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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]

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]