Chunjian Tan

The electronic and optical properties of novel germanene and antimonene heterostructures

In this work, the structural, electronic and optical properties of novel atomically thin systems based on germanene and antimonene nanocomposites have been investigated by means of density functional theory. We find that the germanene and antimonene monolayers are bound to each other via orbital hybridization with enhanced binding strength. Most importantly, the band gap opening can be achieved. Our results demonstrate that the AAII pattern has a direct band gap characteristic with a moderate value of up to 391 meV, while the other three patterns have indirect band gaps tunable from 37 to 171 meV. In particular, changing the direction and strength of the external electric field (E-field) can effectively tune the energy gap of the germanene/antimonene bilayer over a wide range even with a semiconductor–metal transition. The work function of the heterobilayer in the AAII pattern which possesses a direct band gap can be tinkered up from −3.21 to 12.33 eV by applying different E-field intensities. In addition, the germanene/antimonene bilayer exhibits more pronounced optical conductivity. The tunable bandgaps and work function together with a superior visible light response capability make the germanene/antimonene bilayer a viable candidate for optoelectronic applications.

An AlAs/germanene heterostructure with tunable electronic and optical properties via external electric field and strain

By means of comprehensive first-principles calculations, we investigate the stability, electronic and optical properties of an AlAs/germanene heterostructure. In particular, electric field and strain are used to tailor its electronic band gap and dielectric function. The binding energy and interlayer distance indicate that germanene and AlAs monolayers in the AAI pattern are bound together via van der Waals interaction with a maximum indirect-gap of 0.494 eV, which is expected to have potential application in the field of field-effect transistors. Under a negative E-field and compressive strain, the bandgaps of the AAI-stacking show a near-linear and linear decrease behavior, respectively, whereas the response of the bandgaps to a positive E-field and tensile strain displays a dramatic and monotonous decrease relationship. The work function of the AAI-stacking is calculated to be 4.35 eV smaller than that of individual monolayers. Besides, the optical properties are also calculated. The imaginary parts of the dielectric function of the germanene/AlAs heterobilayer exhibit a significant enhancement in comparison with the considered monolayers, indicating the improvement of the capability of absorbing photons. In particular, the imaginary part of the dielectric function of the heterostructure is enhanced with the increase of E-field and mechanical strain, which suggests that the optical properties of the heterostructure can be improved by E-field and mechanical strain. Simultaneously, a red-shift or blue-shift can be observed with the changes in E-field and mechanical strain. All these nontrivial and tunable properties endow the AlAs/germanene nanocomposite with great potential for FETs, strain sensors, photocatalysis, field emission, energy harvesting, and photonic devices.

AlN/BP Heterostructure Photocatalyst for Water Splitting

In this letter, the structural, electronic, and optical properties of blue phosphorene (BP) and graphene-like aluminum nitride (AlN) nanocomposite are investigated by the first-principles method. Despite the indirect bandgap nature of the BP and AlN monolayers, AlN/BP heterostructure exhibits a direct bandgap characteristic in the most stable pattern. Moreover, we also find that the optically active states of the maximum valence and the minimum conduction bands are localized on opposite monolayers, leading to the electrons and holes spontaneously separated (type-II band alignment), which enhances the photocatalytic efficiency. Most interestingly, the AlN/BP heterobilayer exhibits enhanced optical properties in the visible and UV light zone, which is comparable or even superior to pristine BP - overall, the suitable direct gap and band edges positions, type-II band alignment, and fascinating visible and UV light adsorption, which enable AlN/BP heterostructure to have great potential applications in the field of solar energy conversion and photocatalytic water splitting.

The electronic and optical properties of silicene/g-ZnS heterobilayers: a theoretical study

Two-dimensional (2D) nanomaterials have rapidly become the superstars in the fields of nanoelectronics, materials science, and energy storage because of their unusual properties, originating from the quantum size effects. Here we present a systematic theoretical investigation of the electronic and optical properties of silicene/g-ZnS heterobilayers, by means of dispersion-corrected density functional theory (DFT-D) computations. Depending on the stacking, the orbital hybridization or weak interaction defines the conformation of silicene/g-ZnS heterobilayers and contributes to their stability. Unlike silicene, the silicene/g-ZnS heterobilayer in the most stable stacking is a direct band gap semiconductor with a rather low effective mass, which indicates that the heterobilayer has a high carrier mobility. Applying an appropriate external electric field (E-field) or biaxial tensile strain with different strengths, the band gap of the silicene/g-ZnS heterobilayer can be effectively tuned, and correspondingly results in a semiconductor–metal transition. Meanwhile, with increase of the E-field strength, the binding strength of the silicene/g-ZnS heterobilayer can be significantly enhanced. Especially, changing the direction and strength of the external E-field can significantly modulate its work function in a wide range. From analysis of the dielectric function and the absorption coefficient, it is evident that the optical properties of silicene are largely preserved in the heterobilayer, meanwhile, the silicene/g-ZnS heterobilayer exhibits some unique optical properties in the visible light irradiation range. Our findings pave the way for experimental research in the development of 2D materials science using heterostructures and indicate the great application potential of silicene/g-ZnS heterobilayers in future nanoelectronics and optoelectronics.

SiGe/h-BN heterostructure with inspired electronic and optical properties: a first-principles study

The structure along with the electronic and optical properties of a SiGe/BN monolayer heterostructure were theoretically researched using density functional theory calculations. There are small interactions between a SiGe monolayer and a BN monolayer in the stacking model of a SiGe/BN heterostructure via van der Waals forces. The binding energies of the different stacking models, the DOS, and the charge density difference are calculated and analyzed. According to our investigation, the heterostructure maintains the most unique electronic properties of the SiGe monolayer, especially linear dispersion at the K point, and enlarges the band gap to ∼57 meV, benefiting its application in the microelectronic field. Moreover, the band gap can be modified through external electric fields and strains to a large extent. The optical property is also investigated to find an enhancement effect at the ultraviolet region. In general, the calculated results indicate that the SiGe monolayer layered on the BN substrate possesses great potential in microelectronic and optoelectronic applications.

Tunable electronic structure and enhanced optical properties in quasi-metallic hydrogenated/fluorinated SiC heterobilayer

Graphene-like silicon carbide (SiC) has emerged as a rapidly rising star on the horizon of two-dimensional (2D) layered materials. In this work, we execute a systematic theoretical investigation of the atomic and electronic structure of a fully hydrogenated/fluorinated SiC (H/F-SiC) heterobilayer, which has a quasi-metallic character in its most stable stacking pattern, to predict its electronic and optical properties. We demonstrate that a direct band gap at the Γ point can be opened in the quasi-metallic H/F-SiC heterobilayer by applying an external electric field (E-field). Especially, when altering the strength of the E-field, this system undergoes a transition from quasi-metallic state to semiconductor. We predict that the mobilities are rather high due to the low carrier effective mass and high Fermi velocity. Light absorption spectra indicate that the H/F-SiC heterobilayer has evident infrared light absorption, and complete electron–hole separation can enhance the photocatalytic efficiency. Our findings pave the way for experimental research on the development of 2D material science using weak interlayer interactions and indicate the great application potential of the H/F-SiC heterobilayer in future nanoelectronics and optoelectronics.

Fluorosilicene/chlorosilicene bilayer semiconductor with tunable electronic and optical properties

Using comprehensive density functional theory calculations, the structural, electronic, and optical properties of novel fluorosilicene/chlorosilicene (F-silicene/Cl-silicene) heterobilayer are investigated. Our results unveil that the presence of hetero-halogen bonding (Si-F···Cl-Si) has a remarkable influence on the F-silicene/Cl-silicene bilayer. The F-silicene/Cl-silicene heterostructure in the most stable pattern has a moderate band gap of 0.309 eV, lower than that of isolated halogenated silicene. Encouragingly, F-silicene/Cl-silicene heterobilayers all have a direct band gap nature, irrespective of the stacking pattern, thickness and external electric fields (E-fields), which is an advantage over MoS2 layers. In addition, applying appropriate E-field leads to a significant enhancement of binding strength of the F-silicene/Cl-silicene heterobilayer. Especially, the band gap of the F-silicene/Cl-silicene heterobilayer can be effectively modulated by E-fields, even a semiconductor–metal transition occu...