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Use of Aggregation-Induced Emission for Selective Detection of Phase Transformation during Evaporative Crystallization of Hexaphenylsilole
摘要： Crystallization of organic molecules is quite complicated because the crystallization process is governed by the weak intermolecular interactions. By exploiting the aggregation-induced emission (AIE), we attempted to realize the selective detection of phase transformation during the evaporative crystallization of hexaphenylsilole (HPS), which shows different fluorescence colors in the amorphous and crystalline phases. No fluorescence emission was observed in the HPS solution immediately after dropping on the glass substrate due to the non-radiative deactivation induced by intramolecular rotational or vibrational motion, suggesting that HPS exists as a monomer in solution. As time elapsed after dropping, green emission first appeared, which changed to blue after solvent evaporation, because of phase transformation from the amorphous state to the crystalline state. This phenomenon supports not only the two-step nucleation model involving an intermediate such as a liquid-like cluster prior to nucleation, but also the real time-detection of Ostwald’s rule of stages during evaporative crystallization.
关键词： molecular interaction,amorphous-crystal phase transformation,AIE,Ostwald’s rule of stages,evaporative crystallization
更新于2025-09-10 09:29:36
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[Nanostructure Science and Technology] Nanowire Electronics || Metal-Semiconductor Compound Contacts to Nanowire Transistors
摘要： Semiconductor nanowires [1–4] are promising building blocks for next-generation ultrascaled devices for electronic [5–7] and optoelectronic [8–10] applications. An important aspect for the development, maturity, and ef?ciency of these ultrascaled devices is the detailed understanding of and control over the phase transformation that accompanies the formation of their compound contacts for lithography-free self-aligned gate design [11, 12]. The term “compound” here refers to the formed phases that have ?xed stoichiometry between metal and semiconductor elements, to be distinguished from the broader “alloy” term for phases that may include nonstoichiometric or amorphous structure. This distinction is important because the formation of a low resistance, crystalline, and thermally stable compound contact is most preferred for realizing reliable functionality in ultrascaled semiconductor transistors. Usually, the phase of compound contact and its interfacial property with semiconductor nanowire (NW) can largely affect the band alignment and charge injection in NW channels. This demands the detailed studies of the metal-semiconductor solid-state reactions, including the formed compound phases, reaction kinetics, and their correlation to the device performances. In this book chapter, we provide a thorough discussion of these three topics.
关键词： metal-semiconductor solid-state reactions,compound contacts,reaction kinetics,phase transformation,Semiconductor nanowires,device performances
更新于2025-09-10 09:29:36
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[IEEE 2018 International Conference on Electromagnetics in Advanced Applications (ICEAA) - Cartagena des Indias, Colombia (2018.9.10-2018.9.14)] 2018 International Conference on Electromagnetics in Advanced Applications (ICEAA) - A Low-Profile, Planar, Power-Efficient 2D Beam-Steering Antenna Technology
摘要： The paper explains a recently demonstrated 2D beam-steering antenna technology and its potential to develop a low-cost communication-on-the-move (COTM) terminal antenna. A low-cost COTM antenna is critical for receiving TV and internet via existing geostationary and upcoming low-earth-orbit (LEO) satellite constellations. The new beam-steering technology is based on near-field phase transformation and its working is verified by a prototype design reported recently. Performance indicators of the prototype are compared here with some commercially available COTM terminal antennas. A fully passive design, low-profile, low power requirements, and simple design configuration give the new steering antenna a competitive advantage over existing COTM terminal antennas from KYMETA and ThinKom.
关键词： low-earth-orbit (LEO) satellite,communication-on-the-move (COTM),low-profile,beam-steering antenna,near-field phase transformation
更新于2025-09-10 09:29:36
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Phase transformation and luminescence properties of Y2.94Al5-xGaxO12: 0.06Ce3+phosphors
摘要： A series of Ga-substituted Ce3+-doped yttrium aluminum garnet (Y2.94Al5-xGaxO12: 0.06Ce3+) phosphors were synthesized at different atmospheres and temperatures. The structure, optical and thermal stability properties were analyzed using X-ray diffraction (XRD), photoluminescence (PL) and thermal measurements. A novel finding was revealed that gallium oxide (Ga2O3) was unstable in reducing atmosphere by XRD, and we explained the mechanism for the first time. In addition, it was found that Y3Al3Ga2O12 was formed due to Al3+ ions entering the lattice of Y3Ga5O12 gradually and the mechanism was clearly illustrated. The emission intensity of Y2.94Al5-xGaxO12: 0.06Ce3+ phosphors was determined by two aspects—the phase formation temperature and the band gap of host lattice. What’s more, introducing 6 wt% H3BO3 as flux can improve thermal stability to maximum extent and the thermal ionization model was used to explain the thermal quenching mechanism. Finally, the critical parameters including color rendering index (CRI), correlated color temperature (CCT), light efficiency of light emitting diodes (LEDs) packaged with the resultant green phosphors and red phosphors were studied.
关键词： thermal ionization,band gap,YAGG: Ce3+,phase transformation
更新于2025-09-10 09:29:36
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Crystal Morphology and Phase Transformation of LiAlO <sub/>2</sub> : Combined Experimental and First-Principles Studies
摘要： Layered α-LiAlO2 matrix often suffers from detrimental structural and morphological changes during its lifetime, especially under H2 containing fuel inlet environments of molten carbonate fuel cell systems. However, the underlying mechanism of this phase and morphological transformations has rarely been explored. In this study, transmission electron microscopy (TEM) techniques were used to determine the changes in structure and morphology of LiAlO2 samples lifted by a focused ion beam (FIB). In accordance with X-ray diffraction (XRD) analysis, TEM images show that under H-rich conditions the rhombohedral α-LiAlO2 transforms to tetragonal γ-LiAlO2 phase with the appearance of the (101) terminated octahedral shaped γ-LiAlO2 crystallites. We further support, and plausibly rationalize, the observed transformations using density functional theory (DFT) calculation. The DFT computed surface energies of γ-LiAlO2 reveal that the {101} surface becomes the lowest energy surface upon H-adsorption, thus leading to formation of observed octahedral geometry. Contrary to stabilization of γ-LiAlO2 surfaces upon H passivation, DFT revealed H-adsorption on α-LiAlO2 surfaces to be energetically unfavorable. This contrasting behavior of α-LiAlO2 and γ-LiAlO2 under H-rich environments could be a potential driving force for the observed α-LiAlO2 to γ-LiAlO2 phase transformation.
关键词： morphology,phase transformation,TEM,DFT,LiAlO2,XRD
更新于2025-09-10 09:29:36
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Morphological evolution of upconversion nanoparticles and their biomedical signal generation
摘要： Advancements in the fabrication of upconversion nanoparticles (UCNPs) for synthetic control can enable a broad range of applications in biomedical systems. Herein, we experimentally verified the role of the hydrothermal reaction (HR) time in the synthesis of NaYF4:20%Yb3+/3%Er3+ UCNPs on their morphological evolution and phase transformation at different temperatures. Characterizations of the as-prepared UCNPs were conducted using X-ray diffraction (XRD), electron microscopy and spectroscopy, and thermogravimetric and upconversion (UC) luminescence analysis. We demonstrated that determining the optimal HR time, also referred to here as the threshold time, can produce particles with good homogeneity, hexagonal phase, and UC luminescence efficiency. Subsequently, the polymer coated UCNPs maintained their original particle size distribution and luminescence properties, and showed improved dispersibility in a variety of solvents, cellular nontoxicity, in vitro bioimaging, and biocompatibility as compared to the bare UCNP. Besides this, polyacrylic acid conjugated UCNPs (UCNP@PAA) also revealed the strong anticancer effect by conjugating with doxorubicin (DOX) as compared to the free DOX. Based on these findings, we suggest that these particles will be useful in drug-delivery systems and as in vivo bioimaging agents synchronously.
关键词： phase transformation,morphological evolution,biomedical applications,hydrothermal reaction,upconversion nanoparticles
更新于2025-09-09 09:28:46
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Shortening nucleation time to enable ultrafast phase transition in Zn1Sb7Te12 pseudo-binary alloy
摘要： Zn1Sb7Te12 thin films have been deposited by magnetron co-sputtering of ZnTe and Sb2Te3 targets. The microstructure, phase-change speed, optical cycling stability and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give clear evidence on coexistence of trigonal Sb2Te3 and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy. The formation of both phases increases initial nucleation sites, leading to the rapid phase-change speed in the Zn1Sb7Te12 film. The film has a minimum crystallization time of ~3 ns at 70 mW with almost no incubation period for the formation of critical nuclei compared to Ge2Sb2Te5 and other Zn-based films. Moreover, the complete crystallization of Zn1Sb7Te12 thin films is achieved within 10 ns. The ultrafast two-dimensional nucleation and crystal growth speed in Zn1Sb7Te12 obtained from the laser-irradiated system is almost 7 times faster compared to Ge2Sb2Te5 film. Controlling crystallization process through the doping ZnTe into Sb2Te3 is thus promising for the development of high-speed optical switching technology.
关键词： Optical spectroscopy,Thin films,Phase transformation kinetics,Optical materials,STEM HAADF
更新于2025-09-09 09:28:46
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First-principles study of structural phase transformation and dynamical stability of cubic AlN semiconductors
摘要： Phase transformation and stability of cubic aluminium nitride (AlN) phases such as zinc-blende and rock-salt have been investigated using first-principles calculations based on density functional perturbation theory (DFPT) within quasi-harmonic approximation (QHA). The phonon dispersion relations of both the cubic phases have been calculated at various high-symmetry points of the Brillouin Zone. The pressure and volume dependence of phonon frequencies have been investigated. The application of pressure results in opposite trend of transverse acoustic (TA) phonon frequencies for rock-salt and zinc-blende AlN phases. The TA frequencies found to increase for the former one and decrease for the latter one with the increase in pressure. The dynamical instability results in a volume expansion of rock-salt AlN close to the equilibrium volume of zinc-blende AlN. Phase transformation of these cubic phases is further investigated by computing an equilibrium pressure-temperature phase diagram within QHA. The cubic rock-salt AlN is found to form at high pressures and temperatures than zinc-blende AlN. The temperature dependence of lattice constant and the corresponding volume thermal expansion coefficient of both the cubic phases have been investigated.
关键词： Aluminium nitride,First-principles calculations,Density functional perturbation theory,Quasi-harmonic approximation,Phase transformation,Dynamical stability
更新于2025-09-09 09:28:46
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Nanostructured Titania Templated by Natural Cellulose Substance: Effect of Vanadium-Doping on the Anatase-to-Rutile Phase Transformation
摘要： Vanadium-doped rutile titania nanomaterial was synthesized by calcination of titania/vanadia composite thin gel films pre-coated natural cellulose substance (e.g., ordinary filter paper) at a relatively low temperature (600 °C). A better mixture of titanium and vanadium species is achieved during the layer-by-layer (LbL) deposition process with cellulose nanofiber as a template, leading to more vanadium dopants incorporated in the titania crystal lattices. By sufficient vanadium-doping, the phase transformation temperature from anatase to rutile phase of titania is decreased effectively. The doping mode and existing state of vanadium in the titania nanomaterials and the effect on the anatase-to-rutile phase transformation have been studied. This strategy provides a facile and effective route to facilitate the phase transformation of various nanostructured metal oxides templated by natural cellulose substance through doping appropriate functional metal ions in the LbL deposition process.
关键词： Biomimetic,Ceramics,Sol–Gel Preparation,Phase Transformation,Titania
更新于2025-09-04 15:30:14
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High-temperature high pressure synthesis of monoclinic Y2O3
摘要： In this work, synthesis of cubic Y2O3 by calcining yttrium based coordination polymer (Y-CP) which were obtained by microwave-assisted method was reported. Monoclinic Y2O3 was obtained by treating the cubic Y2O3 under high temperature high pressure (HTHP) on a large volume cubic multi-anvil high pressure apparatus. The effect of temperature on the preparation was studied. The morphology and crystal phase of all samples have been characterized by the scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) spectra. What more, the photoluminescence (PL) property of the Y2O3: Eu3+ sample was investigated. This method can be used to prepare other rare earth oxide with various phase.
关键词： Coordination polymer,luminescence,Y2O3,high temperature high pressure,Phase transformation
更新于2025-09-04 15:30:14