Design of a silver nanoparticle for sensitive surface enhanced Raman spectroscopy detection of carmine dye.

Flower-shaped silver nanoparticles have been successfully synthesized by a simple aqueous phase silver nitrate reduction by ascorbic acid in the presence of polyvinylpyrrolidone (PVP) surfactant. The nanoparticles diameters were adjusted from 450 to 1000nm with surface protrusions up to 10-25nm. The growth direction of silver nuclei is controlled by their degree of coating by PVP. The flower-shaped silver nanostructures obtained were used as stable Surface Enhanced Raman Scattering (SERS) substrates with high SERS activity for detecting Rhodamine 6G (R6G), at a concentration of only 10-9M, where the SERS signal is still clear. SERS spectra of the dye carmine was analysed and the characteristic bands were identified. An improved principle component analysis (PCA) was used for carmine detection, at concentrations down to 10-8M. The characteristic peaks of the carmine (1019, 1360, and 1573cm-1) remained at 10-8M. This indicated that the minimum detection limit of AgNP-based substrate for carmine is about 10-8M.

Strain driven enhancement of ferroelectricity and magnetoelectric effect in multiferroic tunnel junction.

The strain effect on the ferroelectric and magnetoelectric coupling in multiferroic tunnel junction (MFTJ) Co/BaTiO3/Co has been investigated systematically by using first-principles calculations within density functional theory. It is found that both in-plane compressive strain and uniaxial tensile strain lead to the enhancement of ferroelectric polarization stability and intensity of magnetoelectric coupling in the MFTJ. There is a transition from the paraelectric phase to the ferroelectric phase for the BaTiO3 layer in MFTJ when the loaded in-plane compressive strain increases up to -2.8% and the corresponding average ferroelectric polarization is about 0.13 C m(-2). Meanwhile, the calculated surface magnetoelectric coefficients increase with increasing in-plane compressive strain. Similar phenomena have been also observed in the case of uniaxial tensile strain implemented in MFTJ. The results suggest that the ferroelectric polarization and magnetoelectric coupling in multiferroic tunnel junctions can be controlled by strain and we expect that this study can provide a theoretical basis for the design of spintronic devices.

Phase separation induced by Au catalysts in ternary InGaAs nanowires.

We report a novel phase separation phenomenon observed in the growth of ternary In(x)Ga(1-x)As nanowires by metalorganic chemical vapor deposition. A spontaneous formation of core-shell nanowires is investigated by cross-sectional transmission electron microscopy, revealing the compositional complexity within the ternary nanowires. It has been found that for In(x)Ga(1-x)As nanowires high precursor flow rates generate ternary In(x)Ga(1-x)As cores with In-rich shells, while low precursor flow rates produce binary GaAs cores with ternary In(x)Ga(1-x)As shells. First-principle calculations combined with thermodynamic considerations suggest that this phenomenon is due to competitive alloying of different group-III elements with Au catalysts, and variations in elemental concentrations of group-III materials in the catalyst under different precursor flow rates. This study shows that precursor flow rates are critical factors for manipulating Au catalysts to produce nanowires of desired composition.

Effect of electrodes on geometric and transport properties of the graphene-based nanomolecular devices.

Graphene-based nanomolecular devices are formed by connecting one of the prototype molecular materials of graphene nanoribbons to two Au electrodes. The geometric structure and electronic properties are calculated by using density functional theory. Basing on the optimized structure and the electronic distributions, we obtain the transport properties of the devices by using the Green's functional method. It is found that that the geometry structures of the molecule and the transport properties are sensitive to the distance between source and drain electrodes. With increasing the distances, the curvature radius of the atomic plane is increased, and the deformation energy is decreased. The current versus voltage curves have almost same threshold voltage with different distances between the electrodes. The transmission probability, the density of states and the external bias voltage play important role in determining the transport properties of the molecular devices.