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Asymmetry of the Defect Structure of Semipolar GaN Grown on Si(001)
摘要： The defect structure of a thick (~15 μ m) semipolar gallium nitride (GaN) layer grown by hydride–chloride vapor phase epitaxy on a Si(001) substrate with buffer layers has been studied by transmission electron microscopy. The asymmetry of the defect structure of GaN epilayer has been revealed and analyzed. The influence of this asymmetry on the rate of decrease in the density of threading dislocations in the growing epitaxial layer is discussed.
关键词： transmission electron microscopy,semipolar GaN,threading dislocations,hydride–chloride vapor phase epitaxy,defect structure
更新于2025-09-04 15:30:14
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Point defect chemistry of donor-doped bismuth titanate ceramic
摘要： This communication reports on the defect chemistry at room temperature of barium (Ba) doped bismuth titanate (Bi4Ti3O12), emphasizing the influence of the point defects on its electrical properties. Pure and Ba doped Bi4Ti3O12 were prepared by a conventional solid-phase reaction technique. The addition of Ba into the crystal structure of Bi4Ti3O12 was monitored by X-ray diffraction measurements combined with Rietveld refinement studies where it was determined that Ba occupies the bismuth (Bi) lattice sites as well as the presence of oxygen vacancies (V??O). The characterization of the point defects was carried out using impedance and electron spin resonance spectroscopies where the results support the models of compensation mechanisms dominated by electrical positive charges (h?) and oxygen vacancies (V??O).
关键词： defect chemistry,X-ray diffraction,Rietveld refinement,impedance spectroscopy,solid-phase reaction,barium doped bismuth titanate,electron spin resonance spectroscopy,electrical properties,oxygen vacancies
更新于2025-09-04 15:30:14
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Image encryption using exclusive-OR with DNA complementary rules and double random phase encoding
摘要： We propose an optical image encryption scheme based on the Deoxyribonucleic Acid (DNA) theory and the double random phase encoding (DRPE) technique. The piecewise linear chaotic map (PWLCM) is used to generate key images and random phase masks, and to determine DNA encoding rules. In order to achieve ultra-fast DNA encryption, we propose using an optical exclusive-OR (XOR) gate to achieve XOR operation in DNA encryption. Different plaintexts use different initial values of PWLCM, which are generated by Message Digest Algorithm 5 (MD5). The plaintext is encrypted by two rounds of DNA and then by DRPE to form a ciphertext. Numerical simulation and the analysis of attacks on encrypted image are implemented to demonstrate the security and validity of the proposed approach.
关键词： Image encryption,DNA encoding,Double random phase encoding
更新于2025-09-04 15:30:14
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http://www.orientjchem.org/vol34no1/optical-pattern-of-liquid-crystalline-structure-in-singular-and-mixed-anionic-cationic-surfactant-system/
摘要： A preliminary study to examine the liquid crystalline region formed by surfactant, DTAB and AOT, individually and mixed, in the presence of various chain length alcohols was carried out. Several ternary phase equilibrium were constructed. Results showed that all the investigated systems apart from forming lyotropic liquid crystalline structure were also able to form self-assembled aggregates such as micelle and reversed micelles. From the optical pattern observation, it was observed that two types of liquid crystalline were formed namely hexagonal and lamellar.
关键词： Optical pattern,Phase diagram,Surfactants
更新于2025-09-04 15:30:14
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Phase behavior of main-chain liquid crystalline polymer networks synthesized by alkyne–azide cycloaddition chemistry
摘要： Liquid crystalline polymer networks (LCNs) couple polymer chain organization to molecular ordering, the switching of which has been shown to impart stimuli-responsive properties, including actuation and one-way shape memory, to the networks. While LCNs have long been proposed as artificial muscles, recent reports have also suggested potential as dynamic biomaterial substrates. In contrast to many existing LCNs synthesized using hydrophobic spacers, this work investigates networks synthesized using more hydrophilic spacers to promote interaction with water. A challenge with such materials is liquid crystalline phases could be disrupted in hydrated networks. This work thus investigates the impact of polyether spacers and mesogen composition on the phase behavior of LCNs. Main-chain LCNs were synthesized using alkyne–azide cycloaddition ("click" chemistry), where two different mesogens (5yH and 5yMe) and a non-LC monomer (5yTe) were coupled with one of two different polyether spacers, poly(ethylene glycol) and poly(propylene glycol), and a crosslinker. The chemistry led to high gel fraction materials, the workup of which resulted in networks that displayed no difference in cellular toxicity due to leachable components compared to tissue culture plastic control. Calorimetric analysis, dynamic mechanical analysis, and X-ray scattering revealed the LC microstructure and temperature-responsive properties of the networks. The use of low molecular weight polyether spacers was found to prevent their crystallization within the LC network, and adjusting mesogen composition to enhance its LC phase stability allowed the use of spacers with larger molecular weights and pendant groups. Hydrated networks were found to rearrange their structure compared to dry networks, while maintaining their LC phases. Like other crosslinked LC materials, the networks display shape changes (actuation) that are tied to changes in LC ordering. The result is a new synthetic approach for polydomain networks that form stable LC phases that are tailorable using polyether spacers and may enable future application as hydrated, stimuli-responsive materials.
关键词： Liquid crystalline polymer networks,Phase behavior,Alkyne–azide cycloaddition,Stimuli-responsive materials,Polyether spacers
更新于2025-09-04 15:30:14
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An upgraded interferometer-polarimeter system for broadband fluctuation measurements
摘要： Measuring high-frequency fluctuations (above tearing mode frequencies) is important for diagnosing instabilities and transport phenomena. The Madison Symmetric Torus interferometer-polarimeter system has been upgraded to utilize improved planar-diode mixer technology. The new mixers reduce phase noise and allow more sensitive measurements of fluctuations at high frequency. Typical polarimeter rms phase noise values of 0.05°–0.07° are obtained with 400 kHz bandwidth. The low phase noise enables the resolution of fluctuations up to 250 kHz for polarimetry and 600 kHz for interferometry. The importance of probe beam alignment for polarimetry is also verified; previously reported tolerances of ≤0.1 mm displacement for equilibrium and tearing mode measurements minimize contamination due to spatial misalignment to within acceptable levels for chords near the magnetic axis.
关键词： Faraday rotation,interferometer-polarimeter,planar-diode mixer,broadband fluctuation measurements,phase noise
更新于2025-09-04 15:30:14
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Stabilization of ferroelectric Hf <sub/>x</sub> Zr <sub/>1?x</sub> O <sub/>2</sub> films using a millisecond flash lamp annealing technique
摘要： We report on the stabilization of ferroelectric HfxZr1?xO2 (HZO) films crystallized using a low thermal budget millisecond flash lamp annealing technique. Utilizing a 120 s 375 ?C preheat step combined with millisecond flash lamp pulses, ferroelectric characteristics can be obtained which are comparable to that achieved using a 300 s 650 ?C rapid thermal anneal. X-ray diffraction, capacitance voltage, and polarization hysteresis analysis consistently point to the formation of the ferroelectric phase of HZO. A remanent polarization (Pr) of ～21 μC/cm2 and a coercive field (Ec) of ～1.1 MV/cm are achieved in 10 nm thick HZO layers. Such a technique promises a new alternative solution for low thermal budget formation of ferroelectric HZO films.
关键词： low thermal budget,ferroelectric HfxZr1?xO2 films,remanent polarization,ferroelectric phase,millisecond flash lamp annealing,coercive field
更新于2025-09-04 15:30:14