completely transformed from Ba5CaAl4O12 to Ba3CaAl2O7 with an increase in the BaO content. After melting, the phase changed from Ba5CaAl4O12 to a mixed phase of Ba5CaAl4O12 and Ba3CaAl2O7. In the high-temperature molten state, the aluminates were in the ionic state, which generated a relatively low-energy Ba5CaAl4O12 phase during cooling crystallization. With every 0.4 mol increase in the BaO content, the initial melting temperature of the aluminates decreased by 10–20 ℃, while the environmental stability deteriorated gradually. When the aluminates reacted with H2O and CO2 in the air, the original phase still existed and the characteristic peaks gradually broadened, but with the formation of Ca(OH)2, CaCO3, and BaCO3. At 1050 °C, with an increase in the BaO content, the evaporation rate of the Ba-W cathodes increased and the emission current density first increased and then decreased. The main components of the Ba-W cathode evaporation were Ba and BaO. At n(BaO):n(CaO):n(Al2O3)=6:1:2, the Ba-W cathode showed the best emission performance, and its pulse emission current density at 1050 °C was as high as 35.31 A/cm2.
关键词： Ba-W cathode,Emission current,BaO content,Phase composition,Evaporation rate
更新于2025-09-09 09:28:46
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Plasma enhanced chemical vapor deposition of SiO <sub/>2</sub> and SiN <sub/>x</sub> on AlGaN: Band offsets and interface studies as a function of Al composition
摘要： In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm?1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions <40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions >40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed.
关键词： PECVD,band offsets,SiO2,AlGaN,interface studies,Al composition,SiNx
更新于2025-09-09 09:28:46