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Mechanically-controllable strong 2D ferroelectricity and optical properties of semiconducting BiN monolayer
摘要： Structural, electronic, ferroelectric, and optical properties of two-dimensional (2D) BiN monolayer material with phosphorene-like structure are studied in terms of the density functional theory and modern Berry phase method of ferroelectric calculation. Both phonon spectra, molecular dynamics simulations, and total energy comparison indicate that the BiN monolayer is a stable 2D ferroelectric with polarization as large as 580 pC/m, with ferroelectric polarization being sustainable up to 500 K. Further study shows that the polarization in the BiN monolayer can be easily switched from [100] to [010] direction over the bridging saddle phase by applying a tensile [010] stress of 2.54 N/m or compressive [100] stress of -1.18 N/m. This phase transition makes its lattice constants vary in a large range compared to other non-ferroelectric 2D materials. Moreover, through applying uniaxial tensile stress parallel to the polarization, one can fix the polarization and change the semiconductor energy gap, from direct to indirect one. The optical properties feature a very strong anisotropy in reflectivity below the photon energy of 4 eV. All these significant ferroelectric, mechanical, electronic, and optical properties make us believe that the 2D BiN monolayer can be used to make stretchable electronic devices and optical applications.
关键词： 2D material,optical property,monolayer,mechanical manipulation,2D ferroelectricity,2D semiconductor
更新于2025-09-23 15:23:52
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[ACM Press the 1st Annual ACM Symposium - Cambridge, Massachusetts (2017.06.12-2017.06.13)] Proceedings of the 1st Annual ACM Symposium on Computational Fabrication - SCF '17 - Shape optimization of fabricated transparent layer for pixel density uniformalization in non-planar rear projection
摘要： When an image is projected onto a non-planer surface, the resolution is not spatially uniform because projectors are normally designed to display an image with spatially uniform pixel density on a flat surface. We propose to insert a transparent layer between a projector and a non-planar surface and optimize its shape to make the projection pixel density spatially uniform, which can be controlled by non-uniformly refracting a projection light through the transparent layer. We use a multi-material 3D printer to fabricate the transparent layer combined with a non-planar surface. From the result of a projection experiment with the surface, we validate our proposed method.
关键词： multi-material 3D printer,rear projection
更新于2025-09-23 15:23:52
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Effect of Hydration Procedure of Fumed Silica Precursor on the Formation of Luminescent Carbon Centers in SiO <sub/>2</sub> :C Nanocomposites
摘要： The effect of hydration procedure of fumed silica precursor on photoluminescent properties of carbonized silica (SiO2:C) nanocomposite after chemo/thermal treatments is studied. Main structural effect is the formation of chemical bonding of phenyl groups to silica surface via multiple C─Si─O bonding bridges. Synthesized samples demonstrate very broad photoluminescence (PL) bands in near ultraviolet and visible ranges with maximum intensity dependent on temperature of thermal annealing. Two main trends in luminescence properties are: 1) hydration-induced blue shift of PL in comparison with PL of unhydrated series; 2) red shift of PL bands with increasing synthesis temperature regardless hydration procedure. Temperature dependent evolution of light emission bands is discussed in terms of surface carbon nanoclusters formation and aggregation processes. It is assumed that blue shift of PL bands in the hydrated series is associated with the decreased surface mobility of carbon atoms and clusters as a result of increased chemical bonding with silica surface that slows down carbon thermally stimulated clusterization/aggregation processes.
关键词： carbonized nanocomposite material,carbonized fumed silica,phenyltrimethoxysilane,wide-band visible photoluminescence,carbon clusters
更新于2025-09-23 15:23:52
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Crystal structure, optical and electrical properties of metal-halide compound [C7H16N2][ZnCl4]
摘要： A new organic–inorganic hybrid compound [C7H16N2][ZnCl4] was synthesized by hydrothermal method and characterized by single-crystal X-ray diffraction, IR and Raman spectroscopy, optical absorption, differential scanning calorimetry and dielectric measurements. Single crystal diffraction results showed that [C7H16N2][ZnCl4] crystallizes in the monoclinic system, space group P21/c at room temperature. In the molecular arrangement, the tetrachlorozincate anions are connected to organic cations through N-H...Cl hydrogen bonds. The Raman and IR analyses confirm the presence of the organic groups and the anionic entities. UV–Visible absorption spectrum revealed the energy of the optical band gap. DSC measurements indicated that [C7H16N2][ZnCl4] undergoes three sequential phase transitions at 287, 338 and 356 K. The dielectric study proved the ferroelectric properties below the 338K and indicates their classical character for this compound. The analysis of Nyquist plots revealed the contribution of the bulk mechanism and the grain boundaries.
关键词： Phase transitions,Hybrid material,Crystal structure,Optical absorption,Ferroelectric properties,Conduction mechanism
更新于2025-09-23 15:23:52
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Light enhanced room temperature resistive NO2 sensor based on a gold-loaded organic–inorganic hybrid perovskite incorporating tin dioxide
摘要： A material is described for sensing NO2 in the gas phase. It has an architecture of type Au/MASnI3/SnO2 (where MA stands for methylammonium cation) and was fabricated by first synthesizing Au/MASnI3 and then crystallizing SnO2 on the surface by calcination. The physical and NO2 sensing properties of the composite were examined at room temperature without and with UV (365 nm) illumination, and the NO2-sensing mechanism was studied. The characterization demonstrated the formation of a p-n heterojunction structure between p-MASnI3 and n-SnO2. The sensor, best operated at a voltage of 1.1 V at room temperature, displays superior NO2 sensing performance. Figures of merit include (a) high response (Rg/Ra = 240 for 5 ppm NO2; where Rg stands for the resistance of a sensor in test gas, and Ra stands for the resistance of a sensor in air), (b) fast recovery (about 12 s), (c) excellent selectivity compared to sensors based on the use of SnO2 or Au/SnO2 only, both at room temperature under UV illumination; (d) a low detection limit (55 ppb), and (e) a linear response between 0.5 and 10 ppm of NO2. The enhanced sensing performance is mainly attributed to the high light absorption capacity of MASnI3, the easy generation and transfer of photo-induced electrons from MASnI3 to the conduction band of SnO2, and the catalytic effect of gold nanoparticles.
关键词： Light absorbing material,SPR effect,Photo generated electrons,Gas sensing,P-n junction,Catalytic effect,Heterojunction,SnO2,UV light,MASnI3
更新于2025-09-23 15:23:52
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Influence of porosity and pore size on sputtering of nanoporous structures by low-energy Ar ions: Molecular dynamics study
摘要： In this paper we have carried out molecular dynamics simulation of the low-energy Ar ion irradiation of nanoporous homogeneous material with different porosity and pore sizes. Our results demonstrate that in a model with small pores (Rpore = 0.8 nm) and relatively low (22%) porosity, the pores at near-surface layers collapsed due to the ion bombardment, whereas in a model with larger pores (Rpore = 2.8 nm) and higher (44%) porosity no significant structural changes occurred under the same irradiation conditions. To study thermal stability of porous structures and to reveal the effects of both the pore radius and the porosity on pore collapsing, our nanoporous structures were subjected to gradual heating. The simulation results demonstrate distinct mechanisms of structural changes in the nanoporous materials depending on the value of the excess surface energy per unit volume.
关键词： low-k dielectrics,plasma treatment,nanoporous material,pore collapse,sputtering
更新于2025-09-23 15:23:52
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Deeply subwavelength phonon-polaritonic crystal made of a van der Waals material
摘要： Photonic crystals (PCs) are periodically patterned dielectrics providing opportunities to shape and slow down the light for processing of optical signals, lasing and spontaneous emission control. Unit cells of conventional PCs are comparable to the wavelength of light and are not suitable for subwavelength scale applications. We engineer a nanoscale hole array in a van der Waals material (h-BN) supporting ultra-confined phonon polaritons (PhPs)—atomic lattice vibrations coupled to electromagnetic fields. Such a hole array represents a polaritonic crystal for mid-infrared frequencies having a unit cell volume of 10??λ?3 (with λ? being the free-space wavelength), where PhPs form ultra-confined Bloch modes with a remarkably flat dispersion band. The latter leads to both angle- and polarization-independent sharp Bragg resonances, as verified by far-field spectroscopy and near-field optical microscopy. Our findings could lead to novel miniaturized angle- and polarization-independent infrared narrow-band couplers, absorbers and thermal emitters based on van der Waals materials and other thin polar materials.
关键词： van der Waals material,near-field microscopy,phonon-polaritonic crystal,mid-infrared,hexagonal boron nitride,Bragg resonance
更新于2025-09-23 15:23:52
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Designing soft pyroelectric and electrocaloric materials using electrets
摘要： A temperature variation can electrically polarize a pyroelectric material. In its converse manifestation, the electrocaloric effect entails a change in temperature due to the application of an electric field. These phenomena have wide applications ranging from infrared detection sensors and solid-state refrigeration to energy harvesting. However, the pyroelectric–electrocaloric effect is typically observed in certain classes of hard, brittle crystalline materials that must satisfy a stringent set of lattice symmetry conditions. Some limited experiments have however demonstrated that embedding immobile charges and dipoles in soft foams (thus creating an electret state) may lead to a pyroelectric-like response as well as large deformations desired from soft matter. In this work, we develop a systematic theory for coupled electrical, thermal and mechanical responses of soft electrets. Using simple illustrative examples, we derive closed-form explicit expressions for the pyroelectric and electrocaloric coefficients of electrets. While pyroelectricity in electrets has been noted before, our derived expressions provide a clear quantitative basis to interpret (and eventually design) this effect as well as insights into how the geometrically nonlinear deformation and Maxwell stress give rise to its emergence. We present conditions to obtain a larger pyroelectric and electrocaloric response. In particular, the electrocaloric effect is predicted for the first time in such materials and we show that a proper design and a reasonable choice of materials can lead to a temperature reduction of as much as 1.5 K under the application of electrical fields of 10 MV cm?1.
关键词： material design,soft matter,theoretical framework,electrets,pyroelectricity,electrocaloric effect
更新于2025-09-23 15:23:52
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Electrically tuned microwave CP cross slot patch antenna using liquid crystal technology
摘要： The rapid progress in material science and electronic technology is great possibility in designing reconfigurable wireless devices which are frequency tunable, flexible and consume low energy. In this paper, the anisotropic propriety of a new liquid crystal mixture 'GT3-23001' in their nematic phase are exploited for designing tunable circular polarized cross slot patch antenna for WLAN applications. Reconfiguration of frequency response is controlled through an electrical external command. The proposed reconfigurable antenna based on liquid crystal satisfies a continuous frequency tuning of 15.83% with a global bandwidth of around 467.92 MHz (19.5%). to validate this novel mixture of liquid crystal, the simulated results are compared with the measured data and a good agreement is noticed.
关键词： liquid crystal mixture,Material science,tunable patch,circular polarized,reconfigurable,frequency tuning
更新于2025-09-23 15:23:52
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Effects of raw materials on NaNbO <sub/>3</sub> nanocube synthesis via the solvothermal method
摘要： A nanocube is a single nanoscale crystal with a cubic shape. Raw materials are an important factor in determining the synthesis of nanocubes. In this study, we investigated various niobium compounds that serve as raw materials, each inducing different effects during nanocube synthesis. NaNbO3 nanocubes were synthesized using a two-step process. The first step in this process, synthesis of the raw materials, was followed by solvothermal synthesis of NaNbO3 nanocubes. The raw material for the first step was obtained by applying heat treatment to a precursor following Nb hydrolysis. The heat treatment was performed at temperatures of 300°C to 1000°C. Nb2O5 was obtained after heat treatment of its precursor, during which its crystalline system morphed into hexagonal, orthorhombic, and monoclinic systems with respective increases in temperature. For the second step, we obtained various NaNbO3 morphologies via the solvothermal method using water, methanol, or ethanol as a reaction medium. NaNbO3 nanocubes were formed by applying the solvothermal method to the synthesized precursor during heat treatment at 800°C. Solvothermal synthesis was performed with methanol as the reaction medium at 200°C, which resulted in the formation of NaNbO3 nanocubes.
关键词： Raw material,Solvothermal method,Nanocube,NaNbO3
更新于2025-09-23 15:23:52