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Role of carbon-rings in polycrystalline GeSb2Te4 phase-change material
摘要： Carbon (C) is used to increase the overall performance of Ge-Sb-Te (GST) phase-change memory material. Yet the C configuration in polycrystalline GST and its microscopic role is unclear. Using the well-studied GeSb2Te4 as an example, this work unravels the microscopic C doping role based on ab initio calculations. Our results reveal that carbon prefers occupying the interstitials at very low C concentrations, while with a roughly critical C concentration of over 2%, carbon atoms will cluster at the grain boundaries, with very few carbon atoms might exist at the interstitials. With further increasing the C concentrations, C atoms tend to form ring-like configurations in the grain boundaries rather than chain-like configurations. This is due to that the covalent bonds in ring-like configurations are stronger than that in chain-like configurations. Further analysis on the lone-pair electrons and electronic densities of states show that C dopants significantly change the number of lone-pair electrons of surrounding atoms, thus affecting the electronic structure. Finally, the diffusion coefficient of C is estimated to be of the order of 10^-13 m^2/s at 400 K, indicating the good stability of C dopants in GeSb2Te4. Our work provides fundamental understanding on the microscopic role of C doping in GST phase-change materials and benefits for improving the properties of the recording materials by controlling the doping concentration.
关键词： Ab initio molecular dynamic simulations,Ab initio calculations,Phase-change materials,Grain boundary,GeSb2Te4,Carbon doping
更新于2025-09-23 15:23:52
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Ab Initio Design of Graphene Block Enables Ultrasensitivity, Multimeter-Like Range Switchable Pressure Sensor
摘要： In pursuit of the next-generation pressure sensors, the fabrication of graphene-based devices is considered to be one of the most promising approaches to address the unsatisfied sensitivity within a wide pressure range. Here, an ab initio design based on the graphene block is proposed to realize a high-performance and multimeter-like range switchable pressure sensor. The sensor contains three designed graphene-based foams with different initial resistances, which enable continuous resistance-change behavior induced by the pressure. Specifically, the reduced graphene oxide (rGO) foam–based sensor demonstrates a three times resistance change within the pressure range of 0–300 Pa, the rGO/polyurethane (rGO/PU) foam–based sensor presents a six times resistance change within the pressure range of 0.09–30 kPa, and the selenium-functionalized rGO/PU (SFrGO/PU) foam–based sensor displays a resistance change of more than 1000-fold within the pressure range of 1–72 kPa. Such different initial resistances and responses endow the device with controllable estimating pressure ranges, offering a switchable multimeter-like function for various applications. This ab initio design, which is applicable to various 2D materials and operation modes, can provide a facile and feasible approach toward the next-generation pressure sensors and other application fields related to 2D materials.
关键词： ultrahigh sensitivity,pressure sensor,graphene block,ab initio design,multimeter-like
更新于2025-09-23 15:23:52
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Substituent effects on H <sub/>3</sub><sup>+</sup> formation via H <sub/>2</sub> roaming mechanisms from organic molecules under strong-field photodissociation
摘要： Roaming chemical reactions are often associated with neutral molecules. The recent findings of roaming processes in ionic species, in particular, ones that lead to the formation of H3+ under strong-field laser excitation, are of considerable interest. Given that such gas-phase reactions are initiated by double ionization and subsequently facilitated through deprotonation, we investigate the strong-field photodissociation of ethanethiol, also known as ethyl mercaptan, and compare it to results from ethanol. Contrary to expectations, the H3+ yield was found to be an order of magnitude lower for ethanethiol at certain laser field intensities, despite its lower ionization energy and higher acidity compared to ethanol. In-depth analysis of the femtosecond time-resolved experimental findings, supported by ab initio quantum mechanical calculations, provides key information regarding the roaming mechanisms related to H3+ formation. Results of this study on the dynamics of dissociative half-collisions involving H3+, a vital cation which acts as a Br?nsted–Lowry acid protonating interstellar organic compounds, may also provide valuable information regarding the formation mechanisms and observed natural abundances of complex organic molecules in interstellar media and planetary atmospheres.
关键词： roaming reactions,strong-field photodissociation,ethanethiol,H3+ formation,ethanol,ab initio calculations
更新于2025-09-23 15:23:52
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Symmetries of modes in Ni <sub/>3</sub> V <sub/>2</sub> O <sub/>8</sub> : Polarized Raman spectroscopy and ab initio phonon calculations
摘要： Knowledge of symmetries of vibrational modes is essential for understanding structural transitions and spin‐phonon coupling in multiferroics where phonons play a vital role. Using polarized Raman spectroscopy, we have identified and assigned symmetries of 30 out of the 36 expected zone‐centred phonon mode Raman active modes in Ni3V2O8. The wavenumbers are calculated using ab initio calculations. The gerade mode wavenumbers are compared with our polarized Raman data whereas ungerade mode wavenumbers are compared with the reported infrared measurements and a good agreement was observed between the experimentally measured wavenumbers and the calculated wavenumbers. The displacements of different types of vibrations calculated and visualized using ab initio phonon calculation are presented. These assignments will be useful for visualization of Raman modes that may be sensitive to different magnetic states and to explore spin–lattice coupling across magnetic transitions.
关键词： displacements of phonon modes,gerade and ungerade modes,polarized Raman spectroscopy,symmetries of Raman active modes,ab initio calculations
更新于2025-09-23 15:23:52
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Theoretical and Experimental Features of Nano-Crystals Rochelle Salt: Piezoelectric Resonance and Phase Transition
摘要： A new methodology based on Three-Electrode System (TES) technique was used to measure both, elastic (C44) and piezoelectric (d14) constants of Rochelle salt (RS) crystal. This technique was also used to observe the phase transitions at ?18 °C and 24 °C, manifested as an increase of the output signal at these temperatures. Mechanical wave attenuation coefficient (α) into the crystal was found. Also, first principle methodology in the framework of the density functional theory was utilized to confirm the electronic structure of Rochelle Salt. The results present high accuracy theoretical/experimental as well as a complete agreement with those known in the literature done by different methodologies.
关键词： Phase Transitions,Rochelle Salt Crystal,Piezoelectric Device,Ab Initio Simulation
更新于2025-09-23 15:22:29
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Effective mass and optical properties of orthorhombic Al1?xInxFeO3 perovskite: An ab-initio study
摘要： Electronic and optical properties of AlFeO3 and Al1?xInxFeO3 (x = 0.25, 0.5, 0.75) are studied using ab-initio calculations. Electronic structure in the vicinity of the conduction band minimum (CBM) and valence band maximum (VBM), the effective masses of holes and electrons at the gamma point are calculated. The calculated effective masses of electrons is smaller than that of holes (mc1⊥, mc1‖ (me*) < mv1⊥, mv1‖, mv2⊥, mv2‖ (mh*)), for all values of x; this is expected to contribute to the desirable photocatalytic performance. Effective mass tensor for electrons is found to be isotropic (unlike holes). The optical constants such as static dielectric constant, refractive index, extinction coefficient and absorption coefficient are comparable with that Si. The maximum absorption exists in the visible light region for all the phases studied; making In-doped AlFeO3 suitable for energy harvesting applications. We noted from our previous work (Sudha Priyanga and Thomas, 2018) that the computed band gap values could be underestimated by as large as ～0.5 eV. Even so, the reported phases would be relevant for light harvesting.
关键词： AlFeO3,Optical properties,Ab-initio calculations,Effective masses,Light-harvesting
更新于2025-09-23 15:22:29
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Metaheuristic <i>Ab Initio</i> Optimum Search for Doping Effects in Nanocarbons
摘要： We have developed a combined approach of metaheuristic optimization algorithms (MOA), such as the genetic algorithm, with an ab-initio materials simulation engine. Concurrent run of the ab-initio calculations with each different parameter set selected by the MOA searches the optimum condition within a given input-parameter space. Using this methodology, the optimum dopant and its position/structure at a graphene edge are found to be a multiple N-atoms doping at graphitic sites, which predicts to lead to better charging/discharging performance when it is used as an anode material of Li-ion battery.
关键词： genetic algorithm,lithium-ion battery,nano-carbon,ab-initio simulation,doping effect
更新于2025-09-23 15:22:29
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Half-metallic ferromagnetic behavior in (Ga, Cr)N and (Ga, Cr, V)N compounds for spintronic technologies: Ab-initio and Monte Carlo methods
摘要： In this article, we investigate the magnetic- and electronic-proprieties of GaN doped with simple- and double-impurities utilizing Ab-initio and Monte Carlo studies. We have predicted that (Ga, Cr)N and (Ga, Cr, V)N compounds exhibit ferromagnetic- and halfmetallic-behavior with 100% spin-polarization at the Fermi-level. Moreover, we have found that Ga1-xCrxN and Ga1-2xCrxVxN (x = 0.04, 0.05 and 0.06) show a 2nd order ferromagnetic transition and that their Tc is above room temperature. These predictions make (Ga, Cr)N and (Ga, Cr, V)N compounds strong-candidates for spintronic-technologies.
关键词： Ab-initio calculations,Monte Carlo method,Diluted magnetic semiconductors,Spintronic,Gallium Nitride
更新于2025-09-23 15:22:29
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Accurate <i>ab initio</i> determination of ballistic electron emission spectroscopy: Application to Au/Ge
摘要： Ab initio nonequilibrium Keldysh formalism based on an N -order renormalization technique is used to compute I (V ) ballistic electron emission microscopy characteristics at the Au/Ge(001) interface. Such a formalism quantitatively reproduces precise experimental measurements under ultrahigh vacuum and low-temperature conditions. At T = 0 K, the ballistic current follows the law (V ? VSB)2.1, VSB being the Schottky barrier. At T > 0 K, temperature effects become signi?cant near the onset and must be taken into account to identify an accurate value for VSB from a best-?t procedure. We ?nd two values for VSB, 0.67 and 0.75 eV, which we associate with two different atomic registries at the interface.
关键词： Au/Ge interface,ab initio,nonequilibrium Keldysh formalism,ballistic electron emission microscopy,Schottky barrier
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Field emission patterns from carbon nanotubes calculated by time-dependent density functional theory
摘要： We calculated the field emission patterns of various types of carbon nanotubes (CNTs). Regarding the near field regime, emission patterns of CNTs and hydrogen terminated CNTs (H-CNTs) well corresponds to the atoms located in the tube tip. We also found different focusing features; a focused-type and an unfocused-type. The beams from armchair (5,5) and (6,6) types are focused, while the beam from zigzag (9,0) types are unfocused.
关键词： field emission,carbon nanotubes,emission pattern,time dependent density functional theory,first principle calculation,ab initio calculation
更新于2025-09-23 15:21:21