Search

Optoelectronic applications require materials both responsive to objective photons and able to transfer carriers, so new two-dimensional (2D) semiconductors with appropriate band gaps and high mobilities are highly desired. A broad range of band gaps and high mobilities of a 2D semiconductor family, composed of monolayer of Group 15 elements (phosphorene, arsenene, antimonene, bismuthene) is presented. The calculated binding energies and phonon band dispersions of 2D Group 15 allotropes exhibit thermodynamic stability. The energy band gaps of 2D semiconducting Group 15 monolayers cover a wide range from 0.36 to 2.62 eV, which are crucial for broadband photoresponse. Significantly, phosphorene, arsenene, and bismuthene possess carrier mobilities as high as several thousand cm2 V−1 s−1. Combining such broad band gaps and superior carrier mobilities, 2D Group 15 monolayers are promising candidates for nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

Optoelectronic applications require materials both responsive to objective photons and able to transfer carriers, so new two-dimensional (2D) semiconductors with appropriate band gaps and high mobilities are highly desired. A broad range of band gaps and high mobilities of a 2D semiconductor family, composed of monolayer of Group 15 elements (phosphorene, arsenene, antimonene, bismuthene) is presented. The calculated binding energies and phonon band dispersions of 2D Group 15 allotropes exhibit thermodynamic stability. The energy band gaps of 2D semiconducting Group 15 monolayers cover a wide range from 0.36 to 2.62 eV, which are crucial for broadband photoresponse. Significantly, phosphorene, arsenene, and bismuthene possess carrier mobilities as high as several thousand cm2 V−1 s−1. Combining such broad band gaps and superior carrier mobilities, 2D Group 15 monolayers are promising candidates for nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

The typical two-dimensional (2D) semiconductors MoS2, MoSe2, WS2, WSe2 and black phosphorus have garnered tremendous interest for their unique electronic, optical, and chemical properties. However, all 2D semiconductors reported thus far feature band gaps that are smaller than 2.0 eV, which has greatly restricted their applications, especially in optoelectronic devices with photoresponse in the blue and UV range. Novel 2D mono-elemental semiconductors, namely monolayered arsenene and antimonene, with wide band gaps and high stability were now developed based on first-principles calculations. Interestingly, although As and Sb are typically semimetals in the bulk, they are transformed into indirect semiconductors with band gaps of 2.49 and 2.28 eV when thinned to one atomic layer. Significantly, under small biaxial strain, these materials were transformed from indirect into direct band-gap semiconductors. Such dramatic changes in the electronic structure could pave the way for transistors with high on/off ratios, optoelectronic devices working under blue or UV light, and mechanical sensors based on new 2D crystals. [ABSTRACT FROM AUTHOR]

The typical two-dimensional (2D) semiconductors MoS2, MoSe2, WS2, WSe2 and black phosphorus have garnered tremendous interest for their unique electronic, optical, and chemical properties. However, all 2D semiconductors reported thus far feature band gaps that are smaller than 2.0 eV, which has greatly restricted their applications, especially in optoelectronic devices with photoresponse in the blue and UV range. Novel 2D mono-elemental semiconductors, namely monolayered arsenene and antimonene, with wide band gaps and high stability were now developed based on first-principles calculations. Interestingly, although As and Sb are typically semimetals in the bulk, they are transformed into indirect semiconductors with band gaps of 2.49 and 2.28 eV when thinned to one atomic layer. Significantly, under small biaxial strain, these materials were transformed from indirect into direct band-gap semiconductors. Such dramatic changes in the electronic structure could pave the way for transistors with high on/off ratios, optoelectronic devices working under blue or UV light, and mechanical sensors based on new 2D crystals. [ABSTRACT FROM AUTHOR]

Abstract: A density functional theory study is performed to understand electronic structures and field emission properties of carbon nanotube–ZnO nanocontacts. The carbon nanotube–ZnO nanocontacts have high energetic stabilities and small energy gaps. The energy gaps of the nanocontacts exhibit an oscillatory behavior as a function of the length of carbon nanotubes. The ionization potentials of all carbon nanotube–ZnO nanocontacts are smaller than 7.155eV of the ZnO nanocage. The ionization potentials of carbon nanotube–ZnO nanocontacts with more 2 carbon layers exhibit odd–even oscillation in the absence and presence of an electric field. The carbon nanotube–ZnO nanocontact with 4 carbon layers has a smallest ionization potential of 3.625eV under 0.2eV/Å external electric field. These results indicate that the field-emission properties of simplex ZnO and carbon nanotube materials can be enhanced significantly by the formation of carbon nanotube–ZnO nanocontacts. [Copyright &y& Elsevier]

In this work, we calculate the band gap and mobility of the two-dimensional (2D) pentagonal MX 2 by means of first-principles method. Heyd Scuseria Ernzerhof (HSE06) hybrid functional calculation shows that the 2D pentagonal MX 2 is an indirect bandgap semiconductor, and the band gap ranged from 1.86 eV to 3.01 eV. The effective mass and carrier mobility of the 2D pentagonal MX 2 are studied and show anisotropic characteristics, the hole mobility of PtS 2 is the highest (5009.42 cm2 V−1 s−1). According to these results, we find that the 2D pentagonal MX 2 satisfied dynamic, chemical, and thermodynamic stability. All of these indicate the great application prospect of the 2D pentagonal MX 2 semiconductor in electronic devices. • MX 2 (M = Pd, Pt; X = S, Se, Te) are all indirect band gap semiconductors. • The band gap of MX 2 decreases in the order of S, Se and Te. • The carrier mobilities of the six MX 2 materials are all anisotropic. • The light absorption coefficient of the monolayer MX 2 reaches 105 cm−1. [ABSTRACT FROM AUTHOR]

[Display omitted] • Type-Ⅰ and type-II band alignment can be achieved simultaneously in CsPbBr 3 /Janus MoSSe heterostructure by modulating the atomic terminal contacts. • The band alignment of vdW heterostructure can be shifted by the interface dipole and its induced interface potential step. • The interface effect renders CsPbBr 3 /Janus MoSSe heterostructure an adjustable band gaps and band types, and an improved light absorption range and intensity in the visible and ultraviolet regions. • The gate voltage regulation can also realize the transition of band alignment from intrinsic type-Ⅱ to type-I or type-III for CsBr-T/SMoSe heterostructure. The flexibility and versatility is crucial for the perovskite-based heterostructure to realize multifunctional integration, while it is hard to be achieved in the conventional systems. Herein, we propose an interface engineering strategy, which utilizes the structural characteristics of perovskite and the mirror asymmetry of 2D Janus material to realize the multifunction of CsPbBr 3 /Janus MoSSe heterostructure. We demonstrate that type-Ⅰ and type-II band alignment can be achieved simultaneously in CsPbBr 3 /Janus MoSSe heterostructure by modulating the atomic terminal contacts. The underlying mechanism is that the band alignment can be shifted by the interface dipole and its induced interface potential step. The interface effect renders CsPbBr 3 /Janus MoSSe heterostructure an adjustable band gaps and band types, and an improved light absorption range and intensity in the visible and ultraviolet regions. More promisingly, we find that gate voltage regulation can also realize the transition of band alignment from intrinsic type-II to type-I or type-III for CsBr-T/SMoSe heterostructure. These findings enrich the functionality of perovskite-based heterostructures and provide more possibilities for realizing high-efficiency multifunctional nanodevices. [ABSTRACT FROM AUTHOR]

We propose a family of hydrogenated- and halogenated-SbIV (SbIVX-2) materials that simultaneously have two-dimensional (2D) structures, high stability and appealing electronic properties. Based on first-principles total-energy and vibrational-spectra calculations, SbIVX-2 monolayers are found both thermally and dynamically stable. Varying IV and X elements can rationally tune the electronic properties of SbIVX-2 monolayers, effectively modulating the band gap from 0 to 3.42 eV. Regarding such superior stability and broad band-gap range, SbIVX-2 monolayers are expected to be synthesized in experiments and taken as promising candidates for low-dimensional electronic and optoelectronic devices, such as blue-to-ultraviolet light-emitting diodes (LED) and photodetectors. [ABSTRACT FROM AUTHOR]

The electronic properties, such as the layer-dependent behavior of the band structure, band gap, work function alignment and dielectric properties of the few-layer GeSe are systematically investigated via gradient-corrected density functional theory computations, inspired by the experimentally observation of two-dimension materials such as graphene, phosphorene, MoS 2 and BN. The results indicate that the few-layer GeSe presents a robust direct band gap, which decreases with increasing the thickness from bilayer (1.15 eV) to six-layer (1.00 eV) around the X point. Furthermore, the work function increases rapidly from monolayer (4.44 eV) to trilayer (4.95 eV). The robust direct band gap characteristics and the layer-dependent band gap suggest that the few-layer GeSe is a promising material for efficient solar energy harvesting applications. The layer dependence of the GeSe work function offers a practical route to tune the Schottky barrier in GeSe based electronic devices. Our results provide new insights on utilizing the layer-controlled band gap of the atomic layers of GeSe. [ABSTRACT FROM AUTHOR]

Through first principle calculations, we studied the structural, electronic and optical properties of ZnO doped by interstitial Mg. With the increase of Mg content ( x ), the derivations of lattice parameters from the wurtzite ZnO become more and more significant. The Mg-doped ZnO with x below 15.79% is found to be n-type semiconductor. The minimum of energy band gap and light transmittance in high energy region (7.5–25 eV) decrease while the conductivity and refractive index increase with increasing x . Further increasing x up to 20%, the Mg-doped ZnO is found to be direct-band-gap semiconductor with great structural derivation from wurtzite phase. The light transmittance increases while the refractive index decreases with the increase of x due to the change of geometry and electronic structure. So, it’s concluded that the electronic and optical properties of ZnO doped by interstitial Mg may be greatly influenced by Mg content. [ABSTRACT FROM AUTHOR]

As elemental group material, germanium, enjoys a high status in the field of two-dimensional (2D) materials. However, 2D germanene is a gapless semiconductor, which greatly limits its application in optoelectronic devices. Herein, we found an interesting class of 2D materials, named GaGeX (X = S, Se, Te), consisting of two outer GaX layers and an inner germanene, a sandwich structure stacked together by interlayer Ga-Ge bonds. Compared with known 2D materials (such as MoX 2), the band gaps gradually decrease in the order of sulfide, selenide, and telluride, the electronic calculations show that they have a unique band gaps reversely enlarging trend of 0.03, 0.46 and 0.72 eV from GaGeS to GaGeTe, respectively. Moreover, GaGeX is predicted to have superior mobility, especially with a hole mobility of up to 5510 cm2 V−1 s−1 in GaGeTe. These novel phenomena are found closely related to the orbital variation. Our findings render these 2D materials potential candidates for future optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: New highly stable structures, (CdTe)12× N (N =1–5) multi-cage nanochains, are proposed and have been investigated by density functional theory. The (CdTe)12 single cage is considered as the building block to assemble two different types of multi-cage nanochains, interconnecting two cages by their four-membered rings and interconnecting two cages by their six-membered rings. The structural and electronic properties are studied in detail. Particular attention is paid to the effects of the number of cages and assembled mode, the connection method of cages, on these properties. The results show that the multi-cage nanochains have higher stability compared with the single cage, and the stability varies with the growth of nanochains and the assembled mode. The properties of energy gap, density of state, charge density distribution, etc., strongly rely on the assembled mode and the number of cages, revealing that the assembled mode and the number of cages are two important factors. [Copyright &y& Elsevier]

As Moore's law is approaching its physical limit, two-dimensional (2D) materials have been expected to be favorable silicon alternatives. Here, the electronic properties and the ballistic quantum transport performances of monolayer InOBr are studied through the density functional theory coupled with nonequilibrium Green function formalism. Monolayer InOBr is a dynamic and thermodynamic stable system and has an indirect bandgap of 3.37 eV at HSE06 level. Interestingly, the ballistic transport simulations show that the monolayer InOBr can effectively suppress the short channel effect at sub-5nm nodes. For high-performance applications, the on-currents of a- and b-directed monolayer InOBr field-effect-transistors (FETs) with 5-nm channel length exceed 3200 μA μm−1 and the sub-threshold swings of about 70 mV/dec. Besides, the 5-nm a-directed FETs can also satisfy the low-power applications with the on/off ratio of more than 107. Thus, monolayer InOBr will be an attractive channel material to extend Moore's law to sub-5 nm. • 2D InOBr mololyer exhibits kinetic and thermodynamic stability. • 2D InOBr monolayer possesses an indirect band gap with 3.37 eV. • 2D InOBr monolayer shows a significant light-harvesting capability in UV region. • Monolayer InOBr with 5-nm channel length possesses a promising switching ability. • The a-directed FETs display more superior electrostatic ability. [ABSTRACT FROM AUTHOR]

The adsorption of glycine, glutamic acid, histidine and phenylalanine on single-layer graphdiyne/ graphene is investigated by ab initio calculations. The results show that for each amino acid molecule, the adsorption energy on graphdiyne is larger than the adsorption energy on graphene and dispersion interactions predominate in the adsorption. Molecular dynamics simulations reveal that at room temperature the amino acid molecules keep migrating and rotating on graphdiyne surface and induce fluctuation in graphdiyne bandgap. Additionally, the photon absorption spectra of graphdiyne-amino-acid systems are investigated. We uncover that the presence of amino acid molecules makes the photon absorption peaks of graphdiyne significantly depressed and shifted. Finally, quantum electronic transport properties of graphdiyne-amino-acid systems are compared with the transport properties of pure graphdiyne. We reveal that the amino acid molecules induce distinct changes in the electronic conductivity of graphdiyne. The results in this paper reveal that graphdiyne is a promising two-dimensional material for sensitively detecting amino acids and may potentially be used in biosensors. [ABSTRACT FROM AUTHOR]