A scheme for simulating multi-level phase change photonics materials

Abstract Chalcogenide phase change materials (PCMs) have been extensively applied in data storage, and they are now being proposed for high resolution displays, holographic displays, reprogrammable photonics, and all-optical neural networks. These wide-ranging applications all exploit the radical property contrast between the PCMs’ different structural phases, extremely fast switching speed, long-term stability, and low energy consumption. Designing PCM photonic devices requires an accurate model to predict the response of the device during phase transitions. Here, we describe an approach that accurately predicts the microstructure and optical response of phase change materials during laser induced heating. The framework couples the Gillespie Cellular Automata approach for modelling phase transitions with effective medium theory and Fresnel equations. The accuracy of the approach is verified by comparing the PCM’s optical response and microstructure evolution with the results of nanosecond laser switching experiments. We anticipate that this approach to simulating the switching response of PCMs will become an important component for designing and simulating programmable photonics devices. The method is particularly important for predicting the multi-level optical response of PCMs, which is important for all-optical neural networks and PCM-programmable perceptrons

Multi-level Optical Switching by Amorphization in Single- and Multi- Phase Change Material Structures

The optical properties of phase-change materials (PCM) can be tuned to multiple levels by controlling the transition between their amorphous and crystalline phases. In multi-material PCM structures, the number of discrete reflectance levels can be increased according to the number of PCM layers. However, the effect of increasing number of layers on quenching and reversibility has not been thoroughly studied. In this work, the phase-change physics and thermal conditions required for reversible switching of single and multi-material PCM switches are discussed based on thermo-optical phase-change models and laser switching experiments. By using nanosecond laser pulses, 16 different reflectance levels in Ge2Sb2Te5 are demonstrated via amorphization. Furthermore, a multi-material switch based on Ge2Sb2Te5 and GeTe with four discrete reflectance levels is experimentally proven with a reversible multi-level response. The results and design principles presented herein will impact active photonics applications that rely on dynamic multi-level operation, such as optical computing, beam steering, and next-generation display technologies.Comment: 25 pages, 8 figure

Low Thermal Conductivity Phase Change Memory Superlattices

Phase change memory devices are typically reset by melt-quenching a material to radically lower its electrical conductance. The high power and concomitantly high current density required to reset phase change materials is the major issue that limits the access times of 3D phase change memory architectures. Phase change superlattices were developed to lower the reset energy by confining the phase transition to the interface between two different phase change materials. However, the high thermal conductivity of the superlattices means that heat is poorly confined within the phase change material, and most of the thermal energy is wasted to the surrounding materials. Here, we identified Ti as a useful dopant for substantially lowering the thermal conductivity of Sb2Te3-GeTe superlattices whilst also stabilising the layered structure from unwanted disordering. We demonstrate via laser heating that lowering the thermal conductivity by doping the Sb2Te3 layers with Ti halves the switching energy compared to superlattices that only use interfacial phase change transitions and strain engineering. The thermally optimized superlattice has (0 0 l) crystallographic orientation yet a thermal conductivity of just 0.25 W/m.K in the "on" (set) state. Prototype phase change memory devices that incorporate this Ti-doped superlattice switch faster and and at a substantially lower voltage than the undoped superlattice. During switching the Ti-doped Sb2Te3 layers remain stable within the superlattice and only the Ge atoms are active and undergo interfacial phase transitions. In conclusion, we show the potential of thermally optimised Sb2Te3-GeTe superlattices for a new generation of energy-efficient electrical and optical phase change memory.Comment: 4 Figures, 7 Supplementary Figures, 27 pages including a supplemen

Effect of Sow Intestinal Flora on the Formation of Endometritis

Endometritis is the main cause of decreased reproductive performance of sows, while one of the most important factors in the etiology of sow endometritis is an aberration of birth canal microbiota. Therefore, people began to pay attention to the microbiota structure and composition of the birth canal of sows with endometritis. Interestingly, we found that the risk of endometritis was increased in the sows with constipation in clinical practice, which may imply that the intestinal flora is related to the occurrence of endometritis. Therefore, understanding the relationship between birth canal microbiota and intestinal microbiota of the host has become exceptionally crucial. In this study, the microbiota of birth canal secretions and fresh feces of four healthy and four endometritis sows were analyzed via sequencing the V3 + V4 region of bacterial 16S ribosomal (rDNA) gene. The results showed a significant difference between endometritis and healthy sows birth canal flora in composition and abundance. Firmicutes (74.36%) and Proteobacteria were the most dominant phyla in birth canal microbiota of healthy sows. However, the majority of beneficial bacteria that belonging to Firmicutes phylum (e.g., Lactobacillus and Enterococcus) declined in endometritis sow. The abundance of Porphyromonas, Clostridium sensu stricto 1, Streptococcus, Fusobacterium, Actinobacillus, and Bacteroides increased significantly in the birth canal microbiota of endometritis sows. Escherichia–Shigella and Bacteroides were the common genera in the birth canal and intestinal flora of endometritis sows. The abundance of Escherichia–Shigella and Bacteroides in the intestines of sows suffering from endometritis were significantly increased than the intestinal microbiota of the healthy sows. We speculated that some intestinal bacteria (such as Escherichia–Shigella and Bacteroides) might be bound up with the onset of sow endometritis based on intestinal microbiota analysis in sows with endometritis and healthy sows. The above results can supply a theoretical basis to research the pathogenesis of endometritis and help others understand the relationship with the microbiota of sow's birth canal and gut

Design, synthesis and in vitro anti-Zika virus evaluation of novel Sinefungin derivatives

We report herein the design and synthesis of a series of novel Sinefungin (SIN) derivatives, based on the structures of SIN and its analogue EPZ004777. Our results reveal that target compounds 1ad-af, 1ba-bb and 1bf-bh show better activity (IC50 = 4.56–20.16 μM) than EPZ004777 (IC50 = 35.19 μM). Surprisingly, SIN was founded to be not as active (IC50 > 50 μM) as we and other research groups predicted. Interestingly, the intermediates 9a-b and 11b display potent anti-ZIKV potency (IC50 = 6.33–29.98 μM), and compound 9a also exhibits acceptable cytotoxicity (CC50 > 200 μM), suggesting their promising potential to be leads for further development

Asymmetric Etalon Effect in Fold-Type Optical Feedback Cavity-Enhanced Absorption Spectroscopy

To further improve the performance of cavity-enhanced spectroscopy systems, a high-quality U-cavity system was established. In the process of the experiment, an asymmetric ripple effect, which is different from the previous etalon effect, was found, which seriously affects the performance of the spectral system. This unique phenomenon mainly manifests in the different amplitudes of the fluctuations of the spectral curves measured by the folding mirror and the end mirror in the U-cavity system. Based on multi-beam interference theory, we analyzed the characteristics of the transmission spectrum of each mirror in the presence of the etalon effect at the end mirror, and obtained the following conclusions: for the U-cavity system, the strength of the etalon effect of each mirror is inversely proportional to its transmission loss value, that is, the larger the loss, the smaller the ripple of the transmission spectrum, and vice versa. In order to eliminate this effect, the most effective way is to eliminate the etalon effect caused by the light feedback of the end mirror. After improving the system, the minimum detectable absorption coefficient of αmin=8.33×10−9cm−1 is obtained with this U-shape Optical Feedback Cavity-Enhanced Absorption Spectroscopy. These works are valuable references for the design of folded Cavity-Enhanced Absorption Spectroscopy systems and have potential for laser wavelength calibration and measurement of a mirror’s reflectance