Carbon dots/ZnO quantum dots composite based white phosphors for white light-emitting diodes

A facile synthesis approach to prepare eco-friendly white fluorescent carbon dots (CDs)/ZnO quantum dots (QDs) composites through electrostatic force was proposed, which can be used for fabrication of high-performance white...

Insight into the stacking and the species-ordering dependences of interlayer bonding in SiC/GeC polar heterostructures

Two-dimensional (2D) polar materials experience an in-plane charge transfer between different elements due to their electron negativities. When they form vertical heterostructures, the electrostatic force triggered by such charge transfer plays an important role in the interlayer bonding beyond van der Waals (vdW) interaction. Our comprehensive first principle study on the structural stability of the 2D SiC/GeC hybrid bilayer heterostructure has found that the electrostatic interlayer interaction can induce the π-π orbital hybridization between adjacent layers under different stacking and out-of-plane species ordering, with strong hybridization in the cases of Si-C and C-Ge species orderings but weak hybridization in the case of the C-C ordering. In particular, the attractive electrostatic interlayer interaction in the cases of Si-C and C-Ge species orderings mainly controls the equilibrium interlayer distance and the vdW interaction makes the system attain a lower binding energy. On the contrary, the vdW interaction mostly controls the equilibrium interlayer distance in the case of the C-C species ordering and the repulsive electrostatic interlayer force has less effect. Interesting finding is that the band structure of the SiC/GeC hybrid bilayer is sensitive to the layer-layer stacking and the out-of-plane species ordering. An indirect band gap of 2.76 eV (or 2.48 eV) was found under the AA stacking with Si-C ordering (or under the AB stacking with C-C ordering). While a direct band gap of 2.00 eV – 2.88 eV was found under other stacking and species orderings, demonstrating its band gap tunable feature. Furthermore, there is a charge redistribution in the interfacial region leading to a built-in electric field. Such field will separate the photo-generated charge carriers in different layers and is expected to reduce the probability of carrier recombination, and eventually give rise to the electron tunneling between layers.

Flexible Vibrotactile Actuator Based on Dielectric Elastomer for Smart Handheld Devices

This paper presents an electroactive and soft vibrotactile actuator based on a dielectric elastomer. The vibrotactile actuator is composed of an upper layer, an adhesive tape layer, a dielectric layer with bumps, and a lower layer. When a voltage is applied to the actuator, an electrostatic force created between the upper and lower layers pulls the upper layer down, compressing the dielectric layer. As soon as the applied voltage is released, the upper layer is quickly restored to its initial state by the elastic force of the compressed dielectric elastomer. Because two forces contribute to the actuation at the same time, the created vibration is sufficiently strong to stimulate human mechanoreceptors. When the applied voltage is removed, the upper layer and dielectric elastomer return to their initial shapes. We conducted experiments to determine the best weight ratio of polydimethylsiloxane (PDMS) and Ecoflex, and to quantitatively investigate the haptic performance of the proposed vibrotactile actuator. The experiments clearly show that the plasticized vibrotactile actuator can create a variety of haptic sensations over a wide frequency range.

Study of a MOEMS XOR gate based on optical ring resonator

Based on ring resonator with Microelectromechanical systems, optical XOR logic gate is proposed in this paper to realize the optical logic gate application. The proposed gate is basically structured on an optical ring resonator with 7µm radius and resonance wavelength of 1.55µm which is placed on the edge of a thin SiC circular diaphragm. In order to apply input voltages to electrodes, two very thin circular gold layers with 50nm air gap spacing are deposited under the diaphragm. Input voltages are considered as logic inputs and resonance wavelength shift as logic output. When an input DC voltage is applied across the diaphragm, an attractive electrostatic force is created between two electrodes. As a result, the diaphragm is deformed and an internal stress is created. This in turn changes the resonator refractive index due to the photoelastic effect and thus shifts its resonance wavelength about 35nm. COMSOL Multiphysics and MATLAB are carried out to verify FEA and numerical analysis of the designed structure, respectively. A good agreement between the simulations and analytical results is obtained. Enhancement of the wavelength shift and FSR are resulted. The proposed structure is used as an optical XOR gate for the first time.

Mechano-Triboelectric Analysis of Surface Charge Generation on Replica-Molded Elastomeric Nanodomes

Replica molding-based triboelectrification has emerged as a new and facile technique to generate nanopatterned tribocharge on elastomer surfaces. The “mechano-triboelectric charging model” has been developed to explain the mechanism of the charge formation and patterning process. However, this model has not been validated to cover the full variety of nanotexture shapes. Moreover, the experimental estimation of the tribocharge’s surface density is still challenging due to the thick and insulating nature of the elastomeric substrate. In this work, we perform experiments in combination with numerical analysis to complete the mechano-triboelectrification charging model. By utilizing Kelvin probe force microscopy (KPFM) and finite element analysis, we reveal that the mechano-triboelectric charging model works for replica molding of both recessed and protruding nanotextures. In addition, by combining KPFM with numerical electrostatic modeling, we improve the accuracy of the surface charge density estimation and cross-calibrate the result against that of electrostatic force microscopy. Overall, the regions which underwent strong interfacial friction during the replica molding exhibited high surface potential and charge density, while those suffering from weak interfacial friction exhibited low values on both. These multi-physical approaches provide useful and important tools for comprehensive analysis of triboelectrification and generation of nanopatterned tribocharge. The results will widen our fundamental understanding of nanoscale triboelectricity and advance the nanopatterned charge generation process for future applications.

Investigation of an electrostatically actuated imperfect circular microplate under transverse pressure for pressure sensor applications

In this paper, we present static and dynamic analysis of an electrostatically actuated imperfect circular microplate under transverse pressure. In modelling of the microplate, we have included both von Kármán geometric and electrostatic force nonlinearities in the development of the equation of motion. The equation of motion has been solved using Galerkin based reduced order modelling technique. The developed reduced order model has been first validated by comparing it with finite element simulation results. Further, the effects of imperfection as initial curvature and uniform transverse pressure have been investigated on the static and dynamic characteristics of the electrostatically actuated circular microplate. We have also investigated the effects of imperfection and applied DC voltage on the pressure sensitivity of the circular microplate. We have found that both imperfection and electrostatic load are responsible for appreciable variations in sensitivity. This detailed investigation is useful to design an imperfect micro pressure sensor.

Modification of Magnetic Graphene Oxide By An Earth-Friendly Deep Eutectic Solvent To Preconcentrate Ultratrace Amounts Pb(II) In Oil Seeds

The aim of this article is presenting an earth-friendly deep eutectic solvent (DES) to preconcentrate ultratrace amounts of Pb(II) prior to its quantification by flame atomic adsorption spectroscopy. The synthesis of adsorbent started by preparing graphene oxide according to the modified Hammer’s method, followed by magnetization by Fe3O4 nanohemispheres. Magnetic graphene oxide was dispersed in a mixture of LiCl and urea at 60° via ultrasonication. All the materials are environmentally-friendly and the preparation strategy is energy efficient. X-ray diffraction, scanning electron microscopy, alternating gradient force magnetometer and Fourier-transform infrared spectroscopy were applied to characterize the products. Graphene oxide has a large surface area and could be functionalized with DESs through π-π interaction and electrostatic force. Urea has active negative sites, which garb heavy metals due to the interaction between negative and positive agents. Accordingly, this adsorbent (UreaLiCl-mGO) could be offered as a capable adsorbent to preconcentrate ultratrace amounts of Pb(II). Conditions were optimized, and under the optimum situation, (a) limit of detection of 99 × 10-8 g L-1, (b) relative standard deviation (n=5) of 1.3%, (c) preconcentration factor of 100 (d) linearity of dynamic range of 5.0 × 10-6 – 23 × 10-6 g L-1, (e) durability of 6 months and (f) reusability of 7 times prove applicability of the adsorbent. The tests of selectivity, effect of interference ions, swelling property, isotherm of adsorption, kinetic of adsorption and thermodynamic of adsorption were completely investigated. Four different oil seeds were successfully applied as real samples.