Recent developments and applications of hybrid surface plasmon resonance interfaces in optical sensing

Nanostructured noble metals exhibit an intense optical near field due to surface plasmon resonance, therefore promising widespread applications and being of interest to a broad spectrum of scientists, ranging from physicists, chemists, and materials scientists to biologists. A wealth of research is available discussing the synthesis, characterization, and application of noble metal nanoparticles in optical sensing. However, with respect to the sensitivity of the frequency and width of these surface plasmon resonance modes to the particle’s shape, size, and environment, in nearly every case, success strongly depends on the availability of highly stable, adhesive, and sensitive nanoparticles. This undoubtedly presents a challenging task to nanofabrication. The past decade has witnessed fascinating advances in this field, in particular, the construction of oxide-based hybrid plasmonic interfaces to overcome the problem addressed above by (1) coating the metallic nanostructures with thin overlayers to form sandwiched structures or (2) embedding metallic nanostructures in a dielectric matrix to obtain metal/dielectric matrix nanocomposite films. In this critical review, we focus on recent work related to this field, beginning with a presentation of hybrid films with enhanced structural and optical stability, readily and selectively designed using chemical and physical techniques. We then illustrate their interesting optical properties and demonstrate exciting evidence for the postulated application in surface plasmon sensing fields. Finally, we survey the work remaining to be done for that potential to be realized.     

Ultrafast spectroscopy and coherent acoustic phonons of Au-Ag core-shell nanorods

We performed the first investigations of coherent acoustic phonons in Au-Ag core-shell nanorods, which were compared with the results of parental Au nanorods. Both breathing and extensional modes were observed in Au-Ag core-shell nanorods with ~11 nm Ag shell while only extensional modes were detected in other core-shell nanorods with 4-7 nm Ag shell. Young's modulus estimated from the oscillation period of extensional modes was found to be larger for Au-Ag core-shell nanorods with ~4 nm Ag shell, as compared with that of Au nanorods. The value of Young's modulus decreases with the increase of the Ag shell thickness and finally becomes smaller than that of Au nanorods. This phenomenon is interpreted in terms of the surface effects and the existence of grain boundaries in the lattice structure of Ag shell.     

Geminate charge recombination in liquid alkane with concentrated CCl4: effects of CCl4 radical anion and narrowing of initial distribution of Cl-

Dynamics of radical cations and electrons in an admixture of a linear saturated hydrocarbon (n-dodecane) and halocarbon (carbon tetrachloride, CCl(4)) were investigated by picosecond electron beam pulse radiolysis. The decay of thermalized electrons (e(th)(-)) observed in infrared transient photoabsorption were simply accelerated by the addition of CCl(4), giving a high rate constant of 2.3 × 10(11) mol(-1) dm(3) s(-1). The decrease of the initial yield of e(th)(-) was quantified by C(37) (50 mmol), which is linked to the reaction of epithermal electrons (e(-)) with CCl(4). In contrast, the n-dodecane radical cation (RH(2)(?+)) monitored in the near-infrared indicated a convex-type dependence of the decay rate on CCl(4) concentration, although the initial yield of RH(2)(?+) remained almost constant up to a much higher CCl(4) concentration. The decay of RH(2)(?+) was analyzed by Monte Carlo simulations of geminate ion recombination with e(th)(-), chlorine anion (Cl(-)) formed via dissociative electron attachment, and CCl(4) radical anion. The results showed a good agreement with the experiments by considering two assumptions: (1) CCl(4) radical anion formed via e(th)(-) attachment and (2) narrowing of the initial distribution of Cl(-). The decrease in the initial yield of RH(2)(?+) at high CCl(4) concentration was well explained by immediate decomposition of CCl(4)(?+) to CCl(3)(+) and hole transfer from CCl(4)(?+) to adjacent RH(2) without diffusive motion of the reactants. Time-dependent density functional theory supported the spectroscopic assignment of intermediate species in the n-dodecane/CCl(4) system. The present results would be of help in understanding the electron capture reaction in multicomponent systems such as a chemically amplified resist in lithography.     

Preparation of carbon quantum dots with tunable photoluminescence by rapid laser passivation in ordinary organic solvents

A simple approach to prepare carbon quantum dots is presented in this communication by laser rapid passivation of nano carbon particles in ordinary organic solvent. The as-prepared carbon dots exhibited visible, tunable and stable photoluminescence (PL). XPS analysis showed that the increased oxygen concentration might be concerned with the origin of PL.     

Visible light photoactivity from a bonding assembly of titanium oxide nanocrystals

TiO(2) nanocrystals are assembled together by interfacial Ti-Ti electronic bonding. Such nanocrystal assemblies have a narrower band gap, greatly enhanced visible light absorption, and solar photocatalysis compared with individual nanocrystals.     

Facile one-pot preparation of thermally and photochemically convertible soluble precursors of copper phthalocyanine and naphthalocyanine

Soluble copper phthalocyanine (CuPc) and naphthalocyanine (CuNc) precursors which can be converted thermally and photochemically into insoluble CuPc and CuNc, respectively, have been synthesized by a one-step reaction using commercially available chemicals.     

Data driven time scale in Gaussian quasi-likelihood inference

We study parametric estimation of ergodic diffusions observed at high frequency. Different from the previous studies, we suppose that sampling stepsize is unknown, thereby making the conventional Gaussian quasi-likelihood not directly applicable. In this situation, we construct estimators of both model parameters and sampling stepsize in a fully explicit way, and prove that they are jointly asymptotically normally distributed. High order uniform integrability of the obtained estimator is also derived. Further, we propose the Schwarz (BIC) type statistics for model selection and show its model-selection consistency. We conducted some numerical experiments and found that the observed finite-sample performance well supports our theoretical findings.

     

Railgun using plasma initiation separated from the projectile

Preacceleration of a projectile is important for reducing the erosion of the bore surface in a railgun. Gas guns, electrothermal guns, and other railguns are commonly used to preaccelerate the projectile. A new method, called the plasma initiation separated from the projectile (PISP) method is proposed, and its effectiveness is confirmed experimentally. A thin copper wire is placed near the edge of the railgun, and it explodes and forms a plasma that has a fast flow velocity due to the Lorentz force. This fast flowing plasma collides with the projectile, which obtains an initial velocity mainly by the momentum transfer. Since the current increases while only the plasma is accelerated, the driving force of the projectile just after the collision of the plasma with the projectile is large. The PISP method works as an inductive energy storage circuit with an opening switch     

Nano-SIMS analysis of Mg, Sr, Ba and U in natural calcium carbonate.

Concentrations of minor (Mg and Sr) and trace (Ba and U) elements in four natural calcium carbonate samples were first analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical dissolution and calibrated against a standard dolomite. Their homogeneities were checked by in situ laser ablation (LA) ICP-MS with 10-20 spots. The carbonate samples were measured by using a high lateral resolution secondary ion mass spectrometer (Nano-SIMS NS50). A approximately 4 nA O- primary beam was used to sputter a 5-6-microm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV and a Mattauch-Herzog geometry. A multi-collector system was adjusted to detect 26Mg+, 43Ca+, 88Sr+, 138Ba+, 238U16O+ and 238U16O2+ ions at the same time. A resolving power of 2500-5000 at 10% peak height was attained by an entrance slit set at 40 microm, and each exit slit at 50 microm with adequate flat-topped peaks. The observed 26Mg/43Ca, 88Sr/43Ca, 138Ba/43Ca and 238U16O2/43Ca ratios agreed well with those measured by LA-ICP-MS. Foraminifera shells were analyzed at 5-6 microm scale by Nano-SIMS. There was a large variation of the Mg/Ca ratios, up to +/- 38%, even in a single fragment of the shell, suggesting that although the ratios provide a useful paleoceanographic proxy at bulk scale, they may reflect a more complex pattern at < 10 microm scale.