Anomalous isoelectronic chalcogen rejection in 2D anisotropic vdW TiS3(1-x)Se3x trichalcogenides

Quasi-One-Dimensional van der Waals Transition Metal Trichalcogenides

The transition metal trichalcogenides (TMTCs) are quasi-one-dimensional (1D) MX3-type van der Waals layered semiconductors, where M is a transition metal element of groups IV and V, and X indicates chalcogen element. Due to the unique quasi-1D crystalline structures, they possess several novel electrical properties such as variable bandgaps, charge density waves, and superconductivity, and highly anisotropic optical, thermoelectric, and magnetic properties. The study of TMTCs plays an essential role in the 1D quantum materials field, enabling new opportunities in the material research dimension. Currently, tremendous progress in both materials and solid-state devices has been made, demonstrating promising applications in the realization of nanoelectronic devices. This review provides a comprehensive overview to survey the state of the art in materials, devices, and applications based on TMTCs. Firstly, the symbolic structure, current primary synthesis methods, and physical properties of TMTCs have been discussed. Secondly, examples of TMTC applications in various fields are presented, such as photodetectors, energy storage devices, catalysts, and sensors. Finally, we give an overview of the opportunities and future perspectives for the research of TMTCs, as well as the challenges in both basic research and practical applications.

Paper-based broadband flexible photodetectors with van der Waals materials

Layered metal chalcogenide materials are exceptionally appealing in optoelectronic devices thanks to their extraordinary optical properties. Recently, their application as flexible and wearable photodetectors have received a lot of attention. Herein, broadband and high-performance paper-based PDs were established in a very facile and inexpensive method by rubbing molybdenum disulfide and titanium trisulfide crystals on papers. Transferred layers were characterized by SEM, EDX mapping, and Raman analyses, and their optoelectronic properties were evaluated in a wavelength range of 405–810 nm. Although the highest and lowest photoresponsivities were respectively measured for TiS₃ (1.50 mA/W) and MoS₂ (1.13 μA/W) PDs, the TiS₃–MoS₂ heterostructure not only had a significant photoresponsivity but also showed the highest on/off ratio (1.82) and fast response time (0.96 s) compared with two other PDs. This advantage is due to the band offset formation at the heterojunction, which efficiently separates the photogenerated electron–hole pairs within the heterostructure. Numerical simulation of the introduced PDs also confirmed the superiority of TiS₃–MoS₂ heterostructure over the other two PDs and exhibited a good agreement with the experimental results. Finally, MoS₂ PD demonstrated very high flexibility under applied strain, but TiS₃ based PDs suffered from its fragility and experience a remarkable drain current reduction at strain larger than ± 0.33%. However, at lower strains, all PDs displayed acceptable performances.

Design and Optimize the Performance of Self-Powered Photodetector Based on PbS/TiS3 Heterostructure by SCAPS-1D

Titanium trisulphide (TiS₃) has been widely used in the field of optoelectronics owing to its superb optical and electronic characteristics. In this work, a self-powered photodetector using bulk PbS/TiS₃ p-n heterojunction is numerically investigated and analyzed by a Solar Cell Capacitance Simulator in one-Dimension (SCAPS-1D) software. The energy bands, electron-holes generation or recombination rate, current density-voltage (J-V), and spectral response properties have been investigated by SCAPS-1D. To improve the performance of photodetectors, the influence of thickness, shallow acceptor or donor density, and defect density are investigated. By optimization, the optimal thickness of the TiS₃ layer and PbS layer are determined to be 2.5 μm and 700 nm, respectively. The density of the superior shallow acceptor (donor) is 10¹⁵ (10²²) cm⁻³. High quality TiS₃ film is required with the defect density of about 10¹⁴ cm⁻³. For the PbS layer, the maximum defect density is 10¹⁷ cm⁻³. As a result, the photodetector based on the heterojunction with optimal parameters exhibits a good photoresponse from 300 nm to 1300 nm. Under the air mass 1.5 global tilt (AM 1.5G) illuminations, the optimal short-circuit current reaches 35.57 mA/cm² and the open circuit voltage is about 870 mV. The responsivity (R) and a detectivity (D*) of the simulated photodetector are 0.36 A W⁻¹ and 3.9 × 10¹³ Jones, respectively. The simulation result provides a promising research direction to further broaden the TiS₃-based optoelectronic device.

Integrated Tapping Mode Kelvin Probe Force Microscopy with Photoinduced Force Microscopy for Correlative Chemical and Surface Potential Mapping

Kelvin probe force microscopy (KPFM) is a popular technique for mapping the surface potential at the nanoscale through measurement of the Coulombic force between an atomic force microscopy (AFM) tip and sample. The lateral resolution of conventional KPFM variants is limited to between ≈35 and 100 nm in ambient conditions due to the long-range nature of the Coulombic force. In this article, a novel way of generating the Coulombic force in tapping mode KPFM without the need for an external AC driving voltage is presented. A field-effect transistor (FET) is used to directly switch the electrical connectivity of the tip and sample on and off periodically. The resulting Coulomb force induced by Fermi level alignment of the tip and sample results in a detectable change of the cantilever oscillation at the FET-switching frequency. The resulting FET-switched KPFM delivers a spatial resolution of ≈25 nm and inherits the high operational speed of the AFM tapping mode. Moreover, the FET-switched KPFM is integrated with photoinduced force microscopy (PiFM), enabling simultaneous acquisitions of high spatial resolution chemical distributions and surface potential maps. The integrated FET-switched KPFM with PiFM is expected to facilitate characterizations of nanoscale electrical properties of photoactive materials, semiconductors, and ferroelectric materials.