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From first-principles calculations, the effects of h-BN and AlN substrates on the topological nontrivial properties of stanene are studied with different strains. We find that the quantum spin Hall phase can be induced in stanene film on a h-BN substrate under a tensile strain of between 6.0% and 9.3% with a stable state confirmed by the phonon spectrum, while for stanene on 5 × 5 h-BN, the quantum spin Hall phase can be preserved without strain. However, for stanene on a AlN substrate, the quantum spin Hall phase cannot be found under compressive or tensile strains less than 10%, while for 2 × 2 stanene on 3 × 3 AlN, the compressive strain needed to induce the quantum spin Hall phase is just 2%. These theoretical results will be helpful in understanding the effect of substrate and strain on stanene and in further realizing the quantum spin Hall effect in stanene on semiconductor substrates.

Based on first-principles calculations, the electronic and topological properties of halogenated (F-, Cl-, Br- and I-) arsenene are investigated in detail. It is found that the halogenated arsenene sheets show Dirac type characteristic in the absence of spin-orbital coupling (SOC), whereas energy gap will be induced by SOC with the values ranging from 0.194 eV for F-arsenene to 0.255 eV for I-arsenene. Noticeably, these four newly proposed two-dimensional (2D) systems are verified to be quantum spin Hall (QSH) insulators by calculating the edge states with obvious linear cross inside bulk energy gap. It should be pointed out that the large energy gap in these 2D materials consisted of commonly used element is quite promising for practical applications of QSH insulators at room temperature.

A nontoxic, simple, inexpensive, and reproducible strategy, which meets the standard of green chemistry, is introduced for the synthesis of copper nanocrystals (Cu NCs) with olive oil as both reducing agent and capping agent. By changing the reaction parameters, the shape, size and surface structure of the Cu NCs can be well controlled. The obtained Cu nanocubes show excellent catalytic properties for the catalytic reduction of dyes and CO oxidation. Moreover, the prepared Cu nanocubes as substrates exhibit surface enhanced Raman scattering (SERS) activity for 4-mercaptopyridine (4-Mpy). Therefore, this facile route provides a useful platform for the fabrication of Cu NCs which have the potential to replace noble metals for certain applications.

Based on first-principles calculations, we systematically investigated the topological surface states of Bi and Sb thin films of 1-5 bilayers in (111) orientation without and with H(F) adsorption, respectively. We find that compared with clean Bi and Sb films, a huge band gap advantageous to observe the quantum spin Hall effect can be opened in chemically decorated bilayer Bi and Sb films, and the quantum phase transition from trivial (non-trivial) to non-trivial (trivial) phase is induced for a three bilayer Bi film and single (four) bilayer Sb film. Surface adsorption is an effective tool to manipulate the geometry, electronic structures and topological properties of film materials.

Based on first-principles calculations, we propose one new category of two-dimensional topological insulators (2D TIs) in chemically functionalized (-CH 3 and -OH) arsenene films. The results show that the surface decorated arsenene (AsCH 3 and AsOH) films are intrinsic 2D TIs with sizeable bulk gap. The bulk energy gaps are 0.184 eV, and 0.304 eV in AsCH 3 and AsOH films, respectively. Such large bulk gaps make them suitable to realize quantum spin Hall effect in an experimentally accessible temperature regime. Topologically helical edge states in these systems are desirable for dissipationless transport. Moreover, we find that the topological properties in these systems are robust against mechanical deformation by exerting biaxial strain. These novel 2D TIs with large bulk gaps are potential candidate in future electronic devices with ultralow dissipation.

We investigated the behavior of edge states in two-dimensional bilayered Bi nanoribbons by atom adsorption based on the density functional method. We found that for a clean Bi zigzag ribbon the penetration depth of well-localized edge states is a function of the momentum-space width of the edge-state dispersion. Depending on the density of adsorbed H, Br and I atoms, respectively, the edge state can be changed from localized within a very narrow region to delocalized over the whole region in real space. Changes in atomic and electronic structures and topological insulator properties associated with the atomic adsorption on the edges of zigzag bilayer nanoribbon (ZBNR) are discussed. Our work suggests that ZBNR could be a possible candidate for nanoelectronic devices under some special conditions.

Gas sensors with high sensitivity at and below room temperature, especially below freezing temperature, have been expected for practical application. The lower working temperature of gas sensor is better for the manufacturability, security and environmental protection. Herein, we propose a H2S gas sensor with high sensitivity at and below room temperature, even as low as −30 °C, based on Cu2O/Co3O4 nano/microstructure heteroarrays prepared by 2D electrodeposition technique. This heteroarray was designed to be a multi-barrier system, and which was confirmed by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and scanning probe microscopy. The sensor demonstrates excellent sensitivity, sub-ppm lever detection, fast response, and high activity at low temperature. The enhanced sensing property of sensor was also discussed with the Cu2O/Co3O4 p-p heterojunction barrier modulation and Cu2S conductance channel. We realize the detection of the noxious H2S gas at ultra-low temperature in a more security and environmental protection way.