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Influence of compression strains on photon absorption of silicene and germanene
摘要： In this paper, optical properties of silicene and germanene under compressive homogeneous strain are investigated within the density function theory. Results show that the optical-field response are strongly depend on the amount of applied strain. As the strain increases, the amount of optical absorption increases. In fact, by applying the compressive strain in the silicene and germanene, the band gap at the Dirac points decreases where ultimately reaches zero. Depending on the amount of strain, absorption peak shows red and blue shifts by increasing the strain. This can be realized by considering the change of the band gap energy and transition rates by the strain. In both of these graphene-like structures, the light absorption along zigzag direction is greater than that of the armchair direction.
关键词： Graphene-like structures,Compressive strain,Density functional theory,Optical properties
更新于2025-09-23 15:23:52
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Time reversal imaging based on joint space–frequency and frequency–frequency data
摘要： A new time reversal (TR) method for target imaging is proposed in this paper. Through single measurement by the antenna array, the received signals are utilized to form the space–frequency–frequency multistatic data matrix (MDM). Singular value decomposition is applied to the matrix to obtain the left singular vectors which span the signal subspace. The obtained vectors are divided into multiple subvectors by two different schemes and used to provide target signatures in the form of coarse frequency dependence and relative phase shifts that can be exploited to construct the imaging function. The performance of the proposed method is investigated through numerical simulations for both single and multiple targets, and the results are compared with the traditional TR method using the frequency–frequency MDM. It turned out that the proposed method is able to achieve high resolution with limited array aperture and shows satisfactory robustness in noise environment. Furthermore, experimental results are provided to show the availability of the method in practical applications.
关键词： time reversal imaging,EM field theory,Radar
更新于2025-09-23 15:23:52
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Scandium Molybdate Microstructures with Tunable Phase and Morphology: Microwave Synthesis, Theoretical Calculations, and Photoluminescence Properties
摘要： In this paper, scandium molybdate microstructures have been prepared from solution via a microwave heating method. By controlling the experimental parameters such as molar ratio of reagent and reaction time, scandium molybdates with tunable phase and diverse morphologies including snowflakes, microflowers, microsheets, and branched spindles were obtained. The density of states and surface energies of Sc2Mo3O12 were primarily studied from first-principles calculations. An indirect band gap of 3.56 eV was observed for crystalline Sc2Mo3O12, and the surface energies of various facets were determined to be 0.27–0.91 J/m2. The influence of n(Sc3+):n(Mo7O24 6?) (short for Sc/Mo) molar ratio was systematically investigated and well-characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and UV–vis absorption spectroscopy (UV–vis). Results indicate that the Sc/Mo molar ratio has a great effect on the phase and morphology. Diffuse reflection spectra (DRS) revealed the Egap can be readily tuned from 3.69 to 4.16 eV, which is in accordance with the theoretical result. The photoluminescence (PL) properties of Eu3+-doped Sc2Mo3O12 were discussed. This facile synthesis strategy could be extended to the synthesis of other molybdates.
关键词： photoluminescence,morphology control,microwave synthesis,scandium molybdate,density functional theory
更新于2025-09-23 15:23:52
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Measurement of Forces between Supported Cationic Bilayers by Colloid Probe Atomic Force Microscopy: Electrolyte Concentration and Composition
摘要： The interactions between supported cationic surfactant bilayers were measured by colloidal probe atomic force spectroscopy, and the effect of different halide salts was investigated. Di(alkylisopropylester)dimethylammonium methylsulfate (DIPEDMAMS) bilayers were fabricated by the vesicle fusion technique on muscovite mica. The interactions between the bilayers were measured in increasing concentrations of NaCl, NaBr, NaI, and CaCl2. In NaCl, the bilayer interactions were repulsive at all concentrations investigated, and the Debye length and surface potential were observed to decrease with increasing concentration. The interactions were found to follow the electrical double layer (EDL) component of DLVO theory well. However, van der Waals forces were not detected; instead, a strong hydration repulsion was observed at short separations. CaCl2 had a similar effect on the interactions as NaCl. NaBr and NaI were observed to be more efficient at decreasing surface potential than the chloride salts, with the efficacy increasing with the ionic radius.
关键词： supported bilayers,DLVO theory,Debye length,surface potential,halide salts,colloidal probe atomic force spectroscopy
更新于2025-09-23 15:23:52
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Domino Reaction for the Sustainable Functionalization of Few-Layer Graphene
摘要： The mechanism for the functionalization of graphene layers with pyrrole compounds was investigated. Liquid 1,2,5-trimethylpyrrole (TMP) was heated in air in the presence of a high surface area nanosized graphite (HSAG), at temperatures between 80 °C and 180 °C. After the thermal treatments solid and liquid samples, separated by centrifugation, were analysed by means of Raman, Fourier Transform Infrared (FT-IR) spectroscopy, X-Rays Photoelectron Spectroscopy (XPS) and 1H-Nuclear Magnetic Resonance (1H NMR) spectroscopy and High Resolution Transmission Electron Microscopy (HRTEM). FT-IR spectra were interpreted with the support of Density Functional Theory (DFT) quantum chemical modelling. Raman findings suggested that the bulk structure of HSAG remained substantially unaltered, without intercalation products. FT-IR and XPS spectra showed the presence of oxidized TMP derivatives on the solid adducts, in a much larger amount than in the liquid. For thermal treatments at T ≥ 150 °C, IR spectral features revealed not only the presence of oxidized products but also the reaction of intra-annular double bond of TMP with HSAG. XPS spectroscopy showed the increase of the ratio between C(sp2)N bonds involved in the aromatic system and C(sp3)N bonds, resulting from reaction of the pyrrole moiety, observed while increasing the temperature from 130 °C to 180 °C. All these findings, supported by modeling, led to hypothesize a cascade reaction involving a carbocatalyzed oxidation of the pyrrole compound followed by Diels-Alder cycloaddition. Graphene layers play a twofold role: at the early stages of the reaction, they behave as a catalyst for the oxidation of TMP and then they become the substrate for the cycloaddition reaction. Such sustainable functionalization, which does not produce by-products, allows us to use the pyrrole compounds for decorating sp2 carbon allotropes without altering their bulk structure and smooths the path for their wider application.
关键词： infrared spectroscopy,Density Functional Theory,pyrrole compounds,quantum chemical modelling,graphene layers,Functional Groups
更新于2025-09-23 15:23:52
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Computational Study of Perovskite Structured CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> and CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub>
摘要： Nowadays, Hybrid Perovskite materials perform a major role in solar cell industry due to their superior power conversion ability. CH3NH3PbI3 is the prominent material in hybrid perovskite, where they comprised with advanced photovoltaic properties. But considering the toxicity, it’s more important to observe the role of metal atom in hybrid perovskite. Therefore, this research is basically focused on the objective of figuring out the fundamental properties of CH3NH3PbI3 and CH3NH3SnI3 with the idea of replacing Pb to Sn in future. Ab-Initio Simulation has been used throughout this research along with basic density function theories (DFT) like Exchange correlation functional, Local-density approximation of Kohn-Sham theory. Moreover, the research was also focused upon the Energy band gap variation, crystallographic orientations, density of states in P, S orbitals of cubic and tetragonal phases in CH3NH3PbI3 and CH3NH3SnI3.
关键词： Energy Bands,Methyl ammonium Tin Iodide perovskite,Density Function Theory,Methyl ammonium lead Iodide,Perovskite structure
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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Up-conversion Luminescence Properties of Er3+/Yb3+ Co-Doped Oxyfluoride Glass Ceramic
摘要： Er3+/Yb3+ co-doped glass ceramic samples were prepared by melt-quenching method utilizing nominal composition 52SiO2-8Na2CO3-16Al2O3-33NaF-3LuF3-0.15Yb2O3-0.03Er2O3 (in mol%). The spectral characteristic was studied based on Judd-Ofelt theory. Spectrum intensity parameters Ωλ(λ=2,4,6) were calculated on the basis of the absorption spectrum. The theoretical and experimental oscillator strengths were calculated according to the spectrum intensity parameters, and the root mean square deviation (δrms) of glass ceramic sample was 4.28x10-6. The parameters such as transition probability, decay branching ratios and level lifetime of Er3+ were obtained. Lifetimes of metastable level 4I13/2 and 4I11/2 in as-prepared samples are respectively 11.64 and 13.61ms which are suitable for up-conversion intermediate levels. Decay branching ratio of 4I13/2→4I15/2 is nearly 100% in Er3+/Yb3+ co-doped oxyfluoride glass ceramic samples which can be used to produce 1543nm laser. Under the excitation of 980 nm diode laser, up-conversion luminescence is observed at the wavelength of 549nm and (653, 664) nm, corresponding to the radiative transitions of Er3+: 4S3/2→4I15/2 and 4F9/2→4I15/2, respectively. The numbers of absorbed photons in the transition process of Er3+/Yb3+ co-doped oxyfluoride glass ceramic samples are estimated at 1.99 and 2.06 respectively according to the relationship between the up-conversion transmitting power and the 980 nm LD laser power. It is determined that the transition process of Er3+/Yb3+ co-doped oxyfluoride glass ceramic samples is two-photon absorption process.
关键词： Glass ceramic,Two-photon absorption,Up-conversion,Judd-Ofelt theory
更新于2025-09-23 15:23:52
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A review on M?+?N theory and its strategies to improve the accuracy of spectrochemical composition analysis of complex liquids
摘要： High-precision spectral analysis for complex liquid components has received much attention in recent years. However, the lack of systematic strategies of measurement and modeling notably appears when multiple internal and external factors vary—e.g., the sample parameters, instruments, and external environment. Many methods have been developed to eliminate these effects. According to the characteristics of error sources and its propagation rules, “M + N” theory integrates and classifies the internal and external factors that affect the analysis of complex liquid components into M factors and N factors systematically. “M” and “N” refers to the M components in a liquid and N interference factors, respectively, and “+” means that the spectral is a response to the interaction of M and N. In this review, “M + N” theory sums up five measurement and modeling strategies used to reduce the effect of various factors on spectral quantitative analysis of complex liquids. Finally, this review summarized the strategies used to improve the accuracy of quantitative analysis of complex liquids and discussed future research directions.
关键词： spectrochemical quantitative analysis,measurement and modeling strategies,Complex liquid,M + N theory
更新于2025-09-23 15:23:52
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Probing interlayer excitons in a vertical van der Waals p-n junction using scanning probe microscopy technique
摘要： Two dimensional (2D) semiconductors feature exceptional optoelectronic properties controlled by strong confinement in one dimension. In this contribution, we studied interlayer excitons in a vertical p-n junction made of bilayer n-type MoS2 and few layers of p-type GaSe using current sensing atomic force microscopy (CSAFM). The p-n interface is prepared by mechanical exfoliation onto highly ordered pyrolytic graphite (HOPG). Thus the heterostructure creates an ideal layered system with HOPG serving as the bottom contact for the electrical characterization. Home-built Au tips are used as the top contact in CSAFM mode. During the basic diode characterization, the p-n interface shows strong rectification behavior with a rectification ratio of 104 at ±1 V. The I-V characteristics reveal pronounced photovoltaic effects with a fill factor of 0.55 by an excitation below the band gap. This phenomenon can be explained by the dissociation of interlayer excitons at the interface. The possibility of the interlayer exciton formation is indicated by density functional theory (DFT) calculations on this heterostructure: the valence band of GaSe and the conduction band of MoS2 contribute to an interface-specific state at an energy of about 1.5 eV. The proof of excitonic transitions to that state is provided by photoluminescence measurements at the p-n interface. Finally, photocurrent mapping at the interface under an excitation wavelength of 785 nm provides evidence of efficient extraction of such excitons. Our results demonstrate a pathway towards a two dimensional device for future optoelectronics and light harvesting assisted by interlayer excitons in a van der Waals heterostructure.
关键词： optoelectronics,van der Waals heterojunction,GaSe,density functional theory,MoS2,interlayer exciton,p-n junction
更新于2025-09-23 15:23:52