From Insulator to Superconductor: A Series of Pressure-Driven Transitions in Quasi-One-Dimensional TiS3 Nanoribbons

Transition metal trichalcogenides (TMTCs) offer remarkable opportunities for tuning electronic states through modifications in chemical composition, temperature, and pressure. Despite considerable interest in TMTCs, there remain significant knowledge gaps concerning the evolution of their electronic properties under compression. In this study, we employ experimental and theoretical approaches to comprehensively explore the high-pressure behavior of the electronic properties of TiS3, a quasi-one-dimensional (Q1D) semiconductor, across various temperature ranges. Through high-pressure electrical resistance and magnetic measurements at elevated pressures, we uncover a distinctive sequence of phase transitions within TiS3, encompassing a transformation from an insulating state at ambient pressure to the emergence of an incipient superconducting state above 70 GPa. Our findings provide compelling evidence that superconductivity at low temperatures of ∼2.9 K is a fundamental characteristic of TiS3, shedding new light on the intriguing high-pressure electronic properties of TiS3 and underscoring the broader implications of our discoveries for TMTCs in general.

Basic aspects of the charge density wave instability of transition metal trichalcogenides NbSe3and monoclinic-TaS3

NbSe₃and monoclinic-TaS₃(m-TaS₃) are quasi-1D metals containing three different types of chains and undergoing two different charge density wave Peierls transitions atTP1andTP2associated with type III and type I chains, respectively. The nature of these transitions is discussed on the basis of first-principles DFT calculation of their Fermi surface (FS) and electron-hole response function. Because of the stronger inter-chain interactions, the FS and electron-hole response function are considerably more complex for NbSe₃thanm-TaS₃; however a common scenario can be put forward to rationalize the results. The intra-chain inter-band nesting processes dominate the strongest response for both type I and type III chains of the two compounds. Two well-defined maxima of the electron-hole response for NbSe₃are found with the (0a^*, 0c^*) and (1/2a^*, 1/2c^*) transverse components atTP1andTP2, respectively, whereas the second maximum is not observed form-TaS₃atTP2. Analysis of the different inter-chain coupling mechanisms leads to the conclusion that FS nesting effects are only relevant to set the transversea^*components in NbSe₃. The strongest inter-chain Coulomb coupling mechanism must be taken into account for the transverse coupling alongc^*in NbSe₃and along botha^*andc^*form-TaS₃. Phonon spectrum calculations reveal the formation of a giant 2k_FKohn anomaly form-TaS₃. All these results support a weak coupling scenario for the Peierls transition of transition metal trichalcogenides.

Slot-Die-Printed Two-Dimensional ZrS3 Charge Transport Layer for Perovskite Light-Emitting Diodes

Liquid-phase exfoliation of zirconium trisulfide (ZrS₃) was used to produce stable and ready-to-use inks for solution-processed semiconductor thin-film deposition. Ribbon-like layered crystals of ZrS₃ were produced by the chemical vapor transport method and were then exfoliated in three different solvents: dimethylformamide, ethanol, and isopropyl alcohol. The resulting ZrS₃ dispersions were compared for stability and the ability to form continuous films on top of the perovskite layer in light-emitting diodes with the ITO/PEDOT:PSS/MAPbBr₃/2D-ZrS₃/LiF/Al structure. Film deposition was performed by using either spray or slot-die coating methods. The slot-die coating route proved to produce better and more uniform films with respect to spray coating. We found that the 2D ZrS₃ electron injection layer (EIL) stabilized the interface between the perovskite and LiF/Al cathode, reducing the turn-on voltage to 2.8 V and showing a luminance that does not degrade during voltage sweep. On the other hand, EIL-free devices show electroluminescence on the first voltage sweep that reduces almost to zero in the subsequent sweeps. Combining physical device simulation and density functional theory calculation, we are able to explain these results in terms of lowering the electron injection barrier at the cathode.

Low Resistivity and High Breakdown Current Density of 10 nm Diameter van der Waals TaSe3 Nanowires by Chemical Vapor Deposition

Micron-scale single-crystal nanowires of metallic TaSe₃, a material that forms -Ta-Se₃-Ta-Se₃- stacks separated from one another by a tubular van der Waals (vdW) gap, have been synthesized using chemical vapor deposition (CVD) on a SiO₂/Si substrate, in a process compatible with semiconductor industry requirements. Their electrical resistivity was found unaffected by downscaling from the bulk to as little as 7 nm in nanowire width and height, in striking contrast to the resistivity of copper for the same dimensions. While the bulk resistivity of TaSe₃ is substantially higher than that of bulk copper, at the nanometer scale the TaSe₃ wires become competitive to similar-sized copper ones. Moreover, we find that the vdW TaSe₃ nanowires sustain current densities in excess of 10⁸ A/cm² and feature an electromigration energy barrier twice that of copper. The results highlight the promise of quasi-one-dimensional transition metal trichalcogenides for electronic interconnect applications and the potential of van der Waals materials for downscaled electronics.

Quasi-1D TiS3 Nanoribbons: Mechanical Exfoliation and Thickness-Dependent Raman Spectroscopy

Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS₃ whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS₃ chains. Theoretical calculations show that the energies required for breaking weak interactions between the two-dimensional (2D) layers and between 1D chains within the layers are comparable and, in turn, are considerably lower than those required for breaking the covalent bonds within the chains. We also emulated macroscopic exfoliation experiments on the nanoscale by applying a local shear force to TiS₃ crystals in different crystallographic directions using a tip of an atomic force microscopy (AFM) probe. In the AFM experiments, it was possible to slide the 2D TiS₃ layers relative to each other as well as to remove selected 1D chains from the layers. We systematically studied the exfoliated TiS₃ crystals by Raman spectroscopy and identified the Raman peaks whose spectral positions were most dependent on the crystals' thickness. These results could be used to distinguish between TiS₃ crystals with thickness ranging from one to about seven monolayers. The conclusions established in this study for the exfoliated TiS₃ crystals can be extended to a variety of transition metal trichalcogenide materials as well as other quasi-1D crystals. The possibility of exfoliation of TiS₃ into narrow (few-nm wide) crystals with smooth edges could be important for the future realization of miniature device channels with reduced edge scattering of charge carriers.