27 results
Search Results
Now showing 1 - 10 of 27
- ItemRaman imaging to study structural and chemical features of the dentin enamel junction(London [u.a.] : Institute of Physics, 2015) Alebrahim, M.A.; Krafft, C.; Popp, J.; El-Khateeb, Mohammad Y.The structure and chemical features of the human dentin enamel junction (DEJ) were characterized using Raman spectroscopic imaging. Slices were prepared from 10 German, and 10 Turkish teeth. Raman images were collected at 785 nm excitation and the average Raman spectra were calculated for analysis. Univariate and multivariate spectral analysis were applied for investigation. Raman images were obtained based on the intensity ratios of CH at 1450 cm-1 (matrix) to phosphate at 960 cm-1 (mineral), and carbonate to phosphate (1070/960) ratios. Different algorithms (HCA, K-means cluster and VCA) also used to study the DEJ. The obtained results showed that the width of DEJ is about 5 pm related to univariate method while it varies from 6 to 12 μm based on multivariate spectral technique. Both spectral analyses showed increasing in carbonate content inside the DEJ compared to the dentin, and the amide I (collagen) peak in dentin spectra is higher than DEJ spectra peak.
- ItemHybrid Optical Fibers – An Innovative Platform for In‐Fiber Photonic Devices(Weinheim : Wiley-VCH, 2015) Alexander Schmidt, Markus; Argyros, Alexander; Sorin, FabienThe field of hybrid optical fibers is one of the most active research areas in current fiber optics and has the vision of integrating sophisticated materials inside fibers, which are not traditionally used in fiber optics. Novel in-fiber devices with unique properties have been developed, opening up new directions for fiber optics in fields of critical interest in modern research, such as biophotonics, environmental science, optoelectronics, metamaterials, remote sensing, medicine, or quantum optics. Here the recent progress in the field of hybrid optical fibers is reviewed from an application perspective, focusing on fiber-integrated devices enabled by including novel materials inside polymer and glass fibers. The topics discussed range from nanowire-based plasmonics and hyperlenses, to integrated semiconductor devices such as optoelectronic detectors, and intense light generation unlocked by highly nonlinear hybrid waveguides.
- ItemEvaluating arbitrary strain configurations and doping in graphene with Raman spectroscopy(Bristol : IOP Publ., 2017-11-6) Mueller, Niclas S.; Heeg, Sebastian; Peña Alvarez, Miriam; Kusch, Patryk; Wasserroth, Sören; Clark, Nick; Schedin, Fredrik; Parthenios, John; Papagelis, Konstantinos; Galiotis, Costas; Kalbáč, Martin; Vijayaraghavan, Aravind; Huebner, Uwe; Gorbachev, Roman; Frank, Otakar; Reich, StephanieThe properties of graphene depend sensitively on strain and doping affecting its behavior in devices and allowing an advanced tailoring of this material. A knowledge of the strain configuration, i.e. the relative magnitude of the components of the strain tensor, is particularly crucial, because it governs effects like band-gap opening, pseudo-magnetic fields, and induced superconductivity. It also enters critically in the analysis of the doping level. We propose a method for evaluating unknown strain configurations and simultaneous doping in graphene using Raman spectroscopy. In our analysis we first extract the bare peak shift of the G and 2D modes by eliminating their splitting due to shear strain. The shifts from hydrostatic strain and doping are separated by a correlation analysis of the 2D and G frequencies, where we find Delta omega(2D)/Delta omega(G) = 2.21 +/- 0.05 for pure hydrostatic strain. We obtain the local hydrostatic strain, shear strain and doping without any assumption on the strain configuration prior to the analysis, as we demonstrate for two model cases: Graphene under uniaxial stress and graphene suspended on nanostructures that induce strain. Raman scattering with circular corotating polarization is ideal for analyzing frequency shifts, especially for weak strain when the peak splitting by shear strain cannot be resolved.
- ItemPhotoluminescence at room temperature of liquid-phase crystallized silicon on glass(New York, NY : American Inst. of Physics, 2016) Vetter, Michael; Schwuchow, Anka; Andrä, GudrunThe room temperature photoluminescence (PL) spectrum due band-to-band recombination in an only 8 μm thick liquid-phase crystallized silicon on glass solar cell absorber is measured over 3 orders of magnitude with a thin 400 μm thick optical fiber directly coupled to the spectrometer. High PL signal is achieved by the possibility to capture the PL spectrum very near to the silicon surface. The spectra measured within microcrystals of the absorber present the same features as spectra of crystalline silicon wafers without showing defect luminescence indicating the high electronic material quality of the liquid-phase multi-crystalline layer after hydrogen plasma treatment.
- ItemHigh-fidelity multimode fibre-based endoscopy for deep brain in vivo imaging(London : Nature Publishing Group, 2018) Turtaev, Sergey; Leite, Ivo T.; Altwegg-Boussac, Tristan; Pakan, Janelle M. P.; Rochefort, Nathalie L.; Čižmár, TomášProgress in neuroscience relies on new techniques for investigating the complex dynamics of neuronal networks. An ongoing challenge is to achieve minimally invasive and high-resolution observations of neuronal activity in vivo inside deep brain areas. Recently introduced methods for holographic control of light propagation in complex media enable the use of a hair-thin multimode optical fibre as an ultranarrow imaging tool. Compared to endoscopes based on graded-index lenses or fibre bundles, this new approach offers a footprint reduction exceeding an order of magnitude, combined with a significant enhancement in resolution. We designed a compact and high-speed system for fluorescent imaging at the tip of a fibre, achieving a resolution of 1.18 ± 0.04 µm across a 50-µm field of view, yielding 7-kilopixel images at a rate of 3.5 frames/s. Furthermore, we demonstrate in vivo observations of cell bodies and processes of inhibitory neurons within deep layers of the visual cortex and hippocampus of anaesthetised mice. This study paves the way for modern microscopy to be applied deep inside tissues of living animal models while exerting a minimal impact on their structural and functional properties.
- ItemLarge-area wet-chemical deposition of nanoporous tungstic silica coatings(London [u.a.] : RSC, 2015) Nielsen, K.H.; Wondraczek, K.; Schubert, U.S.; Wondraczek, L.We report on a facile procedure for synthesis of nanoporous coatings of tungstic silica through wet-chemical deposition and post-treatment of tungsten-doped potassium silicate solutions. The process relies on an aqueous washing and ion exchange step where dispersed potassium salt deposits are removed from a 150 nm silicate gel layer. Through an adjustment of the pH value of the washing agent within the solubility regime of a tungstic salt precursor, the tungsten content of the remaining nanostructured coating can be controlled. We propose this route as a universal approach for the deposition of large-area coatings of nanoporous silica with the potential for incorporating a broad variety of other dopant species. As for the present case, we observe, on the one hand, antireflective properties which enable the reduction of reflection losses from float glass by up to 3.7 percent points. On the other hand, the incorporation of nanoscale tungstic precipitates provides a lever for tailoring the coating hydrophilicity and, eventually, also surface acidity. This may provide a future route for combining optical performance with anti-fouling functionality.
- ItemAdvances in bioimaging - Challenges and potentials(Bristol : IOP Publ., 2018) Eggeling, Christian[No abstract available]
- ItemComplementary studies of lipid membrane dynamics using iSCAT and super-resolved fluorescence correlation spectroscopy(Bristol : IOP Publ., 2018) Reina, Francesco; Galiani, Silvia; Shrestha, Dilip; Sezgin, Erdinc; de Wit, Gabrielle; Cole, Daniel; Christoffer Lagerholm, B.; Kukura, Philipp; Eggeling, ChristianObservation techniques with high spatial and temporal resolution, such as single-particle tracking based on interferometric scattering (iSCAT) microscopy, and fluorescence correlation spectroscopy applied on a super-resolution STED microscope (STED-FCS), have revealed new insights of the molecular organization of membranes. While delivering complementary information, there are still distinct differences between these techniques, most prominently the use of fluorescent dye tagged probes for STED-FCS and a need for larger scattering gold nanoparticle tags for iSCAT. In this work, we have used lipid analogues tagged with a hybrid fluorescent tag–gold nanoparticle construct, to directly compare the results from STED-FCS and iSCAT measurements of phospholipid diffusion on a homogeneous supported lipid bilayer (SLB). These comparative measurements showed that while the mode of diffusion remained free, at least at the spatial (>40 nm) and temporal (50 ⩽ t ⩽ 100 ms) scales probed, the diffussion coefficient was reduced by 20- to 60-fold when tagging with 20 and 40 nm large gold particles as compared to when using dye tagged lipid analogues. These FCS measurements of hybrid fluorescent tag–gold nanoparticle labeled lipids also revealed that commercially supplied streptavidin-coated gold nanoparticles contain large quantities of free streptavidin. Finally, the values of apparent diffusion coefficients obtained by STED-FCS and iSCAT differed by a factor of 2–3 across the techniques, while relative differences in mobility between different species of lipid analogues considered were identical in both approaches. In conclusion, our experiments reveal that large and potentially cross-linking scattering tags introduce a significant slow-down in diffusion on SLBs but no additional bias, and our labeling approach creates a new way of exploiting complementary information from STED-FCS and iSCAT measurements.
- ItemProcess flow to integrate nanostructures on silicon grass in surface micromachined systems(Bristol : IOP Publ., 2016) Mehner, H.; Müller, L.; Biermann, S.; Hänschke, F.; Hoffmann, M.The process flow to integrate metallic nanostructures in surface micromachining processes is presented. The nanostructures are generated by evaporation of microstructured silicon grass with metal. The process flow is based on the lift-off of a thin amorphous silicon layer deposited using a CVD process. All steps feature a low temperature load beneath 120 °C and high compatibility with many materials as only well-established chemicals are used. As a result metallic nanostructures usable for optical applications can be generated as part of multilayered microsystems fabricated in surface micromachining.
- ItemStructure and superconducting characteristics of magnesium diboride, substitution of boron atoms by oxygen and carbon(London [u.a.] : Institute of Physics, 2017) Prikhna, Tetiana; Romaka, Vitaliy; Eisterer, Michael; Shapovalov, Andrii; Kozyrev, Artem; Grechnev, Gennadiy; Boutko, Viktor; Goldacker, Wilfried; Habisreuther, Tobias; Vakaliuk, Oleksii; Halbedel, BerndAn x-ray analysis of MgB2-based materials shows that they contain MgB2 and MgO phases. According to a quantitative Auger analysis (taken after removing the oxidized surface layer by Ar ion etching in the microscope chamber) the MgB2 phase contains some amount of oxygen that approximately corresponds to the composition MgB2.2-1.7O0.4-0.6. Rietveld refinement of the MgB2 phase, based on EDX data with varying B/O content, leads to the composition MgB1.68-1.8O0.2-0.32. Ab-initio modelling of boron substitution by oxygen in MgB2 (ΔH f = -150.6 meV/atom) shows that this is energetically favourable up to the composition MgB1.75O0.25 (ΔH f = -191.4 meV/atom). In contrast to carbon substitution, where very small levels of doping can dramatically affect the superconducting characteristics of the material with concomitant changes in the electron density, oxygen substitution results in very little change in the superconducting properties of MgB2. The formation of vacancies at the Mg site of both MgB2 and substituted MgB1.75O0.25 was modelled as well, but has shown that such processes are energetically disadvantageous (ΔHf of Mg0.875B2 and Mg0.75B1.75O0.25 are equal to -45.5 and -93.5 meV/atom, respectively).
- «
- 1 (current)
- 2
- 3
- »