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The ferroelectric tunnel junction (FTJ), which possesses a simple structure, low power consumption, high operation speed, and nondestructive reading, has attracted great attention for the application of next-generation nonvolatile memory. The complementary metal–oxide–semiconductor-compatible hafnium oxide (HfO2) ferroelectric thin film found in the recent decade is promising for the scalability and industrialization of FTJs. However, the electric performance, such as the tunneling electroresistance (TER) effect, of the current HfO2-based FTJs is not very satisfactory. In this work, we propose a type of high-performance HfO2-based FTJ by utilizing a ferroelectric/dielectric composite barrier strategy. Using density functional theory calculations, we study the electronic and transport properties of the designed Ni/HfO2/MgS/Ni (001) FTJ and demonstrate that the introduction of an ultra-thin non-polar MgS layer facilitates the ferroelectric control of effective potential barrier thickness and leads to a significant TER effect. The OFF/ON resistance ratio of the designed FTJ is found to exceed 4 × 103 based on the transmission calculation. Such an enhanced performance is driven by the resonant tunneling effect of the ON state, which significantly increases transmission across the FTJ when the ferroelectric polarization of HfO2 is pointing to the non-polar layer due to the aroused electron accumulation at the HfO2/MgS interface. Our results provide significant insight for the understanding and development of the FTJs based on the HfO2 ferroelectric/non-polar composite barrier. [ABSTRACT FROM AUTHOR]

Chiral semiconductors have been recently suggested as the basic building blocks for the design of chiral optoelectronic and electronic devices for chiral emission and spintronics. Herein, we report that through the formation of a chiral/achiral heterostructure, one can develop a chiral system that integrates the merits of both chiral and achiral components for developing a demanded chiral emitter. In the R-(+)-(or S-(−)-)1-(1-naphthyl)-ethylammonium lead bromide/CsPbBr3 heterostructure, we show that the photoluminescence of CsPbBr3 carries a degree of circular polarization of around 1% at room temperature. It is explained that such chiral emission is enabled through the chiral self-trapped exitonic absorption of R-(+)- (or S-(−)-)1-(1-naphthyl)-ethylammonium lead bromide. This work may provide an alternative way to generate bright circularly polarized light from achiral materials, which has potential applications in spintronics, biosensing, and signal encryption. [ABSTRACT FROM AUTHOR]

Crystal-orientation-dependent properties in low symmetric two-dimensional material ReS2 have inspired its novel applications in photonics, electronics, and optoelectronics. In this work, Ar+ ion bombardment is used to treat ReS2 with different thicknesses, and different amounts of defect densities are introduced in ReS2 flakes. Angular dependent polarized Raman spectra is used to probe the change in anisotropy. The intensities of mode V exhibit maximum and minimum intensities with incident polarization along the b-axis and perpendicular. The intensity ratio Imin/Imax is used as a quantity to detect the change in anisotropy. It is found that with the same defect density, the change in anisotropy in 1-layer (L) ReS2 is the highest among ReS2 flakes; thus, 1L ReS2 is susceptible to ion bombardment. With an increase in the defect density in 1L ReS2, an increase in the Imin/Imax value is observed. A phenomenological model is established to understand the quantitative relationship between defect density and anisotropy, and the isotropic scattering range associated with defects is obtained. The results here provide ways of quantitatively understanding anisotropy by angular polarized Raman spectroscopy as well as ways of tuning anisotropy in two-dimensional anisotropic materials by ion bombardments. [ABSTRACT FROM AUTHOR]

Thermal transport and energy dissipation are important for a material in both thermoelectric and electronic devices. Here, we investigate the lateral and interfacial thermal transport of two-dimensional (2D) Bi2O2Se by Raman spectroscopy. It is found that thin Bi2O2Se flakes have a low in-plane thermal conductivity while maintaining an appropriate interfacial thermal conductance. The in-plane thermal conductivity of Bi2O2Se decreases with decreasing thickness, to as low as 0.92 ± 0.18 W⋅m−1⋅K−1 at a thickness of ∼8 nm. Such a low thermal conductivity is derived from the low phonon group velocity, strong anharmonicity, and large surface scattering of acoustic phonons of the Bi2O2Se thin layer. Simultaneously, thinner Bi2O2Se presents a higher thermal dissipation to the substrate than the thicker counterparts in the device. The interfacial thermal conductance increases with decreasing thickness, and reaches ∼21 MW⋅m−2⋅K−1 at ∼8 nm. These results provide critical information for the design of thermoelectric devices with high figures of merit and electronics with low-power consumption based on 2D materials. [ABSTRACT FROM AUTHOR]

The room-temperature-made low-voltage electric-double-layer (EDL) thin-film transistors (TFTs) are reported previously with good performance including a huge EDL gate capacitance above 1 μF/cm2. We report a two-dimensional simulation of the carrier transport and subgap density of states (DOS) in low-voltage indium tin oxide EDL TFTs. The simple model with a constant mobility and two-step subgap DOS reproduces well the characteristics of EDL TFTs. A nice fitting to the experimental data was obtained with a changeable effective conduction band DOS and valence band DOS model, which is reasonable to EDL electrostatic modulation mechanism. The EDL TFTs show much lower DOS than the InGaZnO4 TFTs. [ABSTRACT FROM AUTHOR]