Flexible Foil of Hybrid TaS2 /Organic Superlattice: Fabrication and Electrical Properties

Unconventional superconductivity in chiral molecule-TaS2 hybrid superlattices

Chiral superconductors, a unique class of unconventional superconductors in which the complex superconducting order parameter winds clockwise or anticlockwise in the momentum space1, represent a topologically non-trivial system with intrinsic time-reversal symmetry breaking (TRSB) and direct implications for topological quantum computing2,3. Intrinsic chiral superconductors are extremely rare, with only a few arguable examples, including UTe2, UPt3 and Sr2RuO4 (refs. 4-7). It has been suggested that chiral superconductivity may exist in non-centrosymmetric superconductors8,9, although such non-centrosymmetry is uncommon in typical solid-state superconductors. Alternatively, chiral molecules with neither mirror nor inversion symmetry have been widely investigated. We suggest that an incorporation of chiral molecules into conventional superconductor lattices could introduce non-centrosymmetry and help realize chiral superconductivity10. Here we explore unconventional superconductivity in chiral molecule intercalated TaS2 hybrid superlattices. Our studies reveal an exceptionally large in-plane upper critical field Bc2,|| well beyond the Pauli paramagnetic limit, a robust π-phase shift in Little-Parks measurements and a field-free superconducting diode effect (SDE). These experimental signatures of unconventional superconductivity suggest that the intriguing interplay between crystalline atomic layers and the self-assembled chiral molecular layers may lead to exotic topological materials. Our study highlights that the hybrid superlattices could lay a versatile path to artificial quantum materials by combining a vast library of layered crystals of rich physical properties with the nearly infinite variations of molecules of designable structural motifs and functional groups11.

Dielectric Matching by the Unique Dynamic Dipoles in Hybrid Organic/Inorganic Superlattices toward Ultrathin Microwave Absorber

There is an urgent demand of ultrathin high-performance microwave absorbing materials (MAMs) in the electromagnetic protection field. However, minimizing thickness is challenging mainly due to dielectric mismatch at high permittivity from excessive dielectric loss, leading to strong reflection at 2-18 GHz. Here, a hybrid TaS2 /Co(Cp)2 superlattice is fabricated with alternating [TaS2 ] inorganic layers and [Co(Cp)2 ] organic layers. Dynamic Ta─Co dipoles offer a unique interfacial polarization relaxation mechanism involving the inversion and rotation of dynamic Ta─Co dipoles. The prolonged relaxation time of limited dynamic Ta─Co dipoles contributes to enhanced dielectric matching at high permittivity, which is essential for ultrathin high-performance MAMs. Furthermore, the confinement of paramagnetic Co(Cp)2 molecules in the interlayer space of the diamagnetic TaS2 sublattice triggers unexpected ferromagnetism via interfacial magnetic coupling conducive to the improved microwave-absorbing performance at reduced thickness. Therefore, it presents a 1.271-mm thick ultrathin absorber that can attenuate up to 99.99% of electromagnetic wave energy with a broad effective absorption bandwidth of 4.05 GHz, thus pushing the limits of thickness of 2D-based high-performance MAMs. This paper demonstrates a new strategy toward ultrathin MAMs with tunable and decent electromagnetic loss derived from electrical and magnetic coupling at the atomic scale.

Robustly Enhanced Seebeck Coefficient in the MXene/Organics/TiS2 Misfit Structure for Flexible Thermoelectrics

The flexible thermoelectric (TE) generator has emerged as a superior alternative to traditional batteries for powering wearable electronic devices, as it can efficiently convert skin heat into electricity without any safety concerns. MXene, a highly researched two-dimensional material, is known for its exceptional flexibility, hydrophilicity, metallic conductivity, and processability, among other properties, making it a versatile material for a wide range of applications, including supercapacitors, electromagnetic shielding, and sensors. However, the low intrinsic Seebeck coefficient of MXene due to its metallic conducting nature poses a significant challenge to its TE application. Therefore, improving the Seebeck coefficient remains a primary concern. In this regard, a flexible MXene/organics/TiS₂ misfit film was synthesized in this work through organic intercalation, exfoliation, and re-assembly techniques. The absolute value of Seebeck coefficient of the misfit film was significantly enhanced to 44.8 μV K^-1, which is five times higher than that of the original MXene film. This enhancement is attributed primarily to the weighted effect of the Seebeck coefficient and possibly to energy-filtering effects at the heterogeneous interfaces. Additionally, the power factor of the misfit film was considerably improved to 77.2 μW m^-1 K^-2, which is 18 times higher than that of the original MXene film. The maximum output power of the TE device constructed of the misfit film was 95 nW at a temperature difference of 40 K, resulting in a power density of 1.18 W m^-2, demonstrating the significant potential of this technology for driving low-energy consumption wearable electronics.

Regulating the Electrical and Mechanical Properties of TaS2 Films via van der Waals and Electrostatic Interaction for High Performance Electromagnetic Interference Shielding

Low-dimensional transition metal dichalcogenides (TMDs) have unique electronic structure, vibration modes, and physicochemical properties, making them suitable for fundamental studies and cutting-edge applications such as silicon electronics, optoelectronics, and bioelectronics. However, the brittleness, low toughness, and poor mechanical and electrical stabilities of TMD-based films limit their application. Herein, a TaS2 freestanding film with ultralow void ratio of 6.01% is restacked under the effect of bond-free van der Waals (vdW) interactions within the staggered 2H-TaS2 nanosheets. The restacked films demonstrated an exceptionally high electrical conductivity of 2,666 S cm-1, electromagnetic interference shielding effectiveness (EMI SE) of 41.8 dB, and absolute EMI SE (SSE/t) of 27,859 dB cm2 g-1, which is the highest value reported for TMD-based materials. The bond-free vdW interactions between the adjacent 2H-TaS2 nanosheets provide a natural interfacial strain relaxation, achieving excellent flexibility without rupture after 1,000 bends. In addition, the TaS2 nanosheets are further combined with the polymer fibers of bacterial cellulose and aramid nanofibers via electrostatic interactions to significantly enhance the tensile strength and flexibility of the films while maintaining their high electrical conductivity and EMI SE.This work provides promising alternatives for conventional materials used in EMI shielding and nanodevices.

Superlattice-Stabilized WSe2 Cathode for Rechargeable Aluminum Batteries

Rechargeable aluminum batteries (RABs), with abundant aluminum reserves, low cost, and high safety, give them outstanding advantages in the postlithium batteries era. However, the high charge density (364 C mm^-3 ) and large binding energy of three-electron-charge aluminum ions (Al³⁺ ) de-intercalation usually lead to irreversible structural deterioration and decayed battery performance. Herein, to mitigate these inherent defects from Al³⁺ , an unexplored family of superlattice-type tungsten selenide-sodium dodecylbenzene sulfonate (SDBS) (S-WSe₂ ) cathode in RABs with a stably crystal structure, expanded interlayer, and enhanced Al-ion diffusion kinetic process is proposed. Benefiting from the unique advantage of superlattice-type structure, the anionic surfactant SDBS in S-WSe₂ can effectively tune the interlayer spacing of WSe₂ with released crystal strain from high-charge-density Al³⁺ and achieve impressively long-term cycle stability (110 mAh g^-1 over 1500 cycles at 2.0 A g^-1 ). Meanwhile, the optimized S-WSe₂ cathode with intrinsic negative attraction of SDBS significantly accelerates the Al³⁺ diffusion process with one of the best rate performances (165 mAh g^-1 at 2.0 A g^-1 ) in RABs. The findings of this study pave a new direction toward durable and high-performance electrode materials for RABs.

Organic covalent modification to improve thermoelectric properties of TaS2

Organic semiconductors are attracting considerable attention as a new thermoelectric material because of their molecular diversity, non-toxicity and easy processing. The side chains which are introduced into two-dimensional (2D) transition metal dichalcogenides (TMDs) by covalent modification lead to a significant decrease in their thermal conductivity. Here, we describe a simple approach to preparing the side chains covalent modification TaS₂ (SCCM-TaS₂) organic/inorganic hybrid structures, which is a homogeneous and non-destructive technique that does not depend on defects and boundaries. Electrical conductivity of 3,401 S cm^-1 and a power factor of 0.34 mW m^-1 K^-2 are obtained for a hybrid material of SCCM-TaS₂, with an in-plane thermal conductivity of 4.0 W m^-1 K^-1, which is 7 times smaller than the thermal conductivity of the pristine TaS₂ crystal. The power factor and low thermal conductivity contribute to a thermoelectric figure of merit (ZT) of ~0.04 at 443 K.

Chiral molecular intercalation superlattices

The discovery of chiral-induced spin selectivity (CISS) opens up the possibility to manipulate spin orientation without external magnetic fields and enables new spintronic device designs^1-4. Although many approaches have been explored for introducing CISS into solid-state materials and devices, the resulting systems so far are often plagued by high inhomogeneity, low spin selectivity or limited stability, and have difficulties in forming robust spintronic devices^5-8. Here we report a new class of chiral molecular intercalation superlattices (CMIS) as a robust solid-state chiral material platform for exploring CISS. The CMIS were prepared by intercalating layered two-dimensional atomic crystals (2DACs) (such as TaS₂ and TiS₂) with selected chiral molecules (such as R-α-methylbenzylamine and S-α-methylbenzylamine). The X-ray diffraction and transmission electron microscopy studies demonstrate highly ordered superlattice structures with alternating crystalline atomic layers and self-assembled chiral molecular layers. Circular dichroism studies show clear chirality-dependent signals between right-handed (R-) and left-handed (S-) CMIS. Furthermore, by using the resulting CMIS as the spin-filtering layer, we create spin-selective tunnelling junctions with a distinct chirality-dependent tunnelling current, achieving a tunnelling magnetoresistance ratio of more than 300 per cent and a spin polarization ratio of more than 60 per cent. With a large family of 2DACs of widely tunable electronic properties and a vast selection of chiral molecules of designable structural motifs, the CMIS define a rich family of artificial chiral materials for investigating the CISS effect and capturing its potential for new spintronic devices.

Hybrid superlattices of two-dimensional materials and organics

Hybrid inorganic/organic superlattices provide a new path to access the exceptional properties of 2D materials in bulk quantities for macroscopic applications.