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Strongly anisotropic spin relaxation in the neutral silicon vacancy center in diamond
摘要： Color centers in diamond are a promising platform for quantum technologies, and understanding their interactions with the environment is crucial for these applications. We report a study of spin-lattice relaxation (T1) of the neutral charge state of the silicon vacancy center in diamond. Above 20 K, T1 decreases rapidly with a temperature-dependence characteristic of an Orbach process and is strongly anisotropic with respect to magnetic-field orientation. As the angle of the magnetic field is rotated relative to the symmetry axis of the defect, T1 is reduced by over three orders of magnitude. The electron spin coherence time (T2) follows the same temperature dependence but is drastically shorter than T1. We propose that these observations result from phonon-mediated transitions to a low-lying excited state that are spin conserving when the magnetic field is aligned with the defect axis, and we discuss likely candidates for this excited state.
关键词： anisotropy,spin relaxation,quantum technologies,diamond,silicon vacancy center,Orbach process
更新于2025-09-23 15:23:52
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Energy relaxation of hot carriers near the charge neutrality point in HgTe-based 2D topological insulators
摘要： We present experimental results of non-linear transport in HgTe-based 2D topological insulators, where the conductance is dominated by Dirac-like helical edge states when the Fermi level is pinned to the bulk insulating gap. We find that hot carrier’s energy relaxation is faster close to the charge neutrality point (CNP) which can be attributed to localized nature and incompressibility of charge puddles resulting from inhomogeneous charge distribution near CNP. The tunnel-coupling of these puddles (quantum dots) to 1D edge channels can randomize phase memory leading to incoherent inelastic processes. Hot edge carriers, excited by the electric field, relax to equilibrium via thermalization in multiple puddles resulting in the emission of phonons in the puddles. At relatively low temperature (T≤ 10K), the energy relaxation time shows strong temperature dependence (τ_e ∝ T^{-3.5}), which is interpreted as small angle scattering, consistent with resistance saturation at low temperatures.
关键词： Non-linear transport,electron-phonon scattering,energy relaxation mechanisms,inelastic processes,Topological insulators
更新于2025-09-23 15:22:29
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Effects of spectral diffusion on the nonlinear optical properties in two- and three-state quantum systems in a four-wave mixing signal
摘要： Effects of spectral diffusion on the third-order nonlinear susceptibility for two- and three-level quantum systems, immersed in a thermal reservoir, are evaluated with a four-wave mixing (FWM) signal through the density matrix formalism. For this, inhomogeneously broadened two- and three-level quantum systems are used. In these models, the distribution of natural frequencies follows a Lorentzian function. The absorptive and dispersive nonlinear optical responses are determined for the considered quantum models. The results presented in this work show potential applications in the development of optical switches and provide a potential method to measure spectral diffusion relaxation times in three-level quantum systems.
关键词： reservoir state,three-level quantum system,Spectral diffusion,cross-relaxation,four-wave mixing
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Saint Petersburg, Russia (2018.10.22-2018.10.23)] 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Features of Space Charge Relaxation in a Polyimide Printed Circuit Board
摘要： Polyimide films are widely used as substrates for printed circuit boards. The process of space charge accumulating in dielectric substrates is not highly desirable, since space charge distorted the parameters of the electrical circuits. This work is devoted to the study of the accumulation and relaxation of charge in films of thermoplastic polyimide R-BAPB with different degrees of crystallinity, in order to reduce the accumulated charge and the time of its relaxation. Relaxation mechanisms are analyzed and methods for reducing the relaxation time of the space charge are determined.
关键词： PCB,conductivity,electret,homocharge,relaxation,corona discharge,space charge,crystallinity,polyimide
更新于2025-09-23 15:22:29
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Peculiarities of the dielectric properties of ternary 0.5(Y0.1Zr0.9O2) – 0.5(0.6SrTiO3 – 0.4BiScO3) ceramic system
摘要： Ceramic samples of ternary 0.5(Y0.1Zr0.9O2) – 0.5(0.6SrTiO3 – 0.4BiScO3) system consisting of individual Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems were synthesized via solid-state processing techniques. By XRD analysis, a coexistence of tetragonal P42/nmc phase related to the Y0.1Zr0.9O2 subsystem, and cubic Pm m3? and tetragonal P4mm phases associated with the 0.6SrTiO3 – 0.4BiScO3 subsystem was found. A deviation of real composition from nominal one for both Y0.1Zr0.9O2 and SrTiO3 – BiScO3 subsystems due to Sc substituting for Zr in the Y0.1Zr0.9O2 subsystem and, vice versa, Zr substituting for Sc in the SrTiO3 – BiScO3 subsystem was also observed. Peculiarities of the dielectric properties related to both di?use ferroelectric phase transition and dielectric relaxation processes were found and analyzed in comparison with the dielectric properties of two-component 0.6SrTiO3 – 0.4BiScO3 system. It was found that the di?use phase transition in ternary system, ?rstly, shifts to lower temperatures and, secondly, has a less degree of di?useness as compared to two-component system. Such kind of behavior could be attributed to a di?erence of ionic radii of ions Zr4+ and Sc3+. Dielectric relaxation processes associated with the O2- ions migration were observed within temperature 500–800 K for both ternary and two-component systems. Two dielectric relaxation processes related to the Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems were found in ternary system, whereas one dielectric relaxation process was observed in two-component system. The activation energies for the dielectric relaxation processes were estimated as ~ 1.3 eV and ~ 0.9 eV for Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems, respectively, for ternary system, and ~ 0.75 eV for two-component system.
关键词： Dielectric relaxation process,Two-component ceramic system,Y0.1Zr0.9O2 and 0.6SrTiO3 – 0.4BiScO3 subsystems,Ternary ceramic system,Di?use phase transition
更新于2025-09-23 15:22:29
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Contact Angle Relaxation and Long-lasting Hydrophilicity of Sputtered Anatase TiO <sub/>2</sub> Thin Films by Novel Quantitative XPS Analysis
摘要： The contact angle relaxation of TiO2 surfaces is an important problem that must be understood, particularly for long-lasting hydrophilicity under dark conditions. The relaxation of sputtered anatase TiO2 thin films over a long time (~22 days) in an atmospheric environment was observed using quantitative XPS analysis. A new peak was identified as H2O within a donor-acceptor complex at ~2.57 eV above the lattice oxygen peak. This donor?acceptor complex turns out to be a key factor for long lasting hydrophilicity, and our model is presented. Adventitious carbon contamination was not the main cause of the contact angle relaxation. Instead, samples with lower amounts of donor?acceptor complexes (IDAC/Ibulk ≤ ~5%) underwent contact angle relaxation over time, and samples with a high density of donor?acceptor complexes (IDAC/Ibulk ≥ ~10%) showed good hydrophilicity (contact angle ≤ 20°) over 22 days. Larger amounts of basic Ti?OH relative to acidic OHbridge (ITi?OH/Ibridge ≥ 1) resulted in greater amounts of donor?acceptor complexes (IDAC/Ibulk ≥ ~10%). Thus, basic Ti?OH groups interact with H2O by forming a strong electrostatic donor?acceptor complex, leading to long-lasting hydrophilicity. Indeed, TiO2 was transformed to show long lasting hydrophilicity by high-density oxygen plasma treatment by forming sufficient Ti?OH groups and H2O molecules in the donor?acceptor complexes. Contact angle relaxation is closely related to the interactions between water molecules and the TiO2 surface in the dark. It is suggested that the relaxation depends on the number of electrostatic donor?acceptor complexes. This study provides new insight by linking theoretical studies with the experimental contact angle at the TiO2 surface in an ambient environment and is the first study that provides the presented relaxation mechanism.
关键词： Hydrophilicity,Sputtering,Plasma treatment,Contact angle relaxation,XPS analysis,Donor-acceptor complex,TiO2 thin films
更新于2025-09-23 15:22:29
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Joining of AlN and Al with Compositional Graded Layer by Centrifugal Mixed-Powder Method
摘要： In this study, joining of AlN and Al with compositional graded layer is made by centrifugal mixed-powder method (CMPM). The mixed-powder of AlN particles and Al particles is inserted into a spinning mold with bulk-shaped AlN, and then molten Al is poured into the spinning mold with the mixed-powder and bulk-shaped AlN. As a result, the molten Al penetrates into the space between the mixed-powder by the centrifugal force, and at the same time, the Al particles can be melted by heat from the molten Al. Then AlN and Al can be joined with compositional graded layer after solidification. Micromechanics-based analysis is also employed to understand the thermal stress relaxation by the compositional graded layer.
关键词： Joining,Ceramics/metal joining,Thermal stress relaxation,Functionally graded materials (FGMs),Micro-mechanics,Centrifugal mixed-powder method (CMPM)
更新于2025-09-23 15:22:29
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Low Frequency Dielectric Relaxation and Charge Transport in Bi<sub>12</sub>TiO<sub>20 </sub>Photorefractive Sillenite Crystals
摘要： Features of processes of a dielectric relaxation and charge transport in photorefractive sillenite crystals Bi12TiO20 at low frequency range are investigated. It was found that the dispersion of dielectric permittivity ε' in crystals Bi12TiO20 is characterized by its growth with lowering frequency and rising temperature. This behaviour may be related to existence of dipole-relaxation polarization mechanism. The frequency dependence of dielectric loss tgδ reveals the existence of low frequency relaxation peaks in the studied temperature range. From the conductivity dependence on the frequency and temperature it was found that conductivity σ increases as frequency increases in the low frequency range. The observed dependence σ(ω)≈Аωs indicates that transport mechanism is due to hopping of carriers via localized electron states. The charge transport is thermally activated process in which activation energy Ea = (0.82±0.03) eV.
关键词： Charge transport,Photorefractive Sillenite crystals,Dielectric relaxation
更新于2025-09-23 15:21:21
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Phonon-Driven Energy Relaxation in PbS/CdS and PbSe/CdSe Core/Shell Quantum Dots
摘要： We study the impact of the chemical composition on phonon-mediated exciton relaxation in the core/shell quantum dots (QDs), with 1-nm core made of PbX and the monolayer shell made of CdX, where X=S and Se. For this, time-domain non-adiabatic dynamics (NAMD) based on Density Functional Theory (DFT) and Surface Hopping techniques are applied. Simulations reveal twice faster energy relaxation in PbS/CdS than PbSe/CdSe due to dominant couplings to higher-energy optical phonons in structures with sulfur anions. For both QDs, the long-living intermediate states associated with the core-shell interface govern the dynamics. Therefore, a simple exponential model is not appropriate, and the four-state irreversible kinetic model is suggested instead, predicting 0.9 ps and 0.5 ps relaxation rates in PbSe/CdSe and PbS/CdS QDs, respectively. Thus, 2-nm PdSe/CdSe QDs with a single monolayer shell exhibit the phonon-mediated relaxation time sufficient for carrier multiplications to outpace energy dissipation and benefit the solar conversion efficiency.
关键词： Density Functional Theory,phonon-driven energy relaxation,PbSe/CdSe,PbS/CdS,core/shell quantum dots,Surface Hopping techniques,non-adiabatic dynamics
更新于2025-09-23 15:21:01
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Ultrafast relaxation dynamics in bimetallic plasmonic catalysts
摘要： Combining a plasmonic metal, such as gold, with other popular catalysts, such as Ni or Pt, can extend its benefits to many energy-extensive reactions catalyzed by those metals. The efficiency of a plasmon-enhanced catalytic reaction is mainly determined by the light absorption cross section and the photo-excited charge carrier relaxation dynamics of the nanoparticles. We have investigated the charge carrier relaxation dynamics of gold/nickel (Au/Ni) and gold/platinum (Au/Pt) bimetallic nanoparticles. We found that the addition of Ni or Pt to gold can reduce light absorption in gold nanoparticles. However, electron–phonon coupling rates of Au/Ni and Au/Pt nanoparticles are significantly faster than that of pure Au nanoparticles. This is due to the fact that both Ni and Pt possess significantly larger electron–phonon coupling constants and higher densities of states near the Fermi level in comparison with Au. Additionally, the phonon–phonon coupling rate of bimetallic Au/Pt and Au/Ni nanoparticles was significantly different from that of pure gold nanoparticles, due to the acoustic impedance mismatch at the nanoparticle/substrate interface. Our findings provide important insights into the rational design of bimetallic plasmonic catalysts.
关键词： bimetallic nanoparticles,ultrafast relaxation dynamics,electron–phonon coupling,phonon–phonon coupling,plasmonic catalysts
更新于2025-09-23 15:21:01