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Suitability of Raman Spectroscopy for Assessing Anisotropic Strain in Thin Films of Doped Ceria
摘要： A protocol for characterizing relaxation of anisotropic strain in thin films of 10 mol% Eu- or Sm-doped ceria is described. The method is based on comparison of Raman spectra and X-ray diffraction patterns from substrate-supported films, displaying in-plane compressive strain (initial state), with analogous data from 2 mm diameter self-supported films (i.e., membranes), prepared by partial substrate removal (final state). These membranes are found to be relaxed, i.e., approximately unstrained, but with increased unit cell volume. The effective (i.e., 2-state) Grüneisen parameter of the F2g Raman active mode for these films is calculated to be 0.4 ± 0.1, which is ≈30% of the literature value for the corresponding ceramics under isostatic pressure. On this basis, it is found that the observed red-shift of the F2g mode frequency following isothermal strain relaxation of the doped ceria thin films cannot be determined solely by the increase in average unit cell volume. The study presented here may shed light on the suitability of Raman spectroscopy as a technique for characterizing strain in lanthanide-doped ceria thin films.
关键词： doped ceria,Raman spectroscopy,Grüneisen parameter,anelastic relaxation
更新于2025-09-23 15:23:52
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Interface Engineering of Au(111) for the Growth of 1T′-MoSe <sub/>2</sub>
摘要： Phase-controlled synthesis of two-dimensional transition metal dichalcogenides (TMDCs) is of great interest due to the distinct properties of the different phases. However, it is challenging to prepare metallic phase of group-VI TMDCs due to their metastability. At the monolayer level, interface engineering can be used to stabilize the metastable phase. Here, we demonstrate the selective growth of either single-layer 1H or 1T’-MoSe2 on Au(111) by molecular beam epitaxy; the two phases can be unambiguously distinguished using scanning tunnelling microscopy and spectroscopy. While the growth of 1H-MoSe2 is favourable on pristine Au(111), the growth of 1T’-MoSe2 is promoted by the pre-deposition of Se on Au(111). The selective growth of 1T’-MoSe2 phase on Se-pretreated Au(111) is attributed to Mo intercalation-induced stabilization of the 1T’ phase, which is supported by density functional theory calculations. In addition, 1T’ twin boundaries and 1H-1T’ heterojunctions were observed and found to exhibit enhanced tunnelling conductivity. The substrate pre-treatment approach for phase-controlled epitaxy should be applicable to other group-VI TMDCs grown on Au (111).
关键词： phase control,heterojunction,scanning tunnelling microscopy/spectroscopy,interface engineering,transition metal dichalcogenides,MoSe2
更新于2025-09-23 15:23:52
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Optical spectroscopy of the Au4+ cluster: Resolved vibronic structure indicates an unexpected isomer**
摘要： The knowledge of the geometric and electronic structure of gold clusters and nanoparticles is vital for understanding their catalytic and photochemical properties at the molecular level. Herein, we report the vibronic optical photodissociation spectrum of cold and mass-selected Au4+ clusters measured at a resolution high enough to allow for comparison with Franck-Condon simulations of the excited state transitions based on time-dependent density functional theory calculations. The three vibrational frequencies identified for the lowest-lying optically accessible excited state at 2.17 eV stem from the Y-shaped isomer (C2v) and not from the rhombic isomer (D2h) that is considered to be the ground state structure of Au4+. This study demonstrates that an analysis of low-resolution electronic spectra by calculations of vertical transitions alone is not sufficient for a reliable isomer assignment of such metal clusters.
关键词： gold,UV/Vis spectroscopy,structure elucidation,cluster compounds,electronic structure
更新于2025-09-23 15:23:52
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Portable spectroscopic system for <i>in vivo</i> skin neoplasms diagnostics by Raman and autofluorescence analysis
摘要： This paper studies the applicability of a portable cost-effective spectroscopic system for the optical screening of skin tumors. In vivo studies of Raman scattering and autofluorescence of skin tumors with the 785 nm excitation laser in the near infrared region included malignant melanoma, basal cell carcinoma, and various types of benign neoplasms. The efficiency of the portable system was evaluated by comparison with a highly sensitive spectroscopic system and with the diagnosis accuracy of a human oncologist. Partial least square analysis of Raman and autofluorescence spectra was performed; specificity and sensitivity of various skin oncological pathologies detection varied from 78.9% to 100%. 100% accuracy of benign and malignant skin tumors differentiation is possible only with a combined analysis of Raman and autofluorescence signals.
关键词： autofluorescence,optical biopsy,portable spectroscopic equipment,skin neoplasms,melanoma,partial least square analysis,Raman spectroscopy,malignancy
更新于2025-09-23 15:23:52
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Single spin localization and manipulation in graphene open-shell nanostructures
摘要： Turning graphene magnetic is a promising challenge to make it an active material for spintronics. Predictions state that graphene structures with specific shapes can spontaneously develop magnetism driven by Coulomb repulsion of π-electrons, but its experimental verification is demanding. Here, we report on the observation and manipulation of individual magnetic moments in graphene open-shell nanostructures on a gold surface. Using scanning tunneling spectroscopy, we detect the presence of single electron spins localized around certain zigzag sites of the carbon backbone via the Kondo effect. We find near-by spins coupled into a singlet ground state and quantify their exchange interaction via singlet-triplet inelastic electron excitations. Theoretical simulations picture how electron correlations result in spin-polarized radical states with the experimentally observed spatial distributions. Extra hydrogen atoms bound to radical sites quench their magnetic moment and switch the spin of the nanostructure in half-integer amounts. Our work demonstrates the intrinsic π-paramagnetism of graphene nanostructures.
关键词： scanning tunneling spectroscopy,graphene,Kondo effect,magnetism,spintronics
更新于2025-09-23 15:23:52
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Phonon coherences reveal the polaronic character of excitons in two-dimensional lead halide perovskites
摘要： Hybrid organic–inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (?50 cm?1) optical phonons involving motion in the lead iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.
关键词： resonant impulsive stimulated Raman spectroscopy,polaronic character,two-dimensional perovskites,density functional theory,excitons,phonon coherences
更新于2025-09-23 15:23:52
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Doping modulation of quasi-free-standing monolayer graphene formed on SiC(0001) through Sn1-Ge intercalation
摘要： In order to modulate the transfer doping of quasi-free-standing monolayer graphene (QFMLG) formed on SiC(0001), Ge atoms were intercalated additionally into QFMLG already formed by Sn intercalation between ZL and 6H-SiC(0001). By postannealing the Ge-deposited surface at 600 °C, the Sn1-xGex film with the 4 × √3 structure, composed of a bilayer and adatoms with dangling bonds under QFMLG, has been formed. It turns out that, in this Sn1-xGex film, Ge atoms preferentially occupy the bottom layer bound to the top Si atoms of the substrate, while Sn atoms occupy the top adatom sites. Strong correlation among the electrons localized at these adatom sites induces a semiconducting alloy film. As the postannealing temperature is increased up to 800 °C, the concentration of Ge in the intercalated film of the same 4 × √3 structure is gradually increased and the Dirac point also shifts gradually from ?0.16 eV to +0.20 eV relative to the Fermi level. Such a result confirms that the transfer doping of QFMLG on SiC(0001) has been modulated by varying the alloy composition of the Sn1-xGex interfacial film.
关键词： Scanning tunneling microscopy,Quasi-free-standing graphene,SnGe alloy intercalation,Hubbard band,Doping modulation,Photoemission spectroscopy,SiC(0001)
更新于2025-09-23 15:23:52
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Ultrafast spectroscopy of the primary charge transfer and ISC processes in 9-anthraldehyde
摘要： The ultrafast charge transfer (CT) and the following intersystem crossing (ISC) processes of 9-anthraldehyde were investigated in ethanol and hexane using femtosecond transient absorption spectroscopy combined with quantum chemical calculations. The CT was observed within 0.11 ps in ethanol and 0.23 ps in hexane. Due to the stronger polarity in ethanol, the CT is faster than in hexane. The following ISC is determined to be 22.3 ps and 21.4 ps in two solvents, respectively. However, the timescales of ISC are similar in both solvents since the excited energies of the S1 and triplet states are close.
关键词： Time-resolved transient absorption spectroscopy,intramolecular charge transfer,radiationless intersystem crossing
更新于2025-09-23 15:23:52
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IR photodissociation spectra of SixH4x-4+ (x?=?4–8): Evidence for Si H Si proton bridges
摘要： Although silane-type cations of the form SixHy+ are thought to play a significant role in plasma chemistry and astrochemistry, their structural and energetic properties are largely unexplored in the size range x ≥ 3. Herein, infrared photodissociation (IRPD) spectra of mass-selected SixHy+ with x = 4–8, specifically SixH4x-4+, are recorded in the Si–H stretch range and analyzed by dispersion-corrected density functional calculations at the B3LYP-D3/aug-cc-pVDZ level. The SixH4x-4+ ions are produced in a SiH4/H2/He plasma molecular beam expansion. The IRPD process leads to the loss of SiH4 ligands, which corresponds to the lowest-energy fragment channel. Spectral analysis of the IRPD spectra reveals that all SixH4x-4+ ions have at least one Si–H–Si bridge. The characteristic fingerprint of these three-center two-electron (3c-2e) bonds is the highly IR active antisymmetric stretch fundamental of the Si–H–Si bridge (νSiHSi) occurring in the 1600–2100 cm?1 range, whose frequency strongly depends on the structural and energetic details of the Si–H–Si bridge. Although the investigated SixH4x-4+ ions can formally be described by the formula Si2H4+(SiH4)x-2, the cluster growth is more complex. The appearance of the νSiHSi bands confirms that all considered SixH4x-4+ ions with x ≤ 5 are formed by polymerization reactions. Larger clusters (x ≥ 6) show evidence for the additional presence of weakly-bonded SiH4 ligands attached to smaller chemically-bonded core ions. Correlations of the properties of the Si–H–Si bridges (bond distances, bond angles, binding energies, Si–H stretch frequencies), which vary between strong symmetric 3c-2e chemical bonds and weak hydrogen bonds, are discussed.
关键词： Silane ions,IR spectroscopy,Structure elucidation,3c-2e bond,Si H Si bridge
更新于2025-09-23 15:23:52
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Thermal structure of a hot non-flaring corona from Hinode/EIS
摘要： Aims. In previous studies, a very hot plasma component has been diagnosed in solar active regions through the images in three different narrow-band channels of Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). This diagnostic from extreme ultraviolet (EUV) imaging data has also been supported by the matching morphology of emission in the hot Ca XVII line, as observed with Extreme-Ultraviolet Imaging Spectrometer (EIS) on board Hinode. This evidence is debated because of the unknown distribution of the emission measure along the line of sight. Here we investigate in detail the thermal distribution of one such region using EUV spectroscopic data. Methods. In an active region observed with SDO/AIA, Hinode/EIS, and X-ray telescope (XRT), we select a sub-region with a very hot plasma component and another cooler sub-region for comparison. The average spectrum is extracted for both, and 14 intense lines are selected for analysis that probe the 5.5 < log T < 7 temperature range uniformly. From these lines, the emission measure distributions are reconstructed with the Markov-chain Monte Carlo method. Results are cross-checked in comparison with the two sub-regions, with a different inversion method, with the morphology of the images, and with the addition of fluxes measured with narrow, and broadband imagers. Results. We find that, whereas the cool region has a flat and featureless distribution that drops at temperature log T ≥ 6.3, the distribution of the hot region shows a well-defined peak at log T = 6.6 and gradually decreasing trends on both sides, thus supporting the very hot nature of the hot component diagnosed with imagers. The other cross-checks are consistent with this result. Conclusions. This study provides a completion of the analysis of active region components, and the resulting scenario supports the presence of a minor very hot plasma component in the core, with temperatures log T > 6.6.
关键词： techniques: imaging spectroscopy,Sun: UV radiation,Sun: corona,techniques: spectroscopic,Sun: X-rays, gamma rays
更新于2025-09-23 15:23:52