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The Temperature Dependences of the Electron-Piezoelectric Potential Phonon Interacting System of Quasi Two Dimensional System in GaN and ZnS
摘要： We investigated theoretically the temperature dependence of the quantum optical transition of quasi 2-Dimensional Landau splitting system, in GaN and ZnS. We apply the Quantum Transport theory (QTR) to the system in the con?nement of electrons by square well con?nement potential. We use the projected Liouville equation method with Equilibrium Average Projection Scheme (EAPS). Through the analysis of this work, we found the increasing properties of Quantum Transition Line Shapes (QTLSs) and the Quantum Transition Line Widths (QTLWs) of CdS and GaN with the temperature we also found that QTLW, (cid:2)(cid:3)T (cid:4) of ZnS < (cid:2)(cid:3)T (cid:4) of GaN in (cid:5) = 394 (cid:6)m.
关键词： Quantum Transport Theory,Quantum Transition Line Widths (QTLW),Quantum Transition Line Shapes (QTLS),GaN and ZnS,Cyclotron Resonance,Equilibrium Average Projection Scheme (EAPS),Electron Phonon Coupling System
更新于2025-09-23 15:22:29
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Semiconducting B<sub>13</sub>C<sub>2</sub> system: Structure search and DFT-based analysis
摘要： DFT calculation on Boron Carbide in B13C2 stoichiometry using a 15-atom unit cell necessarily results in metallic ground state regardless of the crystal structure. This is because such a unit cell consists of odd number of electrons, and hence complete filling of the top most band(s) of nonzero occupancy is impossible. This is in contrast to the observed semiconducting nature. If the crystal structure of B13C2 is made of a 30-atom unit cell which cannot be reduced to a 15 atom cell, there is a possibility of obtaining either a metallic or a semiconducting state as such a cell consists of an even number of electrons. In this work the evolutionary algorithm based structure search using 30-atom unit cells has yielded a previously unreported semiconducting system of B13C2 with unique bonding pattern. The mechanical and dynamical stability of the system have been properly established through the computation of elastic constants and phonon spectra. Its bond lengths, elastic moduli, hardness and infrared spectrum are in good agreement with experimental data.
关键词： Boron Carbide,elastic constants,evolutionary algorithm,DFT,phonon spectra,semiconducting,structure search,B13C2
更新于2025-09-23 15:22:29
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[IEEE 2017 5th International Conference on Instrumentation, Communications, Information Technology, and Biomedical Engineering (ICICI-BME) - Bandung, Indonesia (2017.11.6-2017.11.7)] 2017 5th International Conference on Instrumentation, Communications, Information Technology, and Biomedical Engineering (ICICI-BME) - Enhancement of Luminescence Light Yield of Ln <sup>3+</sup> Doped Glass By Oxyfluoride Glass Matrix
摘要： Glass is a good material which received attention for doping lanthanide ions. Glass doped Ln3+ ions can show luminescence, but not too strong light yield. It is well known that the host glass plays an important role in the enhancement. This paper has been described effect of Ln3+ ions (Sm3+, Eu3+ and Dy3+) doped oxyfluoride glass by comparing between oxide and oxyfluoride glasses. For the Sm3+ doped gadolinium calcium phosphate oxyfluoride glass, the highest emission peak was 598 nm under 401 nm excitation. While the emission light yield of oxyfluoride glass was higher than oxide glass due to the reduction of phonon and non-radiative losses. In case of Eu3+ doped oxyfluoride glass, the 612 nm emission under 394 nm excitation was observed. The light yield of oxyfluoride glass also was better than oxide glass. The Dy3+-doped phosphate oxide and oxyfluoride glasses were investigated. The luminescence light yield of oxyfluoride glass was more than oxide glass as well, owing to lower OH group of oxyfluoride glass, which can be confirmed by FTIR measurement. As described earlier, it concludes that the oxyfluoride glass is better than glass matrix when compared with oxide glass to enhance luminescence light yield for Ln3+ ions in glass matrix.
关键词： phonon energy,oxyfluoride glass,oxide glass,lanthanide ions
更新于2025-09-23 15:22:29
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Derivation of Line Shape Function in the Optical Conductivity by a New Diagram Method
摘要： A new diagram method for the line shape function in the optical conductivity formula is introduced and the result obtained applying the method to an electron-phonon system is compared with that derived using the projection-reduction method. The result satisfies the population criterion, which states that the distribution functions for electrons and phonons should be combined in multiplicative forms and gives physical intuition to quantum dynamics of electrons in a solid. This method can be called the "KC diagram" method because it originates from the proper application of the Kang-Choi reduction identity and a state-dependent projection operator.
关键词： line shape function,optical conductivity,diagram method,population criterion,electron-phonon system
更新于2025-09-23 15:22:29
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Elastic constants and phonon dispersion relation analysis of graphene sheet with varied Poisson's ratio
摘要： Through the achievement of elastic parameter equivalence by the structural mechanics method, the beam–truss space frame model for graphene sheet has been simpli?ed; moreover a representative unit cell of the periodic graphene structure has been extracted. On this basis, the Bloch theorem is combined with the ?nite element method to determine the phonon dispersion relation of graphene. For the widely used thickness values of the carbon–carbon (C–C) bond, the aspect ratios (thickness/length) are so large that the shear deformation should be considered such that as a result, the negative Poisson's ratio (NPR) characteristic of the C–C bond is observed. Analytical expressions for the elastic constants of graphene sheet have been obtained with varied C–C bond Poisson's ratios. The reasonable coherence with previous results reveals the e?ectiveness of the structural mechanics method for analysing the mechanical properties of nanostructures. The e?ect of deformation modes on the phonon dispersion relation of graphene sheet is further discussed; it is concluded that the acoustic phonon modes are sensitive to the deformation modes of the C–C bond, whereas these deformation modes negligibly in?uence the optical phonon modes. The numerical results also reveal that the shear deformation and the resulting NPR e?ect play an important role in the mechanical property analysis of graphene sheet. To summarise, the interrelation between NPR materials and nano materials has stimulated a wide ?eld of research; moreover, numerous novel phenomena have been observed.
关键词： Elastic constants,Poisson's ratio,Phonon dispersion relation,Graphene sheet,Structural mechanics method
更新于2025-09-23 15:22:29
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Optical modulation of coherent phonon emission in optomechanical cavities
摘要： Optomechanical (OM) structures are well suited to study photon-phonon interactions, and they also turn out to be potential building blocks for phononic circuits and quantum computing. In phononic circuits, in which information is carried and processed by phonons, OM structures could be used as interfaces to photons and electrons thanks to their excellent coupling efficiency. Among the components required for phononic circuits, such structures could be used to create coherent phonon sources and detectors, but more complex functions remain challenging. Here, we propose and demonstrate a way to modulate the coherent phonon emission from OM crystals by a photothermal effect induced by an external laser, effectively creating a phonon switch working at ambient conditions of pressure and temperature and the working speed of which is only limited by the build-up time of the mechanical motion of the OM structure. We additionally demonstrate two other modulation schemes: modulation of harmonics in which the mechanical mode remains active but different harmonics of the optical force are used, and modulation to and from a chaotic regime. Furthermore, due to the local nature of the photothermal effect used here, we expect this method to allow us to selectively modulate the emission of any single cavity on a chip without affecting its surroundings in the absence of mechanical coupling between the structures, which is an important step toward freely controllable networks of OM phonon emitters.
关键词： phonon switch,coherent phonon emission,photothermal effect,Optomechanical structures,phononic circuits
更新于2025-09-23 15:21:21
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Intense red emission and two-way energy transfer in Sm3+, Eu3+ co-doped NaLa(WO4)2 phosphors
摘要： NaLa(WO4)2 phosphors with various Eu3+ and Sm3+ concentrations were prepared via a molten salt method. The structure and luminescent properties of the prepared samples were analyzed by the X-ray diffraction (XRD) and fluorescence spectrophotometer. The results show that the crystal phase of all the prepared samples is single tetragonal crystal structure. The energy transfer type between Eu3+ ions is proved to be the exchange interaction and the electron-phonon coupling is weak. With the increase of the Sm3+ concentration, the energy transfer from Sm3+ to Eu3+ in NaLa(WO4)2:0.15Eu3+,xSm3+ is transformed from Eu3+ to Sm3+, and the mechanism for energy transfer is given.
关键词： Nanophosphor powders NaLa(WO4)2: xEu3+ ySm3+,Electron-phonon coupling,Photoluminescence,Energy transfer
更新于2025-09-23 15:21:21
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Recipe for Dirac Phonon States with a Quantized Valley Berry Phase in Two-Dimensional Hexagonal Lattices
摘要： The topological quantum states in two-dimensional (2D) materials are fascinating subjects of research, which usually highlight electron-related systems. In this work, we present a recipe that leads to Dirac phonon states with quantized valley Berry phase in 2D hexagonal lattices by first-principles calculations. We show that candidates possessing the three-fold rotational symmetry at the corners of the hexagonal Brillouin zone host valley Dirac phonons, which are guaranteed to remain intact with respect to perturbations. We identify that such special topological features populated by Dirac phonons can be realized in various 2D materials. In particular, the monolayer CrI3, an attractive 2D magnetic semiconductor with exotic applications in spintronics, is an ideal platform to investigate nontrivial phonons in experiments. We further confirm that the phonon Berry phase is quantized to ±π at two inequivalent valleys. The phonon edge states terminated at the projection of phonon Dirac cones are clearly visible. This work demonstrates that 2D hexagonal lattices with attractive valley Dirac phonons will extend the knowledge of valley physics, providing wide applications of topological phonons.
关键词： Dirac phonons,first-principles calculations,valley Berry phase,phonon edge states,2D hexagonal lattices
更新于2025-09-23 15:21:21
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Vibrational electron energy loss spectroscopy in truncated dielectric slabs
摘要： Specially designed instrumentation for electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope makes it possible to probe very low-loss excitations in matter with a focused electron beam. Here we study the nanoscale interaction of fast electrons with optical phonon modes in silica. In particular, we analyze the spatial dependence of EEL spectra in two geometrical arrangements: a free-standing truncated slab of silica and a slab with a junction between silica and silicon. In both cases, we identify different loss channels, involving polaritonic and nonpolaritonic contributions to the total electron energy loss, and we obtain the corresponding energy-filtered maps. Furthermore, we present a comparison of the theoretical simulations for a silica-silicon junction with experimental results, and we discuss the spatial resolution attainable from the energy-filtered map considering optical phonon excitations in a conventional experimental arrangement.
关键词： optical phonon modes,nonpolaritonic,polaritonic,silica,electron energy loss spectroscopy,EELS,silicon
更新于2025-09-23 15:21:21
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Hot electron thermoreflectance coefficient of gold during electron-phonon nonequilibrium
摘要： The temperature-dependent reflectivity of metals is quantified by the thermoreflectance coefficient, which is a material dependent parameter that depends on the metallic band structure, electron scattering dynamics, and photon wavelength. After short-pulse laser heating, the electronic sub-system in a metal can be driven to temperatures much higher than that of the lattice, which gives rise to unique non-equilibrium electron and phonon scattering dynamics, leading to a “hot electron” thermoreflectance that is different from the traditionally measured equilibrium coefficient. In this work, we analytically quantify and experimentally measure this hot electron thermoreflectance coefficient through ultrafast pump-probe measurements of thin gold films on silica glass and sapphire substrates. We demonstrate the ability to not only quantify the thermoreflectance during electron-phonon nonequilibrium, but also validate this coefficient’s predicted dependence on the absolute temperature of the electronic subsystem. The approach outlined in this work provides a metrology to further understand and quantify excited-state scattering effects on the dielectric function of metals.
关键词： electron-phonon scattering,Pump-probe,Thermoreflectance,Drude model,electronic temperature
更新于2025-09-23 15:21:21