Research team of Southeast University found thermochromic ferrite with seven physical channel switch
Recently, a team from the International Academy of molecular ferroelectric science and application of Southeast University and the Key Laboratory of molecular ferroelectric science and application of Jiangsu Province has discovered thermochromic ferrite with seven physical channel switches. The related work was published in the top Chemical Journal angelwandte Chemistry International Edition with an academic paper entitled "the first thermal ferroelastic with seven physical channel switches". In addition, the paper was selected as VIP (very importantpaper). It is reported that less than 5% of the received papers can get such a positive evaluation.
In the information age, the signal processing and encryption of electronic intelligent equipment is very important. Multifunctional materials with multiple physical channel bistable switching characteristics have become a rising star. As we all know, a key corresponds to a lock. If we put our property in the safe, we will have another layer of protection. Similarly, each additional physical channel is an additional layer of security. Based on this, we report the first chiral compound with seven physical channels, which can encrypt the information in seven layers and make the information more secure and reliable.
(a) Disordered CTA cations and chiral ordered s-cta and r-cta cations in racemic crystal structure
(b) (R-CTA)2CuCl4
(c) Crystal stacking diagram of (s-cta) 2cucl4
As early as 1999, Wataru Fujita et al. Reported in science that the magnetic bistability (SCIENCE1999, 286, 261 – 262) in 1,3,5-trithia-2,4,6-triazapatentalenyl (ttta) molecule had an obvious magnetic bistability loop in the temperature range of 230 K to 305 K. Its high temperature phase is paramagnetic, and low temperature phase is diamagnetic under the influence of dimerization. Three years later, M.E. itkis et al. Reported in science that the bistable characteristics of three physical channels, electrical, optical and magnetic, were found in the product of fenonenyl neutral radicals (Science 2002, 296, 1443 – 1445). Until 2014, Professor Xiong rengen's team reported in advanced materials that imidazole periodate (IPI) compounds have bistability of five physical channels, including dielectric, piezoelectric, SHG, ferroelectric and electromechanical coupling (adv. material.2014, 26, 4515 – 4520). It can be seen that every additional physical channel is facing a huge challenge. Guided by the principle of molecular ferroelectric "spherical non spherical" and the introduction of chirality, we use the chiral ligands to synthesize, and introduce the chirality switch into it, and successfully assemble (r-cta) 2cucl4 and (s-cta) 2cucl4 (CTA = 3-chloro-2-hydroxypropyltrimethylammonium). These two compounds are in dielectric and conductivity , second-order nonlinearity, piezoelectricity, ferroelasticity, chirality and thermochromism are seven physical channels with switching characteristics. Among them, thermochromism is particularly dazzling, which is different from traditional phase change materials, which provides a new inspiration for spectral encryption of bistable switches.
(a) DSC curve
(b) Multiple bistability diagrams of dielectric, conductivity, piezoelectric and second-order nonlinear optics.
The phase transition points of (RAC CTA) 2cucl4, (r-cta) 2cucl4 and (s-cta) 2cucl4 are around 361, 417 and 420 K, respectively. With the change of temperature, the dielectric constant, conductivity, piezoelectric coefficient and SHG signal intensity of the low temperature phase below the phase transition temperature and the high temperature phase above the phase transition temperature all show two stable states which can be switched.
Ferroelastic domain structure of (s-cta) 2cucl4 and (r-cta) 2cucl4 crystals at 293k
In addition, these chiral compounds are also ferroelastic, and the ferroelastic phase transition is often accompanied by the evolution of ferroelastic domains. Under orthogonal polarized light, ferroelastic domains with different orientations have different birefringence characteristics, thus showing different light and dark structural areas. The crystalline films of (s-cta) 2cucl4 and (r-cta) 2cucl4 show a clear triangular ferroelastic structure at room temperature. When the temperature is higher than the phase transition point, the ferroelastic domain disappears rapidly, showing the extinction characteristic of cubic symmetry. In the subsequent cooling, regular ferroelastic domains appeared quickly, showing obvious switching characteristics.
In addition to ferroelasticity, this pair of chiral crystals also exhibit a convertible thermochromic property. At room temperature, the light absorption of (r-cta) 2cucl4 and (s-cta) 2cucl4 crystals is lower than 540 nm, which is consistent with their yellow appearance. With the increase of temperature, the absorption edge of electron absorption band shifts red. When the temperature exceeds the phase transition point to 423 K, the absorption edge moves to 580 nm, which is the same as that when the crystal is heated to orange. Using thermochromic characteristics to process spectral encryption and signal detection brings new ideas for developing new encryption technology.
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The figure shows the solid UV-Vis absorption spectrum with variable temperature
The work was completed with the joint efforts of doctoral student Lu Siqi (the first author), and Southeast University was the first communication unit. This achievement was supported by the "top ten scientific and technological issues of Southeast University" start-up cultivation fund.
Paper link:
https://onlinelibrary.wiley.com/doi/10.1002/anie.202000290
Academician Cui Tiejun successfully developed a dual channel independent programmable super surface
Recently, the research team of academician Cui Tiejun of Southeast University and Professor Qiu Chengwei of National University of Singapore proposed, designed and tested a kind of super surface with strong reconstruction ability and dual channel independent programmable. The dual programmable hypersurface has an independent control interface, which can adjust and control the x-polarization and y-polarization electromagnetic wave independently in real time, so as to realize multiple complex and novel electromagnetic functions. Compared with the traditional single polarization programmable hypersurface, the dual programmable hypersurface can provide two independent information transmission channels in parallel, thus greatly improving the information processing ability of the programmable hypersurface.
Relevant research results were published in advanced science, a comprehensive academic journal, under the title of "polarization controlled dual programmable metrics". The corresponding authors are Professor Jiang Weixiang, Professor Cui Tiejun of Southeast University and Professor Qiu Chengwei of National University of Singapore. The first author is Zhang Xinge, a doctoral student of Southeast University.
Hypersurface is an ultra-thin platform composed of subwavelength artificial units arranged periodically or aperiodically in two-dimensional plane, which shows a strong ability in regulating electromagnetic wave. In particular, the dynamic super surface can regulate the electromagnetic wave artificially and dynamically under the external control signal. At present, most of the existing dynamic hypersurfaces are tunable and reconfigurable. The function of adjustable hypersurface can achieve fine-tuning, but the function is similar; the reconfigurable hypersurface can obtain significantly different functions, but the number of functions is limited. In order to realize the real-time control and switching of many different functions, Professor Cui Tiejun and others proposed to introduce digital coding representation and field programmable logic gate array (FPGA) into the dynamic hypersurface design in 2014, realizing the field programmable hypersurface. Programmable super surface can realize many different functions on a single platform, and the functions can be switched in real time according to the written program. However, most of the existing programmable hypersurfaces can only show the programmable characteristics under the pre-designed specific polarized electromagnetic wave irradiation, and still show the static characteristics under other polarized electromagnetic wave irradiation. Because the programmable super surface can only be real-time regulated under the irradiation of a single polarized electromagnetic wave, and can only provide an effective information transmission channel, so it can only process multiple tasks on one channel in series, which restricts the ability of parallel processing of multiple tasks.
In order to improve the information processing efficiency and multi task processing ability of hypersurface, researchers developed and designed a dual polarized hypersurface, which can show different electromagnetic responses under different polarizations, and then can provide two independent information channels in parallel. Compared with the single polarization hypersurface, the dual polarization hypersurface can realize more complex functions, such as multi-channel information processing, polarization division multiplexing and dual polarization aperture sharing. Therefore, more advanced functional devices can be realized based on the dual polarized super surface. However, the existing dual polarized hypersurfaces are static or only fine-tuning, and their functions cannot be switched by real-time programming, which greatly limits the multi-function of dual polarized hypersurfaces and their application in ultrafast switching and scanning systems.
In order to solve the above problems, the researchers designed a dual programmable super surface which can independently regulate the x-polarization and y-polarization electromagnetic waves. In order to realize the dual programming hypersurface, the researchers first carefully designed an active hypersurface unit which can independently adjust the reflection phase of x-polarization and y-polarization electromagnetic waves. The active hypersurface element has a special design of metal pattern, and two varactors are integrated in X and Y directions respectively. Through the two bias lines designed, the capacitance of varactors in X and Y directions can be independently controlled, and then the reflection phase of x-polarization and y-polarization electromagnetic waves can be independently controlled. In order to obtain dual programming hypersurface and realize multiple complex electromagnetic functions, the researchers use 24x24 hypersurface units to array, which contains 48 independent control interfaces. In order to realize the effective control of dual programmable hypersurface with multiple independent control interfaces by a single FPGA, the researchers further designed and implemented the extended interface circuit and DC voltage conversion circuit. The extended interface circuit is mainly composed of decoder and latch, which can expand a few FPGA interfaces exponentially. The voltage conversion circuit is mainly composed of transistors and resistors, which can convert the output voltage of FPGA to the bias voltage required by the varactor in the dual programmable super surface. Therefore, the dual programmable hypersurface platform has rich programmability and can realize multiple complex electromagnetic functions. As an experimental demonstration, the researchers verified three different electromagnetic functions on a single platform: exclusive or logic operation for spin control of circularly polarized waves, constant frequency and large angle dual beam scanning and dual polarized aperture sharing. The dual programmable super surface provides a new way to realize large-scale and high integrated electromagnetic devices and systems, and is expected to be applied in advanced devices and systems such as wave based logical operation platform, high-speed scanning radar and multi-channel spatial optical processor.
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Professor Wu Zhishen's team of Southeast University took the lead to obtain the support of national key R & D program
Recently, the national key R & D plan "monitoring, early warning and prevention of major natural disasters" was announced. Professor Wu Zhishen from the school of civil engineering of Southeast University took the lead to obtain the project support of "research and development of technology and equipment for rapid detection and evaluation of large bridge and tunnel structures after disasters". The implementation period of the project is 4 years, with a total fund of 36.33 million yuan.
The project aims at the urgent needs of disaster prevention and mitigation of large-scale bridge and tunnel infrastructure, as well as the needs of disaster relief, emergency rescue and rapid recovery after natural disasters. It develops a fast detection equipment and intelligent evaluation decision platform with the characteristics of mobile, unmanned, refined and comprehensive, so as to improve the level of rapid, high-precision and intelligent detection and evaluation of large-scale bridge and tunnel structures after disasters To enhance the national capacity for disaster relief and mitigation and to ensure the national social and economic security and sustainable development.
The research team of Lin Chengqi and Luo zhuojuan of Southeast University published the latest research results in the international top journal Science Advanced
Recently, the research group of Lin Chengqi and Luo zhuojuan, the Key Laboratory of the Ministry of education of "development and disease related genes" of the College of life science and technology of Southeast University, published in the international top journal science advances