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Phase transition is expected in designing high-performance electrocaloric effect (ECE). However, hidden antiferroelectricity in NaNbO3-based ceramics complicates ECE evolution as compared to conventional ferroic materials. Therefore, a NaNbO3− xBi0.5Li0.5TiO3 ( x = 0.08, 0.10, and 0.12) system is introduced to explore ECE performance in P ( Pbma), Q ( P21ma), and R ( Pnma) phases since a Bi0.5Li0.5TiO3 dopant plays a Janus role in stabilizing ferroelectric Q ( x = 0.08 and 0.10) and inducing the antiferroelectric (AFE) relaxor R phase ( x = 0.12). Rietveld refinement reveals a phase structure change from the P/ Q to R state. Bi0.5Li0.5TiO3 addition makes a downshift of P-to- R transition temperature accompanied by an increase in relaxation property, as certified by dielectric analysis/piezoelectric force images, in situ XRD/Raman spectra, and ferroelectric tests. Additionally, a square P–E loop evolves into less-sharp and finally changes into a slant one with increasing Bi0.5Li0.5TiO3 content. ECE is directly measured, and its peak value increases from 0.15 K for x = 0.08 and 0.21 K for x = 0.10 and finally to 0.11 K for x = 0.12 composition. Interestingly, dual ECE peaks appear in x = 0.10, and it is probably contributed by R relaxor polar nanodomains. This work not only clarifies actual ECE behavior in AFE orthorhombic ( P/ R) NaNbO3-based ceramics but also fulfills understandings of AFE P-to- R transitions in modulating ECE.

All-solid-state lithium-metal batteries have been regarded as the next-generation energy storage due to the potential high safety and high energy density. However, for oxide solid electrolytes (SEs), the relatively low ionic conductivities and the growth of lithium dendrite leading to safety issues limit their commercialization. Here, we systematically investigate the influences of external magnetic field on electrochemical performances of oxide SEs. It reveals that the magnetic field can improve ionic conductivity of SEs and the cycle performance in Li symmetric cells. The enhanced performance is because the magnetohydrodynamics effect can promote diffusion in SEs and homogenize distribution of lithium deposition to avoid the propagation of lithium dendrite. This strategy can be extent to other types of SEs or various energy applications.

TiO2 is regarded as a promising anode for all-solid-state thin film lithium-ion microbatteries due to its high temperature tolerance, good chemical stability, and desirable structural stability. However, its application in thin film batteries has been plagued by its low actual capacity and poor rate capability. Herein, a TiO2 thin film with a unique amorphous-crystalline heterostructure (AC-TO) is prepared by magnetron sputtering at room temperature. The heterostructure design of AC-TO not only takes advantage of faster Li+ diffusion of an amorphous phase and higher electric conductivity of a crystalline phase but also reaps the benefit of fast ion transport, fast electron transfer, and additional lithium storage at the hetero-interfaces, resulting in boosted lithium storage performance. When tested in all-solid-state thin film lithium batteries, the AC-TO based device exhibits an obviously higher reversible specific capacity (204 at 50 mA g−1) than the amorphous TiO2 based device (103 mAh g−1) and the crystalline anatase based device (147 mAh g−1), as well as good rate capability (73 at 1600 mA g−1) and excellent cycling stability (nearly no capacity loss after 400 cycles). This work provides an instructive structural regulation strategy for developing advanced thin-film electrodes for all-solid-state microbatteries.

A chiral soliton lattice (CSL) is a topological spin-texture that has potential applications in next-generation spintronic devices. In this work, we performed angle-dependence of magnetization and electron spin resonance (ESR) investigations on the CSL host Yb(Ni1− xCu x)3Al9 with x = 0.06 (YNCA). The angle-dependent magnetization reveals a peculiar variable magnetic anisotropy. The maximum magnetization axis is parallel to the ab-plane below the field of ∼35.7 kOe while shifts to the c-axis at higher fields. The microwave responses of the CSL helicoid and ferromagnetic resonance (FMR) of the forced ferromagnetic state (FFM) are observed and appear as two resonance lines on ESR spectra with the highest intensities in the ab-plane. When the external field is rotated from [Formula: see text] to [Formula: see text], the resonance field [Formula: see text] corresponding to the CSL helicoid decreases while [Formula: see text] correlated with the FMR increases. Furthermore, the temperature-dependent ESR shows that the CSL persists until 15 K much higher than TC (6.4 K), which suggests a precursor phenomenon. The microwave response in YNCA provides a powerful tool for modulating and researching the CSL.

Realizing dynamic regulation of specific optical components while being easy to integrate with photonic circuits will have a revolutionary impact on tunable laser sources, active filters, and all-optical switching/integration. Here, we demonstrate a temperature tunable Ga-doped ZnO microresonator with a conductivity of ∼1.75 S/cm controlled by the injection current and realize point-to-point heating. The shift in the resonant wavelength with a tuning range of 2 nm for TE66 mode is achieved by the effect of current-induced temperature rising on the refractive index of the microresonator crystal, namely, the thermo-optic effect. Meanwhile, the thermo-optic coefficient of 16.7 × 10−4/K around the bandgap energy of ZnO is also obtained. This operating mode of electronically controlled temperature establishes a solid foundation for the practicality and integration of tunable lasers.

Bulk PtBi2 has attracted much attention for its topological semi-metallic electronic properties and highly promising applications in spintronics. Here, we report large spin–orbit torque (SOT) efficiency in the sputtered PtBi2 alloy with the trigonal-phase. From spin–torque-induced ferromagnetic resonance measurements, the SOT efficiency of 5 nm PtBi2 is estimated to be ∼0.2. Moreover, the spin Hall conductivity of PtBi2 [∼1 × 105 ℏ/2e (Ω m)−1] is comparable to that of topological materials, such PtTe2 and Bi2Te3. The PtBi2 film has much lower resistance than that of Bi-based topological materials, which makes it a useful candidate for application. The results suggest that the PtBi2 alloy is promising for applications in magnetic memory and logic devices driven by SOT.

Natural gas is useful for the transition from traditional fossil fuels to renewable energies. The consumption of liquid natural gas has been rising, and the demand is predicted to double by 2040. In this context, magnetocaloric gas liquefaction, as an emerging and energy-saving technology, could be an alternative to the traditional gas-compression refrigeration. In this work, we report a large magnetic entropy change of 7.42 J/kg K under a magnetic field change of 2 T in Nd2In at 109 K, which is near the boiling temperature of natural gas of 112 K. The maximum adiabatic temperature change reaches 1.13 K under a magnetic field change of 1.95 T and is fully reversible. The magnetic phase transition is confirmed to be of the first-order type with the negligible thermal hysteresis. Further investigations on the thermal expansion and the magnetostriction reveal that the magnetic transition undergoes two stages with a negligible volume change. The longitudinal strain increases with magnetic fields and then decreases. These interesting properties are useful for the practical design of a magnetocaloric natural gas liquefaction system and for the fundamental understanding of the phase transitions in other RE2In intermetallics.

An indium-containing layer positioned underneath the InGaN/GaN quantum well (QW) active region is commonly used in high efficiency blue light-emitting diodes. Recent studies proposed that the role of this underlayer is to trap surface defects (SDs), which, otherwise, generate non-radiative recombination centers in the QWs. However, the origin and the nature of these defects remain unknown. Our previous study revealed that high-temperature growth of GaN promotes SD creation. In this work, we investigate the impact of the GaN-buffer growth temperature on the InGaN/GaN QW efficiency. We show that the 300 K photoluminescence decay time of a single QW deposited on 1- μ m-thick GaN buffer dramatically decreases from few ns to less than 100 ps when the GaN buffer growth temperature is increased from 870 °C to 1045 °C. This internal quantum efficiency collapse is ascribed to the generation of SDs in the GaN buffer. A theoretical study of temperature-dependent defect formation energy in GaN suggests that these SDs are most likely nitrogen vacancies. Finally, we investigate the formation dynamics of SDs and show that they are mainly generated at the early stage of the GaN growth, i.e., within 50 nm, and then reach a steady state concentration mainly fixed by the GaN growth temperature.

Bi2Te3 films always exhibit n-type transport characteristics even under the Bi-rich condition, which, however, was not clarified clearly. Herein, by virtue of advanced techniques such as scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, scanning transmission electron microscopy, and x-ray photoelectron spectroscopy, we are able to identify the structural evolution on the atomic scale for Bi-rich Bi2Te3 films. The excess of Bi content will lead to the formation of p-type BiTe antisite defects; however, there is a doping limit for the excess of Bi to form BiTe antisites. Beyond this limit, the excess of Bi will form the n-type Bi2 planar defects in the van der Waals gap, the excellent electron donors, which can enhance the electron density by over one order of magnitude and up to the 1021 cm−3 range for Bi-rich Bi2Te3 films. Benefiting from the remarkable increase in the electron density and the suppression of carrier intrinsic excitations, Bi2Te3 films with Bi2 planar defects possess a much improved thermoelectric power factor, with a maximum value of 1.4 mW m−1 K−2 at 450 K, showing about 130% enhancement compared to that of the film without Bi2 intercalations. The discovery opens a new avenue to improve the thermoelectric properties of Bi2Te3 films utilizing the Bi2 planar defects.

We prepared a splicing structure by using electron beam lithography, in which Pt and Ta were spliced together as the spin source upon perpendicularly magnetized Pt/Co/Pt heterostructures. It is found that Pt and Ta can modulate both spin–orbit torque and Dzyaloshinskii–Moriya interaction on the same magnetic layer, respectively. The four-state magnetization switching is achieved with the combinations of two spliced parts, which is observed by using a magneto-optical Kerr microscope. The initial nucleation position determines the chirality. The Pt side stabilizes a right-hand Neel domain wall and the Ta side stabilizes a left-hand Neel domain wall. Our study provides a method for further increasing the storage density and studying spin–orbit torque laterally.

Alloying a heavy metal (HM) layer is a useful approach to enhance the current-spin converting efficiency ξSH while keeping a relatively low resistance for spin–orbit torque (SOT) based devices. In this work, we report the enhancement of ξSH and nonlinear modification of the Dzyaloshinskii–Moriya interaction (DMI) by alloying Pt with Cr in a Pt100-xCrx/Co/AlOx trilayer. The maximum of ξSH is found at the composition of Pt75Cr25. At the compositions of Pt75Cr25 and Pt50Cr50, the DMI constant |D| is strongly shifted in the opposite sign, implying ferromagnetic coupling and antiferromagnetic coupling existing in the heavy metal layer can both influence the DMI. Finally, the current-driven switching behavior is observed by the magneto-optical effect. This work shows that adjusting the composition of the magnetic alloyed HM layer is an efficient approach to obtain an optimized SOT performance.

Interactions among various film growth parameters, such as the substrate temperature (Tsub), film thickness (d), and composition, play a crucial role in controlling the type and density of the intrinsic point defects. In turn, the point defects modulate and control electronic transport properties of Bi2Te3 films. We have grown n-type Bi2Te3 films with different d by molecular beam epitaxy at different Tsub. The formation of point defects was analyzed by a combined use of angle-resolved photoelectron spectroscopy (ARPES) and electronic transport measurements. Two important findings were made: (i) the negatively charged vacancies, V Te · ·, initially the dominant intrinsic defects, transform gradually during the growth process into positively charged anti-site defects, B i Te ′, driven by thermal annealing from a continuously heated substrate; and (ii) from the film's surface into the inner strata of the film, the density of V Te · · decreases while the density of B i Te ′ increases, leading to a gradient of vacancies and anti-site defects along the film growth direction. As a result, the electron density in Bi2Te3 films decreases monotonically with increasing d. Moreover, elevating Tsub leads to a more significant in situ annealing effect and an eventual onset of intrinsic excitations that deteriorates electronic transport properties. The thinnest Bi2Te3 film (16 nm) grown at Tsub = 245 °C has the highest electron concentration of 2.03 × 1020 cm−3 and also the maximum room temperature power factor of 1.6 mW m−1 K−2 of all grown epitaxial films. The new insights regarding the defect formation and transformation pave the way for further optimization of electronic transport properties of n-type Bi2Te3-based films.

Chiral magnetic soliton (CMS), an isolated topological kink consisting of spins, has potential applications in spintronics. In this work, the microwave response of layered MnNb3S6, which is suggested as a candidate for CMS, is investigated by the electronic spin resonance (ESR). Angle-dependent ESR spectra show that the microwave response is strong for H ⊥ c while it is weak for H / / c, where c is the c-axis of the single crystal. When H ⊥ c, two resonance lines are observed, which are marked as H r 1 for the higher field and H r 2 for the lower field. It is determined that H r 1 originates from the ferromagnetic resonance of forced ferromagnetic moments, which evolves into paramagnetic resonance above TC. Meanwhile, H r 2 existing only below TC fulfills the Goldstone excitation of CMS. The microwave response of MnNb3S6 supports the existence of CMS in MnNb3S6, and is proved to be an effective means for modulating and investigating CMS.

We study the impact of non-radiative defects on Auger recombination in c-plane InGaN/GaN single quantum wells (SQWs) in the efficiency droop regime using high injection time-resolved photoluminescence. The defect density in the SQW is controlled by tuning the thickness of an InAlN underlayer. When the defect density is increased, apart from Shockley-Read-Hall (SRH) and standard Auger recombination, introducing an extra defect-assisted Auger process is required to reconcile the discrepancy observed between the usual ABC model and experimental data. We derive a linear dependence between the SRH coefficient and the bimolecular defect-assisted Auger coefficient, which suggests that the generated defects can act as scattering centers responsible for indirect Auger processes. In particular, in defective SQWs, the defect-assisted Auger recombination rate can exceed the radiative one. Our results further suggest that the defect-assisted Auger recombination is expected to be all the more critical in green to red III-nitride light-emitting diodes due to their reduced radiative rate.

We investigate the spin–orbit torque (SOT) induced magnetization switching in the Pt/CoFe structure via inserting NiO or MgO interlayers. The effective spin Hall angles are enhanced by inserting a NiO layer and decreased by a MgO interlayer, through the harmonic Hall measurement. Both the MgO and NiO interlayers decrease the critical switching current and the minimum in-plane field required for completely switching, which is decreased down to about 50 Oe for a sample with MgO and 25 Oe for a sample with NiO. This originates from the reduction of the Dzyaloshinskii-Moriya interaction by inserting the oxide interlayers, which is confirmed by the Kerr images for the switching process. We confirm that the oxide interlayer is an efficient way to modify the SOT-induced magnetization switching and reveal the possibility of the SOT-induced switching for double MgO-based perpendicular magnetic tunneling junctions.

Magnetic skyrmions, a kind of localized spin texture topologically protected in magnetic materials, characterized by smaller size and much lower manipulating current density in comparison with ferromagnetic domain walls, are highlighted as potential information carriers for high-density magnetic storage devices. For technological applications, the stabilization of skyrmions in a temperature range around room temperature under a low magnetic field is essential. Here, we demonstrate the formation of magnetic biskyrmions in a low magnetic field at room temperature in a centrosymmetric hexagonal MnPdGa magnet via Lorentz transmission electron microscopy in combination with transport and magnetic measurements. High-density biskyrmions are generated at 300 K in a magnetic field of 0.15 T. In addition, biskyrmions can be generated from ferromagnetic domains and partly remained at zero field when the magnetic field is decreased. A large topological Hall resistivity is observed near room temperature. Furthermore, a wide temperature and magnetic-field window for biskyrmions is deduced from transport and magnetic properties. The simultaneous features of high-density and low magnetic field near room temperature in a single-component material make MnPdGa a promising candidate for future skyrmion-based topological spintronic applications.

The effect of an ultrathin W interlayer on the perpendicular magnetic anisotropy (PMA), spin orbit torque (SOT), and SOT-induced magnetization switching of Ta/CoFeB/MgO films has been investigated. Both the anisotropy energy density and the spin-torque efficiency are enhanced by inserting the ultrathin W interlayer. The results suggest that the large enhancement of the spin-torque efficiency originates from the increase in the interfacial spin transparency using a simplified drift-diffusion model. The minimum in-plane field required for SOT-induced complete switching is reduced to 12 Oe for the sample with the W interlayer, which is confirmed by polar Kerr microscopy. The reversed domain nucleation and propagation of the reversal processes have been observed by Kerr imaging. It is concluded that the ultrathin W interlayer increases the spin transmission and reduces the strength of the Dzyaloshinskii–Moriya interaction. Our result suggests that the interface modification is an efficient way to modulate the PMA and SOT.

We report dynamic magnetotransport measurements in a ballistic quantum point contact (QPC) at gigahertz frequencies. We observed a gate-controlled crossover of the magnetoadmittance from the partially diffusive boundary scattering effect to weak localization. Moreover, the charge relaxation time of this mesoscopic circuit shows similar behaviors, indicating that the density of states of QPC channels is also sensitively adjusted by the boundary scattering in addition to their transmission. Our experiment demonstrates that boundary scattering plays a dominant role in the dynamic transport in a ballistic QPC and could influence the coherent dynamics in other QPC-based phase-coherent systems such as the quantum dots and qubits.

In this letter, we investigated light-induced negative differential resistance (L-NDR) effects in a hybrid photodiode formed by a graphene-silicon (GS) junction and a neighboring graphene-oxide-Si (GOS) capacitor. We observed two distinct L-NDR effects originating from the gate-dependent surface recombination and the potential-well-induced confinement of photo-carriers in the GOS region. We verified this by studying the gate-controlled GS diode, which can distinguish the photocurrent from the GS region with that from the GOS region (gate). A large peak-to-valley ratio of up to 12.1 has been obtained for the L-NDR due to gate-dependent surface recombination. Such strong L-NDR effect provides an opportunity to further engineer the optoelectronic properties of GS junctions along with exploring its potential applications in photodetectors, photo-memories, and position sensitive devices.

Using metal oxides to form a carrier-selective interface on crystalline silicon (c-Si) has recently generated considerable interest for use with c-Si photovoltaics because of the potential to reduce cost. n-type oxides, such as MoO3, V2O5, and WO3, have been widely studied. In this work, a p-type oxide, Cu-doped NiO (NiO:Cu), is explored as a transparent hole-selective contact to n-Si. An ultrathin SiOx layer, fabricated by a wet-chemical method (wet-SiOx), is introduced at the NiO:Cu/n-Si interface to achieve a tunnelling junction solar cell. Interestingly, it was observed that the interface quality of the NiO:Cu/wet-SiOx/n-Si heterojunction was dramatically enhanced by post-deposition annealing (PDA) at a temperature of 200 °C. Our device exhibits an improved power conversion efficiency of 10.8%, which is the highest efficiency among NiO/Si heterojunction photo-electric devices to date. It is demonstrated that the 200 °C PDA treatment enhances the built-in field by a reduction in the interface density of states (Dit) but does not influence the work function of the NiO:Cu thin layer. This stable work function after the PDA treatment is in conflict with the changed built-in field according to the Schottky model. Thus, the Bardeen model is introduced for this physical insight: the enhancement of the built-in field originates from the unpinning of the Fermi levels of NiO:Cu and n-Si by the interface state reduction.

SnSe single crystals have been widely studied lately as a result of their record high ZT and controversial low thermal conductivity. Much research has focused on the high-temperature properties of single crystals and polycrystalline SnSe, but few studies were carried out on the low-temperature properties of doped single-crystalline SnSe. To study the mechanism of the charge carrier and phonon scattering, and to eliminate the ambiguity of the high temperature thermal conductivity measurement, we performed low temperature transport characterization of Na-doped and Ag-doped single-crystalline SnSe by a longitudinal steady-state technique. The electronic transport property measurements suggest that Na is a more efficient p-type dopant in SnSe than Ag. In the thermal conductivity data, we observe pronounced dielectric peak around 10 K with magnitude dependent on the doping level. In the p-type doped samples, we found that our room temperature lattice thermal conductivities (>1.74 W m−1 K−1) are in general higher than those previously reported. Based on these findings, our study implies that the lattice thermal conductivity values of doped and pure single-crystalline SnSe were underestimated.SnSe single crystals have been widely studied lately as a result of their record high ZT and controversial low thermal conductivity. Much research has focused on the high-temperature properties of single crystals and polycrystalline SnSe, but few studies were carried out on the low-temperature properties of doped single-crystalline SnSe. To study the mechanism of the charge carrier and phonon scattering, and to eliminate the ambiguity of the high temperature thermal conductivity measurement, we performed low temperature transport characterization of Na-doped and Ag-doped single-crystalline SnSe by a longitudinal steady-state technique. The electronic transport property measurements suggest that Na is a more efficient p-type dopant in SnSe than Ag. In the thermal conductivity data, we observe pronounced dielectric peak around 10 K with magnitude dependent on the doping level. In the p-type doped samples, we found that our room temperature lattice thermal conductivities (>1.74 W m−1 K−1) are in general high...

A piezoelectric nanogenerator based on poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] nanofibers with an Au interdigital electrode (IDT)/P(VDF-TrFE) nanofiber film/well-ordered cylindrical cavity structure was prepared by combining Au IDTs with a rotary collector to obtain highly aligned P(VDF-TrFE) nanofiber arrays. The Au IDTs work not only as parallel electrodes to collect P(VDF-TrFE) nanofibers during electrospinning but also as charge-collecting electrodes in the nanogenerator. The well-ordered cylindrical cavities improve output performance by enhancing the deformation of P(VDF-TrFE) nanofiber films when subjected to external force. The nanogenerator performs well; as an example of application, we demonstrate energy harvesting from human walking, with a peak output voltage of 5 V and a peak short-circuit current of 1.2 μA. Such a device could have practical applications in wearable, self-powered devices.

SiC has amazing electromagnetic wave absorption properties based on its excellent dielectric properties. The optimized N-doping nano-SiC with in-situ tailored morphology by a facile one-step synthesis strategy is presented. By using a new N source and gas catalyst, acetonitrile ( C2H3N) was exploited to synthesize N-doped nano-SiC with an evolution of morphology from spherical to nanoflake. The surface area of the nanoflake SiC is significantly expanded to support more quantity and types of electric dipoles. Combining the optimized N concentration doping, the complex dielectric and microwave absorption properties of the tailored nano-SiC are clearly improved in the 2–18 GHz range when compared to previously reported SiC and N-doped SiC nanoparticles. The higher e″ and tan δ values are attributed to fortified polarization relaxation by optimized N-doping and novel nanoflake morphology. A wideband reflection loss exceeding –10 dB (90% microwave absorption) reached 4.1 GHz with an absorber thickness of 1.58 mm. A minimum value of −42 dB at 8 GHz was also achieved. The mechanism of dielectric loss of nanoflake N-doped SiC is discussed in detail.

The detailed crystal structure and antiferromagnetic properties of a 42 nm thick CaMnO3 film grown on a LaAlO3 substrate with a 9 nm La0.67Ca0.33MnO3 buffer layer have been investigated. Compared with a CaMnO3 film directly grown on a LaAlO3 substrate, only one kind of orthorhombic b axis orientation along the [100] axis of the substrate is observed in the CaMnO3 film with a La0.67Ca0.33MnO3 buffer layer. To determine the antiferromagnetic ordering type of our CaMnO3 film with a buffer layer, the first-principles calculations were carried out with the results, indicating that the CaMnO3 film, even under a tensile strain of 1.9%, is still a compensated G-type antiferromagnetic order, the same as the bulk. Moreover, the exchange bias effect is observed at the interface of the CaMnO3/La0.67Ca0.33MnO3 film, further confirming the antiferromagnetic ordering of the CaMnO3 film with a buffer layer. In addition, it is concluded that the exchange bias effect originates from the spin glass state at the La0.67Ca0.33...

We show a phase-locked array of quantum cascade lasers with an intracavity spatial filter based on the Talbot effect. All the laser arrays show in-phase operation from the threshold current to full power current with a near-diffraction-limited divergence angle. The maximum power is just about 5 times that of a single-ridge laser for an eleven-laser array device and 3 times for a seven-laser array device. The structure was analyzed by using the multi-slit Fraunhofer diffraction theory, showing very good agreement with the experimental results. Considering the great modal selection ability, simple fabricating process, and potential for achieving continuous wave operation, this phase-locked array may be a hopeful solution to obtain higher coherent power.

Magnetic vortices in patterned nanocomposite structures have been studied. A double-vortex structure consisting of two vortex cores with opposite chiralities and two edge half-vortices is realized in a micron-size circular disk, which consists of [Co/Pd]7/Ru/Py. A systemic study of the magnetization reversal of a double-vortex state and a single vortex state in an out-of-plane applied field has been performed by means of magnetic force microscopy. It is found that the interlayer exchange and dipolar interactions are critical for nucleation and annihilation of the double-vortex and the single vortex states. Micromagnetic simulations prove that the double-vortex state can stably exist in a patterned nanocomposite structure. Magnetic configurations ranging from the double-vortex and single vortex states to other multidomain states and the in-plane single-domain state are observed. The dependence of the magnetic configuration on the thickness of the soft-magnetic layer and spacer layer is presented in an expe...

A single polyethylene chain was reported to have a high metal-like thermal conductivity (TC), which stands in sharp contrast to the thermally insulating feature of common bulk polyethylene materials. This work numerically investigates the impact of torsion and stretching on the TC of polyethylene strands by using equilibrium molecular dynamics simulations. The simulation results show that torsion slightly reduces the TC of a single polyethylene chain. In contrast, the heat conduction of polyethylene strands could be slightly enhanced under torsional loading with a specific torsional angle. Particularly, an apparent improvement of TC of polyethylene strands is achieved by combining torsion and stretching functions. It is found that the TC of torsional polyethylene strands is sensitive to torsional patterns. Our study proposes a specific torsional pattern of polyethylene strands that significantly enhances the heat conduction of the original counterpart. This study will play an essential role in guiding the...

Photocathodes that provide high electron-spin polarization (ESP) and high quantum efficiency (QE) can significantly enhance the physics capabilities of electron accelerators. We report record-level QE from a high-polarization strained GaAs/GaAsP superlattice photocathode fabricated with a Distributed Bragg Reflector (DBR). The DBR photocathode technique enhances the absorption of incident laser light thereby enhancing QE, but as literature suggests, it is very challenging to optimize all of the parameters associated with the fabrication of complicated photocathode structures composed of many distinct layers. Past reports of DBR photocathodes describe high polarization but typically QE of only ∼1%, which is comparable to QE of high polarization photocathodes grown without a DBR structure. This work describes a strained GaAs/GaAsP superlattice DBR photocathode exhibiting a high polarization of 84% and significantly enhanced QE of 6.4%.

We investigate the dynamics of donor bound excitons (D degrees X-A) at T = 10K around an isolated single edge dislocation in homoepitaxial GaN, using a picosecond time-resolved cathodoluminescence (TR-CL) setup with high temporal and spatial resolutions. An similar to 1.3 meV dipole-like energy shift of D degrees X-A is observed around the dislocation, induced by the local strain fields. By simultaneously recording the variations of both the exciton lifetime and the CL intensity across the dislocation, we directly assess the dynamics of excitons around the defect. Our observations are well reproduced by a diffusion model. It allows us to deduce an exciton diffusion length of similar to 24 nm as well as an effective area of the dislocation with a radius of similar to 95 nm, where the recombination can be regarded as entirely non-radiative. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Recently, the piezotronic effect has been observed in two-dimensional single-layer MoS2 materials, which have potential applications in force and pressure triggered or controlled electronic devices, sensors, and human-machine interfaces. However, classical theory faces the difficulty in explaining the mechanism of the piezotronic effect for the top- and enclosed-contacted MoS2 transistors, since the piezoelectric charges are assumed to exist only at the edge of the MoS2 flake that is far from the electronic transport pathway. In the present study, we identify the piezoelectric charges at the MoS2/metal-MoS2 interface by employing both the density functional theory and finite element method simulations. This interface is on the transport pathway of both top- and enclosed-contacted MoS2 transistors, thus it is capable of controlling their transport properties. This study deepens the understanding of piezotronic effect and provides guidance for the design of two-dimensional piezotronic devices.

Aiming to synthesize multiferroic materials in microscale, a microfluidic device capable of generating multiferroic Janus microparticles is demonstrated. Through bonding two polydimethylsiloxane (PDMS) layers “face to face,” laminar flow containing an upper layer and a lower layer can be realized. Accordingly, poly(vinylidene fluoride-trifluoroethylene) ferroelectric polymers and Fe3O4 ferromagnetic particles are separately encapsulated in the two layers of a single droplet. Numerical simulation enables the analysis of cross-mixing between the two counterparts and helps to find an optimized location for adding subsequent ultraviolet treatment, which will polymerize the droplets into Janus particles without any side effect. By modulation of the flow rate, the size of the Janus particles can be precisely tuned. Finally, the ferroelectricity and magnetism of the Janus particles are verified by the magnetization and polarization measurements, indicating the multiferroic nature.

The realization of conducting nanostructures at the interface between LaAlO3 and SrTiO3 is an important step towards the realization of devices and the investigation of exotic physical regimes. We present here a detailed study of the conducting nanowires realized using the atomic force microscopy writing technique. By comparing experiments with numerical simulations, we show that these wires reproduce the ideal case of nanoconducting channels defined in an insulating background very well and that the tip bias is a powerful knob to modulate the size of these structures. We also discuss the role of the air humidity that is found to be a crucial parameter to set the size of the tip-sample effective interaction area.

In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi0.64Sb1.36Te3 with a thickness of 6–200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materials with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bip...

A method for controlled synthesis of coiled carbon nanotubes (CNTs) is demonstrated, in which three-dimensional columns of aligned CNTs are used as a template. The coiled CNTs with pitches and coil diameters from 100 to 300 nm are regrown on the straight CNT arrays and the mesoporous structure between the CNT arrays produces an asymmetric growth condition for the coil formation. As observed using transmission electron microscopy, the graphitic layers on the tube wall are stacking-disordered due to the coil geometry. The growth mechanism of the coiled CNTs is also proposed.

A microfluidic flow sensor based on aligned piezoelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] nanofibers has been developed. The flow sensor is able to linearly measure low flow rates ranging from 13 μl/h to 301 μl/h with a sensitivity of 0.36 mV per 1 μl/h, and the highest voltage difference of 120 mV at a flow rate of 451 μl/h. Moreover, the viscosity of the ethylene glycol aqueous solution ranging from 1 mPa·s to 16.1 mPa·s at 25 °C can be detected in dynamic flow with a stable output. These findings highlight the potential of piezoelectric P(VDF-TrFE) nanofibers in multiferroic applications.

Thermoelectric properties, i.e., thermal conductivity, electrical conductivity, and the Seebeck coefficient, have been measured in the directions parallel (in-plane) and perpendicular to the interface of an n-type Si(80 A)/Ge(20 A) superlattice. A two-wire 3ω method is employed to measure the in-plane and cross-plane thermal conductivities. The cross-plane Seebeck coefficient is deduced by using a differential measurement between the superlattice and reference samples and the cross-plane electrical conductivity is determined through a modified transmission-line method. The in-plane thermal conductivity of the Si/Ge superlattice is 5–6 times higher than the cross-plane one, and the electrical conductivity shows a similar anisotropy. The anisotropy of the Seebeck coefficients is smaller in comparison to electrical and thermal conductivities in the temperature range from 150 to 300 K. However, the cross-plane Seebeck coefficient rises faster with increasing temperature than that of the in-plane direction.

Electron-field-emission properties have been investigated systematically for carbon nanotubes (CNTs) fabricated on a metal tip. With a vacuum gap of 0.7 mm, the threshold field is as low as 0.7 V/μm and the current density approaches 10 mA/cm2 at an electronic field of 1.0 V/μm. The emission current is quite stable with very low fluctuation. The emission behavior is in excellent agreement with Fowler–Nordheim theory and no current saturation is found even with an emission current reaching 1 A/cm2. A universal relationship 1/β=d2/d+1/β0 between the field amplification factor β and the vacuum gap d is developed within a two-region field-emission model. This relationship provides the basis for a microscopic understanding of CNT emitters and is applicable to other systems as well.

The reliability of electroluminescence from metal–oxide–silicon (MOS) tunneling diodes was improved by the incorporation of deuterium. The deuterium was incorporated by the deuterium prebake and the postoxide deuterium annealing. At constant current stress of 100 mA, a deuterium-treated n-channel MOS tunneling light-emitting diode shows that the integrated light emission intensity increases slightly about 6% after 10 000 s operation, while the hydrogen-treated device shows a 30% decrease of the integrated light emission intensity. The hydrogen release by the electrons tunneling from the gate electrode to Si and the formation of interface defects are responsible for the degradation of light output in the hydrogen-treated samples. An annealing model is also given to explain the slight increase of light output in the deuterium-treated samples.

For the nanocomposite magnets (Nd0.9Dy0.1)(Fe0.77Co0.12Nb0.03B0.08)5.5/α-Fe, the best magnetic properties were obtained with the average grain size of α-Fe d=15 nm and with the content of α-Fe cm=45 wt % that is well below the structural percolation threshold of the soft magnetic phase. The measured dependence of the coercivity on the grain size of α-Fe tends to indicate that the optimum grain size dop increases with increasing α-Fe content, for cm>30 wt %. If d>dop, contracted hysteresis is formed; if d

An enhanced anomalous Hall effect (AHE) is observed via interface modification in MgO/[Co/Pt]2/Co/MgO multilayers, due to the insertion of a Hf metal layer at the Co/MgO interface. It is shown that the saturation anomalous Hall resistivity is 215% larger than that in the multilayers without Hf insertion. More importantly, thermally stable AHE and perpendicular magnetic anisotropy features are obtained in MgO/[Co/Pt]2/Co/Hf/MgO multilayers. The AHE is improved for sample MgO/[Co/Pt]2/Co/Hf/MgO by annealing, which is attributed to the enhancement of the side jump contribution.

The piezotronic effect uses strain-induced piezoelectric charges at interfaces and junctions to tune and/or control carrier transport in piezoelectric semiconductor devices. This effect has recently been observed in single-layer 2D MoS2 materials. However, previous work had found that metallic states are generated at the edge of a free-standing MoS2 flat sheet, and these states may screen the piezoelectric charges. Using density functional theory simulations, we found that the metal–MoS2 interface structure plays an important role in enhancing both the piezoelectric and piezotronic effects in MoS2 transistors by breaking the metallic state screening effect at the MoS2 edge. This study not only provides an understanding of the piezoelectric and piezotronic effects based on first principles calculations but also offers guidance for the design of two-dimensional piezotronic devices.

Analyzing the polarization of a circularly polarized light is a critical issue. We have fabricated a spiral nano-structure on the Au film by using focused ion beam etching technique. The fabricated structure can be used as a plasmonic circular polarization analyzer. By designing the relative orientation of two nano-apertures in the spiral structural unit, the propagation direction of the surface plasmon polaritons excited by circularly polarized light of opposite handedness can be controlled. Therefore, the spiral structure could be used to accurately determine the helicity of the excited circularly polarized light. Based on the results of scanning near-field optical microscopy, the obtained circular polarization extinction ratio of this structure was above 500. This structure can be used for a flexible detecting size and a very wide spectrum.

This paper presents the design and simulation results of a high-precision low-cost refractometer that demonstrates the main advantage of a wide measurement range (1 ≤ n ≤ 2). The proposed design is based on the diffractive properties of sub-micron gratings and Snell's Law. The precision and uncertainty factors of the proposed system were tested and analyzed, revealing that the proposed refractometer demonstrates a wide measurement range with sensitivity of 10−4.

This paper introduces a cancer cell capture/release microchip based on the self-sacrificed MnO2 nanofibers. Through electrospinning, lift-off and soft-lithography procedures, MnO2 nanofibers are tactfully fabricated in microchannels to implement enrichment and release of cancer cells in liquid samples. The MnO2 nanofiber net which mimics the extra cellular matrix can lead to high capture ability with the help of a cancer cell-specific antibody bio-conjugation. Subsequently, an effective and friendly release method is carried out by using low concentration of oxalic acid to dissolve the MnO2 nanofiber substrate while keeping high viability of those released cancer cells at the same time. It is conceivable that our microchip may have potentials in realizing biomedical analysis of circulating tumor cells for biological and clinical researches in oncology.

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332 meV to ∼294 meV at 80 A/cm2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs. ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

To improve the performance of ZnO thin film transistors (TFTs) by using appropriate metal contacts, the different roles of contact materials between oxidation interlayer and doping effect are investigated. With careful characterization, an oxidation interlayer has been verified at the interface between ZnO film and Al or Ti contact, which is suggested to be responsible for contact resistance and thermal reliability. On the other hand, it is observed that the doping effect is the main reason for the Sn or Cu contact characteristics. The superior contact using Sn is due to an oxidation-free interface, donor doping effect, and a low barrier height. By using a metal contact with a high Gibbs free energy, the metal layer would hardly consume oxygen from channel layer during sputtering and easily form no oxidation interlayer. Thus, choosing a metal contact is important when fabricating high-performance metal-oxide TFTs for flat-panel displays.