Monolayer germanium sulfide (GeS) has gained significant attention for its exceptional anisotropic electronic conductance, notable excitonic effects, and wide range of applications. In this study we used density functional theory, the nonequilibrium Green's function, and many-body perturbation theory to investigate electronic transport properties and exciton radiative lifetime of single-layer germanium sulfide. Our theoretical findings showed that applying up to 8% compressive strain yielded a nearly threefold increase in carrier mobility and dramatically enhanced device's current intensity. Moreover, we observed that strain engineering allowed for fine-tuning of the electron-hole recombination time. At 6% tensile strain, the effective radiative lifetime was as short as 0.81 ps, which is 4 times faster than the intrinsic case and 24 times faster than at 8% compressive strain. These results highlight the potential of strain engineering to customize the electronic and optical properties of GeS monolayer for specific electronic, optoelectronic, and photovoltaic applications.

The concept of valleytronics has recently gained considerable research attention due to its intriguing physical phenomena and practical applications in optoelectronics and quantum information. In this study, by employing the Green function-Bethe-Salpeter equation (GW-BSE) calculations and symmetry analysis, we demonstrate that single-layer orthorhombic SnS and SnSe possess remarkable carrier mobility and exceptional excitonic effects. These materials display spontaneous linearly polarized optical selectivity, a behavior that differs from the valley-selective circular dichroism observed in the hexagonal lattices. Specifically, when the two-dimensional tin chalcogenide is subjected to a zigzag polarization of light, only the A exciton becomes optically active, while the B exciton remains dark. The armchair-polarized light triggers the opposite behavior. This selective optical excitation arises from the symmetry of the bands under mirror symmetry. Additionally, the study reveals a strong coupling between valley physics and ferroelectricity in layered tin chalcogenides, enabling the manipulation of exciton polarization. Layered tin chalcogenides thus emerge as promising candidates for valleytronic materials.

One-dimensional (1D) novel pentagonal materials have gained significant attention as a new class of materials with unique properties that could influence future technologies. In this report, we studied the structural, electronic, and transport properties of 1D pentagonal PdSe₂ nanotubes (p-PdSe₂ NTs). The stability and electronic properties of p-PdSe₂ NTs with different tube sizes and under uniaxial strain were investigated using density functional theory (DFT). The studied structures showed an indirect-to-direct bandgap transition with slight variation in the bandgap as the tube diameter increased. Specifically, (5 × 5) p-PdSe₂ NT, (6 × 6) p-PdSe₂ NT, (7 × 7) p-PdSe₂ NT, and (8 × 8) p-PdSe₂ NT are indirect bandgap semiconductors, while (9 × 9) p-PdSe₂ NT exhibits a direct bandgap. In addition, under low uniaxial strain, the surveyed structures were stable and maintained the pentagonal ring structure. The structures were fragmented under tensile strain of 24%, and compression of −18% for sample (5 × 5) and −20% for sample (9 × 9). The electronic band structure and bandgap were strongly affected by uniaxial strain. The evolution of the bandgap vs. the strain was linear. The bandgap of p-PdSe₂ NT experienced an indirect–direct–indirect or a direct–indirect–direct transition when axial strain was applied. A deformability effect in the current modulation was observed when the bias voltage ranged from about 1.4 to 2.0 V or from −1.2 to −2.0 V. Calculation of the field effect I–V characteristic showed that the on/off ratio was large with bias potentials from 1.5 to 2.0 V. This ratio increased when the inside of the nanotube contained a dielectric. The results of this investigation provide a better understanding of p-PdSe₂ NTs, and open up potential applications in next-generation electronic devices and electromechanical sensors.

Based on the density functional theory in combination with the nonequilibrium Green’s function formalism, we study the structural, electronic, and transport properties of SS-pSiC₂ NRs under a sequence of uniaxial strains in the range from 10% compression to 10% stretch. The pentagon network of SS-pSiC₂ NRs is still maintained, but the bond length along the strained direction is largely changed under this strain. The electronic band structure and bandgap are strongly affected by the uniaxial compressive strain. The evolution of the bandgap vs the strain is linear. With a bias voltage of 2 V, the current of the 10% compressed sample increased 75 times, and the current of the 10% stretched sample increased 2.5 times compared to the one of the relaxed sample. The I–V characteristic of SS-pSiC₂ NRs seems to be more sensitive to compressive strain than the stretch strain. Our calculations may indicate new applications of strain structures in electromechanical devices based on SS-pSiC₂ NRs.