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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]

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]