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Tunneling ionization of atoms and ions in a linear electromagnetic wave and a constant magnetic field and the “imaginary time” method
摘要： The tunneling ionization of atoms and negative ions in an intense linearly polarized laser ?eld and a constant uniform magnetic ?eld is discussed in the quasiclassical theory framework. We use the “imaginary time” method, where tunneling is described by the classical equations of motion but with purely imaginary “time” to derive the extremal subbarrier trajectory of the photoelectron. This allows to obtain simple analytical expressions for ionization rates in the tunneling regime for an arbitrary angle between a laser beam and a constant magnetic ?eld accounting for the Coulomb interaction of the photoelectron with the atomic core. The resonance case, when the frequency of a monochromatic electromagnetic wave and the cyclotron frequency are equal, is also considered. The limits of weak and strong magnetic ?elds and the expressions for the barrier width and the emission angle of photoelectrons are discussed. It is shown that a magnetic ?eld in the presence of a linear electromagnetic wave increases the barrier width and thus decreases the ionization probability, i.e., stabilizes the bound level.
关键词： linear electromagnetic wave,imaginary time method,atoms,ions,quasiclassical theory,tunneling ionization,constant magnetic field
更新于2025-09-04 15:30:14
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Fullerenes and Relative Materials - Properties and Applications || How Important is Metal-Carbon Back-Bonding for the Stability of Fullerene-Transition Metal Complexes? Role of Cage Sizes, Encapsulated Ions and Metal Ligands
摘要： A density functional study of {η2-(X@Cn)}ML2 complexes with various cage sizes (C60, C70, C76, C84, C90, C96), encapsulated ions (X = F?, 0, Li+) and metal fragments (M = Pt, Pd) is performed, using M06/LANL2DZ levels of theory. The importance of π back-bonding to the thermodynamic stability of fullerene-transition metal complexes ({η2-(X@Cn)}ML2) and the effect of encapsulated ions, metal fragments and cage sizes on the π back-bonding are determined in this study. The theoretical computations suggest that π back-bonding plays an essential role in the formation of fullerene-transition metal complexes. The theoretical evidence also suggests that there is no linear correlation between cage sizes and π back-bonding, but the encapsulated Li+ ion enhances π back-bonding and F? ion results in its deterioration. These computations also show that a platinum center produces stronger π back-bonding than a palladium center. It is hoped that the conclusions that are provided by this study can be used in the design, synthesis and growth of novel fullerene-transition complexes.
关键词： π back-bonding,fullerene-transition metal complex,encapsulated ions,metal fragments and cage sizes
更新于2025-09-04 15:30:14
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Encyclopedia of Spectroscopy and Spectrometry || Spectroscopy of Ions ☆
摘要： Ions and radicals are transient species which are not readily accessible to conventional spectroscopic characterization. There are essentially three problems to be overcome – the production in sufficient concentration, the availability of a sensitive technique enabling their IR or electronic spectra to be recorded and the ability to identify the observed spectral features. The involvement of mass-selection not only leads to the solution of the last problem, but enables methods based on particle detection – fragment ions, electrons and photons – to be incorporated. The aim of the spectroscopic studies is, on the one hand, to provide a fingerprint of the species by its vibrational or electronic spectrum, enabling its identification in various terrestrial and space environments, and on the other hand, the spectroscopic analysis leads to information on geometric structures, force fields and fundamental interactions.
关键词： Electronic spectra,Ions,Spectroscopy,IR spectra,Mass-selection
更新于2025-09-04 15:30:14
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Reference Module in Materials Science and Materials Engineering || Photoelectron Diffraction
摘要： Surface structural information can be derived from a great variety of methods, but most quantitative data are based on elastic scattering of X-rays, electrons, or ions by the near-surface atoms. While the best-known methods based on electron (and X-ray) scattering are conventional diffraction methods, reliant on long-range order, the technique of photoelectron diffraction is a local scattering technique that thus provides local structural information not dependent on long-range periodicity. In this short article the physical principles of photoelectron diffraction are described, highlighting at least two fundamentally distinct versions of the technique. The main areas of utilization of the method are illustrated.
关键词： local scattering technique,long-range order,surface structural information,photoelectron diffraction,X-rays,electrons,elastic scattering,ions
更新于2025-09-04 15:30:14
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Up-conversion luminescence of RE3+ -doped polymer composites KGd(WO4)2&PMMA
摘要： Poly(methyl methacrylate) (PMMA)-based luminescent materials are of prime interest for many new optoelectronic devices. This work presents the spectroscopic properties of PMMA-based composites containing KGd(WO4)2:Yb3+/Er3+/Tm3+, KGd(WO4)2:Yb3+/Tm3+ and KGd(WO4)2:Yb3+/Er3+ powders. These systems exhibit effective multicolor up-conversion luminescence in VIS and NIR spectral range under 980 nm excitation. The vibrational properties of the composites were investigated for the first time using the μ-Raman spectroscopy. The obtained results suggest that the KGd(WO4)2:Yb3+/Er3+/Tm3+&PMMA integrated system can be successfully used as a new phosphor for the up-conversion based optoelectronic devices.
关键词： Micro-crystals,Rare earth ions,PMMA,KGd(WO4)2,Composites,Up-conversion
更新于2025-09-04 15:30:14
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Nickel ion detection by imidazole modified carbon dots
摘要： Nickel ions (Ni2+) were detected by a new imidazole modified carbon dots (CDs) based on fluorescence quenching method. Structural characterization of CD-imidazole quantum dots were accomplished by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). Spectroscopic properties were characterized by ultraviolet absorption spectrum and fluorescence spectrum. Ni2+ concentration showed good linear relationship with fluorescence quenching efficiency in the range of 6-100 mM (R = 0.99) and the limit of detection (LOD) was 0.93 mM. Imidazole modified CDs have strong selectivity of Ni2+ compared with other metal ions in aqueous solution. These results demonstrated that the fluorescence sense platform based on imidazole modified CDs can be applied to Ni2+ detection in environment.
关键词： Nickel ions,Fluorescence quenching,Carbon dots-imidazole quantum dots
更新于2025-09-04 15:30:14
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SOI Thin Microdosimeter Detectors for Low Energy Ions and Radiation Damage Studies
摘要： The responses of two silicon on insulator (SOI) 3D microdosimeters developed by the Centre for Medical Radiation Physics (CMRP) were investigated with a range of different low energy ions, with high linear energy transfer (LET). The two microdosimeters n-SOI and p-SOI were able to measure the LET of different ions including 7Li, 12C, 16O and 48Ti with ranges below 350 μm in silicon. No plasma effects were seen in the SOI microdosimeters when irradiated with the high LET ions. A Monte Carlo simulation using Geant4 was compared to the experimental measurements, whereby some discrepancies were observed for heavier ions at lower energies. This discrepancy can be partly attributed to uncertainties in the thickness of the energy degraders and overlayers of the devices. The microdosimetric measurements of low energy 16O ions were obtained and compared to a therapeutic 16O ion beam. The radiation hardness of the two devices was studied using the Ion Beam Induced Charge Collection technique (IBIC). Both types of microdosimeters when biased had no essential changes in charge collection efficiency (CCE) in the SV after irradiation with low energy ions.
关键词： LET,radiation damage,SOI microdosimeters,Geant4 simulation,low energy ions,IBIC
更新于2025-09-04 15:30:14
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Ionization-Excitation of Helium-Like Ions at Compton Scattering
摘要： Ionization of helium-like ions with simultaneous excitation of the ns-states due to photon scattering is considered. The differential and total cross sections of the process are calculated to leading order of perturbation theory with respect to the electron–electron interaction. The formulas obtained are applicable in the nonrelativistic energy range far beyond the ionization threshold.
关键词： Nonrelativistic energy range,Excitation,Helium-like ions,Ionization,Compton scattering
更新于2025-09-04 15:30:14
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Crystal structure and luminescence properties of the barium europium tetragermanate Ba2Eu2Ge4O13
摘要： The tetragermanate Ba2Eu2Ge4O13 was synthesized for the first time, and its structural and luminescent properties were examined. It crystallizes in a monoclinic system (space group C2/c, Z = 4) and its crystal structure incorporates a unique linear [Ge4O13]10– anion. The photoluminescence spectrum of the sample ( llllex = 280 nm) contains several intense peaks in the orange-red spectral range corresponding to the 4f–4f transitions in Eu3+ ions.
关键词： crystal structure,Ba2Eu2Ge4O13,luminescence,Eu3+ ions,tetragermanate
更新于2025-09-04 15:30:14
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Enhanced etching of tin-doped indium oxide due to surface modification by hydrogen ion injection
摘要： It is known that the etching yield (i.e., sputtering yield) of tin-doped indium oxide (ITO) by hydrocarbon ions (CHx+) is higher than its corresponding physical sputtering yield [H. Li et al., J. Vac. Sci. Technol. A 33, 060606 (2015)]. In this study, the effects of hydrogen in the incident hydrocarbon ion beam on the etching yield of ITO have been examined experimentally and theoretically with the use of a mass-selected ion beam system and by first-principles quantum mechanical (QM) simulation. As in the case of ZnO [H. Li et al., J. Vac. Sci. Technol. A 35, 05C303 (2017)], mass-selected ion beam experiments have shown that the physical sputtering yield of ITO by chemically inert Ne ions increases after a pretreatment of the ITO film by energetic hydrogen ion injection. First-principles QM simulation of the interaction of In2O3 with hydrogen atoms shows that hydrogen atoms embedded in In2O3 readily form hydroxyl (OH) groups and weaken or break In–O bonds around the hydrogen atoms, making the In2O3 film less resistant to physical sputtering. This is consistent with experimental observation of the enhanced etching yields of ITO by CHx+ ions, considering the fact that hydrogen atoms of the incident CHx+ ions are embedded into ITO during the etching process.
关键词： quantum mechanical simulation,sputtering yield,tin-doped indium oxide,hydrogen ion injection,physical sputtering,ITO,etching yield,In2O3,hydrocarbon ions,hydroxyl groups
更新于2025-09-04 15:30:14