Effect Of Zinc Cations On The Kinetics Of Supramolecular Assembly And The Chirality Of Porphyrin J-Aggregates

Dilute aqueous solutions of anionic meso-4-sulfonatophenyl-porphyrin (TPPS) extract zinc(ii) ions from glass or quartz surfaces at room temperature and efficiently form the corresponding metal complex (ZnTPPS). The partial or complete formation of ZnTPPS has been probed by UV/Vis spectroscopy and both static and time-resolved fluorescence. The source of zinc(ii) ions has been clearly identified through inductively coupled plasma optical emission spectrometry. The presence of increasing amounts of ZnTPPS slows down the rate of TPPS J-aggregate formation in acid solution. This influences the nucleation step and has a profound impact on the onset of chirality in these species. This evidence indicates the important role of this adventitious metal ion in the interpretation of various spectroscopic and kinetic data for the self-assembly of the TPPS porphyrin and provides some insights into controversial findings on their chirality. The use of this metal derivative as the starting compound for in situ formation of monomeric TPPS is suggested

Ultrafine particles produced by plasma enhanced chemical vapor deposition -from SiH4, CH4, NH3 and B2H6 gas mixtures- for nanostructured ceramics applications

[eng] Ultrafine particles of silicon and related binary and ternary alloys of the Si-B-C-N system produced in our research group from silane, methane, diborane, ammonia and nitrogen precursor gases by plasma enhanced chemical vapor deposition at low pressure and room temperature are reviewed. The in-situ techniques of plasma analysis and surface characterization (quadrupolar mass spectrometry, optical emission spectroscopy and ellipsometry) providing evidence of powder formation and the polymerization reactions based on the SinH2n- negative radicals electrically confined in the plasma sheath are described. The square wave modulation (SQWM) of the rf power is discussed as an efficient method of controlling the powder particle production with low particle-size dispersion. The properties of the powder particles determined by different structural characterization techniques providing their size and distribution, crystalline order and morphology, chemical composition and chemical bond vibrational characteristics, are analyzed and discussed[cat] Hom presenta una revisió sobre les partícules ultrafines de silici i els seus aliatges binaris i ternaris del sistema Si-B-C-N, produïdes en el nostre grup de recerca a partir dels gasos precursors silà, metà, diborà, amoníac i nitrogen, per dipòsit químic en fase vapor (CVD) reforçat per plasma, a baixa pressió i temperatura ambient. És descrita també la utilització de tècniques in situ d'anàlisi per plasma i de caracterització de superfícies (espectroscòpia de masses quadripolar, espectroscòpia òptica d’emissió i el·lipsometria), que donaren l’evidència de formació de partícules de pols i de reaccions de polimerització basades en radicals negatius SinH2n– confinats elèctricament en l’embolcall del plasma. La modulació d’ona quadrada (SQWM) de la font de rf és estudiada com un eficient mètode de control de la producció de partícules amb una petita dispersió de llurs dimensions. Finalment, hom analitza i discuteix les propietats de les partícules produïdes, determinades per diferents tècniques de caracterització, que permeteren obtenir llurs dimensions i distribució, ordre cristal·lí i morfologia, composició química i les característiques vibracionals dels enllaços químic

エキエキカイメン ブンシ シュウゴウタイ ノ エン ニショクセイ ソクテイ ニカンスル ケンキュウ

著者による幾つか修正のも

Structure vs. excitonic transitions in self-assembled porphyrin nanotubes and their effect on light absorption and scattering

The optical properties of diprotonated meso-tetrakis(4-sulphonatophenyl)porphyrin (TPPS4) J-aggregates of elongated thin particles (nanotubes in solution and ribbons when deposited on solid interfaces) are studied by different polarimetric techniques. The selective light extinction in these structures, which depends on the alignment of the nanoparticle with respect to the polarization of light, is contributed by excitonic absorption bands and by resonance light scattering. The optical response as a function of the polarization of light is complex because, although the quasi-one-dimensional structure confines the local fields along the nanotube axis, there are two orthogonal excitonic bands, of H- and J-character, that can work in favor of or against the field confinement. Results suggest that resonance light scattering is the dominant effect in solid state preparations, i.e. in collective groups (bundles) of ribbons but in diluted solutions, i.e. with isolated nanotubes, the absorption at the excitonic transitions remains dominant and linear dichroism spectra can be a direct probe of the exciton orientations. Therefore, by analyzing scattering and absorption data we can determine the alignment of the excitonic bands within the nanoparticle, i.e. of the orientation of the basic 2D porphyrin architecture in the nanoparticle. This is a necessary first step for understanding the directions of energy transport, charge polarization and non-linear optical properties in these materials

Correlation of circular differential optical absorption with geometric chirality in plasmonic meta-atoms

We report a strong correlation between the calculated broadband circular differential optical absorption (CDOA) and the geometric chirality of plasmonic meta-atoms with two-dimensional chirality. We investigate this correlation using three common gold meta-atom geometries: L-shapes, triangles, and nanorod dimers, over a broad range of geometric parameters. We show that this correlation holds for both contiguous plasmonic meta-atoms and non-contiguous structures which support plasmonic coupling effects. A potential application for this correlation is the rapid optimization of plasmonic nanostructure for maximum broadband CDOA

Influence of pressure and radio frequency power on deposition rate and structural properties of hydrogenated amorphous silicon thin films prepared by plasma deposition

The influence of radio frequency (rf) power and pressure on deposition rate and structural properties of hydrogenated amorphous silicon (a-Si:H) thin films, prepared by rf glow discharge decomposition of silane, have been studied by phase modulated ellipsometry and Fourier transform infrared spectroscopy. It has been found two pressure regions separated by a threshold value around 20 Pa where the deposition rate increases suddenly. This behavior is more marked as rf power rises and reflects the transition between two rf discharges regimes. The best quality films have been obtained at low pressure and at low rf power but with deposition rates below 0.2 nm/s. In the high pressure region, the enhancement of deposition rate as rf power increases first gives rise to a reduction of film density and an increase of content of hydrogen bonded in polyhydride form because of plasma polymerization reactions. Further rise of rf power leads to a decrease of polyhydride bonding and the material density remains unchanged, thus allowing the growth of a-Si:H films at deposition rates above 1 nm/s without any important detriment of material quality. This overcoming of deposition rate limitation has been ascribed to the beneficial effects of ion bombardment on the a-Si:H growing surface by enhancing the surface mobility of adsorbed reactive species and by eliminating hydrogen bonded in polyhydride configurations

Deposition and characterization of PECVD phosphorus doped silicon oxynitride layers for integrated optics applications

Phosphorus-doped silicon oxynitride layers have been deposited by a Plasma Enhanced Chemical Vapor Deposition process from $N_20$, 2% $SiH_4/N_2$ and 5% $PH_3/Ar$ gaseous mixtures. The $PH_3/Ar$ flow rate was varied to investigate the effect of the dopant to the layer properties. As deposited and annealed (600, 800, 900 and 1000 °C) layers were characterized by Fourier transform infrared spectroscopy, Rutherford backscattering spectroscopy and spectroscopic ellipsometry. In this way the refractive index could be determined as well as the amount of hydrogen that is responsible for enhanced absorption in the 3rd telecommunication window around 1550 nm. The N-H bonds concentration was found to decrease with the phosphorus concentration. Furthermore the bonded hydrogen in the entire P-doped layers have been eliminated after annealing at 1000 °C, while undoped SiON layers require annealing at 1150 °C

Detection and characterization of single nanoparticles by interferometric phase modulated ellipsometry

We introduce a new measurement system called Nanopolar interferometer devoted to monitor and characterize single nanoparticles which is based on the interferometric phase modulated ellipsometry technique. The system collects the backscattered light by the particles in the solid angle subtended by a microscope objective and then analyses its frequency components. The results for the detection of 2 μm and 50 nm particles are explained in terms of a cross polarization effect of the polarization vectors when the beam converts from divergent to parallel in the microscope objective. This explanation is supported with the results of the optical modelling using the exact Mie theory for the light scattered by the particles

Computing matrix inversion with optical networks

With this paper we bring about a discussion on the computing potential of complex optical networks and provide experimental demonstration that an optical fiber network can be used as an analog processor to calculate matrix inversion. A 3x3 matrix is inverted as a proof-of-concept demonstration using a fiber network containing three nodes and operating at telecomm wavelength. For an NxN matrix, the overall solving time (including setting time of the matrix elements and calculation time of inversion) scales as O(N^2), whereas matrix inversion by most advanced computer algorithms requires ~O(N^2.37) computational time. For well-conditioned matrices, the error of the inversion performed optically is found to be less than 3%, limited by the accuracy of measurement equipment.Comment: 5 page