Zofia Vértesy

Optical structure and function of the white filamentary hair covering the edelweiss bracts.

The optical properties of the inflorescence of the high-altitude Leontopodium nivale subsp. alpinum (edelweiss) is investigated, in relation with its submicrometer structure, as determined by scanning electron microscopy. The filaments forming the hair layer have been found to exhibit an internal structure which may be one of the few examples of a photonic structure found in a plant. Measurements of light transmission through a self-supported layer of hair pads taken from the bracts supports the idea that the wooly layer covering the plant absorbs near-ultraviolet radiation before it reaches the cellular tissue. Calculations based on a photonic-crystal model provide insight on the way radiation can be absorbed by the filamentary threads.

Catalyst traces and other impurities in chemically purified carbon nanotubes grown by CVD

Multiwall carbon nanotubes grown by the catalytic decomposition of acetylene over supported Co catalyst were subjected to wet and dry oxidation in order to remove the unwanted products and the catalyst traces. The effects of the purification treatment on the Co content Ž. Ž . was monitored by physical methods: Rutherford Backscattering Spectrometry RBS , Particle Induced X-Ray Emission PIXE and Ž. X-Ray Fluorescence XRF . The purified products were investigated by microscopic methods: TEM, Scanning Electron Microscopy Ž. Ž . SEM , Energy Dispersive Spectroscopy EDS and STM. The KMnOrH SO aqueous oxidation procedure was found to be effective in 42 4 reducing the Co content while damaging only moderately the outer wall of the nanotubes. Treatment in HNO rH SO yields a 32 4 bucky-paper like product and produces the increase of the Si and S content of the sample. q 2002 Elsevier Science B.V. All rights reserved.

Improving the sensitivity of Fluxset magnetometer by processing of the sensor core

The processing of the sensor core material was investigated on the operation of the Fluxset magnetic field sensor. Static and dynamic magnetic properties were measured, and the signal of the pick-up coil was investigated as a function of processing. The sensitivity and signal/noise ratio of the sensor can be improved significantly by polishing of the ribbon and heat annealing.

Switching mechanism of single domain particles in a two-dimensional array

The mechanism of switching of uniaxial, single domain, single crystalline epitaxial garnet particles on a 2D square array was investigated. The anisotropy field of the sample is 2 kOe, while the Gaussian switching field distribution is 280/spl plusmn/85 Oe. The dominant contribution to the incoherent switching is from inhomogeneous internal fields and canted moments at the corners and edges, where the switching starts. The interaction field with the surrounding particles, reduced nucleation barriers at crystalline defects, thermal activation, and dynamical effects in FMR also contribute to the observed switching field and its standard deviation.

Bioinspired artificial photonic nanoarchitecture using the elytron of the beetle Trigonophorus rothschildi varians as a 'blueprint'.

An unusual, intercalated photonic nanoarchitecture was discovered in the elytra of Taiwanese Trigonophorus rothschildi varians beetles. It consists of a multilayer structure intercalated with a random distribution of cylindrical holes normal to the plane of the multilayer. The nanoarchitectures were characterized structurally by scanning electron microscopy and optically by normal incidence, integrated and goniometric reflectance measurements. They exhibit an unsaturated specular and saturated non-specular component of the reflected light. Bioinspired, artificial nanoarchitectures of similar structure and with similar properties were realized by drilling holes of submicron size in a multilayer structure, showing that such photonic nanoarchitectures of biological origin may constitute valuable blueprints for artificial photonic materials.

Microstructures and nanostructures of high Andean Penaincisalia lycaenid butterfly scales (Lepidoptera: Lycaenidae): descriptions and interpretations

The scales of one high Andean eumaeine lycaenid butterfly species with pale dorsal coloration and four species with vivid dorsal colour were investigated using field emission scanning electron microscopy. The micro‐ and nanostructures are illustrated, described, measured, and interpreted. The vivid colours in the species are caused by a pepper‐pot nanostructure of Urania‐type scales. This nanostructure is a three‐dimensional lattice within the body of the individual scale. The scales of the non‐vivid orange species are lacking this nanostructure and the surfaces of their scales show high microstructure irregularities. This absence of vivid colour may be correlated with thermal regulation. The irregularity of the scale microstructures suggests a heavy environmental pressure on the populations sampled. Previously unknown structural variations of Urania‐type scales are also described. The existence of closed scale microcell structures, explained as an apomorphic character in the tribe Eumaeini, most probably evolved independently several times. It is hypothesized that scale micro‐ and nanostructure modifications develop syntopically within a population, which in turn can lead to rapid diversification.

Substance specific chemical sensing with pristine and modified photonic nanoarchitectures occurring in blue butterfly wing scales

Butterfly wing scales containing photonic nanoarchitectures act as chemically selective sensors due to their color change when mixing vapors in the atmosphere. Based on butterfly vision, we built a model for efficient characterization of the spectral changes in different atmospheres. The spectral shift is vapor specific and proportional with the vapor concentration. Results were compared to standard principal component analysis. The modification of the chemical properties of the scale surface by the deposition of 5 nm of Al(2)O(3) significantly alters the character of the optical response. This is proof of the possibility to purposefully tune the selectivity of such sensors.

Growth and characterization of Bi, Pr- and Bi, Sc-substituted lutetium iron garnet films with planar magnetization for magneto-optic visualization

The series of epitaxial garnet films of general composition Lu3-x-yBixPryFe5-zAlzO12 and Lu3-xBixFe5-y-zScyAlzO12 were grown on (111) oriented GGG (gadolinium gallium garnet) substrates by the liquid phase epitaxy. Their magnetic and magneto-optical properties were studied using both experimental techniques and modelling. All obtained films demonstrated generally a magnetic anisotropy close to the easy-plane type. The Pr-containing films exhibited large negative uniaxial anisotropy and significant cubic anisotropy. The latter causes a distortion of magnetization curves in samples magnetized in a direction normal to the film plane, especially at low temperatures. The large negative uniaxial anisotropy of Pr-substituted iron garnets allows us to increase the saturation field up to 0.5 T at liquid nitrogen temperature. The Sc-doped films displayed small positive uniaxial anisotropy that did not exceed the shape anisotropy. The magnetization curves of these films did not show any distortion due to the cubic anisotropy. The suitability of Pr- and Sc-doped garnets that meet the requirements for indicator layers for magneto-optic visualization at liquid nitrogen temperature is discussed.

Growth of Bi and Ga substituted YIG and LuIG layers by LPE method

Bi substituted Y- and Lu- iron garnets are very good materials for different kinds of magneto-optical applications. In this work we report the preparation of Bi,Ga: YIG and Bi,Ga: LuIG layers on Gd-Ga garnet (GGG) substrates grown by conventional, isotherm dipping LPE technique using PbO-Bi2O3-B2O3 system as a solvent. Electron microprobe analyses of the garnet films were performed by means of energy-dispersive spectrometer and the refractive index of the layers was determined by spectroscopic ellipsometry. The layer growth rate (v), saturation magnetisation (4 piM(S)) and the Bi content of the layers were determined as a function of the supercooling of the melt (AT) and of the substrate rotation rate (omega) at a given melt composition. From these data the Deltav(L)/DeltaT, Delta4 pi Ms-S/DeltaT, Delta4 piM(S)/Delta(omega)(1/2), Delta Bi/DeltaT and Delta Bi/Delta(omega)(1/2) growth coefficients were calculated. The physical parameters of the films (thickness, 4 piM(S), refractive index, Faraday rotation and the figure of merit) can be very sensitively changed by these growth coefficients. The Faraday rotation (Phi (p)) of our Y2.5Bi0.5Fe3.8Ga1.2O12 and Lu2Bi1Fe4.1Ga0.9O12 garnet layers is similar to 4.8x10(3) and similar to8.3x10(3)deg/cm at 633 nm wavelength, respectively.

Selective nucleation and growth of carbon nanotubes at the CoSi2/Si interface

A patterned CoSi2/Si substrate was used for the catalytic growth of carbon nanostructures and nanotubes in the temperature range of 750–800 °C, using acetylene/N2 as a reaction mixture flowing through a quartz tube at ambient pressure. Selective nucleation confined to the CoSi2/Si interface region was achieved. Scanning electron microscopy and transmission electron microscopy were used to investigate the grown nanostructures.