Superconductivity in Layered van der Waals Hydrogenated Germanene at High Pressure

Pressure-Triggered Fluorescence Intensity Ratio Variations of YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) for High-Sensitivity Optical Pressure Sensing

Optical pressure sensing by phosphors is a growing area of research. However, the main pressure measurement methods rely on the movement of the central peak position, which has significant drawbacks for practical applications. This paper demonstrates the feasibility of using the fluorescence intensity ratio (FIR) of different emission peaks for pressure sensing. The FIR (IBi3+/ILn3+) values of the synthesized YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) phosphors are all first-order exponentially related to pressure, and YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) phosphors have high pressure-sensing sensitivities (Sp and Spr), which are 6 times higher than those from our previously reported work. In addition, the changes in FIR values during the decompression process were also calculated, and the trend was similar to that during the compression process. The YNbO4:Bi3+,Eu3+ phosphor has better pressure recovery performance. In summary, the YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) phosphors reported in this paper are expected to be applied in the field of optical pressure sensing, and this study provides a new approach and perspective for designing new phosphors for pressure measurement.

Controllable Modulation of the Electronic Properties of a Two-Dimensional Ambipolar Semiconductor by Interface Ferroelectric Polarization

Precise control of charge carrier type and density of two-dimensional (2D) ambipolar semiconductors is the prerequisite for their applications in next-generation integrated circuits and electronic devices. Here, by fabricating a heterointerface between a 2D ambipolar semiconductor (hydrogenated germanene, GeH) and a ferroelectric substrate (PbMg1/3Nb2/3O3-PbTiO3, PMN-PT), fine-tuning of charge carrier type and density of GeH is achieved. Due to ambipolar properties, proper band gap, and high carrier mobility of GeH, by applying the opposite local bias (±8 V), a lateral polarization in GeH is constructed with a change of work function by 0.6 eV. Besides, the built-in polarization in GeH nanoflake could promote the separation of photoexcited electron-hole pairs, which lead to 4 times enhancement of the photoconductivity after poling by 200 V. In addition, a gradient regulation of the work function of GeH from 4.94 to 5.21 eV by adjusting the local substrate polarization is demonstrated, which could be used for data storage at the micrometer size by forming p-n homojunctions. This work of constructing such heterointerfaces provides a pathway for applying 2D ambipolar semiconductors in nonvolatile memory devices, photoelectronic devices, and next-generation integrated circuit.

Pressure-Induced Dynamic Tuning of Interlayer Coupling in Twisted WSe2/WSe2 Homobilayers

Moiré superlattices induced by twisted van der Waals (vdW) heterostructures or homostructures have recently gained significant attention due to their potential to generate exotic strong-correlation electronic and phonon phenomena. However, the lack of dynamic tuning for interlayer coupling of moiré superlattices hinders a thorough understanding and development of the moiré correlation state. Here, we present a dynamic tuning method for twisted WSe2/WSe2 homobilayers using a diamond anvil cell (DAC). We demonstrate the powerful tuning of interlayer coupling and observe an enhanced response to pressure for interlayer breathing modes and the rapid descent of indirect excitons in twisted WSe2/WSe2 homobilayers. Our findings indicate that the introduction of a moiré superlattice for WSe2 bilayers gives rise to hybridized excitons, which lead to the different pressure-evolution exciton behaviors compared to natural WSe2 bilayers. Our results provide a novel understanding of moiré physics and offer an effective method to tune interlayer coupling of moiré superlattices.

Strain-engineered thermophysical properties ranging from band-insulating to topological insulating phases in β-antimonene

The use of strain in semiconductors allows extensive modification of their properties. Due to their robust mechanical strength and flexibility, atomically thin 2D materials are very well suited for strain engineering to extract exotic electronic and thermophysical properties. We investigated the structural, electronic, thermal, and vibrational characteristics along with the phonon and carrier dynamics of β-Sb elemental monolayers for achieving the band-insulating phase at no strain and topological insulating phase at ∼15% biaxial strain. A reduction in stiffness was noticed due to the weakening of the π and σ bonds with strain, leading to anharmonicity in the system. This was further reflected by the drop in lattice thermal conductivity (κl) from 4.5 to 3.1 W m-1 K-1 at 15% strain, i.e., in the topological phase. The appearance of helical edge states at 15% strain and meeting the Z2 invariant criterion confirm the non-trivial topological state. The significant contribution of the out-of-plane A1g vibrational mode was noticed in the topological phase compared with the band-insulating phase. Further, the observed larger reduction in hole lifetime could be attributed to strong scattering near the valence band edge. Importantly, the dominance of the out-of-plane optical modes contributes significantly along the band edges to the topological phase, which is primarily due to the reduced buckling height under strain. Thus, this work emphasizes the microscopic origin of the onset of the topological phase in strained β-Sb monolayers and provides strain-engineered structure-property correlations for better insights.

2D Functionalized Germananes: Synthesis and Applications

In the realm of 2D layered materials, the monoelemental group 14 Xene, germanene, as the germanium analog of graphene, has emerged as the next prospective candidate. Preceded by silicon, germanium is widely used in the semiconductor industry; thus, germanene is deemed compatible with existing semiconductor technologies. Germanene consists of mixed sp² -sp³ -hybridized networks in a buckled hexagonal honeycomb structure. Chemical exfoliation of Zintl phases, such as CaGe₂ , specifically the topotactical deintercalation in acidic media, removes the alkaline earth metal ions Ca²⁺ , giving rise to layered germanane (germanene with the Ge centers covalently saturated with terminal hydrogen atoms). Diverse variants of functionalized germananes (with covalent group(s) termination) can be obtained by varying the topotactical deintercalation precursors, elevating the game with limitless functionalization possibilities for customizable properties or new functionalities. The preparation of Zintl phases to the details of functionalized and modified germananes and their properties, and the additional exfoliation step to achieve mono- or few-layer germananes, are comprehensively covered. The progress and challenges of 2D functionalized germananes in optoelectronics, catalysis, energy conversion and storage, sensors, and biomedical areas are reviewed. This review provides insight into designing and exploring this class of atomically thin semiconductors in realizing future nanoarchitectonics.

Environmentally sustainable implementations of two-dimensional nanomaterials

Rapid advancement in nanotechnology has led to the development of a myriad of useful nanomaterials that have novel characteristics resulting from their small size and engineered properties. In particular, two-dimensional (2D) materials have become a major focus in material science and chemistry research worldwide with substantial efforts centered on their synthesis, property characterization, and technological, and environmental applications. Environmental applications of these nanomaterials include but are not limited to adsorbents for wastewater and drinking water treatment, membranes for desalination, and coating materials for filtration. However, it is also important to address the environmental interactions and implications of these nanomaterials in order to develop strategies that minimize their environmental and public health risks. Towards this end, this review covers the most recent literature on the environmental implementations of emerging 2D nanomaterials, thereby providing insights into the future of this fast-evolving field including strategies for ensuring sustainable development of 2D nanomaterials.