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- 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.
- ItemHollow square core fiber sensor for physical parameters measurement(Bristol : IOP Publ., 2022) Pereira, Diana; Bierlich, Jörg; Kobelke, Jens; Ferreira, Marta S.The measurement of physical parameters is important in many current applications, since they often rely on these measurands to operate with the due quality and the necessary safety. In this work, a simple and robust optical fiber sensor based on an antiresonant hollow square core fiber (HSCF) is proposed to measure simultaneously temperature, strain, and curvature. The proposed sensor was designed in a transmission configuration where a segment of HSCF, with a 10 mm length, was spliced between two single mode fibers. In this sensor, a cladding modal interference (CMI) and a Mach-Zehnder interference (MZI) are enhanced along with the antiresonance (AR) guidance. All the present mechanisms exhibit different responses towards the physical parameters. For the temperature, sensitivities of 32.8 pm/°C, 18.9 pm/°C, and 15.7 pm/°C were respectively attained for the MZI, AR, and CMI. As for the strain, sensitivities of 0.45 pm/μϵ, -0.93 pm/μϵ, and -2.72 pm/μϵ were acquired for the MZI, AR and CMI respectively. Meanwhile, for the curvature measurements, two regions of analysis were considered. In the first region (0 m-1 - 0.7 m-1) sensitivities of 0.033 nm/m-1, -0.27 nm/m-1, and -2.21 nm/m-1 were achieved, whilst for the second region (0.7 m-1 - 1.5 m-1) sensitivities of 0.067 nm/m-1, -0.63 nm/m-1, and -0.49 nm/m-1 were acquired for the MZI, AR and CMI, respectively.
- 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.
- ItemCapillary based hybrid fiber sensor in a balloon-like shape for simultaneous measurement of displacement and temperature(Bristol : IOP Publ., 2022) Santos, João P.; Bierlich, Jörg; Kobelke, Jens; Ferreira, Marta S.In this work, a hybrid sensor based on a silica capillary in a balloon-like shape for simultaneous measurement of displacement and temperature is proposed for the first time, to the best of our knowledge. The sensor is fabricated by splicing a segment of a hollow core fiber between two single mode fibers (SMF) and by bending the fiber in a balloon shape with the capillary at the top-center position. In a transmission scheme, the SMF-capillary-SMF configuration excites an antiresonant (AR) guidance and the balloon shape enhances a Mach-Zehnder interferometer (MZI). The different responses of the interferometers to external displacement and temperature variations are conducive to a hybrid application of the sensor for simultaneous measurement of these parameters. Experimental results show that, for a capillary length of 1.2 cm and a balloon length of 4 cm, AR is insensitive to displacement and its sensitivity to temperature is 14.3 pm/°C, while the MZI has a sensitivity to displacement of 1.68 nm/mm and twice the sensitivity of AR to temperature, of 28.6 pm/°C. The proposed fiber sensor consists of only one sensing element in one configuration exciting two interferometers at the same time, which makes it of simple fabrication as well as low cost.
- ItemNear-field interference map due to a dipolar emission near the edge of a monocrystalline gold platelet(Bristol : IOP Publ., 2022) Abbasirad, N.; Barreda, A.; Arslan, D.; Steinert, M.; Chen, Y.-J.; Huang, J.-S.; Staude, I.; Setzpfandt, F.; Pertsch, T.Point source excitation and point detection in the near-field provides new perspective to study the near-field optical phenomena of plasmonic nanostructures. Using the automated dual-tip scanning near-field optical microscope (SNOM), we have measured the optical near-field response of a dipolar emission near the edge of a monocrystalline gold platelet. The image dipole method was used to analytically calculate the interference pattern due to surface plasmon polaritons excited at the position of aperture tip and those reflected from edges of the gold platelet. The near-field enhancement was observed on the edges of the gold platelet. Our results verify that automated dual-tip SNOM is an intriguing technique for quantum plasmonic studies where deterministic coupling of quantum emitters and the detection of the near-field enhancement are of great interest.