Electronic and Optical Properties of Two-Dimensional Tellurene: From First-Principles Calculations

Modeling and tuning the electronic, mechanical and optical properties of a recently synthesized 2D polyaramid: a first principles study

This work delves into a methodology of modeling 2D materials and their structural engineering, considering an example of a recently synthesized 2D polyaramid (2DPA-1). A bottom-up approach similar to experimental techniques is implemented for modeling, and then its electronic structures and phonon spectrum and the quadratic nature of flexural phonons are analyzed. Furthermore, boron and nitrogen atoms are substituted for the carbon atom of the amide group of 2DPA-1, and their effects on its electronic properties, phonon spectrum, and mechanical properties are compared with those of pristine 2DPA-1 using density functional theory calculations. The ab initio molecular dynamics (AIMD) simulations validate the thermal stability of our system at high temperatures. The spin-polarized electronic structures reveal the transformation of pristine 2DPA-1 from a semiconductor to a half-metal and its magnetic behaviour upon nitrogen substitution. Constraining the quadratic nature of flexural phonons using the Born-Huang criteria significantly enhances the phonon spectra, leading to more accurate and reliable simulations. For modulated 2DPA-1, the elastic modulus varies between 17 and 27 N m-1, and the absorption peaks shift from ∼5.15 eV to 2.42 eV, enabling the application of polymeric 2D nanomaterials in photocatalysis and sensing, where light absorption in the near-infrared region is important. Finally, validation of our methodology is confirmed, as computed Young's modulus (11.26-11.76 GPa) of 2DPA-1 matches excellently with the experimental value (12.7 ± 3.8 GPa). Overall, this study reveals the modeling of a newly synthesized polymeric 2D material, and tuning its properties results in smaller bandgaps and half-metallic and magnetic behaviours.

Suppressing the Shuttle Effect via Polypyrrole-Coated Te Nanotubes for Advanced Na-Te Batteries

There is a growing demand for research and development of advanced energy storage devices with high energy density utilizing earth-abundant metal anodes such as sodium metal. Tellurium, a member of the chalcogen group, stands out as a promising cathode material due to its remarkable volumetric capacity, comparable to sulfur, and significantly high electrical conductivity. However, critical issues arise from soluble sodium polytellurides, leading to the shuttle effect. This phenomenon can result in the loss of active materials, self-discharge, and anode instability. Here, we introduce polypyrrole-coated tellurium nanotubes as the cathode materials, where polypyrrole plays a crucial role in preventing the dissolution of polytellurides, as confirmed through operando optical microscopy. The polypyrrole-coated tellurium nanotubes exhibited an outstanding rate performance and long cycle stability in sodium-tellurium batteries. These research findings are anticipated to bolster the viability of polypyrrole-coated tellurium nanotubes as promising cathode materials, making a substantial contribution to the commercialization of sodium-ion battery technology.

Tunability of electronic properties in the 2D MoS2/α-tellurene/WS2 heterotrilayer via biaxial strain and electric field

Alpha-tellurene (α-Te), a two-dimensional (2D) material that has been theoretically predicted and experimentally verified, has garnered significant attention due to its unique properties. In this study, we investigated the 2D trilayer MoS2/α-Te/WS2 van der Waals heterostructure with different stacking orders using first-principles calculations. Our results indicate that this heterotrilayer exhibits an intrinsic type-I band alignment and an indirect band gap similar to that of monolayer α-Te. Notably, the band edges of the heterostructure can be modulated by biaxial strain and an external electric field, enabling these edges to arise from different monolayers. This controlled manipulation facilitates the effective separation of photogenerated electron-hole pairs and prolongs the carrier lifetime. Moreover, the heterostructure can undergo a transition from an indirect to a direct band gap under biaxial compressive strain or a moderate negative electric field, and semiconductor-to-metal transition can also be achieved by intensifying the biaxial strain and external electric field. Overall, our research provides valuable theoretical insights into the potential applications of α-Te-based heterostructures, rendering them promising candidates for the next generation of nanodevices.

Enhanced electronic transport properties of Te roll-like nanostructures

In this work, the electronic transport properties of Te roll-like nanostructures were investigated in a broad temperature range by fabricating single-nanostructure back-gated field-effect-transistors via photolithography. These one-dimensional nanostructures, with a unique roll-like morphology, were produced by a facile synthesis and extensively studied by scanning and transmission electron microscopy. The nanostructures are made of pure and crystalline Tellurium with trigonal structure (t-Te), and exhibit p-type conductivity with enhanced field-effect hole mobility between 273 cm²/Vs at 320 K and 881 cm²/Vs at 5 K. The thermal ionization of shallow acceptors, with small ionization energy between 2 and 4 meV, leads to free-hole conduction at high temperatures. The free-hole mobility follows a negative power-law temperature behavior, with an exponent between -1.28 and -1.42, indicating strong phonon scattering in this temperature range. At lower temperatures, the electronic conduction is dominated by nearest-neighbor hopping (NNH) conduction in the acceptor band, with a small activation energy E _NNH ≈ 0.6 meV and an acceptor concentration of N _A ≈ 1 × 10¹⁶ cm^-3. These results demonstrate the enhanced electrical properties of these nanostructures, with a small disorder, and superior quality for nanodevice applications.

Geometry of tellurene adsorbed on the Si(111)-R30°-Sb surface from first principles calculations

The 2D form of tellurium, named tellurene, is one of the latest discoveries in the family of 2D mono-elemental materials. In a trilayer configuration, free-standing tellurene was predicted theoretically to acquire two crystallographic forms, the α and β phases, corresponding to either a 1T-MoS₂-like geometry or a trilayer slab exposing the Te(101̄0) surface of bulk Te with helical chains lying in-plane and further reconstructed due to the formation of interchain bonds. Either one or the other of the two phases was observed experimentally to prevail depending on the substrate they were grown onto. In the perspective to integrate tellurene on silicon, we here report an ab initio study of the adsorption of tellurene on the Si(111)-R30° surface passivated by antinomy. According to the literature, this substrate is chosen for the growth of several tellurides by molecular beam epitaxy. The calculations reveal that on this substrate the adsorption energy mostly compensates the energy difference between the α and β phases in the free-standing configuration which suggests that the prevalence of one phase over the other might in this case strongly depend on the kinetics effects and deposition conditions.

Emerging Two-Dimensional Tellurene and Tellurides for Broadband Photodetectors

As with all stylish 2D functional materials, tellurene and tellurides possessing excellent physical and chemical properties such as high environmental stability, tunable narrow bandgap, and lower thermal conductivity, have aroused the great interest of the researchers. These properties of such materials also form the basis for relatively newfangled scholarly fields involving advanced topics, especially for broadband photodetectors. Integrating the excellent properties of many 2D materials, tellurene/telluride-based photodetectors show great flexibility, higher frequency response or faster time response, high signal-to-noise ratio, and so on, which make them leading the frontier of photodetector research. To fully understand the excellent properties of tellurene/tellurides and their optoelectronic applications, the recent advances in tellurene/telluride-based photodetectors are maximally summarized. Benefiting from the solid research in this field, the challenges and opportunities of tellurene/tellurides for future optoelectronic applications are also discussed in this review, which might provide possibilities for the realization of state-of-the-art high-performance tellurene/telluride-based devices.

Two-dimensional biomaterials: material science, biological effect and biomedical engineering applications

To date, nanotechnology has increasingly been identified as a promising and efficient means to address a number of challenges associated with public health. In the past decade, two-dimensional (2D) biomaterials, as a unique nanoplatform with planar topology, have attracted explosive interest in various fields such as biomedicine due to their unique morphology, physicochemical properties and biological effect. Motivated by the progress of graphene in biomedicine, dozens of types of ultrathin 2D biomaterials have found versatile bio-applications, including biosensing, biomedical imaging, delivery of therapeutic agents, cancer theranostics, tissue engineering, as well as others. The effective utilization of 2D biomaterials stems from the in-depth knowledge of structure-property-bioactivity-biosafety-application-performance relationships. A comprehensive summary of 2D biomaterials for biomedicine is still lacking. In this comprehensive review, we aim to concentrate on the state-of-the-art 2D biomaterials with a particular focus on their versatile biomedical applications. In particular, we discuss the design, fabrication and functionalization of 2D biomaterials used for diverse biomedical applications based on the up-to-date progress. Furthermore, the interactions between 2D biomaterials and biological systems on the spatial-temporal scale are highlighted, which will deepen the understanding of the underlying action mechanism of 2D biomaterials aiding their design with improved functionalities. Finally, taking the bench-to-bedside as a focus, we conclude this review by proposing the current crucial issues/challenges and presenting the future development directions to advance the clinical translation of these emerging 2D biomaterials.

The nonlinear optical transition bleaching in tellurene

To date, outstanding linear and nonlinear optical properties of tellurene, caused by multiple two-dimensional (2D) phases and optical anisotropy, have attracted considerable interest for potential nanophotonics applications. In this work, the ultrafast nonlinear optical (NLO) properties of α-tellurene have been studied via Z-scan and pump-probe techniques at a broadband spectral region. Typical saturable absorption and band filling effects are observed in tellurene due to the Pauli exclusion principle. Analysis using density functional theory (DFT) computation shows the enhancements in NLO response within the ultraviolet-visible absorption spectral region are owing to the increased optical intraband transition in tellurene. Moreover, the effects of varying the photon energy of the probe pulse were explored. Our results indicated that probe pulses with higher photon energies can make smaller differential transmission signal, this effect is found to be negatively correlated with calculated joint density of states (JDOS). These results offer insights into the intrinsic photophysics of 2D tellurene, driving its applications in photonic and optoelectronic fields.

A review on the use of DFT for the prediction of the properties of nanomaterials

Nanostructured materials have gained immense attraction because of their extraordinary properties compared to the bulk materials to be used in a plethora of applications in myriad fields. In this review article, we have discussed how the Density Functional Theory (DFT) calculation can be used to explain some of the properties of nanomaterials. With some specific examples here, it has been shown that how closely the different properties of nanomaterials (such as optical, optoelectronics, catalytic and magnetic) predicted by DFT calculations match well with the experimentally determined values. Some examples were discussed in detail to inspire the experimental scientists to conduct DFT-based calculations along with the experiments to derive a better understanding of the experimentally obtained results as well as to predict the properties of the nanomaterial. We have pointed out the challenges associated with DFT, and potential future perspectives of this new exciting field.

Large piezoelectric and thermal expansion coefficients with negative Poisson's ratio in strain-modulated tellurene

Two dimensional (2D) chalcogenide monolayers have diversified applications in optoelectronics, piezotronics, sensors and energy harvesting. The group-IV tellurene monolayer is one such emerging material in the 2D family owing to its piezoelectric, thermoelectric and optoelectronic properties. In this paper, the mechanical and piezoelectric properties of 2D tellurene in centrosymmetric β and non-centrosymmetric β' phases are investigated using density functional theory. β'-Te has shown a negative Poisson's ratio of -0.024 along the zigzag direction. Giant in-plane piezoelectric coefficients of -83.89 × 10-10 C m-1 and -42.58 × 10-10 C m-1 are observed for β'-Te under biaxial and uniaxial strains, respectively. The predicted values are remarkably higher, that is 23 and 12 times the piezoelectric coefficient of a MoS2 monolayer with biaxial and uniaxial strain in the zigzag direction, respectively. A large thermal expansion coefficient of tellurene is also estimated using quasi harmonic approximation. High piezoelectricity combined with exotic mechanical and thermal properties makes tellurene a very promising candidate in nanoelectronics.

Highly efficient heterojunction solar cells enabled by edge-modified tellurene nanoribbons

Tellurene, a two-dimensional (2D) semiconductor, meets the requirements for optoelectronic applications with desirable properties, such as a suitable band gap, high carrier mobility, strong visible light absorption and high air stability. Here, we demonstrate that the band engineering of zigzag tellurene nanoribbons (ZTNRs) via edge-modification can be used to construct highly efficient heterojunction solar cells by using first-principles density functional theory (DFT) calculations. We find that edge-modification enhances the stability of ZTNRs and halogen-modified ZTNRs showing suitable band gaps (1.35-1.53 eV) for sunlight absorption. Furthermore, the band gaps of ZTNRs with tetragonal edges do not strongly depend on the edge-modification and ribbon width, which is conducive to experimental realization. The heterojunctions constructed by halogen-modified ZTNRs show desirable type 2 band alignments and small band offsets with reduced band gaps and enhanced sunlight absorption, resulting in high power conversion efficiency (PCE) in heterojunction solar cells. In particular, the calculated maximum PCE of designed heterojunction solar cells based on halogen-modified ZTNRs can reach as high as 22.6%.

Recent Advances of Spatial Self-Phase Modulation in 2D Materials and Passive Photonic Device Applications

Optical nonlinearity in 2D materials excited by spatial Gaussian laser beam is a novel and peculiar optical phenomenon, which exhibits many novel and interesting applications in optical nonlinear devices. Passive photonic devices, such as optical switches, optical logical gates, photonic diodes, and optical modulators, are the key compositions in the future all-optical signal-processing technologies. Passive photonic devices using 2D materials to achieve the device functionality have attracted widespread concern in the past decade. In this Review, an overview of the spatial self-phase modulation (SSPM) in 2D materials is summarized, including the operating mechanism, optical parameter measurement, and tuning for 2D materials, and applications in photonic devices. Moreover, some current challenges are also proposed to solve, and some possible applications of SSPM method are predicted for the future. Therefore, it is anticipated that this summary can contribute to the application of 2D material-based spatial effect in all-optical signal-processing technologies.

Two-Dimensional Tellurium: Progress, Challenges, and Prospects

Since the successful fabrication of two-dimensional (2D) tellurium (Te) in 2017, its fascinating properties including a thickness dependence bandgap, environmental stability, piezoelectric effect, high carrier mobility, and photoresponse among others show great potential for various applications. These include photodetectors, field-effect transistors, piezoelectric devices, modulators, and energy harvesting devices. However, as a new member of the 2D material family, much less known is about 2D Te compared to other 2D materials. Motivated by this lack of knowledge, we review the recent progress of research into 2D Te nanoflakes. Firstly, we introduce the background and motivation of this review. Then, the crystal structures and synthesis methods are presented, followed by an introduction to their physical properties and applications. Finally, the challenges and further development directions are summarized. We believe that milestone investigations of 2D Te nanoflakes will emerge soon, which will bring about great industrial revelations in 2D materials-based nanodevice commercialization.

Electronic properties of bare and functionalized two-dimensional (2D) tellurene structures

H, O, and F functionalized 2D Te. H-β-Te becomes indirect semiconductor, O-β-Te becomes metallic (both stable). Investigated binding to substrate.