Ta Doping Effect on Structural and Optical Properties of InTe Thin Films

Low-Symmetry 2D t-InTe for Polarization-Sensitive UV-Vis-NIR Photodetection

Polarization-sensitive photodetection grounded on low-symmetry 2D materials has immense potential in improving detection accuracy, realizing intelligent detection, and enabling multidimensional visual perception, which has promising application prospects in bio-identification, optical communications, near-infrared imaging, radar, military, and security. However, the majority of the reported polarized photodetection are limited by UV-vis response range and low anisotropic photoresponsivity factor, limiting the achievement of high-performance anisotropic photodetection. Herein, 2D t-InTe crystal is introduced into anisotropic systems and developed to realize broadband-response and high-anisotropy-ratio polarized photodetection. Stemming from its narrow band gap and intrinsic low-symmetry lattice characteristic, 2D t-InTe-based photodetector exhibits a UV-vis-NIR broadband photoresponse and significant photoresponsivity anisotropy behavior, with an exceptional in-plane anisotropic factor of 1.81@808 nm laser, surpassing the performance of most reported 2D counterparts. This work expounds the anisotropic structure-activity relationship of 2D t-InTe crystal, and identifies 2D t-InTe as a prospective candidate for high-performance polarization-sensitive optoelectronics, laying the foundation for future multifunctional device applications.

The Effect of pH Solution in the Sol–Gel Process on the Structure and Properties of Thin SnO2 Films

The synthesis of surface-active structures is important for creating many applications. The structural formation of SnO2 thin films in the range from 1.4 to 1.53 pH is studied in this work. This process occurs on the surface of the sample in the range of 1.4 to 1.49 and in the volume in the range of 1.51 to 1.53. SnO2 is formed after annealing at 400 ∘C, according to XRD. Doping NH4OH to solution stimulates particle coagulation and gel formation. All of these have an impact on the transparency of samples investigated by spectrophotometric methods. By increasing the pH, the resistance raises at room temperature. The Eg calculation along the fundamental absorption edge shows that it is greater than 3.6 eV’ for SnO2 films. According to the Burstein–Moss effect, a change of the bandgap is related to the increased concentration of the free charge carriers. Elemental analysis has shown that chlorine ions are considered to be additional sources of charge carriers. The value pH = 1.49 is critical since there is a drastic change in the structure of the samples, the decrease in transparency is replaced by its increase, and the energy of activation of impurity levels is changed.

Layer-Dependent Nonlinear Optical Properties of WS2, MoS2, and Bi2S3 Films Synthesized by Chemical Vapor Deposition

Two-dimensional (2D) layered materials have shown layer-dependent optical properties in both linear optical and nonlinear optical (NLO) regimes due to prominent interlayer coupling and quantum confinement in an atomic scale. However, the NLO properties become more complicated as both saturable absorption (SA) and reverse saturable absorption (RSA) easily happen in 2D materials, which results in a significant challenge to understand the evolution of nonlinear absorption with layers. Motivated by this, chemical vapor-deposited chalcogenide compounds (WS₂, MoS₂, and Bi₂S₃) are used to investigate the pump intensity and layer number-dependent NLO properties. The values of nonlinear absorption coefficients of these chalcogenide compounds increase with the pump intensity by an 800 nm femtosecond laser, which can be described by an empirical power law function. The SA process due to the large transition probability of the ground state readily takes place in thick samples, while RSA occurs easily in thin samples due to the two-photon absorption (TPA). The transition from TPA to SA is deduced to occur at 13L-WS₂, 15L-MoS₂, and 5L-Bi₂S₃, which is related to the layer-dependent band gaps. Our results provide an efficient way to tune optical nonlinearities with a controlled layer number and to design corresponding NLO devices such as optical switches and saturable absorbers.