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Zhang H.,Shenyang University | Zhang H.,Beijing Computational Science Research Center | Liu L.-M.,Beijing Computational Science Research Center | Lau W.-M.,Beijing Computational Science Research Center | Lau W.-M.,Chengdu Green Energy And Green Manufacturing Technology
Journal of Materials Chemistry A | Year: 2013

Among dozens of layered transition metal dichalcogenides (TMDs), VS 2 has attracted particular interest due to its intrinsic magnetism and potential applications as a high-performance functional nanomaterial. The phase stability and electronic properties of the typical crystal structures of both monolayer and bulk VS2 are carefully investigated based on first-principle calculations. The results reveal that the relative stability between different phases is greatly affected by the thickness of the layers and the temperature. Below room temperature, both bulk and monolayer VS2 prefer to exhibit the hexagonal (H) structure instead of the trigonal (T) structure. Interestingly, at room temperature, although the H monolayer VS 2 remains more stable than the T-VS2, the bulk T-VS 2 becomes more stable than H-VS2. These results reveal that a phase transition between H and T will occur on changing either the thickness of the slab or the temperature. Furthermore, the different crystal structures (H and T) exhibit significantly distinct magnetism: the bulk T-VS2 has the lowest magnetism (0.31 μB), while the monolayer H-VS2 has the largest magnetism (about 1.00 μB) among the structures. Most importantly, our results reveal that the magnetism will increase sharply on the exfoliation of monolayer VS 2 from the bulk at room temperature because of the phase transition from T to H. The present results provide an efficient way to modulate the magnetic moment through controlling the crystal structure and the thickness of the VS2 nanosheets. © 2013 The Royal Society of Chemistry. Source

Fan M.,University of Victoria | Fan M.,Chengdu Green Energy And Green Manufacturing Technology | Wang P.,University of Victoria | Escobedo C.,University of Victoria | And 2 more authors.
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2012

The fabrication and on-chip integration of surface-enhanced Raman scattering (SERS) optrodes are presented. In the optrode configuration, both the laser excitation and the back-scattered Raman signal are transmitted through the same optical fiber. The SERS-active component of the optrode was fabricated through the self-assembly of silver nanoparticles on the tip of optical fibers. The application of SERS optrodes to detect dyes in aqueous solution indicated a limit of quantification below 1 nM, using nile blue A as a molecular probe. Using the optrode-integrated microfluidic chip, it was possible to detect several different dyes from solutions sequentially injected into the same channel. This approach for sequential detection of different analytes is applicable to monitoring on-chip chemical processes. The narrow bandwidth of the vibrational information generated by SERS allowed solutions of different compositions of two chemically similar dyes to be distinguished using a dilution microfluidic chip. These results demonstrate the advantages of the SERS-optrode for microfluidics applications by illustrating the potential of this vibrational method to quantify components in a mixture. © The Royal Society of Chemistry. Source

Song F.,Shanghai JiaoTong University | Su H.,Shanghai JiaoTong University | Han J.,Shanghai JiaoTong University | Lau W.M.,Chengdu Green Energy And Green Manufacturing Technology | And 2 more authors.
Journal of Physical Chemistry C | Year: 2012

Nature is greatly capable of providing inspiration for the novel design of functional materials. Herein, the efficient bioreactors' construction of pollen grains inspires us to mimic them for superior gas sensing application. By developing a facile two-step soakage process and subsequent calcinations, the bioreactors are mimicked fully: (I) biosensitive pollen coats on pollen grains are replaced by gas sensitive tin oxide (SnO 2) coats, and (II) the fine hierarchical scaffolds are maintained by the self-support of newly formed SnO 2 coats. For gas sensing application, as-fabricated SnO 2 microreactors exhibit high and fast responses to nitrogen dioxide (219.5 to NO 2 of 50 ppm) and other gases. The good sensing properties should be indeed ascribed to the specific construction of microreactors, which shows elaborate hierarchical porous structures and large accessible space/surface area favorable for both gas molecule transports and sensing reactions. This present strategy provides us with new insight on the exploring of effective and low-cost gas sensors, and it could further extend to other pollen grains of numerous different morphologies and other types of bioreactors that are abundant in nature. © 2012 American Chemical Society. Source

Zhang H.,Beijing Computational Science Research Center | Zhang Y.-N.,Beijing Computational Science Research Center | Zhang Y.-N.,Chengdu Green Energy And Green Manufacturing Technology | Liu H.,Chengdu Green Energy And Green Manufacturing Technology | Liu L.-M.,Beijing Computational Science Research Center
Journal of Materials Chemistry A | Year: 2014

Two-dimensional graphene-like materials have attracted considerable attention for the further development of nanoscale devices. In this work, the structural, electronic and optical properties of free-standing, graphene-like nitrides XN (X = B, Al and Ga) are studied by density functional calculations with the inclusion of the nonlocal van der Waals correction. The results show that all the studied nitrides are thermodynamically stable and their electronic structures can be easily tuned by forming the heterostructure with MoS 2 monolayer. Although GaN and AlN monolayers retain the indirect band gap of bulk, MoS2-AlN and MoS2-GaN heterostructures have suitable direct gaps, complete electron-hole separation and fascinating visible light adsorption, which is promising for solar energy applications. Moreover, the MoS2-AlN heterostructure is a good candidate for enhanced photocatalytic activity of hydrogen generation from water. © the Partner Organisations 2014. Source

Fan M.,Chengdu Green Energy And Green Manufacturing Technology | Fan M.,University of Victoria | Lai F.-J.,National Taiwan University of Science and Technology | Chou H.-L.,National Taiwan University of Science and Technology | And 4 more authors.
Chemical Science | Year: 2013

Surface-enhanced Raman scattering (SERS) from molecular probes adsorbed on Au:Ag bimetallic nanoparticles with various compositions was investigated. Au:Ag bimetallic nanoparticles (NPs), with the diameters between 3-5 nm, were prepared and characterized by HRTEM and UV-Vis absorption. Their SERS properties were examined by using four different probe molecules, and compared with NPs made of pure Au or Ag. It is found that the SERS property of the alloy NPs is not only dependent on the Au:Ag ratio of the bimetallic NPs, but also on the chemical nature of the SERS probe. For the two positively charged SERS probes, oxazine 720 (Oxa) and Nile Blue A (NBA), the alloy NPs with higher Au content provided the largest SERS signal. However, for the probes 4-hydroxythiophenol (HTP) and thiophenol (TP), the best SERS performance was obtained for the highest Ag ratio. DFT calculations indicated a charge-transfer between Au and Ag atoms in the alloys, creating positively charged domains rich in Ag atom, and negatively charge regions dominated by Au atoms. It is proposed that the probe-specific enhancement is related to the selective binding of probe molecules to the partially charged surface domains in the alloys. Our results suggest that SERS substrate optimizations based on bimetallic nanoparticles should consider the nature of the probes and the electronic-induced effects from the alloys. © 2013 The Royal Society of Chemistry. Source

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