Structure-Dependent Optical Properties of Self-Organized Bi2Se3 Nanostructures: From Nanocrystals to Nanoflakes

Effects of pressure and temperature on topological electronic materials X2Y3 (X = As, Sb, Bi; Y = Se, Te) using first-principles

We systematically study the thermal and topological properties of X2Y3 (X = As, Sb, Bi; Y = Se, Te) and the effects of pressure and temperature on their electronic properties using first-principles. We find that the external pressure-induced electronic topological transition occurs at about 5 GPa for Bi2Se3, and the type of band gap tends to become indirect with the increase of pressure. We also investigate the lattice expansion with temperature in quasi-harmonic approximation and further explore the effect of temperature on the volume, band gap, and volumetric thermal expansion coefficient of the studied selenides and tellurides. Finally, we calculate the evolution of the Wannier charge center of X2Y3 to determine their topological invariants, and theoretically suggest that Bi2Se3 changes from a topological to an ordinary insulator when the pressure decreases to -8 GPa; As2Se3 is found to be an ordinary insulator, while all other four compounds are always strong topological insulators at any pressure or temperature.

Bi2 Te3 /Bi2 Se3 /Bi2 S3 Cascade Heterostructure for Fast-Response and High-Photoresponsivity Photodetector and High-Efficiency Water Splitting with a Small Bias Voltage

Large-scale multi-heterostructure and optimal band alignment are significantly challenging but vital for photoelectrochemical (PEC)-type photodetector and water splitting. Herein, the centimeter-scale bismuth chalcogenides-based cascade heterostructure is successfully synthesized by a sequential vapor phase deposition method. The multi-staggered band alignment of Bi₂ Te₃ /Bi₂ Se₃ /Bi₂ S₃ is optimized and verified by X-ray photoelectron spectroscopy. The PEC photodetectors based on these cascade heterostructures demonstrate the highest photoresponsivity (103 mA W^-1 at -0.1 V and 3.5 mAW^-1 at 0 V under 475 nm light excitation) among the previous reports based on two-dimensional materials and related heterostructures. Furthermore, the photodetectors display a fast response (≈8 ms), a high detectivity (8.96 × 10⁹ Jones), a high external quantum efficiency (26.17%), and a high incident photon-to-current efficiency (27.04%) at 475 nm. Due to the rapid charge transport and efficient light absorption, the Bi₂ Te₃ /Bi₂ Se₃ /Bi₂ S₃ cascade heterostructure demonstrates a highly efficient hydrogen production rate (≈0.416 mmol cm^-2  h^-1 and ≈14.320 µmol cm^-2  h^-1 with or without sacrificial agent, respectively), which is far superior to those of pure bismuth chalcogenides and its type-II heterostructures. The large-scale cascade heterostructure offers an innovative method to improve the performance of optoelectronic devices in the future.

Low Deposition Temperature Amorphous ALD-Ga2O3 Thin Films and Decoration with MoS2 Multilayers toward Flexible Solar-Blind Photodetectors

Flexible sensors and photodetectors are among the robust and powerful strategies for advanced and smart devices. Meanwhile, wide band-gap metal oxides are competitive candidates for fabricating flexible solar-blind photodetectors (SBPDs) but still challenging in both fundamental and practical fields. Here, we demonstrate the amorphous ALD-Ga₂O₃ (am-ALD-Ga₂O₃) thin films realized at a moderate temperature toward flexible SBPDs. The bandgap (E_g) of 4.88-5.04 eV depends on and changes with the thickness of am-ALD-Ga₂O₃ thin films during atomic layer deposition (ALD) processes. The SBPDs are fabricated with the as-grown am-ALD-Ga₂O₃ thin films on desired substrates and exhibit an I_light/I_dark ratio of up to ∼4.5 × 10⁴ and dark current down to ∼10^-13 A. Subsequently, decorating the ALD-Ga₂O₃ channels with MoS₂ multilayers helps improve the photocurrent of SBPDs that worked in the deep ultraviolet region. We expect that our work will offer more opportunities to understand and exploit am-ALD-Ga₂O₃ thin films toward advanced flexible SBPDs and functional sensors.

Evolution of optical properties and electronic structures: band gaps and critical points in MgxZn1-xO (0 ≤ x ≤ 0.2) thin films

MgxZn1-xO (ZMO) thin films with tunable Mg content were deposited by atomic layer deposition (ALD) on silicon substrates at 190 °C. The elemental and structural properties were acquired by X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy and X-ray diffraction. Spectroscopic ellipsometry measurements were performed to reveal the evolution of the dielectric functions and critical points in the ZMO thin films by point-by-point fit in the photon energy range of 1.2-6.0 eV. The dependence of the dielectric functions on doping content is clearly demonstrated and physically explained. The critical point energies and the types of interband optical transitions were extracted from standard lineshape analysis of the second derivatives of the dielectric functions. The critical point features were discussed in terms of band structure modification and structural homogeneity arisen by introducing the Mg dopant into the films. Controlling these transitions by changing the doping content will be of practical significance in emerging ZMO-based thin-film photonic and optoelectronic devices.

Near infrared light activatable PEI-wrapped bismuth selenide nanocomposites for photothermal/photodynamic therapy induced bacterial inactivation and dye degradation

Inactivation of bacteria and degradation of organic pollutants by engineered nanomaterials (NMs) are very effective approaches in producing safe and clean drinking water.