Morphology-dependent space charge polarization and dielectric relaxation of CdO nanomorphotypes

A versatile approach signifying the morphology-dependent dielectric polarization and relaxation mechanisms of cadmium oxide(CdO)nanosphere,nanoflakes and nanoparallelepiped morphotypes as a function of frequency and temperature is presented.Variation of dielectric property is observed due to the changes of space charge/interfacial polarization resulting from the variations of surface to volume ratio of nanomorphology.Accordingly,colossal dielectric constant value has been observed in CdO nano-sphere having larger surface to volume ratio.The order of dielectric constant(dc)values observed for the present nanomorphologies is:dc of sphere>dc of flakes>dc of parallelepiped resembles the order of surface to volume ratios of the present morphologies respectively.The experimental data of complex impedance values are numerically fitted using theoretical models which provide the information of role of grain resistance on dielectric polarization and Cole–Cole type mechanism of dielectric relaxation process.The activation energies for electron transport are found to be 0.087 eV for spheres,0.074 eV for flakes and 0.067 for parallelepiped nanomorphotypes of CdO.The dielectric and impedance spectroscopic analysis of the present material opens up wide scope for morphology-dependent tuning of nanomaterials for electrical applications.

Ferroelectric effect and equivalent polarization charge model of PbZr_(0.2)Ti_(0.8)O_(3)on AlGaN/GaN MIS-HEMT

PbZr_(0.2)Ti_(0.8)O_(3)(PZT)gate insulator with the thickness of 30 nm is grown by pulsed laser deposition(PLD)in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors(MIS-HEMTs).The ferroelectric effect of PZT AlGaN/GaN MIS-HEMT is demonstrated.The polarization charge in PZT varies with different gate voltages.The equivalent polarization charge model(EPCM)is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas(2DEG).The threshold voltage(V_(th))and output current density(I_(DS))can also be obtained by the EPCM.The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT.The polarization charges of PZT can be modulated by different gate-voltage stresses and the V_(th)has a regulation range of 4.0 V.The polarization charge changes after the stress of gate voltage for several seconds.When the gate voltage is stable or changes at high frequency,the output characteristics and the current collapse of the device remain stable.

A simple method of extracting the polarization charge density in the AlGaN/GaN heterostructure from current-voltage and capacitance-voltage characteristics

An Ni Schottky contact on the A1GaN/GaN heterostructure is fabricated. The flat-band voltage for the Schottky contact on the A1GaN/GaN heterostructure is obtained from the forward current-voltage characteristics. With the measured capacitance-voltage curve and the flat-band voltage, the polarization charge density in the A1GaN/GaN heterostructure is investigated, and a simple formula for calculating the polarization charge density is obtained and analyzed. With the approach described in this paper, the obtained polarization charge density agrees well with the one calculated by self-consistently solving Schrodinger＇s and Poisson＇s equations.

Efficient hydrogen peroxide production enabled by exploring layered metal telluride as two electron oxygen reduction reaction electrocatalyst

It is of great interest to develop the novel transition metal-based electrocatalysts with high selectivity and activity for two electron oxygen reduction reaction(2e^(-) ORR).Herein,the nickel ditelluride(NiTe_(2)) with layered structure was explored as the 2e^(-) ORR electrocatalyst,which not only showed the highest 2e^(-) selectivity more than 97%,but also delivered a slight activity decay after 5000 cycles in alkaline media.Moreover,when NiTe_(2) was assembled as the electrocatalyst in H-type electrolyzer,the on-site yield of H_(2)O_(2) could reach up to 672 mmol h^(-1)g^(-1) under 0.45 V vs.RHE.Further in situ Raman spectra,theoretical calculation and post microstructural analysis synergistically unveiled that such a good 2e^(-) ORR performance could be credited to the intrinsic layered crystal structure,the high compositional stability,as well as the electron modulation on the active site Ni atoms by neighboring Te atoms,leading to the exposure of active sites as well as the optimized adsorption free energy of Ni to –OOH.More inspiringly,such telluride electrocatalyst has also been demonstrated to exhibit high activity and selectivity towards 2e^(-) ORR in neutral media.

Thiazoloisoindigo-based Polymer Semiconductors: Synthesis,Structure-Property Relationship, Charge Carrier Polarity, and Field-Effect Transistor Performance

Developing new polymeric semiconductors with excellent device performance is essential for organic electronics. Herein, we synthesized two new thiazoloisoindigo(Tz II)-based polymers, namely, P(Tz II-d Th-d Th) and P(Tz II-d Th-d Tz), by copolymerizing thiophene-flanked Tz II with bithiophene and bithiazole, respectively. Owing to the more electron-deficient nature of bithiazole than bithiophene, P(Tz II-d Th-d Tz)possesses deeper LUMO/HOMO levels of-3.45/-5.47 e V than P(Tz II-d Th-d Th)(-3.34/-5.32 e V). The organic field-effect transistor(OFET) devices based on P(Tz II-d Th-d Th) exhibited p-type behaviors with an average hole mobility value as high as 1.43 cm^(2)·V^(-1)·s^(-1), while P(Tz II-d Th-d Tz)showed typical ambipolar characteristics with average hole and electron mobilities of 0.38 and 0.56 cm^(2)·V^(-1)·s^(-1). In addition, we compared the performances of both polymers with other Tz II-based polymers reported in our previous work, and showed that the charge carrier polarity can be manipulated by adjusting the number of the thiophene units between the acceptor unit. As the increase of the number of thiophene rings,charge carrier polarity shifts from electron-dominated ambipolar transport to hole-dominated ambipolar transport and then to unipolar hole transport in OFETs, which provides an effective molecular design strategy for further optimization of polymer OFET performance.

Experimental realization to efficiently sort vector beams by polarization topological charge via Pancharatnam–Berry phase modulation

This paper reports the experimental realization of efficiently sorting vector beams by polarization topological charge(PTC). The PTC of a vector beam can be defined as the repetition number of polarization state change along the azimuthal axis, while its sign stands for the rotating direction of the polarization. Here, a couple of liquid crystal Pancharatnam–Berry optical elements(PBOEs) have been used to introduce conjugated spatial phase modulations for two orthogonal circular polarization states. Applying these PBOEs in a 4-f optical system,our experiments show the setup can work for PTC sorting with a separation efficiency of more than 58%. This work provides an effective way to decode information from different PTCs, which may be interesting in many fields, especially in optical communication.

Effects of mechanical loadings on the performance of a piezoelectric hetero-junction

A fully-coupled model for a piezoelectric hetero-junction subjected to a pair of stresses is proposed by discarding the depletion layer approximation.The effect of mechanical loadings on PN junction performance is discussed in detail.Numerical examples are carried out for a p-Si/ZnO-n hetero-junction under a pair of stresses acting on the ntype ZnO portion near the PN interface,where ZnO has the piezoelectric property while Si is not.It is found that the bottom of conduction band is lowered/raised near the two loading points due to the decrease/increase in the electron potential energy there induced by a tensile-stress mode via sucking in majority-carriers from two outside regions,which implies appearance of a potential barrier and a potential well near two loading points.Furthermore,the barrier height and well depth gradually become large with increasing tensile stress such that more and more electrons/holes are inhaled in loading region from the n-/p-zone,respectively.Conversely,rising/dropping of conduction band bottom is brought out near the two loading points by a compressive-stress mode due to the increase/decrease in the potential energy of electrons by pumping out the majority-carriers from the loading region to the two outside regions.Therefore,a potential well and a potential barrier are induced near the two loading points,such that more and more electrons/holes are driven away from the loading region to the n-zone/p-zone,respectively,with the increasing compressive stress.These effects are important to tune the carrier recombination rate near the PN interface.Thus,the present study possesses great referential significance to piezotronic devices.

Recent advances in cathode catalyst architecture for lithium–oxygen batteries

Lithium–oxygen(Li–O_(2))batteries have great potential for applications in electric devices and vehicles due to their high theoretical energy density of 3500 Wh kg^(-1).Unfortunately,their practical use is seriously limited by the sluggish decomposition of insulating Li_(2)O_(2),leading to high OER overpotentials and the decomposition of cathodes and electrolytes.Cathode electrocatalysts with high oxygen reduction reaction(ORR)and oxygen evolution re-action(OER)activities are critical to alleviate high charge overpotentials and promote cycling stability in Li–O_(2)batteries.However,constructing catalysts for high OER performance and energy efficiency is always challenging.In this mini-review,we first outline the employment of advanced electrocatalysts such as carbon materials,noble and non-noble metals,and metal–organic frameworks to improve battery performance.We then detail the ORR and OER mechanisms of photo-assisted electrocatalysts and single-atom catalysts for superior Li–O_(2)battery performance.Finally,we offer perspectives on future development directions for cathode electrocatalysts that will boost the OER kinetics.

Magnetic manganese-based composites with multiple loss mechanisms towards broadband absorption

The weak dielectric properties and the lack of magnetic loss of manganese-based absorbers are obstructed as the new generation of electromagnetic wave absorption(EMA)materials applying in microelectronic devices.Herein,the sulfuration and subsequent compounding strategies have been employed to enhance the EMA performance of multi-shell nanosphere-shaped Mn_(2)O_(3)materials.With the narrow bandgap,the as-obtained MnS possesses reinforced electrical conductivity,which is conducive to conductivity loss.More importantly,the presence of potential difference between different phases will form space charge region at the heterogeneous interface,thus favoring interfacial polarization.Additionally,the improvement of magnetic loss is attributed to the presence of Co_(3)O_(4)nanoparticles.Consequently,the composites present enhanced EMA performance than original Mn_(2)O_(3).Specifically,the minimum reflection loss of as-prepared composites is−51.4 dB at the thickness of 1.8 mm and the broad effective absorption bandwidth reaches 6.2 GHz at 1.9 mm.The low matching thickness and high absorption efficiency in this work can provide a convincing reference when designing distinguished manganese-based absorbers.

Ultralow specific ON-resistance high-k LDMOS with vertical field plate

An ultralow specific on-resistance high-k LDMOS with vertical field plate（VFP HK LDMOS） is proposed. The high-k dielectric trench and highly doped interface N＋ layer are made in bulk silicon to reduce the surface field of the drift region in the VFP HK LDMOS. The gate vertical field plate（VFP） pinning in the high-k dielectric trench can modulate the bulk electric field. The high-k dielectric not only provides polarized charges to assist depletion of the drift region, so that the drift region and high-k trench maintain charge balance adaptively,but also can fully assist in depleting the drift region to increase the drift doping concentration and reshape the electric field to avoid premature breakdown. Compared with the conventional structure, the VFP HK LDMOS has the breakdown voltage of 629.1 V at the drift length of 40 μm and the specific on-resistance of 38.4 mΩ·cm^2 at the gate potential of 15 V. Then the power figure of merit is 10.31 MW/cm^2.