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Reflectivity Measurements (reflectivity + measurement)
Kinds of Reflectivity Measurements Selected AbstractsDepletion of PCBM at the Cathode Interface in P3HT/PCBM Thin Films as Quantified via Neutron Reflectivity MeasurementsADVANCED MATERIALS, Issue 22 2010Andrew J. Parnell Using neutron reflectivity, self-stratification in a model P3HT/PCBM blend is observed. The as-spun and solvent-annealed films show a depletion of PCBM near the top surface and enrichment of PCBM at the substrate (see figure). Depletion of PCBM at the cathode interface in a photovoltaic device could act as a barrier to efficient electron extraction. On thermal annealing, the PCBM depleted region is eliminated; an effect that partially explains the improvement of P3HT/PCBM devices on thermal annealing. [source] Dewetting of an Organic Semiconductor Thin Film Observed in Real-time,ADVANCED ENGINEERING MATERIALS, Issue 4 2009Stefan Kowarik We study the growth and the post-growth dewetting process of the organic semiconductor diindenoperylene (DIP) using real-time X-ray reflectivity measurements. We show that a DIP monolayer deposited in UHV onto silicon oxide dewets via the formation of bilayer islands. From the time resolved structural data we estimate the rate constant for interlayer diffusion of DIP molecules. Post-growth AFM measurements confirm the conclusions from the X-ray data and show the morphology of the dewetted film. [source] String Fit: a new structurally oriented X-ray and neutron reflectivity evaluation techniqueJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2001Erich Politsch A novel method for the analysis of neutron and X-ray reflectivity measurements is presented. In contrast to existing methods, the new data fitting approach is structurally oriented and therefore only requires information about the chemical structure of studied molecules and no other ad hoc assumptions. Apart from the inversion of reflectivity into scattering length density profile, the inversion of scattering length density profile into molecular arrangement is addressed systematically for non-trivial molecular conformations for the first time. This includes the calculation of structural characteristics, such as radius of gyration or chain order parameters, based on measured reflectograms. Another important option is the possibility to evaluate simultaneously neutron and X-ray reflectograms of a given sample. For better convergence, especially for complex simultaneous evaluations, an effective extension of the normally used least-squares deviation function is introduced. Different simulated molecular ensembles are used to illustrate the features of the new approach; typically, excellent agreement between the simulated starting and final deduced data sets is achieved. [source] A comparison of nocturnal call counts of migrating birds and reflectivity measurements on Doppler radarJOURNAL OF AVIAN BIOLOGY, Issue 4 2004Andrew Farnsworth Several studies have found that the peak in bird density in the atmosphere during nocturnal migration occurs before midnight, while the peak in vocalizations from migrating birds occurs after midnight, in the hours just before dawn. In a recent study, the patterns of calling from a single species of migrating birds correlated well with the patterns of density estimates of migrating birds. We test the null hypothesis that the patterns of reflectivity measurements and number of vocalizations during nocturnal migration are not related. We sampled radar data and nocturnal flight calls during spring and fall 2000 in northwestern South Carolina and southeastern New York. We analyzed changes in the hour-to-hour patterns of bird density and vocalizations for 556 hours on 58 nights. We also analyzed the night-to-night changes in the patterns of peak hour bird density and peak hour of vocalizations on 32 nights. We found that most of the hour-to-hour and night-to-night patterns of density and vocalization counts are significantly related and reject the null hypothesis. However, despite significant relationships between reflectivity measurements and vocalization counts, a great deal of variation in vocalization counts remains unexplained. These results suggest that factors other than bird density are responsible for the variation in vocalizing by migrating birds. [source] A laser imaging and neutron reflection investigation into the monolayer behaviour of fatty acids used for taste masking microspheresJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2008Sheng Qi Abstract Fatty acid microspheres have been used for taste masking purposes whereby the drug is preferentially released in the lower gastrointestinal tract, although the mechanisms involved are poorly understood. In this study, we use a combination of surface pressure measurements, Brewster angle microscopy (BAM) and neutron reflectivity measurements to study the phase miscibility and escaping tendency from mixed stearic and palmitic acid films with a view to relating this to drug dissolution behaviour. It was noted that mixed systems showed considerably greater film interaction and instability than those composed of the pure lipid, especially in alkaline media. BAM studies were able to identify a range of phase separated structures for both the pure and mixed systems. Neutron reflectivity studies indicated a marked selective dissolution of palmitic acid into the subphase as a function of time and allowed quantification of the rate of dissolution of this species. It is concluded that the fatty acids are interacting within the monolayer and in addition the palmitic acid is escaping the mixed monolayers and dissolving into the alkali subphase. These findings have strong relevance for understanding the mechanism of drug release from the associated microspheres. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97: 1864,1877, 2008 [source] The new diffractometer for surface X-ray diffraction at beamline BL9 of DELTAJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2006Christof Krywka The experimental endstation of the hard X-ray beamline BL9 of the Dortmund Electron Accelerator is equipped with a Huber six-circle diffractometer. It is dedicated to grazing-incidence X-ray diffraction and X-ray reflectivity experiments on solid surfaces and thin films as well as to powder diffraction measurements. A new set-up for grazing-incidence X-ray scattering of liquids has been built up using a silicon mirror to reflect the incident X-ray to the liquid surface at angles of incidence around the critical angle of total reflection of the sample. X-ray reflectivity measurements of a polymer film and grazing-incidence X-ray diffraction measurements of an epitaxically grown Gd40Y60 film, an oxidized surface of Fe-15at.%Al alloy and aqueous salt solutions are presented and discussed. [source] Phonon modes of monoclinic BiB3O6PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2005A. Gössling Abstract We present a detailed study of the phonon modes of the monoclinic compound BiB3O6 based on polarized reflectivity measurements on single crystals. The spectra are analysed by means of a generalized Drude,Lorentz model, which allows us to resolve the modes of A and B symmetry. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exciton localization in MgxZnyCd1,x,ySe alloyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004O. Maksimov Abstract We report photoluminescence and reflectivity measurements of MgxZnyCd1,x,ySe epitaxial layers (0 < x < 0.53) grown by molecular beam epitaxy on InP (100) substrates. Significant emission line broadening, increase in activation energy and Stokes shift are monitored with increasing Mg content. For MgxCdyZn1,x,ySe samples with large Mg content (x > 0.3), we observe an anomalous temperature dependence of both the emission energy and line broadening. This behavior is assigned to the emission from localized states. Different mechanisms of carrier localization are discussed and exciton localization on statistical CdSe clusters is proposed to be the most likely one. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of InGaN/GaN and AlGaN/GaN superlattices by X-ray diffraction and X-ray reflectivity measurementsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010S. Sintonen Abstract The commercial significance of superlattice structures is increasing due to greater demand of optoelectronic devices, such as the light emitting diode (LED). In order to optimize these devices, an accurate and reliable characterization method is needed. This paper describes in detail the characterization of superlattices with X-ray scattering techniques. The thicknesses of the individual layers are determined by X-ray reflectivity (XRR) measurements and the state of strain, the lattice constants and the compositions of ternary compounds by X-ray diffraction (XRD) measurements. The method is non-destructive, and yields unique results, unlike characterizations based on simulation of symmetric XRD scans. These simulations were used for verification of results. The method was tested on InGaN and AlGaN superlattice structures. The measured and simulated parameter values agreed very well. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Initial growth stages of MOVPE InN studied by AFM and specular reflectivityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007A. van der Lee Abstract The initial growth of InN grown by MOVPE was investigated by a combination of atomic force microscopy (AFM) and X-ray specular reflectivity for five different thin films ranging from 57 to 750 Å. Both AFM and specular reflectivity measurements show that during the initial growth the surface is not completely covered but that instead a discontinuous layer resembling quasi two-dimensional islands is formed. Dots with heights between 30 and 100 nm appear at the same time; the number density of these dots decreases with increasing thickness. At 750 Å the surface is completely covered and obtains a granular aspect. The surface coverage of the discontinuous wetting layer is discussed in relation with the apparent porosity calculated from the specular reflectivity data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic properties of ultra-thin epitaxial V/Gd bilayersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2004P. Pankowski Abstract Magnetic properties of a new system of epitaxial vanadium/gadolinium bilayers with different V thickness have been studied. The structure and quality of bilayers was determined by X-ray reflectivity measurements using synchrotron radiation. Hysteresis loops measurements suggest in-plane anisotropy for all samples (Mr/Ms close to 1). Basic magnetic properties: saturation magnetisation, coercive field and remanence were obtained. Average magnetic moment analysis gives a possibility of an induced magnetic moment on vanadium atoms. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conformation and Interaction of a d,l -Alternating Peptide with a Bilayer Membrane: X-ray Reflectivity, CD, and FTIR Spectroscopy,CHEMPHYSCHEM, Issue 16 2007Andrea Küsel Dr. Abstract Peptides with alternating amino acid configuration provide helical secondary structures that are especially known from the membrane channel and pore-forming gramicidin A. In analogy to this natural d,l- alternating pentadecapeptide, the potential of d,l- alternating peptides for membrane insertion is investigated using the model dodecamer peptide H -(Phe- Tyr)5 -Trp- Trp - OH. This aromatic peptide is introduced as a novel pore-forming synthetic analogue of gramicidin A. It forms a well-organized homodimer similar to one of the gramicidin A transmembrane motifs. X-ray reflectivity measurements are performed on solid-supported peptide,lipid complexes to obtain information about the influence of the artificial dodecamer peptide on the bilayer parameters. In addition, Fourier-transform infrared (FTIR) and circular dichroism (CD) spectroscopic studies determine the conformational state of H -(Phe- Tyr)5 -Trp- Trp - OH within the model membrane. Site-specific iodine labeling assists in determining the topology of the membrane-embedded peptide by pinpointing the position of the iodine label within the bilayers. [source] | ||||||||||||||||