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Multiferroic Fe-site engineered lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN] was prepared by partially substituting Fe with Ni, Co, and Cr, which comprise distinct Bohr magnetons, to investigate the effect of the variation in spin configurations on magnetic and multiferroic properties. All the studied compositions exhibited a single-phase perovskite structure, wherein the lattice constant decreased with increasing substitutions. The inherent ferroelectric order was preserved when Ni or Co ions were introduced, while the introduction of Cr made the samples too lossy, which prevented the verification of the possible ferroelectricity. Substitution of Fe with different transition metals in PFN, which is originally paramagnetic at room temperature, resulted in oriented spin configurations that led to distinct magnetic orders: soft ferromagnetic, hard ferromagnetic, and antiferromagnetic orders for Ni, Co, and Cr, respectively. This distinction mainly stems from the interspin distance and the spin moment, both of which are important factors during the spin exchange interaction. The interspin distance of pristine and Cr-substituted PFN is too long and short, respectively, to induce ferromagnetic properties. Moreover, at room temperature, magnetic-field-dependent magnetoelectric coupling was observed only for the Ni- and Co-substituted PFN owing to their asymmetric spin configuration. This research could lead to a general method for modulating the magnetic properties of multiferroic perovskite oxides.

In this study, we report the experimental demonstration of electrically driven on-chip transferrable microdisk light-emitting diodes (LEDs). A vertical p– i– n doped AlGaInP microdisk, including multi-quantum-well structures, is top-down-fabricated, on-chip micro-transferred, and converted into single micro-LEDs. Optically transparent and mechanically flexible multilayered graphene sheets are judiciously designed and introduced to the top and bottom surfaces of a single microdisk, thereby forming the top and bottom contacts. Using electroluminescence measurements, the fabricated micro-LEDs are characterized; they exhibit diode-like transport behaviors, spectroscopic light-out vs current ( L– I) characteristics, and polarization-resolved emission properties. We believe that the proposed all-graphene-contact approach offers a direct and easy current injection scheme and further helps electrify various on-chip transferrable microarchitectures.

In this work, we study the mitigation of stress waves in composite-based woodpile phononic crystals composed of heterogeneous cylindrical rods, whose bending mode exhibits local resonant behavior that strongly interferes with external perturbation. Impulse excitation in this system is transformed into several modulated wave patterns depending on resonant frequencies and their mechanical properties. Thus, these mechanisms have been a candidate for novel methods of shock mitigation without relying on material dissipation. Here, we suggest the mechanical system consisting of the unit cell's composite configuration as an approach for more efficient shock attenuation. To efficiently analyze the nonlinear wave dynamics of the proposed systems, we present an extended discrete element model (DEM) resulting from a combination of an analytic beam theory with the discretization model. We numerically and experimentally demonstrate extreme dispersive waves for shock mitigation by adjusting the weighted composition ratio of the heterogeneous cylinder. Using the verified DEM, we also investigate the strong attenuation performance of incident impulse in disorder-induced systems with different nonlinear strengths. We, thus, expect that these composite-based mechanical systems could be used to design tunable modulation energy transport and efficient impact protector devices.

Hafnia-based ferroelectric thin-film transistors (FeTFTs) are regarded as promising candidates for future nonvolatile memory devices owing to their low power consumption, high operational speed, and complementary metal–oxide–semiconductor compatibility. However, the scalability of hafnia-based materials and the feasibility of three-dimensional (3D) device fabrication should be confirmed for ultrahigh-density memory applications. In this work, we demonstrate that FeTFTs can be scaled down to a 10-nm dimension using the vertical structure with a hafnia-based ferroelectric gate insulating layer and an oxide semiconductor channel. We show that such vertical FeTFTs can be operated with an effective device size of 0.005 μm2, a fast operation speed of 8cycles. Additionally, the string-level NAND operation is demonstrated using the vertical FeTFT array. Finally, device simulation confirms the possibility of ultrahigh-density 3D ferroelectric NAND with 200 gate stacks. These results demonstrate the ultrahigh scalability of FeTFTs as a promising candidate for next-generation 3D nonvolatile memory.

This study presents an investigation of the band structure in a semimetallic two-dimensional (2D) PtSe2 nanosheet based on thermoelectric transport phenomena. Mechanically exfoliated PtSe2 nanosheets, including naturally doped nonneutral samples, were studied. The gate-tuned electrical conductivity and thermoelectric power were measured by varying the temperature. Based on the combined effects of gate-tuning and shifting of zero-gate energy level, the semimetallic band structure of 2D PtSe2 was confirmed in the band over a wide energy range. Furthermore, the temperature dependence of transport properties was investigated to determine the band structure and intrinsic properties.

Spin orbit torque (SOT) is essential to magnetization modulation in various ferromagnet/non-magnet bilayers. In this study, we demonstrated that SOT can be enhanced in a hybrid system composed of a perovskite oxide NdNiO3 (NNO) and a Ni81Fe19/Pt bilayer. We also find that the SOT enhancement might be attributed to spin absorption at the interface between the NNO and Ni81Fe19 layers. Our findings suggest that metal-oxide hybrid structures can be promising systems for the development of efficient spin–orbitronic devices.

We report on the polarization-controlled amplification of excitonic emission in the monolayer WS2 coupled with ZnO microcavity. From polarization-resolved micro-photoluminescence spectroscopy and numerical modeling, we found that the polarization of WS2 excitonic emission can be tailored by the whispering gallery modes of the birefringent ZnO microcavity. Furthermore, the light input–light output curves exhibit the clear threshold kink and the superlinear increase in the output intensity for both the TM and TE polarization modes, indicating the polarization-dependent amplification of excitonic emission. Our results suggest an approach to realize the polarization-controlled photonic devices based on 2D materials.

There is increasing interest in a ferroelectric transistor, mainly using vacuum processed hafnium oxide based materials. We report in this paper a solution processed ZnO thin-film transistor (TFT) with improved ferroelectric performance in Hf0.5Zr0.5O2 (HZO) using a triple layer of ZrOx/HZO/AlOx by spray pyrolysis. The performance enhancement is due to the difference in thermal expansion coefficient between the bottom/top dielectric and HZO layers. Grazing incident x-ray diffraction, current–voltage, capacitance–voltage, polarization–voltage, and anticlockwise hysteresis in transfer curve confirm the excellent ferroelectricity of the triple layer. A memory window as large as ∼3 V, the maximum on/off ratio of 3.5 × 109, the field-effect mobility of 125 cm2/V s, and the subthreshold slope of 0.18 V/decade were obtained from the ZnO TFT with the ZrOx/HZO/AlOx gate insulator, demonstrating the high performance ferroelectric ZnO TFT. This result can open opportunities for ferroelectric oxide TFT for large area electronics on glass, including display.

This study reveals that the stoichiometricity of silicon nitride thin films (SiNx-TFs) significantly governs the packing density and water vapor transmission rate (WVTR), and it can be controlled by chemical reactions accompanied by the removal of oxygen impurities with a nitrogen neutral beam (N-NB). Here, oxygen contents of SiNx-TFs are reduced through the formation of volatile NOx, and their amount is dominated by the energy of the N-NB reflected from a negatively biased reflector (0 to −60 V). The single-layered stoichiometric SiNx-TFs with a thickness of 100 nm provides the WVTR of 6.2 × 10−6 g/(m2day), with a density and composition ratio of N/Si stoichiometry at 3.13 g/cm3 and 1.33, respectively. This optimized SiNx-TF encapsulated top-emission organic light-emitting diode has reliability under harsh condition (85 °C and 85% relative humidity) for 830 h or more.

The integration of single quantum dots (QDs) into a planar Fabry–Perot microcavity has been established as a direct and viable approach to vertically steer photons emitted from the quantum emitters, resulting in a strong increase in the source brightness, which becomes particularly evident when a lens with a low numerical aperture is used. However, the spectral bandwidth of QD–microcavity structures is limited and determined by their intrinsic quality factor; these structures are, thus, not ideal for the extraction of entangled photon pairs or for studies of exciton dynamics. We have found that, when a deterministic low-index solid immersion lens is placed on top of the QD in a QD–microcavity structure, the structure exhibits an enhancement in the bandwidth to 27 nm and a source brightness of 23%. The solid immersion lens is deterministically fabricated via two-photon absorption and can be remade several times without perturbing the QD, ensuring that the QD's intrinsic properties are preserved and ensuring its long-term reliability.

Thin film transistors (TFTs) with a ferroelectric Hf0.5Zr0.5O2 (HZO) gate insulator (GI) have been reported by using the vacuum process for HZO such as sputtering and atomic layer deposition methods. We report in this paper the ZnO TFT with ferroelectric GI using solution processed AlOx/HZO. AlOx assists in the initiation of ferroelectricity by applying large mechanical stress and provides a sufficient amount of oxygen vacancy to the underlying HZO. X-ray diffraction and capacitance-voltage, polarization-voltage, and anti-clockwise hystereses in the transfer curve confirm the formation of the ferroelectric phase of HZO. The AlOx/HZO TFTs exhibited a field-effect mobility of 140 cm2/V s, an on/off current ratio of 109, and a sub-threshold swing of 0.32 V/decade. The TFT shows a good bias-voltage tunable memory window of ∼4.5 V and memory retention characteristics up to 10 000 s for a programing/erasing voltage of ±10 V with a pulse width of 0.5 s. This work demonstrates the fabrication of ferroelectric HZO TFT using the solution process, and the results can be applied to ferroelectric oxide semiconductor TFT electronics.

We demonstrate two-dimensional mapping of current flow in graphene devices by using a single-spin scanning magnetometer based on a nitrogen-vacancy defect center in diamond. We first image the stray magnetic field generated by the current and then reconstruct the current density map from the field data. We focus on the visualization of current flow around a small sized current source of ∼500 nm diameter, which works as an effective point contact. In this paper, we study two types of point-contacted graphene devices and find that the overall current profiles agree with the expected behavior of electron flow in the diffusive transport regime. This work could offer a route to explore interesting carrier dynamics of graphene including ballistic and hydrodynamic transport regimes.