Showing papers by "Shengli Zhang published in 2017"

Antimonene Oxides: Emerging Tunable Direct Bandgap Semiconductor and Novel Topological Insulator

Abstract: Highly stable antimonene, as the cousin of phosphorene from group-VA, has opened up exciting realms in the two-dimensional (2D) materials family. However, pristine antimonene is an indirect band gap semiconductor, which greatly restricts its applications for optoelectronics devices. Identifying suitable materials, both responsive to incident photons and efficient for carrier transfer, is urgently needed for ultrathin devices. Herein, by means of first-principles computations we found that it is rather feasible to realize a new class of 2D materials with a direct bandgap and high carrier mobility, namely antimonene oxides with different content of oxygen. Moreover, these tunable direct bandgaps cover a wide range from 0 to 2.28 eV, which are crucial for solar cell and photodetector applications. Especially, the antimonene oxide (18Sb–18O) is a 2D topological insulator with a sizable global bandgap of 177 meV, which has a nontrivial Z2 topological invariant in the bulk and the topological states on the edge...

Quantum confinement effect of two-dimensional all-inorganic halide perovskites

Abstract: Quantum confinement effect (QCE), an essential physical phenomenon of semiconductors when the size becomes comparable to the exciton Bohr radius, typically results in quite different physical properties of low-dimensional materials from their bulk counterparts and can be exploited to enhance the device performance in various optoelectronic applications. Here, taking CsPbBr3 as an example, we reported QCE in all-inorganic halide perovskite in two-dimensional (2D) nanoplates. Blue shifts in optical absorption and photoluminescence spectra were found to be stronger in thinner nanoplates than that in thicker nanoplates, whose thickness lowered below ~7 nm. The exciton binding energy results showed similar trend as that obtained for the optical absorption and photoluminescence. Meanwile, the function of integrated intensity and full width at half maximum and temperature also showed similar results, further supporting our conclusions. The results displayed the QCE in all-inorganic halide perovskite nanoplates and helped to design the all-inorganic halide perovskites with desired optical properties.

Considering the spin–orbit coupling effect on the photocatalytic performance of AlN/MX2 nanocomposites

Abstract: The enhanced photocatalytic mechanisms for the hybrid AlN/MX2 (MX2 = MoSe2, WS2, and WSe2) nanocomposites are systematically investigated by density-functional-theory calculations. Our theoretical calculations study the photocatalytic performance of AlN/MX2 nanocomposites with the inclusion of the spin–orbit coupling (SOC) effect. The results demonstrate that the band gaps of the AlN/MX2 bilayers vary from 1.72 to 1.93 eV, covering the main region of the visible light. All of the AlN–MX2 bilayers exhibit prominent visible and UV light response compared to their individual constituents, implying their potential applications as excellent light-absorbers. The AlN–MX2 heterobilayers are excellent photocatalysts for splitting water into hydrogen due to the perfect fit of band edge positions with respect to water reduction and oxidation potentials. Particularly, AlN–WS2 has type-II band alignment. Besides, the applied small biaxial tensile strain can not only effectively tune the band edge positions, but can also trigger an indirect–direct band gap transition in AlN–MX2 bilayers maintaining the excellent optical properties. Therefore, the strained AlN–MX2 bilayers are expected to be more promising candidates for photocatalysis. Overall, our theoretical predictions point toward the prospective future of novel AlN–MX2 heterostructures for photocatalysis.

Layer-controlled band alignment, work function and optical properties of few-layer GeSe

Abstract: The electronic properties, such as the layer-dependent behavior of the band structure, band gap, work function alignment and dielectric properties of the few-layer GeSe are systematically investigated via gradient-corrected density functional theory computations, inspired by the experimentally observation of two-dimension materials such as graphene, phosphorene, MoS 2 and BN The results indicate that the few-layer GeSe presents a robust direct band gap, which decreases with increasing the thickness from bilayer (115 eV) to six-layer (100 eV) around the X point Furthermore, the work function increases rapidly from monolayer (444 eV) to trilayer (495 eV) The robust direct band gap characteristics and the layer-dependent band gap suggest that the few-layer GeSe is a promising material for efficient solar energy harvesting applications The layer dependence of the GeSe work function offers a practical route to tune the Schottky barrier in GeSe based electronic devices Our results provide new insights on utilizing the layer-controlled band gap of the atomic layers of GeSe

Metallic oxide nanocrystals with near-infrared plasmon resonance for efficient, stable and biocompatible photothermal cancer therapy

Abstract: Photothermal therapy is regarded as one of the most promising cancer treatment technologies due to its negligible side effects and fast operation. However, its therapeutic efficacy is still limited by the lack of cost-effective photostable and biocompatible therapeutic agents with efficient light absorption in the biological window. Here, taking MoO2 as an example, we propose oxide nanocrystals (NCs), with both a metallic electronic structure and near-infrared (NIR) plasmon resonance, for efficient, stable and biocompatible photothermal cancer therapy. Monoclinic MoO2 NCs with good crystallinity were fabricated through the combination of laser ablation in liquid and solvothermal synthesis. The as-synthesized NCs showed intensive local surface plasmon resonance (LSPR) absorption at 800-1000 nm, the NIR biological window, due to their metallic electronic structure and oxide dielectric function. This unique NIR LSPR characteristic leads to excellent photothermal performance, i.e., the maximum temperature elevation was found to be up to 37.5 °C with a MoO2 NC concentration of 0.05 mg mL-1 under 808 nm laser irradiation. Moreover, MoO2 solution is highly photostable, as it exhibits stable irradiation-induced temperature elevation of about 14.3 °C even after four temperature elevation cycles. As a photothermal therapy agent against 4T1 cancer cells, MoO2 NCs exhibit not only good biocompatibility, but also excellent tumor inhibition effects. The highest inhibition rate was up to 80.45%, and the average tumor volume was 2.73 times smaller than normal growth 14 days after the treatment. The results prove that MoO2 NCs exhibiting NIR LSPR can act as an effective agent for photothermal cancer therapy with great photostability and biocompatibility.

Retraction of “Few-Layer Antimonene: Large Yield Synthesis, Exact Atomical Structure, and Outstanding Optical Limiting”

Abstract: The predictions of arsenene and antimonene open a gate to new two-dimensional (2D) materials. In contrast to the severe unstability of black phosphorus in ambient atmosphere, arsenene and antimonene were recently predicted to be of high stability, as well as outstanding physical and chemical properties, such as extremely high mobility, superior thermal conductivity, high refractive index, and directionally optically transparent. Significantly, monolayer and few-layer antimonenes were recently experimentally fabricated by mechanical exfoliation, however the yield was very low and there’s lack of clear characterizations on the atomical structure and potential applications, which are critical and necessary to promote the developments of this field. Here, we report on a high-yield experimental preparation of high quality, few-layer antimonenes via liquid exfoliation, their atomic level structural elucidation, and unexpected but outstanding nonlinear optical limiting properties even better than graphene in the visible and near infrared region (532 nm-2000 nm) and high transmission (more than 80%) when dispersed in solutions or high concentration doped in Ormosil gel glasses, which might lead to many promising applications in nonlinear optical fields such as laser protection. This work demonstrates that Group 15 2D materials beyond BP could be not only a new 2D crystal family with stability in ambient condition, but also of unique properties