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Laser welding characteristics of Ti-Pb dissimilar couples and element diffusion in the molten pool
摘要： Laser welding lead metal to titanium or titanium alloy, which is a typical dissimilar welding process, have a great challenge. Couples of Ti-Pb, Ti6Al4V-Pb were welded by a 3kW continuous wave Nd:YAG laser. The influences of process parameters such as laser power and laser beam offset on welding depth were investigated. Microstructure, element distribution and micro-hardness of the welds were tested. The element diffusion characteristics during laser welding of Ti-Pb couple and Ti6Al4V-Pb couple were studied based on the experiments data. Experimental results show laser beam offset is a primary factor for welding titanium alloy and lead metal, and laser power plays a critical role for welding pure titanium and lead metal. A chemical potential calculation model of Ti-Pb-Al ternary alloy was established. The calculation results show that chemical potential of Ti element increases with enhancing Pb content in Ti-Pb-Al ternary system, however, the chemical potential of Ti element decreases with increasing Pb content in Ti-Pb binary system. According to the calculation results, for Ti-Pb-Al ternary system, because of the Al element in the molten pool, the Ti element tends to diffuse into the Al element, and the diffusion driving force of Ti element to the Pb element is weak. Compared with the Ti-Pb binary system and the Ti-Pb-Al ternary system, it is more likely to form a mixed fusion weld for the binary system, and the mass transfer interface phenomenon is more serious for the ternary system, which is consistent with EDS line scan and microhardness testing results.
关键词： Chemical potential,Interface,Microstructure,Lead metal,Titanium alloy,Laser dissimilar welding
更新于2025-11-21 11:18:25
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Thermodynamic Analysis of the Transition of Liquid Crystals from Lamellar to Vesicular Phase
摘要： Here, we report the results of thermodynamic analyses on the lamellar-vesicular transition for a cationic amphiphilic species, namely 2-hydroxyethyl di(alkanol)oxyethyl methylammonium methylsulfate (DEAE). Previously, we have shown that spontaneous vesicle formation from a Lα-lamellar liquid crystal (LC) phase only occurs on the addition of a quantitative amount of additives to the DEAE LC at certain temperatures and that this change occurs without the input of any extra mechanical energy. These lamellar-vesicular transitions occur in two steps: the first step is the formation of an excited state, caused by the solubilization of organic substances in the bilayer structure. The second step, induced by the addition of a small amount of inorganic salt to the excited LC state, is the transition from lamellar to vesicular phase. From our experimental data, the change in the Gibbs free energy was estimated by assuming an ideal electrical chemical potential. As a result, the thermodynamic parameters at 303 K for the lamellar-vesicular transition from the initial state (lamellar) to the final state (vesicle) were found to be approximately －2.7 kJ/mol for the Gibbs free energy, －14.6 kJ/mol for the enthalpy change, and －11.9 kJ/mol for the entropy change. Each state change was due to structural changes not only in the LC bilayers but also in the hydration structure of the surrounding water. Moreover, the most significant finding is that the free energy change in lamellar-vesicular transition is negative, which may be explained based on the stabilization of solubilized vesicles with respect to the unsolubilized lamellar phases.
关键词： electrochemical potential,lamellar liquid crystal,chemical potential,vesicle,transition energy
更新于2025-09-23 15:21:01
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Near-field radiative heat transfer between black phosphorus and graphene sheet
摘要： Low thermal conductivity of black phosphorus (BP) makes it difficult to cool BP-based electronic or optoelectronic devices. Therefore, developing a cooling strategy for BP-based nano devices is highly required. We theoretically study the near-field radiative heat transfer between BP sheets as well as between BP and graphene. We find that the heat transfer between BP sheets is determined by its electron doping. Plasmons excited by BP in different directions dominate the heat transfer for different electron doping. At optimum electron doping, heat transfer between the BP sheets increases significantly. The heat transfer between BP and graphene is dependent on both the electron doping of BP and chemical potential of graphene. Modulating the chemical potential of graphene can result in a strong coupling between graphene plasmons and BP plasmons, which will lead to a significant enhancement of heat transfer between BP and graphene. Our results are not only meaningful in controlling the heat transfer between BP-based structures but also helpful in developing cooling strategies for BP-based nano devices.
关键词： near-field radiative heat transfer,plasmons,graphene,black phosphorus,chemical potential,electron doping
更新于2025-09-23 15:21:01
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[IEEE 2019 Days on Diffraction (DD) - St. Petersburg, Russia (2019.6.3-2019.6.7)] 2019 Days on Diffraction (DD) - Normal mode coupling in a waveguide with a range-dependent sound speed profile in the bottom
摘要： In this paper, a novel graphene-based multiple-input multiple-output (MIMO) concept is proposed for high-rate nanoscale wireless communications between transceivers, which are nano/micrometers apart from each other. In particular, the proposed MIMO architecture considers exploiting a deep-subwavelength propagation channel made of graphene. This allows us to increase the number of transmitted symbol streams, while using a deep-subwavelength arrangement of individual plasmonic nanotransmit/receive elements in which the spacing between the transmitters and/or the receivers is tens of times smaller than the wavelength. This exclusive benefit is achieved with the aid of the phenomenon of graphene plasmons, where graphene offers the extremely confined and low-loss plasmon propagation. Hence, the proposed graphene-based MIMO system is capable of combating the fundamental limitations imposed on the classic MIMO configuration. We also present a novel graphene-specific channel adaptation technique, where the chemical potential of the graphene channel is varied to improve the power of the received signals.
关键词： MIMO,surface plasmon polariton,nanoscale communication,chemical potential,graphene,Correlation,diffraction limit,deep subwavelength
更新于2025-09-19 17:13:59
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Multiple Fano Resonances with Tunable Electromagnetic Properties in Graphene Plasmonic Metamolecules
摘要： Multiple Fano resonances (FRs) can be produced by destroying the symmetry of structure or adding additional nanoparticles without changing the spatial symmetry, which has been proved in noble metal structures. However, due to the disadvantages of low modulation depth, large damping rate, and broadband spectral responses, many resonance applications are limited. In this research paper, we propose a graphene plasmonic metamolecule (PMM) by adding an additional 12 nanodiscs around a graphene heptamer, where two Fano resonance modes with different wavelengths are observed in the extinction spectrum. The competition between the two FRs as well as the modulation depth of each FR is investigated by varying the materials and the geometrical parameters of the nanostructure. A simple trimer model, which emulates the radical distribution of the PMM, is employed to understand the electromagnetic field behaviors during the variation of the parameters. Our proposed graphene nanostructures might find significant applications in the fields of single molecule detection, chemical or biochemical sensing, and nanoantenna.
关键词： surface plasmon,chemical potential,Fano resonances,graphene metamolecule,modulation depth,plasmonic coupling
更新于2025-09-19 17:13:59
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Mathematical Modelling of Electrically Controlled Filters of Microwave, subTHz and THza??bands on the Base of Grapheneand-Dielectric Multilayer Structure
摘要： Report is devoted to investigations of graphene meta–surfaces for the transmission of radiation induced by plasmons in subTHz and THz ranges, cell of which consists of structures based on graphene ring and graphene nano–tape. It create regimes of radiation transmission – transparency windows induced by electric dipole resonances. Resonant frequency of transparency window can be dynamically tuned in wide band of subTHz and THz bands by changing the chemical potential (Fermi energy) of graphene by applying external electric field (gating) instead of re–fabricating of structures. Questions of possibilities of electronic controlled filters creating of subTHz and THz bands grounded on different configurations of graphene meta–surfaces are discussed; their characteristics and frequency dependencies are investigated. Mathematical modelling and electrodynamic calculation of the filters characteristics of subTHz and THz bands grounded on multilayer structures of “graphene–dielectric” type are carried out. From results of mathematical modelling it follows that periodic layered microstructures “graphene–dielectric” type can be used for creation of subTHz and THz bands broadband filters of planar construction, controlling by electric field and fast tuning at small changes in Fermi energy level of graphene.
关键词： multilayer structures,filters,subTHz,plasmonic,chemical potential,electric field,graphene,meta-surfaces,electric dipole resonances,THz,Fermi energy
更新于2025-09-16 10:30:52
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Optimized Chemical Potential Graphene-Based Coding Metasurface Approach for Dynamic Manipulation of Terahertz Wavefront
摘要： In this paper, a new method for the design of pixelated graphene-based coding metasurface is proposed. This method suggests a straightforward approach by utilizing graphene tunable pixels (GTP), which can control the reflection phase in a real-time manner at terahertz (THz) frequencies. The proposed unit cell is composed of four distinct graphene patches in the same layer, which has a chemical potential that obtained by utilizing optimization-based methods. By changing the reflection phase profile across the metasurface, the proposed device can manipulate the reflected wave phase, amplitude, and polarization control in various beamforming applications at THz spectrum for modern information systems, data encryption, and THz communication applications. Chemical potential optimization method in graphene-based coding metasurface is not limited to a specific structure for phase-only metasurface. Indeed it has an exceptional capability for metasurface to manipulate electromagnetic (EM) wave in the half-space and generate converged vortex beam, non-diffractive Bessel beam, and EM bump illusion. The simulation and theoretical results show that the suggested method offers a feasible strategy for multifunctional metasurface applications.
关键词： Bessel beam,Illusion,Chemical potential optimization,Vortex beam,Metasurface,Graphene
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - THz excited state level spacing in encapsulated graphene quantum dots
摘要： We report a high-quality encapsulated graphene quantum dot that exhibits stable Coulomb diamonds and excited states with a spacing of 0.4 THz. We performed the first transport spectroscopy measurement under THz illumination of a large quantum dot. The photocurrent map allows to measure with high precision a non-linear chemical potential renormalization of the graphene electrodes via the interaction with the quantum dot states.
关键词： graphene quantum dots,THz,transport spectroscopy,chemical potential renormalization,photocurrent
更新于2025-09-11 14:15:04
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<i>(Invited)</i> Water Transport Along Si/Si Direct Wafer Bonding Interfaces
摘要： The transport of water in a highly confined gap made by the direct bonding of low roughness silicon hydrophilic wafers is studied. We derive the equation for the transport of water from chemical potential gradients, using Stokes and conservation equations. The transport equation is found to be a Porous Medium Equation with exponent 2. A solution for this equation with stepwise boundary conditions is given. The model is tested against different initial conditions for inward and outward flow, and different temperatures and humidity levels.
关键词： silicon direct bonding,chemical potential gradients,Porous Medium Equation,water transport,hydrophilic wafers
更新于2025-09-10 09:29:36