ACS Nano最新文献

As traditional silicon-based materials almost reach their limits in the post-Moore era, two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been regarded as next-generation semiconductors for high-performance electrical and optical devices. Chemical vapor deposition (CVD) is a widely used technique for preparing large-area and high-quality TMDCs. Yet, it suffers from the challenge of transfer due to the strong interaction between 2D materials and substrates. The traditional PMMA-assisted wet etching method tends to induce damage, wrinkles, and inevitable polymer residues. In this work, we propose an etch-free and clean transfer method via a water intercalation strategy for TMDCs, ensuring a high-fidelity, wrinkle-free, and crack-free transfer with negligible residues. Furthermore, metal electrodes can also be transferred via this method and back-gate field-effect transistors (FETs) based on CVD-grown monolayer WSe₂ with van der Waals (vdW) metal/semiconductor contacts are fabricated. Compared to the PMMA-assisted transfer method (∼1.2 cm² V^-1 s^-1 hole mobility with ∼2 × 10⁶ ON/OFF ratio), our high-fidelity transfer method significantly enhances the electrical performance of WSe₂ FET over one order of magnitude, achieving a hole mobility of ∼43 cm² V^-1 s^-1 and a high ON/OFF ratio of ∼5 × 10⁷ in air at room temperature.

Water scarcity has become a global challenge attributed to climate change, deforestation, population growth, and increasing water demand. While advanced water production plants are prevalent in urban areas, remote islands and sparsely populated regions face significant obstacles in establishing such technologies. Consequently, there is an urgent need for efficient, affordable, and sustainable water production technologies in these areas. Herein, we present a facile approach utilizing an ultrashort-pulsed laser to directly convert cotton fabric into graphene under ambient conditions. The resulting laser-induced graphene (LIG) demonstrates the highest light absorption efficiency of 99.0% and a broad absorption range (250-2500 nm). As an excellent solar absorber, LIG on cotton fabric can efficiently absorb 98.6% of the total solar irradiance and its surface temperature can reach 84.5 °C under sunlight without optical concentration. Moreover, we propose a cost-effective 3D LIG evaporator (LIGE) for continuous solar-powered desalination. This innovative design effectively mitigates salt formation issues and enhances the steam generation efficiency. The water evaporation rate and the solar-to-vapor conversion efficiency are measured to be around 1.709 kg m^-2 h^-1 and 95.1%, respectively, which surpass those reported in previous studies. The simplicity, durability, and continuous operational capability of the 3D LIGE offer promising prospects to address the growing challenges in global water scarcity.

The high electrical conductivity and good chemical stability of MXenes offer hopes for their use in many applications, such as wearable electronics, energy storage, and electromagnetic interference shielding. While their optical, electronic, and electrochemical properties have been widely studied, information on the thermal properties of MXenes is scarce. In this study, we investigate the heat transport properties of Ti₃C₂T_x MXene single flakes using scanning thermal microscopy and find exceptionally low anisotropic thermal conductivities within the Ti₃C₂T_x flakes, leading to an effective thermal conductivity of 0.78 ± 0.21 W m^-1 K^-1. This observation is in stark contrast to the predictions of the Wiedemann-Franz law, as the estimated Lorenz number is only 0.25 of the classical value. Due to the combination of low thermal conductivity and low emissivity of Ti₃C₂T_x, the heat loss from it is 2 orders of magnitude smaller than that from common metals. Our study explores the heat transport mechanisms of MXenes and highlights a promising approach for developing thermal insulation, two-dimensional thermoelectric, or infrared stealth materials.

Monolayers of semiconducting transition metal dichalcogenides (TMDs) have long attracted interest for their intriguing optical and electronic properties. Recently, TMDs in their quasi-bulk form have started to show considerable promise for nanophotonics thanks to their high refractive indices, large optical anisotropy, wide transparency windows reaching to the visible, and robust room temperature excitons promising for nonlinear optics. Adherence of TMD layers to any substrate via van der Waals forces is a further key enabler for the nanofabrication of complex photonic structures requiring heterointegration. Here, we use the attractive properties of TMDs and realize topological spin-Hall photonic lattices made of arrays of triangular nanoholes in 50 to 100 nm thick WS₂ flakes exfoliated on SiO₂/Si substrates. High-quality structures are achieved by taking advantage of anisotropic dry etching dictated by the crystal axes of WS₂. Reflectance measurements at room temperature show a photonic gap opening in the near-infrared in trivial and topological phases. Unidirectional propagation along the domain interface is demonstrated in real space via circularly polarized laser excitation in samples with both zigzag and armchair domain boundaries. Finite-difference time-domain simulations are used to interpret optical spectroscopy results. Our work demonstrates the feasibility of more complex nanophotonic devices based on the layered (van der Waals) materials platform.