Elastic anisotropy of OsB2 and RuB2 from first-principles study

The elastic anisotropy of the potential low compressible and hard materials OsB2 and RuB2 were studied by first-principles investigation within density functional theory. The structure, elastic constants, bulk modulus, shear modulus, Poisson's ratio and Debye temperature have been calculated within both local density approximation (LDA) and generalized gradient approximation (GGA). The results indicated that the calculated bulk modulus and shear modulus were in good agreement with the experimental and previous theoretical studies.

Type I collagen-templated assembly of silver nanoparticles and their application in surface-enhanced Raman scattering

Silver nanoparticles (Ag NPs) are one of the active substrates that are employed extensively in surface-enhanced Raman scattering (SERS), and aggregations of Ag NPs play an important role in enhancing the Raman signals. In this paper, we fabricated two kinds of SERS-active substrates utilizing the electrostatic adsorption and superior assembly properties of type I collagen. These were collagen-Ag NP aggregation films and nanoporous Ag films.

Type I collagen-mediated synthesis of noble metallic nanoparticles networks and the applications in Surface-Enhanced Raman Scattering and electrochemistry

In this paper, we demonstrated an effective enviromentally friendly synthesis route to prepare noble metallic (Au, Ag, Pt and Pd) nanoparticles (NPs) networks mediated by type I collagen in the absence of any seeds or surfactants. In the reactions, type I collagen served as stabilizing agent and assembly template for the synthesized metallic NPs. The hydrophobic interaction between collagen and mica interface as well as the hydrogen bonds between inter- and intra-collagen molecules play important roles in the formation of collagen-metallic NPs networks. The noble metallic NPs networks have many advantages in the applications of Surface-Enhanced Raman Scattering (SERS) and electrochemistry detection. Typically, the as-prepared Ag NPs networks reveal great Raman enhancement activity for 4-ATP, and can even be used to detect low concentration of DNA base, adenine.

Atomic force microscopy and surface-enhanced Raman scattering detection of DNA based on DNA-nanoparticle complexes

We report a simple method for the label-free detection of double-stranded DNA using surface-enhanced Raman scattering (SERS). We prepared cetyltrimethylammonium bromide (CTAB)-capped silver nanoparticles and a DNA-nanoparticle complex by adding silver nanoparticles to lambda-DNA solutions. In the present study, the utilization of CTAB-capped silver nanoparticles facilitates the electrostatic interaction between DNA molecules and silver nanoparticles; at the same time, the introduction of DNA avoids adding aggregating agent for the formation of nanoparticle aggregates to obtain large enhancement of DNA, because the DNA acts as both the probe molecules and aggregating agent of Ag nanoparticles.

Structural evolution of tensile deformed high-density polyethylene at elevated temperatures: Scanning synchrotron small- and wide-angle X-ray scattering studies

The structural evolution of an ice-quenched high-density polyethylene (HDPE) subjected to uniaxial tensile deformation at elevated temperatures was examined as a function of the imposed strains by means of combined synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. The data show that when stretching an isotropic sample with the spherulitic structure, intralamellar slipping of crystalline blocks was activated at small deformations, followed by a stress-induced fragmentation and recrystallization process yielding lamellar crystallites with their normal parallel to the stretching direction. Stretching of an isothermally crystallized HDPE sample at 120 degrees C exhibited changes of the SAXS diagram with strain similar to that observed for quenched HDPE elongated at room temperature, implying that the thermal stability of the crystal blocks composing the lamellae is only dependent on the crystallization temperature.

DEFORMATION OF SOFT COLLOIDAL CRYSTALLINE STRUCTURE - THEORETICAL CONSIDERATIONS AND EXPERIMENTAL EVIDENCES BY SYNCHROTRON SMALL-ANGLE X-RAY SCATTERING ON TENSILE STRETCHED POLYMERIC LATEX FILM

Films obtained via drying a polymeric latex dispersion are normally colloidal crystalline where latex particles are packed into a face centered cubic (fcc) structure. Different from conventional atomic crystallites or hard sphere colloidal crystallites, the crystalline structure of these films is normally deformable due to the low glass transition temperature of the latex particles. Upon tensile deformation, depending on the drawing direction with respect to the normal of specific crystallographic plane, one observes different crystalline structural changes. Three typical situations where crystallographic c-axis, body diagonal or face diagonal of the fcc structure of the colloidal crystallites being parallel to the stretching direction were investigated.

Fabrication of Iron Oxide Core/Gold Shell Submicrometer Spheres with Nanoscale Surface Roughness for Efficient Surface-Enhanced Raman Scattering

A method to synthesize Fe3O4 core/Au shell submicrometer structures with very rough surfaces on the nanoscale is reported. The Fe3O4 particles were first modified with uniform polymers through the layer-by-layer technique and then adsorbed a lot of gold nanoseeds for further Au shell formation. The shell was composed of a large number of irregular nanoscale An particles arranged randomly, and there were well-defined boundaries between these Au nanoparticles. The Fe3O4 core/Au shell particles showed strong plasmon resonance absorption in the near-infrared range, and can be separated quickly from solution by an external magnet.

Surface-enhanced Raman scattering of 4-aminothiophenol self-assembled monolayers in sandwich structure with nanoparticle shape dependence: Off-surface plasmon resonance condition

A universal metal-molecule-metal sandwich architecture by the self-assembly of Ag nanoparticles (NPs) and Au NPs of various shapes interconnected with 4-aminothiophenol (4-ATP) molecules was presented. These Ag NPs/4-ATP/Au NPs sandwich structures were characterized by surface enhanced Raman scattering (SERS) using an off-surface plasmon resonance condition. Enhancement factors (EF) on the order of 10(8) for 9b(b(2)) vibration mode were observed for the 4-ATP self-assembled monolayers (SAMs) in such sandwich structures. The factors are 2 orders of magnitude larger than that on the monolayer of Au NPs of various shapes under similar condition. More importantly, remarkable increase in the intensity of b(2) vibrational modes, which is characteristic of the charge transfer (CT) behavior between metal NPs and 4-ATP molecules, was observed in these sandwich structures under 1064 nm excitation. The obtained EF on these sandwich structure for 9b(b(2)) is larger than that for 7a vibration mode by a factor of similar to 10(2), demonstrating the importance of the contribution of the CT mechanism and the CT behavior of metal contacts, which play a significant role in metal-molecule-metal nanosystems.

Surface enhanced Raman scattering of brilliant green on ag nanoparticles and applications in living cells as optical probes

In this article, surface enhanced Raman scattering (SERS) of different concentrations of brilliant green (13G) on Ag nanoparticles (AgNPs) has been investigated. The results indicate that only 10(-12) M BG can be detected on AgNPs while as low as 10(-11) M BG can be detected upon the activation of AgNPs by chloride ions. The additional improvement of the detection of BG mainly derives from the increase of the electromagnetic field around AgNPs and partially from the reorientation of BG on AgNPs induced by chloride ions, which was proved by the different spectra feature in the two systems. Adsorption of BG on AgNPs has also been demonstrated in applications of living cells as optical probes based on SERS, indicating that dye-AgNPs can probe the local environment in the living cells. The related cytotoxicity measurements demonstrated that BG-AgNPs produced little cytotoxicity to the cells, which shows great potential in biornedical applications of BG labeled-AgNPs for SERS nanosensors in cells as optical probes. Meanwhile, SERS spectra of BG on AgNPs in the presence chloride ions are expected to be used in living cells as more sensitive optical probes.

Rectangular Silver Nanorods: Controlled Preparation, Liquid-Liquid Interface Assembly, and Application in Surface-Enhanced Raman Scattering

In this paper, we for the first time report a polyol method for large-scale synthesis of rectangular silver nanorods in the presence of directing agent and seeds. This method has some clear advantages including simplicity, high quality, and ease of scaleup. Silver nanowires or silver nanorods with a submicrometer diameter could also be facilely prepared when the reaction parameters are slightly changed. Furthermore, a liquid-liquid assembly strategy has been employed to construct uniform rectangular silver nanorod arrays on a solid substrate which could be used as surface-enhanced Raman scattering (SERS) substrates with high SERS activity, stability, and reproducibility. It is found that the SERS spectra obtained from the probe molecules with the different concentrations show different SERS intensifies. As the concentration of 4-aminothiophenol (4-ATP) or rhodamine 6G (R6G) increases, the SERS intensities progressively increase. The enhancement factor for 4-ATP and R6G should be as large as 5.06 x 10(4) or much larger than the value of 5.06 x 10(8), respectively.

Type I collagen-mediated synthesis and assembly of UV-photoreduced gold nanoparticles and their application in surface-enhanced Raman scattering

We reported a simple method to synthesize gold nanoparticles (NPs) by photoreducing HAuCl4 in acetic acid solution in the presence of type I collagen. It was found that the collagen takes an important role in the formation of gold NPs. The introduction of collagen made the shape of the synthesized gold nanocrystals change from triangular and hexangular gold nanoplates to size-uniform NPs. On the other hand, thanks to the special characters of collagen molecules, such as its linear nanostructure, are positively charged when the pH < 7, and the excellent self-assembly ability, photoreduced gold NPs were assembled onto the collagen chains and formed gold NPs films and networks. A typical probe molecule, 4-aminothiophenol, was used to test the surface-enhanced Raman scattering activity of these gold NPs films and networks and the results indicated good Raman activity on these substrates.

Silver nanoparticles coated with adenine: preparation, self-assembly and application in surface-enhanced Raman scattering

We describe herein the preparation of silver nanoparticles (AgNPs) using nucleobase adenine as protecting agent through the in situ chemical reduction of AgNO3 with NaBH4 in an aqueous medium at room temperature. As-prepared AgNPs were characterized by UV-visible spectra, transmission electron microscopy and x-ray photoelectron spectroscopy. All these data confirmed the formation of AgNPs. On the basis of electrostatic interactions between as-prepared AgNPs and anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), we successfully fabricated (PSS/AgNP)n (n = 0-9) multilayers on a 3-mercaptopropyltrimethoxysilane/AgNP functionalized indium tin oxide (ITO) substrate via the layer-by-layer self-assembly technique and characterized as-formed multilayers with UV-visible spectra. Furthermore, these ITO substrates coated with multilayers of different thickness were investigated as surface-enhanced Raman scattering (SERS)-active substrates using p-aminothiophenol as a probe molecule, implying that these multilayers substrates may be promising for a new type of SERS-active substrate.

Spontaneous formation of two-dimensional gold networks at the air-water interface and their application in surface-enhanced Raman scattering (SERS)

Two-dimensional (2-D) gold networks were spontaneously formed at the air-water interface after HAuCl4 reacted with fructose at 90 degrees C in a sealed vessel, in a reaction in which fructose acted as both a reducing and a protecting agent. Through fine-tuning of the molar ratio of HAuCl4 to fructose, the thus-formed 2-D gold networks can be changed from a coalesced pattern to an interconnected pattern. In the coalesced pattern, some well-defined single-crystalline gold plates at the micrometer-scale could be seen, while in the interconnected pattern, many sub-micrometer particles and some irregular gold plates instead of well-defined gold plates appeared. It is also found that the 2-D gold networks in the form of an interconnected pattern can be used as substrates for surface-enhanced Raman scattering (SERS) because of the strong localized electromagnetic field produced by the gaps between the neighboring particles in the 2-D gold networks.

Crystal structures and elastic properties of superhard IrN2 and IrN3 from first principles

First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c. Our calculation indicates that the P2(1)/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414 A. These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P2(1)/c. The calculated bulk modulus of 373 GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357 GPa within 4.3% and of 402 GPa within 7.8%, but smaller than the experimental value of 428 GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2. For IrN3, cubic skutterudite structure (Im-3) was assumed.

Structures and elastic properties of OsN2 investigated via first-principles density functional calculations

The structure, elastic, and electronic properties of OsN2 at various space groups: cubic Fm-3m, Pa-3, and orthorhombic Pnnm were studied by first-principles calculations based on density functional theory. Our calculation indicates that the structure in orthorhombic Pnnm phase is energetically more stable compared with cubic systems. It is metallic, mechanically stable and contains diatomic N-N units with the bond distance 1.418 A. These characters are consistent with experimental facts that OsN2 is orthorhombic and metallic. The calculated bulk modulus 394 GPa is also the highest among the considered space groups, slightly larger than previous value 358 GPa. The calculated elastic anisotropic factors and directional bulk modulus showed that OsN2 possess high elastic anisotropy.