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Laser-induced nano-heater performance of B4C submicrometer spherical particles fabricated by pulsed laser melting in liquid
摘要： Gold nanoparticles as promising nano-heater particles utilizing surface plasmon resonance have been extensively studied for various chemical and medical applications, even though the suitable wavelength for nano-heater is only in the visible range and possible maximum temperature is limited due to its relatively low melting point. About a decade ago, a technique called pulsed laser melting in liquid (PLML) was developed to fabricate submicrometer spherical particles as main products. In this process, particles in the submicrometer size range are effectively heated over the melting point by laser irradiation, indicating that submicrometer spherical particles can be developed as novel heater particles that may overcome the drawback of gold nanoparticles. This study examined the potentials of PLML-fabricated B4C submicrometer spherical particles as nano-heater particles since B4C has a wider optical absorption wavelength range and higher melting point than gold. From the thermal modification induced by melting the materials in contact with the B4C particles, the highest attained temperature was estimated by laser irradiation. This experiment showed that B4C particles have sufficient response in 300–1100 nm wavelength range and can act as nano-heater even at temperatures over 2000 K. Thus, B4C submicrometer spherical particles can be used as novel space-selective heater particles.
关键词： Nano-heater,Submicrometer,Phase transition,Boron carbide,Spherical particles
更新于2025-09-23 15:19:57
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Raman scattering obtained from laser excitation of MAPbI3 single crystal
摘要： Finding renewable energy sources is of paramount importance to meet the increasing global energy demand whilst minimizing the impact on the environment. The research community has focused on solar energy as it is endlessly available, and have ranked the methylammonium lead iodide (MAPbI3) as one of the most promising candidate amongst perovskite solar cells. Despite its high efficiency, the MAPbI3 is sensitive to humidity, light, and temperature, its instability affects primarily on the crystalline structure and eventually leads to degradation. Three crystalline structures are known for this material, orthorhombic, tetragonal, and cubic which exist in different temperatures. Here we report on several processes detected from laser excitation of MAPbI3 single crystal at ambient conditions. A phase transition from tetragonal to cubic phase was induced by excitation of over 15 mW laser power. The phases were characterized by LF-Raman and photoluminescence, taken simultaneously with the increase of exciting laser power and the spectral changes were assigned to the structural differences. In addition, Raman stimulation of iodine vapors signal was observed, those vapors were generated from the core of the focus wherein the highest temperature led to degradation. The stimulated Raman phenomenon was enabled due to the unique properties of the MAPbI3 single crystal and revealed viability to use this material for additional applications in other research fields.
关键词： Methylammonium lead iodide,Stimulated Raman,Low frequency Raman,Phase transition,Single crystal
更新于2025-09-23 15:19:57
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Quantum Dipole Effects in a Silicon Transistor under High Electric Fields
摘要： Strongly correlated one-dimensional systems are paradigms for theoretical condensed-matter physics, since various predictions such as spin–charge separation and topological phase transitions can be determined based on mathematically rigid models. Some of these features were experimentally observed in carbon nanotubes and chiral edge states of quantum Hall systems. Here, we show the emergence of another one-dimensional system in a nanoscale silicon field-effect-transistor with a wide and short hole channel when a strong electric field is applied at low temperatures. We observed the quantum dipoles, which form at the ultra-thin gate interface and exhibit a phase transition, and the drain current showed a clear, negative differential conductance due to the screening of electric fields by antiferroelectric ordering. We have also found new current plateaus against drain voltages, which corresponds to the magnetisation plateau theoretically predicted by the one-dimensional spin model. We obtained phase diagrams of the field-induced phase transitions by gate-induced doping.
关键词： silicon transistor,phase transition,quantum dipoles,negative differential conductance,high electric fields,current plateaus
更新于2025-09-23 15:19:57
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Effect of phase transition stress on the photoluminescence of perovskite CH3NH3PbI3 microwires
摘要： CH3NH3PbI3 (MAPbI3) exhibits distinctive properties for applications in photovoltaics, light emitting devices, photodetectors, and fuel cells. The working temperature of an optoelectronic device affects the photophysical properties of the active material, which is closely related to the device performance. In MAPbI3, these properties are intimately connected with its crystalline structure which is temperature dependent. Here, we study the photoluminescence (PL) behavior of MAPbI3 microwires (MWs) under recursive tetragonal-to-cubic and cubic-to-tetragonal phase transitions induced by temperature cycles from 40 °C (tetragonal phase) to 80 °C (cubic phase). MWs emission exhibited an initial redshift in wavelength by increasing the temperature from the tetragonal to the cubic phase, but after several thermal cycles, this trend reversed and the emission blueshifted. In both phases independently, the emission blueshifted and became stronger with increasing the cycles. The results indicate a thermal cycling-dependent PL and a gradual crystalline structure deformation due to a reiterated change in the MWs lattice, which implies variation in the electronic bandgap along the heating–cooling process. The alteration of the electronic band structure was corroborated by thermal cycling-re?ectance measurements. The awareness behavior of material properties upon phase transitions and temperature ?uctuations is of great importance for the optimization of optoelectronic devices.
关键词： MAPbI3,optoelectronic devices,phase transition,thermal cycling,photoluminescence
更新于2025-09-23 15:19:57
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Localized Nanoscale Heating Leads to Ultrafast Hydrogel Volume-Phase Transition
摘要： The rate of the volume-phase transition for stimuli-responsive hydrogel particles ranging in size from millimeters to nanometers is limited by the rate of water transport, which is proportional to the surface area of the particle. Here, we hypothesized that the rate of volume-phase transition could be accelerated if the stimulus is geometrically controlled from the inside-out, thus facilitating outward water ejection. To test this concept, we applied transient absorption spectroscopy, laser temperature-jump spectroscopy and finite-element analysis modeling to characterize the dynamics of the volume-phase transition of hydrogel particles with a gold nanorod core. Our results demonstrate that nanoscale heating of the hydrogel particle core led to an ultrafast, 60 ns particle collapse, which is 2-3 orders of magnitude faster than the response generated from conventional heating. This is the fastest recorded response time of a hydrogel material, thus opening potential applications for such stimuli-responsive materials.
关键词： infrared spectroscopy,dynamic light scattering,nanorods,volume-phase transition,hydrogel,transient absorption
更新于2025-09-23 15:19:57
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Effect of Zr Doping on the Magnetic and Phase Transition Properties of VO2 Powder
摘要： In this work, V1?xZrxO2 powder (x = 0, 0.01, 0.02, 0.04) was synthesized by two step hydrothermal method. The micro-topography, magnetic and phase transition properties have been investigated using various measurement techniques. All prepared V1?xZrxO2 powder samples exhibit monoclinic structure at room temperature. With the Zr4+ ions doping concentration increased, the shapes of VO2 particles change from spherical to rectangular slice. Besides, the saturation magnetic moment of the samples decrease with the increase of doped Zr4+ ions concentration, while their phase transition temperature increase gradually with Zr ions doping at a rate of around 2 ?C/at% on average. We investigated the Zr doping effects on V-V dimers and con?rmed the role of V-V dimers in phase transition. We speculate that more V-V dimers form with Zr doping by magnetic measurements, which result in the monoclinic phase of Zr-doped VO2 sample is more stable than rutile phase. Therefore the phase transition temperature is elevated by Zr doping in our experiment. We further consider that the VO2 phase transition should be ascribed to Peierls transition caused by the changing of V-V dimers.
关键词： V-V dimer,magnetic properties,Zr-doped,phase transition temperature
更新于2025-09-19 17:15:36
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Effect of neutron irradiation on the structural, electrical and optical properties evolution of RPLD VO2 films
摘要： This study reports on the effect of neutron irradiation at different fluences on the properties of VO2 thin films. The irradiations were performed at NUR research reactor, Algiers at a temperature of about 40 °C, with fast neutron fluence (En > 1 MeV) up to 1.9 × 1018 n.cm?2. The induced defects have been investigated using structural, optical and electrical measurements. Both bulk sensitive characterization techniques, Raman and grazing incident angle X-ray diffraction (GIXRD) analysis, show that no structural transformation is induced by neutron irradiation, although strain induced defect production are generated throughout the films while surface sensitive techniques, X-ray photoelectron spectroscopy (XPS) and work function measurements, show that the charge carrier (electron) concentration at room temperature decreases after irradiation. Potentially due to fast neutron irradiation induced defects, mainly in the form of Frenkel pairs, swelling and color center formation occurs in VO2 thin films without amorphization. This is further corroborated by an increase of the room temperature resistivity through the irradiated films. Temperature-dependent electrical and optical transmission measurements confirm that the characteristic semiconductor-to-metal transition of the VO2 films is preserved upon irradiation. We therefore conclude that VO2 is an excellent candidate for thermal shielding and thermal management of small satellites.
关键词： Smart radiator device,Vanadium dioxide,Neutron irradiation,Phase transition,Pulsed laser deposition
更新于2025-09-19 17:15:36
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Strain coupling and dynamic relaxation in multiferroic metal-organic framework [(CH3)2NH2][Mn(HCOO)3] with perovskite structure
摘要： Strain coupling with ferromagnetism and ferroelectricity plays an important role in the development of multiferroic metal-organic frameworks (MOFs) with strong magnetoelectric coupling, but the underlying mechanisms have not been well understood. Strain coupling and dynamic relaxation in multiferroic MOF with perovskite structure [(CH3)2NH2][Mn(HCOO)3] were investigated using X-ray diffraction (XRD), Raman spectroscopy, Infra-red (IR) spectroscopy, differential scanning calorimetry (DSC), magnetic measurements and dynamic mechanical analysis (DMA). DSC results showed peaks at 183 K and 190 K at the rate of 5 K/min during cooling and heating processes, respectively. Magnetic measurements showed magnetic transition at ~ 8.5 K at the heating rate of 2 K/min. Temperature and frequency dependences of elastic properties studied by DMA at frequencies of 0.5 Hz to 10 Hz between 140 K and 300 K at heating rate of 2 K/min indicated that the minimum in storage modulus and the maximum in loss modulus and loss factor occurred near 190 K. The peak height of loss modulus and loss factor decreased at higher frequency, and the peak temperature was independent of frequency, showing the features of first-order phase transition. Near 190 K, paraelectric to ferroelectric phase transition triggered by disorder–order transition of alkylammonium cations located in the framework cavities occurred accompanied by the structural phase transition from rhombohedral space group R c to monoclinic space group Cc. The elastic anomalies and large energy loss near 190 K were associated with the coupling of the local strain with the freezing of dimethylammonium cation and the freezing of twin walls.
关键词： Elastic modulus,Energy loss,Metal-organic framework (MOF),Phase transition,Dynamic mechanical analysis (DMA)
更新于2025-09-19 17:15:36
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Phase- and shape-controlled synthesis of VO2 by a hydrothermal-calcination method
摘要： VO2(M) structures with various shapes were synthesized by vacuum annealed VO2 metastable phase, and this metastable phase (VO2(B/D)) were formed by hydrothermal method used H2C2O4 and V2O5 powders as starting reactants. The phase structure, morphology, surface composition and phase transition characteristics of VO2 were characterized by XRD, SEM, XPS and DSC. Obtained results show that the VO2’s metastable phase structure and morphology strongly depended on the n-butanol/water ratio, molar ratio of V2O5 and H2C2O4 and molar concentration of V2O5, which leads a different synthesis pathway. The influence mechanism has also been studied. Low n-butanol/water ratio (2:45) and low molar ratio (1:1, 1:2) favor the formation of VO2(B) nanosheets/nanorods while high n-butanol/water ratio (45:2) and high molar concentration (0.22 mol/L) favor the formation of VO2(D) micro/nanospheres. Ultimately, the VO2(M) nanoparticles can be obtained at a relatively low vacuum annealing temperature of 300°C, and with a lowest TC was as low as 55.43°C. In addition, the effect of vacuum annealing temperature and morphology on the phase transition characteristic of VO2(M) has also been studied.
关键词： VO2,Various shapes and phase structures,Hydrothermal,Phase transition characteristic,Vacuum annealing
更新于2025-09-19 17:13:59
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Molybdenum Disulfide Nanosheet/Quantum Dot Dynamic Memristive Structure Driven by Photoinduced Phase Transition
摘要： MoS2 2D nanosheets (NS) with intercalated 0D quantum dots (QDs) represent promising structures for creating low-dimensional (LD) resistive memory devices. Nonvolatile memristors based 2D materials demonstrate low power consumption and ultrahigh density. Here, the observation of a photoinduced phase transition in the 2D NS/0D QDs MoS2 structure providing dynamic resistive memory is reported. The resistive switching of the MoS2 NS/QD structure is observed in an electric field and can be controlled through local QD excitations. Photoexcitation of the LD structure at different laser power densities leads to a reversible MoS2 2H-1T phase transition and demonstrates the potential of the LD structure for implementing a new dynamic ultrafast photoresistive memory. The dynamic LD photomemristive structure is attractive for real-time pattern recognition and photoconfiguration of artificial neural networks in a wide spectral range of sensitivity provided by QDs.
关键词： neuromorphic computing,photoinduced phase transition,2D crystals and QDs,dynamic photomemristors,liquid phase exfoliation
更新于2025-09-19 17:13:59