Improvements in the Performance of a Visible-NIR Photodetector Using Horizontally Aligned TiS3 Nanoribbons

High-Sensitive Uncooled Mid-Wave Infrared Detector Based on TiS3 Nanoribbon

High-sensitive uncooled mid-wave infrared (MWIR) photodetection with fast speed is highly desired for biomedical imaging, optical communication, and night vision technology. Low-dimensional materials with low dark current and broadband photoresponse hold great promise for use in MWIR detection. Here, this study reports a high-performance MWIR photodetector based on a titanium trisulfide (TiS3) nanoribbon. This device demonstrates an ultra-broadband photoresponse ranging from the visible spectrum to the MWIR spectrum (405-4275 nm). In the MWIR spectral range, the photodetector achieves competitive high photoresponsivity (R) of 21.1 A W-1, and an impressive specific detectivity (D*) of 5.9 × 1010 cmHz1/2 W-1 in ambient air. Remarkably, the photoresponse speed in the MWIR with τr = 1.3 ms and τd = 1.5 ms is realized which is much faster than the thermal time constant of 15 ms. These findings pave the way for highly sensitive, room-temperature MWIR photodetectors with exceptionally fast response speed.

Physisorption-Mediated Charge Transfer in TiS2 Nanodiscs: A Room Temperature Sensor for Highly Sensitive and Reversible Carbon Dioxide Detection

Real-time and high-performance monitoring of trace carbon dioxide (CO2) has become a necessity due to its substantial impact on the global climate, human health, indoor occupancy, and crop productivity. Two-dimensional materials such as transition metal dichalcogenides (TMDs) have gained significant interest in gas sensing applications owing to their intrinsically high surface-to-volume ratio. However, the research has been limited to prominent TMDs such as WS2 and MoS2. Specifically, the chemiresistive sensing performance of titanium disulfide (TiS2) has rarely been investigated. We present an electric-field-assisted TiS2 nanodisc assembly for the fabrication of a low-cost, low-power CO2 gas sensor based on charge transfer between physisorbed CO2 analyte molecules and TiS2 nanodiscs operating at room temperature. The physiochemical properties of the synthesized TiS2 nanodiscs were investigated via scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The fabricated sensor demonstrated an ultra-high sensor response of 60%, a fast response time of 37 s toward 500 ppm CO2 gas, and the lowest detection limit of 5 ppm under ambient conditions. The low adsorption energies and vdW interaction between CO2 molecules and TiS2 resulted in easy desorption, allowing the sensor to self-recover without the need for external stimuli, which is hardly been witnessed in other 2D material analogues. Furthermore, the sensor has excellent reproducibility and stability for successive analyte exposures, as well as excellent selectivity for CO2 over other interfering gases. This reported sensor based on 2D TMDs is the first of its type to integrate such a broad range of sensor characteristics (such as high sensor response and sensitivity, rapid response and recovery times, a high signal-to-noise ratio, and excellent selectivity at room temperature) into a single, revolutionary device for CO2 detection.

TiS3 Nanoribbons: A Novel Material for Ultra-Sensitive Photodetection across Extreme Temperature Ranges

Photodetectors that can operate over a wide range of temperatures, from cryogenic to elevated temperatures, are crucial for a variety of modern scientific fields, including aerospace, high-energy science, and astro-particle science. In this study, we investigate the temperature-dependent photodetection properties of titanium trisulfide (TiS₃)- in order to develop high-performance photodetectors that can operate across a wide range of temperatures (77 K-543 K). We fabricate a solid-state photodetector using the dielectrophoresis technique, which demonstrates a quick response (response/recovery time ~0.093 s) and high performance over a wide range of temperatures. Specifically, the photodetector exhibits a very high photocurrent (6.95 × 10^-5 A), photoresponsivity (1.624 × 10⁸ A/W), quantum efficiency (3.3 × 10⁸ A/W·nm), and detectivity (4.328 × 10¹⁵ Jones) for a 617 nm wavelength of light with a very weak intensity (~1.0 × 10^-5 W/cm²). The developed photodetector also shows a very high device ON/OFF ratio (~32). Prior to fabrication, the TiS₃ nanoribbons were synthesized using the chemical vapor technique and characterized according to their morphology, structure, stability, and electronic and optoelectronic properties; this was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a UV-Visible-NIR spectrophotometer. We anticipate that this novel solid-state photodetector will have broad applications in modern optoelectronic devices.

Quasi-One-Dimensional ZrS3 Nanoflakes for Broadband and Polarized Photodetection with High Tuning Flexibility

Two-dimensional (2D) layered materials with low crystal symmetries have exhibited unique anisotropic physical properties. Here, we report systematic studies on the photoresponse of field effect transistors (FETs) fabricated using quasi-one-dimensional ZrS₃ nanoflakes. The as-fabricated phototransistors exhibit a broadband photocurrent response from ultraviolet to visible regions, where the responsivity and detectivity can be enhanced via additional gate voltages. Furthermore, benefiting from the strong in-plane anisotropy of ZrS₃, we observe a gate-voltage and illumination wavelength-dependent polarized photocurrent response, while its sub-millisecond-time response speed is also polarization-dependent. Our results demonstrate the flexible tunability of photodetectors based on anisotropic layered semiconductors, which substantially broadens the application of low symmetry layered materials in polarization-sensitive optoelectronic devices.

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.

High-Responsivity Multiband and Polarization-Sensitive Photodetector Based on the TiS3/MoS2 Heterojunction

Two-dimensional (2D) material photodetectors have received considerable attention in optoelectronics as a result of their extraordinary properties, such as passivated surfaces, strong light-matter interactions, and broad spectral responses. However, single 2D material photodetectors still suffer from low responsivity, large dark current, and long response time as a result of their atomic-level thickness, large binding energy, and susceptibility to defects. Here, a transition metal trichalcogenide TiS₃ with excellent photoelectric characteristics, including a direct bandgap (1.1 eV), high mobility, high air stability, and anisotropy, is selected to construct a type-II heterojunction with few-layer MoS₂, aiming to improve the performance of 2D photodetectors. An ultrahigh photoresponsivity of the TiS₃/MoS₂ heterojunction of 48 666 A/W at 365 nm, 20 000 A/W at 625 nm, and 251 A/W at 850 nm is achieved under light-emitting diode illumination. The response time and dark current are 2 and 3 orders of magnitude lower than those of the current TiS₃ photodetector with the highest photoresponsivity (2500 A/W), respectively. Furthermore, polarized four-wave mixing spectroscopy and polarized photocurrent measurements verify its polarization-sensitive characteristics. This work confirms the excellent potential of TiS₃/MoS₂ heterojunctions for air-stable, high-performance, polarization-sensitive, and multiband photodetectors, and the excellent type-II TiS₃/MoS₂ heterojunction system may accelerate the design and fabrication of other 2D functional devices.

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.

Complexities at the Au/ZrS3(001) interface probed by x-ray photoemission spectroscopy

Interaction between the Au adlayers and ZrS₃(001) has been examined via x-ray photoemission spectroscopy (XPS). The angle-resolved XPS measurements reveal that ZrS₃(001) is disulfide (S₂^2-) terminated and the Au thickness-dependent XPS indicates that the observed band bending, for low Au coverage, is consistent with formation of a Schottky barrier at the Au/ZrS₃(001) interface. This band bending, however, appears to be suppressed as the thickness of Au adlayer is increased, indicating varying interfacial interactions at the Au/ZrS₃(001) interface. Such complex interface effects between Au and ZrS₃(001) may explain the observed non-ohmicI-Vcharacteristics for a ZrS₃-based device, and could suppress current injection.

Optoelectronic Artificial Synapses Based on Two-Dimensional Transitional-Metal Trichalcogenide

The memristor is a foundational device for an artificial synapse, which is essential to realize next-generation neuromorphic computing. Herein, an optoelectronic memristor based on a two-dimensional (2D) transitional-metal trichalcogenide (TMTC) is designed and demonstrated. Owing to the excellent optical and electrical characteristics of titanium trisulfide (TiS₃), the memristor exhibits stable bipolar resistance switching (RS) as a result of the controllable formation and rupturing of the conductive aluminum filaments. Multilevel storage is realized with light of multiple wavelengths between 400 and 808 nm, and the synaptic properties such as conduction modulation and spiking timing-dependent plasticity (STDP) are achieved. On the basis of the photonic potentiation and electrical habitual ability, Pavlovian-associative learning is successfully established on this TiS₃-based artificial synapse. All these results reveal the large potential of 2D TMTCs in artificial neuromorphic chips.

Birefringence and Dichroism in Quasi-1D Transition Metal Trichalcogenides: Direct Experimental Investigation

Birefringence and dichroism are very important properties in optical anisotropy. Understanding the intrinsic birefringence and dichroism of a material can provide great help to utilize its optical anisotropy. But the direct experimental investigation of birefringence in nanoscale materials is rarely reported. As typical anisotropic transition metals trichalcogenides (TMTCs) materials with quasi-1D structure, TiS₃ and ZrS₃ have attracted extensive attention due to their special crystal structure and optical anisotropy characteristics. Here, the optical anisotropy properties such as birefringence and dichroism of two kinds of quasi-1D TMTCs, TiS₃ and ZrS₃ , are theoretically and experimentally studied. In experimental results, the anisotropic refraction and anisotropic reflection of TiS₃ and ZrS₃ are studied by polarization-resolved optical microscopy and azimuth-dependent reflectance difference microscopy, respectively. In addition, the birefringence and dichroism of ZrS₃ nanoribbon in experiment are directly measured by spectrometric ellipsometry measurements, and a reasonable result is obtained. This work provides the basic optical anisotropy information of TiS₃ and ZrS₃ . It lays a foundation for the further study of the optical anisotropy of these two materials and provides a feasible method for the study of birefringence and dichroism of other nanomaterials in the future.

Interface Kinetics Assisted Barrier Removal in Large Area 2D-WS2 Growth to Facilitate Mass Scale Device Production

Growth of monolayer WS2 of domain size beyond few microns is a challenge even today; and it is still restricted to traditional exfoliation techniques, with no control over the dimension. Here, we present the synthesis of mono- to few layer WS2 film of centimeter2 size on graphene-oxide (GO) coated Si/SiO2 substrate using the chemical vapor deposition CVD technique. Although the individual size of WS2 crystallites is found smaller, the joining of grain boundaries due to sp 2-bonded carbon nanostructures (~3-6 nm) in GO to reduced graphene-oxide (RGO) transformed film, facilitates the expansion of domain size in continuous fashion resulting in full coverage of the substrate. Another factor, equally important for expanding the domain boundary, is surface roughness of RGO film. This is confirmed by conducting WS2 growth on Si wafer marked with few scratches on polished surface. Interestingly, WS2 growth was observed in and around the rough surface irrespective of whether polished or unpolished. More the roughness is, better the yield in crystalline WS2 flakes. Raman mapping ascertains the uniform mono-to-few layer growth over the entire substrate, and it is reaffirmed by photoluminescence, AFM and HRTEM. This study may open up a new approach for growth of large area WS2 film for device application. We have also demonstrated the potential of the developed film for photodetector application, where the cycling response of the detector is highly repetitive with negligible drift.

Effect of Band Symmetry on Photocurrent Production in Quasi-One-Dimensional Transition-Metal Trichalcogenides

Photocurrent production in quasi-one-dimensional (1D) transition-metal trichalcogenides, TiS₃(001) and ZrS₃(001), was examined using polarization-dependent scanning photocurrent microscopy. The photocurrent intensity was the strongest when the excitation source was polarized along the 1D chains with dichroic ratios of 4:1 and 1.2:1 for ZrS₃ and TiS₃, respectively. This behavior is explained by symmetry selection rules applicable to both valence and conduction band states. Symmetry selection rules are seen to be applicable to the experimental band structure, as is observed in polarization-dependent nanospot angle-resolved photoemission spectroscopy. Based on these band symmetry assignments, it is expected that the dichroic ratios for both materials will be maximized using excitation energies within 1 eV of their band gaps, providing versatile polarization sensitive photodetection across the visible spectrum and into the near-infrared.

WS2 Quantum Dots on e-Textile as a Wearable UV Photodetector: How Well Reduced Graphene Oxide Can Serve as a Carrier Transport Medium?

We document the fabrication and investigations of a novel photodetector based on a WS₂ quantum dots and reduced graphene oxide (RGO) (WS₂-QDs/RGO) heterostructure. The proposed photodetector is simple, scalable, cost-effective, and flexible and works in an ambient environment. An enhanced photodetection efficiency is observed due to the superior electronic properties of WS₂-QDs and excellent electrical as well as thermal properties of the carrier transportation medium, RGO. For device fabrication, GO and WS₂-QDs were separately synthesized via different chemistry followed by decorating WS₂-QDs on RGO coated cotton textile. Characterization studies confirm the transformation of exfoliated WS₂-2D flakes into WS₂-0D quantum dots and graphene oxide (GO) to RGO. The optimized photodetection performance of WS₂-QDs/RGO demonstrates its photoresponsivity of 5.22 mA W^-1 at 1.4 mW mm^-2 power density of a 405 nm illumination source. Other sensor parameters such as photosensitivity (∼20.2%), resolution (∼0.031 mW mm^-2 μA^-1), response time (1.57 s), recovery time (1.83 s), and specific detectivity (∼1.6 × 10⁶ jones) are found for WS₂-QDs/RGO sensor, and a few of these parameters are comparable and even superior to some of the devices as reported. Photosensing mechanism is explained in terms of charge transfer caused by appropriate band alignment across the interface between WS₂-QDs and RGO, where dimensionality and quantum confinement of nanostructures synergistically enhance the overall performance of the heterostructure. The device flexibility is examined through bending, stretching, and twisting experiments and successfully demonstrated its potentiality. Sensor performance even after being soaked in water and subsequent drying shows the possibility of reuse. The attributes of flexibility, high sensitivity and responsivity, superior resolution, and cost-effectiveness of our novel flexible photodetector indicate its promising potential for flexible and wearable optical detectors operating in UV band. Although negative photoconductance of the WS₂-QDs/RGO sensor is a major cause for not allowing the sensor to show its best performance, a trade-off is made with improved device design to qualify the expectations of being a competitive device, and this has been demonstrated with experimental facts.

In-plane anisotropic electronics based on low-symmetry 2D materials: progress and prospects

Low-symmetry layered materials such as black phosphorus (BP) have been revived recently due to their high intrinsic mobility and in-plane anisotropic properties, which can be used in anisotropic electronic and optoelectronic devices. Since the anisotropic properties have a close relationship with their anisotropic structural characters, especially for materials with low-symmetry, exploring new low-symmetry layered materials and investigating their anisotropic properties have inspired numerous research efforts. In this paper, we review the recent experimental progresses on low-symmetry layered materials and their corresponding anisotropic electrical transport, magneto-transport, optoelectronic, thermoelectric, ferroelectric, and piezoelectric properties. The boom of new low-symmetry layered materials with high anisotropy could open up considerable possibilities for next-generation anisotropic multifunctional electronic devices.