ABSTRACT
Plasmonic or exciton/plasmon (plexcitonic) systems are presently described based on electromagnetic models, ignoring the need for an improved microscopic understanding. This is based on the fact that a full quantum mechanical approach on a micrometer scale still represents a considerable challenge. In this paper we report on the experimental observation of plexcitons in 2D gold nanorod array systems coupled to dye molecules and we provide a description of the experimental data using a quantum model. We show that treating the collective behavior in the array as being represented by a single quasiparticle is a suitable approximation that offers the opportunity to avoid the complicated calculation of long-distance interactions between the individual nanoparticles of the plexcitonic, periodic system. This enables us to model the optical response of plasmons in nanostructured arrays in contact with quantum emitters and to derive microscopic informations. Our work provides a potential tool for the design of plexcitonic devices, which rely on periodic metallic nanostructures.
ABSTRACT
Engineered gold nanostructured arrays with feature separation in the sub-10-nm range were fabricated and used for highly sensitive surface enhanced Raman scattering (SERS) detection of biomarkers. Nanostructuring is achieved by combining electron beam lithography with the so-called shadow evaporation technique which involves a two-step Au vapor deposition through a suspended Ge mask while the substrate is tilted in opposite directions. This results in a regular triangular surface pattern with extremely small gap distances that allow positive enhancement of the local electric fields by enabling improvements in the electromagnetic coupling between adjacent nanoparticles. The resulting SERS active surfaces are suitable for the realization of reference procedures for quantifying marker molecules like urea or creatinine at physiologically relevant concentrations.
Subject(s)
Biomarkers/chemistry , Microarray Analysis/instrumentation , Nanotechnology/methods , Spectrum Analysis, Raman/instrumentation , Benzoates/chemistry , Creatinine/chemistry , Equipment Design , Gold/chemistry , Microarray Analysis/methods , Spectrum Analysis, Raman/methods , Sulfhydryl Compounds/chemistry , Surface Properties , Urea/chemistryABSTRACT
The pressure evolution of the local structure and dynamics of polar nanoregions in PbSc(0.5)Nb(0.5)O(3) relaxor ferroelectric is analysed by Raman spectroscopy. The pressure dependence of phonon modes up to 10 GPa reveals three characteristic pressures related to changes in the local structure: near 2 GPa, at which ferroic ordering in the Pb system occurs; near 4 GPa, at which significant structural transformations, involving decoupling of Pb and B-cations in polar nanoclusters and suppression of the B-cation off-centring take place; and near 6 GPa, at which the system reaches a saturation state. The structural transformations observed in PbSc(0.5)Nb(0.5)O(3) are compared to those in PbSc(0.5)Ta(0.5)O(3) and other Pb-based perovskite-type relaxor ferroelectrics.
ABSTRACT
We report pressure-induced structural changes in PbSc(0.5)Ta(0.5)O3 studied by single-crystal x-ray diffraction and Raman scattering. The appearance of a soft mode, a change in the volume compressibility, broadening of the diffraction peaks, and suppression of the x-ray diffuse scattering show that a phase transition occurs near pc approximately 1.9 GPa. The critical pressure is associated with a decoupling of the displacements of the B site and Pb cations in the existing polar nanoregions, leading to the suppression of B-cation off-center shifts and enhancement of the ferroic distortion in the Pb-O system.
ABSTRACT
Single crystals of PbSc(0.5)Ta(0.5)O(3) with suppressed and enhanced oxygen deficiencies and different degrees of long-range B-site ordering were studied by Raman spectroscopy in order to clarify the significance of the different factors for the formation and growth of ferroic clusters in relaxors. It is shown that the presence of oxygen vacancies impacts more strongly on the incipient ferroic clustering than the degree of long-range B-site ordering. The oxygen deficiency hinders the formation of ferroelectric crystalline-type nanoregions, regardless of the presence/absence of long-range B(')/B('')-ordered regions. The low degree of defects in the O system enhances the long-range ferroelectric ordering, even in entirely B-site-disordered materials.
ABSTRACT
Binary mixed monolayers of octadecanoic acid and three related amphiphilic compounds (octadecanamide, octadecylamine, octadecylurea) have been investigated at the air/water interface by surface pressure-area (Pi-Â) isotherms and their resistances to water evaporation (r). In addition, the excess free energies of mixing (DeltaG(E)) were calculated using the Goodrich method. Both the ln r vs x and DeltaG(E) vs x plots exhibit marked deviations from linearity, indicating a high degree of miscibility and nonideal behavior of the components in the mixed films. For all of these binary systems the excess free energies of mixing have been found to be minimum for a certain composition corresponding almost to a maximum in evaporation resistances. Weak interactions were detected in octadecanoic acid/octadecanamide monolayers, whereas significant condensation effects were observed in 1 : 1 mixed films containing octadecanoic acid and octadecylamine. This is attributed to an acid-base equilibrium followed by the formation of a well-ordered arrangement of COO(-) and NH(3)(+) head groups bound to each other by electrostatic forces. The unusual polymorphism of octadecylurea monolayers could be influenced by adding small amounts of octadecanoic acid. The formation of the low-temperature phase (beta-phase) is completely suppressed, if the acid content exceeds 8 mol%. The octadecanoic acid seems to induce the formation of the high-temperature phase (alpha-phase), which is characterized by a vertical orientation of the hydrocarbon chains. Copyright 2000 Academic Press.
ABSTRACT
In a group of 44 children with behaviour disorders, the mode of action of the phenothiazine preparation fluphenazine hydrochloride (Lyorodin) was tested by means of psychophysiological methods of measurement (critical flicker-fuse frequency and measurement of the response time). In some of the comparative examinations before and after administration of the drug significant differences were found. A defined psychic stress resulted in changed measured values in both methods. Children with cerebral injuries showed a lower degree of reaction after the administration of the preparation than children not encephalopathically affected.
