Shift Of Surface Plasmon Band Research Articles

Negative differential resistance and improved optoelectronic properties in Ag nanoparticles-decorated graphene oxide–riboflavin hybrids

Silver nanoparticles (Ag NPs) are decorated on graphene oxide (GO)–riboflavin (R) hybrids produced with three different compositions. The SEM micrographs of the GO–R–Ag materials show a helical fibrillar morphology different from the bar and wrinkled sheet morphology of R and GO, respectively. FT-IR spectra indicate that GO produces a supra molecular complex with R and Ag NPs are stabilized by both R and GO. The UV–vis spectra show a large shift of surface plasmon band from 390 to 570nm and the circular dichroism spectra indicate a drastic change in the GO–R–Ag system over the GO–R system for a weight ratio of GO to R of 13, suggesting that Ag NPs are wrapped by both the GO–R hybrid and R moieties. The PL-intensity of R increases in the GO–R hybrids but it decreases in the GO–R–Ag ones. The dc-conductivity of the GO–R hybrids increases by 2–3 orders of magnitude on addition of Ag NPs. The I–V characteristic curves of the GO–R–Ag (GO/R=1/3) material shows a negative differential resistance. Possible reasons from the charge trapping on the Ag NPs followed by stabilization by R are discussed and a model using the density of states approach is proposed.

Mechanism of polypyrrole and silver nanorod formation in lauric acid–cetyl trimethyl ammonium bromide coacervate gel template: Physical and conductivity properties

Polypyrrole (PPy) and silver (Ag) nanorods are synthesized in cetyl trimethylammonium bromide–lauric acid (CTAB–LA) complex coacervate gel template. When PPy–CTAB–LA system is polymerized with AgNO3, Ag nanorods are produced while use of ammonium persulphate (APS) as initiator yields PPy nanorods. Ag-nanorods are produced from the initial stage while PPy nanorods take a longer time. The average diameter of Ag nanorods varies from 60 to 145nm by increasing AgNO3 concentration from 0.27M to 1.08M and that of PPy varies from 145nm to 345nm by changing pyrrole concentration from 1×10−4 to 2×10−4 M, respectively. Fourier transformed infrared (FTIR) spectra indicate stabilization of Ag nanorods through complexation of PPy with adsorbed Ag+ ions. PPy nanoparticles are stabilized by adsorbed sulphate ions and lauric acid, both are acting as dopant to it. FFT pattern and EDX spectra clearly indicate the presence of Ag nanocrystals and PPy on the surface of Ag nanorods, respectively. The mechanism of nanorod formation is attributed from UV–Vis spectra showing a red shift of surface plasmon band of Ag and π–π* transition band of PPy with time. The highest dc conductivity of PPy–Ag composite is found to be 414.2S/cm, 7 orders higher than that of PPy nanorods (9.3×10−4S/cm). PPy–Ag systems show Ohmic behavior while PPy nanorods exhibit semi-conducting behavior. The preferential formation of Ag nanorod in AgNO3 initiated polymerization is attributed to the higher cohesive force of Ag than that of PPy. With two times higher LA and CTAB concentration in the gel the Ag nanorod diameter decreases only 12% while that of PPy nanorod decreases by 50%. Possible reasons are discussed from the hard and soft nature of the two nanorods and from the elasticity of the gel template.

Study of electrolyte induced aggregation of gold nanoparticles capped by amino acids

This work reports the electrolyte induced aggregation of gold nanoparticles directly conjugated to amino acid by chemical reduction in aqueous solution. The study was focused on three different classes of amino acids depending on the nature of α substituent, viz. l-cysteine, l-leucine, and l-asparagine. The band broadening and the red shift of surface plasmon band with increase in flocculation parameter showed the aggregation of gold nanoparticles with increase in electrolyte concentration and decrease in pH as monitored by UV–visible spectrophotometer. The 1H NMR spectrum demonstrates that the sulfide bond of cysteine and α amino group of leucine and asparagine interact with nanoparticles surface. Furthermore, transmission electron microscope (TEM) and thermogravimetric analysis (TGA) were performed to characterize and to support the fate of stabilization of the gold nanoparticles by amino acid.

Synthesis and characterization of nano metals with core-shell structure

Using Au core-Pt shell as an example, the synthesis and characterization of nano metals with core-shell structure is demonstrated in a systematic study on the amount-dependent morphology change in a series of Au-Pt bimetallic nanoparticles synthesized using chemical reduction. While the amount of Au precursor is kept constant throughout the whole series of compounds to obtain a fixed Au core size (∼7.5 nm), the Au/Pt ratio is varied from 1/1 to 1/4 in order to synthesize Pt shell layers of different thickness. We observed a remarkable shift of surface plasmon band to around 410 nm. With the aid of high resolution transmission electron microscope (HRTEM) and energy-dispersive spectrometer (EDS), the composition of the shell layer is found to be a Pt-enriched Au-Pt alloy. As the amount of Pt increases, string-like Pt clusters form on the surface of the nanoparticles. The average diameter of these Pt clusters is about 2 nm. This special structure may possess unique catalytic properties.

Synthesis and Characterization of Novel Au(core)-Au/Pt Alloy(shell) Nanostructure

AbstractA systematic study is reported about the amount-dependent morphology change in a series of Au-Pt bimetallic nanoparticles synthesized using chemical reduction. The amount of Au precursor is kept constant throughout whole series of compounds to obtain fixed Au core size (∼7.5 nm). The Au/Pt ratio is varied from 1/1 to 1/4 in order to synthesize Pt shell layer of different thickness. We observed a remarkable shift of surface plasmon band around 410 nm. With the aid of high resolution transmission electron microscope (HRTEM) and energy-dispersive spectrometer (EDS), the composition of shell layer is found to be Pt enriched Au-Pt alloy. As the amount of Pt increases, the Pt clusters formed a string-like shape on the surface of nanoparticles. The average diameter of these Pt clusters is about 2 nm. This special structure may exhibit unique catalytic property.

Interaction of F n-centers with gold nanocrystals produced by gold ion implantation in MgO single crystals

Gold ions were implanted at an energy of 1.1 MeV into (1 0 0) oriented MgO single crystals. In order to form gold colloids from the as-implanted samples, the samples were annealed in three different kinds of atmospheres: (1) Ar only, (2) 10% H 2 + 90% Ar, and (3) 10% O 2 + 90% Ar. Annealing over 1200°C enhanced the gold colloid formation as is evident from the appearance of the surface plasmon resonance band of gold. The surface plasmon bands of samples annealed in three kinds of atmospheres were found to be at 560 nm (Ar only), 524 nm (H 2 + Ar), and 560 nm (O 2 + Ar). The band positions of surface plasmon can be reversibly changed by an additional annealing. Fe 3+ impurities in the MgO samples are utilized to monitor the degree of reduction or oxidation of the samples due to annealing. From the absorption measurements of Fe 3+ band, the diffusion constants of F-centers were obtained. We found that the shifts of the surface plasmon bands are correlated with the F-center concentration and that the F n-center (aggregates of F-centers) is responsible for the shifting of the surface plasmon bands. We propose a model to explain the shift of surface plasmon band.