[en] Multiscale simulation combining density functional theory of defect physics and charge transport calculation is carried out to understand the intrinsic mechanism of the lateral charge loss in silicon nitride (Si₃N₄)-based 3D NAND flash memory. In this work, the defects’ structures, trapping centers, and trap levels are investigated by ab initio calculations. Wherein, the focus is put on the nitrogen vacancy (V _N), puckered nitrogen vacancy (V _NP) and H-/O- incorporation. It shows that the V _N P and O atom will introduce extremely shallow electron traps which can be eliminated by the H passivation. The stability of several kinds of defects is also studied. To shed new light on the impact of trap levels on the charge de-trapping and the lateral charge loss, numerical simulations are performed with the drift-diffusion model and Poole–Frenkel model. (paper)

[en] Inspired by the novel mechanism of reducing thermal conductivity by local phonon resonance instead of by inducing structural defects, we investigate the effect of side branching on the thermoelectric properties of nanoribbons, and prove that side branching is a highly efficient mechanism for enhancing the thermoelectricity of different kinds of nanoribbons. For both armchair and zigzag nanoribbons, the side branches result in not only significant blocking of phonon transport but also notable increase of the Seebeck coefficient. Consequently, the thermoelectric figure of merit of the armchair nanoribbon is boosted from 0.72 to as high as 1.93, and the originally non-thermoelectric metallic zigzag nanoribbon is turned into a thermoelectric material due to the appearance of the band gap induced by the side branches. These results mean that the mechanism of branching is not only very efficient, but also takes effect regardless of the original properties of the nanoribbons, and thus will hold great promise for its application in the thermoelectric field. (paper)

[en] Energy distribution and angular distribution of the photoelectrons from InP photocathodes are investigated using a precise Monte Carlo model. It is found that Γ-valley electrons contribute to the first peak of the energy distribution curve, but the second peak is contributed by both Γ-valley and L-valley electrons rather than only L-valley electrons. L valley electrons are shown to have a smaller angular spread than Γ-valley electrons, which is attributed to the much higher potential energy of L-valley minimum. The further simulation indicates that the performance of InP photocathodes can be improved by increasing the hole concentration or decreasing the temperature, but the activation layer thickness variation only has very slight influence on either energy or angular distribution

[en] Two-dimensional (2D) semiconductors present great potential for electronic and optoelectronic applications due to their uniform thickness and tunable band gaps. Using ab initio electronic structure calculations and quantum transport simulations, we demonstrate the asymmetric metal contact design in the case of 2D GeSe, with a systematic study of the interfacial properties and transport properties of three common metal contacts (Ag, Au, and Pd) to the 2D semiconductor. Because of the different work functions, Ag contacted to GeSe forms n-type Schottky contact, while Pd forms p-type Schottky contact, respectively, and the reversed rectifying behaviors can be found in the I–V characteristics of symmetric contacted Ag–GeSe–Ag and Pd–GeSe–Pd junctions. More importantly, rectifying behaviors in both junctions can be significantly enhanced by the design of asymmetric metal contact (with the right-side electrode being replaced by Au). Our results are very helpful for the further design of the transistors based on 2D GeSe. (paper)

[en] The effects of Ta on microstructural stability and mechanical properties of hot corrosion resistant Ni-based single crystal superalloys during long-term thermal exposure at 900 °C were investigated in the present study by comparing two experimental alloys with different content of Ta (6Ta and 6.7Ta). The results indicated that the addition of extra 0.7Ta increased the volume fraction of the γ′ precipitates and accelerated the coarsening rate of γ′ precipitates, facilitated the formation of misfit dislocation and precipitation of σ phases. The 6.7Ta alloy exhibited higher hardness and better stress rupture properties than 6Ta and the variations of stress rupture properties during the exposure for 6Ta and 6.7Ta alloy are significantly different. The effects of γ′ coarsening, formation of σ phases and misfit dislocations were taken into consideration to identify the reasons of variations of mechanical properties during the thermal exposure.

[en] Semiconductive two dimensional (2D) materials have attracted significant research attention due to their rich band structures and promising potential for next-generation electrical devices. In this work, we investigate the MoS₂ field-effect transistors (FETs) with a dual-gated (DG) architecture, which consists of symmetrical thickness for back gate (BG) and top gate (TG) dielectric. The thickness-dependent charge transport in our DG-MoS₂ device is revealed by a four-terminal electrical measurement which excludes the contact influence, and the TCAD simulation is also applied to explain the experimental data. Our results indicate that the impact of quantum confinement effect plays an important role in the charge transport in the MoS₂ channel, as it confines charge carriers in the center of the channel, which reduces the scattering and boosts the mobility compared to the single gating case. Furthermore, temperature-dependent transfer curves reveal that multi-layer MoS₂ DG-FET is in the phonon-limited transport regime, while single layer MoS₂ shows typical Coulomb impurity limited regime. (paper)

[en] Magnetic tunnel junctions (MTJs) have attracted tremendous interests recently because of their potential application in magnetoresistive random access high-density memory and magnetic sensor. However, the performance of them is far from satisfying due to the various problems exist in tunnel barrier materials. Here, we propose to use two-dimensional (2D) ${\mathit{Bi}}_2{O}_2\mathit{Se}$ material, which is advantageous in reducing the MTJ size, as the tunnel barrier, and demonstrate that it is able to generate very large tunnel magnetoresistance (TMR) when integrated with CoFe electrodes. The underlying mechanism is elaborated by analyzing the band structures, electron transmission and interface properties. These results provide important guidance for designing high-density and high-performance MTJs.

[en] Two-dimensional (2D) transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS₂) have been intensively investigated because of their exclusive physical properties for advanced electronics and optoelectronics. In the present work, we study the MoS₂ transistor based on a novel tri-gate device architecture, with dual-gate (Dual-G) in the channel and the buried side-gate (Side-G) for the source/drain regions. All gates can be independently controlled without interference. For a MoS₂ sheet with a thickness of 3.6 nm, the Schottky barrier (SB) and non-overlapped channel region can be effectively tuned by electrostatically doping the source/drain regions with Side-G. Thus, the extrinsic resistance can be effectively lowered, and a boost of the ON-state current can be achieved. Meanwhile, the channel control remains efficient under the Dual-G mode, with an ON-OFF current ratio of 3 × 10⁷ and subthreshold swing of 83 mV/decade. The corresponding band diagram is also discussed to illustrate the device operation mechanism. This novel device structure opens up a new way toward fabrication of high-performance devices based on 2D-TMDs. .

[en] Highlights: • Hot corrosion resistance of single crystal superalloys significantly depended on the ratio of Al/Ti in terms of the formation of a compact and protective NiTiO₃ layer. • Re significantly improved hot corrosion resistance of the experimental single crystal superalloy. • The influence mechanism that adding Re may facilitate diffusion of Cr in γ phase and diffusion of Ti in γ' phase had been explored in combined with first-principle calculation. • Potential design space for developing new type of hot corrosion resistant single-crystal superalloys was proposed. Hot corrosion behavior of three nickel-based single crystal superalloys with different key alloying elements (including Re, Cr, Al and Ti) contents in molten Na₂SO₄ salt at 900 °C was investigated. Comparative study of hot corrosion resistance was conducted on two Re-free superalloys with 12 wt% Cr and different content of Al and Ti. By further adding Re, the experimental alloy with moderate Cr content (8.5 wt%) and Al/Ti > 1 in the present research also exhibited excellent hot corrosion resistance. The influence mechanism of Re on promoting hot corrosion resistance was attempted to be explored in combined with first-principle calculation. In addition, the potential design space of new-developed single crystal superalloys was also proposed.